Analog 12v reference motor driver

Thread Starter

Outathebox

Joined Aug 4, 2022
8
I’m trying to use the output of a 12v DC motor driver to contol a higher amperage motor driver. I can’t simply replace the fist one with a better one I need to use the DC 12v 15a max output to control a motor driver that can do at least 12v DC 25-30a constant motor driver. This is all analog DC brush motor.

any suggestions?
 

Papabravo

Joined Feb 24, 2006
18,964
I’m trying to use the output of a 12v DC motor driver to contol a higher amperage motor driver. I can’t simply replace the fist one with a better one I need to use the DC 12v 15a max output to control a motor driver that can do at least 12v DC 25-30a constant motor driver. This is all analog DC brush motor.

any suggestions?
Can you provide more details on why you "can’t simply replace the first one with a better one"? That assertion makes absolutely no sense to me. There might be a valid reason, but I can't fathom what that might be.
 

Thread Starter

Outathebox

Joined Aug 4, 2022
8
Can you provide more details on why you "can’t simply replace the first one with a better one"? That assertion makes absolutely no sense to me. There might be a valid reason, but I can't fathom what that might be.
Can bus in a automotive application coded to other computers
 

Thread Starter

Outathebox

Joined Aug 4, 2022
8
As Max says, normally fuel pump is either on or off - what makes you think its variable speed?
Is this a low-pressure pump or the high-pressure injection pump?
its a return-less “low pressure” pump that feeds the direct injection pump the module reads the fuel pressure and adjusts the pump speed for demand. It doesn’t have have a fuel pressure regulator. And I’ve confirmed it’s variable voltage

also it is not mapped it simply increases voltage until it sees proper fuel pressure.
 

Irving

Joined Jan 30, 2016
2,979
its a return-less “low pressure” pump that feeds the direct injection pump the module reads the fuel pressure and adjusts the pump speed for demand. It doesn’t have have a fuel pressure regulator. And I’ve confirmed it’s variable voltage

also it is not mapped it simply increases voltage until it sees proper fuel pressure.
And is the variable voltage actually PWM or it is a true analog voltage?
 

Irving

Joined Jan 30, 2016
2,979
Can you repair the old burnt out one by using higher powered FETs etc? That seems the way to go to me.
Not that simple. The existing devices, whether BJT or MOSFET, have limited heatsinking so are likely to be overheating rather than failing from current overload. Its a packaging issue; a 110A rated MOSFET will fail just the same as a 55A device with a similar Rds(on) in the same package. Going from 15A Max output (not device) rating to 30A rating will need 4 times the heatsink area, or a device with a 75% smaller Rds(on), probably a combination of both, which is going to be difficult to do practically.
 
Last edited:

dendad

Joined Feb 20, 2016
4,176
It depends. The original may use transistors, not FETs.
And there are new FETs with very low Rds(on) so it may be ok.
But if it is "variable voltage" then the power dissipation problem remains a constant.
We really need actual info on what the controller is, and the pump too for that matter.
Is the variable voltage really PWM?
If not, it would not be too hard to convert the variable voltage to a PWM signal to drive the motor, but if the original controller is dead, where is the said voltage going to come from? Can the TS please post any technical info, like how it is all connected, motor and controller data sheets or part numbers?
 

Irving

Joined Jan 30, 2016
2,979
I think the TS is stating that experience shows it will blow up, not that the one he has is broken; this is preventative rather than repair.

The power dissipation is an issue; I am surprised that its an analog voltage rather than PWM; though maybe it is PWM but there's no way to tell without a 'scope or a good multimeter with frequency/duty cycle measurement like my Fluke 87-III.

If its analog then I'd propose a BJT emitter follower on a suitably large heatsink (possibly parallel BJT), assuming the pump is ground referenced like most automotive systems, the chassis/body is the return path. This is preferable to a MOSFET source follower as we don't know if we have head-room for the gate drive (Vg could potentially be 4 - 5v above Vpump).

1659701543374.png

If it was unfiltered PWM with a definite on/off duty cycle then I'd use a small N-channel driving a P-channel like so:

1659715128733.png
 

BobTPH

Joined Jun 5, 2013
5,453
I still have my doubts that it is really analog variable voltage. At 6V that would be 90W of dissipated power for the original 15A version. PWM would be so much better in many ways.

How do you know it is variable voltage? If you just measured with a multimeter, that would like like a variable voltage even if it was PWM. A scope would tell you for sure.
 

Thread Starter

Outathebox

Joined Aug 4, 2022
8
Thanks for all the reply’s I will scope the power and verify it’s not a PWM according to the manufacturer there are actually 2 different modes of control depending on unit. One is variable voltage and one is PWM. So I will toss a scope on in in a few weeks and verify control. Hopefully it’s actually PWM. That would make this much cheeper and easyier to add a higher amperage circuit for the pump.
 

BobTPH

Joined Jun 5, 2013
5,453
Thanks for all the reply’s I will scope the power and verify it’s not a PWM according to the manufacturer there are actually 2 different modes of control depending on unit. One is variable voltage and one is PWM. So I will toss a scope on in in a few weeks and verify control. Hopefully it’s actually PWM. That would make this much cheeper and easyier to add a higher amperage circuit for the pump.
Are you sure the two modes are not for the control input? Many LED driver modules will take either as input.
 

Thread Starter

Outathebox

Joined Aug 4, 2022
8
Are you sure the two modes are not for the control input? Many LED driver modules will take either as input.
It’s not 2 modes. There are 2 available contol units for the car. One has a PWM out put to the brush fuel pump and one has variable voltage. So I need to scope to find out. And it will be nice to know what the sweep of the voltage or PWM is before I continue.
 
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