Minimum RPMs for Charging Battery? - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 26 (permalink) Old 03-27-2007, 09:13 AM Thread Starter
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Exclamation Minimum RPMs for Charging Battery?

I realized we're getting into stator/regulator destruction season (otherwise known as "warmer weather"), and thought a heads-up to newcomers about the charging system might be in order. One of the problems with the "parade" riding is that we tend to keep our bikes at a lower idle speed - but the charging system requires a minimum rpm to keep the battery resupplied. (Ergo, stator starts kicking out voltage to keep the bike and its accessories running, regulator's trying to get something to the battery to no avail, 'cause the battery's dropping voltage as you sit there...) Anyone know what it is for the 750? I know Harleys are much lower (something like 1500rpm), but I've heard somewhere on the order of 3500 for our bikes. Anybody know?

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post #2 of 26 (permalink) Old 03-27-2007, 10:44 AM
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It's probably more like 2500. I'm going off the electrical fault finding chart that says if the bike's making 13.5 volts at 2500, it's ok. 13.5 volts is enough to charge a battery. My own voltmeter reads over 14 at about 2000 or so.

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post #3 of 26 (permalink) Old 03-27-2007, 11:14 AM
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Wouldn't be a hard thing to find out by putting a meter on your battery (on a good working system) and starting up the bike, raising the revs until you get over 12.5 volts showing.

Also, the parade riding (slow rolling, idling in traffic etc.) causes your temp to rise which is really hard on the charging (stator) system, especially on hot days. I tend to detour around slow traffic lights with lots of cars waiting just to keep moving on hot days.

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post #4 of 26 (permalink) Old 03-27-2007, 11:29 AM Thread Starter
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Quote:
Originally Posted by fergy View Post
Wouldn't be a hard thing to find out by putting a meter on your battery (on a good working system) and starting up the bike, raising the revs until you get over 12.5 volts showing.

Also, the parade riding (slow rolling, idling in traffic etc.) causes your temp to rise which is really hard on the charging (stator) system, especially on hot days. I tend to detour around slow traffic lights with lots of cars waiting just to keep moving on hot days.
I'll give it a shot and see what results. You're right about the heat, Fergy, making it hard on the charging system. But the minimum rpms is something I didn't know about 'til I'd already done it - and then my only responses were, "What do you mean it's not like the alternator on a car?" followed by, "What the h--- is a stator?"

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post #5 of 26 (permalink) Old 03-27-2007, 11:40 AM
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It's a minimum voltage that will charge the battery, independant of rpm's.

If you are at about 13Vdc (at the battery) or greater, you are charging the battery. Anything less is questionable.

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post #6 of 26 (permalink) Old 03-27-2007, 11:41 AM
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I knew you knew that about the heat Cindy, but thought I'd mention it for the benefit of the newbies. The newbies will soon find out that crobbins is one wrench wench who's been there, done that and we have all learned from her! i.e. the restoration project... We have some amazing ladies on this forum.

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post #7 of 26 (permalink) Old 03-27-2007, 12:39 PM
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You know when on the highway at 5000 rpm dooing 80 mph the battery charges just fine.



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post #8 of 26 (permalink) Old 03-27-2007, 01:02 PM
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Quote:
Originally Posted by LurchChaos View Post
You know when on the highway at 5000 rpm dooing 80 mph the battery charges just fine.
I get better than 14.5Vdc up there, that's where the R/R starts taking a beating as it eats all that extra power.

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post #9 of 26 (permalink) Old 03-27-2007, 01:03 PM
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Quote:
Originally Posted by Ironman View Post
It's probably more like 2500. I'm going off the electrical fault finding chart that says if the bike's making 13.5 volts at 2500, it's ok. 13.5 volts is enough to charge a battery. My own voltmeter reads over 14 at about 2000 or so.
Sounds like your charging system is AOK!

Jon

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MF AGM Battery
Coastered
Degoated
Shaved & Jetted
Iridium's
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Battery/Temp/Clock Gauge
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Dunlop D-404's
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post #10 of 26 (permalink) Old 03-27-2007, 02:13 PM Thread Starter
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Quote:
Originally Posted by fergy View Post
I knew you knew that about the heat Cindy, but thought I'd mention it for the benefit of the newbies. The newbies will soon find out that crobbins is one wrench wench who's been there, done that and we have all learned from her! i.e. the restoration project... We have some amazing ladies on this forum.
I knew you knew I knew about the heat... ...and I may not be correct about the minimum rpms to derive enough output from the stator to keep the battery charged. But I was tihnking about this last night because it was warm, I noticed Jon L. seems to run his bike at higher rpms than I do, and then I got to thinking about the implications of that (lower rpms), which got me thinking about My Unfortunate Trip to Gettysburgh Bike Week last year when I blew my r/r. One of the things several folks noted (as I sat there in the Wal-Mart parking lot) was that while sitting in traffic, I hadn't kept my rpms up enough, which made a difficult stator situation worse. The problem - as I saw it - was that it was hot; and so I was thinking, "Keep the rpms down, it'll put less strain/heat on the engine block." But the low rpms, reportedly, only accelerated the rate at which my battery was discharging itself since the stator output was insufficient to recharge.

Sooooo, then I thought to myself this morning, "Self, let's ask the Forum members 'bout this", 'cause I heard a lot of things that day - some of which were useful, some of which were myth (such as, "You can find anything you need at Wal-Mart...they didn't have a battery for my 750).

So, actually, let me rephrase the question: Is it true that motorcycle charging systems such as ours (three-piece) do not work the same way as a generator/alternator set-up on a car, such that at lower rpms our steadily discharging batteries are not being replenished? Lurch will clearly never have a problem with his...

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