Need a 20amp 12 volt voltage regulator

Thread Starter


Joined Feb 17, 2009
So can anyone help me solve my little problem! I have an electric aftermarket fuel pump on my Diesel truck and I burned up the last motor. I think it might help if the power to the motor was constant. My voltage is not always constant on start up, lights dim high and low and you can hear the pup motor speed changing, until it warms up. The motor makes a lot of noise while pushing a high psi and I think it because it is getting more power and spinning faster, therefore giving me more pressure, more than I need. Once the truck warms up I get a constant 14 volts when running so I would like to regulate/limit the power to the pump to 12 volts.

SO, I need 20amp (less may work) and preferably adjustable but basically need to maintain the 12volts.
- Anyone know the best way I can regulate the 12 volts?
- Is there something I can buy and just wire in, maybe a diode or resistor of some kind or unit made just for what I am looking for?
- Or do I have to make something?



Joined Apr 9, 2009
Wow 12 amps seems high. I am no expert switching regulators appear the way to go for DC regulation when efficiency is a must. That may not be in your case though as you have an alternator running with the engine running. If the fuel pump must run on battery alone for quite some time I would go with a switching voltage regulator.


The biggest regulator they have though craps out at 3amps though. You can put a bunch together for 20 amps but that would be costly (there $25/ea) and may require a higher Vdrop - don't know. Give them a call at (330) 634-1430 and see what they say to your problem.
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MY email is <snip>

I an electronics designer for the past 25 years,;)

You can use an LM78S40 alongwith some opto and mosfets to keep

the output voltage to a fixed level of 12 volts @ 20 amp.

I can send you the circuit which I have designed for free .

Please email me if you like me to send you the diagram.:)

Moderator's note: AAC is a public forum. Trading information in private goes against the purpose of the public forum, which is to place help and answers in front of as many people as possible.
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Joined Oct 2, 2009
I predict that regulating the voltage to the pump will do nothing for its reliability. First, it is a DC motor, which unless you reduce the back pressure it is pumping against, means it draws less current at higher input voltages (due to back emf), so lowering its input voltage will just cause it draw more current, which will cause it to burn out even quicker.

If it is developing a pressure that is way too high, then getting a smaller pump, or driving the existing pump motor in a pressure-regulating PWM servo loop would run the motor at just the power input level required to maintain the set pressure.


Joined May 11, 2009
14 volt in a car then running is normal. Fuel pumps are devices that must be changed. I would look for other reasons. It could be that your pump is not correct for your car fuel system. Since it is an electric aftermarket fuel pump.