Tech Tricks: Homemade Balance Charging Cradles.

[benckie]

this thread is like the Aussie ford and holden, gm or ford, Chevy or doge trucks each person will pick out what they like for there reasons or regurgitate what they have seen else where.

if you want the best dam way to charge batteries its one by one with a 0.25 c charge at you are looking at 50+ hours constant charging for 10 batteries or 10 days if you do one a night

there is a reason why some of use like to series charge and go the extra mile and balance series charge and remember this thread is about balance charging cradles

 

[45/70]

......what most have been saying if the cells are close in voltage parrallel charge i think i said that atlest once, test each cell and go through them all to find the ones that have close voltage and charge them in parrallel, or just put them all together and series ballance charge

Actually, it's the other way around. If the cells are very far off from each other, you would do better to parallel charge them. Most hobby chargers with an "onboard" balancing feature are quite limited as to their balancing capability. If you use a separate balancing unit, along with your charger, then it's not so much of a problem.

Dave

 

[KiwiMark]

Actually, it's the other way around. If the cells are very far off from each other, you would do better to parallel charge them.

If the cells are very far off from each other then I would always charge them individually. I would never recommend charging cells as a group (parallel or series) if they aren't close to each other in voltage at least.
The main reason I have 2 hobby chargers is so that I can charge 2 cells completely independently at the same time, it also allows me to charge 2 groups at the same time - I could balance charge one group on 1 hobby charger and parallel charge another group on the other charger. I can charge 14 cells at once if I need to.

If they are a matched set used together then it should be fine parallel or balance charging them. Parallel charging will mean that you CAN'T get a graph of what goes into each individual cell (as I've mentioned) but they should charge just fine, I'd suggest checking each with your multimeter to ensure close voltages before connecting them in parallel.

 

[45/70]

......I'd suggest checking each with your multimeter to ensure close voltages before connecting them in parallel.

eg. within 0.5 Volts. Did anyone actually read Tom's post I linked to in post #73?

Dave

 

[LuxLuthor]

Actually, it's the other way around. If the cells are very far off from each other, you would do better to parallel charge them. Most hobby chargers with an "onboard" balancing feature are quite limited as to their balancing capability. If you use a separate balancing unit, along with your charger, then it's not so much of a problem.

Dave

Dave, I do not remember ever having read anything myself specifically about this topic to give an authoritative answer, and if you have a reliable resource it would be interesting to read why that makes sense. I'm not afraid of parallel charging, or even just balancing cells with each other separate from charging, but wanted them relatively close before starting (something like within 0.05 to 0.075V (corrected decimal place typo) apart). That's why I made this set of 6 cell magnet parallel leads that can be used for charging or balancing.

​

It didn't make "common sense" when I thought about a simple scenario (admittedly using unlikely extremes to exaggerate my question) where you had two Lithium Cobalt Ion cells that have voltages of say 3.10V and 4.15V.

Connecting them in parallel with a high conducting (low resistance) metal across the terminals is going to result in a high current, rapid discharge from the 4.15V into the 3.10V cell. You would need an oscilloscope to see the initial current spike which may get quite high. It seems that this may also trip the 5 to 6 amp output protection circuit, but doesn't seem to be a good policy for either cell.

 

[LuxLuthor]

eg. within 0.5 Volts. Did anyone actually read Tom's post I linked to in post #73?

Dave

I started my last post, and then went to take that photo and got distracted, and did not see your cross post in the meantime. I had not read your earlier post, or the link to Tom's thread, so thanks for pointing that out again.

While Tom's test has some rigor, I can see a number of issues in part because it is now 4-5 years old. He did not use cells with PCB circuits that have current limits. He did not use an oscilloscope scanning with a high enough frequency to pick up how high the initial current spike went, and I don't regard his $30 Craftsman 82062 DC Clamp Meter as an adequate testing device...so I would take his observations in that instance with a huge grain of salt.

In any case, your previous post contrasting with benckie did not necessarily imply you were talking about voltages within 0.5 Volts, which I do not consider being close to each other. I'm not really sure what you meant by saying "If the cells are very far off from each other, you would do better to parallel charge them." but I don't agree with leaving that impression out there regarding parallel charging.

My general guideline, similar to Kiwi-Mark is that before Li-Ion cells are put in parallel with each other, their voltages should be tested and be within 0.05 to 0.075V of each other.

Edit: Corrected the decimal place, and tried to fix previous paragraph in red to what I meant. Sorry for the confusion.

 

[45/70]

My general guideline, similar to Kiwi-Mark is that before Li-Ion cells are put in parallel with each other, their voltages should be tested and be within 0.5 to 0.75V of each other.

Lux, I'm not sure what your definition of "close in voltage" is, but if you take a LiCo Li-Ion cell that is at 3.7 Volts, or about 15% remaining capacity, and another that is 4.20 Volts, or fully charged, I would call that a fairly wide difference in voltage, yet it is 0.5 Volts. I'd also say that if you have LiCo cells that are 0.75 Volts apart, the lower voltage cell, or cells, are over discharged, or at maximum 3.45 volts.

My next question would be, how often do you charge cells, at the same time, whether in parallel, or in series with balancing, that are basically discharged, along with cells that are fully charged? My point being that this really isn't very likely to happen.

All that said, and I've said this before, I like to have my cells within 0.1 Volt when I parallel charge them. Usually, the cells I charge in parallel are "sets" that are reasonably well matched and are actually closer than 0.1 Volt. And yes, a means of measuring the voltage of your cells is mandatory, when dealing with Li-Ion cells, whether charging, using, or storing, you must monitor the voltage of Li-Ion cells.

Dave

 

[KiwiMark]

Usually, the cells I charge in parallel are "sets" that are reasonably well matched and are actually closer than 0.1 Volt.

This is also how I do it - I charge a set of cells which would typically be more than 1 cell that were bought together and have since been charged the same as each other and put into one device and drained together in series. Often when I remove those cells to charge them they are within 0.05V of each other, definitely nowhere near 0.5V apart.

I have 8 x IMR 16850 in one light, 5 x IMR 26500 in one light, 3 x 32600 in one light, 2 x 32650 in each of 4 lights, 2 x LiFePO4 16350 cells in my A2 and some other multi cell setups. I treat these as sets of cells and they are all the same age/brand/model of cells. If I get a crook cell then I'd buy a full new set and use the remaining good cells in another device, keeping complete sets together.
There really isn't any reason for any of the cells I use in sets to ever be very far apart in voltage or capacity remaining. I should be able to safely charge any set of cells I have in parallel or balance charge in series.

When I pull a 16340 or 14500 or 18650 or 10440 cell from a single cell light I always connect it up to a hobby charger and charge it by itself. I'm not going to pull the 10440 from my LF2XT and the 14500 from my D10 and charge them both up together in parallel, different batteries used separately always get charged separately - that's the way I've always done it and I have no intention of changing that.

 

[LuxLuthor]

Dave, I screwed up a decimal place, and fixed the above posts. Sorry. My personal parallel connection guideline is a bit more conservative than Kiwi-Mark's of 0.1V as I meant to state it as the 0.05 to 0.75V difference.

I still question the basic general idea that "If the cells are very far off from each other, you would do better to parallel charge them." -- for the reasons I stated earlier. I made the mistake of reading your subsequent post as 0.05V and do regard 0.5V as too "far apart" for parallel charging. If you said that based on Tom's earlier study, then I still question that for the reasons stated earlier.

 

[45/70]

Lux, I think your 0.050-0.075 Volt limit is fine, you really can't be too careful, however I think it's being a bit more cautious than necessary.

In Tom's test, his setup had a voltage difference of over 2.00 Volts, not the final recommended maximum of 0.50 Volt. Regardless of the accuracy of the clamp ammeter, the general characteristics of what happened when the cells were paralleled, still applies. The duration of the peak high current, whatever the actual value, was very brief. And, as he mentioned, LiCo cells are comfortable with surges as high as 10C and I really don't see an amperage that high occurring, if the 0.50 Volt differential rule were followed. As for cells with protection circuits, I would think that the surge is so short, that most would not trip and would survive the half second, or so spike. I could be wrong here, as I've certainly never tried it.

Again, I really don't see anyone purposely charging cells that are basically discharged, along with fully charged cells, which is about what you would have to do to get a 0.50 volt difference between cells. That said, I would definitely consider 0.50 Volt as a maximum differential, and a value to best be avoided.

My comment "If the cells are very far off from each other, you would do better to parallel charge them" was considering the fact that the most common hobby chargers used here on the Forum have a maximum discharge current of 100-300mA during balancing. Considering this, parallel charging would be much more suitable for cells that were "very far off" in voltage, as the charger would be limited to a 100-300mAh correction per hour, whereas parallel charging would yield much faster results.

Another point I would like to bring up, is that many here on the Forums believe that because hobby chargers are designed to charge NiCd/NiMh and Li-Ion cells in series, that this is the best way to charge cells. This is not necessarily true. The primary reason hobby chargers are designed to charge cells in series is because in the R/C hobby, cells are usually welded or soldered into "packs". In this situation there is no choice as to how to charge the cells, you can either charge them in series, or charge them in series, and that's it. In our hobby, where we most often use "loose", or individual cells, other means of charging, such as separately, in an independent channel charger, or in parallel for Li-ion cells, often is the better option.

Dave

 

[LuxLuthor]

Dave, thanks for being magnanimous in your posts, given my stupid typo/error! I always enjoy reading your posts, and have learned a lot from you.

I know you (like Tom) have a far above average understandings of proper battery use, and would not do anything unwise. I was more wanting to put reasonable limits on the idea that the farther your Li-Ion cell voltage are from each other, the better it is to parallel charge--which you have subsequently done. You and I have both read too many posts from new or inexperienced users who do not yet know about unique properties of Lithium primary/secondary cells, resulting in their trying to (or asking about) charging Lithium primary, mixing chemistries, not having a DMM, etc.

Thanks for your expertise and contributions!

 

[SilverFox]

Hello LuxLuthor,

I am shocked that you question the "precision" of my camp meter... 🙂

If we look at the theoretical values we come up with a maximum of 18 amps during the initial surge. The 18650 cell had a capacity of 1600 mAh, so it would experience a momentary surge of 11.25C. Most high quality Li-Ion cells are capable of handling a 10C surge without problems, and reality often falls a little short of theoretical expectations, so I still don't have a problem with a momentary surge involved.

The 26500 3200 mAh cell at 18 amps is only seeing a 5.6C theoretical surge.

It would be interesting to see if the protection circuit used on protected cells trip or are able to take this type of surge in stride. It would also be interesting to see if the actual surge current could be more accurately measured.

When using Li-Ion cells in series, the cells need to be well balanced and a 0.05 volt difference would be the maximum difference between cells, but when hooking cells in parallel for charging the difference in voltage can be higher.

Tom

 

[LuxLuthor]

Hello LuxLuthor,

I am shocked that you question the "precision" of my camp meter... 🙂

LOL! Well maybe if you had stepped up to "Radio-Shack Quality" for your 'campy' clamp meter!!! Although "Radio-Shack Quality" may be the modern example of an oxymoron, since "military intelligence" is getting stale.

If we look at the theoretical values we come up with a maximum of 18 amps during the initial surge. The 18650 cell had a capacity of 1600 mAh, so it would experience a momentary surge of 11.25C. Most high quality Li-Ion cells are capable of handling a 10C surge without problems, and reality often falls a little short of theoretical expectations, so I still don't have a problem with a momentary surge involved.

The 26500 3200 mAh cell at 18 amps is only seeing a 5.6C theoretical surge.

It would be interesting to see if the protection circuit used on protected cells trip or are able to take this type of surge in stride. It would also be interesting to see if the actual surge current could be more accurately measured.

When using Li-Ion cells in series, the cells need to be well balanced and a 0.05 volt difference would be the maximum difference between cells, but when hooking cells in parallel for charging the difference in voltage can be higher.

Tom

Yeah, it is more a question of the PCB limits and the oscilloscope confirmed duration, current amount, and condition of the "puppies" (Panasonic vs. Acme) being tested.

Then there's the general safe guideline of what "higher" should be limited to for parallel charging cell differences, under almost all reasonable circumstances.

One man's sensible "higher" may be 0.1V; another man knowing little about Lithium Cobalt may think a 1.75V difference is just fine (to intentionally exaggerate the point).

 

[HKJ]

I also want to check the current between two parallel batteries:

I used the above setup connected to my scope.

First test with two older cells:

A closer look at the initial spike:

Only about 2 ampere, that was not very much, how about using some new quality batteries:

And again a look at the initial spike:

A maximum of 6 ampere.

Note: My equipment can easily show 1 ms spikes.

 

[SilverFox]

Hello HKJ,

Thanks for checking on that.

Another thing to keep in mind is that we are talking about charging cells that have been discharged. The worse case is to parallel a fully charged cell with a fully discharged cell.

When we move to the other end of the spectrum we vary easily could find ourselves in the situation where we are paralleling a cell with a voltage of 3.1 volts to a cell with 3.6 volts. Here we have the same 0.5 volt difference, but both cells have about zero capacity to support a current surge.

Tom

 

[45/70]

HKJ, nice job, as usual!:thumbsup: Very interesting results. I might also point out that the differential voltage here was more than 0.50 Volt in both cases, adding support for this being a safe recommended maximum value, IMO. Just the same, closer is always better.

Lux, thanks for the kind words. I needed that, not so much as pertains to CPF, but just in general.🙂 It seems we both are keeping an eye out for the newcomers, and attempt at least, to prevent them from running into problems.

Dave

 

[LuxLuthor]

HKJ,

That was some superb work, and exactly what I would have wanted to see on many aspects.

1) You demonstrated and captured the ms spike by testing with your oscilloscope

2) You used more up to date AW cells which also answers the question of how this would work with a current spike going through a cell PCB in this scenario. One question was not knowing what amount and duration of a current spike AW has his chips set at before interrupting the circuit. The other was how "hearty" are his PCB components when subjected to higher spikes.

3) You used extreme differences of voltage, in the second case a full 1.0 Volt difference (which is way beyond what someone would run into on a practical basis), which gives a wide margin of safety factor to protect the 'dunderheads.'

4) It appears you used somewhat thicker wire to not have that become a significant resistance barrier to a current spike.
​

If this was repeated a couple more times by others, it would make a strong case that it is safe to connect Lithium Cobalt Ion cells in parallel (for equalizing or charging) with little regard for even knowing the DMM voltages, but in any case could be moved from 45/70's 0.5 up to 1.0 V differences.

Superb work that is an invaluable resource on this subject. (? Put in threads of interest, with link starting at his post ?). :bow:

Another thing to keep in mind is that we are talking about charging cells that have been discharged. The worse case is to parallel a fully charged cell with a fully discharged cell.

And you know someone who doesn't have a DMM will do that. 🙂

HKJ, nice job, as usual!:thumbsup: Very interesting results. I might also point out that the differential voltage here was more than 0.50 Volt in both cases, adding support for this being a safe recommended maximum value, IMO. Just the same, closer is always better.

Lux, thanks for the kind words. I needed that, not so much as pertains to CPF, but just in general.🙂 It seems we both are keeping an eye out for the newcomers, and attempt at least, to prevent them from running into problems.

Dave

Dave, :bow:

 

[benckie]

very nice work HJK

2 amp spike is not much at all for discharge, but charge it might be but ive never used those cells.

6 amp to me might be a bit much, over time it will increase the internal resistance of the battery and slowly lower the end voltage and the life of the battery.

your test on the older batteries show a lower spike and im sure this is because of a higher internal resistance of the batteries, due to age and how they are used.

i will charge lipo,s at 2c but i dont charge my cheap li-ions at more then 0.20c, but thats some great info there, nice work the graphs make it nice and clear.

 

[benckie]

well i made a 6 cell balance charging lead from 2 x 3s balance leads in series with a 2 x 3s to 6s series adaptor so i can balance charge 6 x 18650,s at once, it can be broken down to make 2 x single 3s balance leads and with the 2 x 3s to 6s series adaptor i don't have to use main charge leads to the magnets.

revision 1

i cut the yellow xt60 plug off and added two 4mm bullet connectors and some heat shrink to plug straight into the charger, i brought a couple of these from hobbyking for under 3 bucks each and have used them for rc.

2 x 3s balance leads with 8 x 8 mm nickel coated rare earth magnets soldered on the end's, with a bit of heat shrink added to keep the balance wires in pairs.

all joined together, the balacnce leads simply plug into the adaptor.

all plugged into my icharger and p350 power supply, with 6 x 18650 trustfire flame batteries

individual cell voltage's

it cost around 15 bucks to make most of the cost was the magnets, ill shorten the leads i think and ill make some thing similar using a flat pack battery holder soon.

 

[benckie]

my old man pinched my 2s balance charge lead for his torch so i had to make another, i used shorter 22 awg 20 cm 2s balance extention lead and cut of the female end and used 18 awg main charge leads as the bigger stuff is not needed for these low charge rates and the usual male 4mm bullet connectors to plug in to the charger, lucky i had 3 magnets left over from my other leads i made.