# NiMH charge controller

Registered Users Posts: 12
Does any body recommends a NiMH charge controller to be powered by a 12V, 700mA solar panel? The charge controller must charge at least 3 1.2 batteries. Thanks

• Solar Expert Posts: 10,300 ✭✭✭✭
Re: NiMH charge controller

what exactly are you talking about here, powering a nimh battery charger with solar?
Re: NiMH charge controller

What charge rate are you looking for? If C/10 or slower (at least 10 Hours to recharge from dead)--you don't really even need a charge controller (you could use something like this to monitor the charging rate/voltage).

For example, if you where using 2,000 mAH AA NiMH batteries, the C/10 rate would be 200 mAmps. You could put 1-6 (maximum number of batteries in series depends on the exact Vmp of the solar panel and the ambient temperature) or so batteries in series for 200mAmp rate. And put 3-4 of those (equal battery strings) in parallel behind your 12 volt / 700 mAmp panel. It would take 2-3+ days of full summer sun to recharge the "set" from near dead.

You probably want one blocking diode per string to prevent leakage current at night going back into the solar panel or battery strings leaking into other strings...

Batteries in each series string should be matched sets (same brand, same size, ideally discharged the same amount). You can make some very cheap and reliable current sources so that you can "program" the charging current for each string (AAA/AA/C/D etc.).

If you are planning on D cell NiMH batteries which run around 10,000 mAH ratings... C/10 => 1,000 mAmp or 1 amp... Your 700 mA panel is less than C/10--so you could put between 1 to approximately 6 D Cells in series with one Vmp>12 volt 700mA panel. Again, 5 hours per day:
• 10 AH * 1/0.700 amps * 1/0.66 charging eff * 1/5 hours sunny summer day = 4.3 sunny summer days from dead
If you are are looking to "fast charge" (C/2 to C/0.5 or so) so that you can charge in 30 minutes to 2 hours--you probably are better off with your solar panel charging a standard 12 volt battery then using a standard fast charger that can run off a car adapter (12 volt lighter plug)--or bite the bullet and use an efficient 12 volt to 120 VAC inverter.

The the solar panel (and 12 volt holding battery) would be sized to the AH needs of the charger and how may/how large of batteries are are recharging.

If you can't be at the whims of the weather, then a 12 volt lead acid battery and smart charger is probably the best way to go.

The little I have seen from before when trying to find a "nice" solar AA/etc. battery charger--They have all been very small solar panels and take days to weeks to recharge the batteries.

I have not seen solar based MPPT input chargers for NiMH batteries. Would be interesting to see if there are any out there.

There are other ways of controlling charging--timer, AH counters, etc... But they can be hard on the batteries (if fast charging) or if the batteries are still 3/4 full, etc.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 8,862 ✭✭✭✭✭
Re: NiMH charge controller
xsr_Gx wrote: »
Does any body recommends a NiMH charge controller to be powered by a 12V, 700mA solar panel? The charge controller must charge at least 3 1.2 batteries. Thanks

You can look thru the nimh chargers, and locate one with a 12V car cord:
http://www.thomasdistributing.com/nimh_battery_chargers.htm
and use it to charge from your PV. 700mA PV is not much, and you are more likely to need 2A of PV to charge from.
Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
|| VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

solar: http://tinyurl.com/LMR-Solar
gen: http://tinyurl.com/LMR-Lister ,

• Solar Expert Posts: 5,242 ✭✭✭✭✭
Re: NiMH charge controller

While looking at setting up a panel and batteries for a bicycle trip I learned some of the NiMH batteries (most?) can stand a fairly high charge rate unregulated with out damage, disipating the charge via heat, I think as high as C6, but do your own research to confirm!

I have run a, total loss(unregulated) system with 2 small 6v SLA batteries, charging in series and using in paralell to run a radio, light, etc on a former bike trip of 8 months and they(and I) survived.
Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
Re: NiMH charge controller
Photowhit wrote: »
While looking at setting up a panel and batteries for a bicycle trip I learned some of the NiMH batteries (most?) can stand a fairly high charge rate unregulated with out damage, disipating the charge via heat, I think as high as C6, but do your own research to confirm!

Is that C*6 or C/6?

And yes, NiMH can take high charge rates--up until they get full, then then charge current is turned into 100% heat--hence why high charge rate NiMH have internal protection (I believe they open circuit) and monitoring the temperature for charge completion (and a tiny voltage dip as the charge completes).

C/10 is almost a trickle charge and can certainly be left on for hours after fully charged... If maintained for days to weeks, it will eventually lead to an early end of life for the battery.

Another thing to worry about with NiMH is their high self discharge current. After they get some usage/age on them, they can be flat with in few months or so.

The newer "hybrid" NiMH like the Sanyo Eneloop which can maintain ~80% of their charge after a year. I believe others like Kodak, EverReady, etc. also have hybrid NiMH batteries (on the box, may say the batteries are "pre-charged"). Unfortinatually, it looks like the Sanyo's are only available in AA and AAA sizes.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset