Add Relay 02/09

WARNING THIS PAGE Its not well organized kind a messy. Every time I try to clean up I add more text...hopefully you can glean some info. Simply to turn on or off refrigerator from truck cab
Fig 1 is basic install- as is figure 2 but with addition of switch to turn off & pilot to monitor. Both figs. 1 & 2 involve mounting refer toggle near refer so as not to add to length of main 12v power supply. Fig 3 shows remotely mounting of refer switch which is what I did. This does involve adding a lot more wire, however by adding second relay its not adding to main power supply length.

Warning 2: After this installation I was having intermittent occasions where when truck turned off refer & back on, the refer panel lights were not on. I've since added quenching diodes to relays to bleed off power. It appears the control panel is sensitive to the surge generated when the relays are shut off. The diode is placed between terminals 85 & 86 (not the power in/ out) with the positive (striped) end of the diode to the positive ignition. signal source, the other end goes to relay ground. It is possible to find relays with diodes already installed. This fixed the panel light problem.

Warning 3. Not shown are any fuses-all 12 v sources should be fused.

Warning 4. Generally most automotive switches are rated at 15 amps, insure you get 20 amp min. 30 amp recommended. Our refrigerator uses 17+ amps on 12V

[NOTE if you have Dometic recall safety switches installed this does not affect its intended purpose, new switch and relay are before them-see diagram fig 1].

    FYI: Quenching Diodes: Anytime that a relay coil is driven by a circuit that is not specifically designed to drive a relay, you should use a quenching/suppression diode connected in parallel with the relay coil. The diagram below will show the connection of the diode. Initially, you may think the diode serves no purpose because the voltage applied to the relay cannot pass through the diode. This is true when the relay is energized. The diode comes into play when the power source is removed from the relay coil. When power is applied to the relay coil, a magnetic field is created and energy is stored in the coil. When power is removed, the magnetic field collapses causing a reverse voltage to be generated (it's called inductive kickback or back EMF). The back EMF can easily reach 200 volts. The diode will absorb the reverse voltage spike. This voltage, if not absorbed by the diode, will cause premature failure of switch contacts and may cause the failure of power switching transistors. You can use virtually any type of rectifier or switching diode (i.e. 1N4001, 1N4002, 1N400x... or Radio Shack part #s 276-1101, 276-1102, 276-1103, 276-1104).

Added a relay so that when truck ignition is turned off - 3-way refrigerator 12v power is turned off.

Been on the round toit list since the 1st time I killed the batteries. Our refrigerator is a Dometic 3-way. As neither of us are comfortable using the gas on the road, normally when on the road we use the refrigerator on 12v to keep it cold. However when you stop for any length of time the refrigerator will flat kill the batteries VERY quickly. When stopped for more than a few minutes I would go inside and turn off fridge, we'd also try to turn it off like an hour before our destination to insure batteries were fully charged.

That was the plan, don't know how many times we'd arrive with partial batteries- or stopped and forget to turn off or worse when on the road -after turning off Id forget to turn back on. Or thinking we'd only be a few minutes and it'd be an hour. Never failed...just a pain. Neither of us are comfortable using the propane on the road-but lot of folks do. Dead batteries and/or warm milk just don't cut when boon docking

So decided its time to add a relay. Did some research on this but there's just not much out there other than "I did it". Older control boards for the refer actually used to have a terminal for attaching an ignition on source wire. For exactly the reason I'm adding, to save your batteries. I made the mistake of contacting Dometic customer support for possible guidance-what a joke..I have this picture of a lil room in India, or possibly Indiana and depending on which number you dial in on, the person at the other end turns the page in a tattered binder for the appropriate 3 Technical answerers for a given company....

So this is the plan..It a simple one. Just run the 12v from camper batteries to refer thru a relay that is turned on/off by truck ignition. Also add a switch to refrigerator to select whether main 12v goes thru new relay or directly to fridge as normal. Easy yes, but new electronics and pc boards don't actually respond to my mechanical way of thinking. First I don't know if when power is turned off and back on what the refrigerator will do, Be still in the on or switch to off?

So I turned refer to 12v, went outside and disconnected refer 12v source, then reconnected (pretending to be a relay), to verify that when power was disconnected and then restored that refer would still be in the On & in DC mode. I was afraid, like a lot of new electronics, that it would default in the Off mode.

But it didn't-It is still on and In DC mode! Great-I can proceed.


THE PLAN ...Figures 1 & 2

    You can accomplish this way simpler than I did using fig 1. This just splices an on/off switch on the 12 v feed with relay added after switch. When switch is in off position power must go thru relay, which can only happen if truck key is on.

    Before starting 1st verify your fridge will still be in the on & DC mode when pulling refer power and reconnecting (pull fuse or disconnect at refer board). If your refer defaults to off when 12v power is disconnected and then reconnected your done, this modification wont work for you.
    Second: You'll need a plug between camper & truck. This can be as simple as a single banana/bullet connector but if there's even the remotest possibility you'll add something later, Id use a mounted plug (trailer plug etc) to truck.

    The simple relay
    [fig 1]

    Figure 2 shows similar approach but uses a 3way switch and added pilot light for more control. Basically disconnect 12v power from refer board, run to new 3 way toggle switch. This will act as selector switch. Switch on positions will determine where power goes, to refer for normal operation or thru relay, which can only happen if truck key is on.

    Parts: plug/receptacle, a 30amp min bosh type relay, 30amp toggle switch (w/ screw terminals makes wiring easier) and some 10g wire, 16g wire & female spade, ring &mics connectors. Optional pilot lamp, lighted dash switch.

  • Find a fused hot wire that's only on with ignition (can be any size, 16-18ga) & run to new truck to camper plug (adding a in dash switch to disable ignition hot wire is a good idea, this switch can be 15 amp).
  • Add relay near refer.
  • Run 16g wire from new camper plug (new ignition source wire) to #85 terminal on 30amp relay.
  • Run 16g wire from #86 terminal on relay to ground
  • Adding the switch, this assumes it will be mounted inside or near the exterior access panel. Mount switch, labeling somehow will be convenient.
    Disconnect refrigerator 12v supply wire from 12v feed terminal block, reconnect to one of the 'on' poles of new switch, run a piece of 10g from same pole of switch (or splice into wire) to #87 terminal of relay.
  • Run a10g wire from #30 terminal on relay to the other 'on' pole of switch
  • Add a 10g wire from 12v feed block to new switch (center off pole).

    The original install

    -With switch on (normal side) refer will behave as it did before for electric, propane or 12V use. For truck controlled, on road use of 12V, 1st set switch to normal on,Turn on the refer, set to DC- verify , then turn the toggle switch you added to truck side. Fridge should go off, turn key on in truck & the truck should turn the fridge back on, off, back on, see fig 1. Once at camp flip new refer switch back to Normal on to run as normal for gas or elect. (or an hour or so before arriving at camp if boon docking, turn fridge off to insure batteries are fully charged, this is where switch in truck on ignition hot wire comes in handy cause you can manually turn OFF refer if you want to from inside the truck). There are a few different ways to add a relay controlled by truck.

    Your done.


That's the simple way-Now heres my convoluted approach...

    update 02/04/09" Above [fig 2] is what I did first, This is practical and works unless you want the selector switch inside the camper which involves a lot more wiring. I decided half way thru to put the selector switch inside the camper and proceeded with the parts & plan I had, just extending the travel of the 12volts. wrong---Works great, but the probable voltage drop will affect performance on the road, and now I'm going back and adding another relay [fig 3]. When I decided to put the switch inside I should have stopped and rethought & adopted my plan to new strategy, but I didn't, now I am redoing, that's what happens when you change plans in the middle of the road.

    The original plan works [fig 2], IF I would have put switch in refer outside compartment (or maybe a weather proof switch outside), would have been great and only added bout 12" of wire to main 12v feed to refrigerator. (which is what I recommend). But running the extra wire inside added (up & back) about 14'. Its just way too much wire for the main 12v feed. I could up to 8ga but Id rather the main feed was as short as possible. And because of my switching setup I'm kinda stuck. I'm adding another relay that is turned on by the original for direct 12 feed to refer. I just disconnected output from 1st really which is still turned on/off by truck, Ran the out put that went to refer and used it to signal second relay. Then I ran another 12v lead from main block thru second relay to refer. So the main refer feed is now about 12" long. So my install is as shown in [fig 3], I didn't take pics of the second relay but Ill add in the descriptions. As I had already completed install using one relay-adding the second due to length of wire run, made a lot of the 1st install kinda overkill. Like 10ga wire to selector switch then to second relay could have been 18ga. Oh well Its there. You'll also note, now that its been rewired for 2nd relay and direct (short) feed to refer, I can easily bypass either relay, I could also eliminate really A and entire leg from 3 way switch.
    Enough verbiage, On the install..

As complicated as I made my install, once its done, I can drive stop, leave the truck, get back in and continue down the road- with the fridge running in 12 volts and not worry bout killing the batteries or turning refer on/off. I can monitor/verify the fridge is on and I can manually turn off or to run, the fridge from the truck. With a single switch inside the camper I will be able to set to normal usage or travel usage.


The RELAY plan
[fig 3] The final install

    Basically its just disconnecting the 12 volt feed to refrigerator, run a lead to new 3 way switch (which you can mount anywhere) and a lead to relay "B". On my 3 way switch, one side of switch will go back to refer for normal usage (minimal 12v for gas/electric use). The other side goes to relay "A" which is turned on/off by truck. Relay "A" signals relay "B" which carries full 12v power (17amps) to refrigerator. Adding the second relay allows remotely mounting the toggle switch anywhere without adding to main 12V supply to refer. Run a wire from truck (ignition on source) to activate relay "A". I put a switch w/indicator in truck that allows switching on/off ignition source wire. I can manually turn off if I don't want the refer on, (like an hour before arriving at our destination). I also decided to add a pilot light from refrigerator, ran a wire from refer to truck to activate a pilot lamp when refer has power. This will tell me if refrigerator is getting power. Also by turning off manual ignition source wire switch, if the refer pilot light stays on, means I forgot to flip new selector switch to relay (travel) side and I'm draining the camper batteries (not being controlled by truck).

Getting access

    Running the wires that will plug into truck-thru camper to refrigerator. I removed the main cord box because I wanted the new plug near the main plug. Wow look at that hole. In the truck bed I'll be adding matching plug. I ran 2 wires thru main cord grommet, into camper. Wire runs thru cabinet into water tank cabinet (removed top for access), across to under slide, up under dinette, then thru wall into refer backside. I just followed other wires/gas line to refer. I only had to poke a small hole to get into refer area. That was easy.
    If access is difficult you COULD run a small 2 wire cable across the front of the camper, drill a hole from the refer panel area down and enter from under camper wing.


New plug

    Originally I added new two pin plug out side and covered wires with loom material. I've since replaced with std. 7 pin plug & cord when I added charge line relay. More flexible/ durable, and extra wire. Same on truck side


    Much hesitation at this point. I know what I'm doing but I'm unsure that I want it (the switch) inside the refer panel access compartment, however it would be much easier to wire. It does mean having to remove refer panel to access the switch. Hmm...Running to inside of camper & to front of refer and putting switch there will require a lot more wire.....but would be a lot easier for use..

    Yup I am putting switch inside camper. This is where the plan changed

Wired the board

    Kinda hard to see what's what. I soldered 3 wires to a single terminal, 1 from selector (toggle) switch,1 from relay "B" and 1 from truck pilot. I have 3 10ga wires going to/from front of refer for switch (could have been smaller- but I COULD use for main power), 2 10ga wires to/from relay and 1 18ga to truck plug for pilot.

Wired the relay

    Also decided to put relay in cabinet next to refer-less likely to corrode, less clutter. Also there's is a small box that covers this wiring. It is accessible from dinette seat also. 2 10ga wires to/from refer, I 18ga from truck plug for ignition ON source, 1 18ga ground.
    This is where we differ. Shown is a single relay which is what most should do. I've a second relay but it does what a single does, its just getting its signal from another relay instead of directly from truck. My toggle switch is inside, but more practical as far as wiring would be to add it here or by refer board.


ran power wires

    ats a lot a wire...

    Again, I've an extra wire because I'm using a 3-way switch. You only need a 2 way on/off. Remote/running switch inside is ok (still Id go 10ga min), because this will only be used for normal gas or 110v electric supply which draws little 12v. It can be used for 12v side but really don't recommend it due to length of wire run, however in a pinch it'll work.


Selector switch on

    Against my better judgement, I ran wires up and over the top of fridge, installed inside on the 'eyebrow'. Just to much easier to use but involved running a lot more wire. Just couldn't think of another place that would be easily accessible. This actually works well.


Selector switch off

    Shoulda been like this from day 1.



additional 7 pin receptacle

    Again, originally I had a simple 2 pin plug, but changed to this std 7 pin when charge line was added;
    see solenoid page.


Dash Switch

    Dash was pretty simple. Used a simple lighted rocker switch for ignition feed to camper, and a pilot lamp to monitor fridge. Just ran a ground wire to both switch and pilot, hooked wire from refer to pilot. Taped fuse block for ignition on wire, ran to one side of switch. Connected wire that goes to refer relay to other side. I've since added a mini switch to turn off pilot when camped. See solenoid page

    Placed the switches so Margaret can monitor and switch. (If you look at diagram [fig 3] there's a lot of duplication. I can rewire at least 3 different ways with what's there by just unplugging/ into different places, should either relay fail or switches, I'm thinking its costing me an amp (2nd relay/extra wire) or so-while on truck side charge circuit for this redundancy. Normal consumption for relay is minimal.