Voltage Reduction System - Convertible Hydraulics
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Joined: Oct 2010
Posts: 110
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From: Austin, TX
There is nothing new under the sun. I did not know this, but a common practice in the auto industry for some time has been to insert a resistor in series with the fuel pump to lower its voltage. This is, of course, exactly what we're doing here for the convertible top hydraulic pump.
In the fuel pump application, the resistor is automatically switched in and out as needed. When needed, it is switched in so the pump will not create too much pressure(!) and also to lessen power dissipation in the pump. It is switched out when high flow from the pump is needed. Resistor values are typically chosen so as to lower the pump voltage to 8-10 volts. In our convertible top system, the target is about 8 volts.
(This practice is now giving way to PWM (pulse width modulation) as a means of fuel pump voltage control. PWM is more energy-efficient and can provide variable pump voltage. But PWM would not be a good choice for our purposes because of cost and complexity, and because energy efficiency is unimportant with the convertible top pump running so infrequently.)
Here's a thread selected almost at random that discusses this practice ...
http://www.rx7club.com/showthread.php?t=786591
The resistors shown are heftier than the ones we use, but this is so because they have to work full-time.
So the "resistor method" is not such a peculiar idea after all. Sometimes the problem picks its own solution. It's deja vu all over again.
In the fuel pump application, the resistor is automatically switched in and out as needed. When needed, it is switched in so the pump will not create too much pressure(!) and also to lessen power dissipation in the pump. It is switched out when high flow from the pump is needed. Resistor values are typically chosen so as to lower the pump voltage to 8-10 volts. In our convertible top system, the target is about 8 volts.
(This practice is now giving way to PWM (pulse width modulation) as a means of fuel pump voltage control. PWM is more energy-efficient and can provide variable pump voltage. But PWM would not be a good choice for our purposes because of cost and complexity, and because energy efficiency is unimportant with the convertible top pump running so infrequently.)
Here's a thread selected almost at random that discusses this practice ...
http://www.rx7club.com/showthread.php?t=786591
The resistors shown are heftier than the ones we use, but this is so because they have to work full-time.
So the "resistor method" is not such a peculiar idea after all. Sometimes the problem picks its own solution. It's deja vu all over again.
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Joined: Apr 2010
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From: Arlington VA USA
My '89 Jeep Cherokee also has a resistor in series with the fuel pump.
It is supposed to reduce pump noise and extend pump life. FWIW, after 22 years and 185K miles, the fuel pump is one of the few parts (other than the engine and drivetrain) that has never failed.
It is supposed to reduce pump noise and extend pump life. FWIW, after 22 years and 185K miles, the fuel pump is one of the few parts (other than the engine and drivetrain) that has never failed.
Last edited by WhiteXKR; Feb 16, 2011 at 12:21 PM.
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From: North Carolina
Actually, now that I think about it, the fan speed control for the climate control system on most cars (at least on older ones) is just a resistor pack. Turning the dial just switches different resistors in and out of the circuit. Chrysler Sebrings have a notorious problem with their resistor pack because the low speed resistor burns out frequently. When that happens the fan will only blow on high speed. I've changed out several of them. So there's another example in which a resistor is used to control the power output of a motor.
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From: New Jersey
Thanks, DougBoost, for the kind words. I have been helped so often, by so many people on this forum, that I could scarcely count the times. So the chance to make any contribution is welcome. Quite a place, this is.
Today, in the midst of the worst northeast winter in memory, I woke to a 60+ degree day in Annapolis, Md., confidently put my pressure-reduced convertible top down, and drove home to NJ. Nobody saw this weather coming a week ago, but we'll take it.
Today, in the midst of the worst northeast winter in memory, I woke to a 60+ degree day in Annapolis, Md., confidently put my pressure-reduced convertible top down, and drove home to NJ. Nobody saw this weather coming a week ago, but we'll take it.
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Joined: Feb 2011
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From: Mtn View, CA
I just ordered this:
.22 Ohm 100w resistor. It's not as cheap as the ebay one, but it'll probably arrive a little more quickly:
http://www.newark.com/jsp/search/pro...FC-GB100000001
.22 Ohm 100w resistor. It's not as cheap as the ebay one, but it'll probably arrive a little more quickly:
http://www.newark.com/jsp/search/pro...FC-GB100000001
Member
Joined: Sep 2010
Posts: 30
Likes: 0
From: Evanston, IL
My first mod
Xenophobe,
Thanks for the domestic link. I didn't want to order from Hong Kong and wait a month. I just ordered the .22 ohm 100 watt resistor frm Newark.com.
This will be my first mod to my cat!
Maybe that is why I am still a junior member!
Thanks for the domestic link. I didn't want to order from Hong Kong and wait a month. I just ordered the .22 ohm 100 watt resistor frm Newark.com.
This will be my first mod to my cat!
Maybe that is why I am still a junior member!
Member
Joined: Jul 2010
Posts: 56
Likes: 7
From: san francisco peninsula, calif, usa
duplicate Jag connector source?
After a series of mishaps both related and unrelated to my '99 XK8, and right after I resolve my current "cylinder wash" starting problem, I think I'm ready to install your no-cut solution to the pump's electrics. Thanks for your instructions copy-very well done!! To avoid lost time searching and fiddling with misc non-fitting connectors, has anyone found a straightforward source for a 2-line connector that duplicates the stock unit or a compatible connector that works right off the bat?
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From: Ellijay
Installing a pair of male/female connectors would, indeed, allow installing the resistor where ever you choose. But that is not necessary. The no-cut installation could be shortened into only about 3 inches between the Jaguar connectors and zip tied into an attractive installation.
No, I do not know of compatible connectors.
No, I do not know of compatible connectors.
Member
Joined: Jul 2010
Posts: 56
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From: san francisco peninsula, calif, usa
Thanks mucho for the suggestion. And, again, thanks to those who came up with this approach.
I'm thinking that this pump-pressure solution is so elegant that it demands an elegant application. Simply put, my aesthetic sense is kicking in. Having two "stock" conectors sitting side by side would be really impressive and, for the Concourse types, very appropriate.
I'm thinking that this pump-pressure solution is so elegant that it demands an elegant application. Simply put, my aesthetic sense is kicking in. Having two "stock" conectors sitting side by side would be really impressive and, for the Concourse types, very appropriate.
Member
Joined: Sep 2010
Posts: 30
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From: Evanston, IL
Thanks mucho for the suggestion. And, again, thanks to those who came up with this approach.
I'm thinking that this pump-pressure solution is so elegant that it demands an elegant application. Simply put, my aesthetic sense is kicking in. Having two "stock" conectors sitting side by side would be really impressive and, for the Concourse types, very appropriate.
I'm thinking that this pump-pressure solution is so elegant that it demands an elegant application. Simply put, my aesthetic sense is kicking in. Having two "stock" conectors sitting side by side would be really impressive and, for the Concourse types, very appropriate.
Member
Joined: Sep 2010
Posts: 30
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From: Evanston, IL
Got my Resistor in
I ordered the .22ohm 100w resistor from Newark.com last Saturday and got it today.
It Is Huge. I will put it in in the next few days and let you know how it goes!
Here is a pick of it on a $5 bill for size comparison.
It Is Huge. I will put it in in the next few days and let you know how it goes!
Here is a pick of it on a $5 bill for size comparison.
Member
Joined: Jul 2010
Posts: 56
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From: san francisco peninsula, calif, usa
Mark, great idea except for the little fact that the nearest Jag junkie is some 50 miles away and at $4.13 per gallon, that's a mighty expensive connector. Postage tain't much better so I think I'll settle for the Radio Shack type for the time being.
Senior Member
Joined: Oct 2010
Posts: 110
Likes: 13
From: Austin, TX
Thanks for the picture since I got mine from there and it was less than half the size I expected after reading the doc! As hlgeorge noted, 100W is a lot of power to dissipate.
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From: New Jersey
Doug, where did you get yours (if the info is handy)?
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Joined: Oct 2010
Posts: 110
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From: Austin, TX
I got mine from Newark also. Great service (online ordering showed they had 26 in stock, gave lots of email confirmations, tracking number, etc.). Took less than a week to get.
I was a little concerned I didn't know the trick to pull the Jag connector apart but there is no hidden tang or lock, it's just quite snug due to little "ramps" on the male side of the connector body. I installed it in same manner as Testpoint and even added some electrical tape where my leads went into the connectors just to be sure there'd be no shorts if things bounced around a little.
Works perfectly with key off, and nice to know we have pressure in reserve if need it simply by starting the car!
I was a little concerned I didn't know the trick to pull the Jag connector apart but there is no hidden tang or lock, it's just quite snug due to little "ramps" on the male side of the connector body. I installed it in same manner as Testpoint and even added some electrical tape where my leads went into the connectors just to be sure there'd be no shorts if things bounced around a little.
Works perfectly with key off, and nice to know we have pressure in reserve if need it simply by starting the car!
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Joined: Feb 2011
Posts: 165
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From: Ridge NY
Just finished and it works great! 16 ga heat resistant wire and 1/4" connectors from auto zone 3/16 connectors from Radio Shack directly to resistor (Newark) took about an hour. Zip ties made everything tidy. Now a trip to JAGPRO in Bellmore NY for fluid and filter changes and a once over and I hope to be good to go! 
Thanks Guys!
Thanks Guys!
