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MikeV
Joined: 20 Feb 2004
Posts: 4
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| Somewhat OT: Reading high voltage applied to motor |
 Posted: Tue Dec 12, 2006 2:57 pm |
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I have a DC motor which will gets various voltages applied to it:
1. 10VDC to 120VDC
2. Pulsed 170VDC (PWM frequency of 20kHz, with varying duty cycles)
How do I read the voltage applied across the motor, and get the info to a galvanically isolated PIC?
Are there any ICs to read the voltage? or do i simply use a voltage divider circuit across the motor bus voltage?
Thanks,
Mike |
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kender
Joined: 09 Aug 2004
Posts: 768
Location: Silicon Valley
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| Posted: Wed Dec 13, 2006 1:08 am |
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| MikeV wrote: | | ...do i simply use a voltage divider circuit across the motor bus voltage? |
You might be able to get away with just the voltage divider. But you would risk to introduce EMI into your circuit.
| MikeV wrote: | | How do I read the voltage applied across the motor, and get the info to a galvanically isolated PIC? |
There are 2 options:
1. An additional A/D converter chip on the isolated side. You need to isolate the digital communication between the PIC and the A/D chip with digital optocouplers and to provide power to the A/D chip. This method is good for measuring ultiple voltages on the isolated side.
2. A linear optocoupler such as Clare LOC110. At 20kHz it works quite well.
BTW, I have a friend, who builds galvanic isolation modules commercially (both types 1 and 2).
Cheers,
Nick |
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SherpaDoug
Joined: 07 Sep 2003
Posts: 1640
Location: Cape Cod Mass USA
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| Posted: Wed Dec 13, 2006 10:39 am |
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Check if you REALLY need galvanic isolation. (You might for legal reasons even if you don't really need it for electrical reasons.) If not then consider two voltage dividers from the hot and cold sides of the motor to the PIC local ground. A pair of 40:1 resistor dividers could be a lot cheaper and simpler than true galvanic isolation.
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