Electrical Musings

[Stu Jackson]

Originally Posted by chala

So can you find us links on “grouping of cells” or “cells series parallel” the interest is mostly on “lead storage cell” I will read them.

The 12volt Side of Life (Part 1)

[chala]

Originally Posted by Stu Jackson

The 12volt Side of Life (Part 1)

I read is disclaimer can you find something a little more serious, may be from an institute of technology or manufacturer or gov.

[s/v Jedi]

Originally Posted by chala

I read is disclaimer can you find something a little more serious, may be from an institute of technology or manufacturer or gov.

Delft University of Technology: Study

cheers,
Nick.

[ebaugh]

I've read this thread and thought about posting before...but did not. You don't need an EE degree to understand the issues involved. E = I x R and P = I x E pretty much is as far as you need to go.

Depending on the situation, everyone is right to a degree.....Do a google search on this:

"How to correctly interconnect multiple batteries to form one larger bank"

and read the page on the Smartgauge website. If you are not careful about how you wire your batteries, they will not contribute equally to the loads, and conversely will not charge equally either. In an extreme but unfortunately common wiring example, where the batteries are poorly wired to the load from the same end of the string, the batteries at that end of the string will discharge more under heavy loads, and then actually be charged some under light loads by the fresher batteries on the far end of the string. You could call this "stray current" equalization......

In a properly wired bank, which is also common, this is not really a significant issue.

I just faced this problem with designing a 48 cell lithium array 12 cells in parallel, then 4 in series. I'm still not sure I have it right, so I keep reading.

[s/v Jedi]

Ah, but now we're discussing on how to correctly connect batteries in parallel. The previous discussion was about parallel connection being inefficient, with 20% losses compared to series connection etc. That discussion was not about correct vs incorrect cabling, so we assumed correctly cabled.


Nick.

[ebaugh]

Nick,

I agree...the point is I'm not sure everyone was working under the same set of assumptions when the thread diverged.

Is this wiring optimal...not sure but think I attached a picture. The yellow links are fuses.

[s/v Jedi]

Originally Posted by ebaugh

Is this wiring optimal...not sure but think I attached a picture. The yellow links are fuses.

I'm no expert on these banks but it looks good to me. Make sure all shunts activate at end of charge cycle. I'm sure you're reading about how to balance the pack initially by discharging cells or charging individual cells. I would prefer to charge individual cells but can't deny the other side has equal end results.

Why don't you use bigger cells?


Nick.

[ebaugh]

Originally Posted by s/v Jedi

I'm no expert on these banks but it looks good to me. Make sure all shunts activate at end of charge cycle. I'm sure you're reading about how to balance the pack initially by discharging cells or charging individual cells. I would prefer to charge individual cells but can't deny the other side has equal end results.

Why don't you use bigger cells?


Nick.

The shunts don't activate until 3.55V, don't expect to ever get there normally. Mostly wanted the EMS/BMS for remote electrical panel display of cell voltage and temperature. And as a last ditch safety if I pull some boneheaded move forgetting to charge.

Plan to balance initially at top, at the cell level, prior to installation. Then hopefully never again.

I would have preferred larger cells. But I could not get them to Grenada in a timeframe that worked for us. It sure would make the interconnects simpler. Although I'm not sure if it doesn't just hide some of them in the plastic cases done by the manufacturer.

I will know in 3 years if this was a good idea......if the cells show up in the next couple of days. The container ship from Miami is already 4 days late.

Thanks, Bob

[ebaugh]

BTW, in reference to the OP issues, this is a band aid to the problem. Especially in the Caribbean where solar would work nicely, not as sure about the UK especially in the winter.

But if he stays on the plan to charge/discharge using fossil fuels to charge, lithium theoretically will last much longer and charge more efficiently.

[s/v Jedi]

Originally Posted by ebaugh

BTW, in reference to the OP issues, this is a band aid to the problem. Especially in the Caribbean where solar would work nicely, not as sure about the UK especially in the winter.

But if he stays on the plan to charge/discharge using fossil fuels to charge, lithium theoretically will last much longer and charge more efficiently.

Yes, lithium outperforms in every category incl. price if we believe manufacturer claims for cycle life

ciao!
Nick

[twistedtree]

Dockhand, a while back before everything in this discussion skipped the tracks, you said you were going to check the electrolyte level in your batteries. Did you by change measure the specific gravity? It sounds likely that you are running your batteries in the 80% and under state of charge range, and doing so will result in accumulation of sulfate on the battery plates. As the sulfate, charge cycles will appear to take place very quickly since the sulfated batteries' voltage will rise quickly compared to a battery in good condition. This tricks the charger into declaring the charge cycle complete where it's really far from it. Your low charge current from the Victron, and seemingly successful 1-2hr charge from your engine all point to this. I suspect if you measure SG you will find it very low even though the low-draw voltage suggests the batteries are charged. I had this happen to me with a very large battery bank (48V, 1300Ah) and it took lots and lots of equalizing to finally get things back working properly. Lots of other important suggestions here, especially around validating the measurements that you are getting, but I suspect sulfation may be a contributing problem here.

Good luck,

[Dockhead]

Originally Posted by twistedtree

Dockhand, a while back before everything in this discussion skipped the tracks, you said you were going to check the electrolyte level in your batteries. Did you by change measure the specific gravity? It sounds likely that you are running your batteries in the 80% and under state of charge range, and doing so will result in accumulation of sulfate on the battery plates. As the sulfate, charge cycles will appear to take place very quickly since the sulfated batteries' voltage will rise quickly compared to a battery in good condition. This tricks the charger into declaring the charge cycle complete where it's really far from it. Your low charge current from the Victron, and seemingly successful 1-2hr charge from your engine all point to this. I suspect if you measure SG you will find it very low even though the low-draw voltage suggests the batteries are charged. I had this happen to me with a very large battery bank (48V, 1300Ah) and it took lots and lots of equalizing to finally get things back working properly. Lots of other important suggestions here, especially around validating the measurements that you are getting, but I suspect sulfation may be a contributing problem here.

Good luck,

Thanks, I think this is a very good suggestion, and I strongly suspect that you are right, and that I have not gotten rid of the sulphation from my discharge incident last month. It would explain everything, wouldn't it? It's very good that I will now have the Honda generator which I will simply run continuously for a while when I get back to the boat next week.

A bit of thread drift - should I or should I not equalize all 8 batts at the same time? The Victron manual suggests doing them one at a time, which would be a PITA. And how much equalization is too much? Corrodes the cathodes, doesn't it?

[Dockhead]

Originally Posted by ebaugh

BTW, in reference to the OP issues, this is a band aid to the problem. Especially in the Caribbean where solar would work nicely, not as sure about the UK especially in the winter.

But if he stays on the plan to charge/discharge using fossil fuels to charge, lithium theoretically will last much longer and charge more efficiently.

Oh, believe me, I dream about lithium batteries, after the last year of struggles with all of the perversions of lead-acid technology. Our children so day won't believe our stories of storing power in containers of sulfuric acid and sulfated lead plates, half a ton in the bilges. It sounds positively medieval even now.

I just don't want to be an alpha tester of a new technology. Maybe next set of batts - I'm sure it won't take me long to finish killing this set

[s/v Jedi]

On equalizing: what brand and type of batteries do you have?

cheers,
Nick.

[Dockhead]

Originally Posted by s/v Jedi

On equalizing: what brand and type of batteries do you have?

cheers,
Nick.

Trojan, 12v, 105ah each, 8 of them wired up as 4 virtual 105ah/ 24v batteries, giving (theoretically) 420 ah @ 24v nominal.

They were brand new () just 4 months ago, but I managed to let them die and stay dead for probably two weeks (left compass light on ).

They came back pretty well after that, holding a load quite well and running heavy inverter loads pretty much the same as they did before the incident. I'm hoping some more equalizing will bring further improvement.

It was a favorable contrast to my previous batts, Varta "leisure" batts which basically collapsed and never recovered after a similar incident last year.