40/40 Fridge on Batteries

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40/40 Fridge on Batteries

Postby Craig » Wed Nov 10, 2010 12:34 am

The fridge on the 40/40 is set up to run only when on shore power or when engine is running. There is a way to bypass this so I can kill my batteries. Was wondering if anyone knows how to do this. Then let's see how long it takes me to call sea tow for a boost.
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Re: 40/40 Fridge on Batteries

Postby GeoffSchultz » Wed Nov 10, 2010 8:11 am

It's been my observation that the 40/40s were designed with differing systems. Mine came with both an engine drive and a 120V Grunert system which both chilled cold plates. Note that I pulled both systems out and replaced them with a 12V system that I designed.

If yours only came with a 120V system, it is *possible* to run the 120V system off of the inverter. However, I wouldn't recommend it as it will probably crunch the batteries. It seems to me the Grunert Docksider drew about 7A at 120V, so that would translate to 78A at 12V @ 90% conversion, so you can't run this for long. I'd be running the engine to have the alternator try to keep up. But as you said, SeaTow is just a call away and hopefully your starter battery is isolated and well charged.

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Re: 40/40 Fridge on Batteries

Postby Craig » Sat Nov 13, 2010 1:20 am

It is actually a 12 volt system. When plugged in to shore power, it is the DC amps that are pulled. Same when the engine is running. It is designed to protect us from ourselves and not let us run down the battery. It is not the inverter that is the culprit. There is a switch that I believe is hooked into the oil pressure that will not allow it to run. I guess that I will be taking a trip to Paul Dennis to get the switch disabled.
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Re: 40/40 Fridge on Batteries

Postby THATBOATGUY » Sun Nov 14, 2010 4:17 pm

Craig, If it's like other systems I've worked on that had the oil pressure switch lock-out. You can overcome this by simply providing a 12 volt ground to that wire. I'd have to see the wiring diagram myself before I could give you firm advice on it.

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Re: 40/40 Fridge on Batteries

Postby Craig » Sun Nov 14, 2010 4:23 pm

Any idea where to look for the switch to ground?
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Re: 40/40 Fridge on Batteries

Postby GeoffSchultz » Sun Nov 14, 2010 5:38 pm

Most likely you'll need to install a STDT switch which connects output of the oil pressure switch to one of the switch inputs, either ground or +12 to the other switch input, and the output of the switch to input of the compressor controller. The choice of +12 or ground will be based upon what the controller needs to receive in order to run.

You'll probably have to drill a hole and install the switch yourself on the compressor controller, or pay Paul Dennis to do it.

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Re: 40/40 Fridge on Batteries

Postby THATBOATGUY » Tue Nov 16, 2010 1:07 pm

Craig wrote:Any idea where to look for the switch to ground?


Should be screwed into your engine block with a wire leading away that's not a part of the regular engine harness. Check it engine off with your test meter and then engine on to determine what's what. You can locate your bypass switch where it's convenient for you and I've always used a STST switch in parallel to the engine switch. Not sure why you would need to do otherwise unless the oil pressure switch is shared with an alarm. Was that where you were going Geoff?

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Re: 40/40 Fridge on Batteries

Postby GeoffSchultz » Tue Nov 16, 2010 8:31 pm

THATBOATGUY wrote:
Craig wrote:Any idea where to look for the switch to ground?


Should be screwed into your engine block with a wire leading away that's not a part of the regular engine harness. Check it engine off with your test meter and then engine on to determine what's what. You can locate your bypass switch where it's convenient for you and I've always used a STST switch in parallel to the engine switch. Not sure why you would need to do otherwise unless the oil pressure switch is shared with an alarm. Was that where you were going Geoff?

Where I was going that you should either provide a connection to the sensor or to either ground or +12. I suppose that if it's ground, that you can just let it float. However, for circuitry I like to make sure that I'm providing the correct bias. Thus the SPDT that connects to the sensor or the appropriate voltage.

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