[SOLVED] -- Sparks! Sparks Everywhere!

[Montiey]

One little problem with my build..
I'm using a voltage monitor that has a parallel balance adapter. I have this connected to two of my packs, specifically two that are in parallel on one side of a larger series loop with another parallel set. The problem pops up when I try to plug in two balance leads from either side of the series loop. Sparks! It looks like the damage is being done to the 14.8v pin and the ground pin of the second battery I plug in. Its not a problem with that battery, since when I plug them in while off the loop they are fine, and the loop is stable otherwise (without any balance leads connected or just from one side of the Series).

Any ideas? I'm also quite sure that I didn't try to plug the connector in backwards.

 

[Trbt555]

Can you post a schematic of how everything is connected ?

 

[amberwolf]

SOunds like you are leaving parallel leads connected while trying to hook series leads together of packs that are not actually connected in parallel, or vice-versa.

Post a photo (and a diagram if you can) of your setup, and of what you are trying to do.

 

[Montiey]

Here is how the packs are connected:
http://www.mcminiposts.com/tempdump/leads.JPG
For the parallel balance lead, Its all woven into the board and whatnot. Here:
http://www.mcminiposts.com/tempdump/balance.JPG
Its just your average 4s balance lead in parallel with another.

 

[amberwolf]

Then AFAICS you have four packs, setup as two parallel-connected sets (at their main leads), that are then as sets hooked in series at the main leads.

That means that in order to connect anything in parallel from one series set to the other, you have to first disconnect that series connection. In your case, that is the last yellow connector set where all the packs come together, circled green in this picture


If you don't, you are creating a direct short circuit across one of the series sets when you *also* try to hook that pack in parallel.

You can still connect the balance leads of each already-paralleled pack to the other that already has it's main leads paralleled with it.


If it doesn't make sense the way I have said it, try drawing out yoru wiring on a piece of paper, it should make more sense; you'll see where the short would be made.

You can also look around for the many posts about series-parallel connections, or sparks and balance leads/wires, and there may already be diagrams they've drawn up, and there will be other versions of the explanation.

 

[Montiey]

That makes sense. That's basically what worked (and didn't work) when I was experimenting.
Do you think there was any damage to the packs from the brief spark?
Also, what if I wired 3 cells from two packs on either side of the series as a normal 6s balance lead? The only connection between the two packs then would be the ground. Anyway, what would be likely to become unbalanced? The two packs in series or either of the two sets of packs in parallel? I originally wanted to wire the balance monitor across the series because I thought that those two sets of packs may discharge differently, so I wanted to get a good average. If that's not the case then I'll just use two from the parallel. Or, I could use a single balance lead so I don't blow something up. 8)

 

[amberwolf]

You can't wire ANYTHING together between seriesed packs, or you are shorting across them.


Only packs already paralleled can have their balance leads paralleled.

THe balance leads are exactly the same as the main leads, except that they access individual cells within the packs directly. So you can't do anything with them that you can't do with the main leads.



If you have two sets of seriesed packs, and you want to monitor or balance them, you need two sets of monitors or balancers.

Or monitor or balance them one set at a time, which will take twice as long.

To check for damage, hook each pack up completely separately to your balance monitor or charger and see what it reads.

If it cant' read a cell, but can read the whole pack correctly, then a balance lead is damaged and needs to be fixed. That's usually at the connector itself, but could be anywhere along the wire.

If it can't read a cell, and the pack seems to be down about a whole cell's worth of voltage, or the whole pack doesn't read at all, you may have a problem with a cell itself or it's connection to other cells inside the pack; for that you might have to open the pack to find out what happened.

 

[Montiey]

The cells read their voltages out to the display just fine.
Do you think it's worth it to have two connectors (which could mean sparks again if someone grabs the wrong lead) or just deal with the possibility of having the one pack I measure be off and resulting in over-discharge of the others?

 

[amberwolf]

Mark the two sets of leads so they can't be mixed up, or use colored heatshrink or colored hoods for them.

Personally, with anything like RC LiPo that has so many possible things to go wrong with it for so many reasons, I'd keep monitoring and control over as much of those things as I could, including charge state/voltage/cell health. Without an electronic BMS to automatically do it, that means it's up to the user to do that.

The results of not checking may be nothing, or may be quite dramatic (usually the actual cause of dramatic failures, especially sudden rapid self-disassembly, is not possible to know, so some of this is speculation), so I'm for checking them.

I have an old ammocan full of RC LiPO wired up as a 14s2p (paralleled at the balance wires *and* the main leads of each pack) battery that I didn't do much of that checking on, and abused in other ways (heat, sitting on the bike in the direct Phoenix sun for hours during every work shift, among others), that is now got a number of cells (at least, possibly whole packs) swollen up, and is underperforming by quite a bit, and is stored outside where it can't hurt anything if it ever goes poof, until I either use it to death or decide to sacrifice it's little remaining life/usefulness for a destructive test to see how good that ammocan containment really is.

My present packs are different types; one has a BMS and the other just has balance leads (that I check though not as often as I would if it were RC LiPo).

 

[Montiey]

If I used a BMS, that would optimally be a 16s capable unit. Then again, that would require a common ground.. So, could I ever use a BMS with this setup? And what about everyone else? How are most BMS configured?

 

[amberwolf]

You'd want to read around the forums about the various battery builds to find out how different people do it for different batteries. THere are literally hundreds or more discussions about it, with varying levels of technical talk. There shoudl also be a wiki article in the ES wiki, but I don't know it's state of completion ATM.

But there is no reason you can't use a BMS to monitor all the cells at the same time, if it is designed to monitor that many series cells.

The only reason you can't do what you want with what you have is it isn't meant for that many series cells at once, and you can't parallel already-seriesed cells.

 

[Montiey]

Gotcha.
I think I will just be careful with the two leads, maybe tape the other two out of the way so they don't accidentally get used.