Turn on electric fan, RPM's drop??????
 

Hi Guys,

What is my problem with this??? I am thinking that my alternator is just not supplying enough juice to run the extras, am I correct.

This is what I have: stock 1965 wiring harness connected to the normal, lights, horn, key, etc. Than I have 12 volts on a switch working the Accel 300+ ignition box and coil, 12 volts on a switch working Holley Blue Fuel Pump, and lastly 12 volts on a switch working the electric fan.

To start the car I flip the fuel pump switch, flip the ignition switch and turn the key, car fires up and idles. Temp rises and I flip on electric fan and RPM's drop about 400.

I guess I need more juice, or do I have another problem. All wiring is 12-14ga.

Thansk for your help,
Mark

Are you handy with a digital voltmeter?


If so:

A. Start car, measure from the alternator output to the case of the alternator, this will show you max potential available min load.

B. Turn on fan and measure at same spot above, this will indicate any loss of voltage due to the added load.

C. repeat A and B with engine RPM at 2000 rpm. Notice and voltage dip at this rpm as alt. is now prob supplying more current.

Do you run int or ext reg alt?

If Ext and you;re not concerned about originality, convert to internal and put a 12 si alt on . This is 94 amps and can be used from a 1984 Z28 HO, HO is very important as the non HO is only 78 amps.

Some may recommend the CS series alt BUT they require a pulley swap if you're running a V-groove. I certainly don't want to swap pulleys on the side of the road.

In addition, you must be confident the ground system of your vehicle is more than good. The high current items, fuel pump, fan etc MUST have a direct path to ground, meaning you may consider a 8 ga wire ( from batt neg) to a terminal block that guarantees you a more than adequate ground. Bad grounds are worse than not enough voltage/ current.

You can certainly pM with any more specific questions.

HTH-
JOhn

the extra load from the fans simply may be kicking in the reg. and making the alt. do some work and in return the rpm drop.

Rex

And they keep telling me electric fans only take 1 or 2hp to run!!!

mine does the same thing

You will want to check the amps. comming from alternator, not volts.

I use at least a 100-105 amp. alt. for racing. But that high may be more than enough, in reality.

Sometimes its the battery going bad.

Hi John,

Thanks for the reply.

Currently I do not have a volt/amp meter, I am not very electric savy.

Can you recommend a meter to get for a novice but will tell me what I need to know with my system???

My alternator currently is external regulated and is a autoparts store rebuild, I believe I saw 60amps listed on it.

How easy is it to convert to a internal regulator with my existing factory wiring harness?

Will my factory harness be able to handle the increase in volts and amps of the higher rated alternator???

Thanks,
Mark

Do I check the amps the same way as described by John for voltage????

Mark

This is not recommended. In order to measure current you must break the circuit and insert meter. If your trying to measure full cpacity of the alt you're going to need a wire capable of 100 amps(in theory).

Voltage via resistance is a direct correlation to the current being supplied or consumed.

Any basic 20.00 meter is more that acceptable for our use. No need for a high dollar meter to only measure to 1 decimal. ( 12.X volts).

The point in my dialogue above was to say YES maybe the alt is having a hard time keeping up, only because the integrity of the circuit may not be as good as it can be.

When switching to int regulated, the wires replaced will address the issue of a higher cap alt.

Maybe the battery is going sour, have a load test done it.

john

The engine RPM will drop as you apply electrical loads. The alternator needs to supply the xtra electrical energy to the loads and it does that by converting mechanical energy from the engine, loading it down. It's only about 50% efficeint doing that also.

Unless the idle speed is computer controlled like in newer cars, that is what you will see.

The same situation happens with A/C cars. A/C cars had an xtra solenoid on the throttle arm to increase the idle speed when the A/C was selected.

Using a bigger alternator won't make this problem go away.

A 62 A alternator requires about 3 HP to drive when it's generating full output.

Bottom line, you don't get somethin' for nuthin'.

George

John,

Battery is brand new exide, 900 and some cca.

Alt. is old, probably 15-20 years, but only maybe 2000-3000 miles on it if that, regulator is about the same.

I will get a meter and test to start there.

George,

So you are saying that if I were to get a 100 amp alt., 40 more amps than what I have now, I will still loose RPM when flipping on the electric fan?

Maybe this alt. isn't even strong enough to fire my ignition system properly, but I can't tell since I need that on to run the motor. So maybe I am already working the alt. with just the fuel pump and ignition, than when I flip the fan, that works it even harder.

How do I fix this?? There has to be a way I won't buy that it is what it is.

How do the bracket cars do it with all their fancy electronics, pumps, ignitions, stops, etc.

I am already idling at 1200 in park/800 in gear, can't afford a 400 rpm drop at that range car won't run. I don't think I should have the idle at 1600 to compensate.

Mark

hey mark.....got that carb tuned yet ?

i tried an electric fan and gave up. everytime i switched it on it blew the fuse (30 amp ! :eek: ) i dont know what the hell i was doing wrong. when i wired it with no fuse the darn thing vibrated my whole car ! i was using a relay and wired per manufacturer instructions......went back to mechanical. saving for a new CLUTCH fan assembly.....

Mark, right now I'll bet you are loading the alt to the point where it's maxed out and you are using battery power. a voltage check would confirm or deny this; if the voltage with the loads off is about 14, and with the loads on it dropping to 12.6 and below, the alt is maxed. Not only that, since the RPM drops, the output from the alt drops also; it's a function of shaft speed.

A bigger alt will provide more current at idle, but as i said, it comes with a price, namely, it takes more power to drive it at higher output.

You can't get around physics.

Another factor is your engine is probably not designed to be efficient at idle speeds, so the idle speed drops a lot with the xtra load.

About the only thing you can do is add a idle speed solenoid or use a mechanical fan, at least you won't incur the 50% efficiency by converting mechanical to electrical and back to mechanical energy again.

Steve: you were probably blowing the fuse because motors draw 3 to 5 times more current during startup then at running speed.

The fans are probably the killers here. Electronics by themselves don't eat a lot of power, but motors, like fan motors, what, about 30 A apiece or so? 1 fan will require at least 1 horsepower from the engine to drive it.

George

My Mark8 fan draws 130A momentarily on startup and settles out to 42-45A on full speed. I too used to blow 30A fuses and relays. I upgraded to a 70A relay and 60A fuse and all is good. I have since switched to a fan controller which slowly increases the voltage to help ''soft start'' the fan. The 12SI upgrade is one which i have done aswell.

A fan controller would help some as most of them start the fan at half speed and ramp up the voltage as required per motor temp. An upgraded alt. never hurts either when running additional electrical loads.

yep, Geoff, ONLY 1 or 2 HP. The question is: at idle speed, what is the max output of an engine? Does anyone ever test it at idle speed on a dyno?

I'll bet it's not a lot....Mark's idle dropped from 1200 to 800 when the trans is engaged....the tranny front pump already is absorbing a fair amount of the max available...sounds like not a lot of margin is left.



George

OK than, say I can't fix my electric fan problem, say I remove the electric fan completely. What can I do to get extra cooling power to keep my engine at a decent temp "190". Do I need an external engine oil cooler to get temps down? Is my 850 burning lean enough to cause heat?? When I had the 1050 dominator on the car it burned rich, but the engine temp held at 160, maybe I should go back to the 1050????

I have not driven this car on the road yet so I do not know how engine temps will be effected by driving air being forced into the radiator.

190 is the highest it has reached so far without the fan on, idling in driveway for about 15-20 minutes, which is probably not bad if it holds there, granted it is going to climb since all the radiator is getting is what the clutch fan is supplying.

George, thanks for explaining. So a stock motor is more efficient and stronger at idle (550), than my race motor at idle (800), is this correct??

Mark

I've been looking at this fan. Not sure it's worth the amp draw. I guess if I go to a CS alternator there is little reason not to use it as I'll have amps to burn. Have you found that you even need to run it full speed?

Not sure if it has run full speed. I have not tested it while it is running since i put on the controller. It has held my engine at 190-200 at the hottest i could ever get it (37C, stop and go traffic) and that is with the stock rad. made for a 350. I will be changing to a larger rad this summer and adding cooling lines from the rear of the heads back to the crossover.

I did notice that on a moderatly warm day (20-25C) it rarely runs while i am driving, just freewheels. It sure moves a ton of air when it is on.

Yep Mark, consider that all those go-fast goodies you have in that motor moved and changed the powerband from a lower, flatter band, to a higher RPM peaky band. Down at idle the engine may be worse than stock, (sure seems to be) given you have such a large RPM drop just engaging the trans.

Perhaps a fan controller would help by not adding an instantaneous load to the engine and you can control the fan speed (and load on the engine) without dropping your idle too much.

If you keep your fans, upgrading the alt would be a good idea to try to keep the batt charged under load but it may slow the idle down more.

How about adding an idle stop solenoid to keep the revs up a bit?

Anything you can do to get the idle vacuum up at idle will help by making the engine more efficient at idle. Vacuum is a good indication of loading. How about Rhoades lifters?

Perhaps you should contact Old Man Taylor for more info...he has a bracket car. Perhaps he can make some suggestions.

George

If you think about it, the power output at idle (at a given throttle opening) is EXACTLY the amount needed to overcome all the friction and pumping losses in the whole system. If there was more power available, the engine would speed up.

The only way to keep the engine from slowing down with increased load is to give it more air/fuel mixture (or make it more efficient). Like you said, George, an idle solenoid would fix it.