advertisement


Basic diy Q

The Captain

The Captain

~~~~~~~~~~
Hi chaps,

a simple Q. Following my router dust thread, I got me a temporary Titan £50 wet/dry vac.

Damn thing sometimes -blows- instead of sucks though. Sometimes. Total opposite functioning. Weird.

My question is how can this be, from a basic motor perspective-? Would I be right that the motor must be "in reverse" to achieve this cockup.. & again from a basic electrical pov.. has anyone heard of any 'leccy motor doing this?

Thanks, Capt
 
I have a Rega P3 turntable that, many years ago now, would suddenly go into reverse and the turntable would turn anti clockwise thereby playing the album I was listening to backwards. This is not good for the record, or the stylus. I seem to recall the fault was diagnosed as a failing capacitor on the motor circuit.
 
Oily Rag said:
I have a Rega P3 turntable that, many years ago now, would suddenly go into reverse and the turntable would turn anti clockwise thereby playing the album I was listening to backwards. This is not good for the record, or the stylus. I seem to recall the fault was diagnosed as a failing capacitor on the motor circuit.
Click to expand...

Hmm.. thanks. Now I do recall hearing of a few TT's doing that.. albeit old ones.

This vac is brand new, so seems particularly odd behaviour. I'm likely to get it changed (screwfix) but prolly just for one from same batch you see. I thought this symptom might, possibly have something to do with my house electrics, although the socket & spur are a new build all signed off. Weird.

Capt
 
You can get a domestic socket tester pretty cheaply. I have one that I've used frequently over the years being a keen Try It Yourselfer. It tells you whether all the wired connections behind the socket are intact.

If it's a new machine it certainly shouldn't be down to failing electronics. Maybe it's a control switch fault - loose connection or something. Screwfix should certainly change it for you as it's new.
 
Thanks @Oily Rag yes they'll swap it.. but I just cannot be in the same boat again: having superfine mdf dust blown back all over you, eyes/ mouth etc/ all over workshop is infuriating & hours of workshop cleaning up.

I just wanted to understand how an armature motor, router/ vac/ TT/ anything, can possibly do this sudden reversing trick, electrically speaking. The most likely culprit within a circuit.


TT is a useful example. So if anyone knows how a TT motor, could cause the platter the rotate the wrong way round for example, I might understand this vac blowing.

Thanks Capt
 
I've got one of those extractor vacuums with a socket on it, I use it with my router and tracksaw. Its Brilliant, turn on the tool and the vacuum turns on and turns off a when you finish your cut, bought the bags for it too just over a hundred quid but we'll worth it after using a standard vac for a few years..
 
Steve 57 said:
I've got one of those extractor vacuums with a socket on it, I use it with my router and tracksaw. Its Brilliant, turn on the tool and the vacuum turns on and turns off a when you finish your cut, bought the bags for it too just over a hundred quid but we'll worth it after using a standard vac for a few years..
Click to expand...

No this isn't one of those. Your type is the expensive ones I'm toying with idea of buying. This is a cheapo, but when it does suck, it will possibly suffice as a test to see if my dewalt router jobs, are able to go inside: IE 1.3k of suction -can- remove enough mdf & birch ply dust, in my setup using a router, inside my 4x4m workshop.

No point me spending £300 on a festool extractor vac for eg, if it's not gonna suck sufficient debris out & I'm forced to take it all outside again, (which doesn't necessarily require a vac as wind blows dust away).

When I say socket, I mean the place you insert the hose into same on most vacs-with-hose types.

----

If anyone knows how a TT reverses, I'd be grateful. Thx Capt
 
The Captain said:
Hmm.. thanks. Now I do recall hearing of a few TT's doing that.. albeit old ones.

This vac is brand new, so seems particularly odd behaviour. I'm likely to get it changed (screwfix) but prolly just for one from same batch you see. I thought this symptom might, possibly have something to do with my house electrics, although the socket & spur are a new build all signed off. Weird.

Capt
Click to expand...
A miswired socket cannot cause this. Only three phase motors are fussy about phase order
 
I don't know the details of your motor obviously, but I suspect you have a bad motor cap or a loose connection. I don't believe it is anything to do with your house wiring.
In essence, synchronous AC motors require a phase shift cap that delivers an slightly out of phase supply to one winding on the motor, while the unshifted supply goes to the other. These supplies and their generated magnetic fields 'chase' each other and create the turning force on the rotor. If the cap is bad or missing the motor can stall or it can be a bit of a lottery which way it gets going.
As for the batch thing, no idea. But a batch of bad caps? Possibly I suppose.
I'd probably try another one and go from there.
 
Which are we talking about now? I doubt your router uses a synchronous motor, more likely an induction motor.

80s turntables nearly always used 110V ac synchronous motors, with a dropper resistor for UK mains.
In the 2000s a 24V or less motor is more likely via a transformer.
These days brushless DC motors are more common
 
No, it's the vacuum.
It could well be an induction motor, but still might be a capacitor start. I think that can have similar problems with a bad cap or a loose connection.
 
@davidsrsb The vac only.

I was just using the TT motor as an example, as it was far more likely on a hifi forum to hear of TT motors 'reversing' than vacs. Basically any spinny leccy motor going backwards as examples, would possibly help me understand.

Seems like chief suspect is a dud capacitor then.

Anyway thanks chaps, @Retro especially. Capt
 
The Captain said:
No this isn't one of those. Your type is the expensive ones I'm toying with idea of buying. This is a cheapo, but when it does suck, it will possibly suffice as a test to see if my dewalt router jobs, are able to go inside: IE 1.3k of suction -can- remove enough mdf & birch ply dust, in my setup using a router, inside my 4x4m workshop.

No point me spending £300 on a festool extractor vac for eg, if it's not gonna suck sufficient debris out & I'm forced to take it all outside again, (which doesn't necessarily require a vac as wind blows dust away).

When I say socket, I mean the place you insert the hose into same on most vacs-with-hose types.

----

If anyone knows how a TT reverses, I'd be grateful. Thx Capt
Click to expand...
Mine was not expensive it has been used for quite a lot of jobs and works perfectly it's a step up from using a normal vacuum in my experence

Evolution R15VAC 1000 Watt 15L Wet & Dry Workshop Vacuum Cleaner With 1700W Power Take-off | Evolution Power Tools UK

The R15VAC Wet & Dry Workshop Vacuum is the perfect wet & dry vacuum cleaner for your jobsite, workshop & general cleaning tasks. The powerful 1000w motor has an impressive 42.5L/s of airflow for easy pickup of bulky building debris, f...
shop.evolutionpowertools.com shop.evolutionpowertools.com
 
It’s the phasing cap. An ac motor will run without one but in a random direction.

That brand is very cheaply made although they do work at a nice price of course. The faulty could be anything but no cap seen by the motor or maybe a faulty cap will do this.

My guess would be a bad connection

Get it exchanged. 👍
 
Steve 57 said:
Mine was not expensive it has been used for quite a lot of jobs and works perfectly it's a step up from using a normal vacuum in my experence

Evolution R15VAC 1000 Watt 15L Wet & Dry Workshop Vacuum Cleaner With 1700W Power Take-off | Evolution Power Tools UK

The R15VAC Wet & Dry Workshop Vacuum is the perfect wet & dry vacuum cleaner for your jobsite, workshop & general cleaning tasks. The powerful 1000w motor has an impressive 42.5L/s of airflow for easy pickup of bulky building debris, f...
shop.evolutionpowertools.com shop.evolutionpowertools.com
Click to expand...

Hi Steve, well that's interesting (the festool I was toying with is £300) although 1700w seems like it might be louder.. noise is one thing I need to consider. Stop/ start tho automatically, would be great.

Useful link thanks. capt
 
Eoin said:
It’s the phasing cap. An ac motor will run without one but in a random direction.

That brand is very cheaply made although they do work at a nice price of course. The faulty could be anything but no cap seen by the motor or maybe a faulty cap will do this.

My guess would be a bad connection

Get it exchanged. 👍
Click to expand...

Phasing- that seems to be the word in question: ok will definitely get it swapped now.

Thanks chaps, Capt
 
The Screwfix blokes won’t have heard of that, but the machine is faulty one way or another.
 
The Captain said:
If anyone knows how a TT reverses, I'd be grateful. Thx Capt
Click to expand...
By changing the phasing of the electric motor, assuming it is a synchronous type (like a Linn LP12. Rega, etc) . Do you remember the trick with the 3 fingers in science lessons, where you hold out a thuMb, a First Finger and a seCond finger? M was Motion, F was Field, C was Current. In an AC synchronous motor the voltage is cycling along its wave pattern, up and down. The motor works because you "phase shift" the rotor (part that turns) from the stator (part that doesn't). This means that at any given instant there is a mismatch between the rotor and the stator and a electromagnetic field (the F above) is generated that turns the motor (M above). Because the wave is cycling round this means that the motor is always trying to catch up with the wave, so it goes at the frequency of the wave. This mismatch (phase difference) is carried out by a capacitor in the stator and or rotor windings. If this fails you either get no phase diffeerence (so the motor won't turn) or a reversed phase difference so that instead of the wave "leading" the rotor it follows it with the result that it goes backwards.
If it helps you can imagine this as like a ship's compass. The compass is free to turn. You come along with a magnet, the compass swings round to go for the magnet. If you keep the magnet going round in circles the compass will follow it at the same speed, you have made a motor. This is what you are doing with your AC mains and a capacitor.
 
Last edited:
@stevec67 thanks so much for this explanation. I've read it twice, & need about 10x to get stuck in & comprehend things (alas I didn't get the 3 fingers lesson at school) even with your 'easy way' set out for me here.. which I'm most grateful for. I'll be dipping in over easter wknd away, to glean all I can from it.

Appreciated, Capt
 
You must log in or register to reply here.


advertisement


Back
Top