Electrical issues

Ok so ive had this an air system installed on 2 trucks 450C on a 5gallon tank. On monday i went to leave work and i got a “service charging system” warning so i had the battery and alternator checked all good. so the only thing i got drawing off the battery is the compressor. so i started looking at that i found my connector got obviously HOT on both ends so im thinking something is wrong with the compressor i ran the system all summer pretty much daily without any issues. i will also add the tank and compressor are in a tool box thats covered. I also found that i was using a probably too light of a gauge main power was on a 12g according to the chart i should have used 10g so ill be changing that… but that still doesn’t answer the question of why it has worked thus far without issue.

The longer your wire, the fatter it needs to be. 12 sounds real small for a pump.

The warning could be due to an alternator that is about to fail but hasn’t yet, or any number of other problems that might be hard to diagnose because of all the computer systems in trucks these days.

Yeah but like i said ive been using 12 for the past 2 years without issue. although for safety im redoing it to 10g im only running one pump @ 20amps. I have it after the mega fuse on the battery. is that correct? im thinking i should add a separate fuse at the battery i have one at the relay/pressure switch

The fuse is there only to protect the wire. Think of it this way - if the wire shorts out and there is no fuse or if it is too big, the wire will burn because the battery is essentially a source of unlimited current (usually more than 3000 amps surge). The best place for the fuse is as close to the battery as you can get. If you have smaller control wires, they should have their own smaller fuse.

What’s the amp rating for your compressor? Sorry I don’t have a spec sheet in front of me.

makes sense ill have to add a fuse closer to the battery.

according to the spec sheet it draws 19amps

Here’s a good chart: http://assets.bluesea.com/files/resources/newsletter/images/DC_wire_selection_lg.jpg
If your wire is 15 feet or less, 10 awg should be good. Make sure the crimps are on solid - that’s another source of heat if they are loose.

15ft should be enough. i try to soldier and shrink rap as much as possible.

im wondering what would cause the pump to all of a sudden draw more current then it has in the past

I doubt it has changed much, but loose connectors will make amp draw go way up because they reduce the voltage to the compressor. It’s also possible that the wire has run hot but you didn’t notice since it was working.

With the bigger wire you will also have less voltage drop, which means the compressor might even run a little faster and fill your tank in less time.

In addition to keeping the fuse as close to the power source as possible, a general rule of thumb for safety is to upsize the wire by one gauge for the run you’re doing if you’re close to the maximum rated amperage on the wire for that length of wire.

Thus, if you’re close to 20 amps at 15 feet using 10gauge, move up to 8 gauge.

Also, make sure you’re using pure oxygenated copper wire, as copper clad aluminum, while cheaper, is also less conductive. If your only option is copper clad aluminum due to cost reasons, then upsize the gauge yet again.

Check your grounds. Make sure you have bare shiny metal. A ground with some corrosion will draw more amperage. That would explain the change. It was probably gradual.

EDIT: As mentioned above the fuse should be placed close to the power source. BUT, it has to be sized correctly. It must be rated smaller than the rating of your wire gauge & length. For example if the wire was rated for 20 amps and you had a 30 amp fuse, the wire would melt before the fuse blows. You want the fuse to blow FIRST.

my ground is a connected to the tool box via a self tapping screw nice and tight.

Try a better ground connection. Trays, toolboxes and other bolt on bits can be via rubber grommets etc. which can restrict a smooth path back to ground. Try running a wire straight back to the negative terminal on the battery or to a bolt point directly on the chassis.

If you can get hold of a multimeter try and measure amperage draw of the compressor when under load.

To help prevent corrosion at grounds, you may consider coating your metal-on-metal connections with dielectric grease. It’s inexpensive and VERY good defense against corrosion. If you’re in an area where brine/salt/sand are common in the winter, then you may want to do this several times per year (i.e. clean off the old stuff, clean up the connection, then re-coat) as a maintenance step.

This stuff is commonly called ‘bulb grease’. Don’t buy the little packets of it from the auto stores, instead, get a tube of dielectric grease from Amazon.com – you’ll get a lot more of the stuff for a lot less per oz that way.

Honestly, if you’re having issues I’d replace it all with 4 gauge welding cable.

There are plenty of brick and mortar (and online shops) that carry the stuff, and it comes in both red and black.


And I’m guessing your toolbox is bolted to a painted surface. Maybe there was some bare metal where you drilled holes to mount the toolbox - maybe enough to create a good path to ground. But those are the areas that corrode over time. Just sayin’ you might be better off with a connection to bare metal on the frame.