I'd like to parallel charge four (4) 1500mAh 2s LiPo packs using an iMax B6AC and a fused parallel board. I believe I'm able to charge at 6 amps, but I don't know where to set the capacity - set to 6000mAh or leave it at 1500mAh?

Thanks in advance for your help.

Set it to 6000

Yes... parallel means that 1C is summing all the packs together, you don't even have to have the same capacity pack with parallel charging.

for example, if you had 4 packs
1) 500mAh
2) 1000mAh
3) 1500mAh
4) 2000mAh

you simply add them all up to 5000mAh which would be 1C at 5A

Thanks faqcya and billdelong!

I also just read an article online which corroborates this before I saw your replies - it pretty good explanation at oscarliang.com/parallel-charging-multiple-lipo

unlikely you will be able to charge these 4/4cell 1500mah batteries at 6 amps.. maybe 3amp you have to factor in watts used to charge so what is this charger 50/60 watts?

He said 2S packs, however I do believe his charger is limited to 50W @ 5A max charge rate.

He was correct that 4 x 1500mAh = 6A charge rate for 1C, though the charger will max out at 5A which comes out to 5A/6A = 0.8C

Also note that when charging 2S/4P will not be the most efficient use of the charger.

Consider Ohms Law: W = V x A

4.2V x 2S x 5A = 42W

Sure, 42W is pretty darn close to the 50W max of the charger, but what if you wanted to take advantage of the full capability and squeeze that extra 8W to reduce your charge time by 50W/42W = 19% faster!

It is possible to charge 2 packs in series + 2 packs in parallel, all 4 packs would then max the charger at 50W output

http://scriptasylum.com/rc_speed/lipo.html