Battery Isolator Wiring

[richard5933]

I've now got my new 300-amp battery isolator and a spool of 4/0 battery cable. Before I take the plunge and connect this monster-sized puppy up to the bus, I wanted to run my plan past the gurus out there to be sure that I've got it right.

There are two 8D batteries currently sitting in the battery trays on my PD 4106. The positive of these is connected to a post on the side of the battery bay. A few other cables also connect to the same post. I disconnected all of them and used an ohm meter to verify that the fattest one is connected to the alternator. I assume the others feed various panels in the bus.

My plan is simply to take the cable running from the alternator from its current post and run it to the center post on the new battery isolator. I'll then run a new 4/0 cable back to the place where was previously in the battery bay. From the other post on the isolator I will run another 4/0 cable to feed the house battery bank.

The closest place I can put the isolator is about 5 feet from where the cable from the alternator currently connects. It's far too large to fit in with the batteries, and the next bay is filled with water tanks and plumbing. The round trip to/from the isolator will probably add about 10 feet to the cable length. I am using 4/0 cable and hope that the extra length won't be a problem.

Does this plan sound workable?

I've read online that it might be necessary to readjust the voltage regulator to increase the charge a tad to make up for the loss from the extra cable. Anyone else do the same?

I appreciate any advice on this.

Thanks.
Richard

[oltrunt]

Just a heads up and it may not apply to your system anyway.  I hooked up an isolator like yours on my bus only to discover that my alternator requires a direct connection to a battery to generate (energize)--which the isolator by its very nature does not allow.  I tried "fooling" the alternator with relays and such but no luck short of a SPDT switch which seems to defeat the purpose of the isolator.  Jack

[richard5933]

Just a heads up and it may not apply to your system anyway.  I hooked up an isolator like yours on my bus only to discover that my alternator requires a direct connection to a battery to generate (energize)--which the isolator by its very nature does not allow.  I tried "fooling" the alternator with relays and such but no luck short of a SPDT switch which seems to defeat the purpose of the isolator.  Jack

Jack,

Was yours going on a bus similar in setup to my 4106?

If so, then what options would exist other than either a manual switch or a solenoid?

The previous owner had hooked up a tiny isolator to the electrical panel using #6 or #8 wire, and it was totally insufficient to charge a 520 amp house battery bank. I have to do something better than that.

Richard

1964 PD4106-2412

[oltrunt]

No, different bus and I've used isolators before with no problem.  Someone here will know if your 4106 alt requires voltage to energize.  That specific answer is way above my pay grade.  Ha!  Jack

[richard5933]

To make matters more complicated, if the isolator will work on my bus, I wonder if I also need to separate the cable from the alternator to the battery from the cable which feeds the starter.

According to the wiring diagram the cable doesn't run from alternator directly to the battery and then back to starter...it runs from alternator to the battery by way of the starter. If I just disconnect the cable from the battery end and attach it to the center post of the isolator the starter will get no power.

It seems that I'll have to have a starter-to-battery direct connection, and then also a direct connection from the alternator to the center post of the isolator.

That is, IF the isolator will work on this setup. Hopefully someone will be able to let me know if the alternator will do its thing and charge the batteries when connected through the battery isolator.

[Melbo]

If I recall correctly when I had my isolator installed I had a momentary switch (push button) on the dash and now I would have to look in my old wiring diagrams but once the coach was started the not gen light would stay on until I touched the button. It would start the generator charging everything and it would keep charging until the coach was shut down.  If someone tells you how to wire it up you will be good to go.  If you need me to look it up I will be happy to see if I can find the information.

Melbo

[ol713]

   Richard;
         What you described is what I did 20yrs ago.  Still works fine.
                                               Merle.

[richard5933]

Melbo,

I would like to know where you put the jumper. In my mind it seems that a relay in the battery box to momentarily bypass the diode in the isolator is what you're describing - something that would allow 2-way current flow between the batteries and alternator. It would really ease my mind if you could confirm where that goes though, since all pieces of this equation are more expensive than I care to replace today.

Also, am I correct that I'll need to have cables making direct connections between the starter/batteries and between alternator/isolator?

-----
Merle,

Did you encounter any problems with your alternator charging? Mine already takes a few seconds at a raised idle to start charging, and I'm concerned that without the 2-way current flow between alternator & batteries it won't charge at all

Thanks to you both.
Richard