From: John De Armond Subject: Re: portable air tools Date: Sun, 15 Aug 1999 06:58:27 EDT Newsgroups: rec.autos.tech william Henry Grosvenor wrote: > > I'm looking for a good air tool set up. > Can anyone recommend a good compressor and tool setup that fits in a > truckbed and works off of an inverter? > TIA That's easy. None. Do the math. Figure with losses an electrical HP is worth 1000 watts. 1000 watts @ 13.8 volts is 73 amps, assuming a 100% efficient inverter. The 1000 watt inverter in my catering truck draws 120 amps at full load. It will barely start a 1/4 hp refrigerator compressor. A compressor motor may require as much as 6 times run current to start, even more if the unloader doesn't work. We haven't even looked at alternator capacity yet. You have several options. the best option is what some of the tire roadside service trucks use - an engine-driven compressor controlled with a magnetic clutch similar to the one on an AC compressor. These installations typically put the tank up under the frame rails so you don't lose any bed space. All the air you could possibly want for air tools. An option if you also need 120 VAC power for other loads is a truck engine driven alternator. Norther Hydraulics sells such alternators rated up to 10 kw. Requires the engine speed to be set and governed to maintain the frequency. A conventional electric compressor could then be used. the next best option is a gasoline-engine driven compressor. Bulky, noisy, expensive and yet another engine to maintain. There are fractional HP 12 volt compressors available but they typically produce less than 1 CFM at 100 psi. (not talking about those crappy little compressors Wal Mart sells for [eventually, hopefully] inflating a flat.) I have just such a critter tucked away in my trunk for inflating tires. It would take forever to pump up a storage tank with enough air for even a few seconds of air tool use. And they cost >$200. Check out Graingers if you're interested. John From: John De Armond Subject: Re: DC Powered Air Compressor Date: Wed, 22 Sep 1999 22:39:08 EDT Newsgroups: rec.outdoors.rv-travel TROUTFISH2@webtv.net wrote: > > Looking for feedback as to the purchase of a dc powered air compressor, > suitable for inflating 60 psi on r.v. tires, or less on other vehicles > if necessary. I have heard that some brands don't have the "strength" > to actually push enough air into a 28 footer grossing approx. 5500#, > which is what I have, and it would certainly be a lot simpler than > maneuvering same in the typical gas station parking lot. I'm > assuming that there's one out there on the market with a long enough > cord on it to reach from tow vehicle cigarette lighter [or dc plug in > r.v.] allllllllllll the way back to the tires. If you want something that will actually inflate a tire before your vacation is over, it will be a bit more complicated than buying a wal-mart special "air compressor" (sic) and hopin' and prayin'. There are several reasons. The first reason is that a compressor that costs much over $30 will lack the mass market appeal to be considered by the major marketers (wal-mart, K-mart, Sears, etc). That pretty much limits what content can go into a product. The second consideration is that only a very limited amount of power is available from the cigarette lighter plug. It is generally regarded as pushing the limit to attempt to draw more than about 8 amps from the plug. Yep, some are rated and fused for much more but consider the situation from the manufacturer's perspective. A customer might buy the thing, try to use it in a Yugo or something, set it on fire, kill someone, sue the mfr and win a $50 billion judgment (hey, it happens to GM every week, it seems.) A final consideration is that there is a limited amount of power that can be pushed through the typically 16 ga cord used on consumer appliances. A higher gauge could be used but then it would be bulky, it would strain someone's carpal tunnel syndrome, they'd sue, etc. There is an alternative. The solution consists of two parts, a) sufficient 12 volt power and b) sufficient compressor capacity. Item B is easy. W.W. Graingers (among others) sells a 1/10 HP 12 volt powered oilless compressor. It draws 10 amps. Go here:http://www.grainger.com/cgi-bin/ngs?634540YXkk2860kk5Z679 and look at 5Z349, center of the top row of pictures. Cost: $157.00. This compressor will need either a relief valve or a pressure switch (elsewhere in the Graingers catalog.) This is a very nice compressor. I've used several in various applications. I mount the compressor and a relief valve in a Milwaukee circle saw metal case along with some hose, a milton qucik coupler and some heavy-gauge wire. Makes a very nice package. This compressor could also be mounted permanently on the RV along with a small air reservoir and enough hose to reach all around. Graingers does not sell to individuals. You can either find a Graingers dealer or do what most people I know do, make up a company name and buy with cash at one of their stores located in most medium and large cities. I've solved the power issue across my several vehicles by standardizing on the Molex 20 amp, 2 pin nylon connector available at radio shack. These connectors will easily accept 10 gauge wire, more than enough for the 20 amp rating. The connector is small so it can be hidden and it can be snapped into a rectangular hole. I have some Molex-to-cigarette-lighter adapters made up so that foreign devices can be operated from any outlet. For my stuff, I cut the cord and insert the molex plug in the line to the cigarette lighter plug. That lets the gadget run from a cigarette lighter if I have to use it in someone else's vehicle. In mine, I simply separate the Molex plug and plug it in my outlets. Another option is the Anderson connector. This is the heavy-duty connector used on battery packs on forklifts and the like. Often seen sticking out the front of wreckers to connect jumper cables to. A small version of the connector, rated at 50 amps, is the SB 50 series. Cost is $4.75 ea from Waytek (800 328-2724) http://www.waytekwire.com. Waytek is the place to get just about anything associated with mobile wiring, BTW. If you don't want to spend that much money, there is another option that is a little bit better than dime store compressors. This is one of the compressors used to pump up air shocks. You can get one from a salvage yard from a car like a Lincoln or Caddy that uses air leveling systems. JC Whitney also sells 'em. These are still low capacity compressors but they're better than the Wal-Mart specials. John |