16S Active Balancer just "exploded"?

[kromc5]

I had two running since Jun 29th with no issues, with discharge rates over 140, charge of 80+.amps. It may have just been defective unit.

Very new to solar but started purchasing items, not sure of the final specs of the whole system.

Second order for the Heltec finally arrived:

diysolarforum.com

 

[mrzed001]

Both have been used by electricians to prevent corrosion for about 40+ years.
They are dirt cheap, and effective. They certainly meet code inspections in south Florida.

The problem is that two type is used
1, alu oxidation blocker that can be non conductive
2, conductive grease (that can be an oxidation blocker too).
So it is most important that you know the Ohm cm data of the paste you use.
For MG Chemicals 846 it is 114 Ohm cm (they have better and more expensive ... but this is more than enough for this task)

 

[Just John]

The problem is that two type is used
1, alu oxidation blocker that can be non conductive
2, conductive grease (that can be an oxidation blocker too).
So it is most important that you know the Ohm cm data of the paste you use.
For MG Chemicals 846 it is 114 Ohm cm (they have better and more expensive ... but this is more than enough for this task)

The two Steve brought up were developed specifically to prevent corrosion from an aluminum to copper electrical current carrying connection. They have been used for decades in house and business wiring.

They are cheap, and proven effective for this purpose. I am sure that others may be as effective, but real life data proves these two work, and for 5 to 7 dollars you get what is essentially a lifetime supply.

I have no knowledge of what was used by the original poster, but it does seem to be the root cause of his problem.

 

[mrzed001]

The two Steve brought up were developed specifically to prevent corrosion from an aluminum to copper electrical current carrying connection. They have been used for decades in house and business wiring.

They are cheap, and proven effective for this purpose. I am sure that others may be as effective, but real life data proves these two work, and for 5 to 7 dollars you get what is essentially a lifetime supply.

I have no knowledge of what was used by the original poster, but it does seem to be the root cause of his problem.

You are right this are good product to prevent corrosion if alu used together with copper.
And then only in a thin layer because as @noenegdod showed us it is an insulator

[PSA] Make sure to properly prepare your connections to aluminium terminal posts in order to ensure low contact resistance.

So I see this: https://www.amazon.com/MG-Chemicals-Carbon-Conductive-Assembly/dp/B00MG9X3VG/ref=sr_1_4?crid=3C7J1F6DX1X4T&dchild=1&keywords=carbon+conductive+grease&qid=1613594207&sprefix=Carbon+con%2Caps%2C204&sr=8-4 And this...

diysolarforum.com

It was OP's original problem that he used a similar paste, and used a lot of them. Not thin but thick layer.
As the result it made an insulating coat between the terminal and the busbar.
You can see that his screw had to deliver a lot of current through the washer to the busbar. And typically it should deliver none.

Also we have to deal with an another thing: the not fully contacting flat surfaces problem.
We need a good conductive compound that fills out the roughness and arcs of the surfaces.
If you fill up these holes with insulating paste -> you lower the contact area -> more resistance (same Amps lower surface) -> More heat (and current searches for the least resistance path ... like here through the screw).

TLDR: use conductive paste to make large surface contacts better

 

[Just John]

You are right this are good product to prevent corrosion if alu used together with copper.
And then only in a thin layer because as @noenegdod showed us it is an insulator

[PSA] Make sure to properly prepare your connections to aluminium terminal posts in order to ensure low contact resistance.

So I see this: https://www.amazon.com/MG-Chemicals-Carbon-Conductive-Assembly/dp/B00MG9X3VG/ref=sr_1_4?crid=3C7J1F6DX1X4T&dchild=1&keywords=carbon+conductive+grease&qid=1613594207&sprefix=Carbon+con%2Caps%2C204&sr=8-4 And this...

diysolarforum.com

It was OP's original problem that he used a similar paste, and used a lot of them. Not thin but thick layer.
As the result it made an insulating coat between the terminal and the busbar.
You can see that his screw had to deliver a lot of current through the washer to the busbar. And typically it should deliver none.

Also we have to deal with an another thing: the not fully contacting flat surfaces problem.
We need a good conductive compound that fills out the roughness and arcs of the surfaces.
If you fill up these holes with insulating paste -> you lower the contact area -> more resistance (same Amps lower surface) -> More heat (and current searches for the least resistance path ... like here through the screw).

TLDR: use conductive paste to make large surface contacts better

Yes, more is not better. The purpose is to prevent corrosion, and only a very thin layer is required. I put a dab on my fingertip and wipe the two mating surfaces. All you are trying to do is prevent the oxygen and moisture in the atmosphere from reaching the surface. When properly mated, it should be metal to metal contact, there should be no "squeeze out" of the product.

I would not recommend a carbon based product.

Post in thread '[PSA] Make sure to properly prepare your connections to aluminium terminal posts in order to ensure low contact resistance.' https://diysolarforum.com/threads/p...sure-low-contact-resistance.16019/post-213479

 

[Hedges]

For full documentation - this is a picture of the negative terminal of the mentioned cell 4 (counted from the beginning of the right top pack) after the second stress test without the balancer. This was the indicator of heat generation as it colored dark with a little bit of smoking. But the connection is definetely not soldered, I checked the screw and you can loose it.
View attachment 60623

I think this picture probably shows source of problem.
A burnt spot on battery terminal means there was high power dissipation, a high-resistance connection with current through it. That would cause excessive voltage drop and drive leads of balancer way beyond normal.

Perhaps such gizmos could have PTC fuses in the leads and a clamping circuit. That way they survive more abuse.

The BMS likely showed cell imbalance which would be a tip-off of the issue. By testing at gradually increasing discharge and charge voltages, this might be detected and fixed before damage occurs. DMM could be used to manually check as well. But of course if high resistance develops later something could fail like this. Getting reports from BMS and watching for trends (perform SPC) could be the thing to do.

 

[mrzed001]

Yes, more is not better. The purpose is to prevent corrosion, and only a very thin layer is required. I put a dab on my fingertip and wipe the two mating surfaces. All you are trying to do is prevent the oxygen and moisture in the atmosphere from reaching the surface. When properly mated, it should be metal to metal contact, there should be no "squeeze out" of the product.

I know, you know how to use it.
But here is a lot of beginners in the list. And they will do the same mistake as OP did (again and again).
Even worst if they do not polish the terminals and busbars first (more roughness, more holes, more space filled with insulator, more resistance).

I know that MG 846 is much more expensive
But it solves both problem:
- better contact (full surface contact)
- and oxidation prevention.
It is ideal for the job.

So I think we should recommend the usage of the MG 846 or any other similar conductive carbon paste on the terminals.

User forgot (did not know he has to) polish the terminals?
No problem the carbon grease will fill up the holes.

User used a lot from it (many think more is better) ?
No problem, with this more is really better

 

[Just John]

I know, you know how to use it.
But here is a lot of beginners in the list. And they will do the same mistake as OP did (again and again).
Even worst if they do not polish the terminals and busbars first (more roughness, more holes, more space filled with insulator, more resistance).

I know that MG 846 is much more expensive
But it solves both problem:
- better contact (full surface contact)
- and oxidation prevention.
It is ideal for the job.

So I think we should recommend the usage of the MG 846 or any other similar conductive carbon paste on the terminals.

User forgot (did not know he has to) polish the terminals?
No problem the carbon grease will fill up the holes.

User used a lot from it (many think more is better) ?
No problem, with this more is really better

I'm not so sure about using a carbon based product on the aluminum terminal when carbon is used in the cell chemistry. It may be fine, I just don't know. So I just recommend products that have been used for decades and are specifically produced for the application. Cheap is a bonus.

You are correct, mistakes will be repeated, then someone will show up asking questions.

 

[mrzed001]

I would not recommend a carbon based product.

Post in thread '[PSA] Make sure to properly prepare your connections to aluminium terminal posts in order to ensure low contact resistance.' https://diysolarforum.com/threads/p...sure-low-contact-resistance.16019/post-213479

Yes, carbon or graphite could even more corrode aluminium (since they even have a higher V difference than copper or nickel) but for that to happen the contacting alu-carbon surface needs air, moisture or water.
The grease part prevents that (air seal).
So it will not corrode your alu terminal while it will give good conductivity even between rough surfaces.
Alu surfaces are like this under microscope:



And you press an another evenly rough surface against it.
The pressing force (if strong enough) can cause stronger metal to penetrate weaker (causing surface breaks) and weaker metal to "flow"
So there is a lot of gap between them if not polished.
Without a conductive grease all this gap/hole act as an insulator.
Using insulating paste makes it even worst.

 

[upnorthandpersonal]

I know that MG 846 is much more expensive
But it solves both problem:
- better contact (full surface contact)
- and oxidation prevention.
It is ideal for the job.

MG 847 is better: uses synthetic oil and has a volume resistivity of 23 Ohm cm. I use it on my cell terminals.

 

[mrzed001]

MG 847 is better: uses synthetic oil and has a volume resistivity of 23 Ohm cm. I use it on my cell terminals.

Yes, it is much better. But it cost twice as much.
And higher price means higher resistance (not electric of course ... human)

 

[MattiFin]

The '2200' 6.3v caps in the picture are 2200 uF 6.3v rated aluminum electrolytics. You won't find that in a polymer cap.

The best you can do is look for a 2200 uF with same diameter but taller with a higher voltage rating, like 10v or 15v rating. The higher the voltage rating the lower the internal resistance and more voltage margin will have a bit better reliability.

Afaik Polymer caps would be a bad idea for this kind of application as they have some notable drawbacks compared to ordinary electrolytic capacitors:
1. very sensitive to inrush and peak current
2. failure mode is almost always short-circuit