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Old Dec 26, 2010, 11:10 PM
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Help!
Charging two massive 6s packs

I have a big hovercraft project and wanted to power it with either 4 or 6 6s 5800mah lipos. This would result in a 12 cell 11600mah or a 12 cell 17400mah. This is for a full size rideable craft.

Here is my dilema. Since the batteries will be paired together their entire lives, I wanted to keep them wired together as they charge.

Let's look at one battery set. Can I keep the balance plugs of those 2/3 packs wired togther in parallel. Don't forget that that battery set will be in parallel. The goal is to charge an entire set off of one charge port and one balance port.

Remember that I have two sets. Can I combine the balance plugs and the charge plugs of the two sets together and charge them off of a 6s charger? Afterwards, the cells would all be balanced and the voltage will remain the same until you disconnect the batteries. You wouldn't have to worry about one sagging faster than the other because you plug them up in series as soon as you take the parallel connections apart.

The goal is to maintain the same voltage levels of all 24 or 36 cells. I might have to draw some kind of diagram.

Is this a stupid idea?

Thanks and come check out the project in the hovercraft forum.
Operation X-Craft
Kev
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Old Dec 27, 2010, 01:57 AM
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Charge in parallel, use in series... Brilliant plan provided the packs to be used in series are of the same pedigree, capacity, and usage history.

Back in the day before there were a plethora of balancing chargers to choose from, there were a few very highly regarded battery experts who advocated exactly what you've suggested - charge cells in parallel and then rewire in series to discharge.

It'll work just fine and it's far from a stupid idea.

Mark
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Old Dec 27, 2010, 04:00 AM
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Parallel charging works fine. Of course connecting everything in parallel will give you effectively a 6S 34,800mAh battery to charge. You're going to need a really serious charger if you want to balance charge that in less than a day or two .

Steve
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Old Dec 27, 2010, 04:03 AM
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Here is the wiring diagram I had in mind. The difference between the two is that one is charge (parallel) and the other is (usage). I don't know if I will be able to use six batteries though, but it is the same setup with four batteries. It all depends on the funding...most likely all me. If so, then this may not be worthwhile.

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Old Dec 27, 2010, 04:21 AM
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So we know that the mAh of the 6 pack setup is 37,400mAh.

A x H = AH, where A=5
H = AH / A
37.4 / 5 = 7.48
-------------------------
7 hrs, 28 min

where A=7
37.4 / 7 = 5.3428
-------------------------
5 hrs, 20 min, 34 sec

where A=10
37.4 / 7 = 3.74
-------------------------
3 hrs, 44 min, 24 sec

Max charge current: 74.8 amps
Continuous discharge current: 561 amps
Max burst discharge: 748 amps

I think I'm safe even if I use the biggest motors money can buy.
I'm just having fun here.
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Old Dec 27, 2010, 04:22 AM
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That's a smart idea, and is the best way to go for huge models IMHO.

During this whole autumn I used 4 6S 5000mAh packs in my HPR115, a 115cm Catamaran for speed runs. They are paralleled to 6S 20,000mAh. When charging I parallel the 4 balance tabs altogether using THIS like what you're planning, no problem at all. A permanent connection would be even better if you don't mind the wiring may look a bit massy.

In my new project(a 140cm mono boat), I'll double the number of packs to 8. They'll be configured quite similar to yours, results in 12 cells 20,000mAh.
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Old Dec 27, 2010, 04:36 AM
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One more point based on your diagrams: NEVER forget to unplug the connection between the two groups of paralleled packs before you config them into 12S. You don't want to know what will happen.
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Old Dec 27, 2010, 05:09 AM
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I have a customer who did something similiar. His setup is 6S3P using PowerEdge 5000 6S 30C batteries and has 2 sets in his 63 lbs Giant Double Ugly Stick Twin.

The 2 sets are connected in series to make 12S. Each set is charged on a Bantam BC8HP charger using 3 of the Bantam EAC134P parallel balance connection boards.
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Old Dec 27, 2010, 05:39 AM
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Quote:
Originally Posted by Himalaya View Post
One more point based on your diagrams: NEVER forget to unplug the connection between the two groups of paralleled packs before you config them into 12S. You don't want to know what will happen.
That's right. You cant do that. I never knew why though.

I posted the original and the new.

Balance plugs can be connected as long as they are connected to a pack within their own set right? If so, I want to keep them connected. This would also ensure evenly balanced cells throughout that set.

This is how it wouldn't have been if the issue wasn't caught within the next two months.
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Old Dec 27, 2010, 05:50 AM
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This is it. (I hope) All wires will be concealed.
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Old Dec 27, 2010, 05:55 AM
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Quote:
Originally Posted by RC Accessory View Post
I have a customer who did something similiar. His setup is 6S3P using PowerEdge 5000 6S 30C batteries and has 2 sets in his 63 lbs Giant Double Ugly Stick Twin.

The 2 sets are connected in series to make 12S. Each set is charged on a Bantam BC8HP charger using 3 of the Bantam EAC134P parallel balance connection boards.
This is the same exact cell count and setup, just with bigger cells.
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Old Dec 27, 2010, 12:45 PM
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Parallel charge and series discharge is done often. Seen any 12s chargers lately?

mw
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Old Dec 27, 2010, 01:02 PM
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I knew it! I was wondering why I couldn't find any above 10s.

Thanks for the help guys.

Kevon
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Old Dec 30, 2010, 09:15 AM
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[QUOTE=boredom.is.me;16930064]I knew it! I was wondering why I couldn't find any above 10s.

Thanks for the help guys.


just to let you know at
they have a Hitec X4 Four Port Charger (44151) that charges 6S Lithium pack simultaneously with 50 watt per port the price is good to for that charger
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Old Dec 30, 2010, 10:51 AM
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Looks like you need a pair of FMA PowerLab 8 chargers.
http://www.revolectrix.com/home.htm
Plus a couple of surplus server computer power supplies.

Glen
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