Edgestar Fridge Low Battery Cut Off Issues

Rando

Explorer
I have been having some issues with the low voltage cut-off on my 43L Edgestar fridge and was wondering if anyone else has run into this problem. The issue is that the low voltage cut-off engages at too high a voltage. I was doing some testing last night, and the cut-off would come on (with blinking yellow LED) when my Diehard platinum had a no-load voltage of 12.3V and a loaded voltage of about 12.1 when the compressor was cycling. If I unplug it and plug it back in, the compressor will run for about 10 minutes before it shuts down again. I was under the impression that the low voltage cut off should activate at a loaded voltage closer to 11.5V ?

I have gone through to make sure that there is not excessive resistance in the fridge wiring, it is connected to a my Aux load center with about 2m of 12AWG cable, and I have replaced the cheesy cord and connector that came with it with Anderson Power poles (I originally suspected the cord to be the problem). I really don't need the low voltage cutoff as my battery system/charge controller has this built in. Has anyone figured out a way to bypass it? From my investigations this functionality appears to be built into the thermostat/control unit. Does anyone have a schematic for this?
 

Herbie

Rendezvous Conspirator
I have been having some issues with the low voltage cut-off on my 43L Edgestar fridge and was wondering if anyone else has run into this problem. The issue is that the low voltage cut-off engages at too high a voltage. I was doing some testing last night, and the cut-off would come on (with blinking yellow LED) when my Diehard platinum had a no-load voltage of 12.3V and a loaded voltage of about 12.1 when the compressor was cycling. If I unplug it and plug it back in, the compressor will run for about 10 minutes before it shuts down again. I was under the impression that the low voltage cut off should activate at a loaded voltage closer to 11.5V ?

I have gone through to make sure that there is not excessive resistance in the fridge wiring, it is connected to a my Aux load center with about 2m of 12AWG cable, and I have replaced the cheesy cord and connector that came with it with Anderson Power poles (I originally suspected the cord to be the problem). I really don't need the low voltage cutoff as my battery system/charge controller has this built in. Has anyone figured out a way to bypass it? From my investigations this functionality appears to be built into the thermostat/control unit. Does anyone have a schematic for this?

Hrm, sounds like you're following the right steps. I believe Compact Appliance has emailed/faxed schematics in the past, you might try calling them.
 

Ludedude

Adventurer
I'm guessing the voltage is 12.1 v at the battery terminals? What's the voltage at the fridge itself when it shuts off?

First thing you need to know is that if you have 2m of cable, you have to calculate the drop in 4m of cable. Given roughly 13 feet of 12 awg cable, 5 amps or so max load from the Edgestar compressor, you're looking at somewhere in the neighborhood of 3% drop, or 0.36 volts. That gives you 12.1 volts (at the battery?) - 0.36v so 11.7v which is pretty close to the 11.5 cutoff depending on variables like loss through your auxiliary load center.
 

Rando

Explorer
The 12.1 is battery voltage at the fridge input. Last night I made some measurements inside the fridge, and it does drop another .3V or so between the input and the terminals on the thermostat/control. However after reading the specs on compact appliance, it shouldn't shutdown until 10.5V. I have a feeling there is something wrong with my control unit.
Thanks for the advice.

I'm guessing the voltage is 12.1 v at the battery terminals? What's the voltage at the fridge itself when it shuts off?

First thing you need to know is that if you have 2m of cable, you have to calculate the drop in 4m of cable. Given roughly 13 feet of 12 awg cable, 5 amps or so max load from the Edgestar compressor, you're looking at somewhere in the neighborhood of 3% drop, or 0.36 volts. That gives you 12.1 volts (at the battery?) - 0.36v so 11.7v which is pretty close to the 11.5 cutoff depending on variables like loss through your auxiliary load center.
 

Rando

Explorer
Awesome! Thanks for this information, it was exactly the type of thing i was looking for. Unfortunately I think the Edgestar does not use most of the logic built into the compressor controller, but uses logic built into the digital thermostat. The only connections used on the compressor controller are, +/- 12VDC in, a TTL (5V) signal from the digital thermostat, and 12V out for the fan on the coils. The low voltage protection appears to be done by the digital thermostat unit. You don't happen to know of a data sheet for that do you?

Thanks again for digging this up!

Here is a link with some general info on the compressor in the Edgestar:
http://www.liyoung-compressor.com/DC-Compressor-1.html

And here is an MS WORD document that has the information required if you wish to change the shut off voltage (achieved by connecting the proper resistor in the proper place):
http://zjghengtian.com/HT_CC100DC12-24V-Anen.doc
 

Xterabl

Adventurer
The low voltage protection appears to be done by the digital thermostat unit. You don't happen to know of a data sheet for that do you?

Unfortunately, no. That is one part I couldn't find information for when I was digging around a while ago. IIRC, I even removed it so I could find what looked like a part number...and still I came up with no info for it with a web search.

You may want to call Edgestar (the number in the manual)...I managed to get hold of a pretty good technician when I killed the AC-DC power supply module.

Best of luck; and please post up if you find a solution.
 

Ludedude

Adventurer
The 12.1 is battery voltage at the fridge input. Last night I made some measurements inside the fridge, and it does drop another .3V or so between the input and the terminals on the thermostat/control. However after reading the specs on compact appliance, it shouldn't shutdown until 10.5V. I have a feeling there is something wrong with my control unit.
Thanks for the advice.

I guess that's good news and bad news. Good that the voltage seems adequate at the fridge input, bad that it's shutting down apparently out of spec.

I have more than a passing interest in this as I have an Edgestar 43Q that's finicky in the low voltage department as well. I haven't taken measurements at the fridge though, I just went a different route and plugged it into a 120v inverter and it runs fine. Ultimately I need to solve the 12v input issue as the inverter itself takes its pound of flesh from the battery but I've been lazy since it does run great that way.
 

Rando

Explorer
So I emailed and talked to the Edgestar customer service, and while they were responsive (they even called me when he couldn't explain something in email), they clearly don't know too much about the product they sell. The admitted that this was a known issue that sometimes that Low Battery Cut Off (LBCO) we set to high, however because my unit is 2 months out of warranty they couldn't help me. They also claimed that the LBCO was built into the power supply unit, and it would cost me $148 to replace it. This is clearly untrue from examining the wiring inside the fridge. So without any help from edgestar, I did some diagnostics on my own.

The LBCO IS implemented by the digital thermostat unit. I pulled this out and tested it with a lab power supply. My unit was shutting down somewhere near 11V, which is about 0.5V higher than it should. Breaking open the thermostat unit, it is a fairly simple circuit based on a Samsung micro controller. The input voltage is divided down (using r7 and r8 if anyone cares) then sampled by the uController using an analog to digital pin. In order to adjust the cut off voltage you just need to change the ratio between r7 and r8. In my case the r7 = 10k, r8 = 100k, so the input voltage is divided down by a factor of 11. In order to fool the uController into thinking my input voltage was 20% higher that it is, I simply added a 500k resistor in parallel with the 100k resistor. Now my thermostat won't shut the fridge down until the input voltage gets down to 9V, which is fine by me.

One thing to note, the compressor controller module also has a LBCO, which is externally adjustable by adding resistors across unused terminals. I am going to run my fridge for a while before seeing if I need to mess with this.

Anyway, hopefully this is of use to someone else....
 

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Curmudgeon

Adventurer
You sound pretty knowledgeable about electronics so perhaps you've already considered this, but as the voltage drops the current will rise. If you allow the unit to continue running at too low a voltage (9V) the current may rise enough to burn something up. Been there, done that. Fortunately it wasn't anything expensive in my case, but it was still an OH ******* moment.

JP
 

Rando

Explorer
Quick update. I used my modified edgestar this weekend for a 3 day trip. On the first night my battery started off fairly low (maybe 12.1V) and dropped below 11.5V (at the battery terminals) during the night, and my external battery monitoring system (correctly) shut it down. On the following days (after some sun to charge my battery) the fridge worked just fine. One thing I did notice is that the thermostat will sometimes significantly undershoot its setpoint, which also causes an error on the thermostat (solid yellow light) until the fridge warms back up to the setpoint. All in all, it may be worth ditching the supplied thermostat and putting in a more effective one.

Also, no worries about an under-volt, over current situation as both the compressor and my battery management system have more reliable low voltage cut offs built in.
 

Ludedude

Adventurer
So to be clear, you made the mod by adding a resistor to the existing digital board and not by doing it to the contacts on the compressor right?
 

Rando

Explorer
Yup, I added a resistor to the circuit board inside the digital thermostat unit. Contrary to what Edgestar tech support said, that was the component that was prematurely shutting down the fridge. If you are getting the orange 'Low' led lighting up and the fridge no longer cooling, this is the cause. If it is just stopping cooling (with no orange LED) than it could be the compressor controller low voltage shut off kicking in, which could be adjusted with resistors across the appropriate contacts.

So to be clear, you made the mod by adding a resistor to the existing digital board and not by doing it to the contacts on the compressor right?
 

Ludedude

Adventurer
It's odd, what I get sometimes is the yellow LED on the thermostat blinking briefly, then cooling stops. Subsequent tries to get the compressor going, i.e. by turning the 12 volt source off and then on result in the compressor running for a few seconds then nothing but no blinking LED. Turning on the inverter in any case solves the problem.

When I get back from my Mojave trip this weekend maybe I'll dig into the guts of the thing and see if I have resistors on the compressor.
 

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