Need comments on this electrical issue.....TriMetric / Xantrex/ Coffee

rbertalotto · May 20, 2016

I have a Xantrex ProWatt 1000 installed in my trailer......4g wire less than 18" directly wired to the two 12v, group 31AMG batteries wired in parallel ....250a Circuit breaker between the batteries and the inverter

The "house" main wire is 4g to the circuit breaker / charger panel in the trailer with a 30a circuit breaker at the battery....the run is about 12'

I just bought a Keurig K130 Hotel/Commercial version coffee brewer. I went this route because this unit only draws 700 watts as opposed to all the other Keurig machines that draw up to 1500 watts. Many hotels have insufficient wiring in the rooms so this unit is designed just for them.

So....With trailer disconnected from "shore power"....running just on batteries with 280w solar panels.....when I turn on the coffee machine, drawing AC current through a "Kill-A-Watt" it shows I am using 5.6 amps......But my "TriMetric" battery monitor is showing a drain of -45 AMPS!!! In fact, at start up it goes as high as -52 AMPS.........AND..It is a sunny day and the solar panels are outputting 7 AMPS so those numbers are really -52 and -59 AMPS......

In fact, during one test I tripped the 30a "house" circuit breaker...............Very strange since the Xantrex is not drawing current through this circuit at all. It is directly wired to the two batteries.

I can't figure it out.....Why would the house breaker trip? The only connection between the Xantrex and the house wiring is both are attached to the "+" terminal on the battery and both "-" are connected to the TriMetric's shunt.

Any ideas?

Darryl&Rita · May 20, 2016

You're mixing up AC and DC systems, in your head. 5.6 a AC is roughly 56 a DC. The TriMetric is measuring DC, the Kill-A-Watt is measuring AC The 30 a breaker tripping was an unfortunate coincidence, and not related to the coffee maker load.

horizon36 · May 20, 2016

You're mixing up AC and DC systems, in your head. 5.6 a AC is roughly 56 a DC. The TriMetric is measuring DC, the Kill-A-Watt is measuring AC The 30 a breaker tripping was an unfortunate coincidence, and not related to the coffee maker load.

This is correct. If your coffee maker is drawing 5.6 amps of AC power you can multiply that by 10 to get the DC amps which would be 56. Then divide the 56 by 0.9 to compensate for inverter inefficiency and you get 62 amps of DC to make the 5.6 amps of AC. If the load ran for one hour you would have drawn 62 amp hours from your bank or approximately one amp per minute. If you want to see how much you have drawn from your battery bank either use your kilowatt to tell you the total amps used and apply the above formula, or gustimate it by tracking the number of minutes the AC load ran and, in this case, multiply by one amp per minute.

dartmouth01 · May 20, 2016

This is correct. If your coffee maker is drawing 5.6 amps of AC power you can multiply that by 10 to get the DC amps which would be 56. Then divide the 56 by 0.9 to compensate for inverter inefficiency and you get 62 amps of DC to make the 5.6 amps of AC. If the load ran for one hour you would have drawn 62 amp hours from your bank or approximately one amp per minute. If you want to see how much you have drawn from your battery bank either use your kilowatt to tell you the total amps used and apply the above formula, or gustimate it by tracking the number of minutes the AC load ran and, in this case, multiply by one amp per minute.

Or watch the trimetric to measure the actual usage from the batteries.

Ronbo · May 20, 2016

4g wire from your batteries to your inverter are not large enough.

rbertalotto · May 21, 2016

Thanks guys. It dawned on me after I sent the post that AC and DC would account for the two different readings. Duh!!!

The 4g wire is actually less than 12". I thought at that short length it would be fine. So far it has worked great and the fan has never tuned on in the inverter. Wires don't get warm as the inverter is only used intermittently for high amp draw like this coffee maker. Any comments about this thought process would be greatly appreciated.

lenp · May 21, 2016

Roy,

Measure the voltage at the input to the inverter AND at the batteries when your pulling those 50 amps. If there is more than a couple of tenths of difference the the wire is too small.

I had 2 gauge between my batteries and the inverter (about 14 feet round trip) and it would drop over a volt when my residential fridge kicked in. Changed to double ought and no more problem. Still too long of a run but just cannot get closer to the batteries.

Lenp

rbertalotto · May 21, 2016

Thanks Len,

I'll check that out today when making my first cup of coffee!

rbertalotto · May 22, 2016

Nothing better to do today so I shot a video of the Keurig K130 brewing a cup of coffee in just over 3 minutes.....

http://rvbprecision.com/rv-projects/rv-coffee.html

Bottoms Up!

Yarome · May 23, 2016

There are different factors to consider when wire sizing. One is the distance and ampacity. For an 18" run (3' combined) your 4 gauge wire is just fine and current loss would be extremely minimal. At higher draws.. well under a 1% loss and as the load decreases (like pulling 50-60amps for your coffee maker) that loss will drop to more in the .5% range. Quite acceptable!

The other main factor that doesn't get mentioned much is the actual amp rating of your wiring. Of course there are a multitude of contributing factors there too that will have impact, but generally speaking 4 gauge copper will have a rated max of 60-135. 135 amps for the ground/negative side of the circuit and 60 amps max for the current transmission leg (positive). So in that respect.. it might be just a "touch" light, but under periodic loads like you're talking.. you're still "good to go".

Would it hurt to go a little heavier gauge? Never! Is it needed/warranted in your particular case? Not at all.

rbertalotto · May 24, 2016

Thank You Yarome........I would think it would be like 120/240V where "time" is also a consideration. If I was pulling 60 amps for hours on end, the wire should be larger than pulling the same current for 3 minutes?

When I had my shop wired for a welder, the electrician explained that I could use a smaller wire and still be in code because the circuit was hard wired and used for short periods of time.

Yarome · May 24, 2016

If I was pulling 60 amps for hours on end, the wire should be larger than pulling the same current for 3 minutes?

Exactly. Although.. at 60 amps you are still within ratings of your existing wiring and theoretically 'could' run for hours. What you really want to be looking at though is the max amperage your inverter is 'capable' of pulling (ie., 73 continuous, 92 limited duration, 119 surge for only seconds). So in that respect, as you deduced, you're still good on your 4 gauge for short duration's.

RV loads (12v).. even heavy ones are generally periodic so amp ratings are not 'as' critical (not that it should be ignored). I probably shouldn't have even brought it up, but there were some posts expressing concern that 4 gauge wasn't adequate for your install.. that was the only reason I could think of since load wise (1000w inverter), and considering current loss.. you're good to go.. or at least, doesn't require or justify even the minimal expense of upgrading wiring already in place.

If it was new cabling.. I might have recommended larger, but I'm a "bigger is always better guy". I run a 2000w inverter. For my 18" run I use 2/0.