DC Fuel Pump Controller

[iolair]

A hypothectical DC fuel pump is rated at 12volts/12amps and of sufficient power to maintain 39psi fuel rail pressure? The same pump is also safe to operate at 18volts.

With some kind of a controller (PWM?), could the pump then be run at 18volts/8amps and and still have enough power to maintain 39psi?

I'm not sure what kind of a trade off there is in rpm/torque with the two different configurations.

If it is possible, what are the advantages/disadvantages of the 18/8 config as opposed to the 12/12 config, if not, never mind!

....and yes of course, I don't know squat about electrical/electronic stuff!

Thanks/sorry!

John

 

[ScottyUK]

Think of the PWM as a 'dc transformer'. Your motor still wants 12V @ 12A to produce the 39psi, but the PWM stage converts the 18V supply to a 12V (average) supply. The current on the 12V side is still 12A, but the current on the 18A side is 8A because theoretically power input = power output. The current will actually be slightly higher than the theoretical 8A on the 18V side because the PWM stage has losses which need to be met from the supply.


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If we learn from our mistakes I'm getting a great education!

 

[iolair]

Ok, then at the same load would the power dissipated (heat) in the pump at 12/12 and 18/8 be approximately the same or is there anything else going on here?

Thanks Scotty!

John

 

[itsmoked]

Yes approximately the same. As noted the 18V scheme will have some losses(waste heat) external to the pump.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[iolair]

OK....thanks so much Keith!

John

 

[OperaHouse]

I am a little curious about the 12A for the fuel pump. This may be a maximum spec or fuse rating. Unless you have a monster motor, the current of most fuel pumps for FI is about 4A. Most of these systems are high bypass back to the tank and motor voltage can drop to about 6V and still run a vehicle. Newer returnless fuel systems actually measure fuel pressure and control voltage to the motor.

 

[iolair]

Hi Operahouse,

I once stayed at the Hilton Hanoi Opera hotel, right next door to the operahouse.....same one?

Anyway, 12A was used only as an example......I have no idea what it actually is.

I did have a returnless system in mind when I asked the questions.........I was trying to
understand the threory of operation of the Kenne-Bell BAP.

http://www.kennebell.net/accessories/boostapump/boostapump.htm

I found this 2003 post from Kenne-Bell and posted it on a forum and subsequently got crucified for it!

"As an engineer, we hope you'd agree that higher voltage = less current (less heat), so as long as the voltage limit of the windings isn't exceeded, this will result in a cooler running motor and longer pump (motor) life. The BAP is the component in the system that does all the current handling on its input side to regulate and step-up the output voltage, so virtually all the heat is used up there, not in the pump. Everything we've seen to-date indicates the BAP is practically bullitt proof and is very safe for your fuel pump."

Oh well!

Thanks!

John

 

[OperaHouse]

I wouldn't agree with any of that statement. I see it is controlled by manifold vacuum. At low load (high vacuum) the pump can be run at a lower effective voltage and boosted at high load/low vacuum. The regulator sets the pressure so any fuel bypassed back is wasted energy in the electric motor.

 

[iolair]

es it is interesting.........I didn't know anything about it and only quoted the paragraphs because I assumed they knew what they were talking about. Grrrrr!

Actually this is in regards to a *returnless* fuel system......there is no old style regulator that returns excess fuel to the tank....its a one way trip. The "new regulator" consists of software in the EEC, a fuel pump driver module (FPDM) and a fuel rail pressure sensor. The BAP only kicks in at a certain manifold/boost pressure.

Thanks!

John

 

[LionelHutz]

That statement is true for a 3-phase induction motor up to a certain point anyways. Not so much so for DC motor. You increase the voltage and the motor will try to run faster which ends up doing more work (more fuel moved) and drawing more current.

That thing is designed to increase the pump speed so that more fuel volume is available when it's needed.

 

[iolair]

Could a fixed voltage of 18v be used and then some kind of a control system be used to control pump speed/torque by limiting current?

This way 3 pumps could be used without overtaxing the existing wiring, connectors etc?

Thanks all!

John

 

[danonboost]

If said pump draws 12A at 12V then it will draw way more at 18V. It should flow a lot more too.

 

[LionelHutz]

Yes, new cars use voltage control on the pump to maintain pressure (no return line fuel system). So, you could run 18V with a PWM controller to give the voltage and therefore the flow and pressure you need and change it as the fuel demand changes.

Just know that running a 12V pump on 18V will be hard on it and it won't last as long. The pump will be seeing around 30% over design voltage.

 

[danonboost]

LionelHutz,

There is no need to run it at 18V all the time. You could control it with the TPS or a boost switch like the BAP so it's only pumping hard when you're really into it.

Dan

 

[LionelHutz]

Yes, that is true, but only if the controller lowers the effective voltage back down.


I didn't comment before but I have no idea how doing this would allow 3 pumps to be installed and yet still lower the current draw on the existing wiring and connectors. When large amounts of fuel is required the pumps will need fairly high current to keep up.

 

[iolair]

Would not the power of a pump running at 12v/12a be the same as 18v/8a, but use less current?

John

 

[iolair]

Ooops, let me reverse the above!

Would not the power of a pump running at 18v/8a be the same as 12v/12a, but use less current?

Thanks!

John

 

[danonboost]

John,

Sure, the power would be the same but this is an impossible scenario. Like I mentioned earlier, a pump that draws 12A @12V would NOT draw 8A @18V. Current goes up or down with the voltage applied.

dan

 

[iolair]

Isn't there some kind of a controller out there that could fix the voltage at 18v and control DC pump power by increasing or decreasing the current?

John

 

[danonboost]

Nope. It would have to vary the voltage; the current depends on the motor used.