Battery Off/On Switch

[Just Plain Jeff]

Most boats and POS coaches have a battery ON/OFF switch, which effectively disconnects the battery power from all circuits. It seems as if many conversions do not have such a chassis power switch. It occurs to me that it would be a good idea to put one in a coach if none exists in order to work on the electical system. The DC system in coach carries big amperage; at least it would be a great safety feature for the DYI kinda guy.

[truk4u]

So Jeffee Boy, does that mean my Plastic Trukster (POS in your terms) has one up on a Prevost Conversion?:rolleyes:

What a good day in Plasticville......:p

[hhoppe]

Both of my Prevosts have such power switches. One for Chassis and another for coach.
Hey man you wanna buy a coach. Make you a deal your own mother wouldn't offer you.

[Just Plain Jeff]

Awright you guys.

HH: Your coach should go to Jim Chaloupka, as he hasn't had one yet, gentleman that I am....Jim?

Tom: Just because the resinmobile has such a switch doesn't mean that it works.

Y'know. :D

[Jon Wehrenberg]

I'll pass along some information relative to master battery switches.

The bus has battery disconnects. Generally on DDEC buses there are two, one main and a second for the computer.

I presume the house batteries have been provided with disconnects by the converter. But as an owner give your battery cables from the batteries to the disconnects or master circuit breakers a very close look. The cables between the batteries and the CB or disconnect are unprotected and if they come in contact with the bus chassis that creates a short circuit capable of melting steel. Make certain the unprotected battery cables are secured and the insulation is free of defects. I know for sure that if the positive cables come in contact with a ground such as the chassis the heat generated will cause the insulation to burn with the end result being a fire.

Please inspect your coach to make sure that cannot happen.

A second comment is particularly relevent to coaches that have been modified, but can be applicable to any coach. It is possible to have battery loads that do not go through the master disconnect switches or the main CBs. I have seen coaches with various wires going directly to battery terminals. It is possible and even probable these wires power devices that may not even have circuit protection. At the very least, these wires should be reconnected to the load side of the master switches, and then should have a circuit breaker or fuse right at the connection point.

There may be some loads that you never want disconnected, but I cannot think of any important enough to risk the coach.

[hhoppe]

Jon's correct on the power available to melt steel. I carry a "Mig Master" Wire welder in my off road jeep. It provides enough power to make good emergency welds with just one 12V battery. Think how much power 4 batteries connected to produce 24V would have. Always disconnect the ground wire first before touching other connections on batteries and the ground should be the last to be connected. Gases from batteries are explosive and will make a mess you won't forget if you still have eyesite afterward. Think of them as small bombs.

[Omnitech]

Even with the Prevost 12v and 24v (one of each) disconnects off, you have a parasitic draw on the chassis batteries that will pull them down in less than two weeks to a point where they will not crank the bus. The only good solution to this is to install (if you do not currently have one) a charger for just the chassis batteries. All you need is a couple amps at 24v to do the trick.

With the switches on, key off, the batteries will last less than 3 days before they are too low to crank.

[Omnitech]

I have been an Avionics technician, RV electrician, and electronics technician for a long time. I have been doing this for over 25 years. I do not mind being called "Sparky", because for most people it is out of respect for the those of us who brave the mighty electron for the edification of mankind.

Seriously, most people consider what we do as nothing short of magic, and to tell you the truth, sometimes it feels a bit like it. "Any sufficiently advanced technology is indistinguishable from magic". Food for thought.

[garyde]

My chasis batteries last a long time w/o charge as long as I remember to turn off the toggle switch above the battieries. My Coach batteries will stay up if I keep the inverterson and the Coach plugged in. I have never completely shut down the entire coach, but I have accidently un plugged the coach and had the coach battiries go dead in less than 12 hours.

[Omnitech]

You may have the onboard charger for your chassis batteries installed by the converter. Some do, but strangely, not all.

[Joe Cannarozzi]

I have a couple of questions.

Does it matter if you put a disconnect switch on the pos. or neg.?

What and where exactly is this parasitic draw that can take the bus bats. down even if you switch them off?

[hhoppe]

Joe: I'm no expert on this but when towing my Tahoe the manual said to pull certain fuses out of it before towing. I tried that, only to have a dead battery after towing. I next put a battery switch to disconnect the negative side of the battery. At the end of the trip, I had a dead battery. I changed the battery disconnect switch to the positive side and no dead battery after towing. I don't know what happens, but I like the results. I'm sure Jon or one of the electrical experts will solve this one.

[Omnitech]

The parasitic draw is from a keep-alive for the engine and transmission electronic control units. While the draw is not much, it is enough to deplete the chassis batteries over time if they are left unattended. The chassis batteries are designed for cranking amps, and do not have the long-term amp hour capacity that is usually associated with battery types used for house loads.

The cut-out switches are put on the "hot" and not the ground. If you were to put the cutout on the ground circuit and found yourself touching a battery negative post and chassis ground at the same time (as in leaning over the batteries to get to something during maintenance or troubleshooting) you could find your body as part of the ground circuit.

[Joe Cannarozzi]

O/K so it is the pos. side for the disconnects. I have an all mechanical, no computer bus so I should not experiance this particular draw problem if disconnected:)

[garyde]

Hi Joe. What's becoming more and more prevalent on the newer Conversions is more and more electronics with computers. All of these need to have UPS(un-interrupted power supply) to retain memory. Therefore, they are connected before any disconnects. It is hard chasing them all down depending on the individual Convertors wiring methods.

[Jon Wehrenberg]

Mastr teknishn,

Before everybody goes a little crazy relative to your comments about parasitic draw on the Prevost batteries I think your statement should be amended to reflect "on some coaches".

I have had two Liberties. I rarely turned the master chassis switches off on either coach. I never had the batteries drawn down.

Specifically, I parked the coach on May 15, and it was not shut off. The switches remained on and there was no trickle or maintenance charger providing power to the bus batteries. On Aug 15 I started the bus for the trip I am on right now. It fired right up.

I did find on the first Liberty a home made attachment a previous owner added to the chassis batteries (I forget what it was for) and it drew the batteries down in one week. I removed the load and from that point on I never had to worry about shutting off the bus chassis.

I do not think my experiences are unique.

[Joe Cannarozzi]

Here is a easy solution to needing power outside with only a short extension available:eek:

1541

Deb came home and said, are you sure you know what you are doing? I said, you better hope so:D

Installing lower, outer access door/louvers for a propane fridge that originally did not exzist. Show and tell to come later.