Increasing stepper motor current

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bj23

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Hi all,

Bit of an odd one.
I have an aftermarket car ecu that has a 4 wire stepper motor attached to it.
Unfortunately, the ecu is current limiting to 1 amp.

The motor needs 1.85 amps (6.5 ohm motor, 12volts)

It therefore needs a bigger current supply (no position feedback needed).

It has been suggested that mosfets or BJT transistors be used.

Is there anything I can build or get pre-made that would suit to drive this motor to what the ecu is commanding?

thanks

Rod
 
Stepper motors are often wound with quite low resistance windings, and they have to have external current limiting. I don't know how big the motor is, but 1.85 A on each of two windings at 12 V would mean about 40 W of heating in the motor.

It is far more likely that 12 V is only needed to get the winding current to increase quickly. The current can be limited by analog limiters, but often the supply is modulated with PWM, with a high enough frequency so that the inductance of the windings keeps the current reasonably constant.

Please post more details about what the motor rating is, and what the motor function is.
 
bj23 said:
**broken link removed**
Click to expand...

So your using the car ECU (ECM?) to control a stepper not the VVT solenoid or EGR motor? If your using the ECM for what it's made for why do you think you need a higher amperage out put?
 
The ecu is an aftermarket item (Haltech) and can be fitted into many cars. The stepper output they normally use for Vtech solenoid, idle air control motor or a rotary engine oil metering pump.

The throttles are off a completely different vehicle, hence the mismatch between current limit of the ECU, and the current need of the stepper motor attached to the throttle.
 
So, a cheaper, easier solution would be to buy matching control boards.
 
Sounds like a power BJT (e.g. 2N3055) used as an emitter-follower should do what you want.
 

How are you going to control throttles(?) with the signals meant for something else? Won't that mean some kind of reprogramming of the ECM?
 
The ecu is fully configurable.

Product Overview: Elite 2500 - Haltech

The Elite 2500 is ideal for popular late-model performance and racing applications. It is recommended for: 4, 6, 8 cylinder Drive-By-Wire (DBW) engines, 2, 3, 4 rotor engines, EFI conversions, engines with multiple variable camshafts.Normally aspirated or forced induction applications.
www.haltech.com
.
 
bj23 said:
The ecu is fully configurable.
Click to expand...

Not what I was asking. Your drawing in post #2 you circled the area showing VVT and EGR. But you are talking now about controlling throttles. Two completely different mechanisms.
 
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