NiMh for solar?

[yopappamon]

I have a pile of NiMh F cell packs from some Sharper Image ebike battery packs. I've been thinking about using them in a solar power system for my yard lights. Not a big load, just running a small inverter for a few hours each night, solar charged during the day. Charging would require monitoring cell temperature to shut off the charging when the cells start heating indicating fully charged. I would accomplish this with the existing packs thermisters and an Arduino micro controller, turn of the charge with some FET's. Monitor pack voltage with the Arduino, turn off the load when the pack voltage dropped to a preset point.

Charge to 1.4 - 1.6v per cell, so limit the solar panel output to 14 - 16v, current would be limited by the solar panel wattage (probably a 40 watt panel).

The load would be around 20 1.5w led 120v "bulbs", so 30-40 watts.

Have I thought this through well enough? Any holes in my plan?

 

[liveforphysics]

Have I thought this through well enough? Any holes in my plan?

NiMH is a huge PITA to charge and terminate charge correctly, so make sure ambient temp and normal solar gain and whatever on your battery packs doesn't throw off the ability to terminate, and make sure you start from a pack as balanced as possible, and then it should be OK. NiMH is seriously an epic PITA to work with though.

 

[yopappamon]

Maybe I should sell them to an ebiker and buy some lead.

 

[dak664]

NiMH has a terrible charge efficiency (~66%), as bad as lead-acid. Temperature increase is the least unreliable way to detect end of charge, for low charge rates.

 

[yopappamon]

Alright, you talked me right. I've looked at the Signalab BMS schematic and I think I can mod my 12 cell BMS down to 4 cells with just two jumpers. I didn't want to use my thundeskies for the solar without a proper BMS. So I started looking and just ordered a MiniBMS for the big pack and will mod the Signalab and use it with another set of TS 20ah's I have.

I'll be busy this weekend. Between this project and making my cell phone work as a garage door opener.

 

[999zip999]

Hay Yopappamam, How's the new move ? Going solar Love it.I still have to talk to my friend about solar left overs for you. I got my battery together. Very low sag. What does PITA mean ? Still have 20 more packs to cut up for another batt. Got rit of all those serfa stuff to many boxes.

 

[yopappamon]

PITA = pain in the ass.

I'm exhausted from the move, but it's great to have the space to do all these projects. Let me know if your guy can get me any solar panel mounting rails or hardware. I've got so freaking much stuff going on right now, but maybe we can get together this weekend or next. Have you built your pack yet? I forget do you already have the hub?