Author Topic: poorly seig c3  (Read 1994 times)

Offline awemawson

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 5525
  • Country: gb
  • East Sussex, UK
Re: poorly seig c3
« Reply #25 on: June 08, 2017, 08:43:21 AM »
And does the beast now turn ?
Andrew Mawson
East Sussex

Offline davidcurtis021

  • Jr. Member
  • **
  • Posts: 25
Re: poorly seig c3
« Reply #26 on: June 08, 2017, 08:53:37 AM »
And does the beast now turn ?

yes it does. Thank you for asking

Offline John Rudd

  • Hero Member
  • *****
  • Posts: 2166
  • Country: gb
Re: poorly seig c3
« Reply #27 on: June 08, 2017, 09:00:18 AM »
Just make sure you fit the new fuseholder.....and... Fwiw, despite what fuse is fitted, change it to a 3 amp fuse.....These machines tend to be shipped with fuses with a rating higher than necessary.
The result is either a blown control board or motor or both.....you could also check the fuse in the mains plug....again no more than 3 amps should be sufficient
eccentric millionaire financed by 'er indoors
Location:  near Hull

Skype: chippiejnr

Offline davidcurtis021

  • Jr. Member
  • **
  • Posts: 25
Re: poorly seig c3
« Reply #28 on: June 08, 2017, 09:09:45 AM »
Just make sure you fit the new fuseholder.....and... Fwiw, despite what fuse is fitted, change it to a 3 amp fuse.....These machines tend to be shipped with fuses with a rating higher than necessary.
The result is either a blown control board or motor or both.....you could also check the fuse in the mains plug....again no more than 3 amps should be sufficient

thanks John

i know for definate that the fuse in the plug is a 5 amp so i'll do that straight away.

Offline John Rudd

  • Hero Member
  • *****
  • Posts: 2166
  • Country: gb
Re: poorly seig c3
« Reply #29 on: June 08, 2017, 09:14:33 AM »
So, what is the justification for a smaller fuse?
Simply put, watts is volt x amps.
The motors on these small lathes are around 300-400 watts. So at max load they will consume no more than about 2 amps....Generally the speed controllers have in built protection to avoid over current, but should something  go awry, last level of protection is the fuse....

Thats my take on it and as it happens, is the same approach adopted by Warco, I'm told from sources on another forum
eccentric millionaire financed by 'er indoors
Location:  near Hull

Skype: chippiejnr

Offline PekkaNF

  • Hero Member
  • *****
  • Posts: 1796
  • Country: fi
Re: poorly seig c3
« Reply #30 on: June 08, 2017, 11:21:23 AM »
Time-current characteristics
http://www.littelfuse.com/~/media/automotive/catalogs/littelfuse_fuseology.pdf

Looks like 3,15A fuse blows about 10A in 0,1 sec, would that card withstand 30A for 0,01s?
http://www.farnell.com/datasheets/1447843.pdf

Generally those fuses are fine when they are chosen to blow out on wire short circuit and prevent wires. To dimension these glass tube fuses to protect electronic circuit on small over current or surge load is not easy.

Another issue is selectivity. The mill fuse should blow before plug fuse and plug fuse should blow before mains fuse. Two fuses near same melting current is a bad idea.

Pekka


Offline John Rudd

  • Hero Member
  • *****
  • Posts: 2166
  • Country: gb
Re: poorly seig c3
« Reply #31 on: June 08, 2017, 12:34:50 PM »


Generally those fuses are fine when they are chosen to blow out on wire short circuit and prevent wires. To dimension these glass tube fuses to protect electronic circuit on small over current or surge load is not easy.

Another issue is selectivity. The mill fuse should blow before plug fuse and plug fuse should blow before mains fuse. Two fuses near same melting current is a bad idea.

Pekka

Pekka,
I was merely suggesting that to prolong the life of the machine, the the op change the fuses to a value lower than those originally fitted.
It is cheaper to replace a blown fuse in the event of a fault than have to buy a new motor or pcb.

The manufacturers of these machines will fit protective fuses, albeit with values that are far too high...the number of machines that have come my way for repair have fuses that are far in excess and have not afforded any protection to the motor or electronics....
I did not make my recommendations on a whim, there is evidence from other forums, that members there have had the same recommendation from a major machine tool supplier....
At the end of the day, its no skin off my nose if the op does nothing..however, if I carry out repairs to a machine, I ensure that the equipment fuses are adequate and fit for purpose in order tomoffer any guarantee of repair.

Rant over....
eccentric millionaire financed by 'er indoors
Location:  near Hull

Skype: chippiejnr

Offline PekkaNF

  • Hero Member
  • *****
  • Posts: 1796
  • Country: fi
Re: poorly seig c3
« Reply #32 on: June 08, 2017, 04:07:13 PM »
Something lost in translation :wave:

My intention was not to criticize your choice of fuse on this particular instant. Merely to point out some points to greater public that there is some logic on fuse selection.

I have noticed the same thing about fuse size, maybe they rather sell new card/motor than listen rap about burnt fuses. Also the mill might not reach rated power with smaller fuse, but there is risk of burning something under other circumstances.

Cheers,
pekka

Offline tom osselton

  • Hero Member
  • *****
  • Posts: 837
  • Country: ca
Re: poorly seig c3
« Reply #33 on: June 09, 2017, 12:44:56 AM »
That happened to me on my Craftex mill the doughnut wire wrapped thing (choke?) unsoldered itself and dropped onto wires below! They gave me a different board but the tack has not worked since.

Offline bpud

  • Jr. Member
  • **
  • Posts: 6
Re: poorly seig c3
« Reply #34 on: September 06, 2017, 07:03:18 PM »
I've only just caught up on this thread.  My Sieg C3 had a very similar problem.  A short time after getting the lathe about 11 or 12 years ago the plastic chuck guard was removed, it got in the way all the time.  The switch and metal guard mounting rod were left in place.  Sometimes the rod needed a bit of a tweak to ensure that the switch was open and the motor would run.  The chuck guard microswitch was a bit hair trigger, so it was removed and a small wire link applied to the PCB.  End of problem!!
cheers
Bill

Offline PK

  • Sr. Member
  • ****
  • Posts: 285
  • Country: au
Re: poorly seig c3
« Reply #35 on: September 06, 2017, 08:17:08 PM »
The problem with specifying a fuse is that it has to:
a: blow at a current * time value (it's energy that blows a fuse, not current)
b: withstand the inrush current at startup. which can be 10-100 times the operating current if you have a DC power supply (like those little lathes do)

For a circuit that always draws the same current, you fix this with an NTC thermistor.  This device has a high resistance when cold and this resistance drops as it heats up. What happens is that the high resistance limits the inrush current at startup to sane values (maybe only 4 -5 times operating current) and then heats up.

For a circuit that draws a variable amount of current (eg a motor speed control on a lathe) it's somewhere between VERY hard and impossible to pick an NTC thermistor with the correct characteristics.

So what do you do?
The cheap way is to pick the smallest fuse that has an INRUSH rating up to the task and just live with whatever its maximum continuous rating is.

We went through this process recently where a product did, in fact, draw a fairly constant current of about 100mA at 220V. However it needed to operate from 24V-250V.  As such it had a big bank of capacitors (to deal with the low voltage application). We measured  inrush at around 150A when we ran from 250VAC...