Issues EB PKF 255 /2.5 wn - starting capacitor

[Mcluma]

Was doing some very heavy ripping this weekend and at one moment the saw was binding (wet wood and deep cut) and as the motor didn't want to start immediately the starting capacitor burned out.

I truly mean burn out; the good thing is these Italian capacitors are filled with fire retardant foam that when overheating it will expand and the capacitor will burst but you will have no flames.

The part (not costing more then £7.-) is stupidly mounted on top of the motor, which means you have to take the whole saw apart to get to it.

I have it on order, and hopefully will be in tomorrow so the work can continue

 

[Mcluma]

this starting capacitor is rated for 400v at 37.5 uf

but the machine is 240v

why is that

 

[NetBlindPaul]

This is normal for a motor cap.

The cap creates an artifical 3rd phase thus you are no longer comparing voltages with respect to earth, which is where your 240V, which is now officially 230V by the way! Comes from.
Increased voltage and also temperature as you have found out reduces the life of a cap!

 

[Mcluma]

Thanks for that info

 

[Digit]

Being good little Europeans it was decided that our 240 volt supply should be harmonised with our neighbours, at 230 volt.
Ok, so how much is fourpenny loaf?
Depends on whether that is decided by Brussels or not.
Our 240 volts was +/- 6% IIRC, but now it is 230 volts +10%/-6%.
Spot the difference?
230/240 volts is the RMS (Root Mean Square) voltage, that equates to about 326 volts peak, so for safety we use capacitors rated at 400 volts.

Roy.

 

[Eric The Viking]

Being good little Europeans it was decided that our 240 volt supply should be harmonised with our neighbours, at 230 volt.
Ok, so how much is fourpenny loaf?
Depends on whether that is decided by Brussels or not.
Our 240 volts was +/- 6% IIRC, but now it is 230 volts +10%/-6%.
Spot the difference?
230/240 volts is the RMS (Root Mean Square) voltage, that equates to about 326 volts peak, so for safety we use capacitors rated at 400 volts.

Roy.

And the actual mains voltage should still be 240V, BUT it's now possible to sell 230V apparatus (incl. lightbulbs) as fit for purpose here.

Gotta love the EU for all the benefits it brings us... :evil:

 

[NetBlindPaul]

Eric TV,
The actual mains supply voltage in the UK now, SHOULD be 230V.
However, due to "clever" tolerance bands it is still generally 240V.
All of the wiring regulations etc. etc. have been re-calculated at 230V as this is now the "official" nominal voltage now in the UK.
Regardless of what you may or may not measure at your outlets.
So in fact the actual mains voltage should NOT be 240V it SHOULD be 230V, however, see above.
We can go round in circles here get my drift!

The crux of it is, the "Official" nominal voltage is now 230V in the UK end of.
Clever application of tolerance bands to this allow the generating companies etc. to supply at 240V with the old tolerances and remain within the new 230V tolerances!
I don't make the rules I never joined up to the committee!


Digit,
The capacitor rating depends on whether the maker has rated it as 400V rms or 400V peak etc. The only way to know is ask them, it they speak the same language!!!

BTW
You could push the 230V +10% limit to 253V rms, then the peak would be square root of 2 times (1.414 approx times) that which would be almost 358V.
However, at the other end you would have around 216V rms with around 306V pk

Not a rigorous technical paper I know but it should help!

 

[Digit]

The capacitor rating depends on whether the maker has rated it as 400V rms or 400V peak etc. The only way to know is ask them, it they speak the same language!!!

Oh for the days when we all spoke the same language! As it is it's what I said about a fourpenny loaf. Then of course we have horsepower!
There are occasions when I would be happy to see a line voltage here that was within even the lowest tolerance. I once recorded 208!
I noticed the other day that we 'harmonised' our number plate reading distance as well.

Roy.

 

[Eric The Viking]

The crux of it is, the "Official" nominal voltage is now 230V in the UK

It depends what you mean by 'official': the harmonized EU voltage is 230V, but the normal supply voltage in the UK remains 240V for the forseeable future. this was stated by both the government and the supply companies when the harmonization happened a few years back. Unless, of course it's changed recently.

It is, incidentally, easier than one might suppose for them to alter the supply voltage, as most small substations have voltage adjustment tappings on the xformers, although possibly not 10Vrms down! The tappings are usually used to tune the local distribution to match the local load, so if you complain about excessive over- or under-voltage that's what gets altered (if they believe you!). If local premises change in use or more buildings are supplied from a given substation, they sometimes have to be altered.

There is also an issue with under-voltage for certain applications as it can cause failure of certain types of compressor - fridges spring to mind. I can't remember how this works but I believe they burn out if the volts drop to a certain critical point.

 

[NetBlindPaul]

Eric,
No matter what the distributors send out, or what anyone measures, the voltage supply in the UK is not 230V, this is dictated in ESQCR, BS7671 & other legislation. Thus the distribution voltage in the UK is now 230V. All design calculations are now based on 230V.
DNO distribution transformer tappings will probably be able to give around 25% variation, that combined with load shedding can give quite a level load voltage.
I know very well how easy it is for DNO's to change distribution voltages, there is much more to this than changing a transformer tapping though. DNO network design is quite a complex situation, as it is not just the base load but there are many other things to consider.
There is a large issue with undervoltage on many devices not just some fridge compressors.
Also, by the way, you all notify your local DNO when you install large machines in your homes so that they are aware of this to ensure that the local network is capable of carrying the laod don't you.
Remember that this is a statutory requirement, and the DNO are legally allowed to sumarily disconnet your premises without notice if they believe that the installation does not comply to BS7671 and / or may pose a danger to persons, livestock, or property, or may cause damage or distrubance to the DNO network?...

 

[Digit]

(if they believe you!)

In my case they didn't! They kept turning up in the day time and proudly 'proving' that the supply was within specified areas.
Of course the problem was mainly limited to nightimes, my TS certainly didn't like it!
Eventually I borrwed a chart recorder to prove my point.

Roy.

 

[NetBlindPaul]

They should fit a voltage recorder if you complain, mind I do have a helpful DNO around me.
The other thing is complain of flicker, this can have affects on medical conditions so they are bound to investigate this, and a voltage recorder is the best way.

 

[Digit]

They simply refused to believe my complaint, the line was tested with a coventional digital meter and that was that!

Roy.

 

[NetBlindPaul]

Roy,
You are in Wales, according to your location, WPD are very good, you must be under Scottish Power then surely?
Other option is how you word the complaint!
Other thing could be the condition of the install after the origin.

 

[Mcluma]

Capacitor arrived today, fitted tonight (also had to fit a new fuse) and its working again,

Bought an new blade so ready and set for more cutting tomorrow

 

[Digit]

You are in Wales, according to your location,

That's correct we were on SP but now WPD, as you say, they are OK.
They sorted the problem PDQ.
Tell you what SP were like, their engineer opened the old CU, saw all the spiders and scarpered!

Roy.

Correct that! We were with Swalec! They even threatened to take us to court for non-payment, we were on a token meter!