marlinspike

I have air horns on my car (the kind with the small instant spool compressors). I wanted more volume, so I put on 2 more compressors (one for each trumpet). This worked, but I can't blow the horn at idle with the A/C on. Seems like the car can't spool up the compressors with the draw of the A/C going at idle.

The way the compressors are set us is they all share one relay, with a common ground, and are wired in parallel. If I gave each one its own relay, would that work more efficiently?

Fabrik8

I really don't know anything about air horns, but it should be an easy problem to solve if you give more info. What is the current draw of the compressors (each), what size wire are you using between the relays/horns/battery, how long is the wiring, and what is the battery voltage at idle? Also, what is the voltage at the relay coils at idle?

Adding another relay would only help if the problem was related to the relay and not something else like undersized wiring obviously.

White Devil

I know NOTHING about electrical wiring as it pertains to cars but this actually makes sense to me. Using an ohmmeter and a Haynes manual or service manual will tell you the limits of the draw youre pulling on the system, and if you try to draw more for other things it can tax your other accessories. You may also look into a more powerful alternator (I THINK... dont hold it against me... maybe a new Optima battery as well....) than the one you have if you run more accessories than this, but it really boils down to how much power you are currently drawing from that A/C unit and everything else.

With everything in your car "turned on", does it dim your lights/gauges/etc when you use the horns?

Killerzracing92

Larger wire going directly to the battery test it like that (or get a large swtich that can handle the amperage of the pump) . The larger the gauge the better I would Rec an 8ga or bigger.

I would say the relay is only rated for one compressor anyway correct? You will need a larger relay and a junction box to run both compressors.

Amperage is what these compressors need to run, voltage plays a role too. Make sure the ground is just as large or larger then the feed. Common ground has got to go unless its bigger then the feed.

Fabrik8

Alternator doesn't matter for short term current draw, because it will all come from the battery if it needs to.

White Devil

So possibly the battery as well, but it should more depend on how much hes drawing out for his accessories, correct?

Car electrical is not one of my strong points unfortunately. And I remember winches benefit from replacement batteries and alternators, some people even run extra batts and alts to handle the load.

Killerzracing92

Alternators run for a long time time compared to a compressor which is short term, as long as they dont draw 100 amps each they should be find on stock electrical.

Antother way to get better charging capabilites is to do the Big 3.

[youtube]iX9Rcq5DnKw[/youtube]

Jay

Big 3 can never hurt.

Here are the recommended maximum fuse ratings for the corresponding wire size.

1 awg 250 amps
2 awg 200 amps
4 awg 125 amps
6 awg 80 amps
8 awg 50 amps
10 awg 30 amps
12 awg 20 amps
14 awg 15 amps
16 awg 7.5 amps

IMHO, common point grounding is a good idea for all of the high current stuff.

Fabrik8

Those fuse ratings are for continuous current draw and are rated based on a certain length of wire and a certain temperature rise. They're extremely conservative ratings.

Jay

Source: http://www.bcae1.com/wire.htm