Heat makes it changes but not to the extent people think.This message has been edited. Last edited by: green1,
Would throwing on a meter honestly be able to tell the story? Regardless of if its enough or not, my HOP 100 amp super mini has helped give me confidence in knowing that my car will start every time with my current setup, and even with the electric fuel pump I run the alternator will charge at 18+ volts at around 1300+ rpms and drops down to 17.5 or so at 1000 rpm (about idle). What is interesting is watching how much of a voltage hit my gauge reads when I turn on my fan honestly.
1971 Camaro Split Bumper
Want to manually check the load value with amps and volts and test the alternator. Get a cheap inexpensive carbon pile load tester. They are a hand held unit. You can manually load the alternator and see where the amps and volts are.
Hooks right to the battery. Prices vary
On my 16v system the water pump is 4 or 5 amps and the fan on the radiator is about 16 amps, together they are 20 ! The fan on the trans cooler is 5 amp..
4 X Track Champion ( 2 & 2 )
2 X Run off Winner
Got my CS121 alternator back from Mark Payne after being repaired. The adjustable regulator went bad so I had him install a fixed 16v regulator.
I also found a little tool to measure current draw of each accessory. Don't know why I bothered, but I was more curious than anything to know what each device draws.
Results are as follows:
- Grid ignition (idle) 4.5-5 amps
- h20 pump 9.3 amps
- Spal 12" fan 18.5 amps
- Magnafuel Prostar 500 pump 17.5 amps
- parking lights 4 amps
- headlights (low beam) 6.3 amps
Obviously no real way to check MSD grid draw at max load/rpm.
Next I fired the car to check the alternator charge voltage.
Cold start/low rpm idle (1000 rpm) charge voltage was 17 volts with all the accessories on except the lighting.
With a normal warm engine idle rpm of 1300, the charge voltage was 18.25 volts.
Raising the rpm to 1500 rpm the charge voltage was 19 volts and at 1800+ rpm the voltage was 19.16 volts.
With my pulley ratio I'm well below the alternator max rpm at my engines max on track rpm. I'd like to speed up the alternator 300-400 rpm at idle to improve low rpm charging and stay right at or below the max safe alternator rpm (17,700).
This alternator has Powermaster racing 2.80" billet aluminum pulley. I calculated I need right at a 2 3/8" pulley to meet my target rpm and charging goals.
So far no luck on finding a commercial available pulley, so I may be forced to make one myself or have a friend cnc machine one.
Won't that blow the head lights?
I don’t have headlights in my car but driving lights and marker light with brake lights and only ones I have problems with are the marker lights.
Never blown a headlight. One or two tail light bulbs over maybe 15+ years.
DOTracer, care to share the "little tool" for checking amp load ?
Could you check the alternator output at those rpms ?
4 X Track Champion ( 2 & 2 )
2 X Run off Winner
I was about to buy a clamp on DC amp meter till I found out you can only clamp it wound each devices power wire. Almost all of my accessories are harnessed in pos/neg wire pairs to each device.
I searched and searched for a solution till someone told me about a small device that worked pretty well.
One is from Cen-tech and is called a 30 amp fuse curcuit tester. I couldn't get one delivered in a timely manner so I bought a device called the Fuse Buddy, again 30 amp.
You simply pull out the ATC fuse for the circuit, plug in the device, put the fuse in the tester and turn the accessory power and it reads the amperage draw.
I had to make a quick adapter with a spare fuse holder to attach to the maxi fuse holder that my fuel pump uses.
Now if you have a clamp on DC amp meter you could put it on the main battery cable and then turn on each device one at a time. Same goes for the alternator wire.
I didn't want to invest a couple hundred dollars in a Fluke clamp amp meter as I knew it would probably never get used again.
My alternator is rated 30 amps at idle and 55 down track so if it’s putting out 30 amps at idle then that’s more than my charger is putting out when I didn’t have alternator and was relying on charging between rounds. Guess it was a waste of time.
Well by my load testing if your on gas the draw from the alternator will be at least 50-60 amps at idle. If yours is only rated to put out 30, then your still discharging and will need to charge between rounds.
Myself I finally found a smaller alternator pulley to change the ratio and speed the alternator up and help with low speed charging. I'm waiting for a couple different length belts to get here to be able to test for any improvement.
I always charge between rounds. I wasn’t trying to eliminate charging between rounds only trying to help maintain so at later rounds I don’t get hit with dead battery. I am a one man operation so I just wanted help keeping the battery up. My space was limited and bigger alternator wouldn’t fit. House of Payne may be the answer now but I am not sure his is the same style but going to check with him because I do want a spare. Charger will always be on my car between rounds reguardless.
One thing some people don't take into consideration when it comes to alternators and charging is the pulley ratio and alternator rpm.
As noted before my setup had a 5.2" crank pulley with a 2.8" alternator pulley which was 1.86 to 1 ratio. This put the alternator way below max rpm but also limited low rpm charging.
I just got done replacing the alternator pulley with a 2.375" pulley which raised the ratio to 2.19 to 1.
I then started the car and mapped the charge voltage to see how the regulator was ramping in.
1000 rpm 17.5 volts
1300 (warm idle) 18.9 volts
1500 rpm 19.16 volts
1800 rpm 19.20 volts which appears to be the max regulated voltage.
So with that I feel like that's about as good as I can expect the low rpm charging and not exceed the max rpm of the alternator.
But all of this doesn't matter if the alternator doesn't put out enough amps to run all of the accessories.
I don’t believe the alternator will be able to keep the voltage that high if it isn’t also putting out enough amps. I believe everything will pull the voltage down without the amps.
I was testing some batteries Saturday seeing how much cranking they had in them and had alternator disconnected. After a while I fired up the car forgetting alternator was disconnected and was warming up motor to reset valves when I looked at volt meter in dash and it showed 14 volts. I shut car off hooked alternator back up and had to throw charger on for one minute then car fired up and was showing 16.8 volts at idle, bump idle up 100 and was over 17 volts so my alternator is doing something.
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