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-   -   What side of battery to isolate on chassis battery (https://www.irv2.com/forums/f103/what-side-of-battery-to-isolate-on-chassis-battery-108244.html)

Vegasguzzi 11-14-2011 07:48 PM

What side of battery to isolate on chassis battery
 
Dealer just replaced my chassis batteries and talked me into placing a disconnect switch on the chassis battery. However he placed it on the ground side. Seems backwards to me. I think the disconnect should be on the positive terminal. I now have my cockpit instrumentation lights on when my chassis and house batteries are disconnected. I also have terrible static on my cameras.

Hew are Newmar chassis batteries normally isolated?

Skip426 11-14-2011 10:01 PM

Chassis battery, disconnect on my 99 DSDP,on a freightliner chassis, is a ground side disconnect, installed by freightliner, and refered to in the wiring diagrams as a mechanic's safety switch . Primary use is for the mechanic to disconnect the batteries when servicing the engine or trans. Ground side interupt is commom, because the load on the ground wiring is less, than the load on the positive cables, and re -connecting a ground produces less arcing. So the amp rating can be lower for the switch and it will last longer. All instructions for servicing a battery say to disconnect the ground wire first. Contact the installer on your two problems , they may have missed a ground wire , lights still work, or made a poor connection, static in B/U camera.

OneRVer 11-14-2011 10:17 PM

Hmm, sounds strange to me but........ I have always been taught that you disconnect on the hot side, upstream of the components. I wonder if they install a light switch down stream of the light. JMHO. Your lights and camera are grounded to the chassis and so is your chassis battery.

GaryKD 11-15-2011 04:39 AM

Hi Vegasguzzi,
Does your coach have a "store" button/switch? If so, what was the reason for installing the new switch? Are you trying to solve a problem by installing the switch?

Iron Man 11-15-2011 07:10 AM

Wasn't there already a switch or circuit breaker for the chassis batteries? I thought all the Newmar diesel pushers had them.

ottffss 11-15-2011 08:35 AM

Quote:

Originally Posted by Skip426 (Post 1009428)
...because the load on the ground wiring is less, than the load on the positive cables...

:confused: Just an important point of clarification, pretty sure the physics books will NOT agree with this statement... The load on the positive will (has to) equal the load on the negative. (Aside from trivial internal leakage.)

Vegasguzzi 11-16-2011 08:00 PM

Dealer told me they suspected leakage from the chassis batteries. My Ventana has an isolation for the house battery. That's why it is so curious to isolate the positive for the house batteries and the negative side for the chassis. If my engineering classes memory is correct this sets up a "floating" dc system and would explain why my instrument cluster is still energized with both house and chassis batteries in the storage mode. Just wondering if this was standard on Newmars

OneRVer 11-16-2011 08:19 PM

Quote:

Originally Posted by Vegasguzzi (Post 1010940)
If my engineering classes memory is correct this sets up a "floating" dc system and would explain why my instrument cluster is still energized with both house and chassis batteries in the storage mode.

Your memory is serving you correctly. :thumb: Wish mine would. :blink:

garym114 11-16-2011 09:23 PM

Sounds like your dealer needs to fix something.

Skip426 11-16-2011 09:38 PM

Quote:

Originally Posted by OneRVer (Post 1009436)
Hmm, sounds strange to me but........ I have always been taught that you disconnect on the hot side, upstream of the components. I wonder if they install a light switch down stream of the light. JMHO. Your lights and camera are grounded to the chassis and so is your chassis battery.

As an experiment , USING CAUTION of course, disconnect the positve battery cable, leaving the ground cable hooked up. Then lay a wrench across from the frame to the positive battery terminal. Then with the positive terminal hooked up disconnect the ground cable , then lay a wrench across from the frame to the positive,or negative, terminal. Compare results.
In a 12 volt system a switch could be installed on either side of a load to complete the circuit, but because most load/lights are grounded directly to the frame, not wired back to the battery, the switch is installed in the power wire.

Skip426 11-16-2011 10:04 PM

Quote:

Originally Posted by ottffss (Post 1009609)
:confused: Just an important point of clarification, pretty sure the physics books will NOT agree with this statement... The load on the positive will (has to) equal the load on the negative. (Aside from trivial internal leakage.)

Perhaps, not the best discription on my part , I never studied physics, just auto mechanics. In almost every vehicle I ever worked on the ground cable was smaller than the power cable, in high load situations; engine cranking for example ; the positive cable is subjected to more heat, than the ground. Could we agree on that ?

Qwert66 11-17-2011 07:38 AM

What goes in must come out - period. Either in the form of power and/or heat etc.. The longer dedicated positive starter cord may explain why its bigger vs the many ground connections and their shorter lengths.
Just my opinion.

SuperMike 11-17-2011 07:49 AM

Quote:

Originally Posted by Skip426 (Post 1011013)
As an experiment , USING CAUTION of course, disconnect the positve battery cable, leaving the ground cable hooked up. Then lay a wrench across from the frame to the positive battery terminal. Then with the positive terminal hooked up disconnect the ground cable , then lay a wrench across from the frame to the positive,or negative, terminal. Compare results.
In a 12 volt system a switch could be installed on either side of a load to complete the circuit, but because most load/lights are grounded directly to the frame, not wired back to the battery, the switch is installed in the power wire.

Unless I have misunderstood you, and that of course is possible, DO NOT UNDER ANY CURCUMSTANCES PERFORM THIS TEST. As I am reading it with the ground still connected, you are saying lay a spanner from the chassis (ie the ground) to the positive terminal. Every body take cover. :hide:

GaryKD 11-17-2011 08:27 AM

For my coach the separation of chassis 12 VDC and coach 12 VDC is a great theory, but in practice is not true. I can turn off either the coach store or the chassis kill switch and there will be some (small amount) of VDC on the side I turned off. I'm not sure if this the case on other coaches, but this is how my coach is. Because my coach is used year around this mystery has never made it to the top of my to do list.

ottffss 11-17-2011 09:01 AM

Quote:

Originally Posted by Qwert66 (Post 1011183)
...The longer dedicated positive starter cord may explain why its bigger vs the many ground connections and their shorter lengths.

And you would be exactly correct.

A phenomena of lower voltages like 12v is that "line loss" (due to length) can be exceptionally significant, especially under high amp draws. Hence the larger (and typically longer) positive cable (running all the way to the starter motor - the mega amp draw item).

skip - I am only trying to be technically correct and to provide the best information possible.

wa8yxm 11-17-2011 11:18 AM

Electrically it does not matter if you put it in the negative or positive leads. Either way when the disconnect is open there is not circuit to the batteries.

HOWEVER: if you put it in the NEGATIVE (Chassis ground) lead then you open the disconnect and remove before disconnecting the batteries from the coach.. now, if you are thinking (Which you won't be cause you'll be upset at haveing to buy new batteries... or at least that's your excuse) you will lift the Negative lead first.. But if by some chance you happen to lift the POSITIVE lead first.. and the wrench slips and shorts to chassis.. no damage. Since there is no "Return path" from chassis to battery.

Thus Negative is more then likely the better lead.

"007" 11-17-2011 06:51 PM

You will have a chassis battery drain from your LP detector if you do not operate the switch in your tank display area.
https://www.irv2.com/attachments/phot...icture_158.jpg
There is also battery drain from ECM and radio system you may have but small solar panel will help eliminate this drain.
It has never been necessary to add a battery cut-off, off any battery on Newmar coach it only adds a potential problem in the future.

Vegasguzzi 11-17-2011 07:35 PM

Dealer called me today and informed me they figured it out. They found a couple extra ground wires coming off the chassis batteries which were allowing current flow from one battery bank to the other. The cameras went out because of their cycling the electric so much and all they had to do was reset the monitor. Don't know what the final cost to me will be. Thanks for the discussion.

Vegasguzzi 11-17-2011 07:36 PM

I'll get my coach back in time to head to Ann Arbor for the The Game on the 26th. Go Blue!

"007" 11-17-2011 07:42 PM

DO not know how dealer found extra battery leads if he hooked up the same as original batteries were hooked up.
In Quick Tips there are pictures of different battery hook-ups and this thread will explain how your BIRD System works for charging all your batteries.


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