Compressor Duty Cycle Question

[PJorgen]

Help me understand how the duty cycle applies to my use of the compressor.

I've got a Viair 300P compressor which, according to the Viair website, has a 33% duty cycle. That could mean 10 minutes on and 20 minutes off, it could also mean 20 minutes on and 40 minutes off. Obviously, there's an infinite number of on/off times that yield a 33% duty cycle. So what does this mean to me? Do I use for 10 minutes and shut it off for 20 minutes or do I use it until it shuts off and then just let it cool down until it restarts? Assuming the second option, how do I know how long it will operate until it shuts down?

TIA for constructive comments...

 

[roving1]

Yeah and the duty cycle is often at 100PSI too. So what is it at 35-40PSI? I am also an inquiring mind. If you are not using it with a tank the 100psi number is kind of useless.

 

[67cj5]

If your Duty cycle is 33% then that's 60 (60 minutes) divided by 100 (100%) = 0.6 X 33 = 19.8 minutes =19m 48seconds Minutes Run Time Continuous and then it has to Rest or turn OFF for 40.2 minutes, which is 40 minutes 12 seconds,

Note a Duty Cycle is based on a 60 minute OR 1 Hour measurement of Time, and Every 0.1 is equal to 6 minutes and in every minute every 0.1 is equal 6 seconds, Ok.

Many everyday things we use and own have Duty Cycles from fridges Battery Chargers, Welders and the List goes on,

Hope that helps.

 

[roving1]

Right but a fridge, welder or whatever is usually working at a fixed cycle. The a/c compressor is either on or off and operating in its narrow range of function. But an air compressor operating at a lower psi I would imagine has an effective higher duty cycle. So if its 50% at 40 PSI for instance maybe you can get by on that and not need to jump up to the 100% at 100PSI model for more money and you can get the 33% rated one at 100PSI and be perfectly happy. The 100 PSI rating is only relevant if you are charging a tank to the high pressure cut out all the time and running air tools or something. Just using it to fill tires muddles the rating IMHO.

 

[67cj5]

Right but a fridge, welder or whatever is usually working at a fixed cycle. The a/c compressor is either on or off and operating in its narrow range of function. But an air compressor operating at a lower psi I would imagine has an effective higher duty cycle. So if its 50% at 40 PSI for instance maybe you can get by on that and not need to jump up to the 100% at 100PSI model for more money and you can get the 33% rated one at 100PSI and be perfectly happy. The 100 PSI rating is only relevant if you are charging a tank to the high pressure cut out all the time and running air tools or something. Just using it to fill tires muddles the rating IMHO.

No it does not work like that, If a fridge is left to do it's own thing then yes it has a fixed duty cycle but the moment you open the door or add more food that is at room Temp or cold you over ride it's duty cycle, A 180 Amp Welder with a duty cycle of 60% @ 100Amps only works if you use it at 100amps Bu the moment you turn it up to a normal welding range that welders duty cycle drops.

Back in 2003 I bought the Interdynamics TruckAir 275, It was the first compressor for off Roaders, It/They claim that it can go up to 275psi and that it is made for doing the Big Jobs and has an 8 Hour+ Duty Cycle, well back then it was your only choice unless you had the money for the original ARB which was equal to about $1000+ back then, Compared to other compressors The 275 was fast but not as fast as it says on the Box, Claiming a whopping " 0.49cfm" or 13.875 Litres per minute. Nower days Even the crappiest 4x4 compressor is MEGA Powerful in comparison to the TruckAir 275 but they don't have the Duty cycle. I still have it and it still works well for what it is. but it's duty cycle does not change compared to modern compressors.

The moment you involve a Human with modern Gadgets their duty cycle changes, People will try and blow up 4 60inch tyres on a John Deere and then say a compressor is $£%& but using something for what it was not designed to do is not a fair contest, Ignore all the stupid tests you see on the net because they are not using them as they were intended, They are single use compressors meant for inflating your Tyres, The Key word here is "YOUR" not inflating a production line of Tyre's, another great misconception is speed, I have seen good compressors Air up a Tyre in under a minute yet others claim 2 minutes on the same size Tyre. these compressors must be used with the engine running No If's or But's with a raised RPM to get the best out of them because a drop in voltage means a drop in Duty Cycle, Most compressors with a good Duty Cycle will have a pressure valve that switches the compressor on and off as the Air Line builds up pressure even when it is not connected to the Tyre, Thus keeping the compressor cooler and stopping it from running when it is not needed, All these things help the Duty Cycle

Take the Viair 400/450P and the 400/450A, one is automatic and the other has a higher flow rate So buying the right one for your needs is important, Being made in China and the availability of part is really important, Viair is the only Chinese made compressor that you can get parts for all be it at a premium depending where you are in the world., IE For Me,,, Buying one of the bigger Viair twins would have cost me 5 to 600 Dollars more than the big ARB Twin Portable and with the success I have had with the ARB Single I went with the Home Team and bought the Twin and the parts are available World Wide.

I have had to repair the hose on the Generic Twin twice since march and even though it is a cheaper model it does well, and Once I did some testing and it got very hot, Hot enough to weld it's self to my fore Arm leaving a nasty burn as I picked it up and it brushed against my skin and although it got hot it was no where near it's Duty Cycle, As with any Engine they generate heat so take no notice of all the talk on how hot they get, You might find that you never get anywhere near your compressors duty cycle or if you use it for what it is not meant to do you might exceed it and cause problems, common sense has a lot to do with it.

 

[IdaSHO]

Regardless of compressor, it would be very simple to install a thermo-switch, once you determine the max temp you want it to ever see....

 

[67cj5]

Regardless of compressor, it would be very simple to install a thermo-switch, once you determine the max temp you want it to ever see....

Nearly ever compressor has them built in, I know of only one that does not have one installed, Some have a reset button, some are Automatic and others have a redundant system, One company claims they have them but they only stop when the compressor burns out.

 

[DaveInDenver]

Regardless of compressor, it would be very simple to install a thermo-switch, once you determine the max temp you want it to ever see....

The logic make sense. I'd think you'd want two temperature switches though. The normal operating stay below for acceptable wear temp switch (e.g. the temp represented by typical duty cycle the manufacturer thinks is OK) and the safety don't seize the piston one.

You know, personally, I'd probably put a manual bypass to the operating temp switch because you just know you'll need 1% more to get that last tire than you set with the temperature.

 

[67cj5]

The logic make sense. I'd think you'd want two temperature switches though. The normal operating stay below for acceptable wear temp switch and the safety don't seize the piston one.

That would not work because it would working below it's duty cycle, After 3 minutes of running these compressors or parts are reaching Temps of close to 90 to 120*c/ 194*f - 248*f, some claim silly low temps but these are useless and are just untrue, If you use a Laser to measure them with, the place where it is measured at must be painted Black, as I did when I tested mine because when it was silver them Temp reading was 37 to 40*c / 98 to 104*f,

Most of these cheap compressors use plastic conrods and Gaskets made out of cardboard boxes that were once packaging still with the writing on them, These cheap compressors are a mine field.

 

[DaveInDenver]

That would not work because it would working below it's duty cycle, After 3 minutes of running these compressors or parts are reaching Temps of close to 90 to 120*c/ 194*f - 248*f, some claim silly low temps but these are useless and are just untrue, If you use a Laser to measure them with, the place where it is measured at must be painted Black, as I did when I tested mine because when it was silver them Temp reading was 37 to 40*c / 98 to 104*f,

Most of these cheap compressors use plastic conrods and Gaskets made out of cardboard boxes that were once packaging still with the writing on them, These cheap compressors are a mine field.

True!

But I will admit despite having low expectations for the MV50 I got on sale for $25 has gone 13 years now. I tore it apart once to rewire it, did replumb it with better fittings and for $25 I routinely ignore the duty cycle recommendation (25% I think) and air up all 4 of my, albeit small, 235/85R16 in one shot. When it dies I've long since saved the money for a good brand but it just keeps chugging along.

 

[67cj5]

True!

But I will admit despite having low expectations for the MV50 I got on sale for $25 has gone 13 years now. I tore it apart once to rewire it, did replumb it with better fittings and for $25 I routinely ignore the duty cycle recommendation (25% I think) and air up all 4 of my, albeit small, 235/85R16 in one shot. When it dies I've long since saved the money for a good brand but it just keeps chugging along.

Well you can Hot Rod them and it works well, I also did like wise with the Generic twin,

I noticed it had one of the larger type air fittings, back to that in a SEC. but it has a high flow Hose, but when I checked the male fitting on the compressor (they did it back to front I know) it had the larger male fitting with a wide opening but when I unscrewed it the threaded end the opening was only about 2.8mm, So I drilled it out to 3mm, "Still too small" then 3,5mm, Hmmm not enough !!! at 4.5mm I was happy and then I put on 13 wraps of PTFE tape and screwed it back in and when I tested it, It was pumping out about another 1 to 2 PSI in my Tyre per minute and it was staying cooler because it is not building pressure in the Head or main body and allowing it to flow better, It now takes my road tyres from 15psi to 32 psi in 1 minute 03 seconds where as before it took 1 minute to get it to 30psi. That 2psi might not sound like much but that is 13.3% in power/out put, so I am all for hot rodding them, So Well Done "You".

After measuring the tightest Head Bolt I also undone the head bolts because some were loose and others were tight and I Torqued them up starting at 20 inlb and then 25 28 30 and finally 33inlb, That might seem OTT but like any engine they have a bore a piston and a head and they need to be set up in the same way.

Although I Own the ARB's, there is nothing wrong with the MV-50, It's a rock solid little compressor and if it takes 8 to 10 minutes to Air Up 4 33" tyres "SO WHAT", It's a mighty little Compressor, So don't let any one tell you other wise.
It is a mine field out there with the cheaper models making false claims about flow rates, PSI rates duty cycles, As I said some of them have gaskets made out of cardboard boxes and some don't even have thermal cut outs, just a few things for folks to be aware of.

 

[67cj5]

I come from an engine building back ground so One thing I would like to point out and that is A compressor is basically a Combustion Engine without the Spark Plugs or Glow Plugs, It has the same parts as in a piston a Block and a Head and when we want to get more power out of a Car or Truck the first thing we do is add a free flow Exhaust system by adding Headers/Extractors and a larger exhaust Pipe/system and that normally adds up to 15% more power, Now if you look at a Compressor "ALL" the Air Fittings are in fact the compressors Exhaust System by modding them or/and fitting better parts it has the same effect as it does with a Car/Truck which is why when I did what I did and I saw a 13.3%+ increase in out put, Which is close to the figures of 15% that we see with Automotive Engines, So it is food for thought. not to mention a reduction in wear and heat build up. because when you create pressure you also create Heat.

 

[IdaSHO]

Nearly ever compressor has them built in, I know of only one that does not have one installed, Some have a reset button, some are Automatic and others have a redundant system, One company claims they have them but they only stop when the compressor burns out.

Examples? Most Ive seen are not temperature related safety devices.

Its not a thermo-switch if it has a reset button.
If it has a reset button, it is most likely a re-settable breaker of some sort, using current draw to determine cut-out.
Even the ones that auto reset are using a breaker of some sort. Auto resetting breakers are very common, not only on compressors.

Using such a device that relys upon current draw is great in theory, but if you are actually worried about operating temps, which will ultimately determine the life of the compressor, you really need a thermo-switch.

 

[IdaSHO]

True!

But I will admit despite having low expectations for the MV50 I got on sale for $25 has gone 13 years now. I tore it apart once to rewire it, did replumb it with better fittings and for $25 I routinely ignore the duty cycle recommendation (25% I think) and air up all 4 of my, albeit small, 235/85R16 in one shot. When it dies I've long since saved the money for a good brand but it just keeps chugging along.

The MV50 is a super fab piece of chinesium, thats for certain!

I also routinely try to cook mine. Years later, still kickin'

 

[67cj5]

Examples? Most Ive seen are not temperature related safety devices.

Its not a thermo-switch if it has a reset button.
If it has a reset button, it is most likely a re-settable breaker of some sort, using current draw to determine cut-out.
Even the ones that auto reset are using a breaker of some sort. Auto resetting breakers are very common, not only on compressors.

Using such a device that relys upon current draw is great in theory, but if you are actually worried about operating temps, which will ultimately determine the life of the compressor, you really need a thermo-switch.

As long as they have some form of protection that is all that is needed, whether it is electronic or thermal is not important as long as the device is ok, Some have a thermal switch that reset automatically, some have a thermal switch that needs to be reset manually and some have nothing at all.