Portable Air Compressors

[Wandering Sagebrush]

The annual DeWalt tool sale is on, and I just purchased their 20VDC portable air compressor. At the sale, they offer a free lithium battery with a purchase over $129. I’ve been happy with the DeWalt tools I’ve purchased, so hopefully I will be with this. It uses 3 power sources, the battery, 120 VAC, and 12VDC. The battery option was what made the sale.

I also picked up my first ever copy of Overland Journal. While I’m not impressed with the magazine (it’s just not my style), I did enjoy their review of air compressors. Their choice and value award was the Ironman Air Champ Pro, citing great inflation times, and a price tag about $800 less than an ARB.

 

[AWG_Pics]

After going through several that had long fill times or overheating and such I finally settled on the Smittybilt 2781 5.65 CFM Universal Air Compressor. Very happy with it.

 

[Wandering Sagebrush]

After going through several that had long fill times or overheating and such I finally settled on the Smittybilt 2781 5.65 CFM Universal Air Compressor. Very happy with it.

I use a Viair 400p for the trucks, it’s probably like the Viair that was mentioned in the OJ article. I like it a lot. The DeWalt is just for small stuff around the Fort.

 

[rubberlegs]

My Viair 300P is blowing 40a fuses constantly. We've gone through 4 fuses in one sitting. If any one has tips, let me know. It's sized for 33" tires, and ours are about 31".

I've heard to start it up before attaching to the tire's valve, then you don't get the amperage surge. I've just started that method, used once, and it was ok that time...

 

[craig333]

My Viair has never blown a fuse. My quickair2 (no longer manufactured) in my Jeep would constantly shut off. I got pissed and bypassed the safety switch thinking it would blow up but it has worked fine ever since.

 

[Vic Harder]

Dual Viair 450P in my truck. No blown fuses

 

[rubberlegs]

I forgot to say we didn't blow fuses the first few years with our Viair 300P. It just started last year. Maybe there's something wrong with it.

 

[Vic Harder]

I forgot to say we didn't blow fuses the first few years with our Viair 300P. It just started last year. Maybe there's something wrong with it.

Does it have an air filter? Maybe that is clogged?

 

[rubberlegs]

Vic, good suggestion. Actually I recently changed the filter. Let's see if that helps. I didn't even notice the spare filter in the bag -- silly!

One thing I've done (probably bad) is to put some water on the fins, to help it cool down. I didn't want to have it melt the nylon carrying bag. That's probably a mistake. There's some corrosion in a few places -- Death Valley does have salt in a bunch of places!

 

[Vic Harder]

water? It may have warped, extra friction, blown fuses. Maybe?

 

[kmacafee]

I have an Extreme Outback hard mounted and wired into the truck. 100% duty cycle and its a beast.

https://www.extremeoutback.com/

 

[Outnabout]

Would the Viair 400 be appropriate to fill LT 285 60R20 tires? I’m not really an off roader but go on dirt roads and just want something to fill tires after plugging a flat potentially. Thanks.

 

[rubberlegs]

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.

 

[Vic Harder]

I have a dual viair450 setup and used quite a bit in on a trip to Utah. I run 275/70R18's. It takes about 15-18 minutes to inflate all 4 from 35 psi to 60 psi.

 

[Tom n N]

I’ve got 10 years of trouble free service from my Viair 400P. I use it to regularly air up all four of my 235/85R-16 tires from low teen to street pressure (40-55#), usually in very high desert heat. Never have to wait longer between tires than it takes to get from one to the next. Also used a few times to air up individual completely flat tires, with no problem. Have never blown a fuse, but this reminds me I should add a couple spares to the bag, just in case.

I did reconfigure the rather lightweight hose and valve assembly for a more durable setup that also makes it much easier to use for airing down (I’ll post a picture next time I have it out of the truck). The compressor itself though is very well built and durable. It of course gets a little hot after airing up four tires, so I got rid of the flimsy nylon case and now store it in a heavy weight canvas tool bag (along with my patch and plug kit).

*Rubberlegs - I think you may have a voltage drop problem. Hooking the factory clips directly to the main battery of a running engine will guarantee maximum voltage to the compressor, which will lower the amp draw. Not sure what the SAE connector you refer to is, but the fact that it’s running hot is a concern. If it’s not rated for the 40A that the circuit is fused at, that could be part of the problem. Finally, letting the compressor come up to operating pressure before loading it up is much easier on the unit.

 

[Outnabout]

Thanks so much for all the advice and input. Having a way to fix a flat out in the boonies will give me piece of mind. Thanks again.

 

[rubberlegs]

*Rubberlegs - I think you may have a voltage drop problem. Hooking the factory clips directly to the main battery of a running engine will guarantee maximum voltage to the compressor, which will lower the amp draw. Not sure what the SAE connector you refer to is, but the fact that it’s running hot is a concern. If it’s not rated for the 40A that the circuit is fused at, that could be part of the problem. Finally, letting the compressor come up to operating pressure before loading it up is much easier on the unit.

That's an interesting thought. We have a 3 foot, 10 gage wire with SAE connector, wired directly to the battery. It has its own fuse. I cut off the alligator clips on our Viair wire, and spliced in an SAE connector. There's no heat detected in the wires or the splice, but at the SAE connection it gets quite warm. The IR drop in that extra wire at 30 amps is about 0.2V. I've never timed how long it takes to air up, maybe 15 minutes. We don't rest the compressor between tires. Even my bike pump gets warm with the weak wattage my arms produce -- friction and Bernoulli's equation, after all.

However, the voltage from the lithium camper battery, a bit under 13V (extra wire drops it to, say, 12.6V at the compressor), is surely lower than the alternator. The Tacoma alternator puts out 13.6-14.7V. Assuming with the compressor load it wants to put out 14.7V, that's 17% more. Could be 20% since the camper battery voltage drops under load. Maybe the compressor likes the higher voltage. Next time I'll see what the camper battery voltage is while airing up. You got me curious. Not sure if alternator voltage drops much under its load.

We still have the alligator clips -- I connected them to another SAE plug. Next time we air up, I'll try them and see if there's a difference and if the plug heats up as much -- pretty subjective since it's hard to measure. Having said that, the compressor always got hot during the years we used the alligator clips.

It's way more convenient using the camper battery wire than lifting the hood and running the engine!

SAE connector:

 

[Vic Harder]

mine are hard wired, mounted under the bed and feeding a 2 gal tank, with quick releases mounted to the lower part of the bed on each side. Super handy. And yes, the compressors get hot.

 

[Tom n N]

That's an interesting thought. We have a 3 foot, 10 gage wire with SAE connector, wired directly to the battery. It has its own fuse. I cut off the alligator clips on our Viair wire, and spliced in an SAE connector. There's no heat detected in the wires or the splice, but at the SAE connection it gets quite warm. The IR drop in that extra wire at 30 amps is about 0.2V. I've never timed how long it takes to air up, maybe 15 minutes. We don't rest the compressor between tires. Even my bike pump gets warm with the weak wattage my arms produce -- friction and Bernoulli's equation, after all.

However, the voltage from the lithium camper battery, a bit under 13V (extra wire drops it to, say, 12.6V at the compressor), is surely lower than the alternator. The Tacoma alternator puts out 13.6-14.7V. Assuming with the compressor load it wants to put out 14.7V, that's 17% more. Could be 20% since the camper battery voltage drops under load. Maybe the compressor likes the higher voltage. Next time I'll see what the camper battery voltage is while airing up. You got me curious. Not sure if alternator voltage drops much under its load.

We still have the alligator clips -- I connected them to another SAE plug. Next time we air up, I'll try them and see if there's a difference and if the plug heats up as much -- pretty subjective since it's hard to measure. Having said that, the compressor always got hot during the years we used the alligator clips.

It's way more convenient using the camper battery wire than lifting the hood and running the engine!

SAE connector:

View attachment 1943276

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 and none are marked for voltage or amp rating as any NEMA device would be. I then tried Google, but no manufacturer data that I could find, only speculation based on the attached wire size (maybe others will have better luck). Wire capacity is easy to calculate, but not so with the actual connector. 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. Both are rated 30 FLA, which based on the 80% max load rule results in the correct use of a 40 A fuse. This means every component in the circuit needs to be rated at or above the 40 amps the circuit is protected at, NOT the full load amps. Just looking at the SAE connector, from my experience, I would have guessed an ampacity of maybe 25, definitely not 40. The fact that it gets hot when fully loaded pretty much cinches it, as minimizing heat is the whole reason we properly size components in a circuit. Like yours, my compressor itself also gets quite hot, but it appears to me to be the result of air and piston friction in the head of the unit, not electrical heat from the motor (going to look at that more closely next time I use it).

After reading all of my above rants, some are going to question why original components of the compressor appear to be undersized according to all I’ve just said. The reason is that listed manufactured assemblies follow a whole different set of rules than the circuits that feed them… and that’s another rabbit hole for another day!

Anyway, I guess ultimately a simple amp reading as it’s wired now, versus from the main battery with the motor running, would pretty much settle this. I think your on the right track with your calculated voltage difference of 20%. And of course, the only voltage that matters is what’s showing at the unit under load.

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

 

[craig333]

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