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Hello,
Can anyone give me suitable voltages to set for the various custom settings, bulk, float etc (equalization too?) in a MPPT Smart Solar charger?
My NiMH battery pack has a nominal voltage of 12V. It's being fed by a 50W Sun Power panel. There will always be a load (a 10W battery charger), so I just want the 2Ah battery pack to act as a 'stabilising reservoir' so the load gets a nice consistent flow of power.
Thanks.
You really need to get the spec sheet for your battery and use the manufacturers guidelines.
NiMH batteries are not suitable to be used in a PV solar system.
If you just want to use energy from the Sun to charge your Eneloops, better option would be to use a 12V lead-acid or LiFePO4 battery for the PV solar system and a dedicated NiMH charger which can be powered from 12V DC (one which has a car adapter).
The long answer (and reason) behind this is that the NiMH cells are to be allowed to drop below 0degC, and then the output/load is to be used to charge lithium ions (in a warmer environment). I've done freezer tests with both the eneloops and a small SLA battery, and the eneloops charged much, much better in the cold.
So, I understand that it's unusual, and there's no preset in the Victron battery menu for charging NiMHs, but I'm not sure I underline the red line that makes them impossible to use with a solar charge controller.
Thanks
In addition to what kvegermany said, NiMH require a different (way different) charging algorithm. The NiMH charger monitors the voltage and the temperature of the cells during charging. Based on these, it has to terminate the charging at a certain point (and continue with a trickle charging for a certain duration - charging with very low current, like 0.05C).
Overcharging the NiMH destroys them.
Also, if you charge them incorrectly, they can lose capacity quickly (due to the so-called "memory effect").
When charging is complete, NiMH cells should be removed from the charger.
All these make NiMH not suitable for solar systems.
Thanks Seb. Whilst not at all questioning what you've just said:
For years and years people used to charge NiMHs using dumb timer chargers, which I don't even think had over-voltage cut off.
If it's possible to dumb charge them up to, say, 1.4V per eneloop so 14V for a 10x pack, wouldn't it be possible to give the Victron Smart Solar a similar instruction, so they're not overcharged?
@ahib NiMh requires a different method of full detection. The other cell types work off voltage. NiMh nerds the charger to detect s small drop in current once battery full.
You can install a battery heater if needed. Lead acid works ok below freezing, but at reduced capacity.
I know. Old thread. Just a NiMH brain dump...
NiMH can't reliably be charged with a lead-acid/LFP method due to the aforementioned voltage drop. You could likely establish a fixed but very brief absorption voltage and tail current cut off, but it would require experimentation, potentially be unreliable and likely not consistently get cells to full charge.
The two following options are constant current and time from empty. Voltage independent:
0.3C for 5 hours.
0.1C for 15 hours
Floating at 1.4V/cell can work but if any of the series cells are at a higher state of charge, voltage will drop, current will increase, heat is generated, voltage drops, current is increased, etc.
While NiMH cells are allowed to drop below 0°C, they really don't react well to charging below 10°C. It must be done at a reduced
Lastly, this voltage drop also means you can't safely put NiMH cells in parallel for greater capacity. If one cell fills faster than the other, it's voltage drops, then the parallel cells start dumping current into them as well as all the current from the charger. Once this starts, it doesn't stop until the lower voltage cell gets so hot, it starts to break down, and it's internal resistance increases. This slows the incoming current and allows the voltages to stabilize. The hot cell is ruined.
