Compressor blowing fuses
Turbo Mini Forums

I've got a relatively new compressor, has been fine to date.

Tried it last nigh and it managed about half a turn before popping the fuse. Replaced the fuse and tried again, same thing.

Has anybody any thoughts on what to try? It has oil and isn't seized. The garage is a bit damp at this time of year, but the compressor looks dry.

if you have a switch box on it try taking the cover off and blasting with hair drier

Done now needs redoing lol

Is the off load valve working? Is there pressure in the tank? If so try draining any compressed air in the tank down before starting it again.

Thanks. I'll give both those a go when I have some more fuses. I have literally put it in place and ran it up to pressure a couple of times. the gauge says the tank is empty.

What power rating is it ???

A decent sized compressor will not run off a standard 13A plug even if it is a 240V single phase unit.

Schrödinger's cat - so which one am I ???

It's a sealey SAC5030VE. 3HP V Twin 50l receiver.

Its 240v rated for 13amp supply.

If its blowing the fuse it unlikely a problem with the supply, mine used to do this on startup, I never did get to the bottom of it, but can you give it a few turns manually before trying to start it?

"Cars are a lifetime of pain"

Andy, 3HP is approx 2.3kW

which is approx 9 Amps running.

Start-up current is at least three times that if the compressor is loaded or the motor slow to start.

Most modern ones have a de-load valve to try to minimise the start current - but the valves often stick and don't work.

IMHO you just need a better (higher rated) supply, ie at least 30A, not a 13A plug.

Schrödinger's cat - so which one am I ???

I agree - my mill often blows the breaker on startup, even with a radial 30A supply.despite being only a 2hp motor

had the same prob with my snap on 150l compressor needed a 30 amp supply ,i was trying it on 16 amp supply started up but soon tripped the fuse box

give em hell

hmmm... I had it on and off plenty of times when I first got it.

So how would I get a 30amp supply in my garage? Is it just a case of fitting the 30amp socket to the existing wiring or will it need a new feed.

30 amp supply for a 13 amp applience?! My arse......... Might as well jam a nail in there and not bother with the fuse altogether.

Do not replace a 13 amp fuse with anything other than a 13 amp fuse on a 13 amp applience!! The fuse protects the wiring, not the motor. replacing the fuse with something bigger would see the wiring melt if there was a significant fault that was causing the fuse to blow in the first instance.

13amp plug fuses are HRC fuses which mean they can carry the short term high start currents, but will rupture almost instantly if there is an earth fault. The fuse will carry a great deal of over current for quite some time before it ruptures in an 'overload condition. The fuse IS NOT THE PROBLEM.

Firstly I would check the motor for an earth fault. This is the main reason a fuse pops straight off. put the compressor into a starting scenario without it being plugged into the socket. Ensure the fues is replaced, and then check both the nutral and live pins on the plug individually between the earth pin, with a multi meter set on ohms. Any resistance to earth on the live, I would suggest you need to start looking for a new compressor.

If there is no earth fault, and if the motor has stalled for any reason, when switched on, you will hear a noticable 'hum' for a short period prior to the fuse going pop. I've had a stalled motor with 160amp fuses draw 550 amps for nearly 10 seconds before the fuses went pop. The wiring was very warm to the touch afterwards.

That makes sense Colin.

It starts to turn for maybe 1 second at most and the pop goes the fuse.


When I have some more fuses, I'm going to try firing it up with the line open and and the tank vent open.

Been here many times, as sprocket says the supply is not the problem 3 hp IS the limit of a normal 3 pin outlet, just look through machine mart everything stops a 3hp, there are larger single phase motors out there which is beside the point they are a thing of the past,pressure unloaded is built into the pressure switch a small nylon tube between the non return valve and the pressure switch, this gives the audible hiss when it shuts off, and is why you should not turn the comp off at the wall when running either let it fill or use the small knob on the pressure switch to turn it off. But that ain't your problem either if its blowing that quick like many I have seen it prob the motor that's fucked, these v twin units have an all on one motor unit and they are not great quality/don't generally have a great life span, that's why a belt driven unit of the same size costs a lot more as it has a propper induction motor. I have blown three of these combined units and I now have a belt drive that's lasted longer than all three. Is your garage supply on an rcd at any point, should be really either its own or an and rcd protected circuit in the main dis board if its not taking this out then its not a live earth fault more likely a winding that is duff it possibly one of the capacitors, it may have two, a start cap and a run cap. Dismantle the motor and disconnect the caps one at a time and try it again, if its one of those motor will prob not start but will hum instead of just blowing the fuse straight away, either way tbh its prob not worth messing with.

Edited by oli79 on 7th Feb, 2013.

On 5th Oct, 2014 Shauna said:
What that's crazy, you go commando hahaha! How heavy is your helmet ?

By the way all you above who are knocking breakers out on start up its probably not the supply that is the problem but the breaker itself, domestic are b types, for motor rated applications you need c types, they have a curve to cope with the inrush currents

On 5th Oct, 2014 Shauna said:
What that's crazy, you go commando hahaha! How heavy is your helmet ?

The garage is fed by RCD in the house. It's a C type breaker as I kept tripping the B breaker when I used the spot welder.

I'd be surprised if the motor was fooked Oli, it's barely got an hour's running on it.

Get a meter and measure the resistance between the pins of the plug (with it unplugged of course).

Should be open load (O/L) between +ve and earth and -ve and earth.

If it's not start investigating.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

I would hope it isn't with an hour on it! But stranger things have happened, do the test as will says but its doubtful that is the problem it would knock the rcd off in milliseconds, assuming there is an earth the to garage, had one last month broken earth to garage prob been like that for 20 years lol,.

On 5th Oct, 2014 Shauna said:
What that's crazy, you go commando hahaha! How heavy is your helmet ?

Yes if it's a hard fault, but a high resistance earth fault may give odd symptoms.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

True but a high resistance earth fault would not draw the 13 amps needed to blow the plug fuse either, domestic rcd should be 30 Ma or 0.03 A thats all that would need to pass through the 13 plug fuse and to earth in order for the rcd to operate, but other than the earth between the rcd and garage been broker there is also the wildcard, that the rcd could be fucked, had one of those last month too, and just because the test button works does not mean the rcd does, you need a propper tester to determine that.

On 5th Oct, 2014 Shauna said:
What that's crazy, you go commando hahaha! How heavy is your helmet ?

Also Andy the tank vent open will make no difference to starting load, the pressure builds between the pipe off the top of the compressor and the non return valve, usually its a 90 degree brass valve screwed in the tank and there is a solid metal tube from the 'head' of the compressor and this, dissconnect this tube.

On 5th Oct, 2014 Shauna said:
What that's crazy, you go commando hahaha! How heavy is your helmet ?

Been out to the garage in a very fetching grey striped pyjama bottoms, dressing gown and rigger boots combination. It's bloody cold.

Firstly I don't know what resistance is unless it's in the context of John not wanting to get of his arse to do something...

If I touch all the terminals in the plug (new fuse in) in any combination, it stays at 1 no matter which resistance (upside down horseshoe type symbol) setting on the meter. Popped the top of the switch. Checked the resistance between brown and blue on both sides of the switch and it goes down to zero quite quickly.

Popped the top of the bit where the wires go after the switch and got really confused. No idea what goes where, but there's a big cap in there (4" long, 2" diameter) with what looks like a lump of bluetack on the side with soot sprinkled on it...

All still the same, runs for c. 1 second then pops the fuse. Over pressure valve is free, no pressure in the tank.

As for the garage, it has a big armoured feed from the RCD in the house. All passed part P in 2008, so doubt there is anything majorly wrong with the supply.

Get us a pic of the capacitor, soot sprinkled doesnt sound good

On 5th Oct, 2014 Shauna said:
What that's crazy, you go commando hahaha! How heavy is your helmet ?

I'll get one tomorrow. Top work on the picture.

Confession time - I swapped the blow off valve and the hose connector bit onto the other side of the switch. It ran fine and got up to pressure a few times after that. I'll double check that I put the pipe back on right from the non return valve properly.