First DIY pack for heated gloves

[hyperknot]

I'm a paraglider pilot and I'm using electric heated gloves. The problem is that the gloves barely last 1.5 hours on the highest setting, so I'd like to build a longer lasting pack.

The original pack is 7.4V 2200 mAh LiPo. My idea is to make DIY 2S1P 21700 Li-Ion packs and use them in place. The load is very easy, max 2A, continuous, smooth load.

I'm thinking about using the new high-capacity LG-INR21700-M58T cells, or Samsung INR21700-50E. I think they are ideal for low current usage.

Some things are still not clear though:
- Do I need to use a BMS with balancing functionality or I can use a simple one, like those thin rectangular ones?
- Do I understand correctly that all BMS have a BM point for measuring the individual cell voltages, but only the more complicated ones balance the charging and discharging between the cells?
- Do I need to use a balanced charger like, a B6 Mini, and solder balancing cables? As I see it, balancing cables are not very common on Li-Ion packs, while everyone uses them for LiPo packs, right?
- Can I use the original CCCV charger? It has a Y cable so I believe it charges in parallel. It's very low current, 1.2A for both batteries in parallel, but I'm only planning to charge overnight.
- Do I need anything for building the pack, like those insulators and spacers? I bought a spot welder for this, so the welding should be straightforward, I just don't know about the rest, such as spacers, insulators, etc.

 

[amberwolf]

I'm a paraglider pilot and I'm using an electric heated gloves. The problem is that the gloves barely last 1.5 hours on the highest setting, so I'd like to build a longer lasting pack.

The original pack is 7.4V 2200 mAh LiPo.

How long do you need it to last? If 2.2Ah lasts 1.5 hours, then to last 3 hours you need 4.4Ah. For 6 hours, you'd need 8.8Ah. Etc.

If the cells being used now have better cold-functioning characteristics than the new ones, you may need a proportionally bigger pack than otherwise, to ensure enough voltage over the whole discahrge curve given greater voltage sag at lower temperatures. If the new cells are better in the cold, you can get away with a proportionally smaller pack.

- Do I need to use a BMS which has balancing functionality or I can use a simple one, like those thin rectangular ones?
- Do I understand correctly that all BMS have a BM point for measuring the individual cell voltages, but only the more complicated ones balance the charging and discharging between the cells?
- Do I need to use a balanced charger like a B6 Mini + solder balancing cables? As I see on li-ion packs the balancing cables are not very common, while for lipo packs they are?
- Can I use the original CCCV charger? It has a Y cable so I believe it charges in parallel. It's very low current, 1.2A for both batteries in parallel.
- Do I need anything for building the pack, like those insulators and spacers? I bought a spot welder for this, so the welding should be straight, I just don't know about the rest, spacers, insulators, etc.

Any new pack you build, if it's the same series configuration as the previous (2S?) pack, can use the same charging method. If you didn't need a BMS on those, you don't need one on the new one either. Whatever anti-overdischarge protection (or method) you used on the old pack would work on the new one, as well.

If the charger you have uses a Y-cable to parallel the two cells, then that means you have to disconnect the series connection between the two cells every time you charge, and reconnect them every time you discharge. If that is not true then the Y cable doesn't parallel the cells. How *exactly* do you connect the present charger to your present cells to charge them? If you wire the new pack just like the old one, then you use that same connection method to charge the new one. If the old charger and pack have no balancing cables, and no balancer/bms inside the pack, then there is no balancing happening on the old pack.

Non-RC-Lipo packs don't usually use balancing cables or chargers with such cables, because they usually have the balancers built into the pack (BMS). Sometimes they don't use a BMS or balancers, just not caring if they are balanced, like some powertool packs.

If you prefer a BMS, then balancing functionality is only required if the cells are not matched. If the cells are identical in characteristics, then they won't get unbalanced (at least, until they age enough to become different in characteristics). Then you only need the BMS for overdischarge and overcharge protection.

If the cells are not tested to match them for identical capacity and resistance, etc., then you probably want the BMS to have a balancing function as well.


Physically I recommend using whatever protection (spacers, insulators, etc) are appropriate for the conditions the pack will be used in. End-insulators (rings) to ensure the interconnects can't short across the positive cap to outer shell negative are always a good idea. Cell spacers to keep the bodies of the cells apart so they can't short across their series connection is a good idea, too, (without them vibration could eventually rub the cells together until they wear thru their shrinkwrap and short the cans together).

 

[hyperknot]

Thanks for your detailed answer! I've uploaded a picture of the stock configuration. From factory it's a rectangular 7.4V 2200 mAh LiPo pack. I don't know what's inside, I guess it must be a 2S pack. The charger outputs 8.4V, and it has a Y cable, so I charge 2 of them at the same time.

I'd like to use a BMS to make sure that there is no chance of fire in case of a short-circuit for example. The temperature should not be that bad as the batteries are actually stored inside the glove. If I could double the run-time of the factory solution I'm happy.

About building it, I'll definitely use rings and also an additional layer of heat-shrink around the single cells, as I've read they recommend this for many OEM cells, which doesn't have a very robust insulation from factory.

 

[hyperknot]

What cells would you recommend from the following:

• Samsung 50E
• LG M58T
• LiitoKala 50E

I’m tiny bit concerned about the LG as some people say that it has very thin walls and ends. Also, in those reports it easily gets very hot on somewhat moderate loads.

On the other hand I’ve been using the Samsung 50E in my bike light for years and it’s been flawless in every possible way.

Do you think there are any concerns with the LG? Also, what about the LiitoKala, are these just repackaged Samsung cells?

 

[amberwolf]

I don't know any of the specific cells (there may be threads for them here on ES, as there are numerous cell-testing/etc threads around), but a few thoughts:

Any cell that gets hot has too high an internal resistance for the application, and is being used beyond it's capabilities. Don't use a cell beyond it's capabilities, and it won't get hot. I don't mean beyond it's *claimed* capabilities, where a cell is said to be "3C" or "50A", or whatever, but it's actual ones--meaning, look at it's internal resistance, and your requirements, and see how many cells it would take in parallel to reduce that to something that will create as little voltage sag as possible. (more or less ohm's law). If no real IR measurements are available then the discharge curves from the manufacturer can be used, you can see how much voltage sag a cell has for a given current load. Examples of such data are available at Lgyte.info.dk and similar sites, if you don't have a particular manufacturer site to get it from yet.

Consider that a company that has to repackage cells as if they were their own may not be buying the grade A versions, especially if those cells are cheaper than buying the originals. If the company (reseller / relabeler) doesnt' have a detailed spec sheet publicly available for every cell model like cell manufacturers should, it may be an indication they don't make them. If they don't have grading info, either, then they either aren't making them or aren't testing, sorting, and grading them, which means whoever buys them will need to buy several times more than they need, along with testing and sorting equipment, to match the cells to each other and create batches of matched cells to actually build packs from.

Note also that resellers of cells, from any company, may not be selling htem as matched sets, either, so any buyer may still (probably will) need to do the matching, etc (which also means buying more than needed--how many more depends on how close they need them to be matched (perfectly is best), how many they need in total for a pack, and how closely matched the cells are from the seller. The worse the matching from the seller, and hte more cells in a pack, and the more closely matched the final pack is desired to be, the more spare cells that must be bought--up to at least several times as many cells as would be needed to build the pack from, in the less-good cases.