TrailManor Owner's Forum - View Single Post - Fridge temp control fix, for AC and DC operation. (ANY model, not just N300.3)

**rickst29** · 09-07-2012, 01:42 PM

I started a long(!!!) Thread on this, in which I changed my mind several times. At the end, though, we have a solution which creates provides daily temperature variation in the range of single-digits. (The former Thread was here.) This solution does NOT work for Propane operation, only AC and DC. But the recommended DC circuit design bypasses the front-panel selector switch. So, when boondocking with either a generator or a high-capascity Solar system, you could run the fridge on propane for most of the load, with DC providing "fine tuning" as needed. In the afternoon and early evening, when temperatures are still warm, the DC heater would be working quite hard. As you approach dawn, and the lowest temperatures of the night, the DC heater would run less and less (and maybe not at all). Then, in the daytime, you recover the used battery capacity via solar panels or generator.

This solution has also been confirmed to work by ThePair, although he uses it only for 120VAC. The total parts cost somewhat more than $100, depending on the number and type of "bypass" switches you install. (I installed, but then removed my "bypass" circuitry; if the electronics ever fails, it's very easy to just disconnect power leads from one of the relays, and connect them together with a wire nut or push-in connector Union. Here are links to the necessary temperature control parts to handle both the AC and DC heater circuits:

The electronic "brains", which uses the input temperature measurements to operate the output "SSR control" circuit:
http://www.lightobject.com/JLD7100-D...oller-P66.aspx

The thermometer: http://www.lightobject.com/Premium-S...aded-P681.aspx
Do not try downgrading the Thermometer to type K, because ThePair had bad results using one of the cheap ones.

An electronic switch ("SSR"):
http://www.lightobject.com/25A-Solid...C-Out-P61.aspx

A 4-pin automotive relay, sized for 40A. (These are typically used for turning on headlights, stereo, car alarm, etc.) Available at any auto parts store for a bit more than $5, here's an example:
http://www.ebay.com/itm/Car-12V-40A-...db8562&vxp=mtr
You can buy them with either the pins, or with a wired socket already attached. I recommend a "pinned" version, even though you must use a push-on crimp connector, because the pair of 'power side' wires built into most of those sockets are very small. (Perhaps AWG 14?) IMO, your new DC "power" wires should match TM wiring - 10 AWG stranded copper.
Vibration-Proof, weather-proof wire connectors.
All wire used behind the refrigerator should be THWN, because of the heat which the refrigerator generates.

If using DC independent of the Norcold selector switch, as recommended: ON/OFF/ switch for the PID-DC power wire path. You might consider installing this on the exterior of the TM, using a marine switch or a weather-proof switch cover.

Note: You will be using the existing fuses (the new circuits are wired into the "hot" sides of both existing circuits, 12VDC and 120VAC, after the fuses.)
-----

I mounted the PID device in a new wall plate (a blank plate, with 1/16th DIN cutout made by hand tool). If you care to reach that far up, and don't want Cable TV at RV parks, then you could pull out and replace the existing wall plate with CATV and 2-wire telephone connectors. (We nearly all use cell phones now.). Otherwise, cut your 1/16th DIN hole into the paneling at least 3-4 inches away from the vertical side of the TM interior, and lower down. (You NEED those 3 inches, because there is a big bundle of wires in the TM along the vertical edge. You don't want your new "wall plate" mounting screw going into that bundle of wires.)

This position allows the Thermocouple to easily reach the fridge interior, from the back. I drilled into a place a few inches down from the fluid tank, slightly to the right of the air tube (looking into the back of the fridge). In order to make the thermocouple reach all the way into the interior, you will need to trim off the hex-shaped mounting edge (the one which matches the nut). Use a grinder to make it round, matching the size and shape of the solid stainless column directly behind it. The Thermocouple attaches to the PID as follows: terminals #6 and #7 get wires with the blue wire wraps, and terminal #8 gets the red one. (Pay attention to the plastic wire wraps, NOT the colors of the actual wires.)

Don't dream of modifying the PT-100 thermocouple lead wires or jacket in any way; PT-100 measurement is based on resistance, and properties of the wire leads are critical.
-----

The Thermocouple attached to PID terminals 6, 7, and 8. Terminals 9 and 10 are not used. Next, we wire the PID terminals #1 through #5:

#1 and #4 are tied together, and both get +12V, from any TM "hot" wire in the vicinity.
#2 and #3 are tied together, and both connect to any TM 12V "grounded" conductor.
These two pairs of leads do not have to be #10 wire, they only carry small "controller" current loads. (I used #10 anyway, because I had plenty of it.)

#5 is the +12VDC control output from the PID internal Relay. It provides "sense" voltage to both of the refrigerator power relays in parallel. Create a "Y" from this wire behind the refrigerator, and connect the resulting wires to the "+" terminals of the SSR (for AC power) and the automotive relay (for DC power). Note that the correct terminal is marked with "+" polarity.

And finally, we connect the "-" terminals of the two refrigerator relays to any TM 12V "Grounded" conductor.

We're done with the control side, handling 12VDC and AC. Now Jump to post #6, in which we wire the power leads.

09-07-2012, 01:42 PM	#1
rickst29 yes, they hunt lions. Join Date: Aug 2005 Location: Reno, NV Posts: 1,318	Fridge temp control fix, for AC and DC operation. (ANY model, not just N300.3) I started a long(!!!) Thread on this, in which I changed my mind several times. At the end, though, we have a solution which creates provides daily temperature variation in the range of single-digits. (The former Thread was here.) This solution does NOT work for Propane operation, only AC and DC. But the recommended DC circuit design bypasses the front-panel selector switch. So, when boondocking with either a generator or a high-capascity Solar system, you could run the fridge on propane for most of the load, with DC providing "fine tuning" as needed. In the afternoon and early evening, when temperatures are still warm, the DC heater would be working quite hard. As you approach dawn, and the lowest temperatures of the night, the DC heater would run less and less (and maybe not at all). Then, in the daytime, you recover the used battery capacity via solar panels or generator. This solution has also been confirmed to work by ThePair, although he uses it only for 120VAC. The total parts cost somewhat more than $100, depending on the number and type of "bypass" switches you install. (I installed, but then removed my "bypass" circuitry; if the electronics ever fails, it's very easy to just disconnect power leads from one of the relays, and connect them together with a wire nut or push-in connector Union. Here are links to the necessary temperature control parts to handle both the AC and DC heater circuits: The electronic "brains", which uses the input temperature measurements to operate the output "SSR control" circuit: http://www.lightobject.com/JLD7100-D...oller-P66.aspx The thermometer: http://www.lightobject.com/Premium-S...aded-P681.aspx Do not try downgrading the Thermometer to type K, because ThePair had bad results using one of the cheap ones. An electronic switch ("SSR"): http://www.lightobject.com/25A-Solid...C-Out-P61.aspx A 4-pin automotive relay, sized for 40A. (These are typically used for turning on headlights, stereo, car alarm, etc.) Available at any auto parts store for a bit more than $5, here's an example: http://www.ebay.com/itm/Car-12V-40A-...db8562&vxp=mtr You can buy them with either the pins, or with a wired socket already attached. I recommend a "pinned" version, even though you must use a push-on crimp connector, because the pair of 'power side' wires built into most of those sockets are very small. (Perhaps AWG 14?) IMO, your new DC "power" wires should match TM wiring - 10 AWG stranded copper. Vibration-Proof, weather-proof wire connectors. All wire used behind the refrigerator should be THWN, because of the heat which the refrigerator generates. If using DC independent of the Norcold selector switch, as recommended: ON/OFF/ switch for the PID-DC power wire path. You might consider installing this on the exterior of the TM, using a marine switch or a weather-proof switch cover. Note: You will be using the existing fuses (the new circuits are wired into the "hot" sides of both existing circuits, 12VDC and 120VAC, after the fuses.) ----- I mounted the PID device in a new wall plate (a blank plate, with 1/16th DIN cutout made by hand tool). If you care to reach that far up, and don't want Cable TV at RV parks, then you could pull out and replace the existing wall plate with CATV and 2-wire telephone connectors. (We nearly all use cell phones now.). Otherwise, cut your 1/16th DIN hole into the paneling at least 3-4 inches away from the vertical side of the TM interior, and lower down. (You NEED those 3 inches, because there is a big bundle of wires in the TM along the vertical edge. You don't want your new "wall plate" mounting screw going into that bundle of wires.) This position allows the Thermocouple to easily reach the fridge interior, from the back. I drilled into a place a few inches down from the fluid tank, slightly to the right of the air tube (looking into the back of the fridge). In order to make the thermocouple reach all the way into the interior, you will need to trim off the hex-shaped mounting edge (the one which matches the nut). Use a grinder to make it round, matching the size and shape of the solid stainless column directly behind it. The Thermocouple attaches to the PID as follows: terminals #6 and #7 get wires with the blue wire wraps, and terminal #8 gets the red one. (Pay attention to the plastic wire wraps, NOT the colors of the actual wires.) Don't dream of modifying the PT-100 thermocouple lead wires or jacket in any way; PT-100 measurement is based on resistance, and properties of the wire leads are critical. ----- The Thermocouple attached to PID terminals 6, 7, and 8. Terminals 9 and 10 are not used. Next, we wire the PID terminals #1 through #5: #1 and #4 are tied together, and both get +12V, from any TM "hot" wire in the vicinity. #2 and #3 are tied together, and both connect to any TM 12V "grounded" conductor. These two pairs of leads do not have to be #10 wire, they only carry small "controller" current loads. (I used #10 anyway, because I had plenty of it.) #5 is the +12VDC control output from the PID internal Relay. It provides "sense" voltage to both of the refrigerator power relays in parallel. Create a "Y" from this wire behind the refrigerator, and connect the resulting wires to the "+" terminals of the SSR (for AC power) and the automotive relay (for DC power). Note that the correct terminal is marked with "+" polarity. And finally, we connect the "-" terminals of the two refrigerator relays to any TM 12V "Grounded" conductor. We're done with the control side, handling 12VDC and AC. Now Jump to post #6, in which we wire the power leads. __________________ TM='06 2619 w/5K axle, 15" Maxxis "E" tires. Plumbing protector. 630 watts solar. 450AH LiFePO4 batteries, 3500 watt inverter. CR-1110 E-F/S fridge (compressor). TV = 2007 4runner sport, with a 36 volt "power boost".