Heavy Duty Battery Disconnect

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Heavy Duty Battery Disconnect

March 15, 2012, 03:59:35 pm

It's not a real pain to physically disconnect the ground terminals from the start & coach batteries every time I go to the coach storage facility. But, it's getting to me after 8 years. I need some input on the selection and installation of two heavy duty battery disconnects, one for the two start (Optima Red Top Group 34's) and another for the two coach batteries (Deka Gel 8D's).

Can the attached link's disconnect be mounted to the battery's terminal? Or, does it have to be mounted to a wall, then route the ground cable to the unit & from the unit to the battery negative ground terminal?

Amazon.com: Moroso 74101 Heavy-Duty Battery Disconnect Switch: Automotive

Thanks,

Peter

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Re: Heavy Duty Battery Disconnect

Reply #1 – March 15, 2012, 04:20:11 pm

I have found the Cole Hersey products for battery disconnect to work fine, so here is the general catalog, just scroll down to battery products. They seem to be the only disconnects used on fire trucks, a manual rotary type.
Part # 75908 is rated 2000 A / 300 A continuous.

Catalogs | Cole Hersee - Littelfuse

Dave M

Re: Heavy Duty Battery Disconnect

Reply #2 – March 15, 2012, 04:28:17 pm

I second that. We would only use Cole Hersey products when I was in the municipal fleet world. Put them on all emergency and marine equipment and anything else that needed their items. Cannot remember any of their switches failing.

Keith

Re: Heavy Duty Battery Disconnect

Reply #3 – March 15, 2012, 04:35:07 pm

See below. I got these at Camping World. They have several models, so be sure to get the right one if you go this route. They have worked fine for the house batteries. I only needed one, but ended up with three.... it took me awhile to figure out how to install them. But with three I can isolate each battery if need be. I think they cost in the $25 range.

Re: Heavy Duty Battery Disconnect

Reply #4 – March 15, 2012, 05:21:13 pm

Thanks for the input. I located the switch with the rating I think will work well for the start & house batteries, although I think it may be overkill for the house batteries. But what the heck. Here they are:

Master Disconnect Switch, 75908, Cole Hersee

Now all I need is to figure out how to mount these things in the battery bay and the engine compartment.

Peter

Re: Heavy Duty Battery Disconnect

Reply #5 – March 15, 2012, 05:27:53 pm

Peter,

Remember that the engine must not be running when you disconnect the batteries. Disconnecting with the alternator charging will immediately damage the alternator diodes.

Keith

Re: Heavy Duty Battery Disconnect

Reply #6 – March 15, 2012, 05:33:16 pm

Quote

Remember that the engine must not be running when you disconnect the batteries. Disconnecting with the alternator charging will immediately damage the alternator diodes.

Yes indeed. My shutdown procedure once in the storage slip won't be altered much. It will just be faster without having to get out the wrench and removing the ground terminals from the battery banks.

Peter

Re: Heavy Duty Battery Disconnect

Reply #7 – March 15, 2012, 05:47:09 pm

Peter,

Assume you have no 120 VAC where you store it and that you are indoors so solar panels won't work.

Those are choices #1 and #2 with complete disconnect being #3.

Brett

Re: Heavy Duty Battery Disconnect

Reply #8 – March 15, 2012, 05:57:24 pm

Brett,

I have no available AC power other than the 8Kw coach generator. And yes, the roof does kill the idea of a solar charger (which would be my personal preference). I have not encountered any problems with the disconnect process. The Cummins C8.3 is a mechanical engine. And, I don't really know how the disconnect affects the Allison transmission. So far (knock on wood) there have been no transmission issues either.

I usually run the generator (20 to 40 minutes usually) and take a current reading at the batteries to ensure the alternator doesn't need to work too hard on start-up.

Peter

ps Should I be reading the current at the alternator?

Re: Heavy Duty Battery Disconnect

Reply #9 – March 15, 2012, 05:59:25 pm

Peter,

No need to read amps at alternator. Your idea of exercising the generator BEFORE starting the engine is a good one. That will get the batteries back to a reasonable level of charge before starting.

Brett

Re: Heavy Duty Battery Disconnect

Reply #10 – March 15, 2012, 11:36:02 pm

Quote from: Peter & Beth – March 15, 2012, 05:21:13 pm

Thanks for the input. I located the switch with the rating I think will work well for the start & house batteries, although I think it may be overkill for the house batteries. But what the heck. Here they are:

Master Disconnect Switch, 75908, Cole Hersee

Now all I need is to figure out how to mount these things in the battery bay and the engine compartment.

Peter

I have been thinking about installing disconnects since we do not have access to AC power in our covered storage area and we do not have solar.

We have 2 red top batteries for the chassis batteries and 2 flooded 8Ds for house batteries. Do I need to install a disconnect on the negative terminal of each battery or on only 1 negative terminal in each set? If only on 1 negative terminal, how can I determine which negative terminal I should install it on for each set?

Thank you.

Re: Heavy Duty Battery Disconnect

Reply #11 – March 16, 2012, 06:33:23 am

I was told by FT a long time ago not to put one inline. That disconnecting is the better alternative.
In fact the tech told me he would be fired for installing one.

Re: Heavy Duty Battery Disconnect

Reply #12 – March 16, 2012, 12:56:24 pm

As to installing battery disconnect inline, Foretravel Motorcoach would neither confirm nor deny. This would be the owner's choice.

Isn't there a battery disconnect at entry step for DCV to certain coach circuits? However, if there is reliance on 12VDC for critical circuits (the 1997 U270 does not have any installed from the factory). Then one would have to be certain the coach can take such a break in these circuits.

In the U270, the Coach 12VDC circuits which feed even with the entry step switch in the off position are the propane detector and the refrigerator (I think).

Peter

Re: Heavy Duty Battery Disconnect

Reply #13 – March 16, 2012, 01:04:53 pm

I don't think that I would install a blade type disconnect near any flooded battery. Sparks and the hydrogen that off gasses when charging make a bad combination. JMHO
Gary B

Re: Heavy Duty Battery Disconnect

Reply #14 – March 16, 2012, 01:46:37 pm

Gary,
You're right about the possibility of sparking when using the blade disconnects. I believe that George's picture shows AGM's not liquid acid flooded batteries.

George, I would only use one of those disconnects at the ground wire to the batteries. With that ground disconnected, the circiut is broken to all batteries.

Peter

p.s. Use the other disconnects elsewhere. e.g. One may be used for the toad while towing...

Re: Heavy Duty Battery Disconnect

Reply #15 – March 23, 2012, 04:14:39 pm

Today I installed one of the Cole Hersee battery disconnects. I did the house batteries first. Tomorrow I'll do the start batteries.

I had to fabricate a connecting bar for the terminal to accept the switch. A couple pictures follow:

Re: Heavy Duty Battery Disconnect

Reply #16 – March 23, 2012, 08:27:35 pm

Nice installation. I can't tell from you photo if the aluminum mount also carries electric amps, if so there is a lot of current that will flow through the aluminum bar and single mounting battery clamp bolt.

I think start battery cables are 4/0 (0000) which are pretty big and can carry about 300 amps, some of which are needed for engine starter.

Re: Heavy Duty Battery Disconnect

Reply #17 – March 23, 2012, 08:42:33 pm

Barry,
I used steel stock to fabricate the bar. It is a 3/4 in. by 3/16 in. bar. I thought it would carry the current well...but not 100% sure.
Peter

Re: Heavy Duty Battery Disconnect

Reply #18 – March 23, 2012, 09:54:57 pm

Ideal would be silver clad copper bar,

Dave M

Re: Heavy Duty Battery Disconnect

Reply #19 – March 23, 2012, 10:01:33 pm

Dave,
Thanks for the input. Now I just have to find the silver clad copper bar x 2. And I thought I was finished...

Re: Heavy Duty Battery Disconnect

Reply #20 – March 23, 2012, 10:13:53 pm

I've never made any calculation to determine the size bar that would be needed for this project. Does this make sense:

4/0 copper wire cross section area must equal the cross section of copper bar?

Thoughts?

Oh, I can't locate any silver coated copper bar. This is as close as I get:

110 Copper Rectangular Bar | Cut 2 Size Metals - ESMW

Re: Heavy Duty Battery Disconnect

Reply #21 – March 23, 2012, 10:25:51 pm

That bus bar stock would be fine, and cross-sectional area provides the correct equivalence. Just wire brush before connecting and use dielectric grease.

Re: Heavy Duty Battery Disconnect

Reply #22 – March 23, 2012, 10:35:45 pm

You are probably ok, but there are bus bar amp web pages if you need rating info.

I think switch is ok for house battery bank as 100 amps is a lot of draw for house bank, except when starting with boost switch on.

But start bank is different story when hundreds of amps are needed to start with a cold battery.

But as long as you don't have a starting problem with the switch installed, you are ok.

I found this rating chart, but it was for copper. Electrical Bus Bar Ampacity Chart
Copper Busbar Ampacity Tables

Re: Heavy Duty Battery Disconnect

Reply #23 – March 23, 2012, 10:40:13 pm

Peter, I would first need to know the length of the needed bar, then one of our EE members should simply be able to tell you the correct size bar for the inrush current of approx. 1200 amp during initial starter engagement. I am certain the small bars in your pix would not make it.
Also, I would consider using the 4/0 copper welding cable (It is very flexible), would get the 4/0 ends that have the same size hole as your switch, then crimp and rosin solder correctly for a very fine connection.
A few ways of skinning the ole cat.
Cheers
Dave M

Re: Heavy Duty Battery Disconnect

Reply #24 – March 23, 2012, 10:44:39 pm

Dave, I only need a 2" long bar to make the connections. Then, at either end of this bar would be one 3/8" ID hole and a 1/2" ID hole to hook to the battery terminal on one end and the Cole Hersee battery disconnect at the other end.

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