transformers in parallel

Without a scope, how could I make sure they're in phase? (Besides doing the thermal test: if they get too hot, I know something's wired backwards)

Michael

Let's say I've got a transformer, 110VAC primary, 24V secondary, 1A.

** No.

** Yes.

.... Phil

** There all identical - right ?

Just wire each one the exact * SAME * way.

Jeez - what a dope !

....... Phil

Well, it's not a great idea, but should work - I'd prefer to get a suitable transformer if possible.

Yes, definitely.

If I had to use multiple transformers, I think I'd prefer to use a separate bridge rectifier on each one (then you don't have to worry about the transformer phase), but you only need a single filter capacitor bank. I would probably put a low-value resistor between each rectifier output and the filter capacitor(s), in the hopes of equalising the loading on the four transformers.

--
Peter Bennett, VE7CEI  
peterbb4 (at) interchange.ubc.ca  
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca

"Peter Bennett"

** The only disadvantage of using multiple identical AC supply transformers is that * usually * it costs more and increases the weight compared to a single unit. ** But the OP stated his transformers WERE identical !!!

So no need for additional parts that just WASTE power and money.

IME, mass produced transformers come out identical, the number of turns used is automatically counted and is exact.

One only needs an AC meter to prove the point - by reading ZERO volts when connected across two similar ( in phase) secondary windings joined at one end.

...... Phil

Putting the xformers together like that is fine how ever, make sure you phase them correctly to not short each other. As far as the bridges. You would be better off with a single bridged rectifier that can handle the full load.

"

Yes, they are identical - but the secondaries are just two wires of the same color and it's not clear how they come out of the roll. Hence it's possible to get them "mixed up".

Michael

In this particular instance, ordering a dozen surplus 24V transformers is quite cheap. Much, much cheaper than buying one center-tapped 48V,

200VA transformer (which, ideally, is what I'd want).

k, sounds good.

I think I'll go with Peter's idea and just use one capacitor bank, multiple bridge rectifiers.

Thanks,

Michael

use your volt meter. connect all the primaries to gather in any order in parallel. then connect only one leg of each transformer of the secondary side together. with a volt meter you should not get any significant reading between the other 2 leads. You will ether get a canceled reading between each other which is what you want or, a double voltage reading which is not what you want. if you get the double reading, switch the leads on one xformers secondary and wire the other 2 together. repeat the same action with the rest treating the currently paired xformers as one..

"

** So they are NOT IDENTICAL after all - eh ??

Shit head.

...... Phil

** You are nothing but a f****it ASSHOLE !!

PISS OFF DOPE !!

...... Phil

You have interesting ideas about the word "identical".

I suppose the isotopic composition of the iron core could vary by a few thousandths of a percent...

Michael

lots of cheap surplus switching supplys around!

That's the best way to get the voltage and current required for the OP's amplifier supplies. Two 65 VA switchers would be a complete solution for

130 watts, and would cost $56 total, which includes all required primary fusing, rectification, current limiting, and regulation.

The shipping would be a lot more for surplus transformers, and then you have to add rectifiers, capacitors, and circuit protection components. If you factor in even a little bit for your time, the cheap transformer solution doesn't look so good.

Just a quick check on eBay came up with 124 hits, including 24V 6A Buy It Now for $22:

Or a 200 watt dual output +/- 43V 2A switcher from an audio amp, current bid $9.50:

Or buy it now for $21.50. Hell, I think I'll get one of these babies myself. I just bid on it. Should come in handy when I make my experimental amplifier.

I'd rather do things the easy way.

Paul

Bad idea,,.. The diodes in the rectifier will not allow for even load distribution. You may even have a bridge sitting there doing nothing while another is doing all the work and over loading if self along with the single Xformer it's connected to. Please take good advise and combined all the xformers in parallel into a single bridge rated for the combined load.

"

Ok, thanks.

(See? A good thing I asked. I had a hunch that just wiring the primaries haphazardly would result in a problem...)

Michael

I made a PS a few years back that did just this.

In fact you can parallel the primary side and put the secondary side in series which is what I did. It gave me a +- polarity since they wernt CT. (essentially doubled the secondary side windings) Of course it increased the secondary side current through each by a factor of 2 which isn't necessarily good but it works fine for my low power apps.

Putting both sides in parallel shouldn't have any effect but reduce the power in each just like putting resistors in parallel. Putting both sides in series gives the same ratio but the problem is the current in each will increase and will probably exceed the rating(similar to resistors in series).

i.e., in parallel you have same voltage across each and 1/nth the current. In series you have 1/nth the voltage but the same current. (assuming ideal and identical)

It is easy enough to figure out the phasing with a basic meter. If you connect the secondaries of two of your transformers in series and measure the voltage on the outside two legs, you should get double the voltage if they are in phase and almost nothing if they aren't. You can then move the wires to put them in parallel. Like this

Connections :

1----------> 2-| 3-| 4---------->

2 * V on 1 and 4 means you can then connect 3 to 1 and 4 to 2 and get double the I. Obviously YOU will need to mark the wires as you discover what is what. I would use one transformer as a base and mark all the rest to match it. Make sure to mark and track the primaries too! In act do that first. Just any old AC1 and AC2 will do, you will then use the secondaries to match the phasing.

Jim

Thanks for the replies, y'all. Looks like I was outbid for the transformers anyway...

I thought no one would raise the bid much above $6.

Thanks anyway. Learned a lot in this thread.

Michael