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LiFePO4 batteries in parallel?

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#1 drjustice

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Posted 19 March 2019 - 12:14 AM

Let’s say I had access to LiFePO4 batteries rated as follows:

12v, 20Ah, 2A output

And I wired 3 of them in parallel

Would I end up with:

12v, 60 Ah, 2A output
or
12v, 60 Ah, 6A output

#2 Dynan

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Posted 19 March 2019 - 12:57 AM

Voltage is constant in a parallel circuit and additive in a series circuit and amperage is additive in a parallel circuit and constant in a series circuit.

 

So 6A.


Edited by Dynan, 19 March 2019 - 12:57 AM.

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#3 Noah4x4

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Posted 19 March 2019 - 02:38 AM

Concur with Dynan as regards 6 Amps and  it would give your rig the higher Amps necessary to permit the addition of more accessories. But do you need 6 Amps?

 

Admittedly, your rig will only draw what it needs and being over on Amps is important (too little can cause problems). But what are you trying to achieve? The Amp-hours rating is actually misleading. What matters more is Watt-Hours.

 

The reason I ask is whilst what you propose will increase the available (immediate) Amps, I don't think  it will increase watt-hours, hence won't increase their run time beyond the value of any individual battery e.g. 12v x 20Ah = 240 Wh). However, if you use them separately you would enjoy 3x this 12v longevity, albeit only at their original 12v x 2 Amps. So in summary, you can have 6A x 12v for a third less time than 2A x 12v. Makes sense when you think of it. You might be better served by using one battery for mount, one for camera, one for other peripherals rather than in parallel, albeit that also won't increase run time when drawing six amps compared to 2 amps.


Edited by Noah4x4, 19 March 2019 - 02:43 AM.


#4 HughGilhespie

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Posted 19 March 2019 - 04:12 AM

Hi drjustice,

 

Actually the above post is incorrect. Putting 3 identical batteries in parallel will give you 3 x the watt-hours. So, your 3 by 20 Ah batteries will now give you a total of 60Ah available. Of course if you take a higher current, you will use up the stored energy more quickly. But the total energy is still 3 times as much. 

 

But - and there usually is a but - AFAIK, it's not a good idea to put LiPO4 batteries in parallel. Like all cells based on Li chemistry, they need a carefully controlled charging regime and unless you disconnect the 3 batteries and use a separate charger for each battery, you may get problems. 

 

HTH

 

Regards, Hugh


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#5 drjustice

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Posted 19 March 2019 - 08:18 AM

[...] Actually the above post is incorrect. Putting 3 identical batteries in parallel will give you 3 x the watt-hours. So, your 3 by 20 Ah batteries will now give you a total of 60Ah available. Of course if you take a higher current, you will use up the stored energy more quickly. But the total energy is still 3 times as much. 

 

[...] AFAIK, it's not a good idea to put LiPO4 batteries in parallel. Like all cells based on Li chemistry, they need a carefully controlled charging regime and unless you disconnect the 3 batteries and use a separate charger for each battery, you may get problems. 

 

 

Thanks for the feedback. I was thinking about it in terms of discharge rate and longevity, but keep in mind I'm not EE and certainly an electricity noob.

 

Actually, I was pretty sure the answer would be 6A, but I asked without more specifics because I didn't want to be leading in my question, but here's more behind my thinking:

 

Since the world of batteries is vast, I know some batteries (even of the same general technology (eg: Agm or lead-acid)) can be manufactured for either deep-cycle-slow-discharge (eg: marine batteries) or short-discharge-high-amps (eg: car starter). So, if the batteries were rated at 2A, then maybe there was a reason for the low draw specification of each 12V 20Ah 2A battery, and if I were to put such batteries in parallel, then maybe drawing 6A would put too much strain on batteries which are simply not meant for specs beyond a 2A draw.

 

Also, putting chemistry aside, if the batteries are each rated at 2A output, then presumably the battery's internal cells might be linked together with small gauge wiring, or the battery internals might be otherwise flimsy enough to not support more than a 2A draw, but I have no clue. In any case, if that were to be the case, and the wiring was too small or the internals was too flimsy, perhaps putting several of them might generate side effects that might damage the battery, reduce its life, or perhaps cause a fire, but I actually have no clue.

 

FWIW, I had found on amazon a cell that seems to be nothing but a scam, but more research has yielded this, which I'm curious about:

https://www.amazon.c.../dp/B07KVK4BS3/

 

Also, Aliexpress seems to have countless options that are half price of US equivalents, there's another thread about it which I'm monitoring.

 

Reason for LiFePO4? Weight, because back problems.


Edited by drjustice, 19 March 2019 - 08:21 AM.


#6 WadeH237

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Posted 19 March 2019 - 09:04 AM

The reason I ask is whilst what you propose will increase the available (immediate) Amps, I don't think  it will increase watt-hours...

Sure it will.

 

3x the batteries is 3x the energy.  Watt hours is a unit of energy.



#7 WadeH237

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Posted 19 March 2019 - 09:21 AM

...if I were to put such batteries in parallel, then maybe drawing 6A would put too much strain on batteries which are simply not meant for specs beyond a 2A draw.

If you put them in parallel and drew 6A, each battery would provide 2A.

 

Of course, this assumes that the batteries are charge balanced.  And that would be my biggest concern with this setup.  Depending on how much current you draw, you could end up pulling different amounts from each battery.  I suspect what would happen is that the battery with the highest voltage would provide more current than the others, until they reach equal voltage.  During that time, you might draw more than 2A from that battery.  And then when the batteries are getting low, if the voltage on one drops lower than the others, the others will provide more current then the low one.

 

I think that you would be better off getting a single LifePO4 pack that provides both the current and the capacity that you need.  And I would not try to go cheap with this technology.  There are batteries built for storing power from solar panels for later use.  They are lots more expensive, but I would trust them much more than whatever I could find cheap on Amazon.

 

Of course, YMMV.  There are lots of people using small lithium based batteries to run their mounts.  The brand Talentcell comes up quite a bit.  I don't have any personal experience with them, but people seem to like them.


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#8 dghent

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Posted 19 March 2019 - 11:56 AM

 

FWIW, I had found on amazon a cell that seems to be nothing but a scam, but more research has yielded this, which I'm curious about:

https://www.amazon.c.../dp/B07KVK4BS3/

 

Also, Aliexpress seems to have countless options that are half price of US equivalents, there's another thread about it which I'm monitoring.

With a listed top output of 12.6V I wouldn't use these to power things like a mount. Sounds like motor stall city to me, especially in colder weather when a slewing mount's motors are going to benefit from 14-16V and you're going to be battling cold battery issues by default.

 

Also consider the source and the prices. Low price does not necessarily mean desired performance or reliability. Other issues I see: It claims "waterproof" but lists no IP rating, and it's not UL-certified so performance and safety are firmly in the who-really-knows category.



#9 Noah4x4

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Posted 19 March 2019 - 01:31 PM

Hi drjustice,

 

Actually the above post is incorrect. Putting 3 identical batteries in parallel will give you 3 x the watt-hours. So, your 3 by 20 Ah batteries will now give you a total of 60Ah available. Of course if you take a higher current, you will use up the stored energy more quickly. But the total energy is still 3 times as much. 

 

But - and there usually is a but - AFAIK, it's not a good idea to put LiPO4 batteries in parallel. Like all cells based on Li chemistry, they need a carefully controlled charging regime and unless you disconnect the 3 batteries and use a separate charger for each battery, you may get problems. 

 

HTH

 

Regards, Hugh

Yes it gives you 3x the Amp Hours of stored energy. But that is different to Watt-Hours which takes account of device consumption. Here we don't know the consumption of the OPs rig, hence why I asked that question.

 

Hence....

 

3 x 20 Amp Hour = 60 Amp Hours. AGREED.

But a 12 Watt device (12v x 1 Amp) drawing one Amp at 12v will last 60 hours.

A 24 Watt device (requiring 12v x 2A) will last 30 hours.

A 72 watt device (requiring 12v x 6 A) will last 10 hours.

So we are agreeing in that context - even if we don't agree on currency.

It is the watt hours requirement That will dictate longevity.

 

If the rig is drawing 6 Amps the batteries will indeed last one third of the time compared to at 2 Amps. However, 6 Amps is one hell of a lot for a telescope rig unless powering scope, scope side computer (NUC etc) , camera, accessories. My point was more about your second paragraph. Frankly, it's not a wise methodology.



#10 WadeH237

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Posted 19 March 2019 - 03:11 PM

If the rig is drawing 6 Amps the batteries will indeed last one third of the time compared to at 2 Amps.

No!

 

Forget about amp hours and watt hours.  If a single battery will power something for 2 hours, then 3 identical batteries in parallel will power the same something for 6 hours.

 

Here's the math:

 

Let's say that you have a battery that is rated for 20 amp hours at 12 volts.  Watts is amperage multiplied by voltage.  So this means that this battery has 20x12, or 240 watt hours.  In an ideal world (where you can discharge a battery fully without harming it, and it's voltage is constant through the discharge cycle), it would power a 12 volt, 6 amp device for about 3.33 hours.  Note that a device that's consuming 6 amps at 12 volts is using 6x12 watts, or 72 watts.  240 watts divided by 72 watts is also 3.33, so the math is consistent.

 

Now, let's say that you hook up 3 of these batteries in parallel.  Now, you have 20x3 amp hours at 12 volts.  This is 60 amp hours, or 720 watt hours.  Now you can power your 6 amp, 12 volt device for 10 hours.  And by no coincidence, your 720 watt hours, divided by your 72 watt device, is also exactly 10 hours.  That is 3x the run time of a single battery.

 

Remember that, no matter how much capacity your batteries can store or provide, your device will never consume more power than it needs.

 

In terms of capacity, what the OP wants to do is just fine.

 

The concern that I raised earlier is that his device is pulling more amperage than any one of the batteries is rated for.  If all of the batteries are in an equivalent state, then they will share the load equally and that would be no problem.  But if the batteries are not in an equivalent state, then the 3 batteries might contribute different amounts.  In that case, at least one of the batteries is guaranteed to be delivering more than its rated 2 amps.  What happens in that case, is that the overworked battery might disconnect (if it has a smart battery management system).  Or it might get too hot.  Or it might cause internal damage to the battery.  We really don't know, so it's best to avoid the possibility.

 

The other concern I have about the specific battery that he linked, is that we don't know the actual capacity of the battery.  It claims to be 20,000 milliamp hours.  I would be happier if it said 20 amp hours instead.  When one of these battery vendors lists the capacity in milliamp hours, I have to wonder if they are using the battery voltage or the single-cell voltage when stating the capacity.  The label on that specific battery lists the output at 9.6 to 12.6 volts.  The first red flag here, is that they consider the battery to be in-spec when it's delivering only 9.6 volts, which is not enough to run his rig.  The second observation is that it is likely made up internally of groups of 4 LiFePO4 cells that are each rated at 3.2 volts nominal.  That's great for making 12 volt packs, because 4 of these in parallel makes 12.8 volts - very similar to the top end of the stated output voltage.  But you do need to be aware that when these batteries get near the end of their charge, the voltage will drop.  But getting back to my original point about capacity, some vendors state the capacity in terms of amperage at the single cell voltage.  In that case, this could very well be a 20 amp hour battery at 12.8 volts.  Or it could be a 20 amp hour battery at 3.2 volts.  Because amperage by itself doesn't tell you the actual energy level, this could be 1/4th the capacity the ad is leading you to believe.  I would never buy one of these batteries unless it stated a specific watt hour rating to disambiguate this.

 

Oh, and 6 amps at 12 volts is not an unusual amount of current for a full imaging setup.  I know that's close to what mine uses.



#11 Luna-tic

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Posted 19 March 2019 - 03:54 PM

Let’s say I had access to LiFePO4 batteries rated as follows:

12v, 20Ah, 2A output

And I wired 3 of them in parallel

Would I end up with:

12v, 60 Ah, 2A output
or
12v, 60 Ah, 6A output

You'd get 12VDC with a 60 Ah capacity, capable of delivering 6 amps without a voltage drop. As current requirements exceed the rated delivery rate, voltage will begin to drop. Your equipment draws current from the battery, based on its current needs, rather than the battery actively supplying a specific current. As long as the equipment does not need more current than the battery is capable of delivering at its rated voltage, you're okay.

 

The Amp-hours rating is actually misleading. What matters more is Watt-Hours.

 

Actually, amp-hours is more useful. Watt-hours is just the voltage times the current in amperes delivered over a set time period. We would assume that our equipment requires 12 volts nominal. Amp-hours is the current delivered over a time period, irrespective of the voltage driving it, so figuring watt-hours just adds more to the equation than needed. Batteries are rated in amp-hour capacity, so just knowing how much current a piece of equipment requires to run is all that's necessary to determine how big a battery you need to run the equipment a desired amount of time, and works the same if you're using equipment of different voltages, such as 12V from the big stuff, and maybe have a 3V or 5V USB supplying something else. Just add the current needs from all the pieces together. You do need to figure in a reserve when choosing the size of the battery, due to how much the battery can be drawn down before either damaging it, or before it has lowered the residual capacity to the point that current delivery begins to affect the voltage. Generally, 30% on a deep-cycle battery, more on a starter-type battery, since they aren't designed to be drawn down as much. LiFePO batteries can be drawn down much more before damaging them, and they have a much higher number of charging cycles than other Lithium batteries.

 

 

But - and there usually is a but - AFAIK, it's not a good idea to put LiPO4 batteries in parallel. Like all cells based on Li chemistry, they need a carefully controlled charging regime and unless you disconnect the 3 batteries and use a separate charger for each battery, you may get problems. 

You can parallel or series connect Lithium batteries, just the same way you'd do lead-acid types. I used to do it all the time with radio controlled planes, by interconnecting several packs of differing capacities to get what was needed. Voltage has to be the same between packs, or the stronger pack will overcharge the lesser pack(s) and can overheat them. When I was flying R/C, all we had was LiPoly and Li-ion, LiFePO's hadn't been developed yet.

LiFePO batteries are much more forgiving of their charging regimen than other lithium batteries, but it's probably still a good idea to charge paralleled setups individually if possible. 


Edited by Luna-tic, 19 March 2019 - 03:59 PM.


#12 Noah4x4

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Posted 20 March 2019 - 02:18 AM

We were actually agreeing about the unchanged impact on battery longevity at constant voltage and constant amperage. But the thread opened with a question from the OP,  "will this (parallel chained) combination of batteries generate 2 Amps or 6 Amps"? That question suggested to me that the OP's objective might now be to seek 6 Amps and not be content with the individual batteries native 2 Amps. 

 

My original point therefore was that if we don't know the watt-hour rating (or the amps ACTUALLY being consumed at 12 volts) by the aggregate devices to be powered by these batteries  (and we don't have that information from the OP's original post) we can't advise the OP whether this proposal is going to supply adequate amps or even be wise. 

 

We can then only respond generically to his original question, which could easily lead to misunderstanding.  I was particularly over-thinking things here about how we might accommodate a situation where a specific device in the OPs rig had a variable voltage range  (such as a "12v to 19v" Intel NUC).  We instead got sucked into a largely irrelevant  debate about how long the batteries will last at any constant voltage and constant amp draw, not about whether this route is sensible in the OPs specific circumstances. That is why I asked the questions irrespective of the amps that can be generated, what is the amp draw that is actually required? How does it relate to the (now) available amps?

 

Yes, if you parallel chain three 20 Ah batteries that each output 12v x 2 Amps you get 60Ah stored energy. Yes, if you have a device drawing (say) 2 Amps, then the supplied power will last just as long whether the batteries are used singularly/sequentially or in parallel. I don't disagree with any of that. But if the Amp draw increases, the rate of discharge will do so too. So does the OP need six amps or two? That is crucial missing information.

 

We then all further concluded it is probably unwise to proceed with parallel chained batteries because of issues of irregular discharge and charging. Frankly, best advice, if you want 6 amps and 60 Ah instead get a single 12v battery that can deliver that such as a Tracer, and not risk chaining three cheaper 20 Ah (2 amp) substitutes. Alternatively, use one battery for mount; one for camera etc and keep within their regular rated amps.


Edited by Noah4x4, 20 March 2019 - 02:22 AM.


#13 drjustice

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Posted 20 March 2019 - 03:38 PM

"So does the OP need six amps or two? That is crucial missing information."

 

4-6 amps, powering the following:

 

0.2A guide camera

0.5A capture camera

0.5A camera cooler  (when at temp)

0.5A mount (tracking)

1.0A dew heater  (approx)

1.5A mini computer (guiding, capturing) (approx)

 

Plus some peak draws for slewing and getting the camera at the proper temp in the first place.


Edited by drjustice, 20 March 2019 - 03:38 PM.


#14 Noah4x4

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Posted 21 March 2019 - 07:13 AM

"So does the OP need six amps or two? That is crucial missing information."

 

4-6 amps, powering the following:

 

0.2A guide camera

0.5A capture camera

0.5A camera cooler  (when at temp)

0.5A mount (tracking)

1.0A dew heater  (approx)

1.5A mini computer (guiding, capturing) (approx)

 

Plus some peak draws for slewing and getting the camera at the proper temp in the first place.

I would  use one 12v/2A 20Ah battery to power the cameras/cooler. Another to power mount/dew heater, then the third to power mini-computer. As others have pointed out, Power will last just as long in that configeration as any other without any risk issues as you have 0.5 amp headroom with all 'circuits'. I don't see the point of trying to daisy chain them in parallel and it could lead to a bundle of trouble.

 

I you want to consolidate and have only a single battery, a Tracer 22Ah would support your demands as it will support up to 10 Amps continuous discharge (but the devices only take what they need). Cheaper Chinese batteries often splice together 3.5v cells to attain 12v but sacrifice amps. 



#15 Luna-tic

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Posted 21 March 2019 - 01:14 PM



 We instead got sucked into a largely irrelevant  debate about how long the batteries will last at any constant voltage and constant amp draw, not about whether this route is sensible in the OPs specific circumstances. That is why I asked the questions irrespective of the amps that can be generated, what is the amp draw that is actually required? How does it relate to the (now) available amps?

 

 

We then all further concluded it is probably unwise to proceed with parallel chained batteries because of issues of irregular discharge and charging. Frankly, best advice, if you want 6 amps and 60 Ah instead get a single 12v battery that can deliver that such as a Tracer, and not risk chaining three cheaper 20 Ah (2 amp) substitutes. Alternatively, use one battery for mount; one for camera etc and keep within their regular rated amps.

 

 



I would  use one 12v/2A 20Ah battery to power the cameras/cooler. Another to power mount/dew heater, then the third to power mini-computer. As others have pointed out, Power will last just as long in that configeration as any other without any risk issues as you have 0.5 amp headroom with all 'circuits'. I don't see the point of trying to daisy chain them in parallel and it could lead to a bundle of trouble.

 

I you want to consolidate and have only a single battery, a Tracer 22Ah would support your demands as it will support up to 10 Amps continuous discharge (but the devices only take what they need). Cheaper Chinese batteries often splice together 3.5v cells to attain 12v but sacrifice amps. 

Discussing how much current is needed and how long the battery can deliver it is hardly irrelevant; that's the precise thing you need to know, regardless of whether we're daisy-chaining batteries or using one big one. I do agree entirely, though, that if you're using a single power supply for your equipment, one large battery is preferable over several smaller ones interconnected to reach a specific voltage and capacity. It's quite acceptable, though, to have several smaller batteries and use them for individual pieces of equipment; size each battery for the needs of what it will supply. Weigh the benefits, downsides and cost of either plan and do what seems most reasonable for the occasion. When I go to a star party, I have my 'big' (96 amp-hour) system as my main supply, but have a couple of smaller batteries as backups; I use the smaller ones if I'm just going out in the back yard for a couple of hours.

 

I addressed the OP's question as he asked it, "If I have X and  hook it up Y, do I get Z, or Z', or Z" ?"  I made an assumption that he had several small batteries already and wanted to optimize his power output. It's not how I'd go, but use whatcha got.



#16 WadeH237

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Posted 21 March 2019 - 01:25 PM

Cheaper Chinese batteries often splice together 3.5v cells to attain 12v but sacrifice amps. 

This comment makes no sense.

 

LiFePO4 cells have a nominal 3.2 volts.  This is regardless of their capacity or country of origin.

 

If you want to make a 12 volt LiFePO4 battery, you have two choices.  You can either connect 4 cells in serial to get 12.8 volts, or you can use electronics to boost the voltage.  I'm pretty sure that *everyone* does the first option, and builds packs with groups of 4 cells in serial.  Regarding capacity (which is amp-hours, which is a different thing than amps), if you take 4 cells that each have a capacity of 2 amp-hours, you will end up with a 12.8 volt cell that also has 2 amp-hours of capacity.  To make a battery with higher capacity, you connect many of those groups of 4 in parallel.  Even the batteries in an electric car, with huge amp-hours of capacity, are made this way (but grouping different numbers of cells to get higher voltage).  This method of construction is also independent of country of origin, or price for that matter.  Note that higher price batteries do tend to have higher quality components, and (anecdotally) are better at delivering performance that matches their specs.

 

Finally, if you actually are talking about the number of amps a battery can deliver (ie. the current, not the capacity), the math works the same.  If you take 4 x 3.2v cells that can each deliver 1 amp continuous, and you make a single 12.8v battery, it will also be able to deliver 1 amp continuous.  Note that the wattage delivered by the 12.8v battery will be 4x higher than a single 3.2v cell, so you are not losing anything.



#17 Phil Sherman

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Posted 22 March 2019 - 06:42 AM

This comment makes no sense.

 

LiFePO4 cells have a nominal 3.2 volts.  This is regardless of their capacity or country of origin.

 

If you want to make a 12 volt LiFePO4 battery, you have two choices.  You can either connect 4 cells in serial to get 12.8 volts, or you can use electronics to boost the voltage.  I'm pretty sure that *everyone* does the first option, and builds packs with groups of 4 cells in serial.

 

................

The nominal voltage isn't the full charge voltage which is over 4v. Many 12v LiFePO4 batteries are actually built with three cells in series, not four. These three cell devices only produce 9.6v when close to exhaustion. This voltage is below that of a lead acid battery that's exhausted, 10.8v under a heavy load. 

 

Four cell lithiums have a different problem. With a full charge, their output voltage can be around 16.8v which may be too high for some gear. If I were going to use a 4-series cell lithium battery, I'd add a 12v voltage regulator between it and the gear it's powering.



#18 WadeH237

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Posted 22 March 2019 - 06:54 AM

The nominal voltage isn't the full charge voltage which is over 4v. Many 12v LiFePO4 batteries are actually built with three cells in series, not four. These three cell devices only produce 9.6v when close to exhaustion. This voltage is below that of a lead acid battery that's exhausted, 10.8v under a heavy load. 

 

Four cell lithiums have a different problem. With a full charge, their output voltage can be around 16.8v which may be too high for some gear. If I were going to use a 4-series cell lithium battery, I'd add a 12v voltage regulator between it and the gear it's powering.

I've been thinking about building my own batteries, since I've been unhappy with what's available commercially at the lower cost tiers (mainly due to questionable marketing and lack of specs).  In the course of doing this, I have been doing some study about the different chemistries, construction techniques and battery management systems.

 

Most of what I am reading says that it's common for most lithium batteries to use groups of 3, but LiFePO4 specifically has lower voltage than the others and are typically in groups of 4.



#19 drjustice

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Posted 23 March 2019 - 10:05 PM

Does anybody know these guys in canada?  (CDN prices, divide by 1.33 for usd)

 

Anyone ever heard of LiFePOwer batteries? Any good?

 

http://solarshopping...-12V_p_186.html

 

http://solarshopping...-12V_p_187.html

 

Max charge voltage: 14.6v

Nominal voltage 12.8v

Max continuous discharge: 50a

 

bms included

 

Why would this not be perfect?


Edited by drjustice, 23 March 2019 - 10:36 PM.


#20 Dynan

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Posted 23 March 2019 - 11:58 PM

Why would this not be perfect?

Umm...the PRICE!!?!? scared.gif


Edited by Dynan, 23 March 2019 - 11:59 PM.


#21 jpbutler

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Posted 24 March 2019 - 09:20 AM

Does anybody know these guys in canada?  (CDN prices, divide by 1.33 for usd)

 

Anyone ever heard of LiFePOwer batteries? Any good?

 

http://solarshopping...-12V_p_186.html

 

http://solarshopping...-12V_p_187.html

 

Max charge voltage: 14.6v

Nominal voltage 12.8v

Max continuous discharge: 50a

 

bms included

 

Why would this not be perfect?

If you are willing to pay that much for a 50ah battery,

I was, and my back loves me for it.

Then build a complete setup using powerwerx stuff.

It might not be the absolute best price, but it is good quality stuff.

Atleast to my admittedly non expert self.

 

https://powerwerx.co...ithium-iron-pvc

https://powerwerx.co...oenno-batteries

 

John



#22 pregulla

pregulla

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Posted 26 March 2019 - 11:58 AM


 

But - and there usually is a but - AFAIK, it's not a good idea to put LiPO4 batteries in parallel. Like all cells based on Li chemistry, they need a carefully controlled charging regime and unless you disconnect the 3 batteries and use a separate charger for each battery, you may get problems. 

 

HTH

 

Regards, Hugh

When connected in parallel the batteries will balance themselves, even if capacity/internal resistance don't match. You don't need to worry about it unless you mix between chemistries with different voltages (that's a big no).  Connecting in series is a different story.



#23 dapalmer

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Posted 26 March 2019 - 10:46 PM

I see a lot of dangerous advice being given here.  LiFePO4 batteries should not be connected in parallel. In fact no lithium batteries should be connect in this way.  When you connect these batteries this way they will try to use the opposite batter as a charger. They do not play well together and it can result in excessive heat and can potentially cause a fire. I strongly urge you not to do this. Certainly the use of Ohm's law and basic math seems like a good idea, but this is a matter of the limitations of the cells physical construction - not Ohm's Law.  Lead acid batteries do not share this personality trait. I recommend you do a little research before taking this approach. If you need more capacity either split the loads or buy bigger capacity cells. You may get by with a poor decision for a while but there are scientific reasons why manufacturers recommend against paralleling LiFePO4 batteries.


Edited by dapalmer, 26 March 2019 - 10:52 PM.

  • otocycle likes this

#24 Phil Sherman

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Posted 27 March 2019 - 02:55 AM

I see a lot of dangerous advice being given here.  LiFePO4 batteries should not be connected in parallel. In fact no lithium batteries should be connect in this way.  When you connect these batteries this way they will try to use the opposite batter as a charger. They do not play well together and it can result in excessive heat and can potentially cause a fire. I strongly urge you not to do this. Certainly the use of Ohm's law and basic math seems like a good idea, but this is a matter of the limitations of the cells physical construction - not Ohm's Law.  Lead acid batteries do not share this personality trait. I recommend you do a little research before taking this approach. If you need more capacity either split the loads or buy bigger capacity cells. You may get by with a poor decision for a while but there are scientific reasons why manufacturers recommend against paralleling LiFePO4 batteries.

P,ease pass this information to Tesla, whose batteries are a massive series/parallel arrangement.



#25 dghent

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Posted 27 March 2019 - 05:52 AM

I think we can agree that Tesla isn’t chucking Chinese consumer-grade batteries into their cars.


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