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Old 07-04-2009, 01:02   #1
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stupid fridge compressor

cheers every one

here is one for you: how come the WAECO compressor of my 12V fridge doesn't start unless I am hooked to the shore power or motoring??

my batteries are brand new and read 13V
with the shore power connected they read 14+ the same thing when the alternator of the engine charges them

I guess the compressor needs that kind of voltage to function normally
is there a way to increase the output of the batteries when sailing ?? how can I keep the compressor running on the available otherwise very adequate voltage of the batteries ?

thanks
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Old 07-04-2009, 02:04   #2
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Terminals, wire gauge and length, fuses, switches etc.

Have you measured the voltage at the compressor, compressor off and compressor on?
Have you checked:-
Battery terminals for corrosion, snug fit?
The gauge of the wire used? If there is a long run and the wire is too small then you could expect a significant voltage drop.
That the fuses and switches will carry the current?

I havn't put in a refrigerator yet but calculations suggest a startup current of 5 amps or more. Heavier cables from the battery to the fuse/switch to the compressor may be indicated.
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Old 07-04-2009, 03:23   #3
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Originally Posted by Boracay View Post
Have you measured the voltage at the compressor, compressor off and compressor on?
Have you checked:-
Battery terminals for corrosion, snug fit?
The gauge of the wire used? If there is a long run and the wire is too small then you could expect a significant voltage drop.
That the fuses and switches will carry the current?

I havn't put in a refrigerator yet but calculations suggest a startup current of 5 amps or more. Heavier cables from the battery to the fuse/switch to the compressor may be indicated.
thanks B for the info
the run from the batteries to the fridge is no more than 2 .5 meters
I haven't check the other things yet I will this week end
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Old 07-04-2009, 03:41   #4
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Although your wiring length seems normal, you might want to measure voltage at the compressor when it's attempting to start. Either under battery power or at the dock. Compare this reading against the 13 or 14 volts you described as your system voltage. I suspect what you'll discover is the voltage at the compressor is considerably lower.

As a previous poster mentioned, this can be caused by corrosion on connections. You will have to disassemble, clean and reconnect every connection. Also, estimate the wire size running to the compressor. There are wire size charts versus distance of wire runs for a given current draw. Make sure the wiring is adequate.
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Old 07-04-2009, 04:05   #5
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hi tropic cat
when you say every connection you mean all the connections running from thr compressor to the battery or only the ones on the compressor relay
another thing, since I am not an electric wizard and in order to be on the safe side what gage of wire do you recommend I use
thanks
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Old 07-04-2009, 04:29   #6
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... to be on the safe side what gage of wire do you recommend I use
thanks
What is the current (Amps) or power (Watts) demand (nemeplate rating) of the compressor, and what is the length of cable (Batt to Motor)?
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Old 07-04-2009, 04:41   #7
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What is the current (Amps) or power (Watts) demand (nemeplate rating) of the compressor, and what is the length of cable (Batt to Motor)?
to be honest I have no idea I have to look it up once on the boat but as suggested by Boracay the compressor must draw around 5 amps the cabe run doesnot exceed 3 meters.
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Old 07-04-2009, 05:01   #8
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May sound stupid, but are you sure it is a 12 volt compressor?
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Old 07-04-2009, 05:01   #9
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hi tropic cat
when you say every connection you mean all the connections running from thr compressor to the battery or only the ones on the compressor relay
another thing, since I am not an electric wizard and in order to be on the safe side what gage of wire do you recommend I use
thanks
All connections....

The National Electric Code (NEC) specifies the following formular to determine the wires size in circular mils (CM) for a constant load of I amps, wire length L in feet, and voltage drop V.

CM = (25 x I x L) / V

The CM size can be converted to AWG using tables found on the internet. One example is here:

American Wire Gauge, AWG Cable Size Description for Copper Wire Cable

When I run your 'numbers' I come up with 14 gauge wire for a voltage drop of .2 volts.
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Old 07-04-2009, 05:12   #10
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yeah it runs fine when the shore power or when the alternator charges the batteries
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Old 07-04-2009, 05:14   #11
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All connections....

The National Electric Code (NEC) specifies the following formular to determine the wires size in circular mils (CM) for a constant load of I amps, wire length L in feet, and voltage drop V.

CM = (25 x I x L) / V

The CM size can be converted to AWG using tables found on the internet. One example is here:

American Wire Gauge, AWG Cable Size Description for Copper Wire Cable

When I run your 'numbers' I come up with 14 gauge wire for a voltage drop of .2 volts.
ok tropic cat can you tell what gauge 14 is in metric ?? mm that is
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Old 07-04-2009, 05:18   #12
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I believe this would be 1.5mm

http://www.ilsco.com/newweb/IlscoHom...AWG+Wire+Sizes

You do know how to use Google to leverage the internet?
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Old 07-04-2009, 05:22   #13
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thanks
but no I am not an IT wizard
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Old 07-04-2009, 07:50   #14
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#14AWG is nearly equivalent to 2.5 mm2 (1.63 mm diameter, or 4,110 circular mills). This will be adequate for a 5 Amp RUNNING current, over a total (Pos + Neg) wire length of about 20 feet (6m).
Assuming a STARTING current of 10 Amps, you may require a #10AWG or 6 mm2 (2.59 mm dia, or 10,380 cm) wire.
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Old 07-04-2009, 12:55   #15
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The Waeco's have a low voltage cut out feature, designed to save your batteries by turning off the fridge when voltage gets low. The new ones have 3 settings for that cuttoff voltage, but my understanding is that the older units only have one setting and they have been known to not run with voltage below 12.4 volts. Might be part of your problem.
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