Inverter use question/problem

86Scotty · 02-22-2018, 08:49 AM

I recently got my electric setup mostly complete in my Transit. Awhile back I added 2 6v golf cart batteries wired in series so I have one 12v 230 amp hour bank. I added a Tripplite RV1250 inverter to power a microwave, printer and several chargers.

From factory battery I used 2awg through a BlueSea 7610 isolator with a 150 amp breaker, a setup I've used before with no problems. The run is about 8 feet. Between the house batteries and inverter I have a 0awg wire and a 200 amp ANL fuse with a run of about 5 feet.

I have always believed that it is much easier on the inverter and AC appliances to idle the van when using AC power/inverter so alternator is helping the inverter out and not pulling so hard from just the house batteries. Lights dim and microwave slows down and buzzes if you don't have the van idling which I've always assumed is a pretty bad thing.

Here's the problem: After about 30 seconds of microwave use my 150 amp breaker between isolator and inverter will trip. Every time. Do I simply need a bigger breaker for 2awg? In order to keep using the microwave I've just let the inverter run off the house batteries but I hate the dim lights and buzzing microwave. House battery voltage dips to about 11.3 while micro is in use and then returns to 12.5 or more after.

I've wondered what the norm is among others for awhile anyway. Do you idle when using your inverter?

Scalf77 · 02-22-2018, 09:14 AM

What is the size of the microwave (wattage)?What is the capacity of the alternator? The wire and fuse need to sized to fit the possible output of the alternator. If it had the capability it would put out enough current to provide for microwave and still put some charge in the battery.

A standard Ford Econoline alternator would never have been able to put out that much current. I believe I read your Transit was higher. This would explain why you have not seen it in previous builds.

It could also obviously be a bad breaker, you should put a current meter on it to see what it is pulling.

-greg

86Scotty · 02-22-2018, 09:27 AM

Thanks for chiming in Greg, I was hoping you would. The microwave is tiny, just a 700 watt.

The alternator is the standard 150 amp Transit alternator. There is a bigger 250 amp available but I do not think I have it. I'll have to research that to be sure.

The breaker is a cheapo from Amazon and I'm suspecting that's the problem. It has never tripped until I hooked up the microwave/inverter. It charges the batteries just fine.

Question for you though. Is it a bad thing to use the inverter without supplementing with the alternator/idling? Is the buzz and severe drop of batteries normal and acceptable?

Thanks

Scalf77 · 02-22-2018, 10:05 AM

700 watts should not be that bad, A voltage drop would be expected for that size wire and inverter conversion, although that looks a little excessive for 700 watts. I do believe the Tripplite can get a bit noisy, but I don't remember mine buzzing. Generally it is hard on the batteries if you consistently pull a lot of current especially for smaller banks.

I rarely idle when running the inverter, unless I know that battery is pretty low already.

-greg

BrianW · 02-22-2018, 01:08 PM

I always idle when running our 700w microwave (3-battery bank of about 330ah and a 1500w inverter). It just seems to suck the batteries down too much if I don't. But I'm overly paranoid about that.

carringb · 02-22-2018, 01:23 PM

You might be better off paying extra for a true sine-wave inverter.

Microwaves on modified sine wave put out as much energy typically, and the square wave is also what's making the buzz as the microwave starts pulling more amps. You probably have a smarter microwave that is trying to maintain a constant output, making it pull more amps. An old twist-dial microwave wouldn't do this, it would just heat slower.

Power Inverters and Microwaves | Don Rowe Power Inverters Blog

But yeah, I'd also be suspect of your breaker. It may be simply tripping too fast.

Scalf77 · 02-22-2018, 02:25 PM

If your alternator is 150 amp. it would be unreasonable to expect that at idle, so there would be limited chances that you are really pulling 150 + amps over that breaker. If you had the 250 Amp Alternator, I'm not sure it could still put out 150 + amps at idle, but it would be worthy of checking. Then you get into the load needed to draw that much current. if we take the 700 watts and adjust for conversion cost and modified square wave let's say we get 1100 or 1200 watts. That would put us around 100 amps. We would than need an additional 50 amps of current draw. That could come in the form of charging the battery or additional 12 volt loads.

With all that my first choice would be a bad breaker.

-greg

86Scotty · 02-22-2018, 03:26 PM

Thanks. It’s the microwave that buzzes, not the inverter.

I’ll check and probably replace the breaker.

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1der · 02-22-2018, 11:59 PM

I know on our rig even with the dual alternator setup, simply "idling" is not enough when running the microwave or a heavy draw load. I have watched the draw on the batteries and at idle (670 rpm) , there is still a pretty large draw down. At 1100 to 1150 rpms all is good and I am actually in the positives. I have a high idle setting on the tuner at 1200. If I ever send it back in for additional tunes, I will add a 1100 or 1150 rpm setting.

This does not answer your breaker tripping. Might want to check connections, too.

boywonder · 02-23-2018, 07:28 AM

...as another data point, I have a very similar setup to 86Scotty....

350 AH of house battery, Blue Sea 7610, 2AWG cables and a 150A breaker between the starting battery and house batteries.

..and a 700W microwave (that pulls 1000W 115VAC), and an older ProSine 1000W true sine wave inverter.

I never run the van when using the micro but the house batteries usually dip from 12.8V down to 11.9-11.8V.

There is no way the van alternator is outputting anything close to 150A at idle......