Sportster Electrical Capacity

Discussion in 'Sportster Models' started by scottaudio, Mar 3, 2008.

  1. scottaudio

    scottaudio Member

    Greetings-new to the forum.

    From research on the internet, it seems that the charging system on my 2006 XL1200C is capable of around 22 amps of current. I am curious if anyone knows the standard load on the bike (engine, on-board computer, lights, etc). This knowledge would reveal the "spare" capacity of the system to support additions to my bike.

    I searched the forum under the Sportster category, as well as electrical and did not find any postings with this information.

    Your help is greatly appreciated! Thanks!

    NOTE: I removed the "maxi fuse" and replaced it with my Fluke 87 set to measure DC amps, and found that when the bike is not running, but the ignition switch is on (all lights, etc) it measures around 8 amps draw. With the brake lights we have 10 amps, and with the turn signals around 11.7amps. With the engine running, I end up with about a 5 amp charge going to the battery. Has anyone else made these kind of measurements? Just curious if this is normal. Thanks!
    Last edited: Mar 4, 2008
  2. hjacobson1

    hjacobson1 Active Member

    I own a 2007 Nightster and while I don't have my owners manual with me (traveling for business)I can tell you that you can calculate within a few watts of the needs of your bike.

    Now, if you machine is capable of producing 22 Amps, it may be reasonable to assume that this opccurs @ 14.5 volts as this is generally the voltage needed to keep a 12 volt battery at a state of full charge.

    The law is that amps times volts equal wattage. So with the asumption of 14.5 volts times 22 amps - it is reasonable to assume that you have a total electrical system potential of 319 watts.

    With this knowledge, you can look at every light bulb and write down the wattage used, which is generally on the base of the bulb. If you have the owners manual, very often the manual will tell you the replacement bulb and their respective wattages.

    Add up all the wattages from the bulbs and subtract from your 319 potential watts and you will be left with some number. This number represents the number of watts left after subtracting the potential of all the bulbs on your bike.

    Remember to add both the high beam as wll as the low beam on the headlight as well as the tail lights.

    My guess is that you will not be left with many watts. If you look at the available accessory lighting in the official H-D accessory book, there are only a few choices for additional lights on a Sporty.

    If you need more power, you may be able to put an aftermarket charging system on in place of the stock unit, but beware, your bike may still be under warranty, and I would expect that increaseing the output of your alternator would most definately void the warranty.

    Now, if all you really wanted to know is whether the charging system is functioning correctly, take your meter and get a voltge reading accross the battery with the bike turned off, This should generally be 12+ volts, if it's less, you have a battery that needs to be load checked, which can be done at most auto parts stores.

    Now if your voltage accross the battery was ok, start the bike and let it idle, then check the voltage accross the battery terminals once again. At idle, you should get a voltage reading of more than 12 volts. Then with the bike still running, check the battery once again for voltage whilst increasing the RPM's of the motor, at a moderate throttle opening, you should get 14 - 14.5 volts. If under 14 volts, there may be a charging issue.

    Hope this helps.
  3. scottaudio

    scottaudio Member

    Thanks for the insights! You are right-I've got a good 14.5 volts on the battery with the engine running, so the charging circuit works well.

    I was looking at adding an intercom/CB radio to the bike for music and communications with the other riders on our weekend tours. I was just trying to be sure that the 22 amps was about right for the alternator. We really do not need heated grips or the like here in Nevada. I actually ride my bike to work around 300+ days a year here-one of the perks of the desert weather!

    I will perform the addition of all lights as suggested, but I know that doesn't take into account the trickle currents of the turn signal module and any other drains. I can imagine that the Sportster was never intended to be much of a touring bike, but mine stays the course with the big boys very well. With a windshield and the Sundowner seat, I'm comfortable for long distances. We pulled 326 miles a couple of weeks ago.

    Thank you again for your help! It is truly appreciated!

    Steve Scott