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The tale of a cheap(ish) little air compressor and partial teardown
Posted by Fraser on 22 Jun, 2016 17:48 -
I recently bought an OKI FD1000 solder paste dispenser that requires an air compressor with more pressure than my airbrush compressor could provide.
I began searching for inexpensive air compressors on ebay and noted that something suitable with a 6L tank would cost around £60. I soon reviewed my needs and decided a 24L tank would be more useful as it could power tools etc. New 24L compressors ranged in price but most are around the £100 to £120 mark.
Being retired, I decide to check out the used compressors on ebay. There is often a good selection available but most are for collection only. Some are over-priced, whilst others are 'well used' so it is a bit of a minefield. I eventually stumbled upon a very nice looking STANLEY branded 24L compressor that looked to be in very good condition and bidding was low. The reason ?..... it was faulty. The owner stated that it had been running fine then would not switch on the next time he went to use it. A-ha, I thought.... this could be a good prospect as the fault was likely the power switch or the air pressure switch. Both easily repaired and relatively cheap.
Oooops Dinner time.....to be continued after my Dinner
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Power switch, pressure switch sticking open or capacitor going low in value, so the motor will not start up. Or the non return valve is sticking or leaking, so the compressor cannot start into the head pressure, along with a blocked dump valve on the pressure switch.
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Hi SeanB,
You are right.
The story continues........
Where were we ? Oh yes, I had spotted a nice little STANLEY branded 24L air compressor that had a fault. The good news was that the compressor was located relatively close to me, only 30 miles to my East so collection was not a problem.
I placed a bid on the little compressor and was surprised when I actually won it....for only £10.50.
http://www.ebay.co.uk/itm/Stanley-24l-oil-less-Air-Compressor-/112026461637?_trksid=p2047675.l2557&ssPageName=STRK%3AMEBIDX%3AIT&nma=true&si=i%252F4LbtG6%252FLD9UF0GHMsipNyck8E%253D&orig_cvip=true&rt=nc
I collected the compressor the next day and it was as good as it had appeared in the pictures. I attach the auction pictures here.
The partial teardown will be detailed in my next post.
Fraser
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Pressure test due in 2019, so make a note if you still have it to get the hydrotest done.
So what was dinner, I had a nice little Bobotie, very tasty. -
So what was dinner, I had a nice little Bobotie, very tasty.
+1
I keep watching those nice little Bambi compressors, but they are a bit on the heavy side to get delivered to Ireland. Any for sale locally are taking the mick on price. -
The observant who are familiar with compressors will have already noted the unusual build of this compressor. it is a direct drive oil free unit but it does not have the usual 'black box' and associated plumbing sat outside the motor cover. Such black boxes contain the pressure switch and contactor assembly. In its absence I expected to find a smaller pressure switch, as seen on airbrush compressors, and I was not disappointed
I removed the cover after unscrewing the four self tapping retaining screws. All was revealed......
The STANLEY branded compressor is also available under the Einhell (Germany) brand and I had already obtained the parts schematic. The schematic matched my unit so they are one and the same unit. Einhell make some decent kit and happily provide spare parts, so things were looking up.
An exploded parts view of the STANLEY compressor is to be found here:
http://www.mtmc.co.uk/Stanley-Compressors/Stanley-8216035SCR011-Type-Rev-A-Compressor-Spare-Parts__p-12734901-94723.aspx
The Einell exploded parts view is here:
https://www.isc-gmbh.info/isc_de_en/tools/einhell-blue/stationary-tools/compressed-air-technology/bt-ac-200-24-of-3/
The compressor comprises the following significant parts....
1. The Air reservoir tank.
2. The electric motor and compressor cylinder module
3. An AC 250V 16A rated DPST illuminated rocker switch providing the power control to the compressor electrical systems.
4. A small pressure switch samples the air pressure in the reservoir tank and opens its contacts at 116PSI. Contacts close again at 90PSI.
The pressure switch is wired in series with the motor neutral supply line.
5. A self-resetting over-temperature thermal cut-out is attached to the static windings of the motor and wired in series with its supply line.
6. An air regulator and associated pressure gauge are connected to the reservoir tank output.
So its a pretty simple beast with only a few likely causes of failure.....
1. On/Off switch faulty
2. Air pressure switch faulty and stuck open
3. Motor over-heat protector faulty and stuck open
4. Motor faulty, burnt out.
The quickest test was to bypass the on/off switch........ the compressor burst into life and began pressurizing the reservoir tank. Whoopee! an easy fix
I was not finished though. I needed to inspect all electrical parts of the compressor to see if anything else looked amiss with it.
I found the following not to my liking.....
1. The Lucar spade connectors on the pressure switch are not a tight enough fit and arcing as occurred due to the >5A current passing through them. The pressure switch is still working OK but I have my doubts about its likely life span.
2. The wiring from the motor to the pressure switch and cable connectors is messy and needs tidying a little.
3. One motor supply cable was being crushed under the motor cover due to poor placement. An easy fix as it just needed moving.
4. The use of a cheap 250V 16A DPST rocker switch was just asking for trouble on a compressor. Its contacts were badly burnt and the moving contact had welded itself to the pivot in the open position !
I shall be rectifying these issues as part of the repair. A better quality rocker switch will be tried and if that fails, a high current solenoid will be fitted.
The STANLEY/Einhell compressor is a neat and light weight little unit suitable for my humble needs, but the use of a simple pressure switch and a DPST rocker switch indicates that it is budget product built down to a price. The original owner paid £140 for it so it is not exactly cheap. General build quality is fine though. The motor/compressor cylinder module is neat and well made.
The unit will likely be fine with my light use but I expect issues with the pressure switch at some point in the future. A new one is 18 Euros from Einhell.
I attach the picture that I took of the unit with its covers removed.
Fraser
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More pictures
Motor detail including a picture of the shrouded over-heat protector attached to the winding and the pressure switch arcing evidence.
Pictures of the disassembled rocker switch are also included. It had arced in the mid open position on the pivot contact ! Fortunately it is a cheap and easily purchased part.
Fraser
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Dinner was Cottage pie with all the trimmings and plenty of Hendersons sauce
Thanks for the comment on the tanks re-test date. By the time it is due I expect the unit to have departed this fair world
Plus it would likely be cheaper to buy a new unit than have it tested in the UK.
This unit is most definitely a DIY low budget product but for £10 plus a rocker switch I am not complaining It will definitely power my solder past dispenser, car tyre inflater, nail gun and maybe a small spray gun if needed.
The arcing on the top of the pressure switch is still puzzling me. I cannot see any obvious burns on the spade connectors and the burning on the switch appears to be on the small 'wings' either side of the spades. I am wondering if the marks are out-gassing from the contacts as they arc inside ? I noted that neither this pressure switch, nor the power switch had any snubbers connected. There was an X2 suppressor cap across the Live and Neutral though. I have some snubber caps and resistors that I may fit as part of the repair work.
I attach a picture of a parts donor Einhell version that I found on ebay. The seller is asking £15 plus £10 p&p. I note that the expensive drive belt is missing and the gauge is scrap. I will not be buying that unit but it shows what a good deal I got with my very smart little unit. Having looked around the motor, two fans and air intake, it would appear that my unit has had very little use. That does not bode well for the power switch or the pressure switch (if it is arcing) though. The motor and associated bearings look decent enough quality to last though.
Fraser
Fraser
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Towger,
I looked at the Bambi compressors as well. They are available from other manufacturers as well.
The silent Bambi compressors appear t use compressor modules similar to those found in refrigerators and air conditioners. they do run very quietly but at the cost of air throughput. Most are less than 1CFM so are not suitable for any application that has significant air throughput demands. I note that Bambi have higher CFM models that used several compressor modules in parallel. That gets expensive though.
I decided to pass on some 'silent' compressor auctions that I watched as the uses for such a compressor were somewhat limited. Great for running a solder paste dispenser or dental tool though as they require very little air throughput from the pump.
There are some other quiet compressors available from AFLATEK, Latvia for around £99 for a 10L model. They use a neat twin piston pump with a air throughput of around 3CFM max. Noise level is quoted as 65dBa. it is £99 for the 10L version. I was seriously considering that unit for the lab. There is a video on you tube showing it working.
https://youtu.be/OrLC3t0fuac
ebay advert.....
http://www.ebay.co.uk/itm/122009622875?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT
Fraser
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A minor correction to the failure story.....
The compressor failed whilst IN USE. That is to say the compressor was running and then stopped.
From the fault in the rocker switch, I surmise that the contact surfaces in the switch could not handle the current flow and arcing occurred at the pivot to contact arm interface. The two eventually welded together and the contact arm lifted slightly, opening the contacts. The owner noted that the rocker no longer latched in the on position.
In the pictures you will see two deep notches in the brass contact arm at the pivot point. these should not be present as the other contact is smooth at this point. When I disassembeld the switch I had to literally break the contact arm off of the pivot. It was well and truly welded in place. The black discoloration indicates a lot of arcing during the switches short life.
The rocker switch is a likely failure point on these units so if you own one, check the switch first if it fails to run.
Fraser
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It's interesting to see a compressor with a brushed motor - I thought they were all induction motor powered, It must be physically smaller that it looked from the photos.
For people in this neck of the woods, Aldi and Lidl often have air compressors and associated items in their Monday / Thursday specials (keep an eye on their websites). They're generally pretty good quality and come with 3 year warranties. -
Hi Gyro,
ISC-Gmbh supply Aldi, Stanley and Einhell with power tools and compressors. As you say, the quality is usually pretty good
This page shows the many companies and brands ISC-Gmbh supply with hardware.
https://www.isc-gmbh.info/isc_de_en/tools-8
Fraser -
Quote
This page shows the many companies and brands ISC-Gmbh supply with hardware.
https://www.isc-gmbh.info/isc_de_en/tools-8
Wow!
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The silent Bambi compressors appear t use compressor modules similar to those found in refrigerators and air conditioners. they do run very quietly but at the cost of air throughput. Most are less than 1CFM so are not suitable for any application that has significant air throughput demands. I note that Bambi have higher CFM models that used several compressor modules in parallel. That gets expensive though.
It is just to supply a Metcal desoldering gun and save on buying cans of compressed air, so high CFM is not a requirement. Actually the SWMBO worked for Atlas Capco for a couple of years, so compressors are her area of expertise. I have full wife approval to buy (at the right price) a big industrial compressor, providing it is a screw compressor and made by them.
But, I don't think the neighbors would be happy with a compressor the size of a car, even if it is quiet.
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Towger,
Your need for electronics is similar to mine. Sadly the neat little airbrush type compressors just cannot produce the required pressures for the venturi vacuum generators used in soldering kit. The conventional compact 6L compressors are still very noisy. I like the idea of the neat low noise models but the cost saving of buying and repairing the STANLEY unit made it a no-brainer for me. I have a nice quality 10m long hose on its way to me so can run it outside the lab
Another alternative is to use a pony cylinder that you charge using a conventional noisy compressor in the garage and take to where you need the pressurized air. Not as good as a silent compressor, but cheaper.
Fraser -
Since it uses a universal motor, replace the switch with a dual throw, center off. One side goes direct to the motor as usual and the other to the motor through a diode. The "low" position reduces noise and helps the compressor last longer at the expense of lower output. Also would, in theory, make the switches last twice as long since there's a 50% chance it would open with no current flow.
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The use of an universal motor is a way to reduce cost, as the universal motor has a much higher power to mass ratio over an induction motor, at the expense of motor lifetime, and the higher power losses in the windings along with brush and commutator wear. I would also guess the windings on the motor are made with CCA wire as well, to reduce the cost to a minimum, along with the motor being actually wound to run at 200VAC instead of 240VAC, which further reduces the wire but which reduces motor life considerably at higher voltage, though it does develop more power.
The power switch failing is getting common, as the manufacturers reduce the thickness and size of the contacts to cut cost. The pressure switch deposit is from internal arcing, quite common as it is being run at the top end of the range, along with having a frequent actuation which is going to use the limited cycle life up quite fast. A relay with the new switch just being a pilot would last a long time here.
Funny enough I was looking at a failed mains switch today, used to turn on room lighting. Date on the (unused) dimmer section was 9 June 1988, so it was had a really good innings, though there are others that are much older still in regular use. The failing section was eroded around 2mm down compared to the unused one, and was definitely in need of replacement. The new Crabtree I put in its place ( old one was Crabtree as well) will probably not do nearly 30 years though. -
Hi SeanB,
Thanks for the comments i totally agree on the pressure switch. i will either fit the heavier duty type used on other compressors, or I will fit my spare pressure switch and a heavy duty mains relay to take the load off of the switch. I will run it in standard trim for the moment ans see how long it lasts.
The replacement rocker switch is a quality brand and, whilst still rated at 16A, it is specifically designed for high inrush currents of up to 160A and long life switching high current loads. It costs a bit more, but it is worth it.
Fraser -
Here is the one switch contact, along with the other mostly unworn one. 2 Crabtree switches, with the worn one driving 4 5ft fluorescent lamps, the other was for 3 60W downlighters. Downlighters disused for the last decade, so the switch was only operated by accident.
Taken with phone camera using a very large projector lens ( thanks Kolbep) as a magnifier, and cropped down to remove the sides and shrink size down to forum limits.
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we supply those silent type compressors here at work, they are pretty damn quiet! our one is 400W and puts out 63L/min (about 2.2 CFM).
in regards to the Stanly compressor, we very often have people coming into work asking to repair them and other similar compressors. The main point of failure is the wrist pins and plastic cylinder ring.
Replace the pressure switch with this type, it's the industry standard.
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@thfamilyman,
Nice silent compressor 👍🙂
Thank you for the comment and advice. Much appreciated.
Fraser -
I have another compressor !
I stumbled upon a 'silent' air compressor that was being sold as spared or repair.
The compressor was supplied to me by AIM Tools and maybe seen on their site here.
http://www.aimtools.co.uk/220v-low-noise-50l-air-compressor.html
It is a 1100W motor on a 50L air reservoir and appears nicely built. 8 BAR and 7 CFM is respectable too. My unit looks to be a customer return that 'failed' whilst in use.
The compressor arrived in a wood crate today and I quickly tested it........ it sounded like a machine gun The sound was coming from the left cylinder only. Not such a silent compressor now, hence its return to AIM. The advertisement did clearly state that the unit made a loud noise so I was expecting this test result.
Having listened to the noise the compressor was making I decided it was either a high pressure air leak on the compression stroke or the impact of the connecting rod on the piston. Without further delay, and whilst still in the crate, I removed the left cylinder head and valve plate. The cause of the noise was plain to see. The socket head countersunk machine screw that secures the piston to the connecting rod was very loose. This allowed the connecting rod to hammer on the piston and to leak air on the compression stroke. For those confused about a rigid con rod to piston connection, this is a classic tilting piston design.
I applied some screwlock to the piston securing screw and tightened it to a decent torque. I then checked the right cylinder and that was still fine. The compressor now runs sweetly with a nice low noise level. In fact the great est noise is made by the pressure relief valve when the pressure switch is activated.
I now have a very nice quiet 50L compressor
Fraser
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Minor correction.... the piston design is a wobble piston nd not a tilt piston.
Patent is here:
http://www.google.com/patents/EP0588466B1?cl=en
I have attached it as well.
Fraser
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This took up residents in the sitting room a couple of days ago:
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It was sold as working, but was DOA. Replacing the 2a fuse with a 5a soon fixed that. Gave it a quick clean to get off most of the oil and dust. Cleaned out crud in the auto drain bottle. It does not have a regulator fitted, currently on the lookout for a quality one on eBay. I am not too sure what pressure to go for. I can't find and specs for the factory default which appears to be a rebaged Norgren R07, but can buy one for almost what the compressor cost me. I assume it is up to 7 bar. Is is currently set to start/stop at 6/8 bar. But the compressor is rated up 16 bar and there is a 10 bar option on the parts list. The gauges they come with are 16bar, as is the pressure relief valve. 5.5 bar is all I require for a Metcal desoldering gun. It came with the .01 micron auto drain filter option. Which I also cleaned. I don't see how the auto drain on the filter can work, it just consisted of a plastic plunger/needle valve arrangement. I would have expected spring(s) and a float, so I assume they are missing.