So I have a piece of equipment that uses a 3 phase contactor and the coil on it is 48vac. Some how I ended up buying 24vac version coils for the contactor LB3A1 https://www.geempower.com/ecatalog/ec/EN_NA/p/CLCONTACTS110449/pdf which fit my contactor fine but as I found out when I used one running 48v through a 24v coil, it doesn't last long. I cant return them so I figured I would just get a small transformer to drop the 48vac to 24vac but I cant even find a transformer on digikey or mouser to do this. Any ideas of a easy way to cut the voltage in half so I can make use of these coil contactors?

Thanks,

Jeremy

 

Small transformer with a 48 volt center tapped secondary. Tape off the primary wires, connect the 48 VAC across the entire secondary, and take 24 VAC from one end and the CT.

 

What part of the world are you in? Home Depot has a small 24v secondary transformer.
Max.

 

Series resistor if the power is not a concern.

 

Im in the USA Homedepot is 20 mins away. So I just need a 120v to 24v transformer? I thought I need it to be a 48vac primary and 24v secondary? I cant find anything in that config.

Wouldn't a resistor create allot of heat?

 

The problem with a resistor is with an AC coil the initial resistance is very low until the inrush is over, the inductive reactance kicks in and the contactor armature has sealed in.
One main reason I only use DC coils for contactors, relays and solenoids.
The home depot transformer is 120v pri 24vac secondary. I can post the stock number if needed, I assume H.D. in USA and CA use the same No.?
Max.

 

Ya they should, I can get them on ebay and other places if i know what the min specs I would need. So if a transformer setup for 120v input puts out 24v how can you supply less then half the voltage at 48 and still get 24vac out of the secondary wingdings?

 

Im in the USA Homedepot is 20 mins away. So I just need a 120v to 24v transformer? I thought I need it to be a 48vac primary and 24v secondary? I cant find anything in that config.

Wouldn't a resistor create allot of heat?

Measure the current drawn by the contactor when supplied with 24Vac

Calculate the resistance value that will drop 24V at this current from R = V/I

Place this resistance value in series with the contactor coil.

Don’t forget to calculate the power dissipated by the resistor which is likely to be more than a Watt.

 

You have a 24vac coil right?
The transformer 120v primary has to be connected permanently to 120v and the secondary will feed the contactor coil and be switched by however it was done before.
Do you have any print, schematic or diagram of the present setup?
Max.

 

https://www.ebay.com/itm/40VA-Trans...726357?hash=item3b0af25dd5:g:JVEAAOSwPbla4nKK

https://www.ebay.com/itm/MARS-Motor...739812&hash=item25f50b2066:g:zH4AAOSw92Ra-Kmg

would these work?

 

IMO placing a resistor of the correct value when the contactor coil is sealed in, will be of no use in actually picking up the coil initially due to the actual DC resistance of the AC coil.
But you are welcome to try.
Max.

 

There is no 120v source to pull from. Thats why I am needing to drop the 48vac signal to 24vac so I can use the coils I bought.

 

https://www.ebay.com/itm/40VA-Trans...726357?hash=item3b0af25dd5:g:JVEAAOSwPbla4nKK

https://www.ebay.com/itm/MARS-Motor...739812&hash=item25f50b2066:g:zH4AAOSw92Ra-Kmg

would these work?

They should do it also.
Max.

 

So i am understanding what your saying about the transformer. I actually tried this with a 208 to 24v transformer I had on hand. 3 208 legs feed a large transformer that drops the voltage to 48v to power the router, so I did as you guys are saying and created 24v that I used to operate the contactor coil. Problem is the relay for on and off isnt a latching relay, so it uses current flowing through the relay coil and the coil on the contactor to work. Basically this is a industrial router for granite countertops. There is a momentary off button and momentary on button. On button allows current to flow through the relay coil and the contactor coil and the machine turns on. When off is pressed it cutts off current and the relays clicks off cutting power to the contactor coil and in turn cutting power to the router motor.

I actually used the router like this to get it going but I have to hold down the momentary on button for the motor to stay on. So that's why i am looking to just drop the 48vac signal that normally goes through the contactor coil to 24vac but nothing is ever that easy. I thought I could just find a 2 to 1 ration transformer to do what I need but I cant seem to find anything or im not searching right.

I can try to make a diagram if what I say is confusing. It makes sense in my head but I don't always explain things like they need to be.

 

If whatever is driving the coil is producing 48 volts, a 120v primary is useless.

 

I really don't follow how that series circuit you describe can hold the contactor on....

EDIT:
Are you sure the “contactor” is not actually the coil for the relay, because that could explain what you are saying.

The “contactor” engages the contacts two of which shunt the “on” switch.

 

Use a 120 V to 60 V transformer for 2:1 stepdown. Just be sure the secondary current rating is sufficient. You can't go by the "VA" rating. You will be buying a lot more core and copper than you need, but you will be able to find something off the shelf.

The suggestion at #2 might be less expensive, but again be sure the current rating of the winding is adequate.

edit
https://kentstore.com/content/pdf/CL45A_coil_voltages.pdf
If the linked datasheet is applicable to the coil, the ratio of "inrush" to holding current is fearsome: 45VA:6VA. That's almost 2 A for the 24 V coil. It most certainly puts a resistor solution out of the question unless you have a free auxiliary contact on the contactor.
Using a 120:60 V transformer with adequate secondary current rating (1/2 amp is probably adequate, but it should be fused with a slow-blow in case the contactor ever fails to seal for any reason) might be more expensive than writing off the 24 V coils, and certainly more expensive than the 120:24V approach that has been suggested.

 

What about using a series capacitor to efficiently reduce the voltage?
Or would there be a problem of resonance with the coil inductance?

 

Wouldn't it be far quicker and easier to just buy the right 48vac contactor coil?
Max.

 

I was afraid it would come to buying the right parts. I have 10 of these and just seems like a waste.