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Doorbell needs to be stepped up to 24v for Ring, but what about solenoid in chime?

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maark6000

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Hello all, my house's doorbell circuit uses a 10:1 step-down transformer... I'm getting 11.6 Vac on the secondary. Problem is if I want to install and power a Ring doorbell unit (Pro), it requires 16-24 Vac. It's easy enough to order a 24V transformer... but if the Nutone chime is designed to be only seeing 12V... the doubling of voltage might not be such a good thing. How can I use the higher voltage transformer with the same chime solenoid? Series resistor? Another step-down transformer... 2:1 turn ratio? Or might the voltage not really matter? Also, what kind of amperage is the chime seeing... I modeled this in spice and with 24 Vac the model predicted it would be seeing 29 A! That can't be right, can it? I haven't measure the actual circuit with an ammeter yet.

Some specifics on the solenoid should this help... it has an inductance of 4.11 mH and a resistance of 51 ohms.

All help greatly appreciated!

Mark
 

Hi,

what about reading the datasheets?
Either you or we need to do this. Currently we can´t do this, because we don´t have them.

Klaus
 

I added a second doorbell at a remote area of a house. I hooked it up in parallel to the existing bell. It turned out the solenoid was unreliable in striking the chime. Voltage was barely enough, due to the long wire run (I guess 100 feet round trip). Power came from the transformer which was pretty much standard in the basement of a house to operate devices such as doorbells and thermostats. (32 VAC)

I considered ways to get the distant doorbell working. The easiest way I could think up was to install a relay and wall wart power supply. That way the distant doorbell got enough power. And it did not require much interfering with the original system.
 

Thanks for the replies. Klaus, i have looked for a datasheet and was not able to find one. This doorbell ringer is circa 1961... the model number doesn't even turn up in a google search. I've ordered a 24V transformer capable of 30A. That seems like an amazing amount of current... I think I charge my electric car with about 11 amps, why on earth you need 30 amps to move a chime striker an inch is beyond me. My thinking is that the solenoid is only seeing current when the doorbell (momentary switch) is depressed. The way most people ring a doorbell, the coil is only in use for a fraction of a second, not enough time to heat up even given its thin gauge wire. Worth a shot, if it doesn't work I'll contact NuTone and see if they can sell me two 24V solenoids. Thanks for your help!
 

maark6000 said:
Thanks for the replies. Klaus, i have looked for a datasheet and was not able to find one. This doorbell ringer is circa 1961... the model number doesn't even turn up in a google search. I've ordered a 24V transformer capable of 30A. That seems like an amazing amount of current... I think I charge my electric car with about 11 amps, why on earth you need 30 amps to move a chime striker an inch is beyond me. My thinking is that the solenoid is only seeing current when the doorbell (momentary switch) is depressed. The way most people ring a doorbell, the coil is only in use for a fraction of a second, not enough time to heat up even given its thin gauge wire. Worth a shot, if it doesn't work I'll contact NuTone and see if they can sell me two 24V solenoids. Thanks for your help![/QUOTE

Is your resistance measurement of 51 ohms on your solenoid correct. If it were DC voltage I would expect the current would be less than .50 amp.
24v divided by 51 ohms = .47 amps.
Click to expand...
 

maark6000 said:
....... I've ordered a 24V transformer capable of 30A. That seems like an amazing amount of current...
Click to expand...
That would be a large and expensive transformer.
Are you sure it's 30A?
Or is it a 24V, 30A DC supply?

For the chime solenoid, just add a resistor in series.
The value depends upon the solenoid impedance.
 
Last edited:

According to my simulation using your doorbell values of 51Ω and 4.11mH, gives a solenoid current of 232mA rms with 12Vac, 60Hz applied.
An added 51Ω, 2W resistor in series with the solenoid will give you essentially the same solenoid current with 24Vac applied.
 

I modeled this in spice and with 24 Vac the model predicted it would be seeing 29 A!
(…)
Some specifics on the solenoid should this help... it has an inductance of 4.11 mH and a resistance of 51 ohms.
Click to expand...

Can you show how you achieved 29A with 24V and 51 ohms (+ inductance) in your simulation?
 

He apparently put the resistance in parallel with the inductance instead of in series.
 

    V

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Ha, okay... what the heck is a VA? yes, the transformer is 30 VA. How did I get through electronics school (ahem, self taught) without ever hearing of a VA? Included picture of my simulation showing 28 Amps.

<a href="https://imgur.com/CHQXObc"><img src="https://i.imgur.com/CHQXObc.png" title="source: imgur.com" /></a>
 

Hi,

See if the simulator source voltage/supply has 0 Ohms resistance, and if so, if it lets you change the source resistance to something real.

I suspect that simulators can out-maths me and very reliably so, but sometimes a quirk/incorrect parameter in your set-up drives them into fantasy result land. I've yet to see a 300kA spike on my real power supply and domestic mains supply, but I can have hours of fun and confusion generating them in simulations...
 

maark6000 said:
Ha, okay... what the heck is a VA? yes, the transformer is 30 VA. How did I get through electronics school (ahem, self taught) without ever hearing of a VA? Included picture of my simulation showing 28 Amps.

Click to expand...
There should be a 51 ohm resistor in series with the solenoid inductance (as you stated in your first post).

If you haven't determined it yet, VA is volt-amps (volts times amps).
If the load is resistive that would correspond to watts.
 

Note that a doorbell transformer is Class 2 energy limited, so do not substitute an ordinary power transformer.
Class 2 will limit current if there is a short in the low voltage doorbell wiring, and the transformer contains an internal thermal fuse. I think 60VA is the limit for these.

I have seen a short-circuit (staple) on doorbell/thermostat wiring cause a wiring fire, as the transformer was not properly fused and overloaded the bell wire.
Also, to prevent a transformer fire, a primary fuse is required.
 
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    d123

    d123

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thank you all for the great information. This is the transformer I bought...

https://www.amazon.com/Edwards-Sign...8-1&keywords=edwards+24v+transformer+doorbell

it says it has "Non-regenerative thermal overload protection." I'm also having my electrician install it to code. I'm going to have to see exactly how this Ring thing works... there is the doorbell unit itself which replaces the existing door bell switch, but then there is a separate "power unit" that sits in the chime... is wired in parallel with the solenoid. I'm not sure the purpose of this unit, given the circuit is only energized when the door bell is depressed. Hmm.... more research to do.
 

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