BENCH POWER SUPPLY - Help!

[Al Skierkiewicz]

The Radio Shack power supply is just fine for most of your experimenting. Please keep in mind that this supply may have a problem starting some motors. You might be able to power the RC and the compressor and you might be able to run the Globe motor and possibly the Fisher Price but trying to turn the Chalupa (CIM) motors might prove to be too much current. Remember that a non moving motor is in stall and that means 133 amps for the small and 96 amps for the large Chalupa motors. If you try, the power supply will shut down on high current and the reset may require a power off to restart.

As always, check the polarity of your wiring, twice, before applying power. Many of the electronic devices cannot stand a reverse voltage.

[EricVanWyk]

DO NOT POWER ANY BIG MOTORS OFF OF THIS SUPPLY.

The key point about your bench top supply is that it is a switching regulator. This means that its output looks like a diode followed by a capacitor. Therefore, it will only supply power, it will not sink power.

This is all well and good for powering your control system, as it (should) never attempt to push power back into the supply. However, remember that a DC motor is also a generator. If you were to run a heavy motor full forward and then stop, the energy that is held in the shaft will get pushed back through the victors to your supply. The capacitor will attempt to soak that current, but its voltage will shoot up. The diode will then be reverse biased, effectively eliminating your supply from the circuit.

The end result is that your 12V rail just jumped to some unknown value. If this new voltage is high enough, badness 10000 will occur.

I haven't managed to do this with the KOP, but I've done it before quite painfully on another project. Typically, this will occur while you are presenting.

If you have them laying around, a couple FHCs (Freaking Huge Caps) can help mitigate this, as well as handle the kick over problem.

[Al Skierkiewicz]

Erik,
You are right that switching supplies are a little more unforgiving of motor loads, but the output circuit is essentially the same as an unregulated linear supply. i.e. AC transformer winding feeds a diode rectifier which in turn feeds a low pass (capacitor) filter to smooth the DC voltage. The only difference is that the high frequency of the switching supply does not require the large (high value) capacitors needed to form a 60 Hz low pass filter since their operating frequency is much higher. Unfortuantely, feeding FHC is like starting a motor, the inrush current to charge the caps may trip the supply.

[coreyjon]

Welcome to Chief Delphi first. Second of all, your question is one of caution, and thats good. Don't want to fry anything. That is a very powerful power supply, a bit overkill for the controllor. The input voltage is 12 volts (ideally - as a battery rated at 12 volts will actually have a voltage slightly higher when fully charged, and slightly lower when running out of juice). the power supply is rated at 25 amps (which is a good deal of power). So, if you needed to, you could draw that much current, however, there is no limit to how little current you can draw. Car batteries are often rated for very high amperage, for things like starting your car, but your radio works just fine from the same battery. I can't verify that there is a built in regulator onboard the controllor, although it would make sense. You know you can never assume though. I could be completely wrong, my coffee level is pegged at empty, and it's been a few years since digital electronics - but if it were me, I'de connect it. Just remember to connect first, then turn on power, otherwise you could get a spike in power...and that very well could fry it.