View Full Version : Anyone Know Anything about Air Compressor Motors?

14-11-14, 12:22 PM
My Supercheap Blackridge compressor has decided to bite the dust just as I need it for some concrete chiseling... damn thing!

Basically it runs and gets up to almost but not quite 90PSI but then you can hear the piston slow down and then stop while the motor hums like it hasn't got the gumption to drive it any harder.

I ripped the cover off and can turn it over by hand so the piston's not seizing but I noticed that the big 450V 35uF capacitor has been installed with stupidity and has melted and some of its insides are now on the outside.

What are the chances this is the sole cause of this? The difference is about $40 to replace it or a new compressor... just want to see if the $40 is a waste of money or not before forking out for it first...

Oh, plenty of oil in it too...

14-11-14, 12:48 PM
most likely the capacitor is a good place to start.
It changes the phase if its value has changed the motor will now not make full power.

However before spending any money have a good look at the motor, is any hint of that distinctive burning coil smell? once that starts its over...
some motors have a centrifugal clicker to engage strating circuit at diffrent speeds, does it still work?

Cheers John
Ps if you need a comp for the weekend you can borrow mine...

14-11-14, 01:51 PM
Yes Pete, good chance it is the capacitor, I probably have one of that very value in my tool bag... at work... so may not get it to you until next week, I'd take up Johns offer until then.

14-11-14, 02:19 PM
Thanks guys... I didn't smell anything to indicate the coil or motor is burnt out so sounds like the capacitor is the culprit then.

Reg, if you do that would be awesome as I was going to hunt around for one next week.

Gonna be too damn hot to do anything over the weekend but thanks for the offer John it's very much appreciated.

I have a photo of the culprit but can't see how to post it using the phone, will have to wait til I'm on the PC. The second option is scrolling down to the tab labelled "Attachments" this is where you can choose how to upload images too.

15-11-14, 11:37 AM
Pete, it deffinately sounds like the capacitor has spewed its guts because it has expired (note: the gasses from these when they burnout can be hazardous) and therefore will need replacing. Due to the high voltage ranges if you do change it it has to be the same or higher, never replace it with a lower voltage rating.

As for uploading photos, when you post you will see a tab labelled " Go Advanced" this is where you can upload your images either from another site or directly from your computer.


16-11-14, 06:58 AM
Cheers Shane, the iPhone was making the attachment difficult but all good back on the PC :)

I'll most definitely be sticking with 450V minimum!

Here's the pic... definitely insides on the outside... oh and Reg it mounts with a single stud in the bottom of the capacitor. No stress if you don't have one I'll hunt one up this week.

The design has the underside of the capacitor physically touching the motor which isn't real bright as when it gets hot that heat is transferred directly to the body of the capacitor. I'll adjust the mounting slightly when I replace it.


16-11-14, 01:30 PM
Using extension leads can contribute to capacitor failure. Try to avoid their use or keep as short as possible and with a high amp rating.

17-11-14, 06:43 AM
Thanks for the tip Thomas, unfortunately there's no power point anywhere near where I use it but I'll see what I can do...

I'm pretty sure the main reason is the body of the capacitor being in physical contact with the heat of the motor though in this case. There is definitely what appears to be a melting mark where it contacts it.

17-11-14, 10:40 AM
Pete, I have in my hot little hand, a capacitor of that very value and mounting method you desire, when do you want it?

17-11-14, 11:24 AM
That would make you a legend Reg! I won't get to do anything before Sunday so if you're planning on Power O'ing on Saturday then that would be just fine for me as I plan to be there :)

Let me know what I owe you and if it's nothing then I'll get you a coffee or brekky or something...

17-11-14, 02:05 PM
You owe nothing Pete, it's not new but is ok, I'll bring it to Power O.

18-11-14, 07:26 AM
Awesome Reg, heading up to Mick's this avo' for a new rear tyre so I should be all set for Power O!

24-11-14, 06:06 AM
Thanks again to Reg, the compressor is running like new, and that air hammer certainly gives the concrete a beating!

24-11-14, 08:56 AM
Good to hear Pete, have fun.