Battery guru's please

[pacey]

Hi guys

I would like to make up a nun-chuck style Lipo battery pack using two of these; http://www.zerooneairsoft.com/produc...oducts_id=6007
Why, because the packs fit where I need them and if I don't have to I don't want to start making up packs from scratch.

Would i be right in thinking I can parallel up the pos/pos and neg/neg which will still present a 7.4v load to the gun and double the Mah value or will the Mah rating remain the same?
Secondly,
To charge by the main leads what would the charger see? 7.4v + a doubled mah value or single battery mah value? To balance the batteries would i just run the balance leads in parallel as well, would that present the charger with "2 cells" as per 7.4v standard or would some clever wiring be required?

Thank you please

[dave38x]

Re: Battery guru's please

If your gonna do that you'll have several issues:

One:
NEVER charge a lipo by the main lead - the balance lead is there for a reason - to stop you damaging your lipo - if you let the cells get slightly unbalanced and your voltage drop you may have a situation whereby one cell is out and begins to drop dangerously low while the other still functions - this isnt a good thing.

Two:
If you connect the two batteries in parallel then your main output will see 7.4V (or thereabouts) at the same C rating but twice the capacity, and therefore twice the theoretical max discharge current. If one lipo starts to warm up more than the other it will discharge faster, and run out of charge quicker - you'll then get a voltage mismatch between the two cells and one will begin to "charge" the other (which could be bad, depending on how large the disparity is).

Three:
Charging one via a balance lead will charge the other across both cells - again, not good.

To summarise - if you can seperate the batteries for charging and balance charge them individually you may be okay (may - thats not a will - thats a "to the best of my knowledge of kirchoffs voltage law". Any liposplosions or face-melting/gassing that may occur is entirely your own fault). In fact, just buy a nun-chuck lipo, plenty of them are available. And they arent that expensive.

Re: Fancy wiring on the balance chargers - some clever tricks with diodes may be able to allow you to charge two cells together, but is it really worth it? Far too much hastle/circuitry would be required.

[pacey]

Re: Battery guru's please

Advice noted, think I'll buy a ready made pack. As you point out and which is why I wanted to check, I didn't think they would behave like lead based batteries.

[pacey]

Re: Battery guru's please

Advice noted, think I'll buy a ready made pack. As you point out and which is why I wanted to check, I didn't think they would behave like lead based batteries.

[FlangTal1ty]

Re: Battery guru's please

I can't remeber the name (could't mention it on here anyway) but I believe there is a website that specialises in RC batteries. They pretty much make batteries to size depending on your request. You give them dimensions of the cells, the voltage/mah and connectors and they make them for you.

[Kingwell]

Re: Battery guru's please

What you are proposing is entirely possible, the only thing that you need to do is make sure that the charger balances it as 1 pack.

each cell needs to have its own wire going to the balancer, and obviously the grounds are common.

the only issue you'll run in to is some chargers require the discharge wire to be connected, which will cause an issue as you've got a 4 cell pack showing a 2 cell voltage. unless you've got a high end charger or a cheap one that doesn't require the discharge lead connected.

[Genista]

Re: Battery guru's please

The simplest way to do this is to use a 'Y' cable, with the connectors of your choice, so you can separate you batteries for charging and combine for shooting.

These leads are available commercially.

However, you should consider the point about the increased max current carefully.