I need help with a motor contactor.

[knight_toolworks]

I bought one of these http://www.amazon.com/gp/product/B004Y7RIM8/ref=oh_o00_s00_i00_details but other brands too none of them show the power requirements it takes to turn one on this is a 24v contactor and I bought a 5 amp power supply and after a few minutes the contactor stopped working. I tested another one with a .75 amp wall wart and it will click but not stay on. so it has to be at least 1 amp. so if I have 2 does it take 2 amps? that is if 1 amp is the right amount of course. it looks like I may need power supplies for each contacter setup?

[knight_toolworks]

ok I feel like an idiot. I found out the contactors are ac not dc. but it took a lot of work to find that out. Anyway I have a large lighting rheostat that works by varing voltage right? so I can dial it to 24v and be good to go?

[steve_g]

is that lighting rheostat a variac (variable transformer)? generally they aren't rectified to DC.

Steve

[knight_toolworks]

I need 24ac not dc. I had 24dc and that fried the contactor.
All I know about the rheostat is it was made for heavy duty lighting dimming. I also had one made for controlling the temp on some heating wire.
this is close to what I have
http://www.amazon.com/Mastech-VARIABLE-TRANSFORMER-VARIAC-2000VA/dp/B000E14FME/ref=sr_1_45?ie=UTF8&qid=1332218032&sr=8-45
but thinking about it would not a router speed control one of the external ones work? I only need about 8 amps.

[steve_g]

Sorry... I read the post to fast. likely your lighting rheostat is AC. Do you have a VOM (volt ohm meter)?

[knight_toolworks]

Sorry... I read the post to fast. likely your lighting rheostat is AC. Do you have a VOM (volt ohm meter)?
I can get or borrow one. I was planning on it.

[knight_toolworks]

I can also change the contactors to 120v ones since that takes less power then running motors my 18 gauge wire would be fine.

[tlempicke]

No you can not use a lighting dimmer. Instead just buy a 24 volt transformer from any appliance supply house and you are good to go. The wiring on most all A/C units, furnaces Etc. is 24 volt. That is why you found so many 24 volt contactors out there.

[steve_g]

Tom...

The rheostat Steve has is nothing like what you're thinking about... but so no one else reading this is confused, you are correct that you can't use a typical light dimmer that you install in place of a light switch. what Steve has is more accurately called a variable transformer and is often used in the theatre industry to dim banks of lights... read large current application.

The best thing for Steve to do IMHO is change the coils to 120V, it simplifys things

Steve

[knight_toolworks]

every time I try to keep simple life becomes complicated. at least this was not a costly screwup. the contactors are only 5.50 each the dc power was only 15.00
I need 8 amps so that leaves most 24v ac power supplies out.

[steve_g]

Steve something is wrong... 8 amps must be the 110v rating of the contacts, not the current required to activate them. The 24v current should be very small...

Steve G

[knight_toolworks]

The 24v took about 1.5 amps. but sometimes I will use all 4 at once. but I wonder about that I had all 4 going with my 5 amp dc power supply but I don't know if ac/dc relate in amps

[steve_g]

Steve

I could not find the current draw on 24v coils, even on the manufactures web site... here's the answer to the same question asked on an AC forum...

The typical 24VAC transformer for a residential HVAC system is only 16 to maybe 25 watts - which would be 2/3 to 1 amp - and that current needs to power everything on the low-voltage side of the system.

So - Yeh, half an amp for the contactor coil would be a good guess

Steve G

[knight_toolworks]

it was hard to find. when he checked my contactoer there was a list of the other brands it replaced. so he used that to go to cutler hammer and looked that one up. I know it takes more then .75 amps as I had a .75 dc power source that would not quite trigger them.
I hooked up my ac source and lucked out it is marked with voltage. but I still stared at zero and turned it up till they turned on. so far so good.