pot value in electro-mechanical door chimes

I have a door chime that uses a 16 VAC 10 amp transformer to ring a chime using a solenoid striker. What type of pot can I use to adjust the voltage and the volume of the chime by reducing the force of the solemoid?

holabr said:

I have a door chime that uses a 16 VAC 10 amp transformer to ring a chime using a solenoid striker. What type of pot can I use to adjust the voltage and the volume of the chime by reducing the force of the solemoid?

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My friend, if you have 10A transformer for door bell, I only can imagine how big is that castle. I never saw that big door bell, I must admit, I've never been in castles.

By the way, you will need circuit which will lower voltage or reduce current on secundar side, MOSFET,.... or you can control primary side of transformer with triac, just as light dimmer circuit.

Just because the transformer is rated at 10 amps that does not mean the solenoid striker actually draws 10 amps. It probably draws much less. There is not enough information to say what size pot would cut the power in half, for instance. You would need to measure the current in normal operation to do that. But I can give you some guidelines on picking a resistor.

If you want to substantially lower the striking force you will have a problem. The problem is that it takes a certain minimum current to overcome the spring tension and get the striker to hit the chime at all. If the power were cut in half it might not even reach the chime. And if you get it finely adjusted to just barely hit the chime then the least change in supply voltage or temperature or something could push it beyond the threshold and it won't hit at all.

The next thing to consider is the power level. If you are lowering the power in the solenoid then some power will be dissipated in the resistor (or pot) that you mentioned. If that resistor is not rated for that power then it might burn out. This is especially a concern with pots that are not normally associated with much power dissipation. You might be better off with trial-and-error and fixed resistors. There is one thing that you might have going in your favor - the needs of a door chime are very intermittent. Whatever resistor you put in series with the solenoid is not going to have to carry current for very long. It is possible for a resistor to dissipate more power for a very short time than for a longer time. However if it is possible for a visitor to press and hold the door button and if that causes the solenoid to be engaged as long as the button is held then it is possible for a marginally adequate resistor to burn out.

If you have any resistors in your junk box then I suggest trying them out in some methodical sequence. If the chime does not move at all, use a lower resistance. If the chime moves too much then use a higher resistance. This will be cheaper than buying a power-rated pot. Just as a rough guess I will say that your solenoid draws 2 amps. So if you want 2 amps to drop the voltage in half, then you need a 8/2 = 4 Ohm resistor. So it looks like you will be using some very low resistance values. As for power, 8 volts times 2 amps is 16 watts. That's pretty hefty. But if you have a 1 watt resistor it will probable be OK for very short tests.

Carefully with power resistors, this require additional attention for unforeseen factor. Lets say kids block door bell, and we have nice fiery gates. In winter times this can be useful, I mean on higher temp not on fire. I hope door is made from steel not from wood.

Consider putting rubber on the plunger tip (or adding softer rubber than is already there). That will reduce the volume.

I agree with the above posts, that you can install a low ohm resistor.