Triumphrat

CNYMike · 07-31-2009, 04:10 PM

It is a 73 T100R. I rode it last night for about 100 mile at the end of the trip the battery was almost dead. I charged it up last night, and started checking it out today. At idle with the headlight off it is around 12.5v measured with a meter at the battery terminals. As soon as I rev it up it gets 13-14 volts. Then if I try it with the headlight on it stays at around 12.5v. Voltage dosent go up with RPM's when the head light is on. The bike is new to me so I cant say for sure it has ever really charged the way it is supposed to. I moved the location of the RR and it is firmly attached to the frame and has good conections. Could I have messed it up?? Also on a side note the speedo is fast by about 20 miles an hr or so. I havent looked into it yet. I am assuming there is no adjustment for it that is runs off of a gear. Is there any thing I should look into first to try and fix it.
Thanks.

DerryUK · 07-31-2009, 05:26 PM

well you are down on volts from the charging system.

You say you have a RR and I would suspect that.

A quick test to make sure it's not the alternator is to disconnect it (two wires coming out of the LH primary chain case) switch your meter to AC and connect the meter leads onto the alternator wires.

Start your bike and at around 3000rpm you should see around 32 volts AC on your meter. If you do then your alternator is OK and it's the RR that is broken.

As always though it is worth checking all the wiring connections between alternator, RR and battery.

Let us know how it goes.

CNYMike · 07-31-2009, 06:57 PM

Just went out and checked. It only got up to about 22 volts. I have an extra alternator, but I pulled the wires out of it. So that would be why I bought a used one and put it. Thanks for the help. I will take a look into it this weekend.

DerryUK · 08-01-2009, 10:15 AM

Interesting result Mike. There are a couple of things you can do if you have the time or inclination.

The standard Triumph/Lucas method of testing alternators is to put a 1 ohm load between the alternator output leads and measure the voltage across that. In the case of my alternator quoted above I measured 10.5 volts AC across a 1 ohm load which using Ohms law means that 10.5 amps was flowing through the resistor.

Now that is 110.25 watts which equates quite nicely to a 120 watt alternator.

You could also measure the alternator resistance which in my case measured 0.41 ohms. Now the tricky thing here is measuring low value resistances with a multimeter as the resistance of the leads gets in the way.

The preferred way, which is what I did, is to use the four-wire method of measuring resistances. This requires the use of two multimeters though hence the term four-wire.

thirdbike · 08-01-2009, 11:42 PM

hey DerryUk, Would you care to enlighten us non-electricians on the four wire method? At this point I don't even know why this method is better.
Thanks

DerryUK · 08-02-2009, 12:09 PM

This site gives a reasonable explanation of it.

http://www.allaboutcircuits.com/vol_6/chpt_3/14.html

A couple of points to note. Don't use this method on the bike as you stand a good chance of demagnetising your rotor if only partially! To be safe you really have to remove the stator and do it on the bench.

Also using your battery to test your alternator is not a good idea as large currents will flow. You could use a variable resistor (something around the 12 ohm mark assuming a 12v battery) to reduce the current.

I have a variable power supply at home and used that instead. All I did was adjust the power supply voltage until 1 amp was shown on the meter. At this current the voltage shown on the other meter then equals the stator resistance (R=V/I).

Derry.