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gene, RV Mechanic
Category: RV
Satisfied Customers: 1100
Experience:  28 yrs exp in the industry
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Two 300 amp fuses over batteries in a motorhome. Have Magnum

Customer Question

Two 300 amp fuses over batteries blown in a motorhome. Have Magnum 2000 full wave. ( Up grade) When I put the second one in everything working , turned inverter on a little then off. About 20 to 30 minutes after installing new fuse plugged into a 20 amp AC plug then about 20 minutes later went into the coach and no 12 volt power. Unplugging the AC voltage I noticed the ground fault was tripped. Looking back this happened when the first fuse blue. Where could the severe short be. and what could be the fix. Thanks
JA: Do all the fuses have the correct amperage for the circuits they're in?
Customer: Yes, I have never had to change any fuses since I bought this coach Nov 06. Wheaton
JA: Are you fixing your Magnum yourself? What have you tried so far?
Customer: Talking with Tiffin men I have only changed this 300 amp fuse
JA: Anything else you want the mechanic to know before I connect you?
Customer: This should tell the problem
Submitted: 1 month ago.
Category: RV
Expert:  Randall replied 1 month ago.

Hi! My name is ***** ***** I can assist you with this. I may need some additional information from you first in order to give a complete answer.

Expert:  Randall replied 1 month ago.

I would start with the batteries and the hookups. How old are they and can you send me a photo of the cables and hookups?

Customer: replied 1 month ago.
Batteries 3 yr old. MH is a 07 tiffin Pheaton. wiring is all good ( like new) It appears the fuse is blown when the coach is hooked to an AC plug.
Expert:  Randall replied 1 month ago.

Most RV batteries only last about 3 years and I would have them load tested to be sure they are viable. Something must be wired wrong if that fuse blows when hooking up the AC power as that is only used for the DC input from the batteries to the inverter. Hooking this up to a household 20 amp plug is a very bad idea and that can cause all kinds of problems. You need to wire up the proper feed voltage and amperage plug from the source. Most places that sell batteries can load test them for you. Attach some photos of the hookups if you want using the paperclip icon.

Customer: replied 1 month ago.
15 years with a MH and the batteries last me 5 to 6 years as I do not draw them down to injure them.They are currently combined at 12.51 Volts. I have used this plug for 15 years and never had a problem like this. Every time the fuse has blown after pluging it in it has kicked off the ground fault. There has to be a short and what are the choices?
Expert:  Randall replied 1 month ago.

I don't see me convincing you of much here, so I will opt out of this and allow another tech to offer something if they have another idea. They come and go at all times, so I don't know when that might be.

Customer: replied 1 month ago.
The batteries and wiring are good and on second thought there must be a switch that hasn't switched as it should and I don't know how to trace it. Thanks for your time.
Expert:  Randall replied 1 month ago.

You are welcome...........but, don't respond back here or it locks me back into the question.

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