Power Consumption of Solenoid Valve

[justin15]

I have a 24VAC 50-60Hz solenoid valve that has a power consumption of 125VA (Pull in) and 12VA (Hold in). This is connected to the output of a 230v to 24VAC transformer, however the secondary side of the transformer has two 75VA rated power outputs and the solenoid valve is only connected in series with one of these.

My knowledge is more in electronics and so I'm just wondering why this has been done, because I feel that the wiring from the transformer should be connected to both outputs in order to provide sufficient power to the solenoid valve to account for the initial pull-in.

Although the pull-in is only for a fraction of a second, wouldn't the initial contacts of the solenoid valve struggle to close if the power rating is reduced from what is specified in the data sheet and therefore the valve would struggle to shut. This doesn't seem to be the case though as the system appears to work fine.

 

[telectrix]

basically you're just applying an overload to the tranny for a fraction of a second for pull-in. should be fine. the 75VA rating is presumably a constant output.

 

[static zap]

....however the secondary side of the transformer has two 75VA rated power outputs

So long as the other output remains un-used all should be OK.
(attempting to combine them MAY cause a constant argument / rather than a short term pulse ! - that evens out -So long as gets a rest between activations )
If transformer quickly gets above 60 deg C .. would be a clue of problems.

 

[snowhead]

Is the 125va measured or quoted?
If quoted it may actually be far less depending on the pressure the valve is closing against.

 

[Lucien Nunes]

The rating of the transformer is governed by a few different factors. The total VA output depends on the primary, secondary and the core. The output per secondary is limited by resistive heating in that winding and acceptable voltage regulation. Using only one of the two secondaries to supply a load instead of both will offer twice the resistance, therefore the (secondary) heat dissipation will be doubled and the continuous rating reduced to something above half the nameplate rating. The short term peak power output would not be affected. The extra resistance will degrade the regulation, again not as badly as doubling the voltage droop because the secondary only contributes part of the total.

If the load is brief and not voltage critical, then you won't notice the difference. For continuous use or to optimise regulation, secondaries should be paralleled. Commercial transformers with pairs of identical secondaries are usually designed so that they can be operated in parallel without excessive circulating currents, or in series, as the application requires.

 

[justin15]

Is the 125va measured or quoted?
If quoted it may actually be far less depending on the pressure the valve is closing against.

The 125VA is quoted. I presumed that 125VA would be the maximum specified value and in fact the power consumed by the load at pull-in would actually be less but wasn't certain. I'll get this measured to be sure, Thanks

 

[timbobelfast]

I have a 24VAC 50-60Hz solenoid valve that has a power consumption of 125VA (Pull in) and 12VA (Hold in). This is connected to the output of a 230v to 24VAC transformer, however the secondary side of the transformer has two 75VA rated power outputs and the solenoid valve is only connected in series with one of these.

My knowledge is more in electronics and so I'm just wondering why this has been done, because I feel that the wiring from the transformer should be connected to both outputs in order to provide sufficient power to the solenoid valve to account for the initial pull-in.

Although the pull-in is only for a fraction of a second, wouldn't the initial contacts of the solenoid valve struggle to close if the power rating is reduced from what is specified in the data sheet and therefore the valve would struggle to shut. This doesn't seem to be the case though as the system appears to work fine.

Can you measure the current with a multimeter in series with the circuit?