Compressor 3hp motor DOL starter question

[styleruk]

My mistake miss read the original post and got mixed up thinking you were using a 32A motor. I don't think you will need that DOL starter and overload relay if the pressure switch is a decent one that's rated for 16A you could just use a 2 pole motor protection circuit breaker. These are suitable for motor disconnection as well as overload protection.

I was advised to use the starter as it will pull a lot when it kicks in. Question is, where do I put it in the supply, before pump or on wall going into the pressure switch.

 

[David Prosser]

Not sure what consumer unit you have or if you have spares ways in it but some of them will fit in there if not buy a small housing for switched O/L. I'll PM you some links for the bits when I've finished feeding the family !

 

[davesparks]

I was advised to use the starter as it will pull a lot when it kicks in. Question is, where do I put it in the supply, before pump or on wall going into the pressure switch.

The starter will have no bearing at all on how much the inrush is

 

[styleruk]

fired it up today whilst I await the DOL, works very well. Would like to post a picture but apparently jpg is not recognised so I can't be bothered to figure that out.
The lights flick slightly when it fires up, but I have not run her for a long time yet until I fit the starter.

 

[styleruk]

So, eventually the starter turned up. Meanwhile, been getting mixed messages form various people, most staying, you don't need a starter for that!
But I've got it and fitted now so tough, I have one.
I can't tell the difference with it fitted, maybe it seem to start slightly less aggressively, which, if true, is a good thing.
I'd like to share a picture of it but apparently a 'jpg' is not an image as expected!
But overall, i've repainted the compressor, added a dump valve so the cylinder heads do not have pressure when the motor starts, a one way valve, rebuilt the pressure switch and 3d printed a new cover for it, turned up a new button to switch it on and off, obviously fitted a new pump and motor, all new connector hoses and high temperature hose for the pump to receiver and starter with overload protection set to 10 amp currently. (that's adjustable)...oh and a crap oven isolator which I'm going to send back. I can't believe such a low quality switch could be sold.

Only one frustration in all this. (short rant coming up, I apologise)
1) Strip, sand clean receiver and asy; 2hrs
2) paint, 30mins
3) fit pump and motor, drill new holes, align pullies etc; 1hr
4) fit new regulators and air gadgets to compressor; 20mins
5) fit electrical boxes to wall; 10 mins
6) Align flat head screwdriver to godforsaken retarded, out-of-date, frustratingly irritating, dumb---- flat head screws that all electrical fittings seem to have; 600000000days

Why, for crying out loud, why flat heads? come on, there must be a logical reason to use these? I mean , Philips are so much quicker and easier and secure! It just beggars belief. I curse when I come across the odd one in my 1965 classic car, but all electrical fittings have this crappy screw head that I forever have to fiddle around trying align my screwdriver to, then slip off and swear as I faf around looking for it again. Wiring up took 100x longer than it should have, it's not hard, just stupid. I designed a cover and sent it to my 3d printer quicker than I could do up all the frikin stupid screws on the electrical fittings. Even the ones that hold the front cover on are stupid flat heads.

Rant over, again, I apologise.
Thanks for all your help here.

 

[DPG]

If you pick the correct size screwdriver for the screw then it shouldn't slip off the head.

 

[styleruk]

If you pick the correct size screwdriver for the screw then it shouldn't slip off the head.

I know, just a pet hate. Same with Philips, torx and any other head type, but flat is simply anoying.

 

[telectrix]

I know, just a pet hate. Same with Philips, torx and any other head type, but flat is simply anoying.

forum is having problems with uploading pics. what you can do is either upload as a pdf, or send pic. to image host site, then post a link to it.

 

[pc1966]

So, eventually the starter turned up. Meanwhile, been getting mixed messages form various people, most staying, you don't need a starter for that!
But I've got it and fitted now so tough, I have one.

As already explained, a motor starter has a specific job to deal with: to allow motor start surges while also protecting against motor overload, where as the supply MCB or HRC fuse is there to protect the starter from massive fault currents.

You won't notice a good starter doing its job, but without one if the motor is locked or otherwise overloaded you will find a burned out motor which costs a bit more to replace than the starter costs!

 

[Lucien Nunes]

Align flat head screwdriver to godforsaken retarded, out-of-date, frustratingly irritating, dumb---- flat head screws

Whatever you choose to do in life, never even contemplate becoming an organ-builder.

 

[marconi]

Styleruk - Would like to post a picture but apparently jpg is not recognised so I can't be bothered to figure that out.

pc1966 provided a top tip which I tried and it worked for me too: Post the image to google pictures and then insert a link in a forum message to that google image. To insert a link in a message use the chain button in the toolbar immediately above.

Google Photos - All your photos organized and easy to find - https://www.google.com/photos/about/

 

[Julie.]

Sorry, bit late to the party, but we too have a compressor - 3hp in our home workshop, and it may be worth explaining what I fitted for my husband.

Machine Mart are not electrically qualified, and merely sell the cheapest things at the price their customer's want - so electrically, fitting a cheap motor via a simple switch on a 13A outlet will work. - However, in time this will breakdown at which point they can sell you more cheap parts! - win win!

In our case we had issues - once I found out how it was wired and so on - I did the changes below! (Husband buys stuff, plugs it in - only mentioned to me when it goes wrong!)

The standard arrangement is that the Line comes in through the pressure switch, then direct to the motor - standard run and start capacitors in the motor.

So the little pressure switch makes against the full start current ~50-60A, and once up to pressure breaks the highly inductive full load current of the motor ~10-12A - it doesn't last long!

So, I provided a double pole isolator (Local isolation) with a much higher capacity than strictly needed, and a contactor/overload (DOL), rather importantly I wired the coil to the starter from Line - through the pressure switch, to the coil (other side to neutral) to ensure that it is the starter that makes and breaks the motor current - NOT the pressure switch which is how it is wired as standard by MM.

The isolator is sized to be able to break FLC, but operationally we open this only once the motor has stopped.

It actually starts better than via the pressure switch (I think the high start current lifts the pressure switch contacts a little making a high contact resistance ).

One other issue was that the capacitors in the top of the motor get incredibly hot, as a result they do fail - noticeable once you have a proper overload - for technical reasons the run capacitor reduces the current seen by the overload (Known as power factor correction) once it fails the current goes from 10A to around 15A - this is not protected for by a simple fuse!
(after this I went round to a friend of my husband's, his compressor was just plugged in and destroying plugs and socket outlets repeatedly - his run capacitor was also shot, so had been running for months at 15A or so!

In our case we replaced the capacitors with the same size (electrically), but higher quality (and about 3-4x the physical size) - in an external enclosure. Shug just bought the replacement ones from MM - tiny - they fit inside the motor terminal box, we have not had any issues over the past several years, he had to replace them a couple of times!
[automerge]1589446504[/automerge]
Oops, just realised I lied about the compressor wiring!

After some time I added a timer - so the control circuit is -
Line - Via the contacts on the timer, then through the pressure switch, to the coil (other side to neutral).

Because the Muppet would leave it switched on and it would fire up in the early hours of the morning!!!!

Now it only works 08:00 - 21:00 and we don't annoy the neighbours (well not with this anyway!)

 

[styleruk]

OK, been a while, but I did promise a picture. This is the old girl finished up. the compressor did a grand job and held up nicely spraying, this is my first attempt at spraying, so not perfect, but suits the level of practical classic she is.
The weakest part of the spraying was damp. I bought an inline air dryer, cool piece of kit and suited my budget (second hand of course), but could not do long runs of spraying, however, it did dry the air perfectly.
Now, I do have an issue. Not used the compressor for about 4wks due to holiday etc. Went to turn it on and it tripped the main board.
I checked...
Took belt off pump, same issue
Socket; all checks out good
DOL; all looks secure and good
Auto shut off junction; all good.
Checked starter capacitor, measures 270µf, rated as 200....guess that's OK?
Not yet checked the running capacitor, maybe that's the issue...doubt it though.

I've ran out of things to check, could it be the actual motor faulty? It spins OK, so it's not jammed.
Any thoughts? I'll have another crack at it this weekend, wife don't like it when the house trips and she is left in darkness. So any suggestions (apart from pay an expert), is welcome.

 

[DPG]

View attachment 112072
View attachment 112073

OK, been a while, but I did promise a picture. This is the old girl finished up. the compressor did a grand job and held up nicely spraying, this is my first attempt at spraying, so not perfect, but suits the level of practical classic she is.
The weakest part of the spraying was damp. I bought an inline air dryer, cool piece of kit and suited my budget (second hand of course), but could not do long runs of spraying, however, it did dry the air perfectly.
Now, I do have an issue. Not used the compressor for about 4wks due to holiday etc. Went to turn it on and it tripped the main board.
I checked...
Took belt off pump, same issue
Socket; all checks out good
DOL; all looks secure and good
Auto shut off junction; all good.
Checked starter capacitor, measures 270µf, rated as 200....guess that's OK?
Not yet checked the running capacitor, maybe that's the issue...doubt it though.

I've ran out of things to check, could it be the actual motor faulty? It spins OK, so it's not jammed.
Any thoughts? I'll have another crack at it this weekend, wife don't like it when the house trips and she is left in darkness. So any suggestions (apart from pay an expert), is welcome.

The car looks lovely!

 

[styleruk]

The car looks lovely!

Thank you, if you look closely though (which my paint supplier did), it's not perfect. Don't think I'd spray an exotic classic but next up is an old 84 Land rover.

 

[pc1966]

Not used the compressor for about 4wks due to holiday etc. Went to turn it on and it tripped the main board.

What is tripping, an RCD or MCB?

Any thoughts? I'll have another crack at it this weekend, wife don't like it when the house trips and she is left in darkness. So any suggestions (apart from pay an expert), is welcome.

If lights are going as well, sounds like the RCD. Generally that implies an insulation fault, might be hardware really failed or water in somewhere.

Also at what point is it tripping, the moment the supply is connected, or when you try to start the motor running? That could tell you something about where the fault it.

If it is a hard short somewhere then a multimeter might reveal it, but often you need a high voltage (250V or 500V DC) insulation tester to really find out what is happening as far as 230V AC is concerned.

 

[styleruk]

What is tripping, an RCD or MCB?

If lights are going as well, sounds like the RCD. Generally that implies an insulation fault, might be hardware really failed or water in somewhere.

Also at what point is it tripping, the moment the supply is connected, or when you try to start the motor running? That could tell you something about where the fault it.

If it is a hard short somewhere then a multimeter might reveal it, but often you need a high voltage (250V or 500V DC) insulation tester to really find out what is happening as far as 230V AC is concerned.

RCD trips.
It could be water ingress, there is a small hole in the roof nearby and in extreme weather, like we had when I was on holiday, water may have got in there, never happened before but there is a small chance this could have happened. It seems dry, maybe I should take the motor off and have a good look at it. Pic attached showing the wiring at the top, I took this so I could zoom in on my phone and have a closer look at the wires. (start cap taken off)

 

[marconi]

If an electric motor has been unused for a while and cools down to low temperature its windings can absorb moisture from the air drawn inside the motor casing. Obviously more of a problem during damp conditions like you mentioned. One should not attempt to dry the motor by running it which can damage the windings irrevocably. Instead try and blow warm air on the motor from a fan heater so that its body temperature is elevated to say 40- 60C and maintained there for say 8 hours. Avoid blowing warm air on the capacitors.

 

[styleruk]

Wait, I tested the caps again with my shonky electrical tester. The running cap rated at 50µf measures exactly 50µf. The starter cap rated at 200µf measures 260-274µf. What does this mean? Does this mean the cap is buggered? How does a cap fail, does the farad reading go up or down? To me that seems a lot out.

 

[DPG]

Wait, I tested the caps again with my shonky electrical tester. The running cap rated at 50µf measures exactly 50µf. The starter cap rated at 200µf measures 260-274µf. What does this mean? Does this mean the cap is buggered? How does a cap fail, does the farad reading go up or down? To me that seems a lot out.

A capacitor can still read correctly as far as the capacity (uF) value goes, but can still be duff. Electrolytic capacitor tend to dry out and their ESR (effective series resistance) increases. The ESR can be measured with the right meter, but it's cheaper to try a replacement normally.