Newbie help with regulating voltage please

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 needs.

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"...

Thanks for the reply Sue. The modulation idea sounds promising. Does anyone know of a place to get designs for or buy off the shelf one of these switched supplies?

Thanks!

Jason

By the way, the fuel pump is pretty small. Automotive type and it supplies around 80 psi...

Enjoy!

by a fixed amount or variable?

how big?

always

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.

That link appears to be dead...

thanks

variable

Is there a way to determine the amperage needs of the motor? Will it be on the motor?

thanks much!

Jason

LOL, it died for a few minutes, presumably just as you looked. Try again!

Yes, place a DC ammeter in series with the motor.

with automotive stuff, not likely.

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 very simple.

With all diodes shorted, you have full normal operation.

All,

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 specs:

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 can't handle.

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 job

• Output capacitor

• Output feedback resistor and potentiometer (for adjustable) to set output voltage

• 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 too).

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.

Use a switch mode kit such as

I have used them for speed control on 12V fans. Bill Kaszeta Photovoltaic Resources Int'l Tempe Arizona USA snipped-for-privacy@pvri-removethis.biz

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.

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.

Bill