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Decreasing current to DC Motor

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jonlaury

Joined: 06 Nov 2006
Posts: 336

Posted: Fri Dec 08, 2006 9:22 am Post subject: Decreasing current to DC Motor

I have EFI pumps that move way too much fuel for my  purposes. Is there an inexpensive way to starve the current to the pump  motor so that output is decreased without harming the motor? The pump normally  draws 7 amps.

  

 Thanks

 John

   [quote][b]

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mprather(at)spro.net
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Posted: Fri Dec 08, 2006 11:30 am Post subject: Decreasing current to DC Motor

This is just like the pitot tube question..



Old EFI systems had pressure regulators that returned unused fuel to the

tank.  The pump was big enough to provide all the fuel the engine could

burn plus a little bit (to be returned to the tank).



My understanding is that newer automotive systems have returnless pressure

regulator/pump systems which use pulse width modulation (PWM) to regulate

pump output.  I think it's likely that your pumps could use such a system.



Out of curiousity, wouldn't it make more sense to get pumps that are of

the correct scale for your application?  At the same time, and with no

intent to insult your inteligence..   Fuel systems will require the

correct pressure to be maintained at the full flow rate consumed by the

engine (when flat-out)..  Most IC engines will need around 0.65 lbs/hp/hr

of fuel.  So, a 180hp engine will use 180hp * 0.65 lbs/hp/hr / 6lbs/gal =

19.5gal/hr.  When your make 100hp, you don't want to over lean, so the

system should have some headroom to provide extra fuel..  Maybe 25gal/hr

at system pressure would be a good target for a 180hp engine..

Regards,



Matt-



 	  Quote: 	
		   I have EFI pumps that move way too much fuel for my purposes. Is there an

 inexpensive way to starve the current to the pump motor so that output is

 decreased without harming the motor? The pump normally draws 7 amps.



 Thanks

 John

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jonlaury

Joined: 06 Nov 2006
Posts: 336

Posted: Sat Dec 09, 2006 8:48 am Post subject: Decreasing current to DC Motor

Thanks Matt. 

  

 No offense taken. Knowledge is  knowledge.

  

 I've found that most EFI systems are content to  move copious amounts of fuel and I think that it's because the gearotor pump  design, in the size that is found on cars, seems to move between 40 and 65  gph.One can find pumps of slightly less capacity, but they are almost all fitted  with push on barbed connections. Mine are push-on at the intake (about 1 psi)  and threaded AN fitting on the high pressure end. One pump moves 46 gph (at) 45psi  (at) 7A through 1/4" line! Both push 78 gph. I need a single pump output  of about 30 gph.The problem is my single pump is at the edge of cavitation;  both on, and I can see air in the transparent intake tubing. 

 A fellow lister gave me a part # for a Napa pump  that is the right capacity, but the pump has barbed fittings and needs  adaptation. I'm probably going to go this route, but I thought I'd check with  the List to see if there was an electrical solution. 

 Pulse width modulation is a possibility but has  it's own problems of whacking the bus with surges and potentially causing  problems with other equipment.

  

 JOhn

   [quote][b]

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