Battery Disconnect Switch Failure

[richard5933]

Logical that when starting off the chassis batteries the current flows directly from the batteries to the starter. That starter can easily draw more than 1000 amps during starting. Any disconnect used between the battery and the starter needs to be able to handle lots of current flow, so I wouldn't be surprised if the battery cable going from battery to starter bypasses the disconnect.

When you use the bridge switch/solenoid to bring in the power from the house batteries, you're normally only using the house batteries to add to the current in the chassis batteries. But, if the chassis system is totally dead or malfunctioning, you may be pulling the entire start power from the house batteries and asking them to do a really heavy lift. In this case, the disconnect in the house battery system needs to be able to handle the increased load. If it can't, a meltdown is possible. At least that's my theory.

[dickandlois]

Richard, Did you open the PDF files I forwarded and are your thoughts based on them?

Rich.

[floydfowler]

42 minutes ago, DickandLois said:

What you described is what I might expect to see.

This is some information on your year HR that might help.

  Rich

Starter Wiring.pdf 485.67 kB · 0 downloads 2001 Holiday Rambler VIM Trans.pdf 578.03 kB · 0 downloads Rear Run Box Wiring.pdf 179.97 kB · 0 downloads Starter Wiring.pdf 485.67 kB · 0 downloads

Thank you Sir! This starter wiring diagram confirms my theory.

[floydfowler]

40 minutes ago, richard5933 said:

Logical that when starting off the chassis batteries the current flows directly from the batteries to the starter. That starter can easily draw more than 1000 amps during starting. Any disconnect used between the battery and the starter needs to be able to handle lots of current flow, so I wouldn't be surprised if the battery cable going from battery to starter bypasses the disconnect.

When you use the bridge switch/solenoid to bring in the power from the house batteries, you're normally only using the house batteries to add to the current in the chassis batteries. But, if the chassis system is totally dead or malfunctioning, you may be pulling the entire start power from the house batteries and asking them to do a really heavy lift. In this case, the disconnect in the house battery system needs to be able to handle the increased load. If it can't, a meltdown is possible. At least that's my theory.

And mine as well.  Looking back on my dilemma at the rest area, I had a bad chassis disconnect switch but chassis battery was fine so when I used the boost/bridge switch I was only drawing the 8 or 9 amps from the house batteries that normally flowed through the chassis disconnect switch when starting engine!!  Mystery Solved!! Many thanks to all who contributed!  You guys are awesome.😁

[dickandlois]

Floyd, You are Welcome, it is hard to know what skill sets a member has from the first few posts.

 That makes it difficult to know how allot of the information sheared between the members of the Forum can help or send an owner way off in the wrong direction.

Safe travels and remember who has your back.

Rich.

[tbutler]

To the question of the OP, I'm late to this discussion but my answer is a big yes.  Our 2004 Windsor failed just as you mentioned.  When I examined the switch that failed, I found it had a washer and bolt on one side and was against plastic on the other side.  Examining the chassis switch, I found it had a washer on both sides, giving it more surface contact than the switch that failed.  This meant that drawing higher amps would lead to a higher temperature and this accounted for the melting of the switch.

When this failure happened, we were ready to leave for our summer travels.  We had slides out and couldn't move.  Since the function of a switch is to open or close a circuit, I simply disconnected the two lines to the switch and bolted them together, problem solved, switch on.  The only down side to this is that I would have to remove the bolt and isolate the wires to turn the circuit off.

The long term solution was to put in a new, larger capacity switch.  The fuse should be the over limit failure in any electrical system.  If the switch rating isn't higher than the fuse then that is a flaw in the circuit design.  I didn't try to replace the exact switch, went to an RV Dealer and found a 600 amp switch.  Problem solved, this one won't fail.  There is no harm in having a switch with a larger capacity than the circuit requires.  Again, the fuse is supposed to be the failure point in any circuit.  I eventually replaced the chassis switch with the same 600 amp switch.  Cheap plastic switches are just that, cheap. 

 

[kaypsmith]

On ‎5‎/‎23‎/‎2019 at 5:41 AM, richard5933 said:

Watts consumed will remain the same, but amps will go up or down inverse to the volts according to equation watts = volts x amps.

Let's assume that a residential fridge pulls only 2 amps AC while running. That means 2 x 120 = 240 watts. To calculate the DC draw 240/12 = 20 amps DC, so it is not surprising to see that his fridge is pulling 38 amps from the battery bank. Since the number under consideration is the current flowing through the battery disconnect switch, it's important to know the numbers there. Good job to the OP for doing the homework to find the numbers.

Just want to add a note here concerning battery amps versus AC amperage and trying to figure the amp draw on the DC side. While inverting DC to AC an inverter has a built in overhead for making the inversion. The most streamlined inverter that I have tested used 10% overhead, while the worst tested used 35%, which means that while calculating the amperage being pulled from the batteries, you must add the overhead to the DC draw to be accurate in your calculations. So glad that the OP has resolved your mystery.