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Old 18-09-2013, 02:48   #1
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Fridge Working Continuously

Hi,
I need advice.
In the last couple of weeks my fridge, air cooled Frigoboat 12V with a box of 150lt is working in an odd way. In the early hours of the morning at about 5-6 am ( still dark ) it makes a sound as if stopping and immediately starting again without a pause. It never happens at day time when the solar panels are active.
It is connected to a battery bank of 170A and backed up with 2 solar panels in total 240 W. Solar panels are charging satisfactorily and tha area still has full sun without clouds.
When this happens I check the battery voltage and see it is 12V+. I don't have an A meter so no measuring of amperage of the batteries. While this happens I feel the cooling box and still has ice. The regulator of the solar panels show low state of charge. The batteries are 2 years old, no service type so I assume the acid and water is OK. My guess is they are dying.
- What may cause the problem?
- Is this harmful for the fridge?
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Old 18-09-2013, 05:03   #2
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Re: Fridge Working Continuously

Could be a few things. When you say that you see "12V+" you need to be a bit more specific. A lot of difference between 12.5 and 12.01.

I'd get a multimeter and check the voltage right at the fridge motor (or as close as you can) just to rule out wiring issues.

The fact that when the voltage is up (daytime, solar panels) you don't have the issue makes me thinks the batteries are frying, probably because they're undersized for the load and this is a repeating thing.

Personally I don't believe maintenance free batteries have a place onboard a boat. The whole concept just assumes (somewhat correctly I suppose) basic physics and chemistry can be largely ignored by the public.

Full sun, no clouds, solar working well = you're in a hot place. All that charging, all that heat = no way it's maintenance free if it's lead-acid.
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Old 18-09-2013, 05:50   #3
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When you get new batteries make it a larger bank. You dont want to use more than half your amps before a recharge. Using less is better for long battery life
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Old 18-09-2013, 08:26   #4
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Re: Fridge Working Continuously

Try checking, no try cleaning all the battery connections. Be sure to disconnect the negative ground cable first and reconnect it last. You can use your voltmeter to look for voltage drop (resistance) across connections.
But it does sound like a battery is failing.
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Old 18-09-2013, 08:30   #5
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Re: Fridge Working Continuously

And when you buy new batteries, avoid the "no maintenance" and "dual use" battery types. Get true deep-cycle batteries, preferably 6V golf-cart size if you have the space. They are true deep cycle, have thicker plates than 12V batteries, will last longer, etc., etc.

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Old 18-09-2013, 08:39   #6
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Re: Fridge Working Continuously

The battery heads are clean and covered with vaseline.
I will be in the boat by the weekend so no chance of checking
voltage drop at connections at the moment. I will definetely do it.
Is a threat for the fridge?
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Old 18-09-2013, 08:59   #7
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Re: Fridge Working Continuously

Quote:
Originally Posted by Idle View Post
The battery heads are clean and covered with vaseline.
I will be in the boat by the weekend so no chance of checking
voltage drop at connections at the moment. I will definetely do it.
Is a threat for the fridge?
Sort of but not really. Running a motor with less power than it needs isn't great for it, but probably takes a while to make it terminal.

Regarding the vaseline, why would you put a resister in between two electrical contacts? If it's in an attempt to keep them clean, just take the connectors off the terminals every year or two and clean them with a wire brush.
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Old 18-09-2013, 09:12   #8
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Re: Fridge Working Continuously

I had a similar problem when I recently installed a new Frigoboat in my boat. I checked voltage with an accurate meter right at the terminals on the compressor and it was 12.6V but I was still having problems with startup and intermittent failure.

I ran a new line from the DC 12V panel with all new crimp fittings and problem solved.

The lesson I learned, the Danfoss systems are very sensitive to voltage and it may look good with a meter but when the compressor first starts up there is a high power draw for just a second or so. If the voltage is even slightly low or there is any corrosion on the connections then the compressor may not have enough power to start up easily.

You report this happens in the morning. If you are mainly charging your batteries from solar then morning is when the battery will be the lowest. Also you say you have 170 A of batteries. I assume you mean total capacity of 170 amp hours? If so, that is not a lot for running a compressor all night.

So based on all the above my guess is your batteries are too low in the morning to reliably start the Frigoboat. I would want a minimum of 300 amp hours battery capacity for your situation.
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Old 18-09-2013, 09:19   #9
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Re: Fridge Working Continuously

Quote:
Originally Posted by rebel heart View Post
Regarding the vaseline, why would you put a resister in between two electrical contacts
Vasaline, Lightbulb grease, dielectric paste, silicone grease, are all non conductive, but work well to keep moisture out of electrical contacts.

When the contact is made, the grease is squeezed out so you still get metal to metal contact, but it is protected by a film of grease, so no corrosion.

This definitely works well in problem areas like deck connectors and battery posts.

Give it a try.

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Old 18-09-2013, 09:28   #10
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Re: Fridge Working Continuously

Check thermostat
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Old 18-09-2013, 09:33   #11
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Re: Fridge Working Continuously

I would be happy to increase the battery bank but no easy
room for the extra. Just educate me. If the batteries are OK and if I am right,
the fridge draws 5A/h assuming 10 hrs working
it will draw 50 A which is actually about
half since it works half of the period. Lets take 35A
Pumps etc say 15A because usage is minimum at night
internal illumination about 15A max.
35+15+15=65A so it is still less than half of the total
battery capacity.
Is my expenditure calculation reasonable?
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Old 18-09-2013, 09:43   #12
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That would be right.But are your batteries up where it should be.
An easy way is to take your batteries to a battery shop for overnight testing. That would tell you alot.
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Old 18-09-2013, 09:56   #13
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Re: Fridge Working Continuously

I got my lessons.
So I will check whether the batteries are at the end of their life,
the connections are healty and buy deep cycle batteries (not for the starter) if I can find for the next time.
Thank you all.
Idle
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Old 18-09-2013, 10:09   #14
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Re: Fridge Working Continuously

When you say 170 a, I'll assume 170 a-hr which means probably (2) 12 volt group 24 batteries in parallel. The fact you got 2 years out of these thin plate batteries cycling them at the rate you described is good service for them. One step up from these batteries that in the same service could give 4 years life would be a pair of 6 volt 220 a-hr golf cart batteries in series as btrayfors suggested. For deep cycle use there is a huge difference between thin plate (group 24) and thick plate batteries. Thin plates have a advantage for cranking amps due to more surface area, but what you need is thick plates for the constant cycling.
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Old 18-09-2013, 10:25   #15
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Re: Fridge Working Continuously

If you have the space, a really robust house bank would be (6) 2 volt cells in series. A small group 31 2 volt cell weighs 62 lbs and has 535 a-hr.

Sun Xtender PVX-5340T AGM Sealed Battery
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