17 ms·

Build a Solar Battery Charger for Ni-MH Batteries

38 points by whereistimbo 6y ago

pjc50 6y ago
Well, that ignores the charge termination rules for NiMh, so the effect on long term battery life won't be great ...
- qz2 6y ago
  Yeah if you’re going to do this and forget such things you might as well use a diode and resistor and be done with it. It’s no worse than this circuit.
- whereistimbo 6y ago
  how about this: https://create.arduino.cc/projecthub/aleksand1975/intelligent-charger-for-9v-nimh-rechargeable-batteries-v1-61cbd6 https://create.arduino.cc/projecthub/aleksand1975/intelligen... ?
  - pjc50 6y ago
    That looks a lot better, it recognizes the dv/dt condition and has a number of safety features.
- dragontamer 6y ago
  Trickle charge (less than 15mA) for NiMH was fine for long-term battery life I thought? EDIT: https://data.energizer.com/pdfs/nickelmetalhydride_appman.pdf https://data.energizer.com/pdfs/nickelmetalhydride_appman.pd... >> Finally a maintenance (or trickle) charge rate of less than 0.025 C (C/40) is recommended. The use of very small trickle charges is preferred to reduce the negative effects of overcharging. C/40 constant trickle-charge is good for NiMH chemistry. ----------- The simplicity of trickle-charge is one of the defining reasons to use NiMH over other chemistries. 15mA * 40 == 600mA-hrs, which should be safe for even tiny AAA-NiMH cells. EDIT: Ah, I assumed the article was going for the Trickle Charge technique. Hmmm... it uses a 555-timer for "current limitations" which seems... harder than just using an OpAmp + transistor.
_wldu 6y ago
Here's a great kit I've built in the past. It's popular with remote radio operators, campers and sailors. http://www.cirkits.com/scc3/ http://www.cirkits.com/scc3/
dragontamer 6y ago
The 555-timer as a current-limiter seems... complicated... to think about. I feel like an OpAmp can set a voltage across a resistor, and then a BJT transistor can be set into "current mirror" mode, and easily set the current-control needed to safely work with NiMH batteries. If you wanted 90mA or 100mA (or whatever), that seems like the most straightforward way to set a current across a changing voltage source (which a solar-panel is).

38 points by whereistimbo 6y ago

pjc50 6y ago

Well, that ignores the charge termination rules for NiMh, so the effect on long term battery life won't be great ...

qz2 6y ago
Yeah if you’re going to do this and forget such things you might as well use a diode and resistor and be done with it. It’s no worse than this circuit.
whereistimbo 6y ago
how about this: https://create.arduino.cc/projecthub/aleksand1975/intelligent-charger-for-9v-nimh-rechargeable-batteries-v1-61cbd6 https://create.arduino.cc/projecthub/aleksand1975/intelligen... ?
- pjc50 6y ago
  That looks a lot better, it recognizes the dv/dt condition and has a number of safety features.
dragontamer 6y ago
Trickle charge (less than 15mA) for NiMH was fine for long-term battery life I thought? EDIT: https://data.energizer.com/pdfs/nickelmetalhydride_appman.pdf https://data.energizer.com/pdfs/nickelmetalhydride_appman.pd... >> Finally a maintenance (or trickle) charge rate of less than 0.025 C (C/40) is recommended. The use of very small trickle charges is preferred to reduce the negative effects of overcharging. C/40 constant trickle-charge is good for NiMH chemistry. ----------- The simplicity of trickle-charge is one of the defining reasons to use NiMH over other chemistries. 15mA * 40 == 600mA-hrs, which should be safe for even tiny AAA-NiMH cells. EDIT: Ah, I assumed the article was going for the Trickle Charge technique. Hmmm... it uses a 555-timer for "current limitations" which seems... harder than just using an OpAmp + transistor.

_wldu 6y ago

Here's a great kit I've built in the past. It's popular with remote radio operators, campers and sailors. http://www.cirkits.com/scc3/ http://www.cirkits.com/scc3/

dragontamer 6y ago

The 555-timer as a current-limiter seems... complicated... to think about. I feel like an OpAmp can set a voltage across a resistor, and then a BJT transistor can be set into "current mirror" mode, and easily set the current-control needed to safely work with NiMH batteries. If you wanted 90mA or 100mA (or whatever), that seems like the most straightforward way to set a current across a changing voltage source (which a solar-panel is).