EM-200 PSU

For some reason, I had gotten it into my head that the EM-200 required 4 Amps at 24 Volts, probably because this is what the Tak PSU provides. But checking the Takahashi website, you can see the specs for the various EM-200 mounts.

The Temma2-Jr, which I have,  only requires 0.3 to 2.0 Amps.

So, a 24V, 48W power supply is sufficient. I bought a cheap Apple Powerbook G4 replacement PSU  (24V, 65W) from eBay, and hacked up a cable using a spare connector hacked off another old PSU, extended it with some spare mains wire.

It doesn't look pretty, but it works fine.

The connectors have been taped up since the photo.

I noticed something that seemed strange to me when checking the output of the PSU on my oscilloscope. There was a roughly 1Hz, 1V amplitude triangular signal on top of the base 24V. Yes, 1Hz. I would've expected 50Hz or some harmonic from the mains. I tried various time bases to make sure it wasn't an aliased signal. Nope, definitley around 1Hz.

I'm assuming the EM-200 has a regulator as it can be run off batteries with quite a wide voltage range - I measured about 27V for the two 12V batteries wired in serial that I used before. I don't think this will cause any damage, and even if the variation in voltage gets to the motors, the feedback control from the encoders should deal with it.

Initial tests seem fine. The mount slews and tracks as per normal. The motors do seem to have a regular slight variation in sound when slewing, but I'm not sure if this is any different from running on batteries.

We'll see how it goes long term. I expect it will be fine.