Weak link : fuse questions.

[Scudie]

Hi just a word of warning to any one that is working on or restoring / converting a wall box, or for that matter someone who may be contemplating doing so.

The wallbox requires a 25VAC  power source to allow it to operate. I have worked on / repaired, converted a dozen or so  Wallboxes now, and have always always always fitted a  2 or 3 amp fuse between the 25volt output wire of the transformer & the terminal block marked 25vac or live,  inside the wall box, with a fuse in place it will protect your transformer, if you should accidentally cause a short to common / ground.

I seam to remember my Father telling me that Familiarity breeds Contempt, well Familiarity or forgetfulness has just cost me the price of a new transformer.

Dont forget to fit a Fuse they are much cheaper than transformers!

Cheers Scudie

• This topic was modified 5 years, 8 months ago by Scudie.

[Sooner]

I’ve been putting a fuse in front of the transformer just because that’s the way all other electrical devices I’ve seen are set up.  Any reason why you put yours behind the transformer?

[Scudie]

I have also been replacing the standard 13 amp fuse in the the 3 pin uk plug with a 3amp.
As to in front or behind the transformer I thought that if the fuse was placed in the circuit between the power source and the item it is powering ie motor, lamps etc that this would be the correct place for it.
I believe that in the two descriptions of how to integrate the emulator into wallbox’s on this site they placed the fuse inbetwee the two windings of the terroidal transformer.
I am not an electrician and will stand corrected if I am doing it wrong.

Cheers Scudie

[Scudie]

Just as a trial I have just tried my system with a 1 amp  fuse inserted, which as expected blew as soon as a selection had been made.

Hopefully the 3 amp fuse  in the 25vac circuit should be low enough to protect the system from any further problems.

And the 3 amp in the wall plug to protect any one using it.

Cheers Scudie

[Sooner]

 

I forget about you folks in the UK having a fuse in your power cords. Here in the US there’s always a fuse first thing inside all electrical devices. My thinking on where to put the 3 amp fuse is that if there’s a surge or overload on the output side of the transformer there will also be a similar surge on the input side. My thinking is that because the transformer isn’t 100 efficient the current on the input side is always a little higher than it is on the output side. So putting the 3 amp fuse before the transformer should protect it as well as protect someone touching the wallbox if there was a short occurring before the transformer.  Killing two birds with one stone sort of. I saw where they put it in the instructions but I’m not convinced that’s the right place for it if there’s only one fuse. I probably should research my theory a little though just to be safe.

 

What happened that cause your transformer to blow?

[Scudie]

I was fitting & testing out a credit switch while it was live to see how many credits it would register,  and  momentarily pressed the switch by mistake while one wire was touching ground  & that was it game over. Went to change the fuse and realised my error. The 3amp in the plug was fine.

Cheers Scudie

[Sooner]

Hmm… So my theory may be all wrong.  Good to know.

[Sooner]

Okay… I think I just figured out the error in my theory. If the backside of the transformer is 24V and 3 amps, that’s 72 watts. Assuming 100% efficiency  the front side at 120V and 72 watts would be just 0.6 amps. Conversely, for the front side to be pulling 3 amps at 120V (1800watts), the back side would have to be pulling 15 amps. Not good for a transformer rated at 3 amps.

[Scudie]

That sounds to me that at you might be considering fitting a second  fuse after the transformer?

I use one of the blade type automotive fuses,  pushed into a couple of insulated female spade connectors.

Cheers Scudie

[Sooner]

I think I’ll look for a 0.5 amp to put in front instead of the 3 amp and see how it works. I that blows I’ll increase to 1 amp. (unless I can find a o.75 amp).

[Scudie]

I allready tried a 1 amp it’s ok if you want it for decorative purposes , but blew as soon as the motor began to run. Had look through a box of fuses  I didn’t have a 2 amp so  3 amp was used.

Cheers Scudie

• This reply was modified 5 years, 8 months ago by Scudie.

[Sooner]

Was your 1 amp fuse in front of the transformer? I was talking with someone else and they were using a 1 amp fuse in front with no problem.

[Scudie]

Hi 3 amp in the plug and 1 amp betweenI the transformer and the wallbox blew the 1 amp as the motor started. 3 amp in both has worked fine for me.

Cheers Scudie

• This reply was modified 5 years, 8 months ago by Scudie.

[Sooner]

Yes, I would expect a 1 amp after the transformer to blow.

[Klaatu]

I only use 1 Amp fuse before transformer.

[Scudie]

I guess in France you have a two pin plug ? Does the plug have a fuse inside it ?

Here in the UK we have 3 pin plugs connected to a 3 core flex, live, neutral & earth for 240v AC  13 amp mains.

I fit a 3amp ceramic fuse to the plug and conect the metal body of the wallbox to earth wire. To protect anyone touching the metal casing, should there be a short.

I fit a 3amp auto motive blade type fuse on the 24vac wire from the transformer to the wallbox this protects the transformer from me when I make a mistake while testing or fault finding.

I could buy 1 amp ceramic fuses, but I get the 3amp ones free.

Cheers Scudie

 

[Klaatu]

In France we have 2 or 3 pins but no fuse inside plug.

[Scudie]

Which do you use on your wallbox conversions?

Cheers Scudie

[Klaatu]

Both

[Scudie]

So is the French 3 pin like ours? With a live , neutral , & earth?

[Klaatu]

yes

[Scudie]

So if you use a two pin plug on some conversions, does this have an earth?

[Klaatu]

No, and my apartment isn’t earthed for electricity.

[Scudie]

I had a bit of a read up on French mains electric, (just curious) from what I read France and most of Europe use the same type of plugs & sockets, the earth connection being  part of the socket and does not necessarily rely on a pin like uk plugs.

Also sockets are not switched where as most in the uk are, and plugs are not fused. Aparently the way we wire our houses is also different!

 

[Author]

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