Need help on figuring size of chrager - RC Groups
Dec 10, 2010, 03:01 PM
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# Need help on figuring size of chrager

How do I figure out what size charger I need? I want to charge 2 3S 2200mah batteries at the same time in say 30 min. Can someone explain how to figure this? Sorry Im just not good at this electrical stuff.
Dec 10, 2010, 03:31 PM
TJin(Guy + Tech)
Quote:
 Originally Posted by wgregww How do I figure out what size charger I need? I want to charge 2 3S 2200mah batteries at the same time in say 30 min. Can someone explain how to figure this? Sorry Im just not good at this electrical stuff.
I recommend you do some reading.
Jan 01, 2011, 07:04 PM
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# finally

my hats' off to you tjinguy. it's refreshing to see someone steered in the right direction without a lot of chest beating and overly technical answers that some poor bright eyed shmuck won't understand anyway. i wish every category here had a first page of pertinent info that you had to read before venturing inside that area. it would make me feel better about asking questions. don't get me wrong, this is the best site going, it just gets tiresome reading through miles of stuff and not quite finding what you need. the 2 search features are great but not perfect due to pilot induced oscillation. it's nice finding a link with all that related info in one spot.

uh oh, was i ranting or what?
Last edited by 9XTremist; Jan 01, 2011 at 07:06 PM. Reason: cuz
Jan 02, 2011, 12:16 AM
Registered User
Quote:
 Originally Posted by wgregww How do I figure out what size charger I need? I want to charge 2 3S 2200mah batteries at the same time in say 30 min. Can someone explain how to figure this? Sorry Im just not good at this electrical stuff.
"1C" charge rate will charge a battery in approximately one hour.
The 1C rate is equal to the capacity in mAh divide by 1000. Hence for a 2200mAh battery it would be 2200/1000 = 2.2A

To charge in half that time you double the rate, in the example: 2 x 2.2 = 4.4A

To charge two 3S 2200 batteries at the same time you can connect them in series to make a 6S 2200 or in parallel to make a 3S 4400. Parallel charging is safer, easier and often faster.

Assuming you parallel the packs, the 1C rate becomes 4400/1000 = 4.4A.
To charge in 30min you have to charge at about 2C = 2 x 4.4 = 8.8A

Charging a 3S lipo at 8.8A requires approx 3 x 4.2 x 8.8 = 110W

So to charge two 3S 2200 lipo packs in parallel at 2C you need a lipo charger rated for at least: 3S, 8.8A, 110W.

In today's market there are many, many 6S, 5A/50W chargers but they won't do the job. There are also plenty of 6S, 10A/200W chargers which would certainly be suitable.

Don't forget that once you select a charger you need to ensure you have a suitable power supply. Since chargers are typically around 80% efficient, you need 25% more DC power input than the full rated output. Hence a 200W charger needs a 250W power supply to deliver its full output. Also note that high power chargers usually cannot deliver their full rated output from a 12V supply, needing 15V, 18V, 24V or some even 28V.

A good combination is the iCharger P350 (15V/23A, 350W) power supply and either the 106B+ (6S, 10A/250W) or better, the 206B (6S, 20A/300W).
 Jan 02, 2011, 02:32 AM Gone Insane .... Back Soon!! AWESOME !!!!!!!!! reply kgfly. very informative and you even suggested potential chargers, excellent excellent reply.
 Jan 02, 2011, 04:55 PM Registered User Thanks Meebo, If you want an Aussie vendor for iCharges I can recommend Aiden at arkrc.com.au Otherwise both progressiverc.com and epbuddy.com are highly regarded US vendors that ship to Oz and provide great backup.
Jan 02, 2011, 07:41 PM
Go Packers!
Quote:
 Originally Posted by kgfly "1C" charge rate will charge a battery in approximately one hour. The 1C rate is equal to the capacity in mAh divide by 1000. Hence for a 2200mAh battery it would be 2200/1000 = 2.2A To charge in half that time you double the rate, in the example: 2 x 2.2 = 4.4A To charge two 3S 2200 batteries at the same time you can connect them in series to make a 6S 2200 or in parallel to make a 3S 4400. Parallel charging is safer, easier and often faster. Assuming you parallel the packs, the 1C rate becomes 4400/1000 = 4.4A. To charge in 30min you have to charge at about 2C = 2 x 4.4 = 8.8A Charging a 3S lipo at 8.8A requires approx 3 x 4.2 x 8.8 = 110W So to charge two 3S 2200 lipo packs in parallel at 2C you need a lipo charger rated for at least: 3S, 8.8A, 110W. In today's market there are many, many 6S, 5A/50W chargers but they won't do the job. There are also plenty of 6S, 10A/200W chargers which would certainly be suitable. Don't forget that once you select a charger you need to ensure you have a suitable power supply. Since chargers are typically around 80% efficient, you need 25% more DC power input than the full rated output. Hence a 200W charger needs a 250W power supply to deliver its full output. Also note that high power chargers usually cannot deliver their full rated output from a 12V supply, needing 15V, 18V, 24V or some even 28V. A good combination is the iCharger P350 (15V/23A, 350W) power supply and either the 106B+ (6S, 10A/250W) or better, the 206B (6S, 20A/300W).
I can say I bought the P350 and 206b and love them both. Excellent customer service at Progressive as well.
Jun 21, 2012, 09:07 AM
Registered User
Quote:
 Originally Posted by kgfly Charging a 3S lipo at 8.8A requires approx 3 x 4.2 x 8.8 = 110W
Awesome reference guide, even if it was started a while ago.

I was wondering if you can help me figure out the math in the above equation.
3 = S rating?
4.2= ?
8.8= The above listed Amps result

I am trying to figure this out for a 3300 mAh 3S1P 11.1v 25c lipo battery, where I would need to charge two at the same time, and also checking for a charge rate of 1C vs 2C.
 Jun 21, 2012, 09:29 AM Registered User 4.2 = volts needed to fully charge one LiPo cell. Your other guesses are correct. For your specific example: 1C: 3.3A x 3 x 4.2V = 41.6W per battery, or 83.2W for two of them 2C: Twice that, of course, ie. 166.4W total. Of course it won't hurt anything if your charger/psu is capable of supplying more. They will be operating at lesser stress level and you just might need to do bigger packs in the future.
 Jun 21, 2012, 09:34 AM Registered User The ProgressiveRC calc seriously needs to be a sticky somewhere: http://www.progressiverc.com/chargingdemand Easiest way to do it, no math required for the lazy people!
 Jun 21, 2012, 11:23 AM Registered User Good link ,,,,,I'm the lazy guy Last edited by fast truck; Jun 21, 2012 at 01:03 PM.
 Jun 22, 2012, 03:16 AM Registered User You all are fantastic! Thank you for clearing this up. I was originally going to get a quad charger, then realized I could do with a duo charger, but then figured a decent iCharger would do the trick for me just starting out (still haven't purchased my first plane or anything else yet, but have been hitting the simulators and researching for several weeks). ProgressiveRC seems to have their act together on the iChargers and I will be looking to purchase from them. Great support in the forums, I appreciate it!
Sep 04, 2012, 01:45 AM
Registered User
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