110volt trasnsformer

[Blister]

Hi , most of my hand tools are 110 volt . I purchased a used twin socket

transformer and whenever I switch the power on it trips the fuse ?

I can go and reset the trip and it will be fine :?

Is this normal or is it destined for the scrap heap ??

 

[lurker]

Sounds like a surge
power up the tranny with no load & see what happens?

 

[Blister]

Sounds like a surge
power up the tranny with no load & see what happens?

Still does it with no tools pluged in ?

 

[Racers]

Hi,

It could be a mains filter in the transformer causing it to trip, they have capactiors to the earth connection that need to charge up, but this causes the RCD to trip but after they are charged its o/k, I used to have this problem with rooms full of computers you couldn't turn the power on with out switching them all off.


pete

 

[dickm]

Glad someone else has this problem! I have two 110v transformers, but only get the problem with one of them; similarly, my arc welder causes tripping, but the MIG does not.

An ex-colleague said that it was to do with "phase lag and lead in an inductive circuit", which if I understand it right means that the resulting current in the phase and neutral lines gets out of step and the earth trip thinks this is an earth leak. It also means the precise moment in the current cycle that you switch on is critical. So you just have to keep trying till you get lucky - .
But why one inductive load should cause problems and not another, someone else can explain,

 

[chippy1970]

One of my old 3 kva trannys did the same and I found that if you plug the tranny in slowly with the socket switched on already and no tools connected to it, it will not trip, give it a go.

The newer trannys dont seem to trip out very often.

 

[Niki]

I have a 100V 3kva trans. and it never did it

Maybe, try to switch the wires in the plug (the neutral and phase) and try again...

niki

 

[herdsman]

What is the current rating and class/type of the circuit breaker?

Some mcbs are not suitable for inductive loads even if the current rating is okay.

 

[RobertMP]

One of my old 3 kva trannys did the same and I found that if you plug the tranny in slowly with the socket switched on already and no tools connected to it, it will not trip, give it a go.

The newer trannys dont seem to trip out very often.

The reason for the plugging in slowly working is that you make a bad connection that cannot carry the full current - which lets some magnetism get into the core and hence some resistance to current flow before the final full connection. Not a good idea in the long run as you are deliberately causing arcing of the contacts.

At the moment of connection there is very little resistance to current flow and if the voltage is at a high point in the ac cycle you get a high instantaneous current that trips a std breaker. Switch on at the low point in the 50Hz cycle and you are OK

As said a higher current breaker or inductive load type is the answer. My 3kVA 110V tranny is fine on a 13A fuse and std 20A breaker on the board.

 

[herdsman]

[

As said a higher current breaker or inductive load type is the answer. My 3kVA 110V tranny is fine on a 13A fuse and std 20A breaker on the board.[/quote]

Surely a higher current circuit breaker is not the answer because this could be a potential fire risk by allowing excessive current to flow should a fault occur with the transformer? The correct current rating and class of breaker would be the safest solution in my opinion.

 

[dickm]

The reason for the plugging in slowly working is that you make a bad connection that cannot carry the full current - which lets some magnetism get into the core and hence some resistance to current flow before the final full connection. Not a good idea in the long run as you are deliberately causing arcing of the contacts.

At the moment of connection there is very little resistance to current flow and if the voltage is at a high point in the ac cycle you get a high instantaneous current that trips a std breaker. Switch on at the low point in the 50Hz cycle and you are OK

As said a higher current breaker or inductive load type is the answer. My 3kVA 110V tranny is fine on a 13A fuse and std 20A breaker on the board.

Would I be right in assuming that the difference between transformers in whether or not they cause tripping could be down to residual magnetism in the core when switched off?
And how do you determine whether a breaker is inductive load type?
Is there anything like a "soft start" that you can plug in between socket and transformer to deal with this sort of thing?

 

[herdsman]

Take a look at this data sheet from MK www.farnell.com/datasheets/41288.pdf
It indicates two different classes of circuit breaker; type B and type C, the type C would be suitable for inductive loads such as transformers, single phase motors and some types of lighting

 

[Blister]

thanks for all the replys :lol:

If I use it in the house it trips the fuse under the stairs

If I use it in the workshop or garage it trips the fuse in the garage

I have a 30 amp supply to the garage / shed and a 20 amp trip in the fuse box :lol:

may try one of the type C thingys :?

reading the MK site sheet reminded me of my trip to Egypt :? all hieroglyphics

 

[exigetastic]

thanks for all the replys :lol:

If I use it in the house it trips the fuse under the stairs

If I use it in the workshop or garage it trips the fuse in the garage

I have a 30 amp supply to the garage / shed and a 20 amp trip in the fuse box :lol:

may try one of the type C thingys :?

reading the MK site sheet reminded me of my trip to Egypt :? all hieroglyphics

Does it trip the "fuse" (I'm guessing you MCB) or the RCD?

If it's the MCB a type C may do the trick. The type C MCB is designed for circuits with higher in rush current (a short burst of extra current demand at the moment the initial power is fed in). B's are normally set for 3-5 the rated load, C's 5-10 for very short periods.

Therefore your 20A MCB will trip at between 60 and 100A inrush, a 20A Type C would be 100A-200A.

A simple test could be plugging it into a cooker socket if you have one. My last house had one on a dedicated circuit with a 32A breaker (from memory) This would give you a 96A to 160A inrush ability (close to the 20A on type C) . If it still fails bin it!


This explains it fairly easily.
http://www.voltimum.co.uk/news/1826/inf ... BCD--.html


TBH I'm not sure if your be allowed to change your own MCBs (due to Building Control) so you'd need a sparky. By which time you'd probably be better off getting a new tranny!


Si

 

[Blister]

thanks for all the replys :lol:

If I use it in the house it trips the fuse under the stairs

If I use it in the workshop or garage it trips the fuse in the garage

I have a 30 amp supply to the garage / shed and a 20 amp trip in the fuse box :lol:

may try one of the type C thingys :?

reading the MK site sheet reminded me of my trip to Egypt :? all hieroglyphics

My feed to the garage is the electric cooker one , as we have a gas cooker

So it sounds like " Bin it ! "

:lol:

Does it trip the "fuse" (I'm guessing you MCB) or the RCD?

If it's the MCB a type C may do the trick. The type C MCB is designed for circuits with higher in rush current (a short burst of extra current demand at the moment the initial power is fed in). B's are normally set for 3-5 the rated load, C's 5-10 for very short periods.

Therefore your 20A MCB will trip at between 60 and 100A inrush, a 20A Type C would be 100A-200A.

A simple test could be plugging it into a cooker socket if you have one. My last house had one on a dedicated circuit with a 32A breaker (from memory) This would give you a 96A to 160A inrush ability (close to the 20A on type C) . If it still fails bin it!


This explains it fairly easily.
http://www.voltimum.co.uk/news/1826/inf ... BCD--.html


TBH I'm not sure if your be allowed to change your own MCBs (due to Building Control) so you'd need a sparky. By which time you'd probably be better off getting a new tranny!


Si

 

[soapy]

Hi Blister,
This is by no means unusual, I find that if you leave the socket on and reset the breaker it stay in on the first or second attempt. If you swop the mcb for a C type these require a much lower earth loop reading.
Regards
Soapy.

 

[White House Workshop]

A couple back...

How would anyone know if you'd changed the MCB yourself? I've changed quite a few breakers in my panel, some up and some down, and you can't tell that they have been changed as they are 'plug-in' units.

The only way I think anyone might get suspicious is that the distribution might not be even or in rating order? Typically the panel starts with the highest rating at one end and works across (or down) to the lowest rated breakers at the other. At least in the ones I've worked on. You'd only know there'd been a change if one of the breakers was out of rating order? Of course if you mixed them all up no-one would be any the wiser. Be sure to move the wires at the same time......

Oh yes, I have 2 110V xformers - one 750VA and one 3kVA. Neither of them has ever tripped a breaker, although the fluorescent lights will sometimes go out in the workshop when I switch on the tablesaw because of the sudden inductive load. Usually happens when the tubes are still cold, especially in winter.

 

[chippy1970]

One of my old 3 kva trannys did the same and I found that if you plug the tranny in slowly with the socket switched on already and no tools connected to it, it will not trip, give it a go.

The newer trannys dont seem to trip out very often.

The reason for the plugging in slowly working is that you make a bad connection that cannot carry the full current - which lets some magnetism get into the core and hence some resistance to current flow before the final full connection. Not a good idea in the long run as you are deliberately causing arcing of the contacts.

At the moment of connection there is very little resistance to current flow and if the voltage is at a high point in the ac cycle you get a high instantaneous current that trips a std breaker. Switch on at the low point in the 50Hz cycle and you are OK

As said a higher current breaker or inductive load type is the answer. My 3kVA 110V tranny is fine on a 13A fuse and std 20A breaker on the board.

Robert what I was saying in simple terms was that one of my old trannys did it and the newer ones dont.

I am sure Blister doesnt want to be baffled by science or bored with electrical knowledge.

He just wanted simple advice and I am a joiner not a sparks so I was just saying what happened to me I would never give electrical advice unless I was a fully qualified electrician.

If you did want electrical advice I could always get my father on here who is an electrical engineer so I am sure he could really baffle you :lol:

 

[RobertMP]

Your newer ones probably include a thermistor in the circuit or other clever means of initial current limiting and the old one does not. They could be wound with aluminium like some cheaper welding sets and have internal resistance that limits the current (do they run warm?) - just guesswork.

I'm surprised a higher current rated breaker also trips and I'm not sure I would trust the unit completely.

My electrical theory knowledge comes from college back in the 70's so I'm quite willing to accept I've forgotten a lot or am out of date . I also never meant in my earlier comment that a breaker should be changed in rating if the circuit conductor size was not suitable.

 

[exigetastic]

A couple back...

How would anyone know if you'd changed the MCB yourself? I've changed quite a few breakers in my panel, some up and some down, and you can't tell that they have been changed as they are 'plug-in' units.

The only way I think anyone might get suspicious is that the distribution might not be even or in rating order? Typically the panel starts with the highest rating at one end and works across (or down) to the lowest rated breakers at the other. At least in the ones I've worked on. You'd only know there'd been a change if one of the breakers was out of rating order? Of course if you mixed them all up no-one would be any the wiser. Be sure to move the wires at the same time......

Oh yes, I have 2 110V xformers - one 750VA and one 3kVA. Neither of them has ever tripped a breaker, although the fluorescent lights will sometimes go out in the workshop when I switch on the tablesaw because of the sudden inductive load. Usually happens when the tubes are still cold, especially in winter.

I mentioned changing the breakers, you are right no one would be any the wiser, but strictly speaking..

If only i could get hold of some more black and red twin and earth