Fuse and size - auxllary battery

[dennislbrooks]

I have an auxilary battery setup like would be on a camper special. It has a solenoid isolating the auxillary when the key is off. Key On connects the 2 batteries for charging.

I run my radio settings and 2 amps off the auxillary.

Ok --- key on also then connects the 2 batteries for starting. I have a 4 gauge copper connecting positives on the 2 batteries ---- thru solenoid.

For added safety should I fuse this 4 gauge ---would be on the main battery end and if so how many amps? 120, 150, more?

[homemade87]

I would not . Your main battery to the starter is not fused . Just be sure the wires are secure and not moving and rubbing on something . What I would do is fuse whatever comes off the aux battery .

[dennislbrooks]

I do have everything fused off the auxillary battery, a 5 amp for radio memory and amps turn on, 40 amps for one amplifier and 80 for the other.

The main battery pulloff is fused 30 amps for the ignition --key on. This fuse operates the ignition, radio, heater fan, and starter solenoid/ auxillary solenoid - I think that is all. The radio and heater fan are also fed thru the fuse block. Fuse block is normal.

[homemade87]

I think you are good to go as is . From the sounds of it , what you have is what I would do .

[67 Burb]

If I was to install an auxiliary battery, I would want to keep it out of the starting circuit. Something like this:

[dennislbrooks]

I think I should be able to do that by just adding a relay to my solenoid and using the relay to interrupt the key on/start wire to the solenoid. If I run a wire from the key starter terminal to relay 86? 87A would be in my ON circuit. Then what?? I will have to do some testing on a relay. I just have a 3 wire solenoid. 4 really but the other post is 12v on for coil. A switch would do the same but I would have to remember to turn on and off.

Will ponder this.

Will this work?
87a to my solenoid
30 to key ON
86 to key start
85 to ground

[67 Burb]

In my setup, the isolation relay is grounded through pin 87A (which is normally closed) and pin 30 (common) on the control relay, so when the ignition is turned on, the isolation relay is energized. When you turn the key to start position, the control relay energizes and opens 87A, shutting off the isolation relay as long as the engine is cranking. When you let go of the key, the control relay shuts off, closing 87A and the isolation relay energizes and stays energized as long as the ignition is on.

Yes, a wire connected to the start wire from the ign. switch to #86 and ground #85 controls the control relay.

If, for whatever reason, you could put the control relay on the positive side of the isolation relay.

Let me know if I'm giving too much or not enough info, because I never know how much knowledge someone has with wiring and relays, etc.

[dennislbrooks]

I should be able to do all this under the dash --add relay to interrupt the key On hot wire to my current isolation relay. In pic left big term to main battery +, small white wire to Key ON, and right big term to aux battery +. This is a continuous use solenoid.

Add relay under dash --- 30 and 87a spliced into small white wire from key On, 86 to Key start, and 85 to ground.

[67 Burb]

Are you using that starter solenoid as the auxiliary battery isolation relay? I don't think a starter solenoid is meant to be used in a continuous duty application. That big relay in my photo in post #5 is rated as continuous duty.

Check this discussion out: https://expeditionportal.com/forum/t...olenoid.76484/

[dennislbrooks]

Yes the relay shown is rated as continuous duty like for a golf cart, snow plow and is rated 150 amp continuous - 300 amp max. Been there in use for over 6 years.

[67 Burb]

That's good, I thought it was just a starter solenoid. My bad. haha

[dennislbrooks]

67Burb, I do not use the auxillary battery much with the truck off so I probably will leave it as is for now. But thanks for the suggestion should I develop a need for it.