What type of motor to use for 700W fuel pump?

[treez]

If you were going to make a 700W motor for a back-up fuel pump on a fuel storage site, what type of fuel pump motor would you use, and how would you drive it?

 

[FvM]

I would use the motor povided by the pump manufacturer, typically a three-phase asynchronous motor.

 

[andre_luis]

Are you talking about that ?

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[treez]

yes but if its just a backup fuel pump, it will hardly ever be used, so you want a really cheap pump...that is , a pump based on a brushed dc motor.....but if the motor voltage needs to go up to 34V, and your input supply is just 18 to 32v, then you need to use a buck-boost converter to supply the 34v to the motor....but the problem is, such a buckboost converter is hard to control as its load is inductive (the motor). And also, due to space limitations, one doesn't have much room for much output capacitance in the buckboost converter, so the control becomes even more challenging.
So how do you get round this.?
I am sure that one cannot do a current output regulated smps to supply the motor, as that would give too much sparking to the brushed dc motor's commutator?

 

[FvM]

Much confusion collected in a short post, I think.

Why should a motor converter be hard to control? The motor isn't acting particularly fast (by moment of intertia) the controller should keep up with the speed variation without problems.

There's no "sparking with current regulated output" as long as the converter output has at least a small capacitor.

On the other hand you didn't tell anything about the intended motor operation. I presume it's something like constant voltage with current limiting, similar to running the motor from a lab supply?

 

[BradtheRad]

700W probably goes better with a high voltage AC motor, rather than a low voltage DC motor.

 

[FvM]

700W probably goes better with a high voltage AC motor, rather than a low voltage DC motor.

I would also refer to my comment in post #2, depends on which motors are available of the shelf. Fuel pumps are usually designed for continuous operation, despite the specific operation conditions of a backup pump. So they would be equipped with long-life motors which excludes brushed DC.

In case of doubt, you can use a standard USV inverter and VFD drive.

 

[treez]

we are stuck with the 18-32v input voltage, and I doubt that it would be worth putting in a usb inverter for a backup pump.
So you think that having a smps driving an inductive load is no problem?....remember on page 290 of the switch mode power supply book by Basso, that he warns of having an LC filter on the output of an smps..and how the resonant frequency of this LC filter should be at least 10 times above the crossover frequency of the smps itself.....when your load is an electric motor, it is a very high inductance, and the resonant frequency of the output cap and the motor inductance cannot possibly be made to be 10 times more than the crossover freuqnency of the SMPS....
This shows the problems associated with driving inductive loads (motors) with smps's.

One suggestion was for us to use a current mode buck converter to drive the motor from an input voltage of 28V...however, in some cases, the motor voltage when loaded at 8000rpm will be 27V....this would give a buck converter duty cycle of 0.96. The control of smps’s with such high duty cycle is very challenging indeed. Most controllers don’t offer the ability to drive those duty cycles at all, stopping at about D=0.82 max.

Another suggestion was to place the electric motor inside a current loop, so that the smps could supply controlled current to the motor….but this means that the motor inductance is acting as the upper feedback divider resistor of the smps…..not the easiest smps control challenge in the world.

 

[BradtheRad]

I can only relate my experience when I purchased a DC well pump (preparing for Y2K). My system was 24V. I looked over catalogs from solar/ wind/ hydro suppliers.

There are pumps you put at the bottom of the well, and booster pumps you put between the well and storage tank.

A positive displacement pump is more efficient than the spinning vanes type.

I purchased a Solarjack brand. It drew only a few amps at 24V. It operated down to 12V as I recall. And it was rated to run continuously.

At 700W your pump will draw 25A at 28V. It's a question whether one pump will perform at this level. It may or may not be practical to hook together multiple pumps.

When pumping fuel, the motor/pump construction may be subject to greater electrical safety regulations.

 

[chuckey]

700W ~ 1HP!!, Cars use 12V fuel pumps, do lorries use 24V fuel pumps? They certainly are good for 1000's of hours use, use two in parallel with a Main and a standby with a pressure switch, if you use standard components you get a bigger bang for your buck (use two 12V pumps in series?) It all depends on you pressure/flow requirements.
Frank