Charge regulation for NiMH batteries

[jajbellsouthnet]

I have a 12VDC/.15A exhaust fan on my composting toilet and have experienced a lot of trouble using a lead/acid lawn tractor battery with a solar charger. The battery always sulphates badly and eventually fails to hold a charge overnight (With odorous consequences). I am currently setting up the fan to run off of ten 1.2V/10,000mAH NiMH batteries and am concerned about the warning printed on the batteries about avoiding overcharge. What will happen if they are overcharged? Leakage? Explosion? Fire? I have two spare controllers available. One is a Trace C12, the other a BZ Products Mini PV controller (8A max). Will either of these do the job? Thanks for the help.

[Anon001]

two things... First.... You are using a shallow cycle battery. You need to use a deep cycle battery. Shallow cycle will not last long under any solar conditions. They are not designed for that. Second... you need to use a charge controller. Trace is good, but I'm not familiar with BZ Products.

There is nothing wrong with overcharging "deep cycle" batteries on a regular basis to equalize the cells and keep the sulfation to a minimum as long as possible... Even this "equalizing" charge must be managed.

A side note:... an RV/Marine battery that says "Deep Cycle" on the side of it is not a true deep cycle. It is a hybrid between a deep cycle and an automotive battery and the plates are not heavy duty enough for a solar application.

I am not familiar with the exhaust fans, although I've always wanted a composting toilet, but with typical "solar applications" you never want to discharge the batter more than 20%.

Good Luck,
Paul

[12vman]

Where did you find 10 aHr NiMH batteries?

The C-12 controller is a great unit. The bulk/float charge levels are very adjustable..

NiMH batteries are a little different animal than lead acid. They'll rise to the bulk level faster and you need to be careful on the float voltage. Once they achieve the bulk voltage level, the controller will hold it there for about an hour. You don't want to have that voltage too high. (Around 3 volts higher than the combined voltage of the battery) Once the controller switches to float, keep the voltage just slightly above the combined voltage of the battery. (In this case, 12.3 - 12.5 volts) It may take you a week to get these voltages set but it's crucial that you do.

These adjustments may be wrong and that's why you are destroying your lead acid battery.

[jajbellsouthnet]

12V,
I am using ten 1.2V NiMh D cells made by Tenergy (China) and sold on the net by All-Battery.com. The rating printed on the side of the battery reads "10,000mAH. In a test setup, I have been running my .15A fan for 30 hours so far on a battery pack that was assembled from my stock of spare less-than-fully-charged cells. I started using Tenergy NiMH batteries for powering my radio-controlled airplanes and found that they have none of the corrosion, leakage and memory problems of NiCads.
Thanks for the advice,
John

[12vman]

WOW!! 1 mA. load for 10,000 hours from a "D" cell battery?

I'm sittin' here doin' the math.. ???

10,000 mA. is 10 amps! I understand that the battery will discharge faster with a heavy load but.. :o

In your case, with a .150 mA. load, my calculator says that your battery pac should run the fan for less than 416 days being the load is more than .001mA. when fully charged! Am I missing something here?

Technical Specifications

Dimension: Height 60 mm, Diameter 33 mm
Weight:;0.36lbs per cell;
Capacity: 10,000 mAh
Voltage: 1.2V
Standard Charge: 15 hours @ 800 mA
Rapid Charge: 3 hours @ 4000 mA

[jajbellsouthnet]

12V,
Yeah, they last FOREVER! That's why I started using them in my airplanes. My thumbs and eyes get tired before I run out of juice. I also have some of the same brand in C size (5000mAH) and AA size (2600 mAH). Maybe I should try those. I use the C's and AA's in my radios and I can't remember the last time I changed them. At my age and stage of memory, that may be a month or more.

[DavidOH]

I think you missed it here:
"I have been running my .15A fan for 30 hours"

"In your case, with a .150 mA. load, my calculator says"

That's .15 Amps not .15 milli Amps

416 days? Yeah! :D Send me one of those batteries. ;D

[12vman]

WOW.. I musta been half asleep this morning.. :P

10amps divided by .150 = 66.67.

66.67 divided by 24 hrs. = 2.78 days (At least 2 days)

The fan will use 3.6 aHr. in a 24 hour period @ .15 amp load.

I don't EVEN know where I came up with that 416.. LOL. I can't even reproduce it! (Hay Griz.. Pass me another one, wil ya..) ;D

I'm still hard pressed to believe that a "D" cell would have that kind of capacity.. WOW..

[Grizzy]

(pull'n lil Red Flyer wagon with cooler in there :P ... lotsa ice.... Toss'n yas a cold one........ sigh