40 Amp Reverse Polarity blown

[SamG_28BHBE]

The 40 amp reverse polarity fuses were blown and replaced. I have it plugged into shore power and two days later the bottom one has blown again.
I read in the manual that the only way those fuse's would blow is if the battery is hooked up wrong. Anybody have this issue?
2015 28BHBE
2013 Toyota Tundra

[norty1]

I have had mine blow but it was just doing its job, as I had reversed the battery.

[SamG_28BHBE]

Thanks norty1. I made sure battery was correct and it still happened.

[Mustang65]

I am under the assumption that the battery's + (Positive) terminal has the black cable on it and the battery's -(Negative) terminal has the white cable on it, and it is connected to the frame. Correct? OK..

What is the voltage on the battery without the shore power plugged in? (Wait an hour after unplugging to take voltage reading). Should be around 13+VDC.

A couple things to try:
- Unplug the shore power (with battery still connected) and monitor it for a few days to see if it still blows the fuse.

If not...

- Pull the MAIN battery fuse by the battery and plug in the shore power (without battery connected) and monitor a few days.

This may lead us in the right direction.

Let us know what happens

Just my thoughts,
Don

[RoyBraddy]

About the only things that can cause this is having the battery cables reversed, or removing the battery terminal and touched frame ground when the shore power was hooked up (sparked), or you may have a shorted out battery cell and it exceeds the 40AMP rating trying to charge up.

I also look at the battery case and find the word 'NEG' or the symbol '-' stamped into the battery case. Make sure this goes to frame ground. Also if you have two 6VDC batteries in series there is only ONE way to hook them up...

Check the batteries and see if the fluid level is ok inside. If they have shorted oout some cells those may not have fluids in them. Have you ever had the batteries get real hot on you. Another clue of shorted out cells. Also finding fluids around the battery that has boiled out. They also smell like rotten egg smell. This usually happens when you leave the batteries on shore power for a long time and your converter is a single mode type that only puts out 13.6VDC all the time.

The other thing is ask yourself if you have had the battery terminals off lately. Since both side terminals are the same types it is very easy to mix them up. Normally if RED and BLACK wires are used the Black goes to frame ground and RED is hot +12VDC. If BLACK and WHITE cables are being used then the WHITE cable goes to frame ground and the BLACK is hot +12VDC.

All of your trailer wiring inside uses the BLACK as hot +12VDC and WHITE as -12VDC wiring. Any white wire with a color stripe on it is usually a HOT +12VDC wire.

good luck getting it all figured out. I'm betting it is a bad cell in one of your batteries. If they have ever been run down below 10.5VDC for any length of time they are prone to short out the cells when being charged back up. A fully charged 12VDC battery should read 12.6-12.7VDC with shore power turned off. When you plug into shore power this voltage at the battery terminals should jump to 13.6 VDC if the converter/charger is working normal.

Roy Ken

[norty1]

I am going to buy 2 new 12v batteries tomorrow. I left my rig on a dealer lot for a little over a month and neglected to remove the battery cable. When I picked it up the 4 year old batteries were stone dead.

I put them back in a charge mode when I got home and they did not recover. Had a couple of shorted cells and they battery heated up and stunk like rotten eggs. They are disconnected now and will be history tomorrow.

I need to add a battery disconnect before doing that again.