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post #1 of 11 Old 03-26-2012, 06:17 PM Thread Starter
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on-board air

I've been reading up on all the posts about on-board air and air horns. I'm getting ready to order mine, probably a 2.5 gal tank with the VIAIR 350C, but a question first. The electrical diagram VIAIR has shows the pressure switch driving a 40 amp relay for the air pump. If the pressure switch can handle 30 amps (The way I read the spec anyway) and the pump only draws 17 and the upfitter switch is fused for 30 amps (aux 1), Why do I need the relay?

BTW, my usage will be primarily for tires and air wrenches to change any flats I get on the road, with an occasional use of the air horn. I plan to mount the air horn behind the license plate and the tank and compressor on the passenger frame rail.

2012 F250 CCSB w/Nav
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post #2 of 11 Old 03-26-2012, 06:32 PM
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I have the exact same setup as your thinking and I'm not positive as to why, but I mounted it to my up fitter switch w/ 30 amps...

Convenience more likely!

What size tires do you plan to air up? A 350c is only capable of up to 33" tires... Or it will take a LONG time to get anything done. Plus a 350c is only a 33% duty cycle compared to a 450c which is 100% duty cycle... I found that out after I bought the 350

But I will say that for air horns a 350c w/ a 2.5 gl tank is PLENTY


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post #3 of 11 Old 03-27-2012, 03:24 AM
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Quote:
Originally Posted by countrylife View Post
Why do I need the relay?
Voltage drop.

The shorter the wire run from battery to compressor the less voltage you will loose to resistance in the wires. More voltage at the compressor means more air flow.
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post #4 of 11 Old 03-27-2012, 03:53 AM
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Quote:
Originally Posted by jdonovan View Post
Voltage drop.

The shorter the wire run from battery to compressor the less voltage you will loose to resistance in the wires. More voltage at the compressor means more air flow.
It has absolutely Nothing to do with voltage drop. A pressure switch is considered a control device and usually not rated for high current values....and by high current, I'm talking about the 17 amps that the compressor draws. Something else that has to be considered in this equation is the fact that when a motor starts, there is an inrush of current that is usually several times higher than the full load current......something that the pressure switch definitely cannot take over a period of time........thus the relay. A relay like the one pictured in the Viair electrical drawing, has a purpose....to take a small amount of current from the pressure switch and operate a coil, which in turn closes a set of contacts that are heavy enough to operate the compressor motor. Hope that clears it up for ya.
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post #5 of 11 Old 03-27-2012, 04:18 AM Thread Starter
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Ok, thanks. I'll have to re-check the pump specs, I'm after a 100% duty cycle. And I'll get the relay as well.

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post #6 of 11 Old 03-27-2012, 05:49 AM
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From what I saw when I looked the the 350C on Viair's website, it says that it is a 100% duty cycle.
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post #7 of 11 Old 03-27-2012, 08:57 AM
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VIAIR Corporation - 350C Part No. 35030 35033

Yes, the 350C is 100% dutycycle

Now for the wiring look at the Reccomened Wiring Diagram on that page also.

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post #8 of 11 Old 03-27-2012, 09:09 AM
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you guys are correct..... I bought a 325C


2005 F250 King Ranch Work Truck.

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Warren Comp Tranny w/ PI TC
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post #9 of 11 Old 04-22-2012, 08:56 PM
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Tool box mounted air system for horns and tire inflating

can I have some opinions on mounting compressor and tank in bak box tool box under back flip tonneau cover. For those not familiar with bak box its suspended from tonneau cover rail and doesn't sit on bed floor. I think it would be good mounted in toolbox but don't want to lose bed space of floor mounted box. Not quite sure if bak box its steady enough.I haven't actually seen one in person.Any help would be appreciated.
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post #10 of 11 Old 04-22-2012, 09:14 PM
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i have a 350c on my truck for airing my tires up between the trail and the street. it takes way too long to go from 15 to 25 psi.

it won't power air tools very well either

and the pressure switch my compressor came with was an inline 200psi switch which isn't designed to the the on/off switch for the compressor.
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