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Small Cabin Forum / Off-Grid Living / Overload Issue
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# Posted: 29 May 2019 11:08

Hi all,

Had an issue at the cabin this past weekend. Here's my setup:

12V 210AH battery bank (2 golf cart batteries)
Blue Sea Systems Terminal Fuse Blocks w/ 60A fuses on both positive and negative terminals
Xantrex ProWatt 600W Inverter
#2/0 AWG Cables between Batteries & Inverter
PowerMax Automatic Transfer Switch
Champion 2000W Inverter Generator

I have this setup in such that when the Generator is running the AutoTransfer switch transfers to Generator and the entire cabin is run off of that. When the Generator is shut off, the transfer switch auto switches back to the ProWatt Inverter. Works so fast, that the TV and XBox doesn't even blip

Now, what happened... Unknown to me, my wife tried to run her blow dryer while the generator was running (she thought it would be OK, since she heard it running). Unfortunately, the generator was also running the freezer/TV/XBox/Lights/Shurflo Pump, etc. at the same time....

The Generator went into Overload and the Inverter shut off all at once. Took me about 20 minutes to figure out that the 60A fuse on the negative terminal blew (at first, I thought I lost my Inverter). So apparently, when the Generator went into overload, the transfer switch auto switched to the Inverter and instead of sending the Inverter into Overload, it blew the fuse on the battery!?!?

So... My question:
Why didn't the Inverter go into Overload before blowing the battery fuse? (It's gone into overload once before when my buddy tried to start the coffee maker)

According to the manual, the ProWatt has an internal (non user serviceable) 80A fuse and a Max DC Input Current of 60A. (Hence, why I went with 60A fuses at the battery.) However, It will surge to 1200W 5.8A AC output. That equates to 64A DC :o . (Not sure how the stated 60A Max DC Input current comes into play?). But, does that imply I should maybe bump up to a 75A fuse (that still keeps it below the internal 80A fuse)?

Just want to understand if this is avoidable in the future? (Already planning on putting labels on all the receptacles "Check if OK to run Hair Dryer" :p

Thanks all,


# Posted: 29 May 2019 12:02


I just re-read the ProWatt manual a bit more carefully...

It does NOT have an internal 80A fuse. That's the size fuse they recommend on the battery

So I guess that explains why the 60A blew before the Inverter went into Overload...

Just not sure why that didn't happen with the Coffee Maker incident before??

# Posted: 29 May 2019 12:35

Live and learn.
I would try not to push the inverter into overload. You probably get between 5 and 8 overloads before magic smoke. From my experience. I think I got 4. Lower quality inverter than the prowatt tho.

# Posted: 29 May 2019 12:51

Good point Creeky!

# Posted: 29 May 2019 13:03

Hair dryers and coffee makers. Such small devices but oh so powerful!

I'm fortunate to have as much hair as this guy -> and like to boil water on my propane stove for my drip coffee.

old greybeard
# Posted: 29 May 2019 13:08

French press for coffee, bad hair for wife in summer. In winter she runs the blower on the wood stove for a hair dryer.
I'd keep the 60a fuse inline, it did its job.

# Posted: 29 May 2019 18:01

Fuses differ in how fast they blow when subject to an overcurrent event.

I use a type T fuse to protect the batteries and cables from short circuits. One in any positive cable. Usually one is bolted to the + terminal and all power taken off a buss that is connected to the fuse. Type T are very fast blow and designed for DC use. They smother any arc so may be used right at a lead acid battery where there may be hydrohen in the air.

Type T have NO delay in blowing when the rated amperage is reached. Very good protection. They bolt onto a holder. There are 3 different physical sizes and each comes in a range of amp values.

Most other fuse types have a delay so a 60 amp (ANN, ANL, CNL, etc) may allow 75-80 amps for a second or two or three. When a battery has a dead short circuit you may not have a second or two before the cable insulation starts to melt or battery damage may occur (exploding lead acid battery).

# Posted: 2 Jun 2019 10:12

Been thinking about this some more....

I see Home Depot carries Siemens DIN Rail mounted 1-5A fast trip AC breakers.

Can I install a small AC Breaker inline between the Inverter and the circuit? (I'm thinking a 4A or 5A breaker should trip before the Inverter goes into Overload or blows a fuse)

Nate R
# Posted: 2 Jun 2019 15:43

I dont' see why not. Morningstar recommends it in their inverter, that a 3A fuse be on the AC side, knowing that it can pull more than that for MINUTES.

The Suresine can pull 300W, but is rated for 600W for up to 10 minutes, which is over 5 amps. But breaker trip curves would probably fit well with something like that at when you use a 3A breaker.

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