Easy AC Voltage ramp?

[IanMH]

Hi Guys,

First post here, a few times google has sent me here and I figured I'd better take the hint!

Probably a stupid question I know, but I haven't dealt with circuits for awhile, and this may be in the wrong forum, for both I apologize in advance.

Situation: I am designing a controller for a salt water fish tank, through my PC and will be flipping relays to turn on/off various AC voltage items. Some of these are motors (called power heads) that move water in the tank. During start up these will usually CLICK and rattle a few times and I basically want to reduce that. I'm pretty sure it can be done by ramping the voltage up, but haven't been able to find a way to do it with AC voltage.

Can I simply use a resistor and capacitor in an AC circuit to ramp up voltage from off to 110VAC in say 500 ms? The units only draw about 10-15 watts.

Thanks in advance for any assistance or insight!

Ian

 

[colin55]

I have been told to put the pump on its side.

 

[crutschow]

An resistor capacitor delay only works for DC. You would need something more elaborate for AC.

One way is to use the type of light dimmer that can be controlled with a voltage, something like this **broken link removed**. You could apply a ramp to the control input which would slowly increase the average AC voltage.

But I wonder if the noise is from the relays or switches applying voltage at an arbitrary phase of the 60Hz. Perhaps a solid-state relay with a zero-voltage turn-on such as this **broken link removed** would reduce the noise also.

 

[IanMH]

Eh they get the noise just plugging them in as well. Hmmm thanks for the link though, I think I found a cheaper I/O board!

 

[IanMH]

An resistor capacitor delay only works for DC. You would need something more elaborate for AC.

What I feared...

 

[Diver300]

You could try starting them with a resistor in series at first, then shorting out the resistor.

Or you might get away with a surge protecting thermistor. They are NTC thermistors that start at a high resistance and limit the current. As they get hot, the resistance drops and the load gets the full voltage.

An inverter with a ramp start will work, but is expensive.

 

[IanMH]

Or you might get away with a surge protecting thermistor. They are NTC thermistors that start at a high resistance and limit the current. As they get hot, the resistance drops and the load gets the full voltage.

That sounds like an affordable easy solution.

An inverter with a ramp start will work, but is expensive.

Yea, that is pretty much what I kept getting steered to, and is way to expensive for this project.