samguan

I have a 1800mah 3s and a 2200 mah 3s and was just wondering if i could connect them parallel to double the run time.

locksmack

You could, but you best do it with matched packs.

Remember this will make your ride much heavier.

Access

Just make sure they are at the same charge state before you do it.

PlaneHeli

If they are not at the same charge state at the beginning couldnt you risk overdischarging one pack before the LV cutout operates, risking damaging that battery.

Is there LV cutouts that can be connected to each individual battery to cutout that battery when LV is reached.

Its no prblem paraleling Nicad and NiMh, but they can be run until completely flat without damage.

Access

No, if they are not in the same charge state, one battery will charge the other, and if the voltages are far enough apart it could result in an overcurrent charge condition.

Metallover

I wouldn't do it. To run packs in parallel or series, they basically have to be ran like that all the time. They need to be balance together with an adapter. They need to be the same C rating. They need to be the same capacity.

Now this is all ideal. If you want to risk it it's not like the packs will blow up if you try it. The problem is, all the cells in a pack have to be the same voltage for a pack to run well and not have any problems. The pack with more capacity or a higher c rating will lose voltage slower then the other pack because it has more "power". That means all the cells will not be in balance you you run the risk of damaging the packs.

mattnin

The only issue is what Access said, make sure they are about the same voltage before you try it. Otherwise it will work perfectly. Even if they are different C ratings, and different capacities, it will work. They will auto-balance each other during discharge too. So for instance, if you have a 2300mah 30C cell and a 1100mah 25C cell and hook them up in parallel, you will essentially have a 3400mah 30C cell. Not sure if the current rating increases however.

Here is a battery pack I made doing what I described above using A123s.

Metallover

a123s are a way different battery then lipos are... Lipos won't take the abuse.

Access

With A123 packs you don't have to worry too much about overcurrent charge since they can accept a much higher charge rate.

This generally isn't a problem with LiPos, but with parallel combinations you have to be careful of cross-charge situations happening during rest periods, in reality the numbers are pretty low and they might not actually damage your packs, just don't run a pack with a higher internal resistance (a 16C pack, or an older pack that is nearing the end of its useful life) with one with lower internal resitance (a 40C pack, or a newer one).

I honestly don't understand the fascination people have with using parallel combinations to 'double runtime', unless you are stressing your batteries, running 1 battery and then one more consecutively will get you nearly as much runtime as running them both at the same time (in parallel). Your cost-to-runtime ratio which is the real concern for most people, basically stays the same. With aircraft it can be a real difference since you have to do the whole land, takeoff thing but with a truck it takes maybe 30 seconds to take off the body, change the batteries, put the body back on, unless it's some kind of endurance race or you have a bunch of small-capacity batteries, it just adds weight.