Ever wonder what's happenin' when you start your 12V camping fridge and how much current it sucks in during startup?

e9999

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I did. So I had some fun.
This is an ancient baby Waeco. 18qts I think. Compressor.

LHS is zero current. Every grid interval vertically is 20mV or 2.7A (I'm using an in-line shunt between the battery and the fridge input connector). RHS is the fridge humming away at a bit over 3A. Each horizontal interval is 100ms.

So, looks to me like it starts (I can hear a relay) and for 0.2s it takes in about 3A fairly smoothly getting ready, then the compressor starts, sucks in up to about 11A for about 0.1s, and then settles down at 3A. All that not including the noise.

IOW, the startup peak current is over 3x the steady-state one. No big surprise, of course, but fun to see first-hand:

SDS00001.png


and then, looking at the pulsing on the RHS, and counting them, I get about 2,700 / min, presumably the rotation speed of the motor or some multiple thereof.
 
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Good stuff, I have been trying to determine where and when the low voltage protection measures the voltage because I have an inexpensive Aspensora ( seacop) fridge that will trip the low voltage when that start up spike hits, even if system voltage is above the threshold. That spike trips their low voltage code and you have to unplug and replug to clear code and it works fine after that. It doesnt do it every time but it will screw you if you dont notice. The Engel does not do that. The remote temp device is a great peace of mind.
 

e9999

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If the cutoff is not adjustable, you may be able to avoid the problem if you increase the size of the wire running from the battery to the fridge. It's likely the voltage drop over that wire that does you in.
 
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Agreed, not the wire tho, its the plug, need to delete the socket style connections for good.
 

surfpig

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Agreed, not the wire tho, its the plug, need to delete the socket style connections for good.
Those are giving me trouble as well.

When I used to have old refrigerators (40s - 50s) in the house, I added a soft-starter (?) which I think is mostly just a capacitor to help with that big amp draw because it tended to kill those old compressors.
 
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I mean, go figure, a cig lighter socket, a lot of bouncing, banging, dirt, left outside to rot and it failed, huh, who woulda guessed, its the old take it for granted issue. I will say that the Engel, on same socket has never failed, the little diode failed and caused fridge to draw stupid amps, sold it to Bill for parts then he tells me the solution is an easy fix and fridge works fine.
 

surfpig

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I mean, go figure, a cig lighter socket, a lot of bouncing, banging, dirt, left outside to rot and it failed, huh, who woulda guessed, its the old take it for granted issue. I will say that the Engel, on same socket has never failed, the little diode failed and caused fridge to draw stupid amps, sold it to Bill for parts then he tells me the solution is an easy fix and fridge works fine.
That sounds about right.

:lol:
 

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