How to keep NiFe Batteries Charged?

midijeep

HI,
I have a bank to 40 NiFe 200Ah batteries.  I only use 38 due to my solar setup.  I keep rotating two batteries but would like to at least keep a charge on the two 1.2 V NiFe batteries that I am not using.  The manual states to fully charge the battery needs 1.7 Volts. I just want to keep them charged (1.2V - 1,7v) so I don't have to keep rotating them in and out.  The other option, which I don't want to do is remove the electrolyte.
What equipment would you recommend to "trickle charge" the two 1.2v NiFe batteries e.g. solar panel with charge controller, battery charger, etc...... .
Thanks in advance!

Raj174

@midijeep
It might be possible to use a LiFePO4 charger on 2 cells in series. I read, the maximum charge voltage is 1.8V per cell, so 2 in series would be 3.6V. The LFP charger is 3.65V. I don't know for sure if the 5 mV over recommended voltage would be a problem, if not, maybe a charge current of about 3% or 6 amps would be enough to keep them in a charged state. NiFe are not that efficient so it may take a little more current. Just an educated guess.

Rick

mike95490

I went the route with a charger that has programmable set points and can use all cells. TristarMPPT-60

But it looks like the LFP charger, applied 1x a week, would keep the 2 cells in  shape.  Too much voltage just boils off a bit more water

BB.

For your stored cells... You generally want them to be somewhere around 1/2 charged (around 3.0 volts for typcial LFP... As always check the specifications)... Keeping them at 100% state of charge will age them pretty fast (lose significant capacity in 1-2 years).

Also, the cells need to be disconnected from any loads or Battery Management Systems. If you cannot disconnect the loads, then you will need to check/recharge occasionally.

-Bill

midijeep

I wonder if this would work?
I have a Drok Voltage regulator: 
https://www.amazon.com/gp/product/B01MSJQAKY/ref=oh_aui_detailpage_o08_s00?ie=UTF8&psc=1

I'm thinking of using a spare solar panel I have and running it to a Solar controller by Battery Tender: 

https://www.batterymart.com/p-021-1162-battery-tender-solar-controller.html?gclid=EAIaIQobChMIrPS-6fmD2gIVhYF-Ch08CAtPEAQYAiABEgJJWPD_BwE

and then to the Drok voltage regulator then out to the two NiFe 1.v batteries in series.
Would this be a bad idea?

mike95490

The Drok looks like an interesting piece of gear.  It  would have to be powered by a battery, it is not capable of MPPT operation from a PV panel only.

The battery tender is a 12V gadget, not adjustable to a pair of NiFe batteries. The batteries are likely tougher, and will just need a bit more water, more often.

you are working outside the box here, and will have to learn what works and what burns your house down,

Raj174

@midijeep
This charger should do the job. It's 32 dollars. You might have to put it on a timer to keep the SOC in the right range.

http://www.batteryspace.com/Smart-Charger-6.0A-for-3.2V-1cells-LiFePO4-Battery-Pack-100-240VAC-CE.aspx

Rick

midijeep

Raj174 said:

@midijeep
This charger should do the job. It's 32 dollars. You might have to put it on a timer to keep the SOC in the right range.

http://www.batteryspace.com/Smart-Charger-6.0A-for-3.2V-1cells-LiFePO4-Battery-Pack-100-240VAC-CE.aspx

Rick

Thanks Rick.  Bought the charger and works great for maintaining the two 1.2 NiFe batteries.