Can't find a 15A rated relay

Thread Starter

raisintoe

Joined Mar 24, 2012
46
I need a relay rated for 15A to 20A at 120VAC with a 12V coil, (Or smaller voltage coil if possible). I am having a hard time finding anything rated more than 10A at 120VAC. I did find this relay on ebay. On the package, it says 20A 125VAC, but when I read the datasheet, it still says that it is 10A at 120VAC under a resistive load.

How can I find a relay rated at 15A or more, at 120VAC? I have done my searching, and am having a hard time finding any. I need the high current rating in order to run a 1500W heater.
 

MaxHeadRoom

Joined Jul 18, 2013
19,006
You need to search using contactor, the Telemecanique range are nice to work with and a replacement coil can be changed to 12vac if neccessary.
Max.
 

MikeML

Joined Oct 2, 2009
5,444
Or use a Solid State Relay (SSR). Their input is typically a "logic level"
 

Thread Starter

raisintoe

Joined Mar 24, 2012
46
Or use a Solid State Relay (SSR). Their input is typically a "logic level"
True . . . actually, I do have some MOC3023 Opto-Isolators and 15A rated Triacs on hand. I should just go ahead and use those. I will need to heat sink my Triac well though.
 

MaxHeadRoom

Joined Jul 18, 2013
19,006
True . . . actually, I do have some MOC3023 Opto-Isolators and 15A rated Triacs on hand. I should just go ahead and use those. I will need to heat sink my Triac well though.
You need a zero crossing opto drive rather than random phase type.
These are MOC316X and MOC308X.
Max.
 

Thread Starter

raisintoe

Joined Mar 24, 2012
46
You need a zero crossing opto drive rather than random phase type.
These are MOC316X and MOC308X.
Max.
And those just prevent surge current? Is that necessary? I have been triggering lamps with these 3023s to purposely start at some point in the AC wave to dim the lights. I do this without the use of inductors
 

MaxHeadRoom

Joined Jul 18, 2013
19,006
Phase control of lighting or motor is different to controlling an element or heater on/off, which it seems you want.
Max.
 

Thread Starter

raisintoe

Joined Mar 24, 2012
46
Phase control of lighting or motor is different to controlling an element or heater on/off, which it seems you want.
Max.
OK, I didn't know that, thanks. I am planning to turn the whole personal-heater unit on (including the fan), not just the heat element. So it should be the same as if I were to just plug the unit into the wall. I will have to see if there is any circuitry already in the unit itself which protects the heat element from surge current.
 

Thread Starter

raisintoe

Joined Mar 24, 2012
46
I'd rather not have to order any other parts at this point in my project, so I am going ahead on making a zero-cross detector circuit just with what I have. I have some MOSFETs on hand, but can't understand how to work 'em.

For a test circuit, I am trying to trigger the P-channel MOSFET to run a current through the 180 ohm resistor. I can not figure out what I am doing wrong. It is supposed to turn on for a small moment (at the zero-crossing moment of the AC phase), then turn back off. Instead, it is doing the opposite, and has a small current, (240uA in this LTSpice simulation).

Opto with MOSFET.jpg
 

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