How to charge 2 Li-Ion in series??

[Gogg13s]

Hey ECF I need help bad. I'm not any kind of electrical genius so I need the pros help on this one. I'm building a mod and I want to incorporate a charger in the mod that will charge two 14500s in series. I was looking on the TI website and the have some 2 cell Li-Ion chargers but I don't understand how to wire it up. I'm sure there has been this discussion before bit I don't see it. Is there a pre built board I can buy or does anyone have good schematics I can use. I will appreciate any and all help. Thanks again.

Gogg13s

 

[jhonutz]

I use ltc1732,good IC, but you need to have some electronics knowledge.I don`t know if you find to buy 2 cell charger modules. for schematics you need datasheet of IC http://pdf1.alldatasheet.com/datasheet-pdf/view/105710/LINER/LTC1732EMS-8.4.html . Simple way, try to find an electronic engineer in your town.

 

[VpnDrgn]

Battery Junction has li-ion batt packs that, according to them, have a special pcb with poly switch fuses to allow charging with
a multi-cell charger. The only other generally accepted method is to wire up a double throw switch to change the batts from
series to parallel so that you can use a regular charger. Some members have stated that they charge batts in series with a
regular charging circuit with no problem, but I think the general consensus is that this would not be the safest thing to do
because eventually the batts would become unbalanced.

View attachment VV BOX MOD V2.pdf
Here is a schematic for a VV box that I planned to do using the Batt pack and a Universal multi-cell charger from Battery Junction.

 

[CraigHB]

I believe most of the 2 cell Li-Ion chargers are not balancing chargers (even the controller chips). In other words, they use 2 wires, one on the negative end of the pack and one on the positive end of the pack. The best way to charge a Li-Ion pack is with a balancing charger that uses one wire on the negative end of the pack and a wire for each postive terminal in the pack. For two cells that would be three wires. There's no major issue with using a 2 wire charger that precludes it, but there is the potential for unbalanced charging. If one cell wears fast than the other, the less worn one will get over-charged which damages the cell.

There are two approaches to builit-in charging for a series mod. You can build the electronics into the mod or use a dedicated connector that simply connects the pack to a two cell charger, be it 2 wire or 3 wire.

I don't really see that much advantage to building the electronics into the mod. It's only the difference of using a 9V wall wart or a similarly sized charger. Like 6 of one, half dozen of the other. Personally, I'd just use a balancing charger like this with a dedicated connector built into the mod. I haven't actually done that since I've only been building single cell boosters, but that's how I would do it.

 

[Gogg13s]

@CraigHB

So your saying take apart that charger and incorporate it into the mod?

 

[jhonutz]

no, he say to make that charge external, and use only a connector to charge that 2 batt`s. It`s ok depends what is purpose of that modd after construction, for sale or for self use. If it was 1 batt, charger is good to be built in, to can charge from a laptop/PC.

 

[CraigHB]

Yeah, like jhonutz said. Again, you can either build the electronics into the mod or simply put a connector in the mod to plug the pack directly into a charger. I don't see the the advantage in building charging electronics into the mod. It's a lot more work without any real benefit. The only benefit I can see (and it's not much of one) is that you can use a 9V wall wart which is more commonly available than a pack or balancing charger. If you consider the value of your own time, it's certainly going to be more expensive.

For a single cell mod, it's a different story. In that case, the best option is to build your charging electronics into the mod. It gives you the flexibility to use a USB power source which is very handy. That's not the case with series cells since they require a 9V source. USB is 5V. Though there are ways to incorporate USB charging into a series cell mod, but you're getting into some fairly complicated electronics design. Again, not worth the trouble.

 

[slimest]

Great solution for charging and protection of 2 li-ion accumulators in series. Actually miniature balancer.
Protection Board Charger for 2 Packs Li-ion 18650 7.2V Battery Cell at max. 15A | eBay
This is only balancer with standard protection, it needs a CV/CC power supply 8.4V

 

[Rocketman]

Actually, ALMOST a balancer

Looking at the common connection to both dual Mosfet switches the charge or discharge current will be stopped by the voltage of either cell. When discharging, discharge will be stopped when one of the cells hits the lower voltage limit. Charging will be stopped when one of the cells hits the upper voltage limit. Good safety circuit for two Li-ion cells, but does not appear to be able to "Balance" cells.

I think that is similar to some 3S2P, 3S3P Laptop protection boards (I use some in Flashlight packs) that stop charge/discharge when one of the cell groups reach the upper/lower voltage threshold.