ok so my battery does not seem to charge? : V-Twin Forum: Harley Davidson Forums

hbmc · 09-02-2009, 12:08 AM

I am noticing my battery is not getting a good charge. Actually it seems to be not charging while riding?

You guys running stereos notice that when you use your stereos that you are running the battery down a bit?

I did 70 miles Sunday and had 5 starts total and found that Monday because I did not put my trickle charger on it after a few starts and stops it was running low.
Put the charger on it and it looks to be down so I charged it all is good, but was wondering do you think the stereo 100wt amp and two 4 inch speakers and a fender light would tap it that hard? Ground is good BTW.

jerry34208 · 09-02-2009, 12:54 AM

100 watts? Yes it is possible the amp is drawing more than your charging system puts out but I don't know for certain. If you're talking about your '91, I believe they don't have a real powerful alternator. I'd run without tunes for a few hours and see if it charges up. Or even quicker would be to hook up a voltmeter and see if you're getting 15 volts or so at 2,000 rpm or more with or without the stereo. If not then you may have a charging issue.

trooper113 · 09-02-2009, 01:00 AM

Quote:

Originally Posted by jerry34208

100 watts? Yes it is possible the amp is drawing more than your charging system puts out but I don't know for certain. If you're talking about your '91, I believe they don't have a real powerful alternator. I'd run without tunes for a few hours and see if it charges up. Or even quicker would be to hook up a voltmeter and see if you're getting 15 volts or so at 2,000 rpm or more with or without the stereo. If not then you may have a charging issue.

I agree. The other questions are....how old is your battery, are the connections all clean and tight and what kind of battery do you have?

atrick · 09-02-2009, 12:49 PM

100 watts is 8.33 amps on a 12 volt system if your pulling all 100 watts which you probably are not. Watts divided by voltage will give you the amp draw.

DBotkin · 09-02-2009, 03:08 PM

Welll... that's the correct formula for calculating current from power and voltage, but in this context it's not really the right answer. First off, your electrical system is 12v nominal. It should be at 12.7 with the engine off, and around 14.6 to 15 running - so that number would be closer to 6.5, roughly.

Second, if your amplifier has 100W peak output, it's going to take a lot more than 100W input. Amplifiers aren't anywhere near 100% efficient, probably closer to 50% in the case of a car audio amp (I'm not going to bother looking up specs to see for sure). On the flip side, they're also very often rated at pure fantasy output levels and you're probably not typically running more than a fraction of that output power.

SO... all of this means, hang a volt meter on your battery and see what's going on. If you measure much under 12.7V with no load (everything turned off), you have a weak or discharged battery. You should see around 14.6 (if I recall correctly) with the engine at speed, say 2K-2.5K RPM. If you see much under 14 with everything running and the tunes cranked up, then you most likely have too much stereo for your alternator. If you don't have a volt meter, pick up a cheap one at Wally World, Harbor Freight or wherever.

hbmc · 09-02-2009, 04:54 PM

Thanks everyone for your input that really helped as I will go get a volt meter. thanks for the specs as well. BTW Harley Battery 1 year old and was checked for amps and charge at the dealer in june before my 1 year warranty was up.
It must be the Stereo or a culmination of both the new front fender L.E.D.'s I will check the draw this week.
Thanks again and regards
hbmc