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Old 07-29-2010, 03:37 PM   #1
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More on Batteries

Hello all: Recently I went on a 3 week trip which was basically all dry-camping. I did have to use the furnace in the morning and sometimes for a bit at night. All my lights are LED. Here's what I found out. The battery (one 12 volt mounted on the bumper) was good for the first week. Thereafter, I ran the generator for about an hour each morning to try to keep ahead of the draw on the battery. I was charging through the trailer hook-up connector, but was barely keeping up. Anyway I met an old-timer RV person who told me that this was not the most efficient way to charge the battery. Apparently, the inverter in the 17B typically charges at 6 amps, and one hour at this rate hardly makes a dent in replacing what was drawn down the previous day. He advised me to hook up a regular car-battery charger (from Canadian Tire) directly to the terminals of the battery on the bumper. This type of charger typically puts out 15amps and will charge the battery much more efficiently. Because my high-school physics happened too long ago, I went on line and did some research. In fact, the old-timer was absoulutely correct. I tried it and it worked. I know it worked because I used a specific gravity scale to measure the battery acid in each cell and after one hour per day of charging in this manner, the battery was kept almost 100% full. Here's a chart showing readings for percent charge using a specific gravity (dip-stick type) meter which is the most reliable method of assessing the condition of the battery.
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File Type: doc State of charge chart for 12 volt batteries.doc (23.5 KB, 143 views)
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Old 07-29-2010, 04:29 PM   #2
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Re: More on Batteries

This is very interesting. What was the battery connected to while you were taking the voltage measurements?

(You know that I am, in fact, a high school physics teacher, right?)
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Old 07-29-2010, 05:35 PM   #3
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Re: More on Batteries

Hi Ron: Thanks for your reply. The 17B was parked and unhitched. There was no other electrical input (such as from the tow vehicle). The first time I went directly from the generator to the battery terminals and the battery charger was reading an output of 15amp. I charged it this way for an hour. Then I began to think that I could actually raise the charge input another six amps by connecting the trailer electical connector to the generator while also going directly to the battery terminals. This proved to provide a much faster charge and according to my calculation there were now approx 21amps going into the battery. The battery did not overheat.......became warm to the touch but not hot. I left the cell covers open so that I could see what was going on but the acid did not expand enough to come out over the top of the battery so I concluded that the battery was well able to take the 21 amp charge.
At the end of the hour I disconnected the Canadian Tire battery charger, and the trailer electrical cord and waited about an hour so that I was sure I wasn't just getting a surface-charge reading, and then I dipped each cell. From what I've read, the secret to keeping the battery up is to NEVER allow it to be drawn down to below a reading of 12.25 on the specific gravity tester, but to replace on a daily basis what was used up the previous day, and that seemed to work splendidly for me. BTW did I pass the test, Ron?
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Old 07-29-2010, 05:51 PM   #4
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Re: More on Batteries

This is most interesting. I was impressed with what you have shared and certainly have given me some insights to battery charging. I have been trying to find a way of watching battery life other than the LED gauge inside my Escape. I had researched marine monitoring electronics but found them to be in the 200-300 price range. From what you state:

From what I've read, the secret to keeping the battery up is to NEVER allow it to be drawn down to below a reading of 12.25 on the specific gravity tester

I could use a battery hydrometer to check how my battery is doing. This could be a bit burdensome with two six volt batteries and the need to check every chamber but in this case it may be adaquate to do a spot check on one in each battery. Perhaps this is even more reliable than expensive marine electronics and certainly seems better than four led lights of different color.
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Old 07-29-2010, 06:03 PM   #5
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Re: More on Batteries

Go to this link and read the deep cycle battery FAQ's. This document should answer many of your questions gabe.
There is also a chart to approximate state of charge based on battery voltage for others who do not have a hydrometer (that's what the battery display panel in your escape does).
www.windsun.com/Batteries/Battery_FAQ.htm
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Old 07-29-2010, 06:38 PM   #6
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Re: More on Batteries

Since I had to investigate all this, from what I've read and from what I've been told by auto / marine outlets etc, it seems that the ONLY reliable way of knowing the state of the battery is by using the hydrometer (mine cost about $15) on each cell. And by the way, it takes less than 3 minutes to test every cell on my 12 volt battery.....................presumably double that on two six volt batteries. The monitor panel (idiot lights??) inside the 17B is unreliable and only gives an approximate reading, in fact it even reads the tank levels incorrectly!! Anyway, I'm quite happy to use the battery charger directly on the battery posts, and the hydrometer test until someone comes up with something better. Hope everyone is making the most of the Summer!!
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Old 07-30-2010, 06:51 AM   #7
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Re: More on Batteries

Strawbarry

Your link to battery maintenance was an excellent reference. Lots of good information in there. Having two 6 volt batteries I have two goals, get the longest power use out of them and maintain them for as many years as possible. Since they have to be replaced in pairs and based on prices at my local farm store they can run $90 US each, I want longevity.

As of now I am not recharging when in use, rather draining them down to . . whatever . . level over a six day period. The hydrometer will keep me from waiting too long between charges.

I am in the market for a hydrometer as we speak. It sure seems like a scientific method to measure and maintain ones batteries. I am also considering the purchase of a quality charger to use on the batteries when in winter storage. The charger needs to be one of the "smart" models. I am using a "smart" charger from Maha on my AAA and AA sized rechargables.

Since I maybe implementing solar charging in the future I want to proceed with pruchasing relevant products.
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Old 07-30-2010, 07:16 AM   #8
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Re: More on Batteries

You are on the right path to maintaining your battery. The specific gravity of each cell tells you the state of charge for a battery. It does not tell you the the AH capacity of the battery. Placing a load on the battery at X amps for X time gives you the capacity. As a battery ages the state of charge can be 100% but the capacity at some lower value. This is normal wear and tear from use. A quick test would be to place a 12V load on the battery without your battery charger helping. The refrigerator on DC voltage would be a good one, watch the voltage across the battery. If the voltage dives quickly down to 10.5 to 11 then your battery has very little capacity. A good battery will supply the current and maintain 12 volts. If you do not see a drastic change in voltage then you have a good battery, a battery with a bad cell will be very apparent even when using the battery monitor in your trailer.

A battery is only as good as it's charger. A good 3 stage charger will extend the life of your batteries. I encourage everyone who has questions about their batteries to read the previous link I provided, it is a good general discussion of deep cycle batteries.

"Live each day as if it is your last"
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Old 07-30-2010, 03:20 PM   #9
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Re: More on Batteries

I started shopping around for a decent 3-stage battery charger for deep cycle batteries myself, and got curious as there is a lot on the market. I have, same as Paul, 2 6V batteries on Cafe Egg. Which brand would you recommend? And of the brand, which model would you get? Furthermore, would you go with one made for 6V or 12V? This is still confusing to me.

Now this weekend I will be entirely off-grid, I prohibited myself to bring any computer to this camping trip. I will pick up my kid at daycare after I get off of work, and off we go. So I will only Sunday get a chance and read any answers.
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Old 07-30-2010, 03:53 PM   #10
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Re: More on Batteries

Gerda, I have no good recommendation for you, but a 12V charger will do the trick, as you will just charge across both batteries.

The two 6V batteries are literally connected in series (in line) to total 12V.

If you were to charge them loose and individually, then you would need to charge them at 6V.

Have a fun weekend.
It is a long weekend here, I will be gone from tomorrow morning until Monday night too.
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