Wednesday, August 17, 2011

Inverter Problems Solved

I bought a new 760 watt inverter to replace the old 400 watt one that was having difficulties running the new fridge. Before I installed it I connected it directly to the battery and plugged the fridge in with an extension cord. It worked! Problem solved!

I then moved it to the front of the motorhome and replaced the old inverter with it. It powered on. I plugged in the fridge and it gave an awful whine and immediately blew the 40 amp fuse! The fuse was not heavy enough. You may recall that I wired the inverter with two runs of cable and used two fuses, each 20 amps. I did this because I happen to have a roll of green #6 cable from a previous life. One run was borderline on my amperage / wire size chart so I simply doubled up on it to give me plenty of capacity.

I went down to the local wholesale electrical supply and bought bigger fuses. I wanted two 40 amp fuses to feed the 760 watt inverter but the largest I could buy that fit my fuse holders were 30 amp. Well, not ideal but it might work. I replaced the fuses and turned on the inverter. The fridge went on and started drawing 460 watts on startup! No wonder it blew the fuses! After a few seconds it went down to 220 watts for "normal running". I will have to be very careful to unplug the fridge when we stop for any length of time as my 125 watt solar will not keep up to this kind of draw and it will kill the batteries in hardly any time if left on when the truck is not running. I am happy with this system.

We will not be able to keep perishables in it but it will work nicely for cold water, pop, juice and (when we are parked) beer. Jonna reminded me that it is illegal to carry liquor "within reach" of the driver while traveling. It is nice to have retired cop friends to remind me of these little nuances of the law!


  1. My real knowledge is 10 years old as of Sept 31st! Happily I might add. I can't imagine the law has gotten any looser though.

  2. Happy retirement anniversary! We will have to have a 10th retirement anniversary party in Merida this winter! You listening Chris & Juan? Juan would not need his four layers of blankets this time!

  3. A couple things you may already know: battery life will be shortened a lot by doing deep draw downs. I always try to go no further than 25% down.

    Do you have propane energy as an option on the refrig? A more practical way to go.

    Higher voltages like 24v or 48v systems will reduce current demand, will reduce required wire size and increase efficiency. Sine wave inverters, while more expensive, will operate more efficiently and be easier on some appliances. You probably know all this?

  4. Thanks John. This is just a cheap bar fridge for backup purposes and extra storage of non-perishables. It is electric only and will be turned off overnight when we boondock.

    I agree with the 25% draw down but we blew it while boondocking in Laughlin for two nights with very little sun. I don't know how bad I hurt my two 6 Volt batteries but they went down to 11.5 volts.