Ohm's Law

**Guba** · 07-14-2010, 02:56 AM

I thought this would be of some interest to those wishing to make some electrical mods.

Alternator:
The Rebel has a small alternator, only a 190 watt output at 5,000 RPM. Those 190 watts get used up with little margin for extra accessories. If you add up all the wattage being used on the bike, it looks like the 190 watt alternator can handle it with plenty to spare. Wrong! At idle the alternator won't even charge the battery, at least on the 2001's and later models. It's nice to add extra accessories and make your bike "your own", but sitting at stop light and revving the engine to 5,000 RPMs just to keep the battery on the + side might make you look a little...eccentric.

Battery:
12volt-6amp hour. Don't for one minute think that the battery will last for 6 hours with normal use! 6 amp hours only last's for 2 if your pulling 3 amps an hour. It's also not a deep cycling battery and may be damaged if it goes below 80% of it's charged voltage.

Regulator/rectifier:
All Rebels from '85-2000 years have a 13.5-14volt output at 5,000 RPM regulator. If you have a 2001 or later year, you can expect 14.6-15.6volts at 5,000 RPMs.

Thanks oneway, you just saved me a lot of typing!

The pie charts in the post below are pretty easy to use if you know how to plug in the numbers.

Example: How many amps does a 35 watt head light use? Since amps refers to current, we use the formula I=P/V. I= 35watts(power) divided by 12.5 volts
I= 2.8

Provided your voltage regulator is working properly, the voltage will always be a known constant. I hope this isn't sounding like math class! lol

Example: Using an ohm meter one grip heater measures out at 6.9 ohms. But we want to know how many amps that is, after all we don't like to blow any fuses. Since we are solving for current again and know our resistance (ohms), we can use the formula I=V/R. I=14.3 volts (my '07)/ 6.9 ohms I=2.07 amps

**oneway** · 07-14-2010, 07:40 AM

Here is the triangle and the chart you can use for the formula's.
The triangle E over I R (E / I or R, I x R) can also be used as P over I E (P / I or E, I x E).
I find the triangle easier to remember than the full chart.

**rebel_rider** · 10-01-2010, 02:24 PM

Thanks for the info bro' this is very useful for me...

**vanringo** · 10-01-2010, 10:22 PM

Wow, I just want my bike to work so I can ride to and from work, and if I am lucky the occasional fun ride. That is way too much thinking for me. I cheated my way through college algebra thanks to my wife being in the same class as me. But even though I would never do the math to add something to my bike, thanks for the info. If I ever do decide, I will have my wife do the figures.

**88nightrider** · 10-09-2010, 08:45 AM

Quote:

Originally Posted by vanringo

That is way too much thinking for me

If you think those calculations is hard to do, you should try calculating capasitors or voltage drop in the cables

Even that isnt so hard

Edit: Good and informative for those who dont have so good an understanding about electrisity

**Funkbuqet** · 10-09-2010, 04:00 PM

Oneway, I noticed an error in the pie chart, the 2 and 8 o'clock slots should be I = sqrt (P / R) and V = sqrt (P x R) respectively. I'll see if I can find a graphic for it.

Found One:

**88nightrider** · 10-09-2010, 04:34 PM

Here is an online calculator

Doncaster Cables - Cable Size Calculator

**vanringo** · 10-09-2010, 07:27 PM

Quote:

Originally Posted by 88nightrider

If you think those calculations is hard to do, you should try calculating capasitors or voltage drop in the cables

Even that isnt so hard

Edit: Good and informative for those who dont have so good an understanding about electrisity

It isn't that I can't do the math, I just hate math. There is a reason I did not become an electrical engineer like my uncle wanted me to. I prefered marine biology, but couldn't afford the school that I wanted to go to and so that went out the window. I now work IT currently for Honda Manufacturing of Alabama and hope to soon be working for University of Alabama-Birmingham at their hospital system.

**oneway** · 10-09-2010, 10:30 PM

Quote:

Originally Posted by Funkbuqet

Oneway, I noticed an error in the pie chart, the 2 and 8 o'clock slots should be I = sqrt (P / R) and V = sqrt (P x R) respectively. I'll see if I can find a graphic for it.

Found One:

I always use the smaller chart. I pulled the bigger one off the net and didnt check it for accuracy. I will check it with my electronics books.

**osteve** · 10-09-2010, 10:41 PM

If I was to install additional lights, and other gadgets, ipod, and so on. What would I need? A bigger and more powerful battery?

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