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I am a chemical engineering student doing my master's in control theory on a magnetorheological dampers.

The dampers I plan to purchase need 12VDC input and can handle current between 0A and 1A.

I am completely lost at what is possible to do and how to do it. Is it possible to purchase such a device or is it simpler to build it? I also need the current to be changed by some output from my Raspberry pi or arduino.

Are there any resources that I could read to have at least some sort of knowledge before I ask the electrical engineering staff at the faculty?

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  • \$\begingroup\$ link to the dampers, I doubt they take 12v with variable current, though they might. I am completely lost as to what advice to give, given my inability to read your mind. \$\endgroup\$
    – Neil_UK
    Commented Oct 11, 2016 at 12:09
  • \$\begingroup\$ lordmrstore.com/lord-mr-products/…. There is a pdf datasheet on that page with the info you might need. \$\endgroup\$
    – 22134484
    Commented Oct 11, 2016 at 12:11
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    \$\begingroup\$ ...before I ask the electrical engineering staff at the faculty? As (you being) a Chemical engineer I do not think it is a problem if you just admit that this is not your field of expertise. Just provide all the data about the devices you want to use and the electrical engineers should be able to figure it out what to do. Personally I would prefer people to just admit if they do not know and rely on my experience instead of them trying to take a crash course in electronics and thinking they can do it themselves. \$\endgroup\$ Commented Oct 11, 2016 at 12:12
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    \$\begingroup\$ I appreciate that but if you suggest a variable resistor like in comment below then I as an EE already know that any suggestions you could make will not help me. I would prefer you to just say "can you do this for me" and then we'll sit together and I'll make the suggestions and show you the advantages and disadvantages of the different possible solutions (if you were interested). Your interest in my proposed solution (why this, why like that ?) would compensate for your "can you do this for me", you might learn something, I might learn something, it would be a good day :-) \$\endgroup\$ Commented Oct 11, 2016 at 12:20
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    \$\begingroup\$ Thank you for the advice. Ill go by it and schedule a meeting with someone in the EE faculty. \$\endgroup\$
    – 22134484
    Commented Oct 11, 2016 at 12:26

3 Answers 3

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From the data sheet, you want a controllable current source, controllable between 0 and 1A (up to 2A if you like) with a maximum open circuit voltage of 12v.

The damper is obviously a coil. It specifies the resistance as 5 ohms at ambient, 7 ohms at maximum temperature (yes, copper does has that much of a change of resistance with temperature).

As an alternative, at least for playing with on the bench, you could use a variable 0-6v power supply. But be warned that as the temperature changes, the changing resistance will alter the current drawn, which will alter the damping effect. It's because of this we tend to drive current-sensitive loads with constant current rather than constant voltage sources.

In use, the output voltage of the current source will be whatever the load imposes. If you have programmed it to (say) 500mA, and at the present coil temperature the resistance is 6 ohms, then the output voltage will be 3v steady state, though the coil inductance will make it glitch to other levels during current changes. Make sure your supply is protected against reverse voltage. If it is suddenly programmed to a reduced current, the damper inductance will continue to draw the original current monentarily, dragging the output voltage negative. A diode across the output to source this extra current may be sufficient to protect against this problem.

The inductance is not specified, but they do say response within 15mS, though that's to changes in the field. Not well specified.

The 12v is not well specified, it appears to be a maximum voltage, though it doesn't say this. It also says that the electrical characteritics are typical, not to be used for a specification.

The braking force is a function of current, which can be up to 1A for 30 seconds, and 2A intermittently. Neither well specified, what's inermittent, what do you do after 30 seconds? Wait until it's cooled down, how long, to what temperature, drop current below what, monitor coil resistance to assess temperature?

Did I mention that it doesn't appear to be all that well specified?

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  • \$\begingroup\$ So if I understand you correctly, the voltage does not have to be constant. Thats a start (sort of). Ill email the company asking for a more detailed sheet, but I doubt they can supply it, otherwise it would have been on their site. \$\endgroup\$
    – 22134484
    Commented Oct 11, 2016 at 12:42
  • \$\begingroup\$ If you give it a constant 12v, then at the operating temp with a 7 ohm resistance, the current will be about 1.7A, way above their 30s max 1A. Just because it's not well specified doesn't mean you can't play with it or use it. You can use a variable voltage for controlling it, however as the temperature changes, the current drawn will change, which is why we drive these sorts of current dependent things with a constant current. \$\endgroup\$
    – Neil_UK
    Commented Oct 11, 2016 at 12:48
  • \$\begingroup\$ @Neil_UK 'Constant' current may not be exactly what the OP needs because he will need to modulate the current during regulation... \$\endgroup\$
    – JimmyB
    Commented Oct 11, 2016 at 15:36
  • \$\begingroup\$ @JimmyB ... controllable current source, ie programmable current source \$\endgroup\$
    – Neil_UK
    Commented Oct 11, 2016 at 17:07
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Constant voltage, variable current source

What you want sounds like a constant voltage source.

I also need the current to be changed by some output from my Raspberry pi or arduino.

That is impossible. The current a voltage source sources will depend on the load. That's the nature of electricity – a source can either set the current, or the voltage, never both; for example a resistor has a fixed relationship between current and voltage – for example, if you apply 10 V to a 100 Ohm resistor, there will always be a current of 0.1 A, and you can't change that, physically.

So, you can either have a controlled current, or a control voltage source. Not both.

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  • \$\begingroup\$ Is it possible to use a variable resistor to accomplish this? \$\endgroup\$
    – 22134484
    Commented Oct 11, 2016 at 12:13
  • \$\begingroup\$ it doesn't fulfill the criterium of constant voltage over the dampener, anymore, because the voltage drop over the resistor will depend on the variable resistance. \$\endgroup\$ Commented Oct 11, 2016 at 12:14
  • \$\begingroup\$ That does make sense. How do you think they implement these dampers then? I am now quite sure I am missing something in the way these things work. \$\endgroup\$
    – 22134484
    Commented Oct 11, 2016 at 12:16
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In order to control any mechanical device with a Raspberry Pi or Arduino, some kind of control amplifier is required. You should ask your advisor to recommend a means of learning about control amplifiers and their use with microcontrollers. You also need to have a general understanding of the characteristics of electromagnetic devices. The manufacturer of the magnetorheological dampers appears to be primarily focused on potential customers that are original equipment manufacturers with the potential to purchase many thousands to millions of pieces annually. That may limit their willingness to answer student questions. You should search the literature and find some research papers on the subject. Pay particular attention to the references. They may lead you to basic information about the electrical aspects of controlling the devices.

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  • \$\begingroup\$ There are many papers (especially from IEEE) that aim to accurately model the electromagnetic effects. However, there is a model that for the most part approximates the complex nature of the EM effects (the modified Bouc-Wen model). According to a lot of papers, this model fits experimental data extremely. I have read quite a few papers the past few months but thus far none of them describe the electrical system they used. Just block diagrams of the overall setup of the mechanical system. I will ask the EE faculty staff this coming week. Thank you. \$\endgroup\$
    – 22134484
    Commented Oct 11, 2016 at 16:20
  • \$\begingroup\$ What you want is a control amplifier that drives the device with the current commanded by the microcontroller. The amplifier must apply whatever voltage is necessary up to its 12-volt capability. It will have a closed-loop current control that will assure that the current output stays at the commanded value. I suspect that you can buy that as a module that is compatible with the microcontroller. \$\endgroup\$
    – user80875
    Commented Oct 12, 2016 at 3:21

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