These oil free 'brushless' motor compressors... any good?

[Gazz292]

I have a 'SIP Stratus' direct drive V twin compressor, 50 litre tank..... and live in a residential area
i made a dog house for the compressor to live in that has quietened it down a bit... baffled air in and outlets to the dog house, with a fan into the exhaust air baffle that runs whilst the compressor is running and for 3 mins after it shuts off... so never had any overheating issues, but i think i got away with that as i would only run it one or 2 cycles a week,

I'm getting a plasma cutter so will suddenly need a lot more air, and i imagine i'll have the neighbours complaining soon if i run my current compressor continuously for 20 or so minutes at a time.
One day i'd like to get a small blast cabinet too, but i do mean small, and would only use it occasionally to clean the rust off small parts, this is all just a hobby for me.

So i've been looking at those 'new' compressors that have a motor and 2 short stroke pistons either end, oil free due to a teflon seal etc, but they seem to have fairly low air outputs unless you get one with 3 or 4 of the compressor units on a tank.

Then i saw this compressor : https://www.stahlwerk-schweissgeraete.de/brushless-compressor-st-1250-bl

Each motor runs 4 cylinders rather than the usual 2, and it claims 12 BAR pressure, and upto 500L/min (that's obviously when the tank is pressured to something like 1 BAR, and the real L/min output will go down as the pressure increases)

it seems that instead of pumping that tank upto 12 BAR then using a regulator to vary the outlet pressure, it instead pumps the tank to the pressure you set on the control panel, not sure that's a good idea... i have a pressure regulator inside my workshop anyway, so i'd just set the pressure to max on the compressor all the time.

And this 'brushless motor' bit, mains induction motors are 'brushless' anyway, so is this a DC brushless motor? it has 2 speed settings to vary the amount of noise it makes.
Obviously a lot more electronics to go wrong, this compressor has a 7 year guarantee, but i can see my current compressor still running fine (if noisily) in 20 years time, and it's already 15 or so years old.

 

[not done it yet]

Your plasma may cause more consternation than the compressor - so take care on that front.

I expect the compressor will produce no more than about 12-13 cfm (they are likely not quoting free air delivery).

How much air are you requiring? That should be your starting point. What is the service factor for the machine - continuous or intermittent? “Up to” needs some qualification, I think.

Dry air for plasma cutting is more important than oil-free.

Any service points in the UK (in the event of a warranty failure)?

I’ve no experience of these ‘oil-free’ compressors. Good luck if you buy.

 

[Gazz292]

ahhh, i didn't really think too much about the noise the plasma will make, thats a very good point.

i plan on making / buying a desiccant bead type moisture trap to keep the air dry to the plasma cutter,

i am wondering if a belt drive conventional compressor would be better and i could likely get one second hand for a decent price, but if i was buying new, i am wondering about these so called silent compressors.

 

[frank horton]

I bought a single cyl screamer, oil free comp...still going strong after 20 odd years.....an Aldi special....

 

[not done it yet]

ahhh, i didn't really think too much about the noise the plasma will make, thats a very good point.

i plan on making / buying a desiccant bead type moisture trap to keep the air dry to the plasma cutter,

i am wondering if a belt drive conventional compressor would be better and i could likely get one second hand for a decent price, but if i was buying new, i am wondering about these so called silent compressors.

Neither did I. My thoughts were re the possible electrical interference that might occur.

 

[Smallfry]

Cynical me is thinking a 1500 watt motor to run 4 cylinders ? Most 1500 watt conventional compressors only run one cylinder. Maybe the motors are better and produce a lot more torque ? Brushless ? I think that is just something to fill the brochure to make it seem like you are getting more !

The digital controls would worry me. Although this is a German sounding name, it would be interesting to know where is was made. I don't think you would need three guesses for that one, and the reliability of the controls would be suspect to me. But to be fair, I guess it would not be difficult to engineer that out if needs be. I also wonder how the guarantee would pan out. Will the seller be around to honour it ?

The tank seems a bit small for the claimed output too. That's something like 20 CFM, but that will be piston displacement at whatever RPM the motors are running at, and not free air delivery at maximum pressure. As you say, this will go down a lot when getting up to pressure. 12 bar (175 PSI) max pressure seems a bit high for this type of lightweight tank too, as the whole thing weighs 40 KG. Most tanks are run at about 125 to 145 PSI.

Would be nice to be able to trial it, but its very difficult to meaningfully measure any output at home. I do like the idea of quiet though, although my ancient Broomwade is very quiet compared to the things they make now, as it is slow revving, and most compressor noise comes from the one way valves in the cylinder head/s, downside being that it weighs 220KG for 14CFM FAD

 

[Bravheart]

No idea about the one in your link but those little oil free compressors usually scream their heads off. Often see silent compressors for sale second hand. The type used by dentists surgeries etc. no idea of outputs but obviously would be fine in a residential area. Have you checked them out.

Or of course a plasma with a built-in compressor

 

[Keithmac]

Would you not be better with a Screw type compressor?.

 

[not done it yet]

Or of course a plasma with a built-in compressor

Not unless it dries the air.

 

[Gazz292]

Cynical me is thinking a 1500 watt motor to run 4 cylinders ? Most 1500 watt conventional compressors only run one cylinder. Maybe the motors are better and produce a lot more torque ? Brushless ? I think that is just something to fill the brochure to make it seem like you are getting more !

From what i've read, the 2 cylinder versions of these motor pump units are rated at 750 watts (on the Hyundai compressors etc) so it kinda seems in the ball park for a V4 version to need double that power, the stroke is tiny, something like 35mm, so maybe that 'helps' ?

The digital controls would worry me. Although this is a German sounding name, it would be interesting to know where is was made. I don't think you would need three guesses for that one, and the reliability of the controls would be suspect to me. But to be fair, I guess it would not be difficult to engineer that out if needs be. I also wonder how the guarantee would pan out. Will the seller be around to honour it ?

Yes, those digital controls worry me too, especially as the compressor would live in a 'dog house' where my current one does, it's waterproof but not damp proof... i have to work the current compressors mechanical pressure switch a few times to get it working again after a winter of not using the compressor (but that is one of those cheapie £15 ones off ebay)

Ok the digital controls won't have the mechanical gubbins (maybe a contactor or 2 for the motors and a solenoid valve) but like all electronics, one out of spec due to age surface mount capacitor and it's knackered,

I would want to re-locate the control panel to be inside the workshop... i do wonder why they don't do a plug in remote panel, or make the main screen and buttons a pop out panel like a lot of VFD's do to allow re-locating the controls somewhere better... not many people will locate their compressor where it's easy to use the controls mounted on the bottom of one of the pump units.

The thing with the variable pressure setting for the tank fill, at first i thought 'what a stupid idea, just fill to max and regulate down as normal'
but i do sometimes run my current compressor till the (train brake pressure) gauges on the workshop wall show about 4 BAR then shut it off, giving me enough air to run the blow gun or to pump up a wheelbarrow tyre etc, so maybe setting the tank pressure could be useful,
but not if i have to physically be at the compressor to set it.

Stahlwerk is just a German reseller of chinese stuff it seems, they claim to have been around since 1998, but i imagine back then they didn't re-sell chinses products... and as you say, will they be around for another 7+ years.

The tank seems a bit small for the claimed output too. That's something like 20 CFM, but that will be piston displacement at whatever RPM the motors are running at, and not free air delivery at maximum pressure. As you say, this will go down a lot when getting up to pressure. 12 bar (175 PSI) max pressure seems a bit high for this type of lightweight tank too, as the whole thing weighs 40 KG. Most tanks are run at about 125 to 145 PSI.

I've seen a video by the seller (i think) of these compressors, and they showed a chart with the L/min ratings, but they are for the other compressors they sell, and it is just that, over half the output at full pressure.

I do also wonder about the 12 BAR rating thing too, i think they are just doing what most chinese sellers do and listing the highest numbers they can to make their product look better.

Stahlwerk say that you can call in their shop and test any of their products, i.e. they will let you weld things with their welders, cut things with their plasma cutters, and i guess run air tools with their compressors, but a 1200 mile round trip may be a little too much for me.

 

[Gazz292]

i'm finding other German sellers of these compressors now,

one lists the flow rates at the different pressures:

love how it flows 616 litres a minute when it's empty

I also believe these compressors have an aluminium tank, that explains why they are so light, but how well do alli tanks compare to steel ones over the years, and if they let go do they split apart violently or gently pin hole like a steel tank usually does if it rusts out.

 

[m_c]

love how it flows 616 litres a minute when it's empty

It's more commonly referred to as Free Air Displacement or how much air the compressor pumps out at atmospheric pressure.

 

[JOEPRO]

I also live in a built up area.

With my own increased compressed air use I went from direct drive compressors to belt driven ones which are definitely quieter and alot less of a trashy / annoying noise to them.

 

[brightspark]

I also live in a built up area.

With my own increased compressed air use I went from direct drive compressors to belt driven ones which are definitely quieter and alot less of a trashy / annoying noise to them.

and all the parts can be obtained and be replaced seperately

 

[Smallfry]

i'm finding other German sellers of these compressors now,

one lists the flow rates at the different pressures:
View attachment 404433


love how it flows 616 litres a minute when it's empty

I also believe these compressors have an aluminium tank, that explains why they are so light, but how well do alli tanks compare to steel ones over the years, and if they let go do they split apart violently or gently pin hole like a steel tank usually does if it rusts out.

If these figures are actually correct, that will be about 10 CFM at 90 PSI, which is the pressure most tools operate at. Thats not bad at all for home use.

 

[Gazz292]

i'd love an old compressor, big thick walled tank, slow thumper of a compressor head, but they weigh quite a lot, and are usually a fairly large tank size etc.

My compressors dog house is in a fairly awkward location, i can get to it for maintenance ok, but getting the little 50 litre sip stratus compressor in there needed me to upend it to get it around the corner between the house wall and workshop...
so to get a bigger one in i'd need to dismantle it and get the tank in on a sack barrow... i have 1200mm length by 600mm width and 800mm height in the doghouse... so i might be pushing it to fit in a 100 litre tank lengthwise.

I do wonder if a 3 phase motor driven old style compressor could be run off a VFD, and if i could then vary the speed, so when i only need a bit of air and i need that at 7pm sunday evening, i could let it fill up slowly and quietly by turning the frequency down, and when i need air all day long run it at normal speed.
I know the compressor cooling would suffer run slower, but i have a 200mm mains fan sucking air out through the baffled air outlet that runs when the compressor is on and for 3 minutes after it shuts off.

 

[Seadog]

i'd love an old compressor, big thick walled tank, slow thumper of a compressor head, but they weigh quite a lot, and are usually a fairly large tank size etc.

My compressors dog house is in a fairly awkward location, i can get to it for maintenance ok, but getting the little 50 litre sip stratus compressor in there needed me to upend it to get it around the corner between the house wall and workshop...
so to get a bigger one in i'd need to dismantle it and get the tank in on a sack barrow... i have 1200mm length by 600mm width and 800mm height in the doghouse... so i might be pushing it to fit in a 100 litre tank lengthwise.

I do wonder if a 3 phase motor driven old style compressor could be run off a VFD, and if i could then vary the speed, so when i only need a bit of air and i need that at 7pm sunday evening, i could let it fill up slowly and quietly by turning the frequency down, and when i need air all day long run it at normal speed.
I know the compressor cooling would suffer run slower, but i have a 200mm mains fan sucking air out through the baffled air outlet that runs when the compressor is on and for 3 minutes after it shuts off.

I run my Ingersoll Rand from a VFD. But I keep it at 50Hz