How do I power the UMI-7764?

[aufgeschlossen]

The power supply says 5V, but what should the current rating of the power supply be? I just want to confirm that it is 0.2A as in the user guide, but it says " + user-defined encoder and limit power ". I do not know what that means---but we are in fact using an encoder and stepper motor, so it seems relevant. Thanks for letting me know.

Sincerely,
Christian

[Jochen]

Christian,

0.2 A is the maximum power consumption of the active devices on the UMI-7764. If you connect devices like an encoder to the UMI, you typically power them via the +5V outputs of the UMI-7764. These outputs are feed-through terminals that are directly connected to the +5V input of the UMI, so you will have to add the power consumption of any device that draws current from these outputs.
E. g. if your connect three encoders with 100 mA power consumption each, you will have to use a power supply that is rated for at least 500 mA.

Best regards,

Jochen Klier
National Instruments Germany

[aufgeschlossen]

Hi,

Can I just use a current rating as high as possible? The current will probably depend on the load, so couldnt I in practice use a 5V, 5A or whatever the highest current rating that I have here? Thanks for letting me know.

Chris

[Jochen]

Chris,

sure. You can use a higher rated power supply without problems. In general the efficiency of a power supply is best when it is used closer to it's maximum rating but as we are talking about low-power supplies here, I don't think that  it's worth discussing this issue in this case (the contribution of a single oversized +5 V power supply to global warming is quite low ).

Best regards,

Jochen

[aufgeschlossen]

Al Gore would like your environmentalism. 🙂 Thanks for the quick replies!

[Buechsenschuetz]

The efficiency of switched power supplies (even some "wall transformers" use this technology today) typically is higher than 80 p.c. and does not vary much with load conditions.

The efficiency of linear regulated power supplies usually does not exceed 75 p.c. approx. and varies with load conditions. A 5V/5amp linear regulated suppy will draw quite a bit of quiescent current so efficiency at 200 m amps will be very bad.

Anyhow, we are talking about power comsumptions in the 1 watt range. A single lighting bulb consumes at least 10 times that power.

[aufgeschlossen]

The only voltage sources I have have a rating of 700mA. Is it OK to use this? It may not be efficient, but so long as it does not fry the board, it would be good to at least know that, before plugging anything in.

Chris

[Buechsenschuetz]

It's not the amp rating of the supply that might set the device on fire, rather the voltage... if your supply supplies +5VDC regulated, there will be no problems, and you can even connect some limit switches and/or incremental encoders to the UMI box with this power supply.

[aufgeschlossen]

Thanks for letting me know. I just wanted to clear this concern before connecting anything. It not catching fire, I'd say, is a priority. 🙂