Auto transformer help please

[Michael GilliganParticipant @michaelgilligan61133]

Better logic than mine, I think, Simon

Yes, of course the Blue and Brown should be the 230v input pair

< blush >

MichaelG.

[Ian ParkinParticipant @ianparkin39383]

I’m sure there must be a fault with the transformer…it was sold to my friends as a freeby with the range…its a bugger to get together and i wonder if its not been used since it broke…i wonder if someone had unwired the tranny looking for a fault… the way it looks like its wired to 240v permantely just waiting for the hood to be turned on..not sure that i would want that

the supply goes straight to the tranny then onto the hood switches

I’ll see what the company who made it say when i ring back

[noel shelleyParticipant @noelshelley55608]

Testing the insulation at 3v or there abouts will show a direct short but not a leakage, for this there are tools to do the job, the generic term is megger, though it is also a trade name ! On an RCD circuit if the leakage is about 30Ma or more it will drop. If the unit has been stored in damp conditions, this is possible.  I’ve done my best ! Good Luck Noel.

[Maurice TaylorParticipant @mauricetaylor82093]

Hi,

if the 240volt mains does not power anything other than that transformer ,you could borrow a 110volt site trans to see if the equipment works correctly . A new site transformer could be bought to power it permanently.

It would be safer as well

Maurice

 

[Ian ParkinParticipant @ianparkin39383]

Well success

there must have been a loop or wire between the 2 0v’s on the terminal block

so neutrals to blue 240v to brown

join the whites together and thats the 110v out

[Ian ParkinParticipant @ianparkin39383]

Is putting my meter set to ac current on the input wires …it measures 1/2 amp with no load connected

is this valid?

so that could be 3 kw a day?

[Robert Atkinson 2Participant @robertatkinson2]

I had not noticed the the connections were unknown. In that case, given the continuity testing and logic of colour codes you have two windings that need to be in series with the two white wires connected together and forming the 115V output, brown wire is 230V “live” input and blue wire is neutral common to bothe output and input.

If you have a low voltage transformer, say around 12V output and an AC meter you can check the auto transformer more safely by connecting the mains input (brown & blue) of the autotransformer to the output of the 12V transformer. You should then get 6V AC between blue and white (actually half of the voltage measued between brown and blue).

Comment on 60Hz stands.

Robert.

[Ian ParkinParticipant @ianparkin39383]

I was going to put in  a push button to start a contactor with a timer set to say 90 mins so the transformer wasn’t connected permanently

so when they wanted to use the hood or lights just press the push button and it would be live for 90 mins then switch off with no-one forgetting to turn off the supply

as its just in a domestic environment

[noel shelleyParticipant @noelshelley55608]

I would be cautious of your solution ! Is there 110V on BOTH whites ? So ? Link neutral to both blue (0v) and 0v, 110v is on both whites and fitted to 115v terminal and powers the hood with the 0V and brown is to 230v and to mains supply ? Noel.

[Ian ParkinParticipant @ianparkin39383]

This is how it’s wired now. Would you say this is wrong?

[Ian ParkinParticipant @ianparkin39383]

So 240 in to blue (0v) and brown (240v)

and 115 out from blue (0v) and the pair of whites

[Robert Atkinson 2Participant @robertatkinson2]

Obviously I didn’t type fast enough 🙂

Half an amp of no-load current is not unreasonable. However this does not equate to 120 Watts ( I assume you meant 3kW hour per per day). It is not real power because the voltage and current are not in phase so the correct tern is VA (Volt Amps) not Watts. Fortunatly your domestic electricity meter only responds to real power. There is some real power consumption due to the resistance of the copper wire and magnetic losses in the transformer core. Maybe 10-20W still significant,  80 – 100 kWh (units) per year.

Robert.

[Ian ParkinParticipant @ianparkin39383]

So would you ignore the power consumption and just leave the transformer permanently connected?

[Ian Parkin]

On Ian Parkin Said:

Well success

there must have been a loop or wire between the 2 0v’s on the terminal block

so neutrals to blue 240v to brown

join the whites together and thats the 110v out

How infuriating … that’s the suggestion that I edited-out  in this earlier post:

https://www.model-engineer.co.uk/forums/topic/auto-transformer-help-please/#post-712822

… Glad you have sorted it, Ian

MichaelG.

[Ian Parkin]

On Ian Parkin Said:

So would you ignore the power consumption and just leave the transformer permanently connected?

No.
If the existing switch in the hood is rated for 240V AC I would connect the transformer after the switch. If it’s not 240V rated I would by-pass the existing On-Off switch and have a switched, fused outlet feeding the supply to the transformer so they have to switch it off.

Robert.

[Ian ParkinParticipant @ianparkin39383]

Robert

 

the whole hood is 115v

so I’m sure the transformer was wired into the supply..it has a great big fan 2 heat lamps @250 watts each and 3 tungsten spots. @ 50 watts each

so the transformer is supplying quite a load if everything’s on

i dont want to leave the transformer on all the time and again don’t want to rely on someone switching it off hence my idea of a timed contactor.

heres the diagram for the hood

[Martin ConnellyParticipant @martinconnelly55370]

If you wire it up so one/some of the lights is/are on whenever there is power to the transformer it will encourage people to switch it off when not in use.

Martin C

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Ian, one thing I’ve noticed in your photo above, is the fan blades look as if they have a layer of crud built up on them, this reduces the efficiency of them, and should really be cleaned off, and of course, they will draw a little more power with the extra weight.

Regards Nick.

[Martin Connelly]

On Martin Connelly Said:

If you wire it up so one/some of the lights is/are on whenever there is power to the transformer it will encourage people to switch it off when not in use.

Martin C

Looking at the circuit diagram, I think it already has that feature.  (Possibly not if they are 3-position switches, centre OFF.)  On the face of it, one switch selects either the right or left heating lamp, so one of them is always on.  And the Halogen lamps are always on, except operating the switch puts a diode in circuit, so the lamps run dim at half-power.

Otherwise, the circuit doesn’t help Ian much because it doesn’t show how the unit is normally connected to the mains.

Judging by the size of the hood, it’s meant for a seriously big kitchen, perhaps a restaurant, and normally part of a planned installation with a dedicated switch-board and distribution system.   The hood might simply be switched on and off with all the other cookers when the restaurant opens and closes.   Not rocket science, but could be a bit more complicated than just plugging it into a socket.

Seems a couple of notches more difficult than fitting an ordinary domestic cooker hood.  Doesn’t help that it’s a US unit with 115V 60Hz internals, needing that transformer AND making replacement bulbs mildly painful to source.

Anyway, I recommend Ian asks the owner what he needs the hood to do.  When is it on, when is it off, and does the way the owner intends to use it require anything more complicated than an on/off switch?  Designing the controls after nailing the requirement avoids discovering flaws in the real word by burning the house down or getting a massive surprise electricity bill!

The cut wires are an alarm.  One reason is that the deinstaller rushed the job and didn’t care because it was going in a skip or because there was a commercial objection to the item being sold second-hand.  That’s OK.   But a major reason wires are cut like that is to stop the item being re-used because it’s faulty or unsafe;  I’d think about that possibility because the installer is held responsible if it goes wrong.

Dave

 

[Robert Atkinson 2Participant @robertatkinson2]

Your transformer is not big enough to supply the lights in that hood.
It needs significant work to use on 240V
It also has a “speed control” for the fan which is another worry on 50Hz.

Have they changed the lamps to 240V versions?

Robert.

 

[Peter Cook 6Participant @petercook6]

Sorry not paying attention!

[Maurice TaylorParticipant @mauricetaylor82093]

Hi
The mains input colours are USA white for neutral and black for live,which are the colours on the diagram.

Like I said before try it with a site transformer .

As usual,every post gets complicated.

Maurice

 

[Ian ParkinParticipant @ianparkin39383]

It came from a domestic installation sold on eBay as a freeby with the range the uninstaller i assume had a right job taking this hood apart hence the cut wires and missing screws

i’m guessing its 60 kg in all

heres as it was in situ at previous owners

The transformer is rated at 1200VA so what can it supply at 115v

the motor and bulbs are all controlled by dimmer type switches the diagram suggests switches..

i agree bulbs will be hard to get but they are available online..i could rewire to 240v..

this is what i started with

[noel shelleyParticipant @noelshelley55608]

sOME ARE COMPLICATING THIS ISSUE BY NOT PAYING ATTENTION ! One of the first pictures shows the capacity of the transformer to be 1200VA, to some extent born out by later pictures and the gauge of wire in the windings. The lamps could be rewired with 240v bulbs, the fan after a good blow out to clean it since it has been working on 50Hz should be OK on the 115 at 50HZ from the transformer. The original wire may well be heat reistant in which case I would reuse it if sound. Check out how the light switches work – are they centre off ? The fan motor will consume very little, the halogen bulbs may be 50W each the heat lamps ? The wires on the transformer were not cut just disconnected and 1200VA has worked – so why not now ? Whether the project is worth the candle is for Ian to judge, he has a wiring diagram ! Noel.

[Robert Atkinson 2Participant @robertatkinson2]

OK,
I read the transformer as 200VA I gues the terminal block was hiding a leading 1.
If changing the lights you almost certainly need to change the holders as well. North American light sockets are generally not adequately insulated for 240V.
Make sure al exposed metalwork is properly connected to the protective ground.

Robert.

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