[Fishingeveryday]

Hi guys,

Got a call from an hvac buddy and we couldn't figure out what the problem is with this rtu.

An auto transformer is fed with 600v and stepped down to 255v phase to ground.

On X1 there is a wire going to terminal blocks and 1 side of a capacitor.

Capacitor feeds a condenser.

Off the terminal block a wire goes to the primary side of a 240v to 24v transformer for the controls.

Problem is the primary side of the low voltage transformer burnt out. Replaced with new and it burnt out within a day.

Coil is rated for 240v.

What's going on? Any help is much appreciated.

 

[brian john]

Hi guys,

Got a call from an hvac buddy and we couldn't figure out what the problem is with this rtu.

An auto transformer is fed with 600v and stepped down to 255v phase to ground.

It is generally not practical or economical to step down 600/347 to 255, the amount of metal necessary makes a isolation xmfr as economical.

Problem is the primary side of the low voltage transformer burnt out. Replaced with new and it burnt out within a day.

Coil is rated for 240v.

What's going on? Any help is much appreciated.

What burnt up, the connections, the primary winding, what size xmfr, what was the current.

You fare leaving a lot of information out.

 

[frenchelectrican]

Hi guys,

Got a call from an hvac buddy and we couldn't figure out what the problem is with this rtu.

An auto transformer is fed with 600v and stepped down to 255v phase to ground.

On X1 there is a wire going to terminal blocks and 1 side of a capacitor.

Capacitor feeds a condenser.

Off the terminal block a wire goes to the primary side of a 240v to 24v transformer for the controls.

Problem is the primary side of the low voltage transformer burnt out. Replaced with new and it burnt out within a day.

Coil is rated for 240v.

What's going on? Any help is much appreciated.

Bonsoir Fishingeveryday.,

I know I will echo Brian John's comment and did you say autotransfomer or just a convental transfomer or multi tap transfomer ? I know you mention 600 volts but is that incomming source is in wye or delta format ? if latter it can get little tricky to deal with it.

but you say 255 volts that is pretty high side for 240 volt system.

Did you follow the wiring diagram chart to make sure the connection is correct ?

Really you should use the conventail down step transfomer to proper voltage and size of transfomer as well.

Why do that X1 do hook up to the capataitour? ( check the wiring diagram on the RTU to confirm this one )

I know there are some information is missing but we need more detals to help you on that.

Merci,
Marc

 

[dmxtothemax]

A capacitor and a Condenser are the same thing !

Or are you talking about an A / C condenser ?

Way back in the olden days thay called capacitors "condensers".


View attachment 33938

 

[dmxtothemax]

Hi guys,

Got a call from an hvac buddy and we couldn't figure out what the problem is with this rtu.

An auto transformer is fed with 600v and stepped down to 255v phase to ground.

On X1 there is a wire going to terminal blocks and 1 side of a capacitor.

Capacitor feeds a condenser.

Off the terminal block a wire goes to the primary side of a 240v to 24v transformer for the controls.

Problem is the primary side of the low voltage transformer burnt out. Replaced with new and it burnt out within a day.

Coil is rated for 240v.

What's going on? Any help is much appreciated.

The burned out tranny which one is it ?
Are you talking about the step down tranny ?
Or is it a low voltage tranny to power control circuits ?
If your feeding a 240v primary with 255v thats not going to help ?
What load is on this tranny ?

More specific info is needed !
Like what frenchy said !

 

[Fishingeveryday]

Thanks for the replies guys.

I haven't looked at this set up I am trying to help out a buddy.

To answer your questions.

I believe it is an auto transformer with 120, 208, 240 taps.

The primary side of the 240-24v transformer is burning out.

The. 24v is feeding the control panel, gas valve, and thermostat.

The capacitor is feeding the AC condenser.

I forgot to mention the fan is being fed off x1 as well.

This unit is very old and all the labels and wiring diagrams are worn off.

The unit ran like a top for the last. 5 years. Suddenly the low voltage primary winding keeps burning out.

According to my friend he is not reading anything unusual in terms of voltage.

What information do you need ? I will ask him for the info and get back to you.

 

[dmxtothemax]

The primary winding of a step down tranny consists of many turns of very light gauge fine wire,and it doesn't take much to burn it out !
But its usually one of two things !
Too much current ? Or too much voltage !
Some one mentioned 255v !
If so this is too high !
What about the current on the secondary ?
Have you measured it ?