Can you check alt output at battery?

lance1586

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Feb 13, 2024
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Bellevue, NE
Alternator output at the battery with it running or have to tie into that three wire plug that voltage converter thing V.. something can’t remember now. Just did carbs on my bike and after being on tender 13 volts it will start but battery drops down to 12 volts and don’t think it’s a parasitic draw had the bike a year but new to charging issues. Battery new in Oct TIA
 
I don't know about ST's, but on my Honda Shadow 1100 you could check the AC stator output at the 3-yellow wire connection, before the power goes to the voltage regulator-rectifier. Now, I didn't do that PERSONALLY because my 3-pin plastic connector was all melted and charred black, so I cut the wires, measured the stator output on the alternator side's stubby wires (with the bike running only off a new battery). I got something like 18 volts at idle, 30 volts at half throttle, and 45 volts AC at 3/4 throttle. (I did this test in my garage with the door closed and it was insanely loud thanks to the V&H pipes on that bike, so I ended the test there without going to full throttle).
 
gunsmoker said:
I don't know about ST's, but on my Honda Shadow 1100 you could check the AC stator output at the 3-yellow wire connection, before the power goes to the voltage regulator-rectifier. Now, I didn't do that PERSONALLY because my 3-pin plastic connector was all melted and charred black, so I cut the wires, measured the stator output on the alternator side's stubby wires (with the bike running only off a new battery). I got something like 18 volts at idle, 30 volts at half throttle, and 45 volts AC at 3/4 throttle. (I did this test in my garage with the door closed and it was insanely loud thanks to the V&H pipes on that bike, so I ended the test there without going to full throttle).
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ya don't need to do that.
 
V4 Rider said:
Your Shadow had an external regulator fed from the three yellow wires.

ST has a car style alternator with an internal regulator.
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Is that true for both the 28 and 40 ampers? It wasn't clear to me which one he has.

Doesn't matter if checked either at the battery?
 
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Uncle Phil said:
With the bike running, you should see something like 14.2+- volts across the battery terminals IIRC.
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yeah, its really this simple. If you're seeing a lower voltage like 12.something, then there is an issue with your alternator.

If there's an alternator issue, then further troubleshooting may be different depending on whether you have the 28A or 40A alternator, since they are different in their construction.
 
Ron said:
Is that true for both the 28 and 40 ampers? It wasn't clear to me which one he has.
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They are very different. The 28a (left) has an external regulator; the 40a (right, without adapter) internal.

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Ron said:
Doesn't matter if checked it at the battery?
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Again, that's fine. The voltage doesn't change because of where you read it.
 
Well put fresh charged battery which was at 13.0 volts. Bike fired right up and showing 14.5 volts at battery at idle 1200ish rpm. Could just be a cheap battery Amazon one new in Oct no cycles in it really. My garage when when it was subzero here never got below freezing. We’ll see just didn’t think that mild cold would sap a new battery but I’m new at bikes. Thanks for all the replies fellas much appreciated as always.
 
lance1586 said:
This is what I have in there. 200 CCA
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Batteries are like incandescent light bulbs in one respect. Their life span cannot be predicted and we get an average life from the manufacturers after they test many and determine how long before half of the sample fail. Some will live on for years, others go off like a flashbulb.

That battery you pictured. It says 'Non Spillable. If that is an AGM type, you should know they do not like flooded type battery chargers. AGM batteries do not do well with the flooded type charger's anti sulfation cycle.
 
OK, I have a battery charger and just put it on the lowest setting only left it on like overnight and took it off. Think it says 1.5A per hour something. . But thanks for the heads up.
 
We’ll best I can come up with is I need more than 200CCA this thing is. Even in mild temps we’ve been having. This am checked voltage was at 12.8 on the battery it will grunt and stops doesn’t have enough torque. So, with this battery it will only crank and start if that battery is at 13.0 v so. . . Found me a 500 CCA I’m going to try guess you get what you pay for eh?
 

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Well for whatever reason my 200 CCA battery isn’t cutting it even when it’s warm. Bought it in Oct no clue. Bike won’t turn if battery is less than 12.9 volts. Well it’s turns about half a turn then stops.
 
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