Charging 16s using 2x 8s chargers - what have I done wrong?

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Charging 16s using 2x 8s chargers - what have I done wrong?

Post by inedible » Jul 30 2015 12:10pm

I'm trying to charge a 16S nissan leaf pack (30AH LiMnO4 cells) using two Turnigy Accucel 8150 8S lipo chargers, but I'm having a bit of a problem. As soon as I plug in the second charger, there is a short, magic smoke is released, and this kills the charger. The first time it happened I assumed I got a bunk charger, since a capacitor was rattling around inside when I got it. But, after I killed a replacement charger in the same way, I'm sure it's my wiring.

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I'm sure the problem is somehow the fact they're sharing a connection in the middle, but I don't know how to rectify that. I didn't plan to separate the 16S pack into 2x8S, so there's no way for me to break that connection. The terminals and wires interconnecting the cells have been "potted" with gorilla glue, which would be a royal pain to remove.

I can charge each bank of cells by itself using the good charger, but as soon as I hook up the second, there's a pop, the smell of ozone, one of them says "short circuit error", and then when I go to try and charge again with it, I get "connection break" since it's burned traces on the board.

So, long story short, is there any way to isolate the grounds or install a diode or otherwise somehow prevent this from happening? I'd like to charge all 16S at once, but I have no way to change the configuration from 16S.
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Re: Charging 16s using 2x 8s chargers - what have I done wro

Post by dnmun » Jul 30 2015 12:40pm

no pictures just a diagram. no way to know.

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Re: Charging 16s using 2x 8s chargers - what have I done wro

Post by inedible » Jul 30 2015 1:02pm

Ok then, I can post pics but I'm not sure what you'll learn from them.

http://imgur.com/a/db36D

The terminal block on the top of the battery is connected to each individual cell in the pack, starting with B+ on the left, all the way down to B- on the right, which is a wire coming off the pack since there aren't enough terminals.

I assure you, all the connections are 100% correct, since I used to have a BMS hooked up here, as well as I can charge each set of 8 cells individually, and the charger correctly shows the voltages of each cell, etc.

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Re: Charging 16s using 2x 8s chargers - what have I done wro

Post by dnmun » Jul 30 2015 1:10pm

yes, you are right. your picture does not help figure out why it is shorted. it does look like you have the first sense wire from the JST plug on the wrong cell in your diagram but there is no way to figure it out from your pictures.

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Re: Charging 16s using 2x 8s chargers - what have I done wro

Post by 999zip999 » Jul 30 2015 1:17pm

I would probe and write down on paper each cell voltage starting at the neg. as this is where to start.
1. 3.85v
2. 4.10v


16. Xxx volt
This is the starting point.

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Re: Charging 16s using 2x 8s chargers - what have I done wro

Post by inedible » Jul 30 2015 1:26pm

The cells are all within 0.02v of each other, according to both my multimeter, and a single turnigy charger. Everything works perfectly fine, there is definitely not a short and the cell balance taps are all definitely in the right order. I am one hundred percent sure of that.

Bad things only happen when I plug in the second charger. As soon as there's two chargers plugged in, one of them dies.

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Re: Charging 16s using 2x 8s chargers - what have I done wro

Post by ddk » Jul 30 2015 2:27pm

are you powering both chargers from the same power supply?
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Re: Charging 16s using 2x 8s chargers - what have I done wro

Post by inedible » Jul 30 2015 2:43pm

Yes, and I suspect that might be a part of the problem.

First time I was powering them off a deep cycle marine lead acid battery, second time I was powering them from a server psu.

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Re: Charging 16s using 2x 8s chargers - what have I done wro

Post by ddk » Jul 30 2015 2:48pm

inedible wrote:Yes, and I suspect that might be a part of the problem.

First time I was powering them off a deep cycle marine lead acid battery, second time I was powering them from a server psu.
that IS the problem
simplest solution is power one charger using the battery that itself is not-connected- to- a- line-powered charger, the other charger with the PSU. The power sources need complete isolation from one another.
I do this very thing every day.
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Re: Charging 16s using 2x 8s chargers - what have I done wro

Post by inedible » Jul 30 2015 2:58pm

Hmm, well okay so the plan here is to charge this off a single 12v lead acid battery. Somehow, both chargers will need to get power from the same 12v source.

See, I've built a trailer with solar panels that charge up a SLA battery inside the trailer. I want to be able to charge my bike's battery off the trailer.

Is there any way of isolating them with like diodes or something?

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Re: Charging 16s using 2x 8s chargers - what have I done wro

Post by ddk » Jul 30 2015 3:25pm

inedible wrote:Hmm, well okay so the plan here is to charge this off a single 12v lead acid battery. Somehow, both chargers will need to get power from the same 12v source.

See, I've built a trailer with solar panels that charge up a SLA battery inside the trailer. I want to be able to charge my bike's battery off the trailer.

Is there any way of isolating them with like diodes or something?
Yes and no, diode leak current and won't provide (or might provide) the amount of isolation your R/C chargers require.
Solution: get one more battery for your solar array. Hook both batteries to solar controller's output via a SPST switch to isolate one battery from the next.

For instance: I just use a simple 15Ah 12V switch to disconnect batteries from the solar panels' MPPT. Each battery's output terminals are isolated from one another, terminated to their individual banana plug sockets
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Re: Charging 16s using 2x 8s chargers - what have I done wro

Post by Alan B » Jul 30 2015 3:38pm

The chargers negative leads connect straight through from supply to battery. So you cannot use them both at the same time, it creates a short loop between the negative sides of the two battery halves.

You can use a 12V isolated DC-DC converter to isolate one of the chargers from the other, or do one side at a time.

If you are using AC you can use two separate isolated supplies, one for each charger.

If you want to use car batteries, use 2 separate isolated ones.

Isolation is the key, one of these chargers has to float up away from system ground.

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Re: Charging 16s using 2x 8s chargers - what have I done wro

Post by inedible » Jul 30 2015 3:42pm

ddk wrote:Yes and no, diode leak current and won't provide (or might provide) the amount of isolation your R/C chargers require.
Solution: get one more battery for your solar array. Hook both batteries to solar controller's output via a SPST switch to isolate one battery from the next.

For instance: I just use a simple 15Ah 12V switch to disconnect batteries from the solar panels' MPPT. Each battery's output terminals are isolated from one another, terminated to their individual banana plug sockets
Hmm. My 12v SLA battery is actually made up of 4x 20AH cells in parallel to make a 12v 80AH battery. I wonder, if I set it up as a 24v 2S2P setup, could I then run three leads out, negative, common, with 12v between each, would that isolate the chargers enough?

My MPPT controller doesn't want to be unplugged, it tracks things over time and can tell you the capacity of your batteries, SoC, etc, so I don't really want to go unplugging and rewiring things every time I charge. In fact, I want the solar to be still charging the SLA's while I'm discharging them into the lipo chargers.

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Re: Charging 16s using 2x 8s chargers - what have I done wro

Post by Alan B » Jul 30 2015 4:23pm

That's not isolated, the connection between the two halves will interfere with the charger regulation. The lower half of the charging pack will be connected directly to the lower 12V half of the input pack through the grounds.

You must isolate those grounds somewhere. You must understand what you are doing.

Split your solar system into two separate 12V systems and install a second MPPT controller, or use a 12V-12V isolated DC-DC converter to isolate one charger, or charge one half your pack at a time. You could build a system to charge each half for a few minutes at a time so the balance would not get far out, and then swap to the other half.

The grounds of the two chargers MUST be isolated, by isolating the input power of one charger, or by breaking the charging battery pack in the middle.

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Re: Charging 16s using 2x 8s chargers - what have I done wro

Post by inedible » Jul 30 2015 5:05pm

Alright, in that case I think I'll need to try and install a disconnect between B8+ and B9- so I can separate it as 8s packs, parallel them, and charge them off one charger. 8S2P. That should work I think. It'll just be really slow charging at 150W.

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Re: Charging 16s using 2x 8s chargers - what have I done wro

Post by Alan B » Jul 30 2015 5:38pm

If you break the link you can use an 8150 on each half, twice as fast as a single, and you won't have to mess with connecting all those balance wires in parallel.

Just don't connect the 8150's to the supply until the link is open.

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Re: Charging 16s using 2x 8s chargers - what have I done wro

Post by ddk » Jul 30 2015 7:06pm

lol-just when I came back to correct myself you already got good advice.

I use DPST switches.
...my MPPT only cares if it sees NO BATTERY at all, which is why I can switch two of three battery sections in and out... one section is never switched out because it powers a couple of inverters.
I forget how simple, yet complex my power systems actually are.
I actually charge my 14S batteries in three sections of 5S, 5S and 4S that are never broken down
This is equivalent to using about a 700W charger, which I'd rather not use.

My solar-charged (rarely line-charged) batteries are 6 ea 100A AGMs and a couple of 40A SLA (yes, they don't mind the AGM levels after a couple of years use and are due for retirement this year)
I got the AGMs for almost free because retired people like me give things away to other retired people. We like to trade unneeded for needed items best.
Must be a retired people thing since most of us seem to do this, at least where I live and play.

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Re: Charging 16s using 2x 8s chargers - what have I done wro

Post by inedible » Jul 30 2015 7:25pm

Alan B wrote:If you break the link you can use an 8150 on each half, twice as fast as a single, and you won't have to mess with connecting all those balance wires in parallel.
True, but I've already killed two chargers already. At this point I can't justify the expense of buying another, and I can't warranty them for my own ineptitude.

I can try and repair the one I smoked this morning, but with the first one I killed I already tried repairing all the burned traces and it still didn't work.

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Re: Charging 16s using 2x 8s chargers - what have I done wro

Post by Alan B » Jul 30 2015 8:10pm

Reconfiguring packs to charge them and use them is a recipe for accidents. Pursue this path at your own risk.

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Re: Charging 16s using 2x 8s chargers - what have I done wro

Post by inedible » Jul 31 2015 12:50am

Alan B wrote:Reconfiguring packs to charge them and use them is a recipe for accidents. Pursue this path at your own risk.
Duly noted. I'm aware if I forget to disconnect the parallel "Y" connectors before reconnecting the packs in serial, I will vaporize my balance leads. If I do this I'll be sure to follow a very strict checklist.

Otherwise, you mentioned using an isolated 12v-to-12v DC-DC converter. Any idea where I'd find something like that in the 150W+ range for somewhat cheap? Checking ebay I can't really find anything in the wattage range I would need.

Thanks for the advice!

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Re: Charging 16s using 2x 8s chargers - what have I done wro

Post by Alan B » Jul 31 2015 10:04pm

Cheapest isolator is a DPDT relay or switch to disconnect half your battery pack from the solar/battery system and swing it over to the second charger so it can float during the charge. Wired properly there's no opportunity for smoking everything.

Cheapest 12v-12v isolator on ebay is probably a 12V to 120VAC inverter followed by a 120V to 12V Power supply. There isn't a commodity market that I know of for a 12-12VDC 150W isolator, so what's there is expensive commercial gear. If you take apart a 12DC to 120AC inverter and rewind the transformer you could possibly make one.

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Re: Charging 16s using 2x 8s chargers - what have I done wro

Post by dnmun » Aug 01 2015 2:11am

if you have to charge from a 12V battery then use a 12V-67.2V DC/DC boost converter. it may be easier to use two 12V batteries to store the power from your panels and then you could use a 24V-67.2V converter.

then use a regular BMS to prevent overcharging it and it should balance under the BMS when the pack reaches full charge.

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Re: Charging 16s using 2x 8s chargers - what have I done wro

Post by Skalabala » Aug 01 2015 4:28am

Won't it work if you split the battery from 16S into two 8S and then after charge just series reconnect them?
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Re: Charging 16s using 2x 8s chargers - what have I done wro

Post by Alan B » Aug 01 2015 7:46am

dnmun wrote:if you have to charge from a 12V battery then use a 12V-67.2V DC/DC boost converter. it may be easier to use two 12V batteries to store the power from your panels and then you could use a 24V-67.2V converter.

then use a regular BMS to prevent overcharging it and it should balance under the BMS when the pack reaches full charge.
Good Suggestions dnmun.

Justin's new HV Satiatior programmable charger will be out soon, and that will work nicely with a BMS and give 360W of charging with programmability to control the end voltage. No need to break the series, and good data on charge cycles.

In the meantime, use the one working 8150 to charge each half, just plug in twice. Just make sure the battery system ground is floating with respect to the solar system.

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Re: Charging 16s using 2x 8s chargers - what have I done wro

Post by dnmun » Aug 01 2015 10:17am

we should be able to fix the shorted charger too. i suspect the isolation mosfet on the output is burned so just replacing that should make it work again.

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