Combining dual secondaries of a toroidal transformer

That is what I would try first, assuming that the first color was the start of each winding, and the second color was the end of each winding.

All you need is a volt meter. First connect the the assumed end of the two primaries together (lets sat, white and gray) but connect 120 volts to only one of them (blue to white). Then check that the voltage between the remaining open end (black) to the one you expect to connect it to (blue), (to parallel the primaries, later) has very little voltage between them. I would think that this would be less than a volt. If you measure 240 volts, the two wires you connected together are a start and an end.

Once you get this low difference voltage condition, it is safe to connect the second pair wires together to complete the primary parallel.

Now you can perform the same test on the secondaries.

Say you connect orange and red together, and measure voltage between yellow and green. If you see very low voltage, it is safe to connect yellow and green. If you see about 70 volts, you will have to repeat the test the other way.

Even if you get this all right, it is possible that there is a slight turns miscount on one or more of the windings, and the transformer will circulate current between windings of slightly different voltages, even with no load. If this happens (you can insert an AC amp meter in the loop formed by the two windings to check) you may have to add a turn or two to the low winding to get a perfect match. But this is rare. At least it is easy to do with a toroid.

The peak of a sine wave is the square root of two times the RMS value, so neglecting diode drops, I would expect the unloaded DC to be about 33*1.414=47 volts. It may be a bit higher since the transformer's rated voltage applies at rated current load.

Connect the two secondary commons together. Now check across the other two leads with an ammeter for difference current. If it's only a few mA you are probably OK.

--
.
.
.
.
.
.
.
.

If he only gets a few mA, then the secondaries are phased properly. But what if they're *not* phased properly. Whay do you suppose is going to happen when he connects an ammeter across the other two leads?

Nothing much should happen if you get them backwards. The MMF is just going to push the currents in such a way that they oppose each other and you get no current. It might heat up but if you don't push much through it then you should be able to test. What you can do is hook up a fairly large load and a volt meter and then check both phases and see which one gives you the larger voltage.

33VAC usually means RMS but your filtering will start at the peak so you'll need to convert this into peak value and that will be your DC(So you'll get more). Ofcourse it will not be a true DC as there will be ripple but if you have good filtering then this would be approximately frequency independent. You can simply use an volt meter to measure if you like. I get about 45VDC that you'll get (minus a few volts because of the diode drops and stuff).

--- Absolutely, positively, definitely NOT.

You're a licensed electrician, where???

In the first place, the secondaries don't have "commons", they only have starts and ends. Two leads from the secondaries should be twisted together and one of the primaries energized (with the leads of the other kept separate and, preferably, taped up to avoid danger of shock or short) then the voltage across the unconnected secondaries should be measured with a _voltmeter_. If the reading on the voltmeter is 66 volts, then the start of one secondary winding is connected to the end of the other and they're wired in series. In order to connect them in parallel they should be disconnected and each connected to the other secondary lead.

Once that's done, the primary leads should be twisted together in pairs and those pairs connected to the mains while monitoring the secondary voltage. If the voltage is zero the primaries are wired out of phase and should be connected in reverse. That should cause the secondary voltage to rise to 16V.

-- JF

--
Oops... 33V

but then again, one could read the wire tags looking for the H1, H2, H3, H4 and X1, X2 , X3 and X4 leads.

H1+H3, H2+H4 for the primary.

X1+X3, X2+X4 for the secondary. But i know your aware of this, this is only for other readers.

--
"I\'m never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

If they are not phased properly he doesn't know what he is doing and shouldn't be doing this.

The current will be high.

--
.
.
.
.
.
.
.
.

NO!!!

If the secondaries are parallelled incorrectly, he will have a short circuit, and huge currents will flow through the windings.

As others have said, connect one end of SEC1 to one end of SEC2 (say, yellow to green), and measure the voltage between the free ends - if the voltage is near zero, the windings are correctly phased, and the two free ends may also be connected together. If the voltage between the free ends is about 66 volts, the phasing is wrong, and one winding must be reversed - connect yellow and red instead of yellow and green.

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

This may work for "electrical" transformers (ie: those intended to be installed by electricians), but I have rarely seen an "electronics" transformer (one an electronics tech would install inside equipment) labelled like that.

The best way, regardless of the transformer marking or colour code, is to get a datasheet for the transformer - it should indicate which wires or terminals are the start of the winding, and may even indicate the corrects connections for serial or parallel operation.

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

hmm, thats why I said to add a load. If the two secondaries are out of phase and have exactly the same reactance then there will be no current flow with or without a load.

If you take the two secondaries and put them in series the same effect will happen but you will need a load incase they are in phase. (or you could just measure the voltage, you will either get twice the voltage of one secondary(assuming they are equal) or 0.)

If he doesn't think they are equal then its still easy to tell. You either get +-(V1 + V2) or +-(V1 - V2). He can tell quite easily if they are in the correct phase by using series or not. (because if they are in the same phase then they can only add there voltages together. Ofcourse this assumes that one of the secondaries are not to much greater than the other)

If he wants to use test using parallel then he should add a load to both secondaries and then, say, use a current meter to measure the current. The same stuff applies above but with current. (or he could measure the voltage on the resistor).

The fact is that either they will work with each other or against each other. As always you have to be careful about shorting things out.

Actually no current will flow if these are perfectly identical. The current in one of the secondaries will attempt to flow the opposite way and there will ultimately be no flow because of cancellation. Obviously if one secondary has more turns than the other it will matter but adding a load to it will prevent any larger currents from circulating. The magnetic flux will induce a current in both secondaries equal and opposite direction. "shorting" the secondaries together will not result in any current flow in the ideal case. (Although adding a load will only help).

A 60 watt light bulb at your line voltage, wired in series with the primary winding(s) will prevent any damage to the transformer during testing. If it is wired properly, the lamp will not light. If it lights at close to full brightness, something is out of phase. It is referred to as a "Dim bulb" tester, and has been in use on a lot of workbenches for about 75 years.

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

A load across a short circuit? Its back to "Electricity 101" for you.

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

You still don't get it, do you?

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

The lesson would stick a lot better if he took his own advice and started his own fire.

if you're lucky the transformer will survive the short-circuit created if you get the primaries connected out of phase.

better to measure with a voltmeter, possbily while applying a low voltage AC signal to the secondary or to use a current-limited supply.

Bye. Jasen

--
Yup. I knew something felt wrong...

Thanks.

ITS NOT A FUCKING SHORT IF THEY ARE OUT OF PHASE IN PARALLEL OR SERIES(assuming no load).

Jesus christ. What happens when you hook up two identical batteries up in series out of phase? in phase? (ABSOUTELY NOTHING BECAUSE THERE IS NO CIRCUIT) What happens when you hook them up in parallel out of phase? ABSOLUTELY FUCKING NOTHING! (but there is a circuit)

What happens when you hook them up in parallel in phase? THEN YOU GET A SHORT!!! AND THIS IS WHY I SAID IN MY ORIGINAL POST YOU SHOULD ADD A LOAD. Ofcourse you f****ng neglect that part because you want to start some shit. I guess your life is so boring that the only way you can have some excitment is to get on sci.electronics.basics and start arguments by being illogical(ignoring half the sentence so that the other have then becomes wrong).

Did you guys actually ever goto school or just pretend? Cause I can't imagine that your professors would pass you if you only did the parts of the tests that you wanted.