# Battery Question



## Tarheel (Jan 24, 2010)

A little over 2 years ago I purchased a mighty mule 12 volt gate opener.http://www.mightymule.com/gate-openers-FM200.htm I added a 5 watt solar charger (no grid power close) and this thing has worked like a charm.I had a 12 volt deep cycle marine battery that was on my boat and it was 3 years old at the time so I used it and bought new for the boat.

The first problem that I had was late last summer when the low power alarm started going off so I took the battery off and carried to the shop to charge. I opened the caps to check the water level and the battery was low on water. I then added distilled water to the fill line, charged the battery and put it back in service.

So yesterday I hear the low voltage alarm going off, so I go and check and sure enough no water in the battery. I did the same procedure again and put it back in service. Worked for at least 6 months with no problem and the panel actually gets more sun in the winter than summer because of the leaves on the trees. My best guess is that I need to add a charger controller to the system. Mighty mule says no not until you get to 15 watts. Some days the gate is opened and closed 6 times and then it may go a couple of days and not get opened but 1 time.

So I know the battery is 5 years old and has to be about shot, but I want to cure the problem first and when I do replace it do I go with the same set up (24DC-6) Reserve capacity 100, 75 amp hours. or go with 2-6volt golf cart type. Thanks in advance for your thoughts.


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## TnAndy (Sep 15, 2005)

I'm surprised a 5w panel will even keep the battery up if you use it much....that's barely enough to just trickle charge it the amount of self discharge, I'd think.....don't know what to tell you on the water use.....that DOES sound like enough charging going on to outgas the water....

When you replace, you might want to go with an AGM type battery, like the Optima blue....

http://www.optimabatteries.com/optima_products/


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## 12vman (Feb 17, 2004)

If the battery isn't used a lot, 400 mills could make it boil a small amount. If the discharge is low, the internal resistance is low which would allow an unregulated panel to take the battery to a higher voltage. Some of those small panels can go as high as 21 volts open circuit! I destroyed a small battery in one summer without a charge controller.

Voltage is what makes a battery boil, not so much as current. After a battery is "charged", the internal resistance is low against current but will continue to boil if you let the voltage increase. Charge controllers control voltage, not current. They apply a shunt against the panel(s) to bring the voltage down to a specific level to avoid them from boiling dry. If the voltage is restricted, the internal resistance of the battery will regulate the amount of current it uses/needs.

Uncontrolled voltage on a battery = Hydrogen Generator!

Being that the battery is old, the plates are probably thin and the internal resistance low. This condition would allow the battery to boil more, even with a small panel because of unregulated voltage.


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## artificer (Feb 26, 2007)

What is the problem you're trying to solve? The need for additional water? If so, you can get water miser caps. You'll still need to add water eventually, but it would reduce the frequency.

The solar panel will supply around 6amp-hrs of power. Using the max of 5amps from the manual, if it takes 1 minute to cycle, thats only 1/2amp-hr for 6 cycles.

The manual says to use an "automotive" or marine type battery. I don't think you're using much power, so the battery type isn't as important as one that gets discharged significantly.

If it was my system, I would let the battery go until it dies, unless that will cause dire consequences. After it died, I would use an AGM battery, and probably a smaller one. 32amp-hrs would be fine. Charge controllers are cheap insurance as well.

People with more expertise may have different ideas.

Michael


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## Tarheel (Jan 24, 2010)

Andy, Artificer I am sold on the AGM batteries after reading about them a little. Don't have a problem replacing the battery, just want to correct the problem before I do. I think as 12Vman says for safety I will add a charge controller to the system.(recommendations on where to get what I need ?) As I said the battery had already been used hard on the saltwater boat and charged several times so really it has lasted longer than I ever thought it would. 

As always guys thanks for the help. I will let you know how it works out.


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## 12vman (Feb 17, 2004)

If you use a AGM or a SLA type battery, be sure to use a charge controller! If the electrolyte gets low in one of those, You might as well throw it away. There's no way to replenish the water level. The charge level is very specific with not much room for error.

I use one of these from Harbor Freight. It has a low voltage disconnect to protect the battery and the float charge levels out around 13.6 volts. Nice little unit..

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=96728

I suggest getting on of these also so you don't need to cut the wiring up on the controller.. 

http://www.radioshack.com/product/index.jsp?productId=3870003


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## Tarheel (Jan 24, 2010)

12vman said:


> If you use a AGM or a SLA type battery, be sure to use a charge controller! If the electrolyte gets low in one of those, You might as well throw it away. There's no way to replenish the water level. The charge level is very specific with not much room for error.
> 
> I use one of these from Harbor Freight. It has a low voltage disconnect to protect the battery and the float charge levels out around 13.6 volts. Nice little unit..
> 
> http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=96728


Thank You for the link!


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## wy_white_wolf (Oct 14, 2004)

Sorry I ment to jump in sooner.

Without a charge controller an AGM or SLA battery will be junk in very short order. With a controller they would be lucky to last as long as a vented lead acid battery.

Either one of those I would consider a waste of money for your usage. They do have advantages but I don't see any of there advantages lining up with your needs. A plain old marine deep cycle is your best option.

Also a smaller battery would compound the problem. A smaller battery will increase the panel to battery ratio. It will just reach full charge sooner and have less plate material to absorb the overcharge. Stay with the size you have.

There is 2 things I do think you need to change:

1. Get a charge controller. It will help to reduce the overcharge from the panel. Since the panel is only 5 watts find the smallest cheapest you can get.

2. Put the battery on a *maintance schedule*. Would you consider running your truck with never doing any maintanence on it? Never change the oil or filter? You need to check the battery at least every 3 months for corroded terminals and low cells. Even with a charge controller there is going to be some overcharge. All you can really get for small charge controllers are going to be PWM shunt style controllers (because of cost and size of others). Every pulse is a slight overcharge of the battery. This doesn't end up as much of a problem on systems that are cycled every day. But with your usage it really isn't cycled. Just held at full charge.

I also feel that being a marine deep cycle about 5-7 years is all you should really expect out of it. I'd just go with another one because it would be hard for you to justify the expense of true deep cycle batteries or even 2 golf cart 6 volts.

WWW
just my 3 cents


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## Tarheel (Jan 24, 2010)

wy_white_wolf said:


> Sorry I ment to jump in sooner.
> 
> Without a charge controller an AGM or SLA battery will be junk in very short order. With a controller they would be lucky to last as long as a vented lead acid battery.
> 
> ...


Thanks for all the advice. I did not figure by what I have herd that the 5 watt panel would overcharge the battery. I run batteries on the boat with 10 watt automatic chargers and have never had to add water but they are expensive chargers. (I know they are different animals) I have no complaints what so ever about the life of the deep cycle batteries. I usually get 5-7 as you said out of them.

This has been my first attempt at solar in my 50 plus years, but I am ready to get started on a larger project(got spoiled at TnAndy's) later on and I am sure I will have questions. Thanks every one for the help.


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