Thinking of making a circuit that can do the following:
Safely charge a NiMH battery from USB power.
Safely charge the NiMH battery from solar panel(s).
Prevent overcharging?
Prevent damage of the batteries.
Boost power to a smooth 5v.
No idea what I am going to power yet.
Questions:
How many cells?
Series or parallel?
mah?
Charging rate?
Thanks.
NiMa cells have a nominal voltage of 1.2 volt and being charged some more.
Dig into the theory of that family. I built a charger for the previous type, NiCd but, as I say, get hold of the NiMa theory. No need for helpers to copy what's already written.
Then making the circuitry can take on.
Charging in parallell is No, No. Charging single cells always works the best.
In serie calls for matched cells from the same batch.
The charging current will be known knowing the theory as pointed out above.
The best on-line resource on care and charging of batteries is batteryuniversity.com
Like same age, type and brand?
Age will be hard….
Found this!
Preferably more than that, but that's a minimum + plus the same ah.
just curious but what else?
Charging the cells in serie there's a must they have the same capacity. Else the minor capacity cell will be toast.
Charging in parallell, monitoring each cell, no extra demands.
What voltage should I charge them at? Still reading article.
Not knowing the details I say: Charge with a desired current until a target voltage is reached. For maximum battery life, pick up the details. Note if temperature monitoring is recommended. What You learn from basic theory is worth a lot.
I once bought a quick charger that killed most of my NiMh cells....
Ok. Will get back after I learn more.
Not voltage, current.
Old (safe) recipe.
Discharge to ~1volt.
Charge with a current of 10% of the AmpHour rating of the cell for 14 hours.
Don't trickle-charge.
Leo..
Not needed with NiMh, essential for NiCd.
NiCd have a memory, discharge to, say, 30% and they end up losing the last 30% of their capacity, hence the need to fully discharge before charging. NiMh don't have this problem.
True, but how else is a beginner supposed to know end of charge.
Voltage (1.45volt), or 5% trickle-charge for 24hours is not a very good way.
Partly charging NiMH batteries needs a charger with Delta Peak detection.
That might work on USB power, but OP also needs solar charging.
NiMH is a problematic chemistry. LiPo is easier, LiFePo4 is even easier.
Leo..
Right now solar is second priority. What is needed to charge the batteries on solar?
Regulated current and voltage? How to detect Delta Peak?
So trickle charging is not ideal(I read that it is a good idea to charge them that way but turns out that book is wrong).
As for the LiPo and LiFePo4 batteries:
I know there are lots of modules to charge those but I was curious if it is possible this way.
Another reason I chose NiMH is that I already have some AA and AAA cells.
I know that it would be easier to just buy a LiPo or LiFePo4(or Li ion?) and a charger module for it. I even have a Li Ion battery(salvaged) but I don’t want to use it for this project because I have something planed out for it.
Thank you very much for your advice.
Will learn more about batteries. Not much time right now.
With a delta peak charger chip. They charge with a fairly high current, otherwise that tiny voltage dip at the end of charge can't be detected. You might not always have the required current available on solar.
Leo..
NiMH charge curve is pretty near the same as LiPo / Li-ion.
TP4056-based chargers can be used. The charge current can be modified by changing a programming resistor, easily calculated.
They go into 'trickle charge' mode, but, personally, I prefer to not see that as endorsement of a UPS functionality. Get 'em in and get 'em out. (Maybe a supplemental controller / monitor could kick out a latching relay.)
Please explain how to change end-of-charge voltage to 1.45volt.
Leo..
Charger LiitoKala Lii-100 or LiitoKala Lii-202
3 in series