Battery Disconnects

[Bikestuff]

Gang,

I have another "Inquiring minds" type of question. The other day when the Newell guys were welding on my coach they said that they were going to turn off my power. (Unplug from shore, and turn "OFF" the engine batteries and house batteries. I understood that to mean turn the battery disconnects to the "OFF" position. Now is when it gets weird. They disconnected shore power and turned both disconnects to OFF. Yet...I still had AC power. My coffee maker was still working, I still had AC on my laptop. I told them...and they did some magic around the inverter to shut down power.

Talking to Jim G (Newell) I found out that the disconnect is on the Negative side of the battery and isolates the batteries from the ground. He said that they do this on aircraft and that is why Newell does this. On my coach, I think that there must be a path between the batteries and the inverter that does not go through the disconnect.

I am interested in the subject because I have been building an iPhone checklist app, and I was working on an Emergency Procedures checklist in case of an accident, fire, etc. One of the things that I want to in an emergency is to turn off ALL power to the entire coach. In my simple brain, all I had to do is flip those disconnects. Not so!

So...here are my questions:

1) Why is the disconnect on the negative side of the battery? Why not the positive side. Is there a downside to having two disconnect switches...one on the positive and one on the negative.

1a) Can I use the inverter panel to shut power down...it seems to keep providing AC no matter what I do to that panel. Is this correct?

2) Do you agree that in an emergency it is a good safety practice to shut power down to the coach?

Cheers,
bill

[Bikestuff]

ps. I have added my coach information to my signature...but my coach is a 2003 #653.

[RussWhite]

Well Bill - here is my 2 cents worth....

As far as current flow goes, it makes no difference which side of a battery is disconnected. If either side is truly disconected, no current flow - period!

There is no way your inverter should have kept supplying power if the house battery disconnect switch was opened. Not saying it didn't, just that it shouldn't. I had one occasion when my house disconnect clicked and I assumed it had opened, but it had not. It may be time for a new switch. If I were you I would keep at this one until I was convinced that when I opened the switch, the batteries were isolated and could not supply power. There may be a time when you want to shutdown all current quickly as you menitoned in some kind of an emergency.

Now I wondered about the negative side switching too and have my own theory. If you look at almost any battery bank there are more positive wires leaving running off to all kinds of places, than there are negative connections. I just theorized it was easier and involved less cables to open the side with fewer of them. But hey, it may be an airplane thing too.
I see a BMW bike in your signature. I have given up riding and my poor R1100RT just sits quicklly in the basement filled with good memories.
Russ

[Bikestuff]

Russ,

My theory is that someone connected something directly to one of the batteries and then bolted it to the frame. If that happened, then the inverters could have been drawing current through the wires associated with the "something". Sounds like a fire hazard just waiting to happen. Thanks for the encouragement. I will track this one down before I get on the road again. Will keep you guys posted.

Thanks!
bill

[prairieschooner]

Sounds very similar to what I experienced shortly after getting our '82! I installed a Source Isolation Switch for our HEART Power Inverter as a precaution (required on boats, not sure why it isn't required on RVs). I agree not so sure why they are using the Negative (-) side, I have made sure that the Battery Disconnect Switches are as close as possible to the Batteries and on the Positive (+) side.

[prairieschooner]

As a side note, I would question disconnecting the Negative (-) side. With the numerous systems supplying 12 Volts DC (Batteries, Chargers, and Conveters) I suggest that it would be better to disconnect the Positive (+) side or use a Double Pole Circuit Breaker or similar device to be sure that both sides (+ & -) are disconnected.

[Richard and Rhonda]

Too many common hobbies among the owners group. In the past I have owned (and ridden) R100S, K100RS, and finally a 76 R90S. All supporting my theory of the gearheads who appreciate well constructed pieces.

[Bikestuff]

My brother let me have his baby. He drove it from 5000 to 75000 miles. Now I am adding even more miles. The R1100GS is one amazing machine. It forgives my mistakes and makes me look like a better rider than I really am. It is the perfect compliment to my Newell!

[77newell]

Originally Posted by prairieschooner

As a side note, I would question disconnecting the Negative (-) side. With the numerous systems supplying 12 Volts DC (Batteries, Chargers, and Conveters) I suggest that it would be better to disconnect the Positive (+) side or use a Double Pole Circuit Breaker or similar device to be sure that both sides (+ & -) are disconnected.

From the perspective of electrical current it doesn't matter what side the disconnect is on, unless the current can freely travel from one battery pole out into the coach systems and back again there will be no flow. However, picture the following. I'm safety wiring the nuts on the lid of a battery box in a confined space. The disconnect switch was on the positive side. The wire is a bit wrapped up in my hand when it happens to touch a bit of the positive side of the battery. OUCH - expletive deleted, followed by more of the same. If the ground side of the battery is disconnected no harm occurs when any positive side wiring or shorts to the chassis happens. If the positive side has the disconnect switch any contact to ground (chassis) between the battery and the switch will result in lots of expletives deleted. When the disconnect is on the ground side about the worst that happens if the contact is made to the chassis between the battery and the disconnect is that power to the coach is comes on. This difference matters in only a few cases, but my scars from the burns would say when it matters it really matters.

77 newell, 2007 civic toad, happy campers

[jwe648]

Originally Posted by 77newell

From the perspective of electrical current it doesn't matter what side the disconnect is on, unless the current can freely travel from one battery pole out into the coach systems and back again there will be no flow. However, picture the following. I'm safety wiring the nuts on the lid of a battery box in a confined space. The disconnect switch was on the positive side. The wire is a bit wrapped up in my hand when it happens to touch a bit of the positive side of the battery. OUCH - expletive deleted, followed by more of the same. If the ground side of the battery is disconnected no harm occurs when any positive side wiring or shorts to the chassis happens. If the positive side has the disconnect switch any contact to ground (chassis) between the battery and the switch will result in lots of expletives deleted. When the disconnect is on the ground side about the worst that happens if the contact is made to the chassis between the battery and the disconnect is that power to the coach is comes on. This difference matters in only a few cases, but my scars from the burns would say when it matters it really matters.

77 newell, 2007 civic toad, happy campers

This would be a Simple diagram... the disconnect often times is a relay that would prevent arching

.

[Bikestuff]

Hi gang!

Well we have an answer. I am not sure it is a good answer, but it is an answer. In my coach (and we know that all coaches are different), the switch on the house batteries simply disconnects the 12 house stuff. (12 volt lights and such). It does NOT disconnect the inverters! There is a cable with a fuse running directly from the batteries to the inverters. In my case turning the disconnect switch did not interrupt power to the inverters. Jim G said that some of the coaches are done this way and in some of the other coaches there are separate disconnects to handle the inverters.

I was not comfortable with my arrangement so I asked Newell to put in a separate disconnect for my inverters. So now, when I want to shut down power to the coach, there are three disconnects. 1) engine batteries, 2) House 12V and 3) Inverters.

My brother says that is "A lot of sugar for a dime", but I will sleep better knowing that I can easily kill all the power in the coach. Thanks to all you guys for your input.

Cheers,
bill

[Bikestuff]

Man, those Newell guys do some pretty work!

[77newell]

Originally Posted by jwe648

This would be a Simple diagram... the disconnect often times is a relay that would prevent arching

.

Jimmy: the airplane I was working on when burned was wired just as you described and the DC disconnect was "off". However, power is still on from the positive terminal on the right-hand battery through to the connection on disconnect. If that power can somehow reach the chassis by a short from worn insulation, a wrench on the battery terminal touching the chassis, or as in my case the tip of the safety wire touching an exposed lug, there will be plenty of heat instantly.

My reason for following up on this is that there may be people unfamiliar with how these systems work that will assume that since the disconnect is in the "off" position that it is safe to freely work in what is still a danger zone. When the disconnect is on the positive side the only safe way to work on the positive side up to the disconnect switch is to disconnect the ground side from connection with the chassis. If that is done there is no danger of repeating my hot time in the ole airplane.

77 coach, 2007 Civic toad