How do I find out how many amps my alternator puts out? - Sportbikes.net
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post #1 of 11 (permalink) Old 01-07-2006, 10:22 PM Thread Starter
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Question How do I find out how many amps my alternator puts out?

I been looking into buying some heated gear and was just trying to figure out how many amps my alternator puts out on my 96 F3, I looked in the service manual and only found this bit of info.
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post #2 of 11 (permalink) Old 01-08-2006, 04:59 AM
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Use a multimeter

If you rode half as much as you talk, you would have something to talk about...
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post #3 of 11 (permalink) Old 01-08-2006, 07:40 AM Thread Starter
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Quote:
Originally Posted by Anti-Hero
Use a multimeter
Can you give more details as how to check it with a multimeter?
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post #4 of 11 (permalink) Old 01-08-2006, 06:31 PM
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Ohms law. Measure the alternator resistance with the wires disconnected, then divide it by 13.5 volts. The answer will be your amp output.

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post #5 of 11 (permalink) Old 01-08-2006, 06:57 PM
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Quote:
Originally Posted by TTsixxer
Ohms law. Measure the alternator resistance with the wires disconnected, then divide it by 13.5 volts. The answer will be your amp output.

My gut tells me this won't work - correct me if I'm wrong, but isn't an alternator just an AC generator with a rectifier? If so, I don't see how measuring the input resistance of the output of the generator would allow you to determine the maximum current output.

The easiest way is to find the maximum power output of the generator (in Watts) and divide that by 13.5 volts. I've always been able to find the max power rating of any of my bikes generators in the service manual or owner's manual.


edit: Saw you already looked in the service manual - try looking on the web. Or you could just get a beefy potentiometer and keep increasing the load on the system until the voltage started to drop down under the charging system's voltage. Then you'd know how much of a load you could handle - therefore how much current you could safely draw with your electrics.

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Last edited by ty454; 01-08-2006 at 07:22 PM.
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post #6 of 11 (permalink) Old 01-08-2006, 07:17 PM
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Quote:
Originally Posted by ty454
My gut tells me this won't work - correct me if I'm wrong, but isn't an alternator just an AC generator with a rectifier? If so, I don't see how measuring the input resistance of the output of the generator would allow you to determine the maximum current output.

The easiest way is to find the maximum power output of the generator (in Watts) and divide that by 13.5 volts. I've always been able to find the max power rating of any of my bikes generators in the service manual or owner's manual.
You're right, I totally forgot that a alternator/generator generates AC voltage.

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post #7 of 11 (permalink) Old 01-08-2006, 08:32 PM
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Get a current probe and put it on the positive battey lead and read what it says. Or stop by autozone or something they should have the machine that tells what it is puttin out
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post #8 of 11 (permalink) Old 01-09-2006, 03:16 PM
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Quote:
Originally Posted by thorguy57
Get a current probe and put it on the positive battey lead and read what it says. Or stop by autozone or something they should have the machine that tells what it is puttin out

Unfortunatley that won't tell him the maximum available current his alternator provides, only what it is providing at that particular instance in time. I'm guessing he wants to know what he has available for possibly running electrics.

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post #9 of 11 (permalink) Old 01-09-2006, 05:24 PM
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I was just reading about this in my American Motorcyclist magazine. A guy was asking about heated clothing on his 1999 Honda ST1100. The alternator on the bike was rated at 480 watts. That's a touring bike so it's sure to have a higher output than a sportbike. The magazine said that he should have about 200 watts left over for accessories.

I was looking in my factory service manual and it says my bike is rated at 22A/14V @ 5000RPM.

Hope that helps.
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post #10 of 11 (permalink) Old 01-12-2006, 05:24 AM
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Quote:
Originally Posted by ty454


you could just get a beefy potentiometer and keep increasing the load on the system until the voltage started to drop down under the charging system's voltage. Then you'd know how much of a load you could handle - therefore how much current you could safely draw with your electrics.
Thats a great idea, go to an automotive garage and ask them if their Charging System Check includes an alternator load test in which they test the threshhold of the alternator. Keep in mind motorcycle alternators dont charge much at all at idle, so do one at cruising RPM and one at idle.

if you decide to put the grips on, I would not let the bike idle with all the loads on it. It makes the alternator work at 100% capacity and thats what will kill it
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post #11 of 11 (permalink) Old 01-12-2006, 09:56 AM
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Quote:
Originally Posted by likebikes
I was just reading about this in my American Motorcyclist magazine. A guy was asking about heated clothing on his 1999 Honda ST1100. The alternator on the bike was rated at 480 watts. That's a touring bike so it's sure to have a higher output than a sportbike. The magazine said that he should have about 200 watts left over for accessories.

I was looking in my factory service manual and it says my bike is rated at 22A/14V @ 5000RPM.

Hope that helps.

Using Ohm's law P=IXE then 22X14= 308 watts on your bike....
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