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Old 05-23-2014, 02:31 AM   #1
garyp1029
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Default Parallel Charging

I parallel charge my 3s 1600 amh batteries at the same time. Ditto, the 3s 3200 batteries. My question--Is it safe to parallel 3s batteries of DIFFERENT mah--for example, a 1600, a 2200, and a 3200 at the same time?? My understanding is that I can safely do this---hook the three (all 3s) to the charger and (adding the amps) set the charger for a 1C charge of 1.6+2.2+3.2, or 7 Amps. Is this correct thinking? Thanks. Gary
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Old 05-23-2014, 02:46 AM   #2
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Originally Posted by garyp1029 View Post
I parallel charge my 3s 1600 amh batteries at the same time. Ditto, the 3s 3200 batteries. My question--Is it safe to parallel 3s batteries of DIFFERENT mah--for example, a 1600, a 2200, and a 3200 at the same time?? My understanding is that I can safely do this---hook the three (all 3s) to the charger and (adding the amps) set the charger for a 1C charge of 1.6+2.2+3.2, or 7 Amps. Is this correct thinking? Thanks. Gary
My understanding, as long as your cells are at roughly the same state of discharge, and have exactly the same number of cells, they can be parallel charged.

In fact, Cellpro sells parallel cable sets for this purpose.

http://www.revolectrix.com/cellpro_adapters.htm

http://www.revolectrix.com/MPA_XH.htm

This unit supports up to six parallel connected batteries, and each port is fused. Just in case.

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Old 05-23-2014, 03:41 AM   #3
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Same cell count is required. Same capacity is not.

Starting at the same voltage is desirable, but you can be off by a bit and be OK. I make sure I'm within 0.1v/cell.
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Old 05-23-2014, 04:26 AM   #4
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Originally Posted by fhhuber View Post
Same cell count is required. Same capacity is not.

Starting at the same voltage is desirable, but you can be off by a bit and be OK. I make sure I'm within 0.1v/cell.
Just looked again at the Cellpro parallel charging board, they indicate they have nine Polyfuses per port on each of their six parallel charging ports. Plus what looks to be automotive type 40 Amp fuses for each of the power leads.

A polyfuse is a self contained positive temperature co-efficient resistor type of thing that is very low resistance when cold, and far higher in resistance when they get hot. So, if your cells are perhaps 0.5 volts different as an example, if the current circulation gets to high, or if you reverse polarity something, the corresponding polyfuses will get hot, and shut things down, protecting all your wiring. IMHO, for some $60 or so, seems reasonable enough in price versus hard wiring a bunch of batteries in parallel during the charging process with no over current protection.

Nice thing about polyfuses, when they cool off, they automatically reset back to their "on" position. They've been around for awhile. In the old days, if you accidentally connected 120 VAC to your multimeters resistance ranges, it burned up your meter. Now, they're protected by those polyfuses. Case solved.

Didn't know you can get them at ratings up to 100 Amps though. At work, we used them for only an ampere or three. They are only about 20 cents each in large quantities.

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Old 05-23-2014, 08:54 AM   #5
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Yep, I parallel charge different capacities all the time, it's not an issue at all. As noted above, the batteries must be same cell count and roughly similar state of charge.

When connecting batteries always connect the main power plug first, then the balance lead. This means any short surge of current that will flow if your batteries are not the same voltage goes through the main power lead and not the fragile balance lead.
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Old 05-23-2014, 07:17 PM   #6
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That's interesting, as I have read elsewhere to plug the balance leads in first, as they would act kind of like resistors, limiting excessive current in case you plug in batteries with too big of a difference in charge states. I guess there could be arguments for either case.
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Old 05-23-2014, 07:45 PM   #7
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They would limit the current but in doing so they would burn themselves up and the balance board traces... ask me how I know

Connecting the main power connector first is the way to go for sure.
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Old 05-23-2014, 10:34 PM   #8
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That makes sense about the balance board. Though I wonder about the battery itself if a similar situation happened with the mains plugged in. Perhaps it's better to burn out the balance board and leads rather than have a battery fire? I guess the safest thing is to be absolutely sure the batteries are at similar charge states, but we're only human. Wonder how long until fused balance boards come out? !
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Old 05-23-2014, 10:46 PM   #9
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Originally Posted by xmech2k View Post
That makes sense about the balance board. Though I wonder about the battery itself if a similar situation happened with the mains plugged in. Perhaps it's better to burn out the balance board and leads rather than have a battery fire? I guess the safest thing is to be absolutely sure the batteries are at similar charge states, but we're only human. Wonder how long until fused balance boards come out? !
Check posting #4 of this thread. For $60 you can not make one as good for that number of $$$$.

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Old 05-23-2014, 11:18 PM   #10
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Originally Posted by xmech2k View Post
Though I wonder about the battery itself if a similar situation happened with the mains plugged in. Perhaps it's better to burn out the balance board and leads rather than have a battery fire? I guess the safest thing is to be absolutely sure the batteries are at similar charge states, but we're only human.
The 'danger' from connecting batteries at different charge states is greatly exaggerated. For experimentation purposes I once connected a fully charged and a used 3s 2200MAh battery together, with only a wattmeter in-between.

I got a brief spike of 20 Amps which decayed very quickly and after only seconds was within the 5c charge rate quoted for the LiPo in question. Neither battery got warm, or puffed up let alone burst into flames. 18 months later I still use both batteries, they work as well as any other of the same age showing no ill effects at all.

Where things do get a little 'exciting' is if you inadvertently connect batteries of different cell counts together. I did it once with a 4s and a 3s and burned the traces out on the balance board. The 3s battery got pretty hot but didn't puff up, and again it still works even today.
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Old 05-24-2014, 01:22 AM   #11
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Originally Posted by JetPlaneFlyer View Post
Where things do get a little 'exciting' is if you inadvertently connect batteries of different cell counts together. I did it once with a 4s and a 3s and burned the traces out on the balance board. The 3s battery got pretty hot but didn't puff up, and again it still works even today.
Reminds me of when I inadvertently connected two 4s 4000 to each other instead of connecting them in series to form a 8s (blame the Anderson poles). No explosion. The solder on the battery terminals evaporated within microseconds, effectively acting as a fuse. Still, a huge "don try this at home" on this, especially if burning up $120 worth of batteries isn't your idea of fun!

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Old 05-24-2014, 05:27 AM   #12
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Originally Posted by kyleservicetech View Post
Check posting #4 of this thread. For $60 you can not make one as good for that number of $$$$.
How'd I miss that? That's some neat technology. Thanks.
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Old 05-24-2014, 06:46 AM   #13
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Originally Posted by xmech2k View Post
How'd I miss that? That's some neat technology. Thanks.
Yeah
If someone tried to build a similar unit from scratch, it would cost 5 or 10 times more. Just in parts. Been there, done that.

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Old 05-24-2014, 07:29 AM   #14
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Originally Posted by xmech2k View Post
How'd I miss that? That's some neat technology. Thanks.

Yeah
Cellpro has a video on how this unit is set up with their Cellpro Powerlab 8 charger. Per their web page, this parallel charger setup also works with the '6 and '10xP chargers, as well as various other charger mfg's.

http://revolectrix.com/videos.htm?videoid=43

I've got two of the Cellpro Powerlab 8 chargers. Very nice, very powerful units. IMHO, they are the last charger you'd ever need to buy. One of these units will charge a 6S4P A123 battery pack at 30 Amps, running off of a 12 Volt DC source capable of 60 Amps. Just don't use a big deep cycle marine battery for the 12 Volt/50 Amp supply. They won't last more than a few months. Don't ask.

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Old 05-24-2014, 10:05 AM   #15
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Originally Posted by kyleservicetech View Post
Yeah
If someone tried to build a similar unit from scratch, it would cost 5 or 10 times more. Just in parts. Been there, done that.
Or you could buy one from Hobbyking for a fraction of the price (when in stock!): http://www.hobbyking.co.uk/hobbyking...onnector_.html

The HK version has only 4 outlets as opposed to the Cellpro's 6 but if you need more it's got connections for daisy chaining. You could buy four of the HK boards for the cost of a single Cellpro version. The HK one is also limited to 6s batteries where the Cellpro does 8s, but not many run single packs above 6s anyway.
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Old 05-24-2014, 03:49 PM   #16
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Originally Posted by JetPlaneFlyer View Post
Or you could buy one from Hobbyking for a fraction of the price (when in stock!): http://www.hobbyking.co.uk/hobbyking...onnector_.html

The HK version has only 4 outlets as opposed to the Cellpro's 6 but if you need more it's got connections for daisy chaining. You could buy four of the HK boards for the cost of a single Cellpro version. The HK one is also limited to 6s batteries where the Cellpro does 8s, but not many run single packs above 6s anyway.
Hobby king does not mention polyfuses on each balance lead. That could account for the lower price?

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Old 05-24-2014, 04:20 PM   #17
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Paraboard with poly fuses. Reasonably priced. US seller. I own a couple of them and they work great.

http://www.buddyrc.com/paraboard-v3-xh-t.html

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Old 05-24-2014, 06:46 PM   #18
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Originally Posted by kyleservicetech View Post
Hobby king does not mention polyfuses on each balance lead. That could account for the lower price?
The description doesn't mention polyfuses but you can see them quite clearly on the board just above the balance plugs. Seems to be the exact same board as Buddy RC are selling.
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