Can they be charged on the same chargers?

I have a couple solar lights that need new batteries and I'm wondering if I can substitute nimh. I've never seen nicad AA batteries.

Crap. Just found out my maha 9000 should charge them. They are junk.

I still don't know if i can use nimh.

Where can I buy the cheapest nimh batteries I can get for solar lights? 500 mah to 1000 mah.

eBay.

or Amazon





 

NiMH charger is OK for NiCd. NiCd charger is NOT OK for NiMh.

There are a few online battery stores that carry NiCds. They're toxic so they're distributed way less than they used to be.
IMO NiMH is not an acceptable substitute for solar lights, because the internal structure is damaged by low-rate charging
that solar lights do. So you really want actual NiCd AAs. They have way lower capacity that NiMH, a typical NiCd AA will be
600-700 milliamp hours.

Amazon has gobs of them for solar applications.

I bought 3 different brands of solar lights, 21 in total, in June/July for my dad and they all came with NiMH AAs, but at 350mAh-600mAh.

Generally and according to Maha, we don't want to charge NiMH batteries at any rate under .3C, due to possibly missing a charge termination due to a lack of heat.  

Many NiMH chargers use both a delta V and delta T (voltage and temperature) for termination.  By charging too low, the batteries never heat up to trigger that temperature set point and continue to charge.

NiCad chargers, at least the older ones, are dumb chargers and need to be 'timed' to reach full charge, as the charger won't recognize the Delta V/T termination points.  You can charge NiMH batteries on a NiCad charger, but you need to know the capacity of the batteries, how full they might be before they get charged and finally, you need to know the charging rate of your NiCad charger to kind of figure out how long you should leave them in the charger.

Honestly, Solar chargers don't charge for all that long, so putting in a 2000mAh Eneloop might not be such a big deal with a low level charge rate because the battery probably won't reach that point where it begins to be over charged, but one would have to do the math and know what type of current the LEDs require during the course of a night and know the charge rate of the solar lights, which are probably in the double digit milliamp range.

To be kosher, I don't think that I'd look for massive capacity NiMH batteries as a replacement, but I'd look for the 1000mAh and under versions.

Chris

Going with a much smaller NiMH would be a viable approach, though as you said the solar light
chargers aren't exactly intelligent. The issue with the 0.3C charge rate isn't just having enough
current flowing for charge termination, but also for battery life -- at low rates the metal inside the
battery can end up moving out of the matrix and essentially start plating things internally,
and this kills the battery; also, overcharging at rates above about C 0.05 can cause the battery
to vent and dry out, and without a smart charger terminating this is likely to happen.

Hopefully newer lights using NiMH have a real charge control circuit in them. Without they're
doomed to kill the battery through overcharge or plating via low-rate charge. It wouldn't
be hard to do a NiMH solar light properly, but it would require more components than the NiCd
lights use (which is basically just a solar panel, diode and a phototransistor.)

It really just comes down to how long you want something to last. A AA NiMH is going to survive a
year in a solar light even with a crap charger, but it probably won't survive 3 years. The life of the
light might be limited to a year by the plastic degrading in the sun anyway, but if we were
engineering the perfect light, we'd either go with NiCd or NiMH with a proper controller.

I have a small solar panel that was part of a harbor freight shed light kit. It had a little 4 watt florescent bulb that really didn't run all that long on a charge. I have no idea what happened to the nicad batteries that came with the unit. They were 500 mah each.

I am considering seeing how much charge I can get on 4 eneloops or other cheap rechargeable batteries with this solar charger.


Should I completely discharge the batteries on my maha and then put the charger into direct sunlight for 8 hours, then check the mah on the maha after?  Will this give me a better idea of the mah this panel can deliver?

First, to get any idea of whatcha doing...

You need to take voltage measurements.

Take them during the day and see what your yard light's charging cutoff voltage 'point' is.

Find what the cutoff point is for the type of battery your charging.

Then you will have your answer, likely.


Then using the Maha chgr to evaluate the charge, that should work well.

Yep, that's how I do it. That gives a realistic number for the charge (and now is a good time, obviously you get more charge in summer and less in winter.)
I usually run the discharge cycle twice just to make sure they're good and dead. The second cycle will normally terminate really fast (just a few minutes.)

Depends on the charger.    I have a charger that I use for NiCad, Lipo, LiON, NiMH, and lead acid.



If you are considering NiMH take a look at the Eneloops.  They have a much slower self discharge rate than most NiMH and come in most standard sizes.