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**CountryFit** · 06-30-2017, 03:09 PM

4/0 is recommended but 2/0 i am using for my big load has not yielded a high temp or voltage drop. don't think 4/0 is the cure (no discouragement intended).

ronjhall · 06-30-2017, 04:06 PM

Same Inverter. Was having voltage faults with 1/0 cables. Changed to 2/0, problem solved.

Sweetbriar · 06-30-2017, 04:29 PM

Well since I'm home ran a test using a vacuum cleaner as a load. A moderate start surge but also has a 12 amp listed run power demand which the inverter should handle easily and a good test load for the entire system at 75% of inverter capacity.

Running off the battery bank with no additional DC power source resulted in the same fault conditions as the fridge. A very short duration fault, power loss and reset. Unlike the fridge the vacuum stays switched one on but the motor is coasting so as soon as the inverter reset it's somewhat picking up where it left off. With each cycle the surge would decrease as the motor speed increased. It took about 10 seconds and five cycles to stabilize.

Here's the eye opening part. With everything stable and the vacuum running there's a .5 VDC difference between the battery terminals and the inverter terminals. With no load volts are the same. The start surge is too quick to accurately measure with the meters I have but I suspect it's enough for the inverter to declare a low voltage fault.

Since now I am working in the daylight, can see everything and what Sbrownstein posted, I realize I'm also way undersized for the leads in the battery bank with 4 gauge wire. Also the primary lead coming off the bank to a bulkhead terminal tie point starting getting pretty warm after a few minutes with the vacuum running.

Based on what I found pretty sure I need to upgrade all the wires in the battery bank and the feeds to the inverter. Makes for a pretty big choke point at the source of power during high demand situations. I've got 4/0 on order which is probably overkill for how I use the inverter but if the day ever comes I know using 4/0 I could use the full capacity of the system down to the last volt if necessary. I'll post Monday evening what the results are. Got a wedding on Sunday afternoon that limits RV activities for some strange reason.

One of these days I'll get the set up to a point of being able to do a bit of light arc welding or have a moderate investment in tangible copper.

Sbrownstein · 06-30-2017, 04:51 PM

OK, lets look at this again. That reefer has an energy star power rating of 329 KWH, that is 2/3 of what my Frigidaire has so the power consumption should be 2/3 of what I see or about 66 watts...all the time...or an average draw of 5.5 amps or so, including inverter losses (same inverter!) Now, I do not know if it is an inverter unit (hard to find this stuff out) so it may draw say 600 watts when running. Let's up that to 1000 watts peak and that results in about 88 amps at 12 volts.

At that load the difference between 4/0 and good old #2 is 2.1% or .15 volts, not enough to really screw up anything. Interestingly the power lost is equivalent to about two 6 watt LED ceiling lights! I have attached a spreadsheet for that current and a 15 foot round trip to the batteries...that is the unknown here.

Finally, I don't know much about Magic Chef, but their installation manual for the unit in question specifically says that it is NOT designed to be used in an RV with an inverter. Obviously it does work when running the alternator at a higher voltage level on the inverter. And I am sure that others have used them in an RV.

Sweetbriar · 07-02-2017, 12:20 PM

Cable was delivered this morning, thank you Amazon Prime two day shipping. Rewired the feeds, grounds and battery cross connects and everything works. Fridge cycles normal with no hiccups. Two middle aged generic GC2 batteries might not have the storage capacity for any real meaningful off grid stay time before needing to recharge but should get me thru a parking lot overnight boondocking or a CG quiet time period.

Plus an added bonus, with how much copper I added to the coach I probably doubled the scrap value. 4/0 cable is huge. A bit like filling the gas tank on a Yugo, if you're old enough to remember the jokes about the car.

Sbrownstein · 07-02-2017, 01:11 PM

Quote:

Originally Posted by Sweetbriar

Cable was delivered this morning, thank you Amazon Prime two day shipping. Rewired the feeds, grounds and battery cross connects and everything works...

Glad it works. You replaced not only the cables but all the lugs with new, well connected ones. My bet is that is where the problem was.

Cool thing is than when running down the road it will always work since the alternator will push 14 volts or more into the batteries.

2 GC-2s, if in decent shape, should last at least hours.