General ? On Dual Primary Transformers - Double UP?

[Super_BQ]

This question might be related to 50/60Hz cycle on transformers.

Let's take a toroidal transformer with the following description:

Dual Primary: 115/230VAC
Dual Secondary: 0-18 & 0-18

From a 230VAC mains power source. We would SERIES the primary and to get 0-36 volts on the secondary we would series them also.

My question is, would it be safe to run 230VAC if we PARALLEL the primary so we can get double the voltage output on the secondary? What impact would doing this have? (more noise?)

BQ

 

[jh6you]

As far as I understand, the transformer will anyhow keep its original maximum power rating. If so, doubling up the voltages as you plan will pull the maximum current rating down to half.

 

[moamps]

My question is, would it be safe to run 230VAC if we PARALLEL the primary so we can get double the voltage output on the secondary?

No.
Usually, you will destroy transformer.

Regards
Milan

 

[AudioFreak]

My question is, would it be safe to run 230VAC if we PARALLEL the primary so we can get double the voltage output on the secondary? What impact would doing this have? (more noise?)

Unless you specifically know otherwise with the transformer in question, the answer is no. The usual effect is destruction of the transformer.

 

[jh6you]

Audiofreak,

Is the destruction happening due to increased current in primary side? Or, is the story more complicated? Thanks.

 

[kilowattski]

I don't understand why the transformer would be destroyed? Maybe someone could explain that to me. The only reason I can think of is that the primary current would be doubled and the primary windings may not be able to handle the extra current.

 

[moamps]

I don't understand why the transformer would be destroyed? Maybe someone could explain that to me. The only reason I can think of is that the primary current would be doubled and the primary windings may not be able to handle the extra current.

Hi,

You can find some infos here:
http://www.allaboutcircuits.com/vol_2/chpt_9/11.html

Regards
Milan

 

[dnsey]

Depending on how it's wound, the primary winding might not be designed for the resulting voltage gradient, leading to insulation breakdown, shorted turns, and a possible fire hazard.

 

[jh6you]

Thanks, moamps!!!

 

[moamps]

Thanks, moamps!!!

 

[Super_BQ]

Thanks for the Reply Guys!

moamps,

Thanks for the link I figured saturation would be a serious issue.
Also the article addresses the problem with running the primary at lower voltages.

BQ

 

[D3]

Hi Moamps

We have discussed this before.................the transformer I have
is a single unit with dual primarys and secondaries.

Primarys are 230v and secondaries 18-0-18v.........each are rated at 500va.

I intended to parallel this transformer to get 1000va 18-0-18v

Airlink the uk supplier suggest that this is ok ........ as the coils have the same turns.............

However, am I going to get the dreded coil saturation and transformer burn out???? I am not too technical and would appreciate your advice............

Kind Regards
D3 Bolton uk.........

 

[jh6you]

D3

I think your question is different from the subject of this thread. Here we are talking about the increase of primary voltage from 115Vac to 230Vac.

By the way, I just learned that we need to answer the question raised in this thread, with respect to the magnetization of core—i.e. we need to remember that the magnetic flux is the integral of the (primary) voltage (= area under the voltage wave curve). Therefore, if the voltage is increased, the magnetic flux may go beyond the core flux saturation limit, which makes trouble. One electrician sitting near to me confirms this, blaming my ignorant post #2. He adds: "Buy new one!!"

 

[jh6you]

And, the electrician says: "Your post #2 is ok when the core has enough flux."



But, who (maker) would use that big enough core at cost.

 

[D3]

Core voltage

Hi jh6you

Thanks for your post............your right I'm not increasing voltage of the primary......I just got a bit worried when some real technical / safety issues were highlighted............

Phew .... not too worried now........

Kind regards
D3 (Bolton uk)

 

[moamps]

Re: Hi Moamps

However, am I going to get the dreded coil saturation and transformer burn out????

Hi,
Core saturation isn't primary problem when secondaries are parallel connected. But, if secondary voltages aren't perfectly same, huge current will flow between secondaries and this will be problem. Imagine difference in voltage of only 0,1V and secondary resistance about 0,01ohm or smaller (usually resistance for 500V secondary). Current between secondaries will be 0,1/0,01=10A !!!!!!!!!.

Good solution is using separate bridges and paralleling rails after them.

Regards
Milan

 

[D3]

lots of amps!!!!!

Hi moamps..........thanks for posting
I guess I better be real careful and measure the windings.....and if there is any miss-match use the double rectifier solution......I will attempt to measure soon and get back to you....

Cheers
D3