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2032 3V Lithium batteries in parallel?

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#1 jtsenghas

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Posted 30 June 2020 - 11:57 AM

I'm wondering if those of you with more knowledge of Lithium battery technology can answer a couple questions regarding my possibly wiring a couple of 2032 3 volt lithium batteries in PARALLEL for possible increased capacity and time between battery changes on small devices such as finders.

 

These are the relative standard nickel coin sized batteries used in various electronics such as digital calipers, micrometers, and in red dot finders.

 

Screenshot_20200630-125441_Chrome.jpg

 

I'm aware that in some cases small differences in voltage between power sources wired in parallel can be problematic. 

 

What I'm wondering is if there would be any downside to use two new 2032 batteries wired in parallel for something that usually requires 3 volts, or two stacks each in series of two each in parallel to provide 6 volts. 

 

2032 batteries can't hold a lot of capacity due to their size, but they do very well for their weight.  I'm wondering if it is worth trying this, since these batteries have gradually gotten very cheap and standardized. 

 

I've seen on this forum (I can't remember who did it) examples where people have reworked 11 ounce Telrads and cut  them down for size and weight savings.  This rework also allows for this finder to be mounted further up an OTA for easier viewing.

 

I can imagine making a little battery pack of several 2032 batteries in parallel taking up a mere few millimeters of thickness. I'd expect three or four of them to last three or four times as one individual one would, though I'd expect to replace them as a set. 

 

Would introducing electronics to balance voltages be required for implementation of this?  I can't imagine any reverse currents among these batteries to be significant and would expect them to naturally reach equilibrium.  At these small voltage levels and scale would it be a problem? 

 

One of my current builds would benefit from such lightweighting.


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#2 MarMax

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Posted 30 June 2020 - 12:10 PM

I'm not knowledgeable regarding lithium batteries but applying the standard electronics series or parallel rules will work. No different than how golf carts use 6-6V batteries in series to get 36V.

 

Batteries in parallel will have the same voltage and double the capacity. Batteries in series will have the same capacity and double the voltage. If you want more capacity at twice the voltage you can do a series-parallel arrangement. Put two in series and then put two of the series sets in parallel. Now you have double the voltage and double the capacity.

 

I'm sure you can find the capacity of a 2032 battery if you want to do some calculations before you start making anything.



#3 Arjan

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Posted 30 June 2020 - 12:13 PM

You should really use a diode in series with each battery to prevent one battery discharging over another. Disadvantage is that diodes have a voltage drop, which dissipate energy and lower the working voltage.

Load balancing ICs used in battery packs may be a way to go, these use FETs for switching the batteries.

 

Edit: A very informative site is the battery university

https://batteryunive..._configurations


Edited by Arjan, 30 June 2020 - 12:18 PM.

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#4 jtsenghas

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Posted 30 June 2020 - 12:15 PM

Batteries in series will have the same capacity and double the voltage. If you want more capacity at twice the voltage you can do a series-parallel arrangement. Put two in series and then put two of the series sets in parallel. Now you have double the voltage and double the capacity.

Yes, that's exactly what I described above, however I don't know if there are any issues with seemingly trivial differences in voltage among lithium batteries thus  wired.  I'm perfectly aware of the summing effects of batteries in series. 



#5 pkrallis

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Posted 30 June 2020 - 12:21 PM

Just a thought but if you are going through the trouble of adapting to multiple 2032 you might as well adapt to AA or AAA cells with 2 cell units available on Amazon et al.  I have inadvertently left a finder on for days and it still worked fine for months in normal usage with AA cells.


Edited by pkrallis, 30 June 2020 - 12:23 PM.

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#6 jtsenghas

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Posted 30 June 2020 - 12:35 PM

Just a thought but if you are going through the trouble of adapting to multiple 2032 you might as well adapt to AA or AAA cells with 2 cell units available on Amazon et al.  I have inadvertently left a finder on for days and it still worked fine for months in normal usage with AA cells.

Yes, those are indeed options and still likely. Where size and weight are at a premium, though, I'm exploring options. The idea of several batteries secreted away in a cavity just a few millimeters thick has some appeal to me if it doesn't need to be serviced often. Plastic tape with holes in it to avoid shorts on the negative side and aluminum foil contacts on both sides make this incredibly easy and light to fabricate. 


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#7 kb58

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Posted 30 June 2020 - 12:58 PM

I'm an EE by training and normally I'd say that it's a bad idea. But electric cars use hundreds of individual lithium cells in parallel and apparently have no problem, so the practical answer is that it's probably fine. That said, God help you if one cell goes weak and starts accepting power from the parallel cells. Heating will result, leading to thermal runaway and eventual catastrophic failure of that cell to start, and likely many of its neighbors. Given that you're only using a couple small cells, the worst-case consequences are slight, so it's back to "you'll probably be fine."


Edited by kb58, 30 June 2020 - 01:00 PM.


#8 jtsenghas

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Posted 30 June 2020 - 01:06 PM

...Given that you're only using a couple small cells, the worst-case consequences are slight, so it's back to "you'll probably be fine."

That was my hunch before I asked.  The capacity and voltages are small, and I expect,  the ability of these thin things to dissipate heat good if failure of a single battery occurs. I thought I'd ask, though. 

 

If for no other reason to satisfy my curiosity, I'll probably check each battery with a meter before and after a significant amount of use. My hunch is that slight differences will equalize and all voltages would drop relatively uniformly thereafter. 



#9 jtsenghas

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Posted 30 June 2020 - 01:08 PM

...I mean, how catastrophic can a catastrophic failure of a 2032 3 volt battery be? 



#10 Jon Isaacs

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Posted 30 June 2020 - 01:29 PM

Yes, those are indeed options and still likely. Where size and weight are at a premium, though, I'm exploring options. The idea of several batteries secreted away in a cavity just a few millimeters thick has some appeal to me if it doesn't need to be serviced often. Plastic tape with holes in it to avoid shorts on the negative side and aluminum foil contacts on both sides make this incredibly easy and light to fabricate. 

Two AA batteries weigh 47 grams.  The Telrad, hang it over if you want to place it further forward.  

 

From my point of view, this is complicating something that is very simple and reliable and falls under that category of "If it ain't broke, don't fix it."

 

Of course if weight is a problem.. :)

 

6446676-Birthday Dob CN.jpg
 
Jon

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#11 jtsenghas

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Posted 30 June 2020 - 02:12 PM

Okay,  since I'm being challenged on whether what I want to do for myself would be worth it to me....

 

This is the operation being considered.  I might chop out three inches of a Telrad from just inside the face of the furthest wall to just behind the LED unit next to my thumbnail in this photo.

 

20200630_142015_compress40.jpg

 

I could epoxy the face on there.  I could then chop three inches off of the lid to suit.  The remaining cavity doesn't allow for enough room for even AAA batteries, and I don't want to mount them externally the way they are on my Rigel Quikfinder. I COULD, however arrange several 2032 batteries on the inside of a side wall of that cavity without getting between the reticule and mirror.  Wired in parallel I expect to RARELY have to change them. 

 

Finally, if I don't want to make a new riser pedestal I could chop three inches out of the middle of the provided one and epoxy that together, possibly with a hidden splint on the underside. 

 

Weight savings would be about three ounces, not a lot admittedly, but something. I could probably leave the Telrad on more too, with less risk of it getting bumped or damaged. 

 

The only loss would be the molded sun warning on the lid and Mr. K's name on the side. 

 

MORE importantly, the unit will be three inches shorter and could be placed three inches further up the UTA without overhanging so that I could glance at the Telrad circles from the eyepiece of my nearly completed scope. This would be slightly further from the eyepiece of my current scope rather than slightly closer. 

 

I SLIGHTLY prefer the Telrad over the Quikfinder for a few reasons.  This mod would reduce the differences between the two for size, which I've learned from others, DOES matter. 

 

You may say, "If it ain't broke, don't fix it".

 

I say,  "Wouldn't that be neat to try? It will allow for more room for the RACI finder too!"

 

MOST importantly, it would be, well, CUTE!  


Edited by jtsenghas, 30 June 2020 - 08:23 PM.


#12 Jon Isaacs

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Posted 30 June 2020 - 02:50 PM

I say,  "Wouldn't that be neat to try? It will allow for more room for the RACI finder too!"

 

 

When you are out there under stars, maybe you've traveled some distance to get to some dark skies, and the Telrad quits working or the mount fall apart, think of me.. 

 

There are somethings that need improving.  There are somethings that are best left alone. 

 

Jon



#13 jtsenghas

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Posted 30 June 2020 - 02:59 PM

There are somethings that need improving.  There are somethings that are best left alone. 

Okay, Jon, I'll leave your Telrad alone. 


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#14 kb58

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Posted 30 June 2020 - 03:03 PM

Okay, Jon, I'll leave your Telrad alone. 

Well played, sir.

 

I always get wound up when people tell me how to spend my money, but that's fodder for another thread.


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#15 halx

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Posted 30 June 2020 - 03:15 PM

Kinda cumbersome to use multiple battery holder. No? Or you've got a pack for a dollar off eBay?

For Telrad, I'd just get a SINGLE flat 3.7V LiPO cell in a most suitable size (there are dozens of sizes available) and a charger for it. Near zero DIY work (just add a larger resistor in series). E.g.: https://www.ebay.com...or-Recorder-MP4 Get two to swap them on the go.

 

On a side note, I'm using a USB powerbank to power my Telrad and now the QuInsight.

 

For RDF finders using the coin-cell (I have two). They are actually lasting for quite a good time on low. However, may get bad quickly from exposure to heat and moisture. Also I heard that in some newer models they might have a short-circuit-like conditions increasing the self-discharge. So it's advised to remove the cell when not in use for a long time, or use the cell contact breaker where possible (tape it).


Edited by halx, 30 June 2020 - 03:40 PM.

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#16 halx

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Posted 30 June 2020 - 03:19 PM

Oh, and for the size reduction. You don't have to mount it entirely on the OTA. I'm currently working on the 3DP shoe which puts the QuInsight entirely OUTSIDE of the UTA rim. So it takes just ~1" on the OTA edge for the shoe. Same is possible with the Telrad.


Edited by halx, 30 June 2020 - 03:41 PM.


#17 SteveV

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Posted 30 June 2020 - 03:22 PM

The AA's in the bottom corners of the back cavity don't obstruct the reticle on mine.  Well as long as the wires are out of the way. Do they on yours?  AA's or probably AAA's could fit in the back cavity then?  It appears AAA have 5X the capacity of 2032.  

 

Also placed a drop of ABS glue and PVC glue on the base.  Both softened up the plastic.  Any idea what The Telrad is made of?  Would it be better to weld with solvent than expoxy it back together?  



#18 jtsenghas

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Posted 30 June 2020 - 04:15 PM

There are somethings that need improving.  There are somethings that are best left alone. 

Jon, I hope you weren't put off by my dry sense of humor.  I appreciate your input, but perhaps as an inherent tinkerer I may be far more willing fix something not broken than you are.  

 

Last year I came close to reworking a Telrad and making it a vertical "Quik-Rad" of about the same size as I'm contemplating here with a mere shortening.  I REALLY would love to make this excellent tool just a wee bit smaller without loss of function.  I'm confident I can avoid loss of function. 


Edited by jtsenghas, 30 June 2020 - 05:06 PM.


#19 jtsenghas

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Posted 30 June 2020 - 04:25 PM

...Also placed a drop of ABS glue and PVC glue on the base.  Both softened up the plastic.  Any idea what The Telrad is made of?  Would it be better to weld with solvent than expoxy it back together?  

These appear to me to be made of  an ABS plastic, which lends itself well to injection molding.  ABS is the same material Astroscan scopes and Legos are made from. I'd expect it epoxy well, but would test the cut off pieces.  I would probably roughen the adhesive surfaces and the inside corners and use a reinforced epoxy paste, either JB Weld or it's faster and slightly weaker version JB Quik. JB Weld worked just fine on the patch on the Astroscan rebuild I did last year when I put a real focuser on a reworked tube. 

 

I'm quite confident that my Telrad won't fall apart or stop working as a result of my efforts. 



#20 jtsenghas

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Posted 30 June 2020 - 04:35 PM

Kinda cumbersome to use multiple battery holder. No? Or you've got a pack for a dollar off eBay?

For Telrad, I'd just get a SINGLE flat 3.7V LiPO cell in a most suitable size (there are dozens of sizes available) and a charger for it. Near zero DIY work...

I was forgetting about thin rechargeable batteries! That may be a good way to go.  

 

Since a Telrad uses so very little power, as evidenced by the numerous stories of it being left in for a LOOOONG time and still working, my hunch is I needn't overcomplicate this.  A little custom made 2032 battery holder could be trivial indeed, and definitely thin enough. 

 

I'm sure the slightly elevated voltage of those 3.7 LiPo flat batteries would be fine.  LEDs are pretty forgiving with modest over voltages.

 

Your link was already broken (unavailable) and many sources of cheap flat batteries aren't giving dimensions, but it DOES look likely that one of those would fit without obstruction in the reticule and mirror chamber.  That would allow for a third of the unit to go.

 

My opinion is that SOME of us at least would find that worthwhile. I do have a lot of 2032 batteries now, but a thin rechargeable battery has its appeal. 



#21 phonehome

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Posted 30 June 2020 - 04:35 PM

I'd look at a single CR123(a) 3 volt lithium battery.  It can be placed sideways in the battery cavity saving a lot of space.  You'd have more capacity than a pair of 2032's and probably a lot easier to fab one set of connectors - maybe even from the existing Telrad AA holder.

 

Ed


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#22 jtsenghas

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Posted 30 June 2020 - 04:46 PM

I'd look at a single CR123(a) 3 volt lithium battery.  It can be placed sideways in the battery cavity saving a lot of space.  You'd have more capacity than a pair of 2032's and probably a lot easier to fab one set of connectors - maybe even from the existing Telrad AA holder.

 

Ed

To be clear, I'm looking to chop off the entire 3 inches of the existing battery chamber shown in post 11 above and mount whatever I use for a battery in the side of the smaller chamber that has the reticule and mirror, without obstructing the image. 

 

I want to keep everything self contained for ease of use and flexibility for moving this mini Telrad among scopes. Customized mounts would be simple for me to make and on some scopes would allow for more elevation. 



#23 danmdak

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Posted 30 June 2020 - 04:53 PM

2 Decades ago I cut my Telrad down the 3" you mentioned. I mounted the AA battery pack off the scope, running small wires to the telrad. This reduced  Telrad worked fantastic and the weight difference, on  barely marginal mount and regarding balance issues, WAS noticed. I never thought of using 2032's...GREAT idea.... but I do think when I have time I will modify my other Telrads to take 2 of the 2032s in parallel. In the old days I would modify this tonite and report to you tomorrow, but taking care of ailing family members gives me little time right now.


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#24 jtsenghas

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Posted 30 June 2020 - 05:59 PM

Oooo oooo! I just ordered something that cost almost nothing and should arrive with free shipping eventually. The tax was $0.13 USD (Now isn't THAT a sign of the times! )

 

At some point I should receive FIVE of these nifty little 2032 cases with SWITCHES! 

 

20200630_184237.jpg

 

I could mount two or three of them wired in parallel to the sides of that small chamber on the Telrad with the switches accessible and turn individual ones on and off as needed. If I end up with a bum battery dragging down the voltage, or any issues with this wiring I could turn individual ones off to troubleshoot.

 

I could even use them one at a time and if I forget to turn off my Telrad or it gets accidentally turned on when not in use only the battery or batteries turned on will get drained.  If I'm out observing and a battery fails I can just switch on another by peering into my Telrad and flicking switches. Eventually I could change out all of them with a replacement card of them.  They are really cheap at some retailers. 

 

This will take a while, I'm sure while a two ounce package floats across the Pacific, but sometime this summer I should have a quick rework to do. 

 

Stay tuned.  Like many of my threads, something most of you have forgotten by the time it resurfaces should get updated with yet something else "fixed that wasn't broken"!

 

 


Edited by jtsenghas, 30 June 2020 - 07:05 PM.

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#25 halx

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Posted 30 June 2020 - 07:01 PM

Nice find indeed. Are they for 2pcs? That's prob. fits your bill best then. I've got several "cards" with these and other small batteries once when I have realized the rip off prices on them at all USA retailers. One tiny watches battery was priced at $30(!) at Target, when I've got 60 of them for $3 shipped (to be honest, the original casio one lasted for a couple of years, the china one need to be replaced every year...)

My link is dead indeed. Not sure why, prob. cookies-based. But it was just a random search.


Edited by halx, 30 June 2020 - 07:14 PM.



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