40 replies to this topic

[carolinaskies]

I picked up my first big LifePo4 100A 12v battery today and want to get a decent charger for it without throwing out huge gobs of money. 

I'm leaning towards one of the 20A chargers vs the lesser 10A to make recharging in time sensative situations easier.   

For those who've gone the LifePo4 route what chargers have/are you using and which might you suggest?

I note there are dedicated 14.6v models as well as multi-type which say they work with Lithium/Lifepo4.  Also, what's your experience with storage between use and whether there is an actual need for a 'maintenance' mode or not because the batteries aren't supposed to lose much charge when stored above 70%.      

 

[WadeH237]

In my experience, LiFePO4 batteries are much easier to charge than lead batteries.

 

With lead batteries, you need 3 phases:  bulk, acceptance and float.  For a fully customizable charger, you have to correctly set the parameters for each of the phases.

 

None of that applies to LiFePO4.  All you need to do is provide a top voltage, usually 14.6.  The charger provides whatever amperage is needed (up to it's rating) until the target voltage is reached, and then it just needs to hold it there.  This is similar to the bulk charge phases for lead batteries.  There is no need for either acceptance or float charging.

 

Where it gets a bit tricky is that nobody runs a single cell battery to power their rigs.  Most of us are using a pack with 4 cells in series.  The battery management system (BMS) keeps track of voltage for each cell, temperature, and other parameters.  If any of them go outside of tolerances, the BMS will deactivate the battery.

 

One of my LiFePO4 chargers is a zero configuration unit.  It's compact and fixed at 14.6 volts.  It's a PowerWerx unit, so it should be good quality.  I hate it.  The reason is that one of my battery packs has some inconsistencies in the individual cell charge voltage.  As a result, one of the cells often reaches the target voltage before the others do.  Since the charger knows nothing about the internal state of the individual cells, it just keeps supplying voltage.  This causes the one high voltage cell to exceed the max voltage and the BMS shuts the entire battery down for a period of time.

 

To work around this, I prefer chargers with fully user configurable settings (in addition to specific settings for the different types).  So if you end up with a pack that's a bit off, like mine, you can lower the voltage a bit, to prevent over voltage of a single cell.

 

Neither setup actually harms the battery, since the BMS protects it (this goes on inside of lots of battery packs; the difference with my setup is that I monitor the BMS closely, because I like to know the geeky bits).  Interestingly, I can get a bit of a better charge with a lower target voltage because the cells stay more balanced.  I have multiple LiFePO4 battery packs, and only one of them really exhibits this behavior.  All of them, though, benefit from small tweaks to the voltage.

 

This is probably far more detail that you were looking for, but I find it all pretty interesting.

 

My practical advice is to get a charger that has a dedicated setting for LiFePO4, and also fully customizable settings.  That way, you have the no-tweaking option, and also the ability to make a custom profile for your battery.  In terms of amperage, LiFePO4 cells can be more aggressively charged and discharged than lead batteries.  So if you want faster charging, go ahead and get the 20 amp charger.

[DeepSky Di]

Mine came with its own charger. It has quite a loud fan.

[ngatel]

I picked up my first big LifePo4 100A 12v battery today and want to get a decent charger for it without throwing out huge gobs of money. 

I'm leaning towards one of the 20A chargers vs the lesser 10A to make recharging in time sensative situations easier.   

For those who've gone the LifePo4 route what chargers have/are you using and which might you suggest?

I note there are dedicated 14.6v models as well as multi-type which say they work with Lithium/Lifepo4.  Also, what's your experience with storage between use and whether there is an actual need for a 'maintenance' mode or not because the batteries aren't supposed to lose much charge when stored above 70%.      

 

 

 

In my experience, LiFePO4 batteries are much easier to charge than lead batteries.

 

With lead batteries, you need 3 phases:  bulk, acceptance and float.  For a fully customizable charger, you have to correctly set the parameters for each of the phases.

 

None of that applies to LiFePO4.  All you need to do is provide a top voltage, usually 14.6.  The charger provides whatever amperage is needed (up to it's rating) until the target voltage is reached, and then it just needs to hold it there.  This is similar to the bulk charge phases for lead batteries.  There is no need for either acceptance or float charging.

 

Where it gets a bit tricky is that nobody runs a single cell battery to power their rigs.  Most of us are using a pack with 4 cells in series.  The battery management system (BMS) keeps track of voltage for each cell, temperature, and other parameters.  If any of them go outside of tolerances, the BMS will deactivate the battery.

 

One of my LiFePO4 chargers is a zero configuration unit.  It's compact and fixed at 14.6 volts.  It's a PowerWerx unit, so it should be good quality.  I hate it.  The reason is that one of my battery packs has some inconsistencies in the individual cell charge voltage.  As a result, one of the cells often reaches the target voltage before the others do.  Since the charger knows nothing about the internal state of the individual cells, it just keeps supplying voltage.  This causes the one high voltage cell to exceed the max voltage and the BMS shuts the entire battery down for a period of time.

 

To work around this, I prefer chargers with fully user configurable settings (in addition to specific settings for the different types).  So if you end up with a pack that's a bit off, like mine, you can lower the voltage a bit, to prevent over voltage of a single cell.

 

Neither setup actually harms the battery, since the BMS protects it (this goes on inside of lots of battery packs; the difference with my setup is that I monitor the BMS closely, because I like to know the geeky bits).  Interestingly, I can get a bit of a better charge with a lower target voltage because the cells stay more balanced.  I have multiple LiFePO4 battery packs, and only one of them really exhibits this behavior.  All of them, though, benefit from small tweaks to the voltage.

 

This is probably far more detail that you were looking for, but I find it all pretty interesting.

 

My practical advice is to get a charger that has a dedicated setting for LiFePO4, and also fully customizable settings.  That way, you have the no-tweaking option, and also the ability to make a custom profile for your battery.  In terms of amperage, LiFePO4 cells can be more aggressively charged and discharged than lead batteries.  So if you want faster charging, go ahead and get the 20 amp charger.

A lot of good information from Wade, although I am extremely happy with my PowerWerx chargers.

 

You can charge a LiFePo4 at 0.5C, which for you would be 50 amps. I would go with the 20 amp or more.

 

I use two PowerWerx 30 Amp variable DC power supplies. I image almost every night using two mounts and recharge them every morning.

 

 

An advantage to using variable power supplies is I can use them for other things besides just charging batteries. If I wanted to, I could use them to power my astro rigs. I also use them for other projects around the house.

 

I also have a portable 100W solar for charging when we are camping, which is around 3 months per year. 

 

As far as discharge in storage goes, it is difficult to actually measure it unless one has a shunt type battery monitor, like the one below:

 

I don't "store" my astro LiFePo4 batteries since I image so often. However I have a 300AH LiFePo4 in my travel trailer. The longest I have left it in storage was 6 months with temperatures down to about 32°F in winter. Also there is a very slight draw on the system from the battery monitor. After 6 months in storage the battery capacity was 72%.

 

You can discharge a LiFePo4 down to zero without damaging it. But just like a lead-acid battery, the more you discharge a battery the fewer charge cycles you will have. So I generally don't discharge below 50%. I have a couple 48AH battery banks, plus a 100AH battery for astrophotography. One of my 48AH banks (really cheap brand) has over 700 charge cycles on it and the capacity has dropped down to around 43% or 20AH. This battery was discharged down to 55% of capacity almost every night.

 

Here's a link to the 100AH battery bank set up I built about a year ago.

[carolinaskies]

Thanks for a bevvy of information.   

As I say, I'm leaning toward the 20A charge option, I've got to look at some of the chargers and see which truly can balance price and capability.  I'm not at a point where I'll have to need continuous charging right now, so it's good to know that once charged I should still have a viable charge available off the bat.  I have a couple of older 17/20ah lead acict units which when left unused for >6mos are nigh useless without a recharge.  I might upgrade one of them with a Lithium battery which would be better for the inconsistent use. 

Nick, I wonder if Wade's information on varying the charge voltage might have helped with your 3-battery combo recharge failure? 

[ngatel]

Nick, I wonder if Wade's information on varying the charge voltage might have helped with your 3-battery combo recharge failure? 

 

That's observant and a good question.

 

It is my understanding that Li batteries cannot be shipped unless the state of charge is 30% or less. I have never received a battery that was even close to 100% SOC. They all had to be charged.

 

When I got the small LiFePo4 batteries ( 3 @ 16AH) I discharged all three to 0% state of charge. Then I charged all three individually to top balance the bank, let them sit overnight and then tested the voltage of each — they were all equal. Then I connected them in parallel. When they capacity started dropping I would test the voltage of each and they were still equal. Keep in mind that these three were the absolutely cheapest LiFePo4 batteries I could find, as I was more interested in experimentation and education.

 

I bought a second trio of 16AH LiFePo4 batteries a year later, not the same brand because that brand was no longer available, but the cheapest on Amazon. (I suspect the same factory built the two different brands). This newer battery bank of 3 batteries is 48AH and has over 500 charge cycles and the capacity is still over 80%.

 

So the experimentation with these cheap batteries was really me questioning the high charge life cycles of LiFePo4 batteries claimed by manufacturers. Part of my skepticism was due to manufacturers mis-stating the data on lead-acid batteries as it relates to discharge and charge cycles, which is contrary to my 20+ years of experience with lead-acid batteries and solar systems. But LiFePo4 battery prices have come down to almost match lead-acid, so there is no advantage to lead-acid — except for those environmentally concerned, lead-acid is a recycling success story; Li-ion not so much. That will hopefully change.

 

Anyway . . . I am now at the point where I am convinced that quality LiFePo4 batteries do have a significantly higher charge-cycle life; just buy a quality brand. Last year I bought a highly rated 100AH LiTime LiFePo4 battery. It has enough capacity to run both my astro rigs for two nights. But I usually just run one mount and still use the smaller 48AH bank on the other one, mostly to see how much life it will really have. I do charge each battery each morning.

[astrohamp]

In field remote I often use my big LiFePo4 DIY battery with this charger to bring up my 24Ah and 50Ah LiFePO4 batteries.  It is a DC-to-DC unit with 2/4/8A 14.6v settings.  It is only about 80% efficient though.

 

The larger LiFePO4 needs a bit more charge power.  This comes from a 300 watt solar array (3 series connected 100 watt rigid panels ( the similarly set up old dual array seen here along with the battery box/cover).  They feed a Victron SmartSolar MPPT 100/30 charge controller.  Only getting just over 20 amps out on a good day due to the need to make it all manageable.

If have AC mains power available the Victron Blue Smart IP22 Charger is pulled out and can safely charge all three LiFePO4 batteries I am currently using.  Fixed 7.5,15,30 amp (and variable) output current, with adjustable chemistry and user set able charge parameters as well.  Can actually use both solar and the Blue Smart charger in parallel if need be for the 200+Ah LiFePO4.

 

Thanks to a CN member for reminding me of the potential short hazard my battery box posed.  The cell bus bars are now covered and I should make a cover for the entire cell well.  The Smart Solar charger (which can also be operated as a user set point DC power supply) runs near burn your fingers hot full on so I added a second vent fan to push air up out of the Victron box drawing down from the sides.  Cannot charge on high with lid closed.

What ever charger you get the nice (need) to have is a Blue Tooth function that tracks power in-out at least.  Some LiFePO4 batteries have the feature built in, or can be installed with a DIY battery/BMS build.

[WadeH237]

A lot of good information from Wade, although I am extremely happy with my PowerWerx chargers.

To be sure, I wouldn't want anyone to think that I was saying anything bad about PowerWerx products.  I use PowerWerx power supplies.  They are excellent, and my first choice for my imaging rig.

 

The charger that I am talking about is this one.  I bought it specifically because it was small and light enough to affix to the back of one of my portable solar panels.  It works exactly as described and has no configuration options at all.  If my battery pack didn't tend to get one cell voltage spiking early, it would be perfect.

 

I'd also note that the only reason that I know that I have one cell spiking early is because I assembled the pack myself and used a BMS that reports lots of internal numbers.  If I were using an off-the-shelf, pre-made 12v battery, it's possible that the same thing would be happening internally and I'd never know it.  As I mentioned, the BMS protects the pack, so the only practical effect is that it doesn't get quite a full charge.  And since it only happens when the battery nears a full charge, the impact to capacity is minimal.

[TelescopeGreg]

How deep do you expect to be drawing the battery, and how fast do you need to get it back to full charge?  That will determine the size of the charger you need.

 

Note that LiFePO4 batteries generally can be charged at up to 0.5C, but most manufacturers recommend not exceeding 0.2C on a regular basis.  For a 100AH battery, that's 20 amps, which would do a full charge in something like 5 hours or so.  Slower is nicer to all components involved.  What's the rush?

 

I strongly do not recommend using a simple 14.4v power supply for charging, unless you are very sure that it has a functional current limiter and doesn't mind using it.  A discharged 100 AH battery is capable of sucking an enormous amount of current, which can fry an unprotected power supply or the wires that connect the two.  There can also be a large spike in voltage from the supply when the battery's BMS determines that the battery (or one of its cells) is totally full, as it will spontaneously disconnect the battery from the circuit to prevent a dangerous overcharge.  A proper battery charger is designed to manage both ends of the charging session.  They aren't expensive, and will protect your battery and any attached equipment.

 

To storage, the LiFePO4 batteries hold their charge very well, though I don't leave mine along long enough to know just how long.  Do be sure to keep them in a place that doesn't get below freezing; they can withstand going a little below if they're not being used or charged, but absolutely cannot be charged when cold.  Period, full stop. If you're in a "cold place" (snow, etc.) get a battery that has an integral heating blanket, and keep it in something insulated.

[triplemon]

I would not worry about a lead-acid charger not having a working current limit. All those that dont have it, die within seconds of using them

That comes from an electrical engineer that built many of them at home and even designed some integrated circuits used for commerical battery chargers ...

The only noteworthy difference between AGM, flooded lead acid and LiFePO4 charging is the voltage limit that comes into effect once the battery stopped drawing all the current it can get, i.e. after the "bulk charging" and during the "acceptance' or "absorbing" phases of the charging.
For LIF you want a few hundred millivolts higher of a voltage, around 14.6 to 14.8 volts, while the other chemistries rather want 14.1 to 14.4 volts. It also depends a little bit on temperature and the particular manufacturer. If you choose too low of a voltage, you will simply not charge the battery to its full capacity. So the 14.4V LCA charger will simply not get the LIF more  than some 80% charged. But not cause any damage at all. Actually - as Li battery lifespan does depend notably on the time the battery is held at this maximum voltage/state of charge, many charger very intentionally charge only to some lower voltage like that in order to increase life span. Just look at the charger settings for that in any electric car, IPhone's and many of the other better Li powered gadgets these days.

The other difference is what to do when the battery is finally fully charged and draws very little current any more while still being held at the intended absorbing state voltage. A LCA battery could be held for days at that voltage without much ill effect. Only if you intend to keep it more or less permanent on the charger (float or tickle charger), you will want to eventually reduce that voltage to the infamous 13.8V or even a tad lower.
Lithium batteries (LIF as well as all Li-Polymer and Li-Ion flavours) take it MUCH worse if held too long at this high charging voltage. Some Li-Ion chemistries would heat up and catch fire within less than an hour. So monitoring the charge current to fall to a low level and even an hard time limit as a backup and then entirely end any charging is essential.
LIF are fortunately the most forgiving of all li chemistries in this respect. I would not worry about holding them for a few hours at that voltage. But after that, the standby voltage should be reduced to even lower than 13.8V (13.5V is likely fine with most) to not reduce the battery life.

 

So with that its possible to "slow" charge a LCA battery by putting it on a fixed voltage charger of 13.8V and it will eventually reach 100% charge. No "monitoring" or "termination" of any kind required, its also at times called a "2-stage charger". While for LIF there isn't any one voltage that gets you to any higher than 50% charge and still does not require some monitoring and termination of the charging process. As an engineer, I would not call this "its easier' to charge.

But for occasional, manual charging there is IMO no special circuitry needed to do this charge termination for either LCA nor LIF batteries, Just look every hour or two at the residual charge current and once it falls to some 1% of capacity (i.e. 1 or 2 amps for a big battery) - disconnect the charger and be done. So no special charger needed for either, just any adjustable voltage power supply and some instruments to monitor the current every now and then.

 

Be aware that the BMS protection circuits in any battery pack will NOT help you with meetig these safe current, voltage or time limitations for charging. These circuits kick in at much higher limits where some (minor) damage may already occurr and they simply disconnect the battery entirely. Think of them more as being a self-resetting fuse, only.

 

Edit; All the voltages mentioned here are for 6 cell LCA or 4 cell LIF batteries, commonly called a "12V battery".  Li-PO or other Li-ION have different per cell voltages and also a lot more variation during discharge, so they dont lead to making a useful 12v pack. Battery packs based on those are using all kinds of cell counts and any charger for those would have to be much more configurable wrt charging voltages. But the fundamental charging strategy is the exact same. While NiCAD and NiMH cells behave very different while charging and the charging strategy is quite different.

Edited by triplemon, 08 November 2024 - 03:49 PM.

[Bob4BVM]

I would not worry about a lead-acid charger not having a working current limit. All those that dont have it, die within seconds of using them

That comes from an electrical engineer that built many of them at home and even designed some integrated circuits used for commerical battery chargers ...

The only noteworthy difference between AGM, flooded lead acid and LiFePO4 charging is the voltage limit that comes into effect once the battery stopped drawing all the current it can get, i.e. after the "bulk charging" and during the "acceptance' or "absorbing" phases of the charging.
For LIF you want a few hundred millivolts higher of a voltage, around 14.6 to 14.8 volts, while the other chemistries rather want 14.1 to 14.4 volts. It also depends a little bit on temperature and the particular manufacturer. If you choose too low of a voltage, you will simply not charge the battery to its full capacity. So the 14.4V LCA charger will simply not get the LIF more  than some 80% charged. But not cause any damage at all. Actually - as Li battery lifespan does depend notably on the time the battery is held at this maximum voltage/state of charge, many charger very intentionally charge only to some lower voltage like that in order to increase life span. Just look at the charger settings for that in any electric car, IPhone's and many of the other better Li powered gadgets these days.

The other difference is what to do when the battery is finally fully charged and draws very little current any more while still being held at the intended absorbing state voltage. A LCA battery could be held for days at that voltage without much ill effect. Only if you intend to keep it more or less permanent on the charger (float or tickle charger), you will want to eventually reduce that voltage to the infamous 13.8V or even a tad lower.
Lithium batteries (LIF as well as all Li-Polymer and Li-Ion flavours) take it MUCH worse if held too long at this high charging voltage. Some Li-Ion chemistries would heat up and catch fire within less than an hour. So monitoring the charge current to fall to a low level and even an hard time limit as a backup and then entirely end any charging is essential.
LIF are fortunately the most forgiving of all li chemistries in this respect. I would not worry about holding them for a few hours at that voltage. But after that, the standby voltage should be reduced to even lower than 13.8V (13.5V is likely fine with most) to not reduce the battery life.

 

So with that its possible to "slow" charge a LCA battery by putting it on a fixed voltage charger of 13.8V and it will eventually reach 100% charge. so no "monitoring" or "termination" of any kind required. While for LIF there isn't any one voltage that gets you to any higher than 50% charge and still does not require some monitoring and termination of the charging process. As an engineer, I would not call this "its easier' to charge.

But for occasional, manual charging there is IMO no special circuitry needed to do this charge termination for either LCA nor LIF batteries, Just look every hour or two at the residual charge current and once it falls to some 1% of capacity (i.e. 1 or 2 amps for a big battery) - disconnect the charger and be done. So no special charger needed for either, just any adjustable voltage power supply and some instruments to monitor the voltage and current every now and then.

 

Be aware that the BMS protection circuits in most LIF battery packs will NOT help you with meetig these safe current, voltage or time limitations for charging. These circuits kick in at much higher limits where some (minor) damage may already occurr and they simply disconnect the battery entirely. Think of them more as being a self-resetting fuse.

 

Edit; All the voltages mentioned here are for 6 cell LCA or 4 cell LIF batteries, commonly called a "12V bettery".  Li-PO or other Li-ION have different per cell voltages and also a lot more variation during discharge, so they can't be used to make a good 12v pack. Battery packs based on those are using all kinds of cell counts and any charger for those would have to be much more configurable wrt charging voltages. But the fundamental charging strategy is the exact same. While NiCAD and NiMH cells behave very different while charging and the charging strategy is quite different.

That's what i do for my 25AH LiFePO4's.

I also still use a FLA battery

Both get charged with a "manual" lead-acid charger

For charging LiFePO4's, I set the charge to 14.4V, 4A output.

My scope has built-in power metering, so when the LiFePO4 reaches 13.85V, it's done

I do have to watch the meter, so i recharge when i can be around.

Been working well for a couple years now.

[CA Curtis 17]

As Telescope Greg said, while most LiFePO4 battery manufacturer's spec the max charging rate at 0.5C they always recommend charging slower, typically 0.2C.  The reason for this is similar to the reason LiFePO4 batteries should not be charged below 0C.  Charging drives Li ions from the copper cathode to the graphite anode where the Li ions need to diffuse into interstitial sites between the graphite planes.  When the temp is low, the diffusion rate is low and Li ions can pile up at the outside of the anode and begin to plate as Li metal.  The same thing happens at even elevated temperatures when the Li ions arrive too quickly, i.e. when the charging current is too high.  So it is better to charge at the slower rate, especially when the temperature is low.

 

Also, the typical self discharge rate of LiFePO4 batteries is 3% per month.  This is in line with Nick's data on his battery dropping down to 72% after 6 months considering he had a latent current as well.

 

Finally, LiFePO4 batteries are typically rated for 2K or more full discharge cycles.  After that they should supply 75 - 80% of the original capacity, although I have never seen anyone spec for how many more additional full discharges.  One should not have to avoid using the full capacity because of worries that it will loose capacity faster.  Per Nick's comment I suspect he is correct that you are more likely to get the rated performance from a known brand rather than a cheaper no-name brand which may not use grade A cells.

 

Regards,

Curtis

[triplemon]

Its not about grade A cells. Its about declaring the capacity honestly. Just look at the weight of a bunch of similar capacity batts - why does it vary some 20 to 30%? 

With the lightest being the one with the highest advertised capacity and the lowest price. Yeah, right.

[davidmalanick]

I picked up my first big LifePo4 100A 12v battery today and want to get a decent charger for it without throwing out huge gobs of money. 

I'm leaning towards one of the 20A chargers vs the lesser 10A to make recharging in time sensative situations easier.   

For those who've gone the LifePo4 route what chargers have/are you using and which might you suggest?

I note there are dedicated 14.6v models as well as multi-type which say they work with Lithium/Lifepo4.  Also, what's your experience with storage between use and whether there is an actual need for a 'maintenance' mode or not because the batteries aren't supposed to lose much charge when stored above 70%.      

 

https://www.litime.c...battery-charger

 

I use this brand, battery and charger.  No problems and their sale prices are great.

[CA Curtis 17]

Its not about grade A cells. Its about declaring the capacity honestly. Just look at the weight of a bunch of similar capacity batts - why does it vary some 20 to 30%? 

With the lightest being the one with the highest advertised capacity and the lowest price. Yeah, right.

I would be curious to check these out if you would care to provide some examples.

 

I know that the well know brands actually target a capacity greater than spec'd so that their batteries supply at least the advertised capacity.  I have tested 4 batteries from Li Time and one from Battleborn, for example.  The LiTime batteries always come in at ~103% of the rated capacity.  Battleborn (not popular for us astronomy folks because of the much higher price) actually designs their battteries to have between 104 and 108% of the rated capacity.  I toured their production line in Reno, NV and saw the stacks of cells tested and labeled so that they could assemble the right combination to meet their target capacity.  

 

I would be careful of buying the cheapest battery one could find.  Not because they mislead about capacity, but because I would be concerned about the quality of the components and the assembly.  I have watched enough tear down videos and even taken one apart myself to check its quality to know that there are often significant differences in quality.

[triplemon]

Sorry, I do not have examples of high end assemblies. I only work with bare batteries from white label manufacturers in China. More comparable to the spread an individual customer would see when comparing specs and different brands on Amazon.

 

And yes, if you test and bin every cell before combining them in an custom assembly, you should hit any given capacity you want spot on. Plus with that kind of relationship with a vendor, this enduser marketing "new normal" of shamelessly overstating specs obviously gets cut out. But adding such an extra layer of QC comes at a cost, though, these devices cost 3-5x of the bare batteries themselves. Its a nice market niche to be in, though, similar to aviation and military markets.

 

Wrt the original question an answer like yours is IMO incredibly unhelpful, though. The OP asked how to find a economical charging solution thats "good enough". Basically optimize the bang for the buck. Telling him he shouldn't do that and rather pay a steep premium does not seem to help that.

Edited by triplemon, 10 November 2024 - 05:44 PM.

[CA Curtis 17]

Wrt the original question an answer like yours is IMO incredibly unhelpful, though. The OP asked how to find a economical charging solution thats "good enough". Basically optimize the bang for the buck. Telling him he shouldn't do that and rather pay a steep premium does not seem to help that.

I don't know where you got the idea I suggested the OP should pay a steep premium.   I mentioned Li Time which I use and which Nick also mentioned as a quality brand that meets its specs at a price that I would not call a steep premium.  If someone prefers to buy a brand they never heard of because it is priced lower, I stick with my recommendation to look for a tear down video so that you see what you are getting before you buy.  In the end, we all choose the path that we think best for ourselves.

 

Regards,

Curtis

[carolinaskies]

Since most of us are on some measure of a budget, paying nearly as much for a charger as what a battery is averaging these days doesn't seem like a budget friendly option.  If I was abundantly funded and/or had multiple batteries needing efficient effective charging then I'd definitely look to spend more.  But if I can keep my budget for a charger under $100 and provide reasonable performance that's budget-wise.   

As the OP, remember, I'm asking about reasonable value within basic parameters.  I think a 20A model meets the time to charge desire as needed and if it has 14.6v capability for the bulk period up to 80%ish that's reasonable.  I think I'll check in to some of the Ytube videos and see what some real world testers are discovering.  

I appreciate peoples comments and suggestions so far.  

[ngatel]

I would recommend the LiTime battery. When I bought my 100AH it wasn't much more money than a 100AH AGM.

 

Will Prowse (a real expert) has plenty of good to say about them. You can watch his tear-down videos here — 

 

https://www.youtube....llProwse/videos

 

IIRC both Battle Born and LiTime recommend charging at 14.4 +/- 0.2. I prefer 14.6 (from my lead-acid days of pushing in all the amps with the highest voltage recommended by the battery manufacturer)

[WadeH237]

But if I can keep my budget for a charger under $100 and provide reasonable performance that's budget-wise.

This shouldn't be difficult.

 

My point about LiFePO4 batteries being "easier" to charge is that you could use something as simple as a bench power supply.  Just set the voltage to somewhere between 14.4 and 14.6 volts, and set the maximum current to be 20 amps or less.  When the power supply shows very little current draw, you are charged.  Yes, the battery can accept current at a high enough rate to cause problems if the charger (or power supply) isn't current limited.  And yes, you can harm the battery by holding it at 14.6 volts for an extended period of time.  I made the (perhaps poor) assumption that this would be common sense.

 

For what it's worth, here is how I charge my 100ah LiFePO4 imaging battery:

 

In normal use, I have 2 x 100 watt solar panels with this simple charge controller.  It's not as efficient as an MPPT charger, but it's a drop-in replacement for my folding 200w solar panel kit (which originally included a charge controller without sufficient configuration options to work well with my battery), but with 200w of panels, it's plenty.  Off the top of my head, I believe that I have it configured to bulk charge at 14.4 volts, with acceptance and float voltages set to 12.5, which is lower than the nominal voltage of the pack. so it goes idle after full charge is reached.  In the rare cases that I charge it from A/C power, I have this LiFePO4 charger, which works well.

 

The above is the simple answer, with links to specific products.  Below, I've expanded a bit on some unusual usage situations, and how I store the batteries long term.  I fear that I've dragged this topic down a bit of a rabbit hole, and I am sorry for that (although there is lots of good info from many folks).  So just skip the below if you want to just keep it simple.

 

Summer before last, we went through a period of time where we were having somewhat frequent power interruptions.  They were just short blips, but often rebooted computers.  I normally run with a power supply, instead of a battery, at home.  But during that time, I ran things from the battery and kept a bench power supply connected with the voltage set somewhere in the mid 13's for voltage.  This kept everything going when the power blipped.  To find the specific voltage to use, I let the battery run down to about 50%, and then turned on the power supply and dialed the voltage to match the state of the battery.  The voltage curve is so flat with LiFePO4, that it's not practical to hold the battery at a specific state of charge when in use, but this kept it pretty much between 30% and 60%, according to the BMS.  I checked it daily while it was connected to the bench supply, and made occasional adjustments.

 

I rarely travel for imaging in the winter, so don't use the battery much for about half the year.  Before storing the battery for the winter, I put a load on it until the BMS indicates about 50% charge left.  I then disconnect it and store it in that state.  I do the same thing with my much bigger LiFePO4 pack (300ah at 24v) in the motorhome.  For reference, the charger for the motorhome is integrated into the inverter.  That system is much more expensive than what we are talking about here.  It manages charging and use of the battery, the solar panels, and the A/C shore power.  Per my configuration settings, it will automatically select either solar or shore power as the source for charge power, and it seamlessly switches between drawing power from the battery, the panels, or the shore power, depending on the state of the system.

[ngatel]

With a bench power supply the battery BMS will stop accepting a charge when it is fully charged. This happens with all my batteries. When the battery is fully charged the power supply will show zero amps, whereas when it started charging the amps were over 10 amps. When the power supply shows zero amps I know the battery is charged.

 

I have done this over 2,000 times with my 3 different battery banks, which for a non-scientific field guy must be an adequate sample size ;-)

[triplemon]

Ah - no. The BMS will NOT do a charge termination or current reduction for you. Its not the BMS that reduces the charge current - its the voltage limit in the device used to charge.that does that. If you set that voltage a little bit high, you will damage your battery even before the current starts to drop, i.e. you extend the bulk charging for too long, charge with too high of a current during the absorbing phase and might even reach the final termination criteria "current dropped to near zero" too late.

 

If you set the charger voltage limit so high that the BMS triggers near the end of the bulk charging - the BMS will completely stop the charging there and then by disconnecting the battery terminal from the battery. You will be left with a battery that is charged a lot less than full. Possibly as low as 60% only. This is due to the BMS not having he ability to dissipate all the heat that would be created if it would drop the charging voltage to safe levels while under high current.

Wrt the maximum charger current vs charging time, all charging mehods (manual/power supply or any fancy, fully automatic charger alike) do not run all the time at that maximum current. So the bigger charger is in many situations no faster at all. Actually, even on a drop dead battery the 2x current charger will not get you anywhere near 2x as fast to full charge, as roughly half the charging time to full is spent at less and towards the end even way, way less than maximum current.

 

So for recharging a battery at home for the next use in a few days, for topping off a half discharged battery in the field, the maximum current has little relevance. Only when you're in the field AND waited way past half discarge AND its not cold AND you have a narrow time slot to "catch some partial charge", then the high current charging device shines.

 

For the range from drop dead to about half full, the lower voltage lead acid battery charger also will run exactly as well and as fast as a specialized LIF charger. So if you happen to still have such a old charger or can compromise on "charge to quickly recover from really low levels", a smaller (cheaper !!!), LIF capable one might do just fine.

Edited by triplemon, 12 November 2024 - 12:57 AM.

[ngatel]

Ah - no. The BMS will NOT do a charge termination or current reduction for you. Its not the BMS that reduces the charge current - its the voltage limit in the device used to charge.that does that. If you set that voltage a little bit high, you will damage your battery even before the current starts to drop, i.e. you extend the bulk charging for too long, charge with too high of a current during the absorbing phase and might even reach the final termination criteria "current dropped to near zero" too late.

 

Hmm . . .

 

I'm not a scientist or an engineer. And I am not arguing, because I really don't know how these BMS are designed. I do know that they have a high voltage cut off. As to exactly how the high voltage cutoff works, from the little I have read: when the battery (or the highest cell if they are out of balance) reaches the cut off voltage, the BMS no longer allows the battery to charge — is that correct?

 

The BMS doesn't need to measure the current, it just needs to know when to stop allowing charging, which is done by monitoring the battery voltage. If the voltage to the battery is cut off by the BMS, then no current can flow. Is this correct or wrong? Not being argumentative, just asking.

 

So I did some experimentation today when I was doing my daily LiFePo4 charging routine. I charged my LiTime 100AH battery and my 48AH (3 x 16AH battery bank) at 14.6 volts. After a few hours I went into the garage and both PowerWerx bench power supplies showed 14.6 volts and 0.00 amps of charging current. The inline amp meters I had connected to each battery also showed 0.00 amps of current flowing.

 

Then I cranked each power supply up to 15 volts for an hour and both batteries stayed at 0.00 amps of current. I did this while working on my laptop in the garage so I could monitor the charging process, since my wife would be upset with me if the house caught fire and burnt to the ground.

 

Just to do a 3rd test, I charged my other 48AH (16AH X 3) battery bank. This is the one I mentioned that had dropped down to 43% of capacity after around 700 charge cycles. After a while the PowerWerx charger showed 14.6 volts and 0.00 amps. I let it sit for an hour and the battery voltage dropped to 13.6 volts, which is typical. Since this battery bank has lost so much capacity, and I'm not going to keep it, I cranked the voltage up to 16.5 volts. The amps on both the PowerWerx and inline gauge went up to around 6.5 amps on the power supply and the inline ammeter, then quickly dropped to 0.00 amps on both meters — this happened in about 10 seconds.

[triplemon]

If your battery capacity dropped this low this fast - you got maybe 1/6th of the expected life out of it. Normal endurance would be something like 70% capacity after 2000 cycles.

 

Cranking up the voltage to 15V or even to 16.5V is definitely one of those things you really don't want to do if you want to get the full life out of your LIF battery.  They are not like flooded lead acid batteries where you can apply an overvoltage for equalizing and the later refill the water you cooked off. And yes, it looks like the overvoltage protection kicked in and did an emergency disconnect to prevent overheating and possible explosion from internal pressure buildup. LIF can still explode, its just they won't get into a thermal runaway where the Lithium burns off like in a magnesium fire.

Edited by triplemon, 12 November 2024 - 01:43 AM.

[ngatel]

Cranking up the voltage to 15V or even to 16.5V is definitely one of those things you really don't want to do if you want to get the full life out of your LIF battery.  They are not like flooded lead acid batteries where you can apply an overvoltage for equalizing and the later refill the water you cooked off. And yes, it looks like the overvoltage protection kicked in and did an emergency disconnect to prevent overheating and possible explosion from internal pressure buildup. LIF can still explode, its just they won't get into a thermal runaway where the Lithium burns off like in a magnesium fire.

It was just an experiment (with caution and monitoring on my part). I am very careful to charge batteries per the manufacturer’s specifications. All three battery banks would not accept a charge once the battery banks were at  ~14.6V as I expected would happen, even when I increased the voltage. Pretty interesting how the last battery performed at 16.5V (I was wearing safety glasses, standing always from the battery, and ready to turn off the power supply).

 

So it just confirms, to me, that a bench type power supply is a good charging solution with the caveat that it should be monitored and disconnected when the battery is fully charged.

 

Now solar charging is a little different, especially when the battery bank is being used day and night; and only charged during the day. My trailer had a 280W array with a 45A PWM charger and flooded lead acid batteries for 10 years. When I went with a larger AH LiFePo4 battery, I upgraded the solar to 880W. To save money, I kept the old solar system and added a second 600W array with a MPPT. Now both arrays charge the battery — two solar chargers. These are not “LiFePo4” solar chargers, but I was able to program both with the following settings:

• disable equalization
• absorption = 14.6V
• float = 13.4
• cancel float = 13.5V
• high voltage disconnect = 15.0V
• high voltage reconnect = 14.2V

Most of the set points I got from an article on Battle Born’s website for use with Morningstar TriStar charge controllers. I know this is a bit of thread drift, but think it might be valuable for the discussion of charging LiFePo4 batteries.