School me on Return Fuel Regulators - Ford Mustang Forums : Corral.net Mustang Forum
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post #1 of 39 Old 06-02-2016, 06:30 PM Thread Starter
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School me on Return Fuel Regulators

I just received my On3 fuel hat and regulator and I have an concern with the design of the regulator that I hope people can confirm or correct my suspicion concerning the Return Port size.

With all the talk about needing to make sure the fuel return line is large enough to return the fuel under cruise RPM shouldn't the return port be fairly large? This regulator comes with -10 threads but the actual port diameter is only .140 diameter. If running dual 340 pumps does the excess fuel that the engine doesn't use actually flow through this tiny port? If so what's the point of running a -8 or -10 line back to the tank?

The return port is on the bottom, correct?

Convince me this port is large enough to warrant a -8 return line.

ks

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post #2 of 39 Old 06-02-2016, 08:43 PM
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dont know much about those regulators.
Normal convention, return is on the bottom.

The 9950-boost is a fantastic regulator for doing the speed limit to the grocery store.
I switched from the 340's and 9925-boost to the 4303 & 9950. When I called MP and told them I was thinking of keeping the 9925, I sure got an ear full.

Give magna fuel a phone call. It was an interesting phone call for me.


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post #3 of 39 Old 06-02-2016, 09:02 PM Thread Starter
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dont know much about those regulators.
Normal convention, return is on the bottom.

The 9950-boost is a fantastic regulator for doing the speed limit to the grocery store.
I switched from the 340's and 9925-boost to the 4303 & 9950. When I called MP and told them I was thinking of keeping the 9925, I sure got an ear full.

Give magna fuel a phone call. It was an interesting phone call for me.
What's the difference between the 9925 and 9950? Where's the extra cost/durability come from?

ks


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post #4 of 39 Old 06-03-2016, 08:20 AM
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The fuel line and every fitting is like a resistor. If the flow rate is below turbulence, it is pretty linear with pressure.

There are online calculators that calculate pressure drop with distance. I think Goodyear or Gates has a good one. For example my car is perfectly OK with a 1500-2000 HP capable pump with only a #10 hose feed and a #6 hose return for the long lengths front to rear, and some smaller hose and fittings for short lengths. The return can be small because the differential pressure, is from rail pressure to ambient pressure. With 35 psi rail (under vacuum) there is a 35 psi delta on the return, which allows my #6 to flow enough to keep pressure at 35 or less. I think when I tested it, it would pull down to 25 or 30 on the rails.

Regulators traditionally, because of design, are fairly small flow areas in the valve area. It is a short length where cross section is small, so the fuel simply speeds up in that area. As long as it isn't going too turbulent and developing too much pressure differential, it will be OK.


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post #5 of 39 Old 06-03-2016, 08:29 AM Thread Starter
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Regulators traditionally, because of design, are fairly small flow areas in the valve area. It is a short length where cross section is small, so the fuel simply speeds up in that area. As long as it isn't going too turbulent and developing too much pressure differential, it will be OK.
A few people from another forum are measuring their regulators to see what the return hole diameter measures. Based on what I've seen I can't see where a -10 return line is warranted on a regulator with a .140 diameter return hole.

The one I received from On3 is an Areomotive regulator p/n 13101 A1000-10.

ks


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post #6 of 39 Old 06-03-2016, 02:18 PM Thread Starter
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I discovered that the return ports can be different sizes depending on the regulators. For example the more costly Magnafuel 9950 is designed for higher HP cars uses a 3/8" hole for the return port and I think this is what I want to go with. Maybe (probably?) I don't need this large of return hole with the fuel system staged but I would rather be safe than sorry so I'll send this one back.

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post #7 of 39 Old 06-03-2016, 11:48 PM
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Your thinking is correct, and you can probably drill that one out a bit. There is no point in running a return line larger than -6 with that regulator. I was on the edge of overwhelming my fuel regulator with a 340lph in tank, and since that one started running out of fuel, I put in a 450lph Walbro that completely overwhelms the regulator. Idle pressure won't go below 78 psi when the alternator's fully charging. I did a little testing and found a quarter ohm, 100w resistor was not quite enough to drop the idle psi to normal (and it got really hot), so I wired 4 1.5 ohm 100 watt resistors in parallel and put them on a heatsink for .38 ohm, 400 watt resistor. I'll be installing my "module" as soon as I get a chance - any day now.

Here's what it looks like:



One relay is for powering the pump through the resistors (low voltage), another for bypassing the resistors (full voltage) and the third is for turning on my A/W intercooler pump. FWIW, I first tried a 40 amp PWM module for the pump without success. Dunno why it didn't work. It works on a lower current motor just fine. Then I found out the resistor dropping idea is what OEMs use (Nissan, et al). Seems primitive, but it's easy.

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post #8 of 39 Old 06-04-2016, 08:52 AM
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Alex, wouldn't you rather have a FPR that can handle the fuel pump or pumps, rather than reducing the current/power that reach the pump(s)?

This should concern a bunch of people who have fuel supplies way past OEM flow levels and typical regulators. I'm planning a dual 255lt/hr system myself, and obviously it'll need a different FPR. I like the TFS injector rails, but hadn't thought about the FPR yet.

Kevin, that tiny FPR outlet does bother me too, it's interesting that it seems that the hole is part of the regulator function. I'd have guessed at an 8AN return for your level of fuel flow, but I bow to the experts who have run that high power level for real, and for a long time.

You guys are dealing with some subjects that don't get a ton of attention on forums. I like hearing about it.

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post #9 of 39 Old 06-04-2016, 10:17 AM Thread Starter
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Alex, I'm guessing that once you get the electronics done you'll be getting a different regulator that can handle the bypassed fuel?

I find it strange that nobody has ever thought about this and actually looked into the design of the regulators before blindly buying one. People are buying what they feel are correct simply based off of what the advertised specs are and the MFR's are screwing us to some degree. I researched regulators for weeks and all I could find are the "fitting/port sizes", ie -6, -8, -10, etc. But the fitting size has absolutely no correlation to how large the drilled holes are that the fuel has to flow through. Case in point are the pics I posted above. The advertised port sizes are a -10 but you can clearly see that the return hole is nowhere near that size at .140 diameter and this spec is not advertised anywhere. Even some suppliers have no clue what's going on. I Specifically asked about this and I was told that it would flow a lot b/c it was a -10 port. Now I have to pay to ship it back and a 20% restocking fee b/c it won't work for my needs.

ks


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post #10 of 39 Old 06-04-2016, 10:58 AM
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Originally Posted by CDW6212R View Post
Alex, wouldn't you rather have a FPR that can handle the fuel pump or pumps, rather than reducing the current/power that reach the pump(s)?
I thought about this for a bit before choosing the path I did. I street drive this car mostly, and continuously circulating massive amounts of fuel is supposed to heat up the fuel. I have nothing but anecdotal data to confirm that. Since this is a technique used by OEMs in high-powered cars that have warranties, it must have some logic behind it. Even on pumps that draw less.

This is a .74 ohm EVO factory fuel pump resistor:



I need about half of that resistance. It should actually help with pump life, too.


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Alex, I'm guessing that once you get the electronics done you'll be getting a different regulator that can handle the bypassed fuel?
ks
No. For the reasons I explained above and I'm really digging my regulator packaging. This thing is intended for a Toyota or Isuzu or something (many import regulators look the same):





It'd be hard to improve upon that packaging, and it's NHRA legal (not firewall mounted).

When I was looking into this exact issue a few months back, there was another point that was made - having an 1/8" orifice is not nearly as restrictive as having a 5' long piece of 1/8" ID tubing. The math got surprisingly complicated quickly, so eventually I just said, "F it." Which is unusual for me, so take that for what it's worth.


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post #11 of 39 Old 06-04-2016, 10:31 PM
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Quote:
Originally Posted by KEVIN$ View Post
A few people from another forum are measuring their regulators to see what the return hole diameter measures. Based on what I've seen I can't see where a -10 return line is warranted on a regulator with a .140 diameter return hole.

The one I received from On3 is an Areomotive regulator p/n 13101 A1000-10.

ks
It would be better to slow the pump, if you can do that without overheating the pump motor.

A surprising amount of fuel can flow through a short small diameter restriction. The real issue is if fuel velocity gets so high flow becomes turbulent.

A long line, however, will kill with pressure drop even when much larger.


Quote:
I did a little testing and found a quarter ohm, 100w resistor was not quite enough to drop the idle psi to normal (and it got really hot), so I wired 4 1.5 ohm 100 watt resistors in parallel and put them on a heatsink for .38 ohm, 400 watt resistor. I'll be installing my "module" as soon as I get a chance - any day now.
sqrt of 400 *.38 = 32 So your pump draws something less than 32 amps. Do you know approximately how much current it draws??


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I didn't measure it, but here's a chart:



The regulator I have is preset to 49 psi. If the chart is accurate, it looks like current draw is about 16 amps.

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post #13 of 39 Old 06-06-2016, 02:00 PM
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I switched from the 340's and 9925-boost to the 4303 & 9950. When I called MP and told them I was thinking of keeping the 9925, I sure got an ear full.

Give magna fuel a phone call. It was an interesting phone call for me.
Quote:
Originally Posted by KEVIN$ View Post
I find it strange that nobody has ever thought about this and actually looked into the design of the regulators before blindly buying one. People are buying what they feel are correct simply based off of what the advertised specs are and the MFR's are screwing us to some degree.ks
That's a pretty bold statement saying no one has ever thought about fuel regulators, wouldn't you say? Just because there isn't 100 posts on them doesn't mean that the community is a bunch of sheep. Rather it's a simple 10 minute phone call to the manufacturer that clears up a lot of internet questions. Spend days researching on the internet or 10 minutes on the phone? I guess we choose 2 different ways to skin the cat, eh?

Yes you are correct that the consumer is the one who looses in the end. We get fuel systems rated at HP when perhaps flow would be better? A pump rating for HP seems consistently rated for a carb & N/a. Regulators unfortunately fall under the same rating system, the HP rated system. It's not an apples to apples comparison. And it's not very easy to see the difference between the 9925 & 9950 from the internet. Although the sales rep had no reservations into the HP rating and the physical dimensional differences between the two.
Add in years of experience. In the early 2000's I ran a mustang with the Aeromotive pump with the voltage regulator. Nothing but issues including vapor lock. I got fed up and went with a Weldon and instantly a lot of my issues went away, including issues I thought was being caused by the "tune."
in 2004 I bought a 6.0L LSx truck with a LQ9 and put a whipple charger on it. Ran a BAP and would consistently run lean for a fraction of a second when I went WOT & 4PSI where the pressure switch turned on the BAP. When the internet says voltage regulation is a Band-Aid, well that's my personal experience as well. The Aeromotive voltage regulators were more grief than good, and the BAP wasn't much better. After I changed to Weldon, I swore off anything Aeromotive again.

jump forward a few decades and cars, when it was time for me to build a fuel system instead of internet opinions I went to a manufacturer that supports many fast cars. Hence my recommendation to call magnafuel and have a short phone call with them.
*We talked about initial fuel pressures right at WOT.
*fuel pressure when just off WOT
*Idle fuel pressure and injectors
*Deadhead systems
*fuel delivery & return
*fittings & general layout

It was when I discussed 'general layout' with magnafuel the sales rep talked about vehicle acceleration. I hold a masters degree in engineering myself but what I forgot about was the 60' at the track in all my models. That's the difference between it working on paper, but not at the track. As simple as feeding both rails from the back and why that is the preferred method. As soon as the guy said at launch of a car the fuel stays at the line and the car moves forward, the light went on for me.
It's not a closed loop system, rather it is very dynamic in nature. Can you replicate 1.0g acceleration on a fuel system model? The point is, you can but there is a potential that you are forgetting about another variable in the equation. That's when I took my engineering hat off, and had a 10 minute conversation with the guys in the physical world.

now I run a liquid bath 4303 and the 9950. But there's more to it than just part numbers. It's the layout of the entire system.

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That's a pretty bold statement saying no one has ever thought about fuel regulators, wouldn't you say? Just because there isn't 100 posts on them doesn't mean that the community is a bunch of sheep. Rather it's a simple 10 minute phone call to the manufacturer that clears up a lot of internet questions. Spend days researching on the internet or 10 minutes on the phone? I guess we choose 2 different ways to skin the cat, eh?
You forget the other thought that when a MFR is called and they won't tell you anything useful thus leaving me to look for answers on the i-net. Yes, I called Magnafuel and he wasn't much help, "just buy X it will be good enough b/c it's designed for X hp."

My questions were eventually answered in a thread that I posted in the below thread and only when other people started digging deeper into what they have been using and posting pics of their own regulators. IMO, it seems that some of the people posting pictures were surprised of the design differences. Based on your comments above and the pics that were posted I now have a 9950 on order and I think this thread is has/will help others choose the right parts. So, no, I don't think my statement is bold at all unless someone takes every word literally but surely no one does that on forums. And for the record I never called anyone any names as you said that I did...but that's taking what you said literally isn't it?

Dead Head Return Fuel setup or no? - Page 5

From what I'm reading about your past experience it seems that you've also fallen into the trap of believing the sales pitch of parts being good enough for a X hp. While this may be good for some (most?) I prefer not to fall into the trap that a lot of us have experienced by being sold parts that won't work well for our application and, like you, prefer to design it with good/solid design specification info when needed.

ks


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post #15 of 39 Old 06-06-2016, 03:48 PM
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16 amps should be easy to handle.


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I hope so. Even if I have to drop down to three resistors (.5 ohms, 300 watts) if I need more voltage drop.

If it doesn't work, I guess I'll look into the magnfuel regulator. $200 for a regulator just feels wrong, you know? It's like paying $500 for a belt tensioner.

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Originally Posted by AlexLTDLX View Post
I hope so. Even if I have to drop down to three resistors (.5 ohms, 300 watts) if I need more voltage drop.

If it doesn't work, I guess I'll look into the magnfuel regulator. $200 for a regulator just feels wrong, you know? It's like paying $500 for a belt tensioner.
Keep posting any details of what you learn and do. I'm always up for learning new things, and if there's a better way, it's good to see it sooner than after my version is done. I'm slow so mine will surely be six months or more before I get to my fuel tank project.

Don
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post #18 of 39 Old 06-06-2016, 11:12 PM
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I'm a geek about getting data - you know I'll report back, good, bad or indifferent.

Speaking of which, I was able to sneak out for a 10 minute drive tonight. The resistor/full voltage trigger is temporarily wired to a toggle switch - when I switch on the IC pump, the fuel pump gets full voltage.

Going through the resistors, idle fuel pressure was right at 50 psi. Flip the toggle, and it shoots up to 78 psi. After a 10 minute drive, the resistors measured 133 degrees Fahrenheit and the heatsink's definitely working.

Not sure what those resistors can handle temp-wise (anyone know? Tom?), but I think they'll be fine.

Initial testing looks promising.

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I wish I understood electronics the way you Gents do. What you guys do with your knowledge is pretty amazing. Keep up the great work!

ks


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post #20 of 39 Old 06-06-2016, 11:40 PM
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It's not difficult - you'd easily grasp it if you took a little time, no doubt. I can draw up a schematic for you if you want; just literally connect the dots one at a time.

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How much total current is flowing through the 4 parallel resistors, or how much voltage drop is across them?

Are you sure they are in parallel pairs? Not series parallel?


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Don't let the look of the wiring fool you - they are indeed all parallel. It was a concession to solid wire and the fact that my barrier strips have two screws each.

Using this calculator:

Voltage Divider Calculator - RapidTables.com

I get a voltage drop of 4.2 across the resistors and 9.3 across the pump at 13.5 volts, assuming the pump is drawing 16 amps (pump @ .84 ohms).

Thoughts on power resistor max temps?

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Quote:
Originally Posted by AlexLTDLX View Post
Don't let the look of the wiring fool you - they are indeed all parallel. It was a concession to solid wire and the fact that my barrier strips have two screws each.

Using this calculator:

Voltage Divider Calculator - RapidTables.com

I get a voltage drop of 4.2 across the resistors and 9.3 across the pump at 13.5 volts, assuming the pump is drawing 16 amps (pump @ .84 ohms).

Thoughts on power resistor max temps?
Yeah, that's what I'm wondering about, the heat created and the power being consumed to reduce pump function.

I'd also like to know the practical limits of the common regulators used with return style fuel rails, or the ones mounted in the lines. If I could choose one that isn't overpowered(in normal driving) by a 255lthr pump on a 332 hitting 550hp, I'd be happy with that.

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post #24 of 39 Old 06-07-2016, 09:13 AM
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I can tell you for certain a 255 lph pump will not overpower a stock 5.0 regulator. In my case, a 340 didn't either.

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Originally Posted by AlexLTDLX View Post
I can tell you for certain a 255 lph pump will not overpower a stock 5.0 regulator. In my case, a 340 didn't either.
Thanks, that's what I've thought, but the posts here and recently made me wonder where that threshold is. Mine will always be a street vehicle, an SUV for nice things/fun, never dirty work(I have two others for that). So if I can do the twin 255 pumps right(wire the switch and label it and the pump locations inside the tank), then I can easily figure out which pump has to be replaced if it ever comes to that.

I don't yet want to cut a hole in the floorboard, but I did last week see the best version of that done for a 91-01 Explorer. Brian1 on the EF forum fabricates anything in real steel super well, and he made a plate(L-shaped) that fit perfectly and has a large seal around it. I could like that, because the hole is very large at the back of the rear seat floor. Dropping a fuel tank is no fun.

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post #26 of 39 Old 06-07-2016, 10:15 AM
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I run an Aeromotive Eliminator fuel pump with -12 feed line up to the engine compartment, Y off to dual -8 lines to the front of the fuel rails, -8 out of the back of the fuel rails to the Aeromotive 13101 regulator and a -6 return line to the tank. No issues making over 900 whp. Fuel pressure is spot on.

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post #27 of 39 Old 06-07-2016, 10:42 AM
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Quote:
Originally Posted by Saleen414 View Post
I run an Aeromotive Eliminator fuel pump with -12 feed line up to the engine compartment, Y off to dual -8 lines to the front of the fuel rails, -8 out of the back of the fuel rails to the Aeromotive 13101 regulator and a -6 return line to the tank. No issues making over 900 whp. Fuel pressure is spot on.
That sounds great Kevin. To me, it looks like your feed lines and fuel rails are excellent, and the only questions are the balance of the sizing and flow capacities of the pump versus the regulator and return line. I would prefer to have all of the lines more than adequate, and let the pump, regulator, and fittings be the limiting factors. It sounds like you are there but for questioning the return line size. Given your power level I would have made the return AN8 just to be sure it was enough.

But you guys are experts compared to my thoughts, and observing. Thanks for your sharing and thoughts, and allowing me to brain storm with you.

Don
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post #28 of 39 Old 06-07-2016, 11:46 AM
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I'm running a 340lph pump with stock return line. If the fuel pressure doesnt creep up at idle then I dont see why I would need a bigger return line. I'm using the least amount of fuel at idle so that would be the most amount flowing down the return line..

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post #29 of 39 Old 06-07-2016, 09:14 PM
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Originally Posted by AlexLTDLX View Post
Don't let the look of the wiring fool you - they are indeed all parallel. It was a concession to solid wire and the fact that my barrier strips have two screws each.

Using this calculator:

Voltage Divider Calculator - RapidTables.com

I get a voltage drop of 4.2 across the resistors and 9.3 across the pump at 13.5 volts, assuming the pump is drawing 16 amps (pump @ .84 ohms).

Thoughts on power resistor max temps?
If you did not measure it, a calculator will not work.

You need to get eyes on a meter connected across the resistors at idle. From that voltage and your pump supply voltage from the battery system, we will know everything about the system.

Then I can tell you something about heat, but normally the heat you have would never be an issue. The hotter the case temp the lower the safe dissipation becomes. This is because the element inside the resistor has thermal resistance to the case. It is the temperature inside the case on the wire element itself that determines if the resistor is "safe". To get that temperature, I have to know the outside case temp and the actual power dissipated.

....but you are probably way safe as an educated guess.


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post #30 of 39 Old 06-07-2016, 09:22 PM
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The return line can be much more restricted than the feed, because the feed has to maintain pump pressure at high flow rates with minimal pressure drop.

The return can have a pressure drop of full idle rail pressure at bypass flow.

So on one line, the feed, we worry about developing a few pounds of delta at full pump flow. On the return, all we care about is if at idle (minimum rail pressure) the return can flow the pump excess back at rail (maybe 32-35psi?) to zero pressure from end to end on that line. 30 psi delta can push a lot of fuel through a small hole.


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post #31 of 39 Old 06-07-2016, 11:47 PM
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Quote:
Originally Posted by TomR View Post
If you did not measure it, a calculator will not work.

You need to get eyes on a meter connected across the resistors at idle. From that voltage and your pump supply voltage from the battery system, we will know everything about the system.

Then I can tell you something about heat, but normally the heat you have would never be an issue. The hotter the case temp the lower the safe dissipation becomes. This is because the element inside the resistor has thermal resistance to the case. It is the temperature inside the case on the wire element itself that determines if the resistor is "safe". To get that temperature, I have to know the outside case temp and the actual power dissipated.

....but you are probably way safe as an educated guess.
Measure what? The resistors? I did when they came in and they were reasonably close. But my thinking was the temperature swing and the impedance of the pump motor are going to change things anyway, and honestly outside my wheelhouse in terms of level of understanding.

This is the part I'm most interested in: "....but you are probably way safe as an educated guess." Thanks.

AlexLTDLX

'84 LTD LX - 9.83 at 140.09. Whippled 365 SBF with a glide and 3.08 gears. Driven to and from the track 60 miles without even changing tire pressure.
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post #32 of 39 Old 06-08-2016, 12:05 AM
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FWIW, Tom, I have a dumb question that's always bothered me. Let's say we have a pump that draws 15 amps at 12 volts. That means the motor is presenting .8 ohms of resistance (ignoring all the dynamics therein). And we want to drop a few volts off that pump, so we put a .2 ohm resistor in parallel with the pump. The pump is now turning a little slower because of reduced voltage, but are we not drawing less current total? .2 ohm + .8 ohm = 1 ohm; and at 12 volts, that's 12 amps - less than the original 15 right? The pump's only using 9.6 amps and the resistors 2.4, right? (this might be where I start going off base). Coincidentally, the pump's only dropping 9.6 volts while the resistors 2.4 volts (12 amps and 12 volts now).

Without the resistor, the pump was pulling 180 watts (12 volts x 15 amps). With the .2 ohm resistor in series, the pump is now only pulling 92 watts (9.6 volts x 9.6 amps) - only about half of what it was before, and the resistor is pulling 5.76 watts (2.4 x 2.4).

Where did I go wrong? It seems way off to go from a total load of 180 watts to less than 100 by only adding a .2 ohm resistor...

AlexLTDLX

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Quote:
Originally Posted by AlexLTDLX View Post
FWIW, Tom, I have a dumb question that's always bothered me. Let's say we have a pump that draws 15 amps at 12 volts. That means the motor is presenting .8 ohms of resistance (ignoring all the dynamics therein). And we want to drop a few volts off that pump, so we put a .2 ohm resistor in parallel with the pump. The pump is now turning a little slower because of reduced voltage, but are we not drawing less current total? .2 ohm + .8 ohm = 1 ohm; and at 12 volts, that's 12 amps - less than the original 15 right?
Brush type electric motors have some odd characteristics. They can be non- linear with supply voltage or load.

An efficient motor will not limit current via winding resistance. It limits current by generating a counter EMF in the armature. The armature acts like a generator as it spins, generating an opposing voltage. That opposing voltage subtracts from the supply voltage until loss resistance and the voltage difference set the run current.

This is why, when locked shaft or under heavy load, current goes way up. This is also why starting current is so high. A typical efficient motor might draw 5-10 times the start current as run current when on a stiff voltage source. It does this because only "copper resistance" sets zero speed current, and armature counter EMF is zero volts. This means the full supply voltage is across the static resistance.

When it spins up, the internal voltage subtracts from the supply voltage to make a new lower effective potential across that fixed resistance. At some speed it all reaches equilibrium.

Another thing also happens. Some motors depend on forced liquid or air flow for cooling. When slowed they cool less, so they *might* get warmer.

Shaft loading also comes into play. It can make current increase with decreased voltage. That makes heat increase as voltage is reduced, since dissipative resistance is constant.

This is why you should measure the run current and source voltage (battery) feeding the resistor/pump combo. If you know the source voltage and value of series external resistance along with voltage across that resistance, then you know pump motor heat dissipation, resistor dissipation, pump running voltage, and everything else.

Just assuming the motor resistance based on full speed run current does not work.


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post #34 of 39 Old 06-19-2016, 08:03 AM Thread Starter
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Update and Question:
I got the new regulator installed and the fuel lines all run. The return line is plumbed to the bottom of the regulator.

With key ON and engine OFF the pump turns on and pumps fuel but there is a LOT of fuel returning back to the tank which seems backwards. With engine OFF there is no vacuum to pull the check ball off the seat to allow fuel to return to the tank.

Is this correct?

ks


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post #35 of 39 Old 06-21-2016, 02:58 PM
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Tom - thanks for the reply; I'll study it when I don't have a headache (seriously - gotta be this storm droppng hail on us).

Kevin - That's normal. Since fuel in liquid form isn't compressible, once the regulator's pressure is reached, all the remaining fuel gets bypassed and returns to the tank. The system should hold pressure for a good long while after you shut it off too. If pressure starts to drop soon after power off, either the pump's check valve is leaking or you have a leak somewhere.

BTW, put my car on the dyno recently, and the pump control module above works like a charm. Just FYI.

AlexLTDLX

'84 LTD LX - 9.83 at 140.09. Whippled 365 SBF with a glide and 3.08 gears. Driven to and from the track 60 miles without even changing tire pressure.
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