I have an application where I have 12v dc power to a fuel pump. I want
to lower the fuel pump pressure by regulating the voltage to the pump.
What sort of device or devices would I need to put inline on that
circuit to allow me to easily turn the pump up and down?
Will I need to worry about heat dissipation? Heat sinks?
Basically, I need something like a dimmer switch for lights I guess.
Thanks for any help.
You don't say the size of the fuel pump.
One possibility is to look for a very inexpensive 12v cordless electric
drill, with variable speed, and cannibalise that for the speed controller.
Another is to go to a model shop and see what speed controllers they
have, eg for model electric boats and cars. They should also be able to
sell you a "servo tester" that will allow you to directly control the
speed, without using a remote control.
If the pump is small enough, a linear or circular rheostat may meet your
Iy you want to build your own electronic one, then there are many
designs for low voltage motor control. The better ones typically switch
the supply on and off very quickly, with the ratio of the time on to the
time off setting the speed by varying the *average* voltage. This still
applies full voltage for starting and makes for a more reliable solution.
Another possible solution is to use a Quantum Tunnelling Compound Pill,
in a home-made "flower-press"...
This could be anything from a resistor, a pot, a solid state controller or
even a light bulb in series.
come up with a spec like: DC voltage regulator to operate between 13.8 VDC
and 6 VDC at 2 amps.
Unit must operate from a 10.0 to 13.8 volt source.
You might consider putting a bunch of diodes in series and shorting them in
series with a rotary
switch. This would drop the voltage by about .6 volts per diode.
This would provide a robust and reliable and economical circuit plus its is
With all diodes shorted, you have full normal operation.
Amazed at the responses so far. Very few of them seem to suggest
something that will actually *regulate* the voltage.
What you really need, is a voltage regulator, either linear or SMPS
(switched mode power supply). SMPS is a hell of a lot more
complicated, and linear's are not efficient.
As someone previously mentioned, you need to identify the following
1) Input voltage range
2) Output voltage range
3) Output current requirement
You want a regulator, since it has feedback. Without feedback, even
minor changes in the input voltage or output current will rapidly
change the output voltage, potentially to a value that the fuel pump
I'd suggest getting an adjustable output linear regulator and
heatsinking it. A potentiometer can be used to turn the voltage up or
down (like a dimmer switch). The efficiency of a linear is very easy
to approximate: just voltage out divided by voltage in (ignoring
quiescent current consumption, which is really neglible except for low-
power applications). The lower the efficiency, the more the regulator
will heat up.
For a linear, you really need minimal components:
* Input capacitor
* Linear regulator IC - even the ancient LM317 may be fine for this
* Output capacitor
* Output feedback resistor and potentiometer (for adjustable) to set
* A through-hole proto board to solder the stuff down to (or wirewrap)
* Heatsink - this could even just be a big piece of metal - you can
even use a metal enclosure to put this all in and use that as the
heatsink, but make sure the tab of the regulator is *not* live (make
sure it's ground)
That's it. Very simple setup and cheap. If you don't have a soldering
iron, you can even wirewrap them (just need some insulated wire, a
wire stripper and some needlenose pliers, maybe some electrical tape
I'm curious, any reason why no one has suggested this?
Possibly because simply changing the supply voltage isn't a particularly
good way of varying the delivery pressure of a 12v pump. Varying the
mark-space ratio of a 12v supply is likely to be far more effective.
Particularly at low demand.
It's a 12v dc motor. The fuse fitted to the circuit will give a pretty
good starting point for the maximum design current for the speed
controller. There are plenty of 12v motor speed controller designs,
kits and modules - the OP simply needs to pick one matched to the fuse
rating or to the known maximum current.
It will be a switching controller - not linear. So won't need anything
like the same size heatsink that a linear would need.
Changing the input voltage to a pump motor doesn't necessarily change
the output pressure. There's a
fuzzy and complex relationship for a centrifugal pump, and there may be
no effect other than stalling the
motor on a positive-displacement pump.
It is likely that the fuel flow will be the same regardless of the
voltage (up to a point) if you make the assumption that its designed to work
over typical motor vehicle conditions, i.e. it needs to start the engine
even under low battery voltage conditions.
More likely the poster will discover he needs a remote controllable valve.
Also likely is the engine wont run when its starved for fuel.
Use a switch mode kit such as
I have used them for speed control on 12V fans.
Photovoltaic Resources Int'l
Tempe Arizona USA
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