Toroidal Transformer blowing fuses

[emperor]

Hi guys, i have a Toroidal tranny which is 35v-35v. It is running on 240 volts, (UK). i am building an Amp, and only yesterday I wired it up, brown and blue, to a mains IEC socket, to do a test.

i wired the grey and violet wires together, left hanging, And i had two secondarys, black/red , orange/yellow, that were giving me both 35 volts.

Now when i do the test, it blows the fuse on the IEC socket to the mains. And I am guessing, as im rather new to electronics, that i should not cut the unused violet and grey wires ?

Would that be right?

As at the same length, yesterday, it was perefectly allright.

Any input would be appreciated

[AndrewT]

What rating is the transformer?
What rating of fuse is blowing?
Have you built and used a mains light bulb tester?

[troystg]

Please elaborate on the transformer and the load.

Pics would be good.


There was a problem with my original description on Apex.jr transformers and BrianGT's PCB's... That was cleaned up and correct instructions on Steve's (apex.jr) website.

[emperor]

Hi Andrew

rating is 35 - 35volts, its a 5amp fuse to the 240volt plug, and the IEC sockets fuse is a fast blow, kind, that it not blowing at all, its the mains plug fuse.

and no, i have not built the lightbulb tester.

I purely was checking the 35v secondarys yesterday, i cut the 115 volt violet and grey wires down, soldered them together and today this happens.

thanks for the input

[emperor]

Sorry its 500VA, (35volt x 2 Secondarys)

[AndrewT]

500VA/220Vac*3~=6.8A
use a T8A fuse.
Frightening!!
Try using a soft start and you should be able to start the transformer on a T2A or T2.5A fuse.

[emperor]

thankyou Andrew and Troy.

I have now resoldered the violet and grey wires to their original size, and its all working fine.

The transformer i have requires that when you wire up the primarys in series, to get 240 volts, so the Blue, neutral , and brown ,live, go to the power switch, and the Violet and grey wires, have to be put together and left, floating.

i made the mistake of cutting the wires which must have ,messed with the windings. the only reason i say that as After doing a few searches online for cutting the grey and violet wires.

One Amplifiers instructions i cam across said that the Violet and grey wires should not be cut. Smacks own hand. Im so glad it was'nt in the finished Amp.

[emperor]

Try using a soft start and you should be able to start the transformer on a T2A or T2.5A fuse.

Actually for the Amp, yes i do have one, and speaker relay protection. Only the best for Truey

[kevinkr]

Originally posted by AndrewT
500VA/220Vac*3~=6.8A
use a T8A fuse.
Frightening!!
Try using a soft start and you should be able to start the transformer on a T2A or T2.5A fuse.

AndrewT just wondering where you came up with that equation? Typically I would use/recommend about a 3A or 4A slow blow with a 500Va transformer on 230V.

[richie00boy]

Violet and Grey are just random colours and will vary from toroid to toroid, you can't apply anything on the web.

The toroid itself should have a label on depicting connection scheme. Usually though for 230V operation the two primaries are connected in series which sounds like what you did.

A 500VA toroid needs a soft start. There is a very simple one on my website. Once you fit a soft start then you can size the fuse normally using

I = VA / Volts

or in your case 500 / 230 = 2.17 or a 2.5A rated time delay