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How is easy is it to replace a transformer?

post #1 of 12
5/27/10 at 11:17pm
Thread Starter 

Hi everyone, I have a 13.8V 4A linear power supply, its a samlex rps1204. I want to replace the steel plate transformer it has with a toroidal transformer.

 

There's no info anywhere on the transformer. The transformer has two cables for the AC input and 3 output cables that go to the small circuit board. 

 

How easy would it be to replace it?  Ive seen several 12v toroidal transformers on ebay and partsexpress would any of these be an ok drop in replacement?

 

I have experience working on house wiring, I know how to use a multi-meter, and I can solder. thanks


Edited by Kawai_man - 5/27/10 at 11:41pm
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post #2 of 12
5/28/10 at 12:47am

if its a drop in replacement then its just the matter of desoldering and soldering again. just you have to pay attention to the wiring. too easy

Your one is center tapped I guess. somethg like 12-0-12

it should be written on the trafo anyways?


Edited by tamu - 5/28/10 at 12:54am
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post #3 of 12
5/28/10 at 2:08am
Thread Starter 

Theres nothing written on the transformer, I even removed the chassis around the transformer and checked around it and nothing.

 

 

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post #4 of 12
5/28/10 at 2:19am

so you need to measure between the first secondary and the ct then do the same for the other one(if you havent done so). it might as well be 6vac in each secondaries and you dont want to blow the regulators.

then your ready to go. also dont forget to measure too. you want somethg that fits in the case.

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post #5 of 12
5/28/10 at 2:52am
Thread Starter 

Sorry Im still not really familiar with the terminologies, so the transformer has three output wires, 2 are secondaries and one is a CT? What does CT stand for? thanks

 

I measured the three output wires from the transformer: when I measured 1 & 2 it gave me 18.80vac, for 2 & 3 it was also 18.80 vac, and for 1 & 3 it gave me 37.62vac.

 

I can post pics of insides of the power supply if needed.

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post #6 of 12
5/28/10 at 3:53am

553-VPT36-4440. search this on mouser. I think this is what you need.. Better check with someone else aswell.

 

Maybe email samlex and ask for the specs of the transformer? It can make it so much easier:D

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post #7 of 12
5/28/10 at 4:37am

CT - center-tap

 

You probably have a ~36v transformer with a center-tap. 18-0-18, maybe lower.

That's 25v rectified using half the transformer, I can't make much sense of it =/

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post #8 of 12
5/28/10 at 6:32am

By Steel plate, do you mean EI?

 

Here is a photo of a cheap EI transformer:

EI-Transformer-EI-15-.jpg

 

They can also be made to lay flat, or mount to a PCB but are characterized by the laminations.

 

I have to ask, WHY!!!111?

 

There are some advantages to toroidal transformers with regards to efficiency and "flux leakage" (although IME that's BS, most toroidal transformers leak flux in and in an unpredictable pattern)

 

OTOH, a large advantage to an EI transformer actually comes as a side effect from its inefficiency. The bandwidth of an EI transformer is not as wide as a toroid and accordingly noise on the power line is often rejected. EI transformers also provide better overload characteristics (particularly if there is any DC on the power line which saturates toroidal transformers surprisingly quickly and makes their retarded leakage worse), and a VERY predictable flux leakage pattern

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post #9 of 12
5/28/10 at 1:45pm
Thread Starter 


 

Quote:
Originally Posted by tamu View Post

553-VPT36-4440. search this on mouser. I think this is what you need.. Better check with someone else aswell.

 

Maybe email samlex and ask for the specs of the transformer? It can make it so much easier:D



I checked the spec sheet for this PS just in case but there was no info regarding the transformer, I sent samlex an email.

 

 

 

"By Steel plate, do you mean EI?"

 

Yes I believe so , here's a pic of the current transformer.

 

 

Photobucket

 

 

"I have to ask, WHY!!!111?"

 

From what Ive been reading it seem it might offer some sonic improvement such as lower noise, everyone seems to like toroidal transformers for their DIY builds and also most high end gear seems to use them , I think it will also be good practice since I would like to replace the transformer on my tube dac with a toriodal one eventually.

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post #10 of 12
6/1/10 at 4:32pm
Thread Starter 

Samlex finally got back to me with the transformer specs

 

Power:                                                                                 200VA

Primary :                                                                              120 VAC, 60 HZ

Center tapped Secondary  (No load):                      37.5 V ( 18.8 V from one leg to the center tap)

 

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post #11 of 12
6/1/10 at 11:38pm

Sweet. So now you know what to get.. Make sure you measure the space and compare it to the new toroidal. You dont want to end up with somethg thats not going to fit.

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post #12 of 12
6/1/10 at 11:50pm


 

Quote:

 

 

"I have to ask, WHY!!!111?"

 

From what Ive been reading it seem it might offer some sonic improvement such as lower noise, everyone seems to like toroidal transformers for their DIY builds and also most high end gear seems to use them , I think it will also be good practice since I would like to replace the transformer on my tube dac with a toriodal one eventually.


You are incorrect.  Toroidals are used by a lot of DIYers because they don't know any better.  EI power transformers are lower bandwidth, which means they only let through the 60Hz you want, and not the high frequency noise you don't want, meaning they act as noise filters. Toroidals let it all in, which makes them higher noise.

 

The reasons one might use a toroidal is because you can get more power from a smaller core meaning that the transformer can be smaller (read cheaper) and because they give off a smaller magnetic field.  But, you do not seem to be power limited, and this is an external PS so you don't need to worry about magnetic interference.

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