Wheelock 712-24 Problems

Alright, so for Christmas I purchased a really rare Wheelock 712-24 mechanical chime meant for general signaling off eBay for $30. I was told it came out of some sort of answering office, so it was most likely used with telephones.

The device runs on 24 volts dc and has two tiny wires coming out of the bottom, one red, and one green. When I wired it up to my Simplex 4004, no juice. I reversed the wires, still nothing. So I unhooked the batteries from the 4004 and attempted to test it on just that. I hooked the green wire to the negative and the red wire to the positive, and all I got was sparking from the wires. I reversed the polarity, and I got the same thing, just sparks. It made absolutely no attempt to ring.

So, before I conclude that it’s completely fried, I wanted to know if there is anything else I should try to make it work. If it is fried, is there any sort of place I can take it and have it repaired? I know that sounds a bit ridiculous, but I know they are rare, and I would be really disappointed to have to throw it out.

I can provide pictures if needed. Thanks in advance!

My guess is that the red and green wires are meant to be hooked up to a telephone wire, although I am not completely sure. Is there a sticker that says 24 VDC?

That’s what I guessed as well. There isn’t a sticker explicitly saying that, but Destin had one of these and was using it on a regular 24 volt system. Plus I did some research on the The Fire Panel Wiki, and I believe it says these take 24 volts dc.

Is there any label on the unit that specifies a “REN” proceeded or followed by a number? This stands for the “ringer equivalence number” - something from back in the old days of mechanical telephone ringers that pulled a lot of current from the telephone company. All telephones and any accessories must have the REN value listed on them. Anyway, if the label says “REN” on it anywhere, probably needs to be connected directly to a telephone line to work. You could modify it to work off 24VDC, but would have to open up the unit an know a little bit about electronics to do so.

I just checked everywhere on the device. No “REN” number. But the fact it has two very tiny green and red wires might be good indications it may have to be plugged into a telephone line.

Hard to say - the red and green wires may have just been put in place by the office telephone guy to connect it up to a relay or voltage to fire the unit off when the phone rang, isolated from the tip and ring of the telephone system. Heck, when I had to run a pair of wires to my thermostat, I used some spare 18/2 firewire I had laying around! If you get a chance post some pictures of what you got, maybe even take off the back cover if you can. May help a little better.

Can you please post a photo of the inside of your chime?

Does it actually say 712-24 on it? The -24 in the part number is usually a huge clue for the voltage on wheelock devices.

Are you sure your NAC output works? Try hooking it up to the 24vdc aux output on your 4004.

Here are the pictures, as requested.

Yes, it does say 712-24. Yes, my NAC outputs are fine. Hooked up one of my other alarms afterwards and it worked fine.

It looks like an AC powered device. Notice how there are no switching contacts and the wires go directly to the solenoid. That is why it wouldn’t ring, it needs the oscillation of AC current to draw the hammer back and forth through the solenoid. The solenoid pulls back the hammer, and holds it there, resulting in the sparking from the batteries due to the relatively low resistance circuit through the solenoid and induction within its windings. When connected to an AC power source, the magnetic field of the solenoid would switch back and forth at 60Hz, drawing the hammer off the gong and then ringing it against it.

You are correct, kcin556.

This is an AC powered signal. Are there any signals on it anywhere that would indicate what voltage it is?

That’s how old phones worked… DC power was put in to operate the speakers and then when a call came a AC signal was turned on to ring the bell.

Found this on Google:

When the phone is not in use, this is a constant DC signal (about 50-60 volts). When the phone rings, the signal is a 20 hertz AC signal (about 90 volts). When in use it is a modulated DC signal (between 6 and 12 volts). The phones lines even have power during a blackout in most cases.

Yes, there is a voltage label. Here is a picture:

Well, thank you everyone for the explanation. That’s the explanation I least expected to hear, haha. I thought all of the 712 series devices were DC. I know the 711 series chimes are identical to this but run on 6 volts AC, and when Destin tested one off a regular panel, I was pretty confident in buying it that it would work with my setup.

Well, now I don’t know what to do with it. Is there anyway I can still use it on my system?

Transformer with a relay perhaps? That’s how Andrew did with on of his videos with the 4030

I’ve actually never done anything like that. I don’t know if I’d want to spend the money for a transformer, and I don’t know how to use relays right now. I might just consider selling or trading it. It just doesn’t seem worth it.

I’m sure someone here will trade it or buy it from you. I can think of a couple who will in a heartbeat.

I’m sure, haha. Okay, well then I guess I’ll start taking offers for it. I’m going to aim for getting my $30 back or a fair trade.

Thea fact that the label says DC on it mean this was probably intended as a “single-stroke” chime. Have you tried removing the tiny wires and powering it on the larger wires connected to the device? At .22 amps (not a lot in the grand scheme of things but…) it could be too great of a current for the little wires, especially if they are damaged in some way.

Do you own a multimeter? You can find is your coil is damaged or shorted in some way. Using the amperes rating, voltage range, and ohm’s law (V=I*R), you can estimate the normal resistance of the coil.

Starting with the low end of the range, plugging in 18V and .22Amps into R=V/I (solved the equation for resistance), results in R= 82 Ohms.

The high end of the listed range, 31.2V, results in R= 141 Ohms.

So, when you test with a multimeter, the acceptable range should be 82-141 Ohms across the solenoid. Keep in mind that I have found this effective on some devices, but due to variables in the wiring for others the calculations have not held true, so use them just as guidelines.

No, I have not tried that yet. How can I do that? Should I cut off the plastic connectors inside and tie on larger wires? That’d be nice if that was the problem.

My Dad does own a multimeter which I can borrow after he gets home from work today. Thanks for that information. I’ll try that this afternoon if replacing the wires doesn’t work.

I would cut off the connectors like you said and use to wire nuts or crimps to attach heavier gauge wire.