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366 Posts
Discussion Starter · #1 ·
On my ST2, I have upgraded the headlights to HID, installed an air horn and just bought heated gloves (should I feel its cold enough to need them). Last fall I pick up some LED running lights that I would like to install. My question revolves around the output of the charging system. How much can I add onto this bike before I overload the bikes ability to run and charge? If I feel I need the gloves plugged in, should I turn off the running lights? Or would (should - all thing operating correctly) there be plenty of power to run it all? Headlights and airhorn both run off of relays, so they pull power directly from the battery. I'll do the same with the running lights, too.

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1,028 Posts
The ST2 has a 420 W charging system.

Here's how the generator power output is intended to be used:
low beam (55 W)
high beam (55 W)
sidelight (5 W)
tail lights plus brake lights (21 W)
turn signal lights (10 W)
number plate light (5 W)
instrument cluster bulb (2 W)
warning light bulb (1.2 W)
fuel pump (clean filter) (60 W)
horn (60 W)
cooling fan (60 W)
electronic ignition (48 W)
computer (24 W)

If only the high beam or the low beam headlight is on at one time, the total of the above loads is 350 W. This is called the system design basis used to size the alternator. However, this is different from the normal operating conditions.

For example, a common operating condition for your model would be:
low beam on (55 W)
high beam off (0 W)
sidelight off (0 W)
tail lights plus brake lights on (21 W)
turn signal lights off (0 W)
number plate light on (5 W)
instrument cluster bulb on (2 W)
warning light bulb off (0 W)
fuel pump on (60 W)
horn off (0 W)
cooling fan on (60 W)
electronic ignition on (48 W)
computer on (24 W)

The total of the above loads for this operating condition is 275 W (although one owner (Stick) has posted that he measured the power draw during the normal running condition at about 200 W).

This leaves 145 W (420-275) available to run auxiliary equipment and to charge the battery.

· Registered
5,346 Posts
For a 2000 model you *might* have to get another flasher relay (I didn't on my 900SS until I changed the turnsignals), but change the combo brake/tail light bulb to LED. Since the stop light is occasional use, LED will keep the draw on the system way down when it is active. It's also a much brighter bulb.

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4,017 Posts
1997 (EU) and 1998 ST2 were the only years with a 420W single phase alternator. All the other DUCs around then had 350W.
Your 2000 has a 520W output. 520W / 13V = 40 Amps. It takes maybe 15 Amps to run the bike, 20 Amps on hi-beam on the older STs. You have a LOT of overhead.

I beat the crap outta my older ST2's electrical. I added two 55W running lights, heated grips (30W), heated jacket (140W (home-made!)), and heated gloves (30W). I was able to run all of this stuff simultaneously. I did it mainly in my driveway to see if/ when something would "pop". Never did.
Never had issues on the road, either.

So it's safe to say you can add a few items without issue. Plus, since you went to HIDs, you actually reduced your headdlights from 55W each to 35W each. You budgeted URself a little extra right there.

· Registered
366 Posts
Discussion Starter · #8 ·
Yeah, now I just have to add in an extra little fuse block due to all the wires coming off my battery! :D That's okay. I've got some extra room since I went with the Gel battery vs. the big lead acid one.
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