Hello Batrium community, thanks for joining me in! )).
On your opinion is it possible to use Batrium products to work with automotive NiMH cells that has 6S connection inside each monolith cell (about 7,5V to 9V output depends on charge level). Need to connect 28pcs such 7.5V cells to high voltage Deye inverter.
Could Batrium solutions be connected between each 6S NiMH:
1 (7.5V) - 6 (15V) -12(22,5V) -18(30V)… - 168 (210V)
Would be appreciate for any suggestion what Batrium products would be useful for this purpose.
Thanks in advance,
Regards,
Slav
If there are 6 cells connected in series in each monolith cell, how do you balance these cells?
Hi Slav, Kleini
NiMH cells can do a similar thing to lead acid batteries where they can sort of boil/burn off overfull cells on their own if charged to a high enough voltage.
We don’t have a cell monitor that can measure higher than 5V, so I don’t think we are a good fit for this specific project.
Have you considered a Lithium or Sodium-based alternative?
I know. Old thread. Maybe someone else will come along.
I assume you are using Prius or other hybrid vehicle NiMH modules. Given the cell count, it’s almost a certainty.
This is likely an extraordinarily bad idea.
First, unless these are the very rare high capacity modules (which are not 6S), you are likely planning to parallel them. You can’t parallel NiMH chemistry.
Second, if you’re not planning to parallel them, then you are going to accept a very low capacity battery. Prius pack is only 1.31kWh when new, and very few - even new - test to this level. If it’s in reasonable shape, it’s closer to 1.1kWh.
Even in a vehicle where charge amps can hit 90A and discharge amps hit 150A, NiMH is only lightly managed, and then only every 12 cells.
You could conceivably rig up a 14S battery that monitors every 10 cells with a voltage divider.
For the love of all that is holy, make sure you keep the modules in the clamp. They swell like mad above 70% SoC.
Lastly, why can’t you parallel NiMH?
Because it’s like rolling out the red carpet for thermal runaway. NiMH and NiCD chargers work by detecting the voltage DROP when the cells are full. If you have them in parallel, and one fills up first, its voltage drops. Then all parallel cells dump their capacity into it, and any attached chargers dump their current into it. It gets hotter, its voltage drops more, more current from parallel cells and the charger, etc.
This is not theoretical. I have personally observed it on an experimental setup. I collaborate with others that have experienced the same thing. It’s why the only production NiMH based EVs (90’s gen2 EV1, 2000s Rav4) used much larger NiMH 10S modules with only cells in parallel.
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Thanks snoobler! This is a great write up, and a good explanation as to almost all big batteries are LFP or NMC these days.
We can still monitor anything lithium or sodium based!
I was on a roll and got my terminology crossed in my head… Last sentence corrected:
It’s why the only production NiMH based EVs (90’s gen2 EV1, 2000s Rav4) used much larger NiMH 10S modules with only cells in SERIES.
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