Hello all,

Been playing around with my data logger and I found a sensor that would allow me to log electrical load on the system in amps. I have it on my alternator wire right now and it seems to work quite well. Curious to see what it shows me, and if I can learn anything from it.

Second thing I am getting ready to experiment is be to log the torque of the engine in real time. I have already ordered a load cell. My plan is to mount it in such a way that it will measure measure the twisting force of the engine. I have a solid motor mount on one side and a rubber one on the other. Hopefully that will give me the movement needed to measure this. Still thinking about ways to calibrate it. If it works the way I plan, using a math channel in my logger, I will be able to compute hp as the car goes down the track. Should be interesting to see if I can get it to work as I think that data would be very helpful in understanding why the car picks up or slows down to a finer degree.

I welcome any comment or ideas.

Thanks

This should prove enlightening.
Please let us know what/whose components you used.

I think you will find your biggest draws are starting and the launch.

I'd want to put the electrical load sensor on the battery ground side, to capture all current flow.?

Sounds like fun stuff!

I planned on moving the sensor around to different points to learn how the current flows.

I didnt have alot of time to mess with it but its confirm my initial calculations when I first put my alternator on the car. I wanted an alternator that get supply the max system load at idle. I calculated with everything turned on it was around 50 amps. So my alternator is never loaded more than half of its capacity.

At idle it was showing around 18 amps. This is with a 7530t ignition, electric water pump, and all the gauges and datalogger.

With everything on, headlights and double fans it was showing around 50 amps. Engaging the transbrake show another around 10 amps.

Definitely seems that the alternator assumes all loads once it running which make sense. So when I move it to ground, I would expect the same readings.

In figure once I establish a baseline, it will help me keep an eye on the health of the electrical system.

My 2 cents about alternators. They get a bad rap for costing power and being incosistant. I argue that a system set up properly,the difference is a few thousands of a second. At max efficiency alternators are in the 40% efficiency range. It takes approximately 1 horsepower to produce 745 watts. Assuming I am pushing 20 amps going down the tracks that works out to about 280 watts( voltages x amps 14 x 20 = 280) at 40% that's about 700 watts, or less than 1 hp, add a little in there for the belt efficiencies. You may be pulling 1.5 hp, how much et is that? I have seen this in my car where the alternator failed, so I just pulled off the belt and continued racing. Car ran the same.

Most alternators peak efficiency is between 30-40% load at 2000 rpms. I selected the alternator I did to operate in this range at idle with the max load it will see because that is where the engine spends the majority of time. Efficiency falls off significantly as you increase %load and rpms. You drive it too slow, efficiency drops significantly.

Where people get themselves into trouble, they get these mini alternators, and under drive them. So they are not to maintain a state of charge at idle on the battery. So when you run down the track, the alternator is trying to charge the battery and keep up with the electrical load. So the alternator is operating at max capacity, at high rpms where it is least efficient, in these circumstances, you will see it effect et more. The other caveats to this is if the state of charge of the battery isn't the same between runs, you will get inconsistantcy.

Had a buddy were the car was pretty consistent first couple of runs and then would slowly fall off as the race progressed. I saw they he had a mini alternator on there with a 1 to 1 drive. Told him to take the belt off and the car picked up and consistancy came back. Basically as the state of charge got lower and lower, the alternator had to work harder going down the track, thus slowing the car down.

If you run an alternator, easy way to tell if you set up correctly, fire up the car and turn everything on, at a minimum, the voltage at the battery needs to be at 13.8 volts. If not, your not maintaining a state of charge on your battery and its probably adding some inconsistancy to your runs.

Also with the way we have to wire a racecar, a 3 wire is a better way to go. But that's for another time. I think I have sidetracked my thread enough.

Bill,
You are correct in your thinking.
The alternator will only put out what is being demanded of it.

With a 60 amp draw and producing 13.8 volts the HP required is 1.39.

Let's say with the same 60 amp alternator the car only draws 30 amps. That is .69 HP

If that 1.39 HP loss which most dynoes can't successfully repeat measure is a concern to anyone running 300 cubes and up, give up a donut or two to compensate.

AS I recall an alternator needs to see 2500 rpm to begin working. That is why you pulley it up.
Recalling again I think it takes 3750 rpm for it to put out it's full potential. It will only put out the max if there is enough draw.
They are kind of smart in that way. I pulley them so they can put out the max if required at launch.

You have to keep those MSD boxes well fueled with electricity or they get grumpy.

Most oem cars are way overdriven so the lights don't dim at the stoplight with the air running, etc. Anyone who has driven a car from the 70s and down will now what this means.

Running an alternator on a race car will often negate having to charge the battery between laps.

This message has been edited. Last edited by: Dave Koehler,

It depends on the alternator, most one wire alternators have an rpm they have to reach before they start charging.

My philosophy on alternators and racecars, is that the majority of the time the car is running it is at idle or low rpm driving around the pits. So to me, its important for there to be plenty of capacity there to keep the battery charged while running everything. If not, it will start to discharge the battery and it will charge going down the track which is where you don't want it.

quote:

Originally posted by banjo:
It depends on the alternator, most one wire alternators have an rpm they have to reach before they start charging.

My philosophy on alternators and racecars, is that the majority of the time the car is running it is at idle or low rpm driving around the pits. So to me, its important for there to be plenty of capacity there to keep the battery charged while running everything. If not, it will start to discharge the battery and it will charge going down the track which is where you don't want it.

I guess I don't know for sure that it works, but I'll often give the engine a little 'rip' after starting for the sole purpose of exciting the alternator.

quote:

Originally posted by Lenny5160:

quote:

Originally posted by banjo:
It depends on the alternator, most one wire alternators have an rpm they have to reach before they start charging.

My philosophy on alternators and racecars, is that the majority of the time the car is running it is at idle or low rpm driving around the pits. So to me, its important for there to be plenty of capacity there to keep the battery charged while running everything. If not, it will start to discharge the battery and it will charge going down the track which is where you don't want it.

I guess I don't know for sure that it works, but I'll often give the engine a little 'rip' after starting for the sole purpose of exciting the alternator.

I have seen some 1-wire alternators require this to start charging.

quote:

Originally posted by Mike Beck:

quote:

Originally posted by Lenny5160:

quote:

Originally posted by banjo:
It depends on the alternator, most one wire alternators have an rpm they have to reach before they start charging.

I guess I don't know for sure that it works, but I'll often give the engine a little 'rip' after starting for the sole purpose of exciting the alternator.

I have seen some 1-wire alternators require this to start charging.

My one wire alternator needs a short rpm increase to 2000 rpm to start it charging if disconnected from the battery. When continuously connected to the battery after initial start this is not needed for the remainder of the day. My alternator uses a separate disconnect from the main.

My pulley ratio is now 1.57 and I’m increasing it to 2.0 this year which I believe will help eliminate this.

1750 crankshaft RPM's to excite my standard 60A Delcotron one wire, standard pulley driven by a 50% underdrive crank pulley.Running an 1131 battery I don't need to charge between rounds, but I do. I like to have the charger on it for running the fan and water pump.

I'm thinking about getting a data logger so the grandkids will have some duties to perform in the pits.

I have come to the realization that my wet finger in the air is behind the times.

quote:

Originally posted by smokinjeff:
I have come to the realization that my wet finger in the air is behind the times.

Not really, even with a high zoot weather station and ET prediction program, I simply verified that my finger was calibrated correctly.
If it works, it works....

This is an interesting thread. I've had an on going inconsistency problem causing me a lot of rounds. With my attention towards my alternator(regulator), with heat or vibration can it do this; time run, 1.34, 5.97, 9.38- time run #2 1.33, 5.99, 9.41 then rd #1 (9.40 dialed) 1.31, 5.85, on the brakes 9.27? Let me say this car is mostly sorted out and I addressed fuel, ignition, converter and suspension. That said, I'm a veteran driver and this example has happened maybe 6-8 times in the last year and a half and when it does I'm surprised. I do have a volt gauge in the dash but can't see it while driving. Any thoughts would be much appreciated.

What is your voltage at idle?

What alternator?

What is the pulley ratio?

What is all on your electrical system?

quote:

Originally posted by Mr498:
This is an interesting thread. I've had an on going inconsistency problem causing me a lot of rounds. I do have a volt gauge in the dash but can't see it while driving. Any thoughts would be much appreciated.

If you do not have data acquisition, consider this. You can add a MSD 7730 Grid programmable ignition control to your present ignition for $395 today with Jegs Mothers Day sale and racer pricing. Full 1 year warranty and easy to wire to a present analog ignition.

Grid has 13 channels that will log to include voltage. When you have a run that is dramatically faster than normal you can overlay this faster run onto a normal and perhaps draw some conclusions.

Program Grid to shift the car also. The more you let Grid control the more knowledge you can possibly gain.

quote:

Originally posted by Mr498:
This is an interesting thread. I've had an on going inconsistency problem causing me a lot of rounds. With my attention towards my alternator(regulator), with heat or vibration can it do this; time run, 1.34, 5.97, 9.38- time run #2 1.33, 5.99, 9.41 then rd #1 (9.40 dialed) 1.31, 5.85, on the brakes 9.27? Let me say this car is mostly sorted out and I addressed fuel, ignition, converter and suspension. That said, I'm a veteran driver and this example has happened maybe 6-8 times in the last year and a half and when it does I'm surprised. I do have a volt gauge in the dash but can't see it while driving. Any thoughts would be much appreciated.

What was your 1/8 mile mph on those runs?

Banjo: voltage at idle about 12.5-13v. Stock type alt. off of a citation 80amp (just had it checked, they said it was good). Pulley ratio; 4" crank 2.5" alt. Electrical system; 2 red tops, 7al-2 box, pro power coil, moroso master relay, msd 8555-1 dist.,msd crank trigger( just put on new pick-up), moroso 40 wires, ngk plugs, welded chassis stud for main ground also ground strap to motor. Bud: #1-114.35 #2-113.8 #3-115.93. Wondering if voltage changes can affect the ign. box in a way to change timing, but always after a couple of runs and from the hit?

My theory on this, you need 13.7-14.5 volts at idle.
Your alternator is not putting out enough power to maintain the batteries with that pulley ratio and alternator.

Another thing, what size alternator wire do you run and how long is the run?

I run a 4 gauge approximately 15 feet from the alternator to the battery If your are running a smaller wire, it will increase the voltage drop, thus making your alternator less efficient. Easy way to test this is get a voltmeter, but one end on the positive battery terminal, and the other on the alternator positive post. Fire the car up, turn everything on and see what it reads if your seeing more than .3 volts, you can benefit from a larger wire and or improving your connections.

Btw you can use that little test to check any circuit. For it to work properly the circuit needs to be loaded. Found many bad connectors and connections using this.


The car spends most of the time at idle, therefore, it needs to be able to charge the batteries at idle and handle max load.

What I believe is happening in your case, you start off with a good charge, car runs its fastest. Then the alternator is not able to keep the batteries topped off at idle, so what happens is the alternator is charging going down the track. Depending on the state of charge will cause the alternator load to vary.

I run a cs130 alternator autozone special, which puts out 50 ramps at idle with a 2 to 1 ratio, idling around 1200 rpms. I can turn on everything on in the car and it not go below 14 volt.

quote:

Originally posted by Mr498:
This is an interesting thread. I've had an on going inconsistency problem causing me a lot of rounds. With my attention towards my alternator(regulator), with heat or vibration can it do this; time run, 1.34, 5.97, 9.38- time run #2 1.33, 5.99, 9.41 then rd #1 (9.40 dialed) 1.31, 5.85, on the brakes 9.27? Let me say this car is mostly sorted out and I addressed fuel, ignition, converter and suspension. That said, I'm a veteran driver and this example has happened maybe 6-8 times in the last year and a half and when it does I'm surprised. I do have a volt gauge in the dash but can't see it while driving. Any thoughts would be much appreciated.

I had a TH350 that did this to me. Changed a LOT of stuff, wound up being the trans, the power glide with the same convertor was perfect!

Update on what I am seeing with my amp sensor.

First pass out of the gate, it typically shows 25-30 amp. I made 14 passes this weekend, and on the last pass it was showing in the 50-55 amp range. No decernable different in the way the car runs. I would expect that because assuming 50% efficiency, 50-55 amps at 14 volts requires about 2 hp.

I never charge between rounds, but I am going to try it to see if it makes a difference. Granted I understand I am playing with .001s of a second.

I though it was interesting though. Did catch that
I left my cooling fans on a couple of times