[BILTIT]

The only way to increase current is by reducing resistance or increase voltage. This is why wires burn up when they are shorted to ground (resistance=0, current=max available). The reason things burn up is because the bad connections act as a resistance. These resistances have a voltage drop across them. The voltage which is ''dropped'' is actually turned into heat! It is the build up of heat from these poor connections (resistances/voltage drops) that can melt switches, overheat connections, etc.

Wattage is used to show how much current a motor will draw at a given voltage.

[BILTIT]

LPete- you have a good point with the back EMF.

[65gto69]

Originally Posted by Jagtec1

Put an internally regulated 12SI from an '85 (I think) Riviera, with AC. Add a voltmeter, and go.

My RPM drops somewhat with my fan on also...so what? It doesn't matter. Been to the track yet? I'm curious to see what your new setup runs!! Gonna be quick.

Hey Darin,

Nope haven't been to the track yet, Might try it in September at the Cecil Springs Outlaw Nationals Inaugural Event. Gaydosh told me about it, so I think I am going to trailer the car down and give it a run.

There is definitely a lot of power in the motor, I can feel it just sitting in the driveway and snapping the throttle. A couple of times for testing, I backed the car up in the driveway and just blipped the throttle a little bit and put down black patches. Doesn't take much even with the 275/60/15 drag radials.

It will be a handfull.

Mark

[misaac]

BILTIT hits the nail on the head. Lowering voltage will reduce amp draw. Exception is SOME motors will increase current because of the reduced cemf. I have tested fuel pumps to prove that current will always decrease with lower voltage. The pumps tested dropped amperage as voltage decreased. There was only a slight rebound in amp draw when voltage got down to 4 volts. The pump was hardly spinning, and the amp increase was minimal. Most factory fan set ups have dual or variable speeds. Let's use a GM or Ford for example with a simple 2 speed fan. How do they achieve the lower fan speed? They use a RESISTOR to reduce voltage supplied to the fan. Lower voltage, lower amperage. High fan speed is high (full) voltage, high amperage. If lower voltage results in higher current draw in an automotive circuit, please give me an example different than the following: (Low battery voltage can cause high starter amp draw due to reduced cemf AND increased mechanical resistance.)

Burned and melted connectors add resistance to a circuit resulting in REDUCED amp draw. The energy emitted from a bad connection is heat. This voltage drop is stealing voltage from the rest of the circuit. Reduced voltage, reduced amperage. A good thing to remember about DC electrical motors is: mechanical resistance will INCREASE amp draw and, electrical resistance will DECREASE amp draw.

[Jagtec1]

Originally Posted by 65gto69

Hey Darin,

Nope haven't been to the track yet, Might try it in September at the Cecil Springs Outlaw Nationals Inaugural Event. Gaydosh told me about it, so I think I am going to trailer the car down and give it a run.

There is definitely a lot of power in the motor, I can feel it just sitting in the driveway and snapping the throttle. A couple of times for testing, I backed the car up in the driveway and just blipped the throttle a little bit and put down black patches. Doesn't take much even with the 275/60/15 drag radials.

It will be a handfull.

Mark

Come to Beaver Springs next week!

[ponjohn]

Originally Posted by george kujanski

ponjohn: you are missing one thing, tho. for a resistive load, as the voltage goes down, the current does not go up. volts = current x resistance. If resistance stays the same, reduce the voltage and you REDUCE the current. Has to be.

If you were correct, we could supply the entire world with current by reducing our supply voltages to zero. Doesn't happen.

George

George-

A motor is not a resistive load, it is an inductive load with a dc resisitive component. It is an active device pulling current, a pure resisitve load IE, light bulb, follows the principal you and biltit quote.

As it is pulling current to maintain speed if the voltage varies the current is going to vary in reverse proportion......agreed to a degree where the source gives up the farm. If your charging sytem voltage varies by 10% the current (as long as it is available) is going to vary by 10%, maybe more than 10% because your not operating the fan, fuel pump etc in the range of voltage it was designed, the hot spot if you will.

The formula is...wattage=volt x current

After this discussion, I too am going to do some testing. I am currently looking for a used alt tester. Not a load tester but the type that spins the alt.

John

[65gto69]

Originally Posted by Jagtec1

Come to Beaver Springs next week!

Darin,

I would like to, but car is not ready to go down the track yet. I haven't even had it on the road yet for test driving, so I am not going to take it to high speeds without testing at low speeds.

I am no NHRA pit crew, I believe I do good work, but yet don't feel I am good enough to build it and than turn 130 mph. I am a testing kinda person, don't trust anything until I feel confident that every nut, bolt, screw, and adjustment is set.

My car embarrassed me one time at a cruise night, I got it in to leave and it wouldn't start, just cranked. Finally got it started, and said you will never do that again, and it hasn't since.

Yes I do talk to my car, it listens to me and I listen to it.

I will feel ready by cecil in sept.

Mark

[george kujanski]

Yep, ponjohn, I'm familiar with the characteristic of motors which is why i specified a resistive load, to make it easier on myself. The motor speed adds to the complexity of the situation since it's back EMF affects the current draw.

It would be neat to have a proper apparatus that would test the motor and record the motor current and speed during this startup phenomenon as the line voltage droops, or borrow '65's car and attach voltage and current probes to it.

You may be able to find an alt tester like the type a parts store uses, but i think those use a single speed for testing.

Back in the day, we had variable speed motors and adjustable loads to characterize our alternators over the full operating speed and temp range. The largest we had used a 15 HP motor with a drive shaft into a temp chamber with a torque sensor on the coupling to measure drive HP on 180A truck alternators.

I have a Delco manual with output current versus speed graphs I can scan if you are interested.

George

[ponjohn]

Absolutely, I have found a few online with little or no info about the history of the unit, basically being offered as is.

Years ago I worked for a firm that was designing an invertor for marine use. It was great on resistive loads, plug it into an inductive load and it would obliterate the output FET's from the emf. Eventually got it sorted out but motors are nasty, noisy ( electrical) loads.

To me this fascinating, I would like to get more involved by doing some of this sort of work at home.

John

[65gto69]

Originally Posted by george kujanski

It would be neat to have a proper apparatus that would test the motor and record the motor current and speed during this startup phenomenon as the line voltage droops, or borrow '65's car and attach voltage and current probes to it.

George

Hey, if this is going to help a lot of people out and solve electrical problems, test away, I don't have a freakin clue about electric and I don't have a problem saying it.

I am going to get a volt meter this weekend, take some readings and post them here. I will leave it up to you guys to figure it out and let me know what to do.

Mark

[Geoff]

George K,
My comment in post #4, about electric fans only consuming 1 or 2hp, was meant to be facetious, as shown by the exclamation marks!!!
As you would know from reading & posting in the Heating & Cooling section, some people have the idea that there is no penalty, everything is win-win, with electric fans.
I was attempting to show in a witty manner that there are no free lunches, even with electric fans, as evidenced by the large rpm drop from the engine in question.

[65gto69]

OK, Had my dad come over to give me hand with this, actually he did the testing for me because, like I said early, have no idea what I am doing or looking at with electric.

This is what he came up with:

With car idling at 1400 rpms with fuel pump, ignition and fan on, reading was 12.5 to 13 volts. When rpms were taken up to 2500, voltage only increased to near 14.

All wiring is grounded properly, and there was no resistance when tested.

Conclusion: we think the alternator is not putting out what it should be.

Going to order a internal regulated alt. around 100 amps.

Any other suggestions????

Thanks,
Mark

[george kujanski]

Go right ahead and install a higher rated alternator. That may improve yuor charging situation at low speeds and heavy loading. I doubt if it'll cure your RPM drop when you engage the fans.

Geoff: I noted the tougue-in-cheek humor in your comment.

My take on the electric fan thing is that it's only real advantage is to improve airflow thru the radiator at low engine speeds, but there's a cost associated with it....as I've said B4, you don't get sumthin' for nuthin'.

George

[65gto69]

George,

I am doing this because it definitely looks like I need to replace the alt., so if I have to replace I may as well update it.

After replaced if my rpms do still drop, than I will have to find another way to keep my engine cool without the use of an electric fan.

Thanks for the help and suggestions, I will keep posting results.

Mark

[BILTIT]

You can keep the fan, just use an idle solenoid.

[NHRASuperStock455SD]

I didnt read all the posts, so excuse me if this has been stated.

1.) Are the fans and electric water pump hooked to the same circuit? If they are run them separately.

2.) Most switches are rated for 15amps. Never run the load directly, run a relay. The switches and the additional wire through the load cant take it.

3.) Always run the MSD box (or any box) ground wire all the way back to the battery. Terminal ground is bad for an engine ignition as it picks up eddy currents backwards through the ground wire. We had an electric fan that would turn into a generator until it stop spinning and the engine would stay running till the electric water pump quit.

4.) Use a relay on all fuel pumps as those switches and wire are pushing the limits of load, too.

Lynn

[ponjohn]

My particular situation was the car ran cool on highway and warmed up to the point where I was extremely nervous 230.

I installed the fan and electirc pump at the same time and changed to a 160* tstat and it now is below 200.


I would highly recommend the 12 si, 84 z28 HO alt I use. available anywhere, Advance also sells it with a lifetime warranty.

John

[BILTIT]

Yup, i second the 12SI alt.

[screamingchief]

How much electrical power do these devices draw (if you know):

Accel 300+ CD ignition system (box and coil)

Holley electric fuel pump (blue)

Electric fan 1800 cfm (I guess this can vary per make and motor)

A:The accel 300 CDI box is stated to draw 6 amps maximum,actual draw likely varies with RPM much like MSD boxes,the accel box is suggested to be wired with a 10A fuse in-line.

B:The holley "blue" electric fuel pump is stated to draw roughly 3 amps,suggested fusing is 7.5 amps when wired directly,15 amps when a relay is used.

C:Yeah,this will vary by actual unit used,but I would expect such a fan to draw around 10 amps roughly,almost certainly less than 20 amps.

A bigger fan with more CFM can quickly change that situation.

Many OE fans draw more than the aftermarket units too,so this should be considered too.

HTH answer the above "quoted" question.

I agree it's almost always a good idea to use relays for the fan and the fuel pump,even when their actual draw is fairly minimal.

And the ignition box wiring should be drawn pretty much directly from the battery and not the chassis harness somewhere.

If you choose to upgrade the charging system,be sure to visit the MAD electrical website for some good info to digest,will answer a good many questions,and likely will spawn some new questions too!

MAD electrical tech info.

HTH.

[65gto69]

Thanks screamingchief,

All electrical wiring for those 3 devices are pulling power from the battery, the ground is to the chassis. All 3 devices are connected to a separate toggle switch (the plastic colored/lighted ones), nothing goes through the OE fuse block.

Per you advice I will pull ground from negative side of battery. Nothing is fuse linked, I will purchase those and wire in.

I do not know much about the electric fan, it is generic, no specs on the electrical from the exposed side of the fan. Fan is 18", straight blade, 2000 rpm, 1800 cfm. I don't know if that will help any of you electrical gurus out, but that is all I know about the fan.

Thanks,
Mark