Mini Refrigerator Inverter Question

[flboy]

I am confused on what you mean by cycling the inverter on and off means. The inverters are usually on and in standby until a load is turned on. Can you explain more?

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[featherliteCT1]

There is an external temperature controller with a wire running to a temperature probe placed inside the freezer.

The on off switch on the inverter is set to the “on” position at all times. The positive wire from the inverter is not connected directly to the battery. Rather, the positive wire from the inverter runs to a large post on a big relay. The other large post on the big relay runs to the battery.

When the temperature controller calls for power, a little relay inside the controller closes and sends power to and energizes the big relay. Then the big relay sends power to the inverter.

Consequently, the invertor is powered and cycled on and off by the big relay when the temperature controller energizes the big relay.

Hope this makes sense.

[McDave]

Hmmm,
I wasn't aware Artic king made a small upright freezer till now. Is the controller/relay and inverter part of a kit sold for this purpose? It would seem like the relay would be unnecessary unless perhaps it is for truck application. (Key on?) But even then it may be a rough way to start the freezer, although the inverter may have some sort of delay before powering the reefer up. I would think having it in stand by mode would be a safer way but you would eat some juice when in stand by. What does it use to trigger the relay? The same 12v source? The controller is 12v?

McDave

Edit; I just re read your post and answered my question about the controller. Duh.
Edit 2: Or does the controller have its own power source i.e. D-cell, 9v etc.?

[featherliteCT1]

McDave,

Thanks for the response. I was hoping you would respond because of your experience with refrigeration ... thanks! I figure with you, flboy and the rest of the guys on this forum I can get my questions answered.

Here is a photo from a web page showing one guy's set up. I hesitated uploading this photo because the wiring is not exactly correct. One of the members of this site posted a link to this web page a while back ... that is how I got the idea. Currently, my bench test set up is dismantled because I am reconfiguring my trailer to accommodate the freezer. Otherwise, I would post photos of my actual setup.

200510 Freezer Wiring Photo f Web.png (354.58 KiB) Viewed 2834 times

The DC to DC buck converter ($12) converts the fluctuating battery voltage, via an adjustable pot (potentiometer), to output exactly 12v. into the temperature controller.

The adjustable temperature controller ($15) has a nice digital readout and works great.

When I get my system permanently installed, I will post photos of my setup and explain the set up in detail as well as amp draws under differing conditions.

One of the guys on the web has been running this system successfully for over a year without inverter failure (so far).

I

[McDave]

Ahhh. I like it. Something funky about that manual switch.... but I like the buck xfmr to feed clean 12v to controller, and the probe is a thermistor? So should be accurate and little variance. You have a renogy inverter, for solar systems? It may be more sophisticated than some where it senses a load and verifies 110vac before powering output, or it may be that you have sufficient amperage with the battery bank to overcome the voltage drop when inverter and reefer start simultaneously. I guess the test would be to watch the 110 at output or compressor during start up and check amperage. Otherwise it should work OK although I don't know how much you save powering controller/buck xfmr 24/7 vs standby. Might be significant.

McDave

[featherliteCT1]

The temperature controller is necessary for the freezer because the OEM freezer temperature knob inside the freezer won't maintain a steady temperature like 40 degrees ...the highest OEM setting still freezes everything. I presume the temp controller is not needed with an ordinary refrigerator. So there is no ability to use the inverter on standby with the freezer setup.

The manual switch is to allow the inverter to be used when the freezer is unplugged so you can use the inverter to also power other 120v devices with the freezer off.

The temp controller and buck converter together draw about .15 amps at all times when hooked up.

The inverter draws about .5 amps on standby (n/a with this setup).

The freezer draws about 30 amps on initial startup, but for just a fraction of a second (as far as I can tell).

This particular 700 watt model inverter does not appear to have any features unique to solar systems, although the Renogy 2000 watt model has an eco mode feature when on standby.

My battery bank is 235 amps total.

[McDave]

I gotcha. Manual switch bypasses controller relay and triggers main relay. OK. well you could just bypass freezer control and replace with main relay contacts if they are rated high enough. Leave plugged in and on stand by. It would cost additional .5/hr at this point. or a fridge cold control but if what ya got works I say go with it. That's not the most expensive freezer ever and it might work forever. Plus you save .35a/hr this way. That's 8 ah/day or 10 addl. run hrs? Could make all the diff. if you get rained out and are using lights etc. for a few days.

McDave

[Trebor English]

My Harbor Freight inverter has a switch to turn it on and off. I opened it and attached a pair of wires to the back side of the switch. That pair of wires goes to the temperature controller relay. If the inverter switch is on the inverter runs. If the inverter switch is off the relay controls the inverter. That eliminates the need to switch the DC input to the inverter. The inverter has a big capacitor on its input. The high current on connection will eat relay contacts.

[flboy]

Sorry, I have been off grid last few days on a dual sport trip. Will get a chance to study this a bit tomorrow and comment.

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[featherliteCT1]

My Harbor Freight inverter has a switch to turn it on and off. I opened it and attached a pair of wires to the back side of the switch. That pair of wires goes to the temperature controller relay. If the inverter switch is on the inverter runs. If the inverter switch is off the relay controls the inverter. That eliminates the need to switch the DC input to the inverter. The inverter has a big capacitor on its input. The high current on connection will eat relay contacts.

That sounds like a great idea.

Am I correct to assume that the wiring connected to and from the OEM switch for the inverter carries only a small amp load?

My temp controller only draws .25 A/Hr. I do not think that my temperature controller (that would be wired to the OEM switch) can handle much more than an amp.

In due course, I will test to see how many amps the temp controller sends to my external relay.

[Trebor English]

The thermostat I got has a tiny relay for it's output. The inverter switch has 5 volts across it when it's open so that's probably an input to digital logic. The inverter switch is a tiny thing that is probably not good for more than a tenth of an amp.
.

[flboy]

Looking at the diagram, I can see how this "can" work. So if I understand this properly, all this is to use a freezer as a refrigerator and overcome the limitation of the freezer thermostat? Have you tried to get a schematic for the freezer control circuitry to see if there was something you could do to tweek that? Maybe just need to change a resistor value or add one in series with existing thermostat to shift the baseline?

[Augie Dog]

Good info here as I'm planning my build as soon as I pick my trailer up in June. I want to have solar capability for off grid camping (2 weeks or more) but need it mainly for a fridge (3.3/4.3 cu. ft.) and fan ventilation. A 1500 Watt Pure sine wave inverter has been suggested to handle the fridge so how many batteries and what type will I need,a good solar controller and the number of solar panels at say 100 watt per panel. I do not want to mount them permanently but have the ability to set up on support system outside my trailer. Also a source with good quality products. I am learning when it comes to this solar stuff it's not always advisable to go cheap.I have been reading info in the electrical/solar section of this site and most of the posts are addressing appliances run strictly off of solar with no inverter or batteries. Mostly TD applications. Just keepin it simple what are your thoughts?