# Motor start Capacitor, help needed.



## 12345Peter (17 Dec 2012)

The capacitor is dead for a lathe motor I have. The capacitor is a Bosch and I have searched rs-online, farnell, maplins and several others, but I can't find exactly the same one, in fact I can't find any from Bosch. I also phoned RS and told them what was marked on the one I have, but they couldn't help.

There are a couple that have similar figures, but as I know nothing about Capacitors I can't tell if they are compatible.

The one I have is aluminium with two terminal on top and a stud mount on the bottom. I have seen some that have wires instead of terminals, am I right to assume that if everything else is okay then the wires are no problem.

Is there any supplier you know of that could help?

All the info printed on the capacitor is 
Bosch MP
0 670 314 205
12 uF +-10%
450V DB
-25/85 degrees C
HPFNT
FZ5
1029
BS5267

Regards
Peter


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## tekno.mage (17 Dec 2012)

The important things you need to know about your capacitor are the 12 uF and the 450V. The make or brand is irrelevant. Other things that may be important are the physical size and type of terminals - although the terminal type is less important as you can probably a get around any problems here if you are able to wield a soldering iron!

I suggest you type "Start Capacitor 12uF 450V" into google and see what comes up (I just did it and there are loads listed), then look through the listings until you find one that is the right physical size and terminal type for your requirements. Actually, as you don't say if yours is a Start Capacitor or a Start & Run Capacitor, try using the search "Start Run Capacitor 12uF 450V".

It's unlikely you'll find one in an aluminium casing nowadays - they all seem to be plastic cases now. High price is not necessarily an indicator of capacitor quality any more (most are made in China anyway). I recently sourced one for my own lathe motor and found the most suitable one on Amazon - and it was the cheapest and with free delivery. Shame it came in straight from Hong Kong, though - it took 2 weeks to arrive!


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## 12345Peter (17 Dec 2012)

Thanks for the reply, I don't know if it is a start run capacitor, I assumed it was a start as when I turn the lathe on the motor tries to start and if I assist it with a nudge on the pulley then it will work until switched off.

Regards
Peter


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## tekno.mage (17 Dec 2012)

From that description of the motor running ok if you help it manually to start with - it is a start capacitor.


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## CHJ (18 Dec 2012)

If in doubt, fit a Run rated item.
Only downside is physical size, run rated will normally be bigger.

Start capacitors are designed for short working duration, run capacitors will carry current continuously without overheating.

A good many of the cheaper motors have one capacitor that is serving both functions, a shifted phase to start it spinning in the correct direction and as a power contributor for increasing torque whilst running.


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## loz (18 Dec 2012)

Off Topic - Just having some memorable flashbacks to my RAF days, discharging via Brinkley sticks before maintenance on high power HF transmitters.

bang bang bang


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## JWLeaper (18 Dec 2012)

And similar to Loz I also remember from my RAF days reverse charging an electrolytic capacitor and watching it go bang; what a mess.

Back to the OP, I think I am right in saying you do NOT want a polarised or electrolytic capacitor.


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## DonJohnson (18 Dec 2012)

*12345Peter* - When you find your capacitor, you might consider connecting it via a switch.

In the 'on' position your lathe will start normally. In the 'off' position - as you found - it will not start by itself, and you have to give it a spin to get it going. But you can spin it *backwards* for reverse sanding.

Obviously, you should try it backwards before finding a switch and mounting it safely.


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## 12345Peter (18 Dec 2012)

DonJohnson":hy3c1dlh said:


> *12345Peter* - When you find your capacitor, you might consider connecting it via a switch.
> 
> In the 'on' position your lathe will start normally. In the 'off' position - as you found - it will not start by itself, and you have to give it a spin to get it going. But you can spin it *backwards* for reverse sanding.
> 
> Obviously, you should try it backwards before finding a switch and mounting it safely.



The lathe already has a reverse switch. It's a screwcutting lathe so I won't be doing much sanding on it, but thanks for the thought.

Regards
Peter


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## parvum (20 Dec 2012)

Hello Peter a good source of 440V AC Motor run rated capacitors local to us is Maplins in either Aylesbury or Slough

regards Paul


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## 12345Peter (20 Dec 2012)

parvum":37ap1ahj said:


> Hello Peter a good source of 440V AC Motor run rated capacitors local to us is Maplins in either Aylesbury or Slough
> 
> regards Paul



Hi Paul, I tried maplins online and they didn't have 12uf 450v capacitors. There is one also in Uxbridge, which is more local to me, albeit a small branch.

I have got one now, but haven't managed to fit it yet, tomorrow with a bit of luck.

Regards
Peter


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## 12345Peter (20 Dec 2012)

tekno.mage":18qqpk9f said:


> It's unlikely you'll find one in an aluminium casing nowadays - they all seem to be plastic cases now. High price is not necessarily an indicator of capacitor quality any more (most are made in China anyway). I recently sourced one for my own lathe motor and found the most suitable one on Amazon - and it was the cheapest and with free delivery. Shame it came in straight from Hong Kong, though - it took 2 weeks to arrive!



I did find a metal one that may have been okay, but when I phone the company to ask about it, they said they were not electricians on suppliers and that I should speak to an electrician, so I didn't really want to buy from them and gave them a swerve.

I have had all sorts of excuses from suppliers why they can't say their product is the one I need. I think it is because it is a relatively cheap component nobody wants to spend much time trying to help.

I have got one now, plastic cased and supposedly a match for the one I have, so I will fit it tomorrow and hope it doesn't go pop.

Thanks for your help.

Regards
Peter


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