Go Down

Topic: Solar charger IC for NiMH just like the TP4056 for LiPo (Read 628 times) previous topic - next topic

mbobinger

Or, how about one of these:


Dear ReverseEMF,

Thank you a lot for your useful comments! The ICs with adjustable switching voltage regulator you sent me are just perfect.

My probably last questions are, at what voltage shall I recharge the NiMH batteries? I have purchased following batteries:
https://www.reichelt.de/nimh-akku-aa-mignon-2100-mah-1er-pack-xc-x2100aa-p190936.html?&trstct=pos_0

In the datasheet, there are some plots with Chinese axis but it is clear what is shown (page 7 in the pdf):
https://cdn-reichelt.de/documents/datenblatt/D500/XC_X2100AA_DB.pdf

Fully charged, the batteries hold a voltage of around 1.4V. For lower temperatures, that voltage exceeds even 1.5V.

Looks to me like I can go for a charging voltage of 1.4V. What do you think?

The solar panel should be placed outdoor to recharge the NiMH batteries over the whole year and power an MCU that records sensor values. I am not sure whether it will work to operate the NiMH battery and the charger in a temperature window of -10 to 50°C.

Thank you!
Marco


ReverseEMF

#16
Jul 25, 2019, 08:46 pm Last Edit: Jul 25, 2019, 08:59 pm by ReverseEMF
My probably last questions are, at what voltage shall I recharge the NiMH batteries? I have purchased following batteries:
https://www.reichelt.de/nimh-akku-aa-mignon-2100-mah-1er-pack-xc-x2100aa-p190936.html?&trstct=pos_0

In the datasheet, there are some plots with Chinese axis but it is clear what is shown (page 7 in the pdf):
https://cdn-reichelt.de/documents/datenblatt/D500/XC_X2100AA_DB.pdf

Fully charged, the batteries hold a voltage of around 1.4V. For lower temperatures, that voltage exceeds even 1.5V.

Looks to me like I can go for a charging voltage of 1.4V. What do you think?

The solar panel should be placed outdoor to recharge the NiMH batteries over the whole year and power an MCU that records sensor values. I am not sure whether it will work to operate the NiMH battery and the charger in a temperature window of -10 to 50°C.
OK...didn't know about the wide operating temperature stipulation.  Like I said before, this is a solution for charging at room temperature.  I've never dealt with temperatures wider than around 55°F to 104°F [~13°C to ~40°C].  So, can't guarantee this is a viable solution for such extreme temps.
Also, at temps below 0°C and above 40°C you should only do a trickle charge [i.e. C/10, e.g. if the battery capacity is 220mAHr, then the C/10 charge rate would be 22mA] -- so, you might want to consider, a constant voltage charger with current limited to  a trickle charge -- that way, it will, also, properly reduce the charge rate, when the battery reaches the set voltage plateau.   'cuz, not good to trickle charge a NiMH battery beyond it's full charge point.
And, reminder: as I said, before, this solution will, likely, NOT fully charge the battery.  It's a trade-off between cost/complex of the charger, and battery economy.
But, if you're still onboard, I've generally used ~1.42V.  Which, if you wind up using a series diode to prevent battery discharge, is pretty hard to hit, so, yeah, lets call it 1.4V.  The chargers I design, typically have some sort of switching circuit -- e.g. an OptoIsolator "solid-state relay" with two MOSFETs on the output, or a N-Ch Low Gate Threshold MOSFET that relies on the regulator DropOut voltage to turn it on.

For Instance:





D1 is for reverse voltage protection, but the RTR030N05TL is vulnerable to voltages greater than -12V, so there's that.  D1 also provides a bit more MOSFET turn-on voltage, but, with this MOSFET, not really needed.

Be advised: this is an old design, and that MOSFET has since become "Not recommended for new designs".  Mouser still has over 120 thousand of them, but choose accordingly ;)

And, I just noticed: That note that says "Adjust R6..." it should be R8.  The note was composed in an even earlier schematic, and since, the Part Reference Numbers were updated, and I forgot to update the note!
"It's a big galaxy, Mr. Scott"

Please DON'T Private Message to me, what should be part of the Public Conversation -- especially if it's to correct a mistake, or contradict a statement!  Let it ALL hang out!!

Go Up