12 VDC Relay - Odd Question
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Mountain Pass
Joined: Dec 2020
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12 VDC Relay - Odd Question
I have a 12 VDC heavy duty relay that I was going to use for a project, but I cannot really tell if the contacts will handle the voltage (current will be fine).
What I need is a 12 VDC controlled relay that will be attached to an electronic timer and "bounce" between open and closed about every 1/2 second. I have the circuit all drawn out and breadboarded and it works. But, I need to "control" two separate C9 (Christmas bulbs; 120 VAC) with the relay. Any thought on using this relay to do that? It is 12 VDC controlled, and 30 amps, but doesn't really specify what the voltage max is for the contacts. Does anyone see an issue using this particular relay where the common is 120 VAC and the relay switches between open and closed contact at 120 VAC?
Here is a link on Amazon that is the relay in question.
If folks think that 120 VAC to a Christmas bulb is too much for this relay, does anyone know of a 12 VDC controlled relay with 120 VAC rated switching contacts?
Thanks,
Scott
What I need is a 12 VDC controlled relay that will be attached to an electronic timer and "bounce" between open and closed about every 1/2 second. I have the circuit all drawn out and breadboarded and it works. But, I need to "control" two separate C9 (Christmas bulbs; 120 VAC) with the relay. Any thought on using this relay to do that? It is 12 VDC controlled, and 30 amps, but doesn't really specify what the voltage max is for the contacts. Does anyone see an issue using this particular relay where the common is 120 VAC and the relay switches between open and closed contact at 120 VAC?
Here is a link on Amazon that is the relay in question.
If folks think that 120 VAC to a Christmas bulb is too much for this relay, does anyone know of a 12 VDC controlled relay with 120 VAC rated switching contacts?
Thanks,
Scott
Fleet Mechanic
Joined: Jan 2023
Posts: 1,316
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Yes, the dry contacts on the relay will handle DC and AC voltage. Since these relays are sold to the automotive market they do not list the contact voltage rating but it typically goes up to 250 VAC.
Look at the micro relay on this product:
https://a.co/d/9cHAYJs
Since the relay will switch so frequently, you should put a reversed bias diode (diode installed backwards) across the relay coil.
Look at the micro relay on this product:
https://a.co/d/9cHAYJs
Since the relay will switch so frequently, you should put a reversed bias diode (diode installed backwards) across the relay coil.
More Turbo
Joined: Aug 2005
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Maybe consider a solid state relay if you are switching every 1/2 second? Regardless of the current passing through I would think the mechanical contacts would wear pretty fast in an inexpensive, common automotive relay. They are more expensive, but I think more dependable in the long run for frequent, constant switching.
Fleet Mechanic
Joined: Jan 2023
Posts: 1,316
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Maybe consider a solid state relay if you are switching every 1/2 second? Regardless of the current passing through I would think the mechanical contacts would wear pretty fast in an inexpensive, common automotive relay. They are more expensive, but I think more dependable in the long run for frequent, constant switching.
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Mountain Pass
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Yep, good idea. I have never used a solid state relay. Do you know if the "dry" contact will hand 2-3 amps at 120 VAC? All I doing is taking an old train crossing signal that had both red lights on constantly and making them flash side to side like the real thing. In addition to truck, I also collect O gauge post-war model trains and found this online. But, it doesn't switch side. So, I was just using the output of a 555 timer to control the interval. I have a variable resister in there to dial in the exact timing of the interval.
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Mountain Pass
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Well, I just did a quick search. I can't find much that is 12VDC control, 120 VAC @ 3 amps, through hold mount SPDT solid state relay. I checked Mouser and Digikey, So, if someone knows a source, please share! I may just have to make the mechanical relay easily replaceable!
Fleet Mechanic
Joined: Jan 2023
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A SSR will not have multiple output states. It's output is a solid state device (triac or SCR) that is either on or off. You would need to design a circuit that controlled two SSRs and turn them on/off alternately.
Maybe feed the 555 timer square wave into a comparator that outputs HIGH when the wave is LOW, fed into a SSR, and also directly to a second SSR that will turn on when the wave is HIGH.
Maybe feed the 555 timer square wave into a comparator that outputs HIGH when the wave is LOW, fed into a SSR, and also directly to a second SSR that will turn on when the wave is HIGH.
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Mountain Pass
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That explains the lack of SSRs in an SPDT package. Since my circuit is designed and 3/4 assembled, I am reluctant to make it more complicated by adding two SSRs into it at this point. I mean, after all, it is only to control a train signal crossing light (C-9 bulbs) that will only be on when power to the track is applied. I certainly appreciate the though (and tolerance for asking this in a truck forum), but I think I will stay with my mechanical relays and just replace them when the contact wear out.
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Mountain Pass
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Yep, I think so too. I can replace quite a few of those with less hassle than redesigning the entire circuit, getting a new board printed and populating it. I will just put quick disconnects in for the relay for easy removal / installation.
More Turbo
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Mountain Pass
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