How can I reduce voltage in a line. What do I use
10-30-03, 03:05 PM
#1
How can I reduce voltage in a line. What do I use
Im trying to set up a 2 stage voltage switch for my fuel pump. Its a Aeromotive a700 (I do not have the money for a fuel pump controller).
what should I use to bring the voltage down, and any idea how much I should drop it?
what should I use to bring the voltage down, and any idea how much I should drop it?
10-30-03, 06:27 PM
#5
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the resistor needs to have a very high power rating. about 120w. a regular variable resistor will not do. i would just use a stock fuel pump resistor from an FD. you also dont need those diodes in the above diagram.
10-30-03, 07:18 PM
#6
sorry about the diodes i I started with a low voltage transistor circuit i made some time back and didn't think to get rid of them. I did not remember till you brought it up but FC TII had a fuel pump resistor as well. this should be found at a junk yard. it is under the air box in the front passenger side of the engine bay.
ps. it is a white "by now off white" block that is about .25"x.25"x1"
if your not that good at soldering i will make it for you at cost + shipping.
ps. it is a white "by now off white" block that is about .25"x.25"x1"
if your not that good at soldering i will make it for you at cost + shipping.
Last edited by nillahcaz; 10-30-03 at 07:20 PM.
10-31-03, 04:19 AM
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In our EE power lab at school we have a few 10A-rated pots. They're wirewound and a tad larger than the wheel on my FD. 
This is why the variable FP controllers use PWM. Come to think of it, I think the RX-8's pump is PWM controlled.
This is why the variable FP controllers use PWM. Come to think of it, I think the RX-8's pump is PWM controlled.
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10-31-03, 06:33 PM
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Why not get some old sub voice coils and (after working out what value you need) arrange them in different configurations to get the correct resistance/current flow ability
10-31-03, 11:07 PM
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nillahcaz, you're going to need a single big MOSFET. Probably less than $8 for one that can withstand the flyback voltage from the FP motor. Other than that, the little parts (a 555 or what have you) shouldn't run more than $10 for a homebrew.
11-01-03, 01:27 AM
#12
i was thinking a LM324n quad op-amp
78L12 volt reg
and irf521 mosfet
plus some parts i "can but wont" get from radio shack
i would say i could probly get it to your door for $25-30
. i just have not had time to call gateway elc.
i will let you know sat or monday.
also InsaneGideon. do you think i should put a cap on the DC pulse out to help make it a a constant voltage rather than a pulse? i don't know if the pulse could "would" make the brushes in the pump spark. this is assuming it is not a brush less motor. nice mini
78L12 volt reg
and irf521 mosfet
plus some parts i "can but wont" get from radio shack
i would say i could probly get it to your door for $25-30
. i just have not had time to call gateway elc.
i will let you know sat or monday.
also InsaneGideon. do you think i should put a cap on the DC pulse out to help make it a a constant voltage rather than a pulse? i don't know if the pulse could "would" make the brushes in the pump spark. this is assuming it is not a brush less motor. nice mini
Last edited by nillahcaz; 11-01-03 at 01:31 AM.
11-01-03, 02:11 AM
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Alright, someone noticed the Mini! The logo at the top of the clevage says "FHM"... in case anybody was wondering.
Yea, good call. The cap will help reduce EMI emitted from the flyback current, especialy if it's close to the motor on the harness. Kinda like a condenser-cap on a distributor. I'm remembering my R/C days when the little motors had little disc capacitors soldered directly across the motor's terminals. If they weren't there, the radio electronics would go nuts. It'd definitely have to be a high volt cap.
Watch out for the 7812. They require more than 12V to keep regulating (Like at least 13-14V). If the "12V" car power really dips to 12V strange things might happen. Maybe try a 7809 instead, and run the opamp at a 9V instead. Or use a Zener diode to regulate opamp power. This is assuming you plan to feed the MOSFET the unregulated B+.
The logo at the top of the clevage says "FHM"... in case anybody was wondering.Yea, good call. The cap will help reduce EMI emitted from the flyback current, especialy if it's close to the motor on the harness. Kinda like a condenser-cap on a distributor. I'm remembering my R/C days when the little motors had little disc capacitors soldered directly across the motor's terminals. If they weren't there, the radio electronics would go nuts. It'd definitely have to be a high volt cap.
Watch out for the 7812. They require more than 12V to keep regulating (Like at least 13-14V). If the "12V" car power really dips to 12V strange things might happen. Maybe try a 7809 instead, and run the opamp at a 9V instead. Or use a Zener diode to regulate opamp power. This is assuming you plan to feed the MOSFET the unregulated B+.
Last edited by InsaneGideon; 11-01-03 at 02:17 AM.
thanks for the heads up about the 7812. i was told it was good to 11v.
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