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DC Board


Bowshock
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Hi Everyone,

In addition to doing the animated light thing, my boys and I like to race slot cars. I was looking at the DC board to use as a power supply for a home built wood track which brings me to my question:

I assume you can vary the voltage on each channel, but can you vary the amps put out by each channel?

Thanks!

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The LOR card has a presumption that there is a resistive component to the load. So current follows voltage. Of course, the card actually does not control voltage, but rather does PWM (Pulse Width Modulation). So it changes the percentage of the time that full voltage is applied to the load. PWM is how most DC motors are best speed controlled. I'd think you would be OK. I would suggest though that you want a reverse biased fast diode in parallel with the motor, so that any inductive, or EMF spikes generated by the motor in the off cycle are shorted back through the motor..

The other thing to remember is that the DC card is not in itself a power supply, but rather a PWM controller to go between a power supply, and your load.

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Thanks klb!!

I know it's not a power supply, but a way to vary the voltage from the power supply to the motor. When you build a slot track, one lane is always a bit faster when all things are equal. My thought was I could use this to equalize the lanes by varying the voltage on each lane independently.

Sounds like it might work.....I'll have to dig a bit deeper on the diode thing.

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  • 2 weeks later...

blah! any time you have a switching (on and off) DC circuit attached to an inductive load such as a relay/contactor. And the device doing the switching is a solid state device like a transistor or SCR or ect. A surpressing diode better be on the inductive coil or you are going to zap the solid state device. See when current runs through the coil you produce a magnetic field. And as you remember when a wire passes through a magnetic field you generate electricity, right. Well same thing happens when a magnetic field moves around a wire. But magnetic lines of force can move much, much faster than a wire can. So, when you open the circuit feeding a coil, the magnetic field collapses and creates what is called "counter electric motive force". Translation of CEMF is that a huge reverse spike of voltage is sent back to the solid state device, destroying it. Example and I am pulling numbers out of the air to give you a picture of what I mean by huge CEMF. Lets say I apply 24VDC to a relay. I can expect some where around 80VDC spike and in a reverse polarity than what I applied. So we install a diode of a rating of lets say 1A and 50V PIV (Peak inverse voltage) and it is installed to only conduct when the CEMF is produced, but it is not to conduct when the relay is energized.

Max

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