Blown transformer. What is secondary voltage

Huge #10awg wires on the primary #16 on the secondary

I don't know what it's for or how to order a new one

230v primary

Can anyone identify this?

Thanks

1955 wiad

The photo is too blurry. Can you post the info on the label? I can't even read the numbers when I zoom in.

Need:
Manufacturer (Dongan) can read that
Catalog #
Primary voltage
Secondary voltage

and if anything has a number followed by "V A" (volt-amperes)

Dongan
Cat no. 33-003mm
V.A. 3
Primary 230
Secondary 4T #10

I don't know what 4T #10 means

Four turns of number 10 wire. Without knowing primary turns it is impossible to know voltage ratio.

That doesn't show up in the 33 series catalog but if you call them during the week they should be able to help.

http://donganonlinesales.com/33-series-control.html

So the 10 wires are the secondary?

They were hooked to L1 and L2 230volts

Maybe that's why it blew
Previous owner must've wired it that way

Thanks for the info
I'll call on Monday

The #10 wires are the primary and are in series with one line. They are used as a current sensing transformer. If the #10 winding is burned open, just use a length of building wire.

the other winding is open the #16 wires

That was my first thought also, that the 4 turns gets wired in series with one of the lines as a current sense transformer. If you can get Dongan to tell you the specs there are plenty of current transformers around and you should be able to cross-reference it.

I suspect the reason the #10 wire side is labeled as the secondary was just a manufacturing convention to prevent confusion on the shop floor.

My schematic shows only one current transformer
There are two of these . Located on the board behind the tombstone
Could they be grid transformers?

I did some online searching and it seems that many of the Monarch schematics have a chart showing number of turns for primary and secondary according to input voltage and horsepower. Most of them seemed to have less than 6-8 turns so I imagine it should be possible to unwind and count the turns followed by rewinding by hand.

Is the other transformer the same part number? I've never owned or worked on a Monarch but it seems some of them may have a 2nd current transformer feeding a gauge or indicator.

There are 2cts in the circuit I found replacements from a guy on pm

I have a pair of the CTs but they are on a complete panel so i am not anxious to sell one. Since you found one, I don't have to.

The transformer does have a 240 volt winding, measured by monitoring the current while increasing voltage until there is a sharp rise. Because saturation with normal silicon steel cores is a gradual effect rather than a sudden jump, it is difficult to make a definite measurement, but it is about there. At 240 v on that winding, the four turn winding reads 3.58 V. This implies a ratio of 68:1. These cores are run at 15,000 Gauss max in voltage transformer service but in CTs it is customary to run at about 3,000 - 3,500 Gauss for better linearity. At that level there would be less than a volt drop across the primary ( that is the four turn winding, never mind what the label says ) and around 40 to 50 V on the secondary. This size transformer would be rated at about 10 to 15 VA, so running it at about 1/5 normal flux density would be somewhere around 3 VA

This transformer is intended for use on a 480 V supply to a Modular 5 hp lathe. Running on 240 V the manual shows a coil of hookup wire connected across the primary to shunt half of the larger current.

I am sure that the manufacturer did not make a whole new transformer for the application, but modified an existing product. They would have made a normal 240 V winding that was used in a low voltage transformer, probably 6, 12, or 24 V and just added the four turns instead of the normal secondary. The tag is probably a standard one modified.

It would be easy to modify an existing transformer such as is available from one of the electronic supply houses. Look for one about the same size with the 240 V winding on the inside, dismantle it and unwind the low voltage winding, and add the 10 Ga one. If anyone wants to do it, I will walk him through it.

Bill

Thanks Bill for your very informative reply

My lathe was wired for 440v. I bought a step up transformer for the coil at the main contactor.
I have been running the lathe at 220v single phase. Should i have done something to these cts for them to run at the lower voltage?
Thanks
Rich

lectrician1 said:

Thanks Bill for your very informative reply

My lathe was wired for 440v. I bought a step up transformer for the coil at the main contactor.
I have been running the lathe at 220v single phase. Should i have done something to these cts for them to run at the lower voltage?
Thanks
Rich

Click to expand...

The Modular manual says to connect a 20" length of 14 ga wire across the secondary for 240 V operation. This is a Modular and I have never even seen a WIAD, so perhaps someone with a WIAD manual will confirm that. The note is on the circuit diagram for that function. The 480 V heaters on the contactors will work as long as you do not load heavily but they will trip at full load. The manual should cover this. Be sure the CT load resistors are good. Running the CTs unloaded will cause insulation breakdown. An unloaded CT can produce amazing spikes.

Bilol

where would i find the ct load resistors?

I got the new ct and installed it.
I also installed three new resistors in the dc panel 2k ohm and 2-1600 ohm that are near the ap relay

everything seems to be working well

Bill
I was blowing fuses at the main disconnect(the 20A ones.) it usually happened when i turned the power, on not when the machine was already running. I traced the problem back to the ct.

I replaced the ct. it all worked ok for a day or two then the fuses started blowing again. I just ran a 20" long #14wire across the secondary of each CT as you suggested and it seems to working ok

That shouldn't have anything to do with blowing fuses. If they are the fuses used when it was run on 480 V, they are half the size they should be for 240 V.

Bill

They are 20 amp fuses
They only blow on start up
Not under load
I thought it was weird maybe a short somewhere
I'm going to run it for a few days with those # 14 wires and see what happens

I called monarch today . Should bec30amp fuses in there