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Topic: Solenoid & Stepper Motor power problem. PROTECT ME! (Read 3 times) previous topic - next topic


Now if only someone could teach me how to power this contraption with only one power supply

Bit of a waste of power but:

19v-------7812 regulator
  |             |        |
  |             |        --------------------------7805 regulator
  |             |                                              |
  |             ---------- solenoid supply           ---------- logic supply
  ----------- stepper motor supply

- Scotty


So I will have quite a bit of power loss?

I could just use a voltage divider for the solenoid, because I don't need a regulated voltage. I only need to make sure the current draw from the solenoid or motor does not impede or burn out the logic.

that's why i don't want to use 19 v on the solenoid. I don't need that much current being drawn from the solenoid. It is a killer. I would rather it draw ~12 V, So about 1 amp instead of 2 amps at 19v.

Will these type of regulators help to protect me from surges from the motor or solenoid? Noise?


I wouldn't call it a power loss; that suggests not having enough power. It would be a power waste in that the differential between input an output of a regulator is burned off as heat. e.g. for the 7812 the input is 19, the output 12 so 7 volts is 'burned off'. How much power is wasted can be determined by multiplying the voltage differential by the current going through the device. If your not energizing the solenoid ALOT, I wouldn't worry about it unless your running off a battery or battery pack; and I doubt that since 19 v would be an uncommon battery voltage. Same with the 7805. With your circuit you are only powering two ICs and the logic voltage they use is only for signals. The other way to go about it is to use switching regulators but they are significantly costlier.

Using a voltage divider for power is pretty much a no-no. In order not to have significant current flowing through the divider when connected across a potential, you've got to use some pretty high resistances. When you go to power a device with the divider, one or the other of those resistances will be in series with that load. A good amount of the voltage you need for your device will be dropped across the resistor.

Keep in mind that the 78xx series of regulators are only good for about an amp. They both have big brothers available in a TO3 package good for about 3 amps.

- Scotty


If your worried about noise take a good long look at this

http://www.fightingrobots.co.uk/documents/EMIGuidelines.pdf this papers well worth a read by any one dealing with robots/motors and other things with coils in them.


PS you don't need to use just one power supply you just need to make sure that they all have a common ground!



Thanks for the explanation! This really helps!

I am probably going to run everything off a 12V supply and just get a 5v regulator for the arduino. Also, can anybody recommend places to put diodes that would prevent any further damage to my arduino. I guess i can place i diode between the arduino and the ground & b/w the arduino and the Vdd on the H-bridge?

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