Forum Discussion

happycamper002's avatar
happycamper002
Explorer
Apr 15, 2017

Inverter Disconnect (Lengthy)

I'm in the process of installing an inverter disconnect relay. This will cut off the feed from the battery--not the 120 volt output to devices/appliances.

Here is my hypothesis if you want to call it that way:

I tried the generic cylindrical type 12 volt similar to starter relay. I didn't like the protruding terminals because of the tight spot where I decide to install this. So I found a 100Amp cube type slightly larger than the conventional plug-in relay which fits in nicely.

The reason I decide to have this is: I want to disconnect the batteries on the fly (meaning while I'm driving) whenever my batteries are depleted--if for some reason the alternator is not able to replenish the battery/ies.
The inverter (1500 watt) is only meant to keep the fridge operating on a long drive. It draws 300 watts which translates to around 30 amps more or less on the 12v side.

I bench tested it and it works like a champ--however, when I tried it on the rig it blew the 30 A fuse. Not only that it blows the fuse after running a few minutes, it is also intermittent. It only turns on when it wants to before ultimately blowing the fuse.
(sounds like having a mind of its own) LOL

I suspected the inrush current to the relay coil was too much for the 30 Amp fuse but this fuse only powers the control circuit--not the inverter.
So I replaced the fuse but the same thing happens. My bench tester 12 volt source is from a selectable output exactly the same voltage as the rig--no ripples or things like that.

System works if I connect the inverter direct to the battery without going through the relay contacts.

In other words, inverter doesn't like having a disconnect.

If any of you guys encountered this problem, I would appreciate inputs...otherwise I'm ready to go to solid state relay hoping it will work or even scuttle the whole project altogether.

Thanks
  • pianotuna's avatar
    pianotuna
    Nomad III
    Apr 15, 2017
    Hi Happy,

    As I have two charging paths from the engine, I used twin 100 amp remotely controlled continuous duty solenoids. The "activation" coil on each draws 0.88 amps. I have replaced the OEM 60 amp fuse with twin 50 amp auto reset circuit breakers.

    The inverter is direct connected to the twin "house" banks. I use a Napa 1000 amp contacting 100 amp continues duty switches. (the type with a plastic "key")

    All the switch live behind the driver's seat so I can disconnect on the fly.

    I find I can run the 1200 watt water heater for about 20 minutes at highway speeds before voltage starts to sag on the engine side. I disconnect when I see 12.3 volts and allow the alternator to catch up for 30 minutes.
  • time2roll's avatar
    time2roll
    Nomad
    Apr 15, 2017
    1500 watt inverter should have about 150 amp fuse and wire to match.
    Skip the cut off and wire the inverter properly.
    Inverter will automatically shut down if the battery discharges.
  • CA_Traveler's avatar
    CA_Traveler
    Explorer III
    Apr 15, 2017
    Have you had a case when the alternator not keep up with battery charging? If there is a issue you could just turn the inverter off or it will shut down when the DC input is to low.

    Is the refer an absorption refer that you run on AC when driving? 300W is a lot for modern res refers.

    Or perhaps use a 200A continuous duty solenoid on the DC input to the inverter.
  • dougrainer's avatar
    dougrainer
    Nomad
    Apr 15, 2017
    A 1500 Watt Inverter will require a Cole Hersee 200 amp continuous draw solenoid. NOT ALL solenoids are 200 amp and not ALL 200 amp are rated for continuous draw. The activation fuse for this type solenoid is 5 amp. The FEED battery cable should have a minimum 150 amp fuse between the battery and the solenoid. Doug

    PS, this is the setup Airstream B vans use.
  • happycamper002's avatar
    happycamper002
    Explorer
    Apr 16, 2017
    I think I got this nipped in the bud.

    First of all I want to thank all who contributed their efforts to come up with answers. I took notice for comments made by Piano T. Your set up replicates the concept that prompted me to take on this project.

    Although it differs a little bit from my system criteria, they are identical nevertheless.

    This system, along with my Tri Metric, has a warning system that I added on.

    It monitors the battery voltage just like my TriMetric. When the battery voltage sags to around 12.3 volt (approx) a piezo (high tone) audible signal warns me that I have two minutes (thereabouts) to make corrective action or the system will shut down.

    The system works perfectly on the bench by simulating the scenario mentioned. It is kind of touchy because the "precise" voltage that it senses before entering the low voltage threshold varies. Temperature rise in the compartment could affect performance of the ICs that trigger a gate to trigger the piezo. So false alarm is a possibility.

    This is one that motivates me to take on this project.

    Now, going back to how I got this nipped in the bud.

    After almost throwing in the towel, I figured I'll give it another shot. I dismantled the whole thing and even went back to the drawing board so to speak.

    I assembled this gizmo with wire harnesses that allows me to easily separate each section (three component enclosures) with molex connectors. What I found in the molex was one barrel (female pin) that mates with the male pin got pushed in not allowing the two to mate together. It was momentarily making contact when I wiggle the harness, which explains the intermittent operation.

    As to why it blew the fuse, I would take the hint from Piano T in going to a heavier fuse.

    So,thanks a million to everyone for your comments.

    Now I can really call myself a Happy Camper.

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