| [GMCnet] Wireless air controller with an AC compressor [message #141555] |
Mon, 29 August 2011 14:24  |
glwgmc
Messages: 1014
Registered: June 2004
Karma: 10
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Senior Member |
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My 78 royale originally came with two 12vdc compressors and electrically operated solenoid valves to control the pressure in the rear air bags. When I bought the coach one of those compressors was bad so I just put Schrader values in the ends of the air bags as a temporary fix. Ten years later they were still there and I found it more convenient to air up my bags with a small 120vac air compressor running off one of my inverters. It was much faster than the stock system since the 120vac compressor displaced so much more air than did the 12vdc units. The downside was I had my body near the air bags every time I added or subtracted air and that is a dangerous place to be if one of those air bags decided to burst unexpectedly.
A while back several of our members reported good success using a wirelessly controlled air manifold that integrates a radio, pressure sensors, two air valves and a control relay into one nicely done package. The hand unit is battery powered and the included wire harness features what appears to be a good quality sealed power relay rated for 30/50 amps. While the tech support people tend to give out confusing and sometimes contradictory responses to questions, most users report adding a small air tank, a pressure lease safety valve, air bag shut off valves and a one way check valve to prevent air from leaking back through the valves in the head of the compressor.
Given the good experience I have had for a decade of heavy use with the 120vac compressor, and the fact that I already had a small Senco air gun compressor and tank system that would fit into the same compartment where the original dual compressor unit fit, I decided to use it instead of a 100% duty cycle Valair or other good quality 12vdc compressor. I already had the inverter capacity and a 120vac inverter power line easily accessible so that made my decision easier. Besides, if something does go wrong I can walk into any big box store in the country and buy a replacement Senco unit including the compressor, air tank, safety valves, etc. for $100 to $150 where a 100% duty cycle Viair or other quality 12dc compressor has to be ordered and is priced more like $250 to $300 by our major suppliers.
A Valair compressor with about the same air output as this Senco unit draws 19 amps DC when running. That is right at the limit for a 12 gauge stranded wire. If the run on the DC side is more than a few feet, voltage loss on the DC side will cause the amperage to go up which will exceed the capacity of a 12 gauge stranded wire. So, to be safe it would be best to wire the 12dc compressor with 10 gauge wire. The supplied harness uses 12 gauge wire and the power relay is sealed to the existing harness so it would be difficult to replace.
Using an inverter to power the 120vac compressor means that all the high dc voltage flows just the short distance from the battery to the inverter. The AC power run can be any good quality 3 wire extension cord. The Senco compressor system I used only draws a maximum of 4 amps AC and because it is a simple electric motor with no electronic controls, it really doesn't care what wave form the inverter puts out. When running it draws about one half an amp hour out of my batteries for each minute of operation and even filling the bags from empty requires only a few minutes of operation so it is not hard on the batteries at all.
I removed the air pressure on/off switch and the regulator from the Senco unit and wired the AC from the inverter to the power relay on the kit harness to switch the hot leg. Air goes directly from the compressor to the tank and from the tank 10" to the inlet on the wireless air pressure control manifold. From there two air lines run to a shut off valve and then to each air bag. Very simple and far fewer places where air can leak than in the stock setup.
In use, the wireless air manifold receives a radio signal from the hand control unit telling it what pressure to maintain in each air bag independently. If the manifold requires more air to reach one of those pressures, it closes an internal switch which in turn closes the power relay causing the compressor to run. When the manifold senses the correct pressure it opens the internal switch to turn off power to the compressor. Not much to it and so far, it looks like it works well. No bleed down at all after 48 hours. My rear ride height is exactly where I set it.
The ride height sensors from the original system are not used so you are on your own to set the correct bag pressure to maintain proper ride height as you change weight distribution in your coach. The kit wire harness assumes you will power the wireless manifold with 12vdc switched power. It uses very small wires so there can't be much power draw and I don't know if there is any harm in leaving it on all the time or not. Since I did not have switched 12dc power handy in the rear of my coach, I installed a temporary on/off toggle switch to power the manifold. If I can get their tech support to answer the question I may leave it on all the time or bring a switched 12vdc power line to the rear when I get around to it.
Jerry
Jerry Work
The Dovetail Joint
Fine furniture designed and hand crafted in the 1907 former Masonic Temple building in historic Kerby, OR
Visitors always welcome!
glwork@mac.com
http://jerrywork.com
541-592-5360
Founder of the Southern Oregon Guild
www.southernoregonguild.org
Member of the Siskiyou Guild
www.siskiyouguild.org
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Jerry & Sharon Work
78 Royale
Kerby, OR
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