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Old 05-24-2010, 08:22 AM   #1
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dryflie
Electrical question

Questions, I've got lots of them. This one relates to Battery dropping it's charge. I've got a brand new AGM single 12v on the trailer and while parked at home I've had the Trailer on shore power. I pulled the plug yesterday to check the fridge on gas. When I pulled the plug I check the battery voltage and it read 13.7v, this morning it's down to 12.4. Now as best I know there is nothing on whatsoever. So what is pulling the voltage down? Is there simply a small system draw when the battery is connected?

As I've mentioned here recently my campground has cut off power completely so we're left with generators and batteries for the season. Anything and everything related to batteries is now a major major concern to me.

Thanks in advance for any help or advice.
Al
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Old 05-24-2010, 09:05 AM   #2
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There are a few things that draw constantly, the CO detector, the smoke detector, the radio, etc. but they shouldn't draw it down overnight.

Are you sure all the appliances were OFF? Even if they are running on gas, they still use power for controls, fans, etc.

Other less likely possibilities include a short somewhere, and the new battery is bad.

Mack
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Old 05-24-2010, 09:13 AM   #3
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Mack, the only appliance on is the fridge (running on gas). It has the small control panel lit but as best I know that's it. Radio is off, TV off all lights off, Smoke Detector is AA battery operated. The AGM is brand new and should be fine. Thing is this happened with another battery as well so I purchased the new AGM just to take the battery out of the equation.
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Old 05-24-2010, 11:14 AM   #4
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I believe the 13.7 volts you read is the voltage of the battery with the inverter on or just after you shut the inverter off. This sounds like the charging voltage and not the normal fully charged at rest voltage.

The normal at rest voltage of a fully charged battery is around 12.5 volts.
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Old 05-24-2010, 08:41 PM   #5
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Hi Dryflie

Do you have an amp meter? An amp meter between the battery and the camper in series tells a lot.

A few things.

13.65 - 13.7 volts is the standard charge voltage of a converter. Even after you yank the 120 VAC shore power that 13.7 VDC hangs in there for many hours on end and they call it a surface charge. The voltage you are reading is real but it is not indicative of state of charge of the battery. Checking an unloaded battery after 8,16 and 24 hours tells a more clear state of charge.

13.25 or 13.3 is a float voltage by the converter and if yours has it, 14.4 volts is boost or bulk mode.

Once the surface charge is gone 12.65 VDC is what lead acid batteries declare as 100%. And there is also a level of error that can be in your volt meter. If it is off by 0.1 or 0.2 volts that is a big difference.

Here are a few sites that have some good reading.
http://www.batteryuniversity.com/partone-13.htm

http://www.marxrv.com/12volt/12volt.htm

This spring I hooked my meter up to my twin bank of Group 27’s and checking some things out. There is one real power grabber that got me and I forgot about it. The roof TV antenna. I did not even have a TV in the TT but the amplifier was on, little green light top and that thing sucks a fair amount of drain. So check that.

There is also a defrost strip in many RV fridges. I do not know if your has it but it does really draw a lot. Turn it off.

The only true way to track this down is to put and amp meter in series with the battery and start pulling fuses until no power flows. They you know for sure what is going on.

Same on the voltage. For sure unhook the battery some time once it is fully charged and let it sit for 8 to 12 hours then read it. I have heard that it takes some batteries several charge, use, charge cycles before you can reach 100%. It may stop at 95 or 98% Again this is lead acid based not AGM. I have not made it to that level yet.

Good luck and hope this helps

John
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Old 05-25-2010, 07:53 AM   #6
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Thanks John and Norm, excellent information. Good to know about the Inverter float charge. As it happens a check of the charge about 8 hours after the power was pulled showed it at 12.4v, a day later it was 12.3 and this morning 12.1. Is this small daily drop normal?

I'll be pulling the trailer north this Thursday and getting it set for the season up north. Typically we're there only 4-5 days in May, then back again in mid June for 4-5 days, away again and back at the beginning of July for 10-12 days. This back and forth goes on until the end of Sept.
It will be interesting to see how the battery holds up using the Onan Gen Set for backup. We're also looking for a solar back up for times we are away. My plan would be to disconnect the battery each time we leave and to bring a fully charge 2nd battery up with us each time. If the solar looks/works good perhaps we can leave things hooked up.
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Old 05-25-2010, 09:23 AM   #7
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We never remove our batteries. When not in camping we leave them on the Inverter or in the case of the Trailer on the solar panels. This does not seem to be detrimental to the batteries.

This winter we left the Motorhome batteries on as we do all winter and the water level was down when we returned home after six months but not to the plate level. As I've stated a couple of times our batteries in the motorhome are 13 years old and still fine.

Though we have a little trailer, our 200 watt solar cells are easily capable of charging our battery when parked. As well the solar panels can almost meet our typical electrical usage (2.5KW per day) when actively camping (if we're not under trees).

We do carry a generator when we're really away from power but it only weighs 40 pounds, provides 1000 watts and easily powers our configuration.

Another ability we've added is the ability to charge the battery while driving from the car. Sometimes on hot days we run the convertor to provide AC to our AC only refrigerator. While running the Inverter and charging from the car, the battery stays topped off. I installed a dashboard switch that allows me to switch charging on/off while driving.

I might also mention that we rarely shut our refrigerator off when not camping. Some how I intuitively believe that the ammonia cycle used in the gas/ac/dc refrigerator likes to run and not sit. I may be wrong but that's my intuition.
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Old 05-25-2010, 01:55 PM   #8
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Norm, some good notes there thanks. I'm going to look into the solar situation, could you tell me the model/maker you're using, if your happy with it? You comment about the fridge was interesting, I always left my older 1986 Sunline fridge plugged in all summer but in winter storage it was completely disconnected. Ran fine for about 22 years that way. With no power now I can only run it on gas now and really do not know what the gas consumption is going to be. I have two 30# tanks but no auto switch over so if it goes through one tank and I'm not around it's going to shut off any way.

Anyone got any ideas how long a 30# tank can run the fridge?
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Old 05-25-2010, 02:07 PM   #9
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I don't know. I never run it on gas for long periods. Running or not running fridge is something I was hoping to provoke conversation on.

I assume you mean the make and model of the solar panels. I made my own solar panels purchasing the cells on Ebay. I think I spent about $150to make 2 100 watt panels.

solar panel

This will take you to the thread.

If it's the make of refrigerator, it's a 4.1 cubic foot Magic Chef, about $120 also.
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Old 05-25-2010, 09:42 PM   #10
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Quote:
Originally Posted by dryflie View Post

Anyone got any ideas how long a 30# tank can run the fridge?
Here is an educated guess... this takes place at ambient temps and assumes you have a Dometic RM2652 fridge which you may not.

The RM2652 draws 1,500 BTU/hour if it is running constant. Note the word "constant"

Consumer Propane Cylinders and LP Gas Bottles

A 30# LP cylinder has 649,980 BTU's if you can ever get them all out of the tank.

If the fridge never shut off, ever and you could get all 649,980 BTU's
out of the tank then 649,980/1,500= 433.33 hours guesimate.

Our fridges do shut off and night time is less then day time to cool. So it may get you 18 (100%) to 36 (50% duty cylce) days a tank.

Temperature affects the BTU level and I have to read up more to explain that. Winter I know we do not get as much umph as we do in the summer.

If we have a LP service guy here, they may be able to help correct or filling in my missing parts.

Hope this helps

John
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