Charging battery for dump trailer

The only safe way is a dual isolator diode. One diode goes between the alternator and the truck battery and the second one goes between the alternator and the auxiliary battery. They are available at motor home parts places and any auto electric shop should have them and tell you how to hook them up. You can't use just any old diode. It has to be big enough to handle the full charging current of the alternator.

This way neither battery will pull the other one down. The only problem with this is that you get about .5 to .7 volts drop in the diodes. That lowers the charging rate from the alternator. This can be gotten around by hooking the sense wire from the alternators regulator direct to the battery rather than before the diode. That will raise the alternator output and correct for the voltage drop of the diode. Some alternators don't have that feature available though. Best to check with a local auto electric shop. They should be able to tell you just what you need.

Regards
Gary

However, having said that, 95% of the people who do vehicle wiring have no business doing it. I make real good money straightening out electrical systems.

Does that include putting out fires that you cause?

Sorry but "the metal ones" (solenoids) will NOT operate continuos duty unless they are rated for continuous duty. Starter solenoids are not rated for continuous duty. There are special solenoids available that ARE rated for continuous however, but they are not sold as starter solenoids.

You didn't tell us how you are going to be sure that solenoid is not going to be engaged when either the starter or auxiliary battery are being used so as to avoid cooking that #10 wire.

Regards
Gary

The way you will know the solonoid is not connected while the pickup is starting or the trailer is being dumped assumes two things. One, that whoever is running the dump trailer has shut off his Pickup and set the parking brake while he is out dumping, and the other assumes that the switched wire going to the solonoid to turn it on is on the accessory circuit from the ignition switch. You know, the one the radio is hooked to that turns off while starting. If someone wants to listen to the radio while dumping, then the solonoid will be connected and it may blow the 30 amp fuse.

I don't know where you get your metal starter solonoids but I get mine from an RV supplier for about $12 each and they last many years. They are not something special.

However, the simplest way to keep from blowing the fuse is like another poster said, Just unplug the trailer connector while using the dump.

Another thought for why using a 30 amp fuse is the trailer plug won't take much more anyway. I don't know where all this talk about fires came from unless everyone forgot there is a fuse in the circuit. Even if this was set up with the charging isolators (fancy diode) and no fuse with the pickup running you could heat the wire provided the pickup alternator was putting out enough to charge the trailer battery. The only change I make when using the isolators is using a 30 amp circuit breaker in place of the fuse. They will take more surge and will reset if tripped without operator input.

THen there is the really neat and fairly new setups that are electronic controlled. They will connect all batteries to the charger when any battery falls below 12.4 volts and will shed charging load as the batteries come back up over 13.2. Pretty neat for RV's as it takes wasted load off the chassis alternator.

Another thing that would be a good idea is to place a second fuse or circuit breaker at the auxiliary battery in the charging line. So if there would be a short in that wire in or near the truck the auxiliary battery would not fry the wire from that end.

The guy is almost back to his original problem. But the solenoid is a good idea rather that leaving the auxiliary battery hooked up all the time. If one or the other battery were low it would discharge the other if not disconnected while setting idle.

Yes the electronic combiners solve some of the problems that the diode combiners have but they are rather expensive.

I suggested the dual diode setup as it is pretty much fool proof in operation. You don't have to remember to disconnect anything or to turn the truck off etc. Both batteries are totally isolated from one another but yet both will get charged.

Starter solenoids are generally not continuous duty rated. If you buy the solenoids at rv supply places then you are probably getting continuos duty type solenoids. They are selling them for the purpose of battery combining etc. and not as starter solenoids. Even though everyone calls them that. There is a difference.

My point being that if you go into an auto supply place and just ask for a starter solenoid, you will probably get just that. And it will not last long. They look the same but the coil in the continuos duty units are different. They are designed for continuos operation where starter units are meant to only be energized for short periods at a time. Both will usually carry the same amount of current through their contacts. The coil load current will usually be less on the continuos duty unit.

Regards
Gary