transformer with two primaries ?

[dogdog]

I have this transformer laying around that have two primaries and one secondary... can some one explain that to me how it works or what was the purpose of that 2nd primary?
Can I repurposed it to be a secondary for 1:1 isolation output ?

transformer is Toroidal 375VA with 2 110v primary and 24V secondary...


Normally I would only see a 2 lead primary or multiple tap primary.... but this one seems to have two individual primaries... .. weird.

 

[66cj225]

doorbell circuit at the embassy? Their power/network vs ours?

 

[Bert_]

120/240 V primary?

Transformers over a few hundred VA usually do not use taps for different voltages. Unless it is just to make small changes like a couple volts.

 

[wyliesdiesels]

Are you sure its 2 primaries?

Post a pic of the wiring diagram

 

[htmdude57]

There's 2 things I can think of: it could be a dual input voltage transformer that can be wired with both primaries in parallel to handle 120V in, or wired in series to handle 240V in.
Or, it could be an isolation transformer, so that the second 120V winding is an output. These are sometimes used in medical equipment to make it so that the equipment is not running on grid. It is safer for the user.
Actually, any transformer can work both of the above ways.

 

[wyliesdiesels]

Yes if its 4 lead primary it could be 120/240v.

 

[dogdog]

doorbell circuit at the embassy? Their power/network vs ours?

LMFAO...\but haven't you heard, Embassay's don't use door bells .. they save those transformers for shock treatments

Na... have a 115Vdc 1/10hp gear motor I would like to use by adding a bridge rectifier and a capacitor..if I can use that other primary as secondary... not too sure how these Toridal transformers works.

 

[American Locomotive]

Transformers don't care. A winding being a "primary" or a "secondary" is just a label we put on it. You could feed 24vAC into the "secondary", and it would then become the primary.

As others mentioned, it's likely configured so that you'd run both primaries in parallel for 120v operation, and in series for 240v operation. You could hook up one primary, and then use the other as an isolated 120vAC secondary if you wanted. The only issue is you'd lose half the capacity of the transformer.

 

[dogdog]

Are you sure its 2 primaries?

Post a pic of the wiring diagram

Yea at least on the label it is Most of the other toroidal transformer of this kind that I have are straight forward 120V primary and 24V secondary some with extra secondary taps for what other voltage stuff... but only this one listed 2 primary... Maybe it is for 120/240 thing... will test.. just thought I would ask first, maybe someone is familiar, I do remember there are few people here that are transformer experts here... some time back, don't know if they are still here... per se...

pic attached...




I would love to build a 1000VA one like this guy but finding those raw materials here would probably cost the first born.

 

[Sevenhills1952]

LMFAO...\but haven't you heard, Embassay's don't use door bells .. they save those transformers for shock treatments

Na... have a 115Vdc 1/10hp gear motor I would like to use by adding a bridge rectifier and a capacitor..if I can use that other primary as secondary... not too sure how these Toridal transformers works.

As others say, dual primary is for 120 or 240v in. That 115 VDC motor you wouldn't want to run off of 120 VAC with bridge and capacitor. Reason is DC output will be about 169 VDC. You would either need a regulator, 169vdc in, 115vdc out or a transformer with 120vac primary, 83v~ secondary.

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[Bert_]

Kink of strange they don't give you a diagram or something. If it is a 120/240 primary you would have to figure out what color goes to each winding and figure out the phasing.

 

[larry_g]

Kink of strange they don't give you a diagram or something. If it is a 120/240 primary you would have to figure out what color goes to each winding and figure out the phasing.

Not if it is a machine specific part. Common to have 120/240 machines where just connect to a listed set of terminals. Inside the machine the wiring is done to use the correct inputs to get the 24v out for control wiring.

lg
no neat sig line

 

[ddawg16]

Wire the two primaries in series....and you can hook it up to 240 Vac

Wire them in parallel.....you run it off 120

Or

Wire the two primaries in series...connect to 120Vac......and you get 12 Vac out....

But....you need to know the terminal #'s..

The primary side should be something like H1, H2, H3, H4....typically, you would tie H2 and H3 together for series operation. And 'typically', for 120Vac...H1-H2 together and H3-H4 together....typically

 

[dogdog]

As others say, dual primary is for 120 or 240v in. That 115 VDC motor you wouldn't want to run off of 120 VAC with bridge and capacitor. Reason is DC output will be about 169 VDC. You would either need a regulator, 169vdc in, 115vdc out or a transformer with 120vac primary, 83v~ secondary.

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yes will take into account for RMS.

 

[dogdog]

Kink of strange they don't give you a diagram or something. If it is a 120/240 primary you would have to figure out what color goes to each winding and figure out the phasing.

I think that would be harder to find out.. the phasing... it can't be done with a regular multi-meter... maybe a function generator and a scope?

 

[dogdog]

Transformers don't care. A winding being a "primary" or a "secondary" is just a label we put on it. You could feed 24vAC into the "secondary", and it would then become the primary.

As others mentioned, it's likely configured so that you'd run both primaries in parallel for 120v operation, and in series for 240v operation. You could hook up one primary, and then use the other as an isolated 120vAC secondary if you wanted. The only issue is you'd lose half the capacity of the transformer.

This is a weird one... at least different... I just don't wanted to be surprised like this guy when hooking it up... Primary/Secondary is not interchangeable... but this one listed 2 primary and it's a Toroidal transformer instead of a E-I core... that I don't know...

 

[Bert_]

I think that would be harder to find out.. the phasing... it can't be done with a regular multi-meter... maybe a function generator and a scope?

Connect one winding to 120 then measure between one lead of the unconnected winding and the one you are powering. Leads that have 0 volts between them would go together for 120v operation.

 

[FordTruckWench]

Connect one winding to 120 then measure between one lead of the unconnected winding and the one you are powering. Leads that have 0 volts between them would go together for 120v operation.

Won't work, you have to connect one lead of the "alternate" primary before you can measure anything. With the alternate floating, you'll read zero volts no matter the end - or actually, if your meter has high enough input impedance, you might read 60VAC due to leakage.

So: Connect neutral to one lead of both primaries. Connect hot to the remaining lead of one primary. Now measure between hot and the remaining primary lead. If you measure 0VAC, then the neutral is connected properly and you can just connect the last lead to hot. If you measure 240VAC, then you need to "flip" the second primary.

 

[Bert_]

Won't work, you have to connect one lead of the "alternate" primary before you can measure anything. With the alternate floating, you'll read zero volts no matter the end - or actually, if your meter has high enough input impedance, you might read 60VAC due to leakage.

So: Connect neutral to one lead of both primaries. Connect hot to the remaining lead of one primary. Now measure between hot and the remaining primary lead. If you measure 0VAC, then the neutral is connected properly and you can just connect the last lead to hot. If you measure 240VAC, then you need to "flip" the second primary.

Your right. I didn't think that through well enough.

 

[Sevenhills1952]

First, an ohm meter will give you an idea of the windings. An unknown transformer if two leads are, say, 50 ohms and two are 5 ohms you know 50 is the primary, 5 is secondary and about 10:1 ratio.
Here's a tester you can make, I use it all the time. You need a lamp base, 7W lamp, 6ft. lamp cord, two alligator clips.
The narrow a.c. cord plug spade is hot, cut this lead a foot or so from plug...series in light socket, then to an alligator clip. Wide neutral alligator clip on end.
Be careful when using...but it's basically shock proof (7 watt bulb).
Shown...I'm touching the leads.
Shorting clips together lights the light.
It's a simple $5 current limited supply.
You can check transformers perfectly because the 120V goes through the light. Using higher wattage lamp=more current.
Accidentally connect to secondary does no harm...light will be bright. Primary you can measure output voltage, light will be dim.
I keep one over work benches to test fuses, lights, even automotive, etc.

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[dogdog]

hmmm thx that is a great idea...to use bulb as current limiting...

Well, will test all the suggestions folks, right after the turkey digested Not sure why my eyes can't keep wide open after the turkey.

Thx folks... Happy Turkey Day.

 

[log man]

Your tester is quite like my “cheater” but I don’t have the bulb in series. I’m a sparky and quite comfortable with it. However, I erred and let my neighbor see it and he made one. I made him promise to call me and I’d come up if he wants to use it....

 

[nadogail]

I like the 7 watt current limited visual indicating continuity checker.

Thanks for sharing.