Maker Pro
Maker Pro

Embaressingly simple: 120v power relay,

CrashAlpha

Mar 1, 2011
3
Joined
Mar 1, 2011
Messages
3
Sorry for being so low-tech - I have a kitchen range exhaust fan with lights built into it which are just ridiculous. For some reason the manufacturer thought that 2 X 2 Watt LED lamps were adequate lighting. They barely qualify as night lights. No wonder this super expensive-looking hood was so cheap!

The lamps are switched from a solid-state control panel. It occured to me that I could take the power to the LED lamps, cut them and use them to control a 120v power relay, and then plug in proper halogen lamps (which I would mount in place of the LED lamps). This way I would still be controlling the lamps from the control panel and it would not look like I had jury-rigged anything.

Any ideas on how to accomplish this? One cocnerm is - of course - not frying the control panel from spikes as the relay turns on and off.

Help would be appreciated and - if you can't already tell - my knowledge of electronics is limited.

Thanks,

Crash
 

shrtrnd

Jan 15, 2010
3,826
Joined
Jan 15, 2010
Messages
3,826
The concept sounds fine. You should find plenty of information on the internet on relays and wiring them.
You'll have to trigger the relay with the low voltage LED circuit, and use the CONTACTS of the relay to run your high voltage (independently to run the halogen lamp).
That will entail running the halogen power separately from the hoods power input source. Which won't tax the existing LED power circuit.
NOt sure what else you'd need to know.
Just use the house power, through the relay contacts. (separate from the hood LED circuitry, which will actuate the relay itself).
My GUESS would be, the fan itself runs off the house power, so you'd just route power from that, through the relay contacts to run the halogen lamp.
 

CrashAlpha

Mar 1, 2011
3
Joined
Mar 1, 2011
Messages
3
Yes, that was exactly what I was planning. In fact, the fan is plugged into a conventional 110 socket built into the wall for the purpose.

A sticker above the lamps says 2W 12V (do I assume this is DC?). The idea would be to get a project box, mount a relay that handles a 12VDC control voltage and wire accordingly.

Questions:
Is it safe to assume that the 12V for LED lamps is DC?
Can I use a meter to safely determine positive and negative leads?
Will I need to add any components, e.g. a diode to protect the control circuit from on/off spikes?
Any guidelines for selecting the relay, for example, solid state over electromechanical?
 

shrtrnd

Jan 15, 2010
3,826
Joined
Jan 15, 2010
Messages
3,826
Do you have a DVM to check the 12V, I wouldn't assume it's DC (sure, the LEDs run DC, but it's getting rectified to DC somewhere in there). You'll need to pick off the 12vdc after the rectifier circuit (which will lead to the LED assy). Sounds like you have a 'meter'. If you're on the DC scale, (LOW voltage 12v check), you can determine the polarity, because the meter will read plus or minus 12V depending on how you connect the leads.
There are a LOT of relays out there specifically made to operate on the 5V or 12vdc made for interfacing with computer outputs, check with any electronic supply store or computer part supply place near you. What you'll need to pay attention to, is the ratings of the CONTACTS for your fan power circuit. Some of those halogen lamps draw a lot of current. Make sure the relay contacts will handle whatever current your halogen bulbs will draw. Some electronic parts stores have maginally competent employees. If you try one, tell them what you want to do, and see if they can point you in the right direction concerning their relay product line.
The relay should not require special diode or other part compensation, because you're triggering it off the 12DC (most diodes in relay protection are for AC power). But you can ask the store you get the relay from, if it requires special consideration.
Electromechanical relays almost always cost more than solid state, cause it takes more to physically construct them. But you have to watch out for itsy-bitsy solid state relays, who's contacts may not be able to handle the current of the halogen lamp. Check with the relay supplier, if you've got questions.
 

CrashAlpha

Mar 1, 2011
3
Joined
Mar 1, 2011
Messages
3
No, I don't have a meter - I'm doing this all from memories of my high school electronics classes! I'll get one, though.

I checked again, the labels over the lamps definitely say 12V d.c 2 W (just like that!) so I think I am ready to move on to the next step, which is the electronic parts store - thanks!
 
Top