Electronic Alarms and Home Security Devices - 16VAC intercom output, 24VDC strike

What is the typical acceptable supply voltage range for 12V nominal relay coils?

I have an apartment intercom that puts out 16VAC to the door strike contacts. I have a door strike that is rated for 24VDC. So I figure I'll put in a relay with a 16VAC coil and just switch the 24 VDC. Wrong; couldn't find a 16V relay in AC or DC.

Tried a 24 VDC relay, but the rectifier drop is 1.7V so I only get about 14-15 volts, not enough to change state on the relay.

So I figure 14 VDC is not too far from 12V. I tested a 12VDC relay with the same rectifier and it worked fine for four or five cycles lasting up to about 30 seconds.

Now this is a $1 surplus relay so I realize it isn't guaranteed for anything, but if I cycle this for say 100 cycles per day at 15 seconds per cycle, will it last for a month? I just have to get by until the new intercom panel can be set up and installed.

Run the 16vac into a power card like an ELK -P624 (http://www.elkproducts.com/products/elk-p624.htm). That will provide you with a 12vdc output.

DC coil relays do not like being fed AC. It won't last long, but you will get a few cycles out of it.

Run the 16vac into a power card like an ELK -P624 (http://www.elkproducts.com/products/elk-p624.htm). That will provide you with a 12vdc output.

DC coil relays do not like being fed AC. It won't last long, but you will get a few cycles out of it.

1. That's the sort of thing I was looking for. Unfortunately I need 24V output, but as you say it will only put out 12 VDC with a 16VAC input. Then I would still need a DC to DC converter.

2. I am not feeding it AC. I am running the 16 VAC supply through a full-wave bridge. That brings it down to about 14-15 VDC output. I measured AC on the output and I get less than 0.5 VAC.

I don't have filtering caps on it, but it is working OK as of now. We'll see how it does during the day.

You could get a 7812 voltage regulator (http://www.radioshack.com/product/index.jsp?productId=2062600), but 14v shouldn't kill a 12v relay.

Then you should be OK. That power supply card is just a bridge rectifier and voltage regulator on a single card 14volts momentarily should be fine for that relay. The normal output of most 12vdc power supplies is in the 13.5-13.8 volt range.

You could get a 7812 voltage regulator (http://www.radioshack.com/product/index.jsp?productId=2062600), but 14v shouldn't kill a 12v relay.

THANK YOU!

I used to work on this stuff in the early 90s and I'd used voltage regulators before, but I can't believe I didn't think about it now. I've gotten pretty rusty since I moved to the cube farm.

If this one dies I will put in a voltage regulator before I solder in the backup.

The skill of working at the discrete component level is getting rarer. I've run in to many journeyman level electricians and electronics techs that can't work with something as basic as relays and rectifiers.

Keep the flame burning.

The skill of working at the discrete component level is getting rarer.
Surface mount technology has killed the bench tech. Heck, I can't even see the components let alone see their solder connections! :(

However, if you want to see boatloads of relays, look at a school paging system. Those 7-foot racks contain rows of relay cards, and there are at least three relays for every one of those tiny switches on the front panel of the rack. If a school has 100 speakers, there are probably 500 relays in the rack. Many have been running 24/7 for 15 years or longer.

Also, regardless of whatever processor controls them, the field devices in nurse call systems, fire alarm systems, and door control systems live & die by contact closures & diodes.

The relay is alive & well. ;)