24Vac Solenoid powered from 110/230Vac?

[nodee]

Hello all,

I have a 24V 0.4~0.5A solenoid that until now I have run from rectified (no smoothing) 24Vac, I am looking to create another version of the project running from 230Vac or 110Vac. Space is tight and will not fit a transformer or large components, and I also want to use the same solenoid.

Couple of ideas:
-Could I Triac/SCR the 230Vac so that the solenoid is getting 24Vac RMS?
-Should I use a 110Vac Solenoid and triac/scr that one for the 110 and 230 versions, using a separate solenoid for 24Vac version?
-What about a Planar transformer, coil on the top layer of PCB and separate coil on the bottom to drop the 110Vac to 24Vac, add more/less coils for 230Vac versions?

Any input would be appreciated!!
Thanks,
nodee

 

[FvM]

One thing sounds confused. Having the solenoid supplied with rectified AC (smoothed or not) suggests a DC, not an AC solenoid. The point should be sorted out before thinking about a solution. In case of a DC solenoid, a regular buck or flyback converter seems appropriate. 24V DC/AC inverters in a solenoid socket are pretty standard these days.

 

[nodee]

Yeah thats correct a DC solenoid, I was describing a 24Vac solenoid to avoid talk about smoothing the output etc for DC as there is no need, ill just stick a bridge on the end.

Thanks,
nodee

 

[KerimF]

Hi Nodee,

The simplest solution (its basic idea) could be by using a capacitor (Cs) in series to limit the current and 4-diode bridge to rectify it. For Idc = 400mA and Vrms=220V, Cs value is about 10uF (rated for 250Vac). The drawback of this solution is the bulky Cs. So a switched converter as already pointed out by FvM could fill your tight space.

Also using a triac could be an option but the power factor will be very low since the 400mA will be provided by a relatively high peak current of narrow triangular pulses (about 4A peak and 2.25 ms wide) on the side of the mains. (Added, see below).

An intermediate solution to increase the power factor is by switching the mains voltage using a high voltage MOSFET at a relatively low frequency as 1 KHz. But this is another story

Kerim

Added:
Therefore the RMS of the relay current will be higher too (about 1A) and this means that its coil dissipation (in its internal resistance) will be much higher (about 60W !!! instead of 10W). So I guess this is not a good option. By adding a capacitor at the bridge output, the power factor would be lowered even more.

 

[BradtheRad]

On the chance you're in the mood to experiment...

The solenoid specs suggest it has an impedance of 48 ohms.

I have been running simulations, creating reactance by installing various components in series with a 48 ohm load.
Supply is 120VAC at 60Hz.

This data is approximate.

To bring it down to .5 A at the solenoid, requires an impedance of 180 ohms. A plain resistor needs to be rated at 70W.

To do this using a coil, it should be .6 Henry. Rated 50 W or so. (Probably too large to consider trying.)

Or a capacitor of 12uF. The cap must be non-polarized and must be rated for 170 V in both directions. (This isn't to say for certain that a capacitor will be suitable in this application.)

The above does not factor in any effect from the inductance of the solenoid. It is based on AC current through the components. Using a diode bridge probably won't change their behavior much, if your load is constant.

I'm posting this since you asked for options.