waecos in a camper trailer

Submitted: Tuesday, Jun 06, 2006 at 20:19
ThreadID: 34683 Views:2309 Replies:7 FollowUps:6
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G'day all, I have 2 Waeco 35l fridges running from a 75ah battery in my Trak Shak. I have installed a volt meter to tell me what's happening to the battery. During the weekend, after running the fridges off and on, the volt meter showed that the battery had 11.7 volts. The fridges, which were set to the "low" setting alternately cut out (usually a sign of low voltage), but they are not supposed to cut out until the battery is at 10.4 volts. My cigarette lighter connections are a bit dodgey - could that cause a voltage drop? Could there be another reason?
Any helpful suggestions appreciated.
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Reply By: nowimnumberone - Tuesday, Jun 06, 2006 at 20:57

Tuesday, Jun 06, 2006 at 20:57
first of all get rid of the dodgy conections and run a heavy duty dedicated wire system to the fridges.
should help
cheers
AnswerID: 177099

Reply By: Darian (SA) - Tuesday, Jun 06, 2006 at 21:19

Tuesday, Jun 06, 2006 at 21:19
Been learning this stuff myself recently - While the meter said you had 11.7 at the battery you would have had 10.4 at the fridge ! Lot of voltage drop in the cables and connections if not in ideal condition and spec. As mentioned, improve it all to the extent possible - heavier cable to the fridge and better connections - far as the fridges are concerned, they only want to know what the voltage is at their inlet point - and they need to be tested for voltage while running too ! If you have the pointy probes on the voltmeter, you can poke them into the pos - neg wires of the shielded cable to see what the voltage is - I found too much voltage drop in the original Waeco cable too - made my own up with heavier cable, and patched their plug onto the end of that - when the warranty runs out, I might wire MY heavier cable directly in through the case and onto the terminals inside.
AnswerID: 177104

Reply By: Sand Man (SA) - Wednesday, Jun 07, 2006 at 10:15

Wednesday, Jun 07, 2006 at 10:15
11.7 volts is also almost dead flat (11.6 volts) so if the batteries are at this voltage, it doesn't matter what voltage (10.4 volts) the fridge auto cut out is set for.
Bill


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AnswerID: 177178

Follow Up By: ozidave - Wednesday, Jun 07, 2006 at 10:28

Wednesday, Jun 07, 2006 at 10:28
when my battery is fully charged (I use a mobitronics 8amp intellicharger) the volt meter reads about 12.8v. Does that mean the batteries are flat when they drop by just over 1 volt?
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FollowupID: 433181

Follow Up By: Mike Harding - Friday, Jun 09, 2006 at 16:26

Friday, Jun 09, 2006 at 16:26
A lead acid battery in good condition should be capable of being discharged to a terminal voltage of about 10V5 not 11V6. It's not a great idea to take them below 11V or so very often because it will shorten the battery life. My 88Ah AGM data sheet has a discharge curve down to 9V6 but I suspect it would not stand too many cycles to that depth of discharge.

As others suggest; improve the wiring to the fridges and destroy any cigarette lighter connectors you may have - they are evil :)

Mike Harding
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FollowupID: 433832

Reply By: Sand Man (SA) - Wednesday, Jun 07, 2006 at 11:11

Wednesday, Jun 07, 2006 at 11:11
OK, looks like I need to be a little more accurate.

at 11.58 the battery is down to 20% and generally this is as low as you should allow the battery to go, or you risk shortening its usable life.

So,

11.58 volts 20% 1.93 volts/cell
11.31 volts 10% 1.89 volts/cell
10.50 volts 0% 1.75 volts/cell

So, an auto cut out system that cuts out the fridge at 10.4 volts is totally useless. The battery is already "flat as a tack" and the device connected to it would have already ceased to operate. What the risk then is that the battery will "sulfate" causing even more of a problem.
Bill


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AnswerID: 177185

Follow Up By: ozidave - Wednesday, Jun 07, 2006 at 11:19

Wednesday, Jun 07, 2006 at 11:19
Sandman, I appreciate your patience - this is all new to me. What should my voltmeter read when battery is 100%? Can you tell me the percentage step-downs from 100% to 20% (ie at what votage is my battery 80%, then at what voltage is it 50% etc)
thanks,
Dave
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FollowupID: 433187

Follow Up By: Patrol22 - Wednesday, Jun 07, 2006 at 12:57

Wednesday, Jun 07, 2006 at 12:57
Sand Man - I know that this holds true for cranking batteries but does it also hold true for deep cycling batteries. I was under the impression that deep cycling batteries could be discharged much much further and much more often than the standard cranking battery.

Cheers
Pete
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FollowupID: 433205

Follow Up By: Sand Man (SA) - Wednesday, Jun 07, 2006 at 15:02

Wednesday, Jun 07, 2006 at 15:02
Pete,

To the best of my knowledge, it has nothing to do specifically with cranking batteries.

It is recommended that wet cell batteries not be taken below 30% too often, or permanent damage will result.

AGM batteries are a more tollerant but still shouldn't be drained completely on a regular basis.
Bill


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Reply By: Sand Man (SA) - Wednesday, Jun 07, 2006 at 15:05

Wednesday, Jun 07, 2006 at 15:05
Ozidave,

Here's a web site containing much information about batteries and it should provide you with most knowledge you should need.

Batteries - FAQ

Bill


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AnswerID: 177233

Reply By: brett - Wednesday, Jun 07, 2006 at 19:23

Wednesday, Jun 07, 2006 at 19:23
Your battery is 11.7V with no load and as said, pretty much flat. Stick a load on it of around 5 amps and you will see it instantly drop to below 11V, this is why your fridge comes on for a second then cuts out as the voltage quickly drops to below 10.4V due to the startup current drawn by the compressor.

How do you find the fridges run inside the trailer, does it get too hot? I tried experimenting with running a 3way inside my trakshak on 12V but with the tailgate closed it just got way too hot, the compressor fridge will be a lot better I imagine but they still pump out hot air and your trailer is pretty much air tight.
AnswerID: 177274

Follow Up By: ozidave - Friday, Jun 09, 2006 at 16:02

Friday, Jun 09, 2006 at 16:02
Hi Brett, the 2 Weacos in the trailer don't get too hot, they actually operate quite well. Thanks for your advice re voltage drop. That and the site given by Sandman have improved my knowledge of batteries.
cheers,
Dave
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FollowupID: 433827

Reply By: Mbr - Taz & Milka-Queanbeyan - Saturday, Jun 10, 2006 at 18:21

Saturday, Jun 10, 2006 at 18:21
I am playing around with planning for AGM's and fridges in either the trailer or back of the Prado as well. I found Collyn Rivers site very helpful especially his articles concerning all forms of vehicle electrics etc.

Do a search for caravansandmotorhomes dot com dot au.... I think thats it.

Cheers....Taz
AnswerID: 177848

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