Charging problem maybe? - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 12 (permalink) Old 08-04-2019, 12:37 PM Thread Starter
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Charging problem maybe?

Ok so I recently got my bike going good enough to run it around town. Brakes need replaced so of course I kept it slow and short distances. I rode it around for a week or so about half mile trips at a time, if that. Just once a day. I stopped to get gas bike fired right up.

When leaving the gas station everything seemed fine like normal I went across the road shut the bike back off talked to a buddy for few and when I tried to start the bike it turned over pretty slow-dead battery.

I got lucky enough it just happen to hit and fire up so I went straight home. About 7 blocks down the road. When I got home I shut the bike off and tried to fire it back up and motor would barely turn.

I went ahead and put battery on charge newish -AGM- battery by the way, and bike fired right up when battery was done charging. I let the battery sit for a 3 days and checked the voltage it was fine.

So today I went ahead and fired the bike up and checked the voltage going to the battery.

At Idle shows-12.66v —— bike idles around 1k rpm

2000rpm shows about 13.62V

but anything over like 3-3500 rpms shows voltage dropping to 13.30V

Any suggestions? Surely that’s not normal I would think the higher the rev the more voltage not less.

And the speed limit in town is 20mph as a side note
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post #2 of 12 (permalink) Old 08-04-2019, 01:57 PM
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The voltage levels don’t care about speed, it’s related to rpms so you can test it in neutral if you need to. Have you checked your stator and R/R? You can check the stator voltage outputs and also check resistance levels across the leads, and lastly make sure it’s not grounded out to the bike. There are similar tests for the R/R too (output and resistance across leads) but one thing you said was “newish” AGM battery, l learned the hard way, even though AGM is better than a wet cell, newish still don’t cut it, if you fully charge it and it maxes out at 12.6 with the bike off, that battery might be getting shot. But I’d focus on checking your charging system first because if it’s messed up it will continue to eat up batteries until it dies itself. All the measurement readings for the tests are on this site
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post #3 of 12 (permalink) Old 08-04-2019, 02:39 PM Thread Starter
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Battery is only couple months old and has been load tested. It’s fine. Stator was replaced not long ago and I had tested it when I started tackling the project and it had tested good.

the R/R had tested good as well.... I suppose it wouldn’t hurt to test everything again since I’ve put some run time on it.

The R/R still yet has not been replaced. Maybe the whole problem. I will get to testing everything again here shortly and see what readings I get.
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post #4 of 12 (permalink) Old 08-04-2019, 03:15 PM
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I would replace the stock R/R with a MOSFET version almost out of hand they are so much better

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post #5 of 12 (permalink) Old 08-04-2019, 03:39 PM
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My stator chewed up the AGM battery I bought in April, after i replaced the stator I realized it was not holding a good charge, so as much as it sucked to spend more money I got another one. Major difference
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post #6 of 12 (permalink) Old 08-04-2019, 04:30 PM
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13.3-13.6v isn't horrible, but the 12.6v at idle is no charging at all. Add that to a 20 mph speed which will cause the fan to run, and voltage will be even lower. From idle to around 25 mph, your bike is probably running on the battery alone.

It could be suffering with the bugs in Junction Box which pull the voltage down. Two-Wire mod could help if that's the case. Blue Wire mod also bypasses one of the three solid state relays in the JB that are known to short out.

Voltage dropping off slightly with higher rpm is common to see.

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post #7 of 12 (permalink) Old 08-04-2019, 04:39 PM Thread Starter
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I have done both mods already, blue wire and two wire mod. I do have a question I’m not good at reading manuals I have my book out (will upload the pics)

but according to #11 chart- I should take the ground on my multimeter and touch it to (M) and the positive to (B) and be able to see 10k ohms on my meter? Am I doing this correctly?

If so I’m not showing anything at all on g,m,d however if I was to use say (A1) and (G) I would see some ohms.
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post #8 of 12 (permalink) Old 08-04-2019, 05:00 PM
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Sounds like you have it right. Whatever the value is in the intersection of the row and the column on the chart is what you should see.
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post #9 of 12 (permalink) Old 08-04-2019, 05:12 PM Thread Starter
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R/R maybe the problem then I’m not getting any kind of reading out of it. Will order a new one tonight and see if that don’t fix it
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Sounds like you have it right. Whatever the value is in the intersection of the row and the column on the chart is what you should see.
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post #10 of 12 (permalink) Old 08-05-2019, 01:11 AM
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I have done both mods already, blue wire and two wire mod. I do have a question I’m not good at reading manuals I have my book out (will upload the pics)

but according to #11 chart- I should take the ground on my multimeter and touch it to (M) and the positive to (B) and be able to see 10k ohms on my meter? Am I doing this correctly?

If so I’m not showing anything at all on g,m,d however if I was to use say (A1) and (G) I would see some ohms.
I have a strong suspicion (nobody has either verified or proved me wrong) that the published chart for the R/R ohm test is BACKWARDS. The Meter (+) and Meter (-) labels seem to be reversed. You should be able to put the positive lead of your tester on any A1,2,3 terminal and measure .2~.6kOhm with the negative lead on the battery terminal. The same reading should be possible putting the positive lead on the ground terminal and the negative lead on any A1,2,3 terminal.

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