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ChrisH07/11/2010 13:37:11
1023 forum posts
30 photos
Howard, Steve,
Many thanks for your advice.  I will see if I can get a 'D' type MCB.  I suspected that it was the initial voltage surge on switching on that was causing the problem, which is why I tried a 20A job in a naive attempt to fix the problem. 
Ian S C08/11/2010 10:28:37
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7468 forum posts
230 photos
Chris, is the fan still working, or has it got clogged up, maybe with spider webs. Ian S C
Ian Abbott08/11/2010 18:22:23
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279 forum posts
21 photos
Speaking of LIDL's good stuff, I was in there the other day and they had something like 10" pots with four foot trees, labeled "Giant Bonsai Trees".
 
Ian 
ChrisH08/11/2010 18:30:04
1023 forum posts
30 photos
Ian, Yes the fan is still working, could hear it before I then took the cover off to hunt further, as the first thing I thought about was dead spiders or some other insect shorting across something, but it was all clear.
 
I thought it must be the start current surge as I switched the welder on whilst holding the MCB in (don't tell the H & S gestapo, they don't understand real life) and she switched on no worries.  Didn't know about this C rush stuff, or such things as A, B, C and D type MCB's, but you never stop learning and I do now!
 Chris
blowlamp08/11/2010 18:38:01
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1885 forum posts
111 photos
Ian.
In a similar vein, I was taken aback the other day when I saw that Ty-phoo QT has now been relabled as "Instant black tea with whitener".
 
Martin.
Stub Mandrel11/11/2010 22:18:50
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4318 forum posts
291 photos
1 articles
> Ty-phoo QT
 
Does that mean it doesn't work as brazing pickle any more?
 
Good tip i was given for a welder that sets off trips on switch on - use it at the end of a long extension lead, it helps limit the inrush current. Make sure the lead is unwound so it doesn't overheat. Works every time with my welder.
 
Neil
John Olsen11/11/2010 23:41:00
1294 forum posts
108 photos
1 articles
There is an interesting thing with inrush current, the actual size of the current pulse depends on the point in the cycle at which the switch makes contact. This is why you can get the situation where a transformer will just sometimes blow the fuse or trip the breaker on startup. (fuse aging can also affect this of course. )
 
One of our lecturers went through this at university, it is a good exercise in solving differential equations. However, it is now thirty years since I have had to solve one of those, so I will refrain from attempting it here.

regards
John
Martin W12/11/2010 00:19:41
940 forum posts
30 photos
Hi
 
Another method is to use a 'Zero Crossing Switch', these as their name implies switch when the mains voltage passes through or near to 0V which solves the current inrush problem but they are usually semiconductor based devices requiring a low voltage DC voltage to act as the switch so require a power supply to operate. That said I suspect there may well be self contained units on the market by now.
 
Cheers
 
Martin
ChrisH12/11/2010 10:02:05
1023 forum posts
30 photos
Hi Neil,
 
Thanks for the tip on using a long extension lead on the welder - I have a long meaty lead, I will try that.  If it works then that would be a lot cheaper than a new D type MCB!
 
Thinking about it, the lead on the welder is quite short and when used in the past it has always been on an extension lead - now in a new (to us!) house it is the first time I have been able to plug it into a socket direct, and the socket is quite close to the MCB.  
 
This tip should go into the "Hints and Tips" thread! 

Edited By ChrisH on 12/11/2010 10:02:52

Nicholas Farr12/11/2010 10:16:19
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3988 forum posts
1799 photos
Hi,
    "Zero Crossing Switch" or "Zero Voltage Switch" as it is also refered to, for AC would probaly involve the use of Triacs. Because of the high amperage needed to strike up an arc each time as well as the initial turn on inrush, these would have to have a higher rating to cope with the demands. I would think that such triacs would be much more expensive than a suitable MCB. With my large welder I have to limit the amount of weld current that I use, because the strike up amperage at the top end is as high if not higher than the meter rating. This is served by a 30A fuse rather than an MCB and through a deddicated 32A socket/plug. I've had no problem wiyh this. Needless to say I can't put my cooker on and then go and get on with a bit of welding while it is warming up.
 
Regards Nick.
Martin W12/11/2010 12:04:02
940 forum posts
30 photos
Hi Nick
 
The units I have looked at run at 30A rms, can withstand a peak of 630A for about 20ms and cost around £40 but of course this doesn't include a DC supply to control the unit. As you say it is probably cheaper to replace the MCB provided that one can get one that will fit the consumer unit.
 
Cheers
 
 
Martin
Les Jones 112/11/2010 18:32:24
2292 forum posts
159 photos
Hi Chris,
                  One thing you could try is to have a suitable value high power resistor in series with the supply to the welder and a high power relay (contactor) with the coil connected in parallel with the welder. Connect the contacts on the relay across the resistor. When first switched on there will be a significant voltage drop across the resistor so the relay will not pull in. When the initial current surge has gone away the relay will have enough voltage across the coil to pull in. The resistor will then be shorted out. The resistor needed would need to be between about 2 an 5 ohms.  You would probably have to make a suitable resistor from a long length of wire coiled up.
Les.
Stub Mandrel16/11/2010 21:05:01
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4318 forum posts
291 photos
1 articles
Money saver alert
 
For us sad old scrotes who still use imperial, Screwfix are selling  a usable set of 1/16" to 1/4" bits by 1/64" half of already low price, about £2.50.
 
The catalogue does not list the reduction, it just came through when I saw the bill, so check first.
 
Useful havinga set or two as spares, even if you have better ones.
 
Neil
ChrisH11/01/2011 17:05:36
1023 forum posts
30 photos
At last, back in the UK and a rare cold visit to the workshop, I tried the trick of using a long meaty extension lead to connect the welder to the socket that kept tripping and bingo, worked every time!  So that is that problem solved and a big thank you to Neil for the tip.
 
Chris 
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