Mains power for motor focuser

[JamesF]

I'm looking to convert the motor focuser I've just put on the Mak to run on mains power. Normally the motor uses a 9V PP3 battery in the handset.

My plan was to add a socket in the box wall and use an old 9V wall-wart to power it. I've just fished one out of the drawer where I keep my supply of recycled transformers, but whilst it says 9V on the label according to my multimeter it's actually producing almost 13V in open circuit. As such I'm not desperately keen to connect it up to a circuit that is expecting 9V.

Does anyone know if it's common for these transformers to produce higher than rated voltages in open circuit, and do they drop closer to the expected output under load?

James

[NEM]

Yes, the unregulated ones will float up to about 1.4 times the rated voltage when they're not loaded. How much the voltage will drop when connected to the focuser depends on how much current it takes. The voltage will change depending on whether the motor is moving or not.

Regards,

Noel

[JamesF]

Thanks. In that case I think I might err on the side of caution and see if I can find a lower-rated one that still works.

James

[Gina]

Get a regulated PSU.

[JamesF]

Well, yes, I know, I know It's just that when you have a drawer full of these things...

James

[themos]

Put a load on it and see how much the voltage drops. If you have a multimeter then you can also measure how much current your focuser draws from the 9v battery.