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clint

Posted 9/15/2015 09:48 (#4790122)
Subject: electric help? wiring a compressor on truck

Georgetown, Kentucky

I have a service truck w a 13hp elct start Honda engine compressor.

it has a battery tray in the walk in part on the truck. I forget to charge it. a lot.

can I run a heavy welding style wire to the front batteries and have the rear charge? then run a disconnect and turn cut out the compressor lead except when actually starting and running? I would like to run the fuel tank pump off this same lead

would this work? what do other guys do?

jd4930

Posted 9/15/2015 10:21 (#4790155 - in reply to #4790122)
Subject: RE: electric help? wiring a compressor on truck

Central ND

That's how we did ours

ccjersey

Posted 9/15/2015 12:14 (#4790283 - in reply to #4790122)
Subject: RE: electric help? wiring a compressor on truck

Faunsdale, AL

We have two different trucks with electric start equipment permanently mounted in the back. Both of them have no battery in the compressor or whatever, they are just connected to the vehicle batteries with a 4 gauge copper cable and grounded directly to the frame. After all, if the truck won't start, you cannot take the welder, compressor or whatever where you need to use it anyway. The small 12 volt garden tractor size batteries used in lots of this type equipment don't have a very long life here, so much happier just eliminating the batteries.

A disconnect might be nice, but. Don't have any. One fuel pump we had came with a fuse to put

Edited by ccjersey 9/15/2015 12:18

razorsedge2003

Posted 9/15/2015 14:09 (#4790395 - in reply to #4790283)
Subject: RE: electric help? wiring a compressor on truck

Fowlerville, Mi

I did this also. Works good. Truck has main battery disconnect switch.

Hayhauler

Posted 9/15/2015 12:20 (#4790288 - in reply to #4790122)
Subject: RE: electric help? wiring a compressor on truck

Northeast CO

I have a compressor with electric start on mine, its wired directly to the battery with 4 gauge wire and a circuit breaker. I also tied my fuel pump into it as well, works fine.

Indianajones

Posted 9/15/2015 12:22 (#4790290 - in reply to #4790122)
Subject: RE: electric help? wiring a compressor on truck

I have wired a couple service trucks and used the battery doctor isolator so that the rear battery does not drain the front starting batteries. Used #4 battery cable and had good success.
http://www.batterymart.com/p-acc-20092-battery-isolator.html?utm_so...
INDY

KWinWCIL

Posted 9/15/2015 19:34 (#4790725 - in reply to #4790290)
Subject: RE: electric help? wiring a compressor on truck

Vermont, IL

My service truck has a Lincoln Ranger 8 welder as well as a Honda powered air compressor. Both of these share a full size battery which also powers the 12V fuel transfer pump. It in turn is connected via a battery isolator to the trucks alternator. So, truck engine charges the aux battery and if aux is discharged it doesn't affect the starting ability of the truck.

Fingers77

Posted 9/15/2015 12:39 (#4790316 - in reply to #4790122)
Subject: RE: electric help? wiring a compressor on truck

We just use left over large gauge wire and run them directly off the truck batteries. No isolator needed, and haven't had a need for a shut off... yet.

Gerald J.

Posted 9/15/2015 13:16 (#4790354 - in reply to #4790122)
Subject: RE: electric help? wiring a compressor on truck

There are multiple solutions that will all work.

You can run welding cable (2 or maybe 4 gauge for sure larger) from the truck battery to the compressor and remove the compressor battery. Start the compressor from the truck battery. A bigger wire means less voltage drop and better cranking. This is simplest.

You can run a compressor charging wire that is isolated when cranking the truck engine. You don't need as fat a wire, probably 8 or 10 gauge, but you do not want that connected when the truck is cranking because the wire can't survive carrying a big fraction of the truck cranking current and the small battery at the compressor might not survive such happenings either. On my pickup when running a second battery for amateur radio, I connect to the trailer outlet power where there is a battery charge line that is only powered when the truck engine is running. That's standard in a RV trailer connector for charging the trailer battery and preventing it trying to help start the truck engine.

Without the RV trailer connector and circuit you can make one. Add a T to the oil pressure sensor plumbing and mount a switch that closes on pressure rise. NAPA has some, I have one here somewhere. Use those contacts to apply power to a 30 or 50 amp headlight (cube) relay to connect the compressor battery to the truck battery only when the truck engine is running. And that can be 8 or 10 gauge wire since its protected from cranking current.

Before the computer in the trucks did the RV battery charging isolation, it was common to use an alternator isolator that basically is two huge diodes. Anodes to the alternator, and one diode cathode to the truck battery and one to the RV battery. The alternator has to put out more voltage to correct for the voltage drop, but if wired right with voltage sense on the truck battery side of the isolator it will never notice the addition of the isolator. The diodes keep the truck from drawing power from the RV battery and the RV circuit from drawing power from the truck cranking battery so the wire is protected from cranking currents and using the RV battery won't run down the truck starting battery.

There probably have been slightly smarter RV battery isolators that don't have the voltage drop of the diode isolators based on precision sensing of alternator voltage to connect the RV battery only when the engine is running. I think the oil pressure switch is easier to setup if that isn't already in the truck's computer.

Running fat enough wires to crank the compressor from the truck battery can be the simplest though the wire cost can be significant. It reduces the batteries needing service which is a good thing. The oil pressure switch and relay isn't very complicated if you can locate the engine oil pressure sensor and find suitable plumbing to add the oil pressure switch.. If the truck has the factory towing package the RV trailer circuit or receptacle has the isolated battery charging wire and wouldn't be complicated to wire. The other isolator schemes are more complex to wire.

Gerald J.

biggrntractor

Posted 9/15/2015 20:17 (#4790838 - in reply to #4790354)
Subject: RE: electric help? wiring a compressor on truck

Northern Illinois

Have a 13' Ford 6.7L. We have a HD battery disconnect to turn the whole body on/off which powers the welder. Have done it this way for years. We bought a Kohler welder with the fuel injected, electronic ignition. the ECM on the welder smoked twice. Of course the Kohler dealer blames truck power. Have not had other items due to direct power from truck. I am curious what is actually the problem. Welder had the 2 failures with less than 10 hrs. of use....Don't use it much.

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