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-   -   Transformer, Relay, Low Voltage (http://www.diychatroom.com/f18/transformer-relay-low-voltage-90165/)

Kermit911 12-21-2010 01:29 PM

Transformer, Relay, Low Voltage
 
1 Attachment(s)
Hello everyone, I found this site through Google and thought you guys might be able to help me out.

For Christmas I am installing a VacPan in my fathers kitchen. A VacPan is an attachment that goes to a central vacuum system. I am trying to connect it up to a shop vac out in his garage. The VacPan has a low voltage foot switch that turns on the vacuum. Here is where the small problem comes in to play. (Stupid Low Voltage) but safety first right?

From my understanding I will need a 120VAC Transformer to 12VDC then a 12VDC Relay to control the 120VAC. I attached a diagram, I hope it uploaded. If this is correct my next problem is where do I find this stuff? Radio Shack now a days sucks, Home Depot has no clue, as does Loews. I just need to make sure I am buying the correct stuff and wiring it right.

Thanks everyone
Dave

jbfan 12-21-2010 02:41 PM

A door bell transformer and an ice cube relay.
You may have to go to a supply house to get the relay.

Kermit911 12-21-2010 03:12 PM

Great idea for the transformer, thanks! Now it comes down to the relay.

Dave

WDR 12-21-2010 06:11 PM

relay
 
There are a lot of companies online that have electrical components, I have had good luck with McMaster Carr.

joed 12-21-2010 06:20 PM

A door bell transformer is only a transformer. You indicate DC voltage on your drawing. You need more than just a transformer to get DC.

Or you need an AC relay not a DC one.

Kermit911 12-21-2010 07:46 PM

See... there in lies the problem. I know what I need (vaguely), I know I need a transformer to lower the voltage, and I know I need a relay that the lower voltage can switch to turn on the higher voltage. Now it is the specifics that I need help with. There are soooo many transformers and relays I'm not sure "exactly" what I need. Any ideas?

Do I need DC? No, but I belive DC is safer then AC correct?
Does the low voltage have to be 12V? No, it can also be 24V but the transformer and the relay have to match. So I don;t want to buy a transformer not knowing if the relay is going to work with it or not. Got to LOVE electricity, one little thing will change everything... then blow up. :)

Lets try this, will this work for what I am trying to do?
http://cgi.ebay.com/ws/eBayISAPI.dll...=STRK:MEWAX:IT
I know it is 24V that's fine and I know it is probably AC current not DC which I am also fine with. As long as it works.


Thanks
Dave

joed 12-21-2010 08:10 PM

Here is one ready made for you.

http://www.pennstateind.com/store/LRMSET110.html

http://www.pennstateind.com/graphics.../LRMSET110.jpg


Keep everything AC and you will be fine. The contacts on the relay need to be motor rated. A vacuum is a significant load. A tiny isn't going to cut it.

Here is one example of a motor contactor.

http://www.ferret.com.au/odin/images...cts-166999.jpg

WDR 12-21-2010 08:21 PM

This relay and transformer should together. You would have to cut the plug off of the adapter cord and get a box to put the relay in.The relay has quik connect terminals, you can get the matching ones at a auto parts store or order them, you could also order a box for the relay

this is the transformer item # 70235K68

this the relay item # 7678K41

they are both from www.mcmaster.com

Kermit911 12-21-2010 09:07 PM

You guys ROCK!!! I think I might like it here. Thanks for all the help everyone and all the suggestions.:thumbsup:

dvanallen 06-20-2013 12:32 AM

Bringing this thread back from the dead. I'm doing the same project and wanted to verify some details.

What wattage should the transformer be rated? Is 80W high enough...at least it's higher than a doorbell transformer.

I also need some clarification to understand the schematic in this thread. Is this right?
1) 120V AC power comes from the breaker through the relay and into the outlet. The transformer also has a 120V AC feed from the breaker.
2) The shop vac is plugged into the outlet that's hot is interrupted by the relay.
3) The relay connects to the transformer and the vac pan accessory.

Looking at the drawing, I guess I'm confused as to where the power comes in and how the relay works...

Here are the parts I'm working with:
Solid Stare Relay (SSR) 25DA with heat sink
Small Shop Vac (1 HP, 6A)
120VAC to 12V DC 80 Watt Transformer

Can anyone help?!

biggles 06-20-2013 11:12 AM

what's with the 12VDC controlling the sequence...:huh:...? just do it with 24VAC TR and 24VAC general purpose relay all is availible at local Grainger we're not talking Three Mile Island tranformers as shown.. here :wink: need to relax with low voltages....the VA rating on a TR is critical if you have a long control wire run out...or the contolling relay will buzz chatter or nothing with voltage on it at the coil http://www.youtube.com/watch?v=I3jwMuuaJnI

dvanallen 06-20-2013 01:58 PM

Thanks for the reply. So I've already bought those parts...It's good to know now that the transformer might be a bit oversized. My concern was that the 6A motor would stress a smaller one, and it wasn't that expensive anyway. I understand now that the transformer doesn't have to handle an inrush load from the motor -- it's only powering the relay, so it can be smaller . . .

My original Q was about how to wire it all together. I need some help translating the schematic into English! Can you help with that?

biggles 06-20-2013 02:14 PM

on the control side (low voltage) wire the TR directly to the control relay coil...then break the yellow or red HOT off the TR with a switch.on the 115V motor side the relay has Common/Normally open/Normally closed contacts...you want N.O. ---I I--- and C.115v house feed "black" to relay C then N.O. to motor,other motor wire to "white" neutral from house.when the control powers the coil (close control switch) the relay will close the contacts on same relay and run the motor.that 6A rating is good but check the relay rating on the contacts should show max

dvanallen 06-20-2013 04:08 PM

That makes sense. To confirm my understanding, is this right:
  • So in the diagram above, in the lower left corner (120V AC Plug w/ gnd), that is one of the two feeds coming from my my circuit breaker.
  • The other feed from the circuit breaker powers the transformer. If I feed the transformer according to the diagram, it addresses the black (hot) and white (neutral/ground) wires. I would just wire the bare (ground) wire to the 120VAC Outlet w/gnd box.
  • On the bottom middle of the diagram where it's labeled 120VAC Outlet w/gnd, that's the outlet that my Shop Vac is plugged into.
  • You mention breaking the yellow or red HOT off the TR with a switch -- that switch is the 12VDC Vac Pan accessory.

Is all of this correct? Thanks!

Quote:

Originally Posted by biggles (Post 1204473)
on the control side (low voltage) wire the TR directly to the control relay coil...then break the yellow or red HOT off the TR with a switch.on the 115V motor side the relay has Common/Normally open/Normally closed contacts...you want N.O. ---I I--- and C.115v house feed "black" to relay C then N.O. to motor,other motor wire to "white" neutral from house.when the control powers the coil (close control switch) the relay will close the contacts on same relay and run the motor.that 6A rating is good but check the relay rating on the contacts should show max


biggles 06-20-2013 04:50 PM

the ground as label is really the white neutral on all 115VAC wiring 3-wires black/white/copper bare.the ground is raw copper from the CB panel to any place a wire nut is used to continue it thru the set up.the plug should be 3 prong...only need one 115VAC CB feed then that transformer can be tapped off the 115VAC plug before the relay,so when your unplugged (no 115VAC to the contacts of the relay) the TR is powered down :wink: .the white is considered the electrical ground insulated,and the raw copper is a mechanical ground...Vac Pan Ac is the low voltage ON/OFF:thumbsup: raw copper grounding wire is connected to anything that can conduct electricity metal casing switchs..green screw is the landing point if seen anywhere.


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