Voltage variance after short

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Ozjet   10 W

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Voltage variance after short

Post by Ozjet » Jan 11 2013 11:25am

Well this is embarrassing,
Today I plugged in my 48v nanotech lipo pack (4 times 6s8000mah) with the leads from the controller reverse polarity.
I think I have hurt both myself and the pack
Checking each pack after the event I found two to be at 75 percent via checker ( expected after some use ) but the other two were at 43 percent.
Question is could this be the result of the short or what?
This is the first time I've used Lipo in a series parallel situation.
Here's a pic of the temporary harness I'm using.
Could that be the problem???
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NeilP   10 GW

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Re: Voltage variance after short

Post by NeilP » Jan 11 2013 11:54am

Connecting the battery the wrogn way to the controller is unlikely to damage the pack as far as I can see.
I suppose there could be a slight chance of battery damage, if you mabe connected a single pack revers polarity to a controller that had previously been powered at much higer voltage, the the capacitors had not discharged..so yo put the full higher pack voltage, now stored in the capacitors, across a single pack

If you have connected one battery to another, then there woudl have been big saprks/fire and molten connectors.

Also what do you mean by 75 and 43 %?

Best you strip the pack down to individual packs and then use a balance charger or Battery medic /Cell log to show the voltage of individual cells in the packs.

But just the fact you have the controller wired so it is possible to reverso polarity connect it is worrying. Positive terminal on the battery should be shielded female connector and the negative a male connector..that way you can only connect to the controller in the correct polarity
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neptronix   100 GW

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Re: Voltage variance after short

Post by neptronix » Jan 11 2013 12:13pm

linkage to the first or last cell in the packs can be blown from something like this.

http://endless-sphere.com/forums/viewto ... 14&t=35162

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Ozjet   10 W

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Re: Voltage variance after short

Post by Ozjet » Jan 11 2013 12:40pm

NeilP wrote:Connecting the battery the wrogn way to the controller is unlikely to damage the pack as far as I can see.
I suppose there could be a slight chance of battery damage, if you mabe connected a single pack revers polarity to a controller that had previously been powered at much higer voltage, the the capacitors had not discharged..so yo put the full higher pack voltage, now stored in the capacitors, across a single pack

If you have connected one battery to another, then there woudl have been big saprks/fire and molten connectors.

Also what do you mean by 75 and 43 %?

Best you strip the pack down to individual packs and then use a balance charger or Battery medic /Cell log to show the voltage of individual cells in the packs.

But just the fact you have the controller wired so it is possible to reverso polarity connect it is worrying. Positive terminal on the battery should be shielded female connector and the negative a male connector..that way you can only connect to the controller in the correct polarity
This is the golden motor controller I had it out of the bike and putting it back in I messed up. It has spade terminals to connect to I put them round the wrong way the deans was çonected to that.
Here's a pic of my checker and the plug, made my hand one third black , I'm surprised everything ain't shistered.
The bottom pic is where I went wrong, no excuses clearly marked. So that's like an installation issue not an everyday connection. Fuze going in later today! As shown in that pic of my checker it gives an indication of remaining charge, and shows individual cell voltages, the packs all showed good balance but two of the four packs showed they were flatter. :?
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Ozjet   10 W

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Re: Voltage variance after short

Post by Ozjet » Jan 11 2013 1:10pm

neptronix wrote:linkage to the first or last cell in the packs can be blown from something like this.

http://endless-sphere.com/forums/viewto ... 14&t=35162

I maded a thread.
They all show up ok
No visible sign of my stupidity on the packs
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dogman dan   100 GW

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Re: Voltage variance after short

Post by dogman dan » Jan 12 2013 8:47am

What did you mean by shows up 45%. That sure sounds like one cell less voltage or more to me. After a KFF, you can have packs that read 0v, because one tab fried breaking the connection in the series string inside. I guess you just have some packs way out of balance?

If the cells are all connected still, charge them and see what voltage you get then, and then the next day. KFF is routine, but try to slow down, always plug and unplug exactly the same way, and eliminate mistakes the same way pilots always do the preflight exactly the same routine.

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Re: Voltage variance after short

Post by Ozjet » Jan 12 2013 8:44pm

dogman wrote:What did you mean by shows up 45%. That sure sounds like one cell less voltage or more to me. After a KFF, you can have packs that read 0v, because one tab fried breaking the connection in the series string inside. I guess you just have some packs way out of balance?

If the cells are all connected still, charge them and see what voltage you get then, and then the next day. KFF is routine, but try to slow down, always plug and unplug exactly the same way, and eliminate mistakes the same way pilots always do the preflight exactly the same routine.
In a pic above there is my futaba battrey checker, it gives an indication of charge 0-100 percent, and also individual cell voltages, all cells showed up and were still balanced, but two pack showed 75 percent remaining charge and the other two showed 45 percent remaining charge.
Could it be the length of my wires in my connecting harness?
All four cells charged to the same voltage and are holding it. I haven't used them again.
I'm waiting for someone to come visit so I can ask them to plug it in for me ! :roll: :twisted:
Only kidding, not looking forward to that again though, regular really? Oh dear :shock:
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dogman dan   100 GW

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Re: Voltage variance after short

Post by dogman dan » Jan 13 2013 7:56am

That's what I was fishing for. Did you have any cells with 0v, and the answer is no. A pack with a 0v cell would of course be seen by the battery checker as having lower than expected voltage when checking the main leads. The only reasonable explanation then, is that you did not have some of the packs fully charged, or you have discharged them some, and they have differing capacities.

Enough of a short to discharge a pack 50% nearly instantly, surely would have melted stuff a lot more.

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Re: Voltage variance after short

Post by Ozjet » Jan 13 2013 8:48am

dogman wrote:That's what I was fishing for. Did you have any cells with 0v, and the answer is no. A pack with a 0v cell would of course be seen by the battery checker as having lower than expected voltage when checking the main leads. The only reasonable explanation then, is that you did not have some of the packs fully charged, or you have discharged them some, and they have differing capacities.

Enough of a short to discharge a pack 50% nearly instantly, surely would have melted stuff a lot more.
I made sure they were all the same when I put them together, I'm a bit miffed as to what they were telling me there.
I guess next time I discharge that pack ( those four cells are marked with the dreaded short circuit note) I would be hoping they discharge evenly.
I did make sure it was a good short by having the negative in place then shoving the pos in, it went right off mate!
Could it be the lengths of wire in my series parallel harness?
Please forgive my ignorance, I had to look up a schematic to find out how to do that.
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dogman dan   100 GW

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Re: Voltage variance after short

Post by dogman dan » Jan 13 2013 4:07pm

All I can say is charge them , balance them well, then ride some and see if they stay balanced. If wires are toasted, they could be thowing off readings, so I'm assuming you will replace any burnt wires.

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Re: Voltage variance after short

Post by Ozjet » Jan 14 2013 2:38am

dogman wrote:All I can say is charge them , balance them well, then ride some and see if they stay balanced. If wires are toasted, they could be thowing off readings, so I'm assuming you will replace any burnt wires.
Shall do,
Keep a good eye on them as they discharge , make sure two don't go below lvc
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dogman dan   100 GW

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Re: Voltage variance after short

Post by dogman dan » Jan 14 2013 8:08am

I suppose it's possible that you have some weak cells, but only really noticed them after this event. I'm betting it was just more out of balance than you thought though.

Were you monitoring real close before this happened? Or just watching pack voltage?

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Re: Voltage variance after short

Post by Ozjet » Jan 14 2013 8:08pm

dogman wrote:I suppose it's possible that you have some weak cells, but only really noticed them after this event. I'm betting it was just more out of balance than you thought though.

Were you monitoring real close before this happened? Or just watching pack voltage?
They were all good,
I have made my battrey holder to fit 4 packs in and connect them together each time so the packs were all at the same voltage when they went in, they were charged individually and checked. They were virgins. Mabee better after A couple cycles.
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Re: Voltage variance after short

Post by Ricky_nz » Jan 14 2013 8:18pm

If the sort circuit (reverse polarity controller appears as a short) was enough to get the wires in your harness warm then even a small difference in wire lengths could cause one pair of batterys to discharge more than the other.
A few milliohms makes for a noticable volt drop at 100A let alone the full short circuit current of your packs.
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Re: Voltage variance after short

Post by dogman dan » Jan 15 2013 8:06am

Sometimes virgin cells need a couple of cycles to develop thier 100% capacity. So it's possible that had an effect as well.

Break em in easy with some (2-3) short shallow discharges, followed by complete recharges, then evaluate em after a longer ride. You can expect 10% to have a weak cell if they are HK lipo packs.

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Re: Voltage variance after short

Post by Ozjet » Jan 15 2013 2:04pm

Ricky_nz wrote:If the sort circuit (reverse polarity controller appears as a short) was enough to get the wires in your harness warm then even a small difference in wire lengths could cause one pair of batterys to discharge more than the other.
A few milliohms makes for a noticable volt drop at 100A let alone the full short circuit current of your packs.
Cool thanks for the input guys ,
I guess what your saying there , it would be best to make sure the wire length in my new harness should have same length for normal use.
I don't intend on shorting it for a test though!
dogman wrote:Sometimes virgin cells need a couple of cycles to develop thier 100% capacity. So it's possible that had an effect as well.

Break em in easy with some (2-3) short shallow discharges, followed by complete recharges, then evaluate em after a longer ride. You can expect 10% to have a weak cell if they are HK lipo packs.
I have learned a lot , thanks for you help , appreciated.
I will do that, I still got two more virgin packs to go , be good to compare. The cells shorted have been branded.
The nanos came nicely balanced, the zippy packs were all over the place. Started balancing on the charger but looked like it would have taken weeks ,so I made a rig to dump them a bit quicker, got them all done in an hour or so.i had the motor disconnected for a look with the wattsup found the lowest cell/ highest, connected the motor and hit the high one looking at the watts up while it was under load I got to know how much was enough , fair method?
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Re: Voltage variance after short

Post by dogman dan » Jan 17 2013 7:05am

You'd have to do a discharge capacity test, to know anything about variance in capacity. So the wattmeter, plus a load, run till it's empty, say 3.5v per cell perhaps, log the capacity. Do some break in cycles before the 100% discharge though.

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Re: Voltage variance after short

Post by Ozjet » Jan 18 2013 6:08am

dogman wrote:You'd have to do a discharge capacity test, to know anything about variance in capacity. So the wattmeter, plus a load, run till it's empty, say 3.5v per cell perhaps, log the capacity. Do some break in cycles before the 100% discharge though.
I will do that, look at the cells that were shorted closely,
I used the rig above only to do an initial balance, puting the multimeter leads conected to the watts up on individual cells to find the highest one
Then give it some motor action , repeat on all cells till the same then top up balance charge.
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Re: Voltage variance after short

Post by Ozjet » Jan 29 2013 12:29am

Well good news,
I have partly discharged the packs that were shorted and they are all discharging evenly, phew.
That with the old harness still.
So it seems it was the short.
Lesson learned, the hard way.
Interesting reverse polarity protection on the golden controller, just blow the terminal off :roll:
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