Motor Reverser

[jwax]

I'm looking for a relay-less way to drive a small DC motor, forward and reverse.
I have two sources of 12 volts DC, with a common ground.
When source A goes to 12 VDC, the motor turns clockwise.
When source B goes to 12 VDC, the motor turns counter-clockwise.
(Only source A or source B can be on at a time)

A relay would work fine, but I'd like an alternative maybe with diodes? (Relayless)

Any wiring ideas are appreciated!
John

[Bob Scott]

If source A is grounded when it is not connected to B+, and if source B is grounded when it is not connected to B+, then you can just connect the motor terminals between A and B, say Motor+ to source A and Motor- to source B.

[jwax]

Ah but that's not the case Bob. I wish! When A is ON, B just floats, and vice-versa.

[sghioto]

The LB1645 motor driver chip.



Steve G.

[jwax]

sghioto- That ought to work great! Cheap chip, and super simple!
I'll order some today!
Thanks very much!
John

[jwax]

Found another option at All Electronics ($2)- Rohm BA6886N.
http://www.allelectronics.com/mas_asset ... A6886N.pdf

[Einar M]

Hi jwax. Either IC is worth having on hand, but all your situation needs is two transistors. Connect emittor/sources to ground and the collector/drains to one side of the motor each and the bases/gates to the other side of the motor through a suitable resistor. Now, when V+ is applied to one side the other is grounded through the transistor.

[jwax]

Interesting concept Einar, but could you provide a schematic?

[sghioto]

Interesting concept Einar, but could you provide a schematic?

Yeah I would like to see that schematic too

A motor reversal circuit will require at least 4 transistors generally called a "H" bridge.
Something like this:


Steve G.

[dyarker]

In first post he said he had two supplies, though he didn't say one was positive and one negative. If he has both polarities, two transistors will do.

Cheers,

[CeaSaR]

In first post he said he had two supplies, though he didn't say one was positive and one negative. If he has both polarities, two transistors will do.

Cheers,

Actually, It doesn't matter if the supplies are positive or negative as long as they don't share
a common ground to themselves. Just hook them up like batteries in series with the motor ground
in the middle, use a SPDT (or 1/2 a DPDT) switch with the remaining Pos and Neg from the PS's
to the outside of the switch and the pos from the motor hooked to the switch center. You can
use 2 transistors to do this also, replacing each half of the switch. Ultimately the easiest way
as far as I can see, IF the PS's allow it.

CeaSaR

[jwax]

Both 12 volt supplies share a common ground. When one is +12, the other is floating.
The motor is to turn CW when wire A goes +12, and CCW when wire B goes +12.
With both A and B are OFF, motor is stopped. A and B are never both ON.
Seems the four transistor approach of Steve G. (sghioto) ought to do it.

[CeaSaR]

Yeah, the H bridge is probably the best for a single polarity supply.
Plus, you'll only need one of them (supply, that is).

CeaSaR

[Einar M]

I have drawn up the circuit I described earlier. The circuit Steve gives is the standard but is not a good choice for the DIY ; it self destructs if both inputs go high. I have included a cicuit that does not do this as well. Go to Photobucket.com enter Einarscircuits and look for motor drivers.

[jwax]

That's an intriguing circuit Einar M! What is the function of the zeners? Reverse spike protection?