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Basic Electronics » Since it is kinda slow around here I thought I'd ask ....

March 11, 2013
by Ralphxyz
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I purchased a variable power supply off ebay.

I have received the power supply and have turned it on and seen it light up but I have not used it yet.

Now I understand the variable voltage but I am stumped on the variable current.

What exactly is the variable current doing?

Is the output of the power supply limited to the set current, I think that is my assumption but thought I'd better ask.

The current setting would be for a potential maximum current, right.

I might be consuming less current but that would be OK, is that correct?

Well like I said it's kinda slow so ...

Ralph

March 11, 2013
by sask55
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Hi Ralph

I believe you are correct.

The supply will ether maintains a constant voltage that you have set. or In the event that the load resistance is so low the current reaches a level that you have set is will maintain that constant current level.

I have wandered about what is meant by a constant current source also.

It is apparent that any supply will have a maximum value for both voltage and current. When operating as a constant voltage supply there is a lower limit to the resistance of the load, when the load resistance become to low the supply is not capable of supplying enough current. It would be just the opposite when the supply is operating as a constant current power supply which would be limited by its maximum voltage level. When the resistance of the load on the supply reaches an upper limit the supply would no longer be capable of maintaining the voltage required to maintain the set current level.

constant current

I think this is a fairly good explanation of what is meant by a constant current supply.

although i have never used a constant current power supply.I can see from reading a few related pages on the web there are times when a constant current power source would be very helpful.

Darryl

March 14, 2013
by mongo
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Hey Ralph,

I have a B&K Precision 0-35V DC power supply that has adjustable current from 0 to 10 Amps.

The adjustable voltage is a given but I wondered why adjustable current for a long time. Here is what I figured:

If you build a circuit that mathematically figures to need a certain current at a certain voltage, you can set the power supply for them. If the circuit loads it down, then there may be some troubleshooting needed without letting out the magic smoke that everything runs on.

March 15, 2013
by sask55
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Ralph

Mongo's idea of using a current limiting function of your supply as a kind of safety control is interesting. It could be almost like a user set variable value fuse or circuit breaker that could be used to limit the current without an actual break in the supply.

If you do a net search on “ constant current power supply” you get a lot of interesting applications for a power source that maintains a constant current rather than voltage. A couple of the applications I have come across have peeked my interest to the extent that I am seriously considering ordering a power supply like yours. The price seems reasonable. Does anyone have any comments on what to look for in a good value inexpensive power supply. As I have said the one you have looks good to me.

March 15, 2013
by Ralphxyz
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I just did my regular, yup that looks good, price is right purchase.

I play with some motors and wanted at least 24 volt so the 30 volt 5 amp seemed fine.

If anything I might have gone with a 10 amp version.

Ralph

March 15, 2013
by sask55
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Ralph

It seems to me that using the constant current mode to drive stepper motors should greatly improve the performance of the motor. By using a very high voltage level and setting the supply to a constant current level near the motors upper limit it may be possible to overdrive the motor. That is the technique that is used by the Toshiba motor control chips I have been using. Basically the idea is to use high voltage to compensate for the high impedance that is present as the windings are initially energized, then limiting the max current to protect the motor during slow seed operation when the inductance load is not as significant. The biggest issue I can think of is how do we deal with motor controller modes when there are two winding coils energized at the same time. It would be interesting to try a few motor control tests using the more basic type of controllers that are not capable of making use of overdriving voltage levels while controlling maximum current to the windings.

I never realized how useful or even what a constant current supply was before you started this thread. It is very interesting.

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