Energy Matters Forums

[davef]

I would be keeping a close eye on battery terminal voltage, say as you go above 13.8V. Plot a graph of battery voltage versus time (at a constant 10A charge).

[Al510]

Switching off the charger, its at 13.48v, but still taking 8 amps. It should be safe to keep going untill the amps tail off to 2 or so ?

[Al510]

My panels have a vmp of 37v , so i guess i would be giving up a fair chunk then?

[davef]

My understanding is that it will keep on taking 10Amps, in your case, up to the point where they would be damaged. At 28.2V there is still 30-40Amps going into mine. My rated charge current is 600A. You gotta stop charging when they get to the recommended charge voltage ... they don't taper off.

The only reason I back off my charge rate when they first hit 28.2V each day is a perhaps incorrect assumption that it might make life easier on the cells. There is a "theory" that time spent charging should be short rather than dragging it out, but I haven't seen any research papers. Then there is the topic of "microcycles".

They are very efficient near full charge whereas Lead-acid start to heat up. LiFePO4 will eventually heatup but that will be above 4V/cell.

Here is a link to my cells. http://en.winston-battery.com/index.php/products/power-battery/item/wb-lyp200ahab?category_id=176

[davef]

OK, you have 72 cell panels. Check out Electrodaus on Youtube, he had a video about that trade-off.

At 37Vmp you will lose some. A MPPT controller will maybe give you an extra 5-10% ... it is probably cheaper to put up 10% more panel these days.

CU tmw

[Al510]

With me charging at a constant 13.8v , assuming all cells are equal, wouldn't it be impossible to go over 3.45v per cell? Isn't that why the amps tail off when full?

[davef]

Correct. So, it is your charger that is tapering off not the batteries. The recommended charge voltage for your batteries was 14.4 to 14.6V.

Just try lifting the 13.8V up to 14.1V.

Even at 13.8V if you did a proper discharge test on them you should get close to the 100AH. You need to be extremely careful if you do that ... that you do not go below a voltage that should be recommended by the manufacturer.

My read of your battery spec sheet is that HVD and LVD is built-in. Have you a spec sheet for that battery? The one I found was quite brief.

[davef]

Actually, before raising the voltage or doing a discharge test maybe there is another way to reduce the problem that you seeing.

How low can the float voltage setting be made on your controller?

Victron is a well-known company ... do they have detailed instructions for charging LiFePO4?

https://community.victronenergy.com/questions/2939/mppt-10020-lithium-battery-configuration.html

https://community.victronenergy.com/questions/4429/charging-arbitrary-lithium-chemistry-and-voltage-w.html

This last one seems to have some useful hints.

[Al510]

I have finished charging this afternoon, it took another hour or so to tail off to 2 amps. The voltage this afternoon before i reconnected the charger was 13.35. After charging it was 13.71. All up it took about another 30 to 40 ah.
When i first got this battery i charged it at 13.8v until the charge current dropped to 2amps and then hooked up an inverter running a fridge and i discharged 94ah before i switched it off.at that point it was still going but i was happy enough that it was close to rated ah.
I guess victron would suggest that you use the lithium setting, which is bulk until 14.2v and then absorption at 14.2v until current drops to 2 amps or the time is up, and then float at 13.5v . Most stuff you read now suggests charging to 14.2 is ok but the charging should then stop, not continue to float. It seems its not possible to have that configuration with the victron.
With the loss of capacity in the technomadia battery, i wonder how much could be attributed to floating at 13.5v as well as the high temps?

[Al510]

Im planning on the winston cells as well, for my main battery, but in the 400ah. The bms that i liked the look of was the ev power one from WA. But the cost would be similar to the electrodacus sbms. It might be worth forgoing the small percentage gain from the mppt and get the sbms120 for my main battery.
I think the victron float can go as low as you want. It definitely goes as low as 13.3, i didn't try any lower.
Im not too concerned about how this 12v battery behaves on the solar charger, it will only have a small load on it and hopefully lasts a few years, if not i will replace it when the time comes. I was more interested in why the voltage rises so fast to 13.8v when in bulk mode, even though its nowhere near fully charged, and if a larger pack of cells will do the same thing.
With your sbms, the cutoff voltage being 3.55v per cell, it switches the pv of then? At what voltage does it drop to before switching back on?
I have connected my fridge to the 12v battery, and I'll run it down to 20% soc and see how it goes on the victron with a reduced current, maybe 10amps.