Portable Air Compressors

[rubberlegs]

Well now you’ve got me thinking…Like you, I love a good engineering puzzle, so down the rabbit hole I go…

I looked at all the SAE connectors I have around the house... As with any chain or electrical circuit, it’s always the weak link you have to worry about!

Interesting that the specs for your 300 and my 400 are virtually identical. Not sure what the difference is.

Funny how I guess I miss the days of getting paid to have these kinds of discussions before I retired. Oh well, let us all know what you eventually come up with.

Tom, I also wondered why the 300 and 400 had such similar specs. Maybe the 400 fins are larger to dissipate more heat. The power and energy produced is likely similar. I've never seen the two side by side.

I got the 10 gage SAE cable without thinking about the connector. A brief search indicates it may be sized for only 10-15 amps. Why do they sell such a cable?! I need a more robust connector, like the Anderson SB50.

I also enjoy these kinds of discussions, also as a retiree. I'm happy to discuss this stuff for free. However, I wasn't an electrical engineer (just a mechanical who designed aircraft mechanisms), and any engineer who didn't drive a choo choo train is no engineer! They won't let me drive one.

Never blown a fuse hooking my viair directly to the truck batteries. It does get hot. Not nearly as fast as my CO2 tank but heck, I'm not in a hurry

Just to clarify, our blown fuses (at least 10 times), happened when connected to the truck battery with engine on, compressor attached to the tire valve, then flipping the power switch.

Someone suggested turning the compressor on before connecting to the tire, and we've not blown a fuse since.

 

[craig333]

That is the way I do it but I'd be curious to put an ammeter on it. I doubt hooking it up to the tire first would make that much difference.

 

[DesertDog]

I got the 10 gage SAE cable without thinking about the connector. A brief search indicates it may be sized for only 10-15 amps. Why do they sell such a cable?! I need a more robust connector, like the Anderson SB50.

One thing to watch for is that a lot of the import cable manufacturers have started to use copper tinned aluminum wire as less expensive than pure copper wire. From what I read, the general rule is in this case to treat the Cu/Al wire as 1 AWG smaller diameter. Thus if you have a 10 AWG cable of copper tinned aluminum, you should treat it as a 12 AWG wire for current sizing. If you do remove your SAE connector, you may want to check the cut wire under a magnify glass to see if it is pure copper.

 

[Tom n N]

Rubberlegs,
Glad to hear you figured it out. Your solution makes perfect sense, and I like your idea of a 50A Anderson connector (installed a lot of those for forklift chargers), problem solved!

While I have an engineering degree (Industrial), I spent my entire career in the trenches (often literally) as a union electrician, a large part as a troubleshooter. I loved every minute of it, and would have gladly done it for free! I had many people boast of being Engineers while trying to convince me to do something stupid or illegal. I would always give them a puzzled look and ask what sitting at the front of a train had to do with what we were talking about…that always shut them up!

DesertDog,
Never heard of copper clad aluminum before. You’re correct about derating by one size, but really best to avoid it altogether. Sounds like a recipe for disaster, as copper and aluminum usually doesn’t play well together. While aluminum wire has it’s place (the service drop to your house is probably aluminum), the only type wire that should ever be used in our campers or trucks is fine stranded copper.
Thanks for the heads up.

Tom

 

[Tom n N]

Thought I’d include a picture of my modified air chuck setup. Can’t remember exactly what it looked like originally, as I’ve been fine tuning it for over ten years.

The quick disconnect at the top allows me to use different chucks, depending on rim type
The black handled valve at the bottom of the T is for filling, and the one on the left is for airing down.
If the yellow hose is disconnected I can use either or both valves to quickly air down, while still keeping track of pressure on the gauge.

I used to have a T setup so I could do two tires at a time, but the extra hose took up more room than I wanted, and the Viair is plenty quick for my needs

 

[rubberlegs]

While I have an engineering degree (Industrial), I spent my entire career in the trenches (often literally) as a union electrician, a large part as a troubleshooter.

Tom, it sounds like you didn't drive a choo choo train either! Well, that's ok, you were a good engineer, I'm sure. My engineering career was fun, too, most of the time.

I ordered a bunch o' parts to convert my compressor setup to an Anderson plug. Already had some 8 awg, but needed the plugs and a fuse, ring terminals, etc.

Actually I think the high temperature of our compressor is ok. It gets hot though.

 

[Tom n N]

Tom, it sounds like you didn't drive a choo choo train either! Well, that's ok, you were a good engineer, I'm sure. My engineering career was fun, too, most of the time.

I ordered a bunch o' parts to convert my compressor setup to an Anderson plug. Already had some 8 awg, but needed the plugs and a fuse, ring terminals, etc.

Actually I think the high temperature of our compressor is ok. It gets hot though.

Sounds like a good plan. Be sure and post a picture so we can all see what you come up with.
Tom

 

[Defulmmt]

We originally had 31" tires, 265/70R16* and use the Viair 300P. It gets pretty hot, but works well if we turn it on before connected to the tire valve. If we connected to the tire first, then turned it on, the amp surge was blowing the fuse. We use it off road, so we're typically pressurizing three tires, occasionally four, to 2-3 times off road pressures. (Three since I use a bike pump for the 4th tire. Great exercise! Also a backup just in case.)

You might get by with the 300P if only using it for on one tire at a time. Our experience is it doesn't get too hot doing one or two tires, increasing about +35psi rear (or +30 front), not starting with a flat tire though. Definitely 400P if you need to pressurize all four tires. I'd get a package of fuses just in case -- they are inexpensive.

According to Viair chart (see the "Portable Tire Inflator section), the 400P is good for 35" tires. Your tires are 33.5" per Tiresize calculator. (Our 300P is good for 33" tires).

Both our 300P and your proposed 400P are 30amps, so probably the 400P for all four tires would get as hot as ours. They have the same 30% duty cycle though, and 30 amps. I sorta wish I'd gone up a size, thinking it wouldn't get as hot, but can't complain since it's working fine. We plug into our camper lithium battery with the truck off, instead of the truck battery with the engine on. Our SAE connector gets pretty warm too...

* Now we use 32" tires, but narrow, 235/85R16, and the same compressor.

I just ordered a 300P for our November trip south. Do you follow the duty cycle 0f 3.5minutes operating and 6.5 minutes cooling when using the compressor. Info I found, for 33" tires is about 1/2 hour for four tires 35psi to 60psi using this duty cycle.

 

[rubberlegs]

No, we just inflate all tires with virtually no cooling in between. Instructions that came with it didn't specify any duty cycle advice. I'd guess it takes about 15 minutes total. The compressor works harder for the rear tires (higher pressure), so we do those first.

 

[DesertDog]

Actually I think the high temperature of our compressor is ok. It gets hot though.

Another retired engineer chiming in. Natural for any compressor to get hot as it is compressing a gas under near adiabatic conditions. In theory, compressing the air to 45 psi (3 atm) can result in air outlet temperature approaching 375 F. Fortunately, and by design, there is a lot of aluminum housing for some of the heat to dissipate into - thus the outlet air temperature, nor compressor housing, nor lubricating oil reaches this temperatureswhen operated for short time intervals.

 

[craig333]

Had to google adiabatic. Never hurts the old noggin to learn something new

 

[Tom n N]

Seems like you can’t swing a slide rule on this site without hitting an old engineer in the pocket protector…maybe we could start our own railroad!

Seriously though, I’m constantly amazed by the vast store of knowledge in this group. I love that I seem to always learn something new every time I log on, and it’s often something I had no idea I wanted to know. Who would have guessed a site dedicated to people wandering around in the wilderness could be so interesting?

 

[rubberlegs]

Wait. Engineers are interesting?

Anyone else enjoy Don McMillan's Powerpoint engineering comedy?

 

[Vic Harder]

yep, that's pretty funny.

 

[goinoregon]

i worked with engineers for years, and they are great.... up to a point

 

[Bos_Trok]

I have had and still carry around a few compressors, I have the ARB one installed for my lockers, a nice Viair 300 that has served me well for years, but the NAPA dual piston is the best bang for the buck so far. Its two piston, so it is faster than the singles, and seems to be holding up just fine. They will go on sale from time to time for about 120.00 IIRC

I modify them to have a quick release just like any other compressor, so I can easily use the hoses and tools that I use for my home compressors. You can go down a YouTube rabbit hole on these, they are very popular to use and modify.

NAPA dual piston 12V Compressor

Dude modifying one on youtube

II made a dual hose setup that I use with the NAPA, the Viair I use for one tire at a time, and the ARB isn't worth messing with for truck tires unless I didn't have anything else, that's just used for the lockers, bike tires, and airbags.
With two people working, its only 10-15 minutes to get 4 tires aired back up using the NAPA and Viair combo. two NAPAs would be even faster.

 

[Outnabout]

I have had and still carry around a few compressors, I have the ARB one installed for my lockers, a nice Viair 300 that has served me well for years, but the NAPA dual piston is the best bang for the buck so far. Its two piston, so it is faster than the singles, and seems to be holding up just fine. They will go on sale from time to time for about 120.00 IIRC

I modify them to have a quick release just like any other compressor, so I can easily use the hoses and tools that I use for my home compressors. You can go down a YouTube rabbit hole on these, they are very popular to use and modify.

NAPA dual piston 12V Compressor

Dude modifying one on youtube

II made a dual hose setup that I use with the NAPA, the Viair I use for one tire at a time, and the ARB isn't worth messing with for truck tires unless I didn't have anything else, that's just used for the lockers, bike tires, and airbags.
With two people working, it’s only 10-15 minutes to get 4 tires aired back up using the NAPA and Viair combo. two NAPAs would be even faster.

I asked earlier about the Viair and its ability to inflate a truck tire but I don’t think I asked the right question, which is: are the Viair or this Napa compressor capable of inflating a full size truck tire from practically flat to 70-80psi? I don’t need speed, just the capability of getting the tire back up to pressure if I need to plug and it has gone flat. Thanks for mentioning the NAPA compressor as I hadn’t looked at those, or really any other than the Viair.

 

[rubberlegs]

Our Viair 300 can easily do one full size tire. We have a mid size truck, and it'll do all four tires, fronts from 15 to 47psi, rears 20 to 67psi. By the last tire, it's getting fairly hot.

 

[Outnabout]

Our Viair 300 can easily do one full size tire. We have a mid size truck, and it'll do all four tires, fronts from 15 to 47psi, rears 20 to 67psi. By the last tire, it's getting fairly hot.

Thank you. I appreciate you sharing your experience with the compressor.

 

[Outnabout]

I found this Viair compressor. Looks pretty capable and is less than the 300. Although after reading the information on the website I see the full rate is only showing increasing the psi about 10, so maybe not ideal for fixing a flat and needing to go from 0-70psi.

89P RVS Portable Compressor