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RB16 board


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4 replies to this topic

#1 Bicky22

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Posted 29 April 2013 - 01:11 PM

Hi all, I am having a slight issue that I don't understand... I have a RB16 board with a U12 labjack that I am using to control (reverse/forward) a 24v DC motor. (simple enough) I have a grayhill 70M-ODC5 relay hooked up on one leg of motor to open and close contact with that leg. (close, contact = motor runs.. open, no contact = motor doesn't run... again simple) To reverse the motor I simply reverse the +/- on the legs. This works fine when the motor is in forward motion and there is a +24V power through the relay. (the relay will open and close to stop and start the motor turning) When the motor is in reverse and the negative leg goes thought the relay, the relay will not open and close to stop and start the motor from turning. So... everything works except that I lose control of the relay when I am using the relay to control the negative leg of the motor... any thoughts? Thank you

#2 LabJack Support

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Posted 29 April 2013 - 08:16 PM

The load terminals of the 70M-ODC5 specify a positive and negative terminal. The voltage across those terminals can range from +3 to +60 volts. Are you saying you are trying to put -24 volts across those terminals?

http://lgrws01.grayh...d_DC_Output.pdf

#3 Bicky22

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Posted 30 April 2013 - 05:23 AM

Yes. I saw the specs said 3-60 Vdc. When I first read this I thought the sign wouldn't matter and that I could put -3 to -60 or +3 to +60. Obviously when they weren't working I quickly put 2 and 2 together.... What about these modules don't allow you to put negative voltage to them? My thought was that it was a simple relay when the switch is close and contact is made, current should flow and the sign of voltage shouldn't matter. I understand limitations of voltage/current to the relay but i'm just not 100% sure why this wouldn't be able to work in both direction. Obviously I am not an electrical guy so I was just looking for an understanding of what is going on. Thank you

#4 LabJack Support

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Posted 30 April 2013 - 10:15 AM

One thing to consider is the 70M-ODC is a solid-state relay, so there can be various details depending on the type of transistor that is used, how the transistor is protected, and how the transistor is controlled. On the datasheet for the 70M-ODC it shows a box labeled "voltage spike protection" across the load terminals. We know from the spec tables that this clamps at +80V, but I don't see a spec for the negative clamping voltage. If it acted like the zener diode shown in the OpenLine diagram, it would probably clamp starting around -1V.

#5 Bicky22

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Posted 01 May 2013 - 06:36 AM

Thank you very much, I appreciate the response.


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