Some voltage readings - Team Camaro Tech
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post #1 of 6 (permalink) Old Feb 28th, 08, 02:34 PM Thread Starter
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Some voltage readings

Note... Alt wire goes from the alt to the batt in trunk. Car feed wire goes from batt in trunk to distribution block under hood.

Car at idle at Alternator
At Alt = 11.4 Amps / 14.4 V
At Alt with lights on = 25 Amps / 14.5 V
At Alt with lights and heater = 25 Amps / 12.9 V

Car at idle at distribution block
At block = 1.6 Amps / 14.2 V
At block with lights on = 18.8 Amps / 14.0V
At block with Lights and heater on = 25.4 Amps 12.2 V

Car at 2000rpm at Alternator
At Alt = 11.4 Amps / 14.2 V
At Alt with lights on = 25 Amps / 14.8 V
At Alt with lights and heater on = 42.3 Amps / 15.2 V

Car at 2000rpm a distribution block
At block = 1.6 Amps / 14.2 V
At block with lights on = 16 Amps / 14.2 V
At block with lights and heater = 30 Amps / 14.2 V

What do you make of it? The 11.4 Amps at the alt and 1.6A at the block is weird. Is the batt calling for 10 or so amps to charge and the car is calling for 1.6? If you add in all the acc the amps add up minus the 11 or so. Sound right?

Also can you explain the 15.2 V at alt to make 14.2 at the block when the amperage goes up?

From what it looks like the Alt only puts out 25 Amps at idle.

1968 Camaro Convertible ,350 TWIN TURBO , PTC 3000 stall, Hotchkis TVS kit / Subframe connectors, Caltracs, 9" rear, Street Star wheels (P275/40ZR17 / P235/45/17) , Electric cutouts. [B] .....FOR SALE.....

Last edited by mnm99; Nov 15th, 08 at 06:24 AM.
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post #2 of 6 (permalink) Old Feb 28th, 08, 02:54 PM
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Re: Some voltage readings

Your numbers look fine.
25 amps at idle is what I would expect from a stock 61 amp alternator.

The 15 volts @ 2k is because the "remote voltage sense" wire from your external regulator is connecto to the main feed in the harness, up by the horn relay. This is good, cause you WANT the system to maintain the voltage there.

I wish I'd been paying more attention to your other posts, I would have suggested connecting the alternator to the distribution block rather than the battery, woulda saved you a bunch of wire, as well as putting your power where you needed it.

If you have some left over cable, you might make a connection directly from the alternator to the distribution black and see what effect that has. Looking at your readings, it may have no effect at all, they really look pretty good.

The 1.6 amps at the block with the lights off looks good to, the only draw from the car would be the ignition, so you have 9.8 amps charging the battery.

The only point I see where you are drawing more power than the alternator is putting out is idle with lights and heater on, alt output = 25 amps, car draw = 25.4. With .4 amps coming out of the battery, you could let the car idle like that for a week without draining the battery.





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post #3 of 6 (permalink) Old Feb 28th, 08, 03:08 PM Thread Starter
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Re: Some voltage readings

Quote:
Originally Posted by JimM View Post
Your numbers look fine.
25 amps at idle is what I would expect from a stock 61 amp alternator.

The 15 volts @ 2k is because the "remote voltage sense" wire from your external regulator is connecto to the main feed in the harness, up by the horn relay. This is good, cause you WANT the system to maintain the voltage there.

I wish I'd been paying more attention to your other posts, I would have suggested connecting the alternator to the distribution block rather than the battery, woulda saved you a bunch of wire, as well as putting your power where you needed it.

If you have some left over cable, you might make a connection directly from the alternator to the distribution black and see what effect that has. Looking at your readings, it may have no effect at all, they really look pretty good.

The 1.6 amps at the block with the lights off looks good to, the only draw from the car would be the ignition, so you have 9.8 amps charging the battery.

The only point I see where you are drawing more power than the alternator is putting out is idle with lights and heater on, alt output = 25 amps, car draw = 25.4. With .4 amps coming out of the battery, you could let the car idle like that for a week without draining the battery.
Thats all kinda what I thought. If I was to go to a 1 wire alt as say 130 amps my charging at idle should be around 50A or so letting me idle and use all my acc if needed. Right? I'm just thinking about the electric fans in the future.

What about the 15 or so volts at the alt to make 14 at the block? Is it true a 1 wire alt will only give me 14.5v all the time?

Also the reason I ran the wire to the trunk is because of the disconnect switch that cuts off the whole car. If I connected it to the block it would still run with the switch off.

1968 Camaro Convertible ,350 TWIN TURBO , PTC 3000 stall, Hotchkis TVS kit / Subframe connectors, Caltracs, 9" rear, Street Star wheels (P275/40ZR17 / P235/45/17) , Electric cutouts. [B] .....FOR SALE.....

Last edited by mnm99; Feb 28th, 08 at 04:26 PM.
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post #4 of 6 (permalink) Old Feb 28th, 08, 05:57 PM
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Re: Some voltage readings

The voltage drops you are seeing are due to resistance in the electrical system. The heavy load values show 15.2 at the alternator and 14.2 at the distribution block. Thats a 1 volt drop. If the current is 30A (or is it 42.3 - I'm confused), then the resistance is 1V/30A = 0.0303 ohms of resistance.

We can also estimate the power (heating effects) by multiplying voltage drop and current measurments. 1V * 30A = 30 watts of heating which seems a little high depending on the length. You're always going to have resistance in your electrical system. Larger wire will help reduce the resitance and heating effects. Longer runs need bigger wire. How warm does that wire get when you flow the high load through it for a minute or two? If it gets very warm, I'd up-size it.

I personally think the charge wire should be connected nearest to the battery if remote sensing is used. I also advocate installing power taps for headlamp relays, electric fan relays, and other high current loads to the battery end (junction block). The remote sensing wire will ensure the electrical system (horn relay) is well regulated. The alternator will step up the voltage as needed to maintain regulation. The end result is the battery gets a good charge, and high current accessories receive plenty of voltage to run. Check out https://www.camaros.net/techref/electrical/dnult_alt/ for more.

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post #5 of 6 (permalink) Old Feb 29th, 08, 04:27 PM Thread Starter
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Re: Some voltage readings

Made a little change today Jim . I ended up keeping everything the was it was with one exception. I ran another 4ga wire off the fuse block right next to the alt and directly to the distribution block (around 3 feet long) like you said. My amperage readings are around the same at 7.2 amps at the alt and 1.6 at the distribution block, BUT my voltage never goes below 14.4 volts. It will go to 13.1 now with all acc on at idle but reving the car quickly brings it back to 14.4 and now the alt is also putting out 14.4 so there is no voltage drop anymore. Amperage going back to the battery was the full load of everything before. Now I only get the 7 or so charging amps through the wire running in the car with everything on. All the load is under the hood now. I feel it's much safer, don't you?

If I ever go to the track all I have to do is disconnect the one wire from the dist block and I will have a full cutoff.

1968 Camaro Convertible ,350 TWIN TURBO , PTC 3000 stall, Hotchkis TVS kit / Subframe connectors, Caltracs, 9" rear, Street Star wheels (P275/40ZR17 / P235/45/17) , Electric cutouts. [B] .....FOR SALE.....

Last edited by mnm99; Feb 29th, 08 at 05:10 PM.
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post #6 of 6 (permalink) Old Feb 29th, 08, 06:05 PM
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Re: Some voltage readings

yes, how you have it is how General Motors designed it in the first place. Put the power to the load.





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