HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Jun 20, 2009, 06:25 PM
I miss my planes...
Lag_Janson's Avatar
Canada, ON, Milton
Joined Dec 2006
509 Posts
Discussion
Using Lipo batteries in Parallel

I've got a pair of 3s 2200mah batteries I bought at the same time, unfortunately, discovered I should have got large for the amps I'm going to draw. While the 2200 theoretically can handle the amperage, it seems safer to use both batteries to lighten the load. Using two batteries would also help with the CG on my plane.

The question is, what is the correct procedure for using lipo batteries in parallel? Is there a certain order of plugging things in which would be safest?
Lag_Janson is offline Find More Posts by Lag_Janson
Reply With Quote
Sign up now
to remove ads between posts
Old Jun 20, 2009, 08:30 PM
Registered User
ebill3's Avatar
United States, WA, Puyallup
Joined Oct 2004
5,965 Posts
Quote:
Originally Posted by Lag_Janson
The question is, what is the correct procedure for using lipo batteries in parallel? Is there a certain order of plugging things in which would be safest?
Make sure both packs are very close to the same voltage, or charge each pack separately. Connect the two packs with a parallel harness, then the harness to the ESC.

Then just leave them in paralal for charging.

Bill
ebill3 is offline Find More Posts by ebill3
Last edited by ebill3; Jun 20, 2009 at 08:36 PM.
Reply With Quote
Old Jun 20, 2009, 08:36 PM
Average User
M Ashmore's Avatar
Bakersfield, California
Joined Aug 2003
1,726 Posts
I've ran a pair of 3s 2500's in my Superstar for about 3 years. I always connect the parallel harness first. Then I install the pack in the plane and connect the esc. I charge the batteries separately, but only because it's faster using the 2 chargers I have.

Mike
M Ashmore is offline Find More Posts by M Ashmore
Reply With Quote
Old Jun 20, 2009, 08:38 PM
I miss my planes...
Lag_Janson's Avatar
Canada, ON, Milton
Joined Dec 2006
509 Posts
Yeah, I plan to charge separately. I'm never in any hurry at the field anyway. Thanks.
Lag_Janson is offline Find More Posts by Lag_Janson
Reply With Quote
Old Jun 20, 2009, 11:30 PM
Registered User
Prof100's Avatar
Canton, Michigan USA
Joined Jul 2007
16,562 Posts
Two same size, same brand, same age packs in parallel are a great way of increasing your amp capability and your run time. I do it all the time. I, too, use the two packs to help with weight distribution as well.

Bill
Prof100 is offline Find More Posts by Prof100
RCG Plus Member
Old Jun 21, 2009, 02:37 AM
Registered User
EricJ320's Avatar
Knoxville, TN
Joined Dec 2005
1,502 Posts
Quote:
Originally Posted by Prof100
Two same size, same brand, same age packs in parallel are a great way of increasing your amp capability and your run time. I do it all the time.

It's my understanding this is true when running packs in series, but isn't necessary for parallel. Packs can be of varying size, C rating, and age, just cell count and starting voltage must match. However, you must only use them to the output capability of the weakest pack in the parallel setup. For example, a 10C 3S 1500 mah and a 25C 3S 2000 mah pack in parallel should only be expected to put out 35 amps, or 10C of a 3500 mah parallel setup.

If that is wrong, someone please correct me. But that is what I have been told , and read here over and over about paralleling.

Eric
EricJ320 is offline Find More Posts by EricJ320
Reply With Quote
Old Jun 21, 2009, 03:45 AM
Registered User
Prof100's Avatar
Canton, Michigan USA
Joined Jul 2007
16,562 Posts
Quote:
Originally Posted by EricJ320
It's my understanding this is true when running packs in series, but isn't necessary for parallel. Packs can be of varying size, C rating, and age, just cell count and starting voltage must match. However, you must only use them to the output capability of the weakest pack in the parallel setup. For example, a 10C 3S 1500 mah and a 25C 3S 2000 mah pack in parallel should only be expected to put out 35 amps, or 10C of a 3500 mah parallel setup.

If that is wrong, someone please correct me. But that is what I have been told , and read here over and over about paralleling.

Eric
Eric,

I have no idea if what you said is true, but I, for one, would not connect a 10C 1000 mah pack in parallel with 20C 4000 mah pack so the combination was less capable than one of packs alone. It's a experiment not worth trying.

Bill
Prof100 is offline Find More Posts by Prof100
RCG Plus Member
Old Jun 21, 2009, 03:47 AM
Registered User
Staffs, UK
Joined Nov 2003
10,556 Posts
Quote:
Originally Posted by EricJ320
However, you must only use them to the output capability of the weakest pack in the parallel setup. For example, a 10C 3S 1500 mah and a 25C 3S 2000 mah pack in parallel should only be expected to put out 35 amps, or 10C of a 3500 mah parallel setup.
The words and the calculation are at odds...the output capability of the weaker battery is only 15A (1500mAh @ 10C). And anyway it's the current capabilities that are of interest not just the C-ratings.

It's reasonable to derate the output a little but you don't need to go as low as 15A or even 35A. I generally allow myself around 70% of the total current capabilities of the two packs. So for your combination 15A + 50A = 65A, I'd use no more than about 45A. For the more usual combination of two equal packs e.g. 2 x 2000mAh 25C = 100A, I'd use up to 70A (whereas your calculation seems to suggest the full 100A is fine ?).

But there are no hard and fast rules. Lower currents are always safer and easier on the batteries but then you're perhaps buying more bigger expensive batteries than you really need.

Steve
slipstick is offline Find More Posts by slipstick
Reply With Quote
Old Jun 21, 2009, 03:53 AM
Registered User
Staffs, UK
Joined Nov 2003
10,556 Posts
Quote:
Originally Posted by Prof100
I have no idea if what you said is true, but I, for one, would not connect a 10C 1000 mah pack in parallel with 20C 4000 mah pack so the combination was less capable than one of packs alone. It's a experiment not worth trying.
It's an experiment that has been done successfully many times...but I agree that your particularly extreme example of a 10A capable battery in parallel with an 80A capable battery 4 times its size is pointless. You'd get no more current and very little extra capacity.

Steve
slipstick is offline Find More Posts by slipstick
Reply With Quote
Old Jun 21, 2009, 04:06 AM
Registered User
Joined Jun 2008
583 Posts
One little tid-bit of info that was bestowed on me just this week about parallel packs is to as much as possible have the same ammount of resistance on both legs of the Y adaptor. If one leg has a bad solder joing causing higher resistance the esc will draw less "juice" from that back, pulling the bulk of it's energy from the path of least resistance....meaning... the pack on the side with less resistance will be drained at a faster rate. Even if you have LVC built into your ESC it's wise it get a audible or visual low voltage monitor for EACH pack. That was if one pack gets sapped more than the other you'll know it. Otherwise you'll have one overly discharged, possibly dammaged lipo and one still partially charged by the time the esc's LVC kicks in.... food for thought...

It's kinda funny. I asked about parallel'ing lipo's when I first got inot the hobby last year. I wanted to buy smaller/cheaper/lower C rating batteries and run them parallel to save on some $$. I asked if running them in parallel doubled the C rating the same way it doubles the mAh. I was told no, it didnt work that way. Now that I'm older and wiser I realise I prbly asked the wrong question, or used the wrong terms. Running in parallel if fact does not double the C rating at all.... It cut's the Amp draw in half....ROFL!!!!!
Tripod333 is offline Find More Posts by Tripod333
Reply With Quote
Old Jun 21, 2009, 04:11 AM
Registered User
Prof100's Avatar
Canton, Michigan USA
Joined Jul 2007
16,562 Posts
Quote:
Originally Posted by slipstick
It's an experiment that has been done successfully many times...but I agree that your particularly extreme example of a 10A capable battery in parallel with an 80A capable battery 4 times its size is pointless. You'd get no more current and very little extra capacity.

Steve
Steve,

It is like I said, an experiment not worth doing since you usually are paralleling packs to increase run time and would also like to enjoy increasd capacity for delivering the same or more current to your motor.

Bill
Prof100 is offline Find More Posts by Prof100
RCG Plus Member
Old Jun 21, 2009, 04:29 AM
Registered User
EricJ320's Avatar
Knoxville, TN
Joined Dec 2005
1,502 Posts
I think you guys are focusing too much on the numbers I used instead of the idea. I'm not saying I'd use those packs, I was using them only as a reference to show the idea that packs don't have to be identical, and 10C was easy math for 3:30 am. I agree it would be useless to use that pack configuration, and I guess I should have explained that better. But the principal still applies. Thanks for keeping me on my toes this early though!

Eric
EricJ320 is offline Find More Posts by EricJ320
Reply With Quote
Old Jun 21, 2009, 04:41 AM
Registered User
Prof100's Avatar
Canton, Michigan USA
Joined Jul 2007
16,562 Posts
Quote:
Originally Posted by Tripod333
...Running in parallel if fact does not double the C rating at all.... It cut's the Amp draw in half....ROFL!!!!!
That's a good way of looking at it. I think parallel packs are OK or best if the packs are very similar in terms of MAH, age, C rating and resistance.
Prof100 is offline Find More Posts by Prof100
RCG Plus Member
Old Jun 21, 2009, 05:27 AM
Registered User
Himalaya's Avatar
Joined May 2009
505 Posts
I soldered two pairs of 10AWG wire on the ESC, connect one pack, then the other.
Run them this way puts least stress on each connector and wire, wastes less power in wires and connectors.
Himalaya is offline Find More Posts by Himalaya
Reply With Quote
Old Jun 21, 2009, 04:28 PM
Registered User
Staffs, UK
Joined Nov 2003
10,556 Posts
Quote:
Originally Posted by EricJ320
I think you guys are focusing too much on the numbers I used instead of the idea. I'm not saying I'd use those packs, I was using them only as a reference to show the idea that packs don't have to be identical, and 10C was easy math for 3:30 am. I agree it would be useless to use that pack configuration, and I guess I should have explained that better. But the principal still applies.
Nope I wasn't focusing on the numbers at all I was pointing out that the principle was wrong and your numbers made that fact very clear.

Take some slightly more sensible numbers. If you connect a 2000mAh 10C pack and a 2000mAh 25C pack that's one battery that can do 20A and one that is happy at 50A. Your formula suggests treating them as a 4000mAh 10C pack i.e. maximum current 40A. That's less current than one of the packs on its own could supply and that simply doesn't make any practical sense.

Steve
slipstick is offline Find More Posts by slipstick
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion Using 2 lipo packs in parallel Absolut Beginner Training Area (Aircraft-Electric) 11 Mar 17, 2009 09:06 PM
Discussion Charging two lipo batteries in parallel yjin Batteries and Chargers 8 Nov 17, 2008 11:15 AM
Discussion Using Batteries in Parallel - or is it series .. ? Cooker Batteries and Chargers 3 Jun 30, 2008 08:22 PM
Discussion connecting lipo batteries in parallel for charging nashiem Batteries and Chargers 21 Jun 08, 2008 05:02 PM
Discussion LiPo batteries in parallel BigR Batteries and Chargers 1 Aug 29, 2006 09:05 PM