Mains voltage step down

Neal · Post by **Neal** » Mon Mar 10, 2014 3:11 pm

Guys whats the best way to step down the mains voltage?

I've just bought a nice turntable but its rated for 220v, our mains can be 250v+ when the PV system is generating and the TT has no voltage regulation. Autotransformers seem incredibly expensive and I don't what to use my Variac on a full time basis!

Cheers.

pre65 · Post by **pre65** » Mon Mar 10, 2014 3:20 pm

Hi Neal, just been checking my transformer box.

I have an autoformer transformer 0-115v one side and 0 - 220-230-240v the other.

Walsall transformers Model AXT2250A 250va.

If you can do anything with it yours for the cost of postage.

ed · Post by ed » Mon Mar 10, 2014 4:18 pm

Neal wrote:Guys whats the best way to step down the mains voltage?

I've just bought a nice turntable but its rated for 220v, our mains can be 250v+ when the PV system is generating and the TT has no voltage regulation. Autotransformers seem incredibly expensive and I don't what to use my Variac on a full time basis!

Cheers.

Hi Neal

I have a 250-220 step down toroid. Wound by Canterbury about 5 years ago. Totally unused and fitted in plastic box.

Email me if it's of any interest.

Neal · Post by **Neal** » Mon Mar 10, 2014 4:53 pm

Guys, many thanks, Ed I think yours sounds the best solution, PM sent

Neal · Post by **Neal** » Mon Mar 10, 2014 5:25 pm

Ah! Another way, Bucking transformer:

http://sound.westhost.com/articles/buck-xfmr.htm#s10

Paul Barker · Post by **Paul Barker** » Mon Mar 10, 2014 10:28 pm

The bucking transformer is alright, but another approach sometimes used is to just connect the low voltage secondary of a transformer in series with the mains, of sufficient secondary current for the job in hand. That way the primary doesn't have to be humungous, so you are getting the job done with a cheap little torroid. For example 12v torroids are ridiculously cheap because they are left over from the halogen lamp period which we are moving away from, and it is many years since iron ac transformers were used, it has been switch mode now for many years. If you get one with two secondaries you can drop 12v or 24v. If you have a preamp project you can even pick up the primary as a secondary and supply HT from it. If you aren't planning to use the ht winding isolate it for safety, obviously don't short it or you have made a short lived one ring hob.

Neal · Post by **Neal** » Tue Mar 11, 2014 8:26 pm

I've implemented an old 24v toroidal as a bucking tx and it works a treat!

Mike H · Post by **Mike H** » Wed Mar 12, 2014 10:04 am

Never seen that before, I would have instinctively used the series method, but very neat.

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