how to drive 12 Vdc 1 amp motor

Lee Sadeli

what component (and how's the wiring) should i used to drive a 12 Vdc 1 amp motor and
110 or 220·Vac 100 watt from BStamp output (which can turn and off the motor instantly) and without harming the stamp. Thanks

Jon Williams

If you don't need speed control for the DC motor, either can be controlled from relays, specifically solid state relays (SSR) which have lower current requirements on the input end and optical isolation which can protect the BASIC Stamp.

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Jon Williams
Applications Engineer, Parallax
Dallas Office

Lee Sadeli

is this a magnetic type relay ? anything without dynamic parts ? how about if i need speed control for the dc motor ?

Jon Williams

If you need speed control with the DC motor you'll need some sort of H-Bridge circuit. There are lots of ready-made parts with serial inputs that you can use, though you'll need to check current ratings carefully.

SSRs use optically coupled triacs (AC) or transistors (DC) to do the switch, so they are easy do deal with; no mechanical parts, no worry about inductive backlash from a coil.

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Jon Williams
Applications Engineer, Parallax
Dallas Office

scribb

I always use the old fashioned mechanical relay for controlling motors/lights, etc.· (it's usually cheaper too).

I use a general purpose transistor to drive the relay (see attachment).· I don't use diodes for the 'inductive backlash' because I've never blown a transistor yet.· Yet, I guess it's a good safety feature.

I hope this helps,
Sheldon

KenM

Regarding the lack of diodes for the inductive backlash, two thoughts come to mind.

1. If the rate of current decay in your relay coil is "slow" (driving transistor turns off "slow") then there will be very little back emf from the relay coil·as· Vinductor = di/dt. So if delta t is long, not much Vinductor.

2. If your relays typically come from salvaged car parts, it is very possible that the relay has either a diode or resistor across the coil.

Many many many years ago,a Japansese·manufacturer (Honda) had diodes intrinsic to relay coils, and that evolved to a resistor in place of the diode. I have not done the math, but if you know the current decay time, and know that it will be consistent, an appropriate value resistor can be used in place of a diode. When you build hundreds of thousands of vehicles a year, multiplied by X number of relays per vehicle, the resistor in place of the diode is a smart cost saving solution.

Ken

scribb said...
I always use the old fashioned mechanical relay for controlling motors/lights, etc.· (it's usually cheaper too).

I use a general purpose transistor to drive the relay (see attachment).· I don't use diodes for the 'inductive backlash' because I've never blown a transistor yet.· Yet, I guess it's a good safety feature.

I hope this helps,
Sheldon

AlWilliamsAWC

For the 12V you can use a FET very easily. For the 110 I would definitely use a relay (either mechanical or SSR). However, note that controlling AC motor speed is not done the same way as controlling DC motor speed. It wasn't clear to me if your 110 was controlling a motor.

Read: http://www.al-williams.com/fetrly.htm

Regards,

Al Williams
AWC
http://www.awce.com
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