|I=E/R|| Not just a good idea;
it's The Law. - Ohm's Law
Keeping this in mind, if we're having trouble with dead or dying batteries, we must determine whether our charging system is applying enough E - charging voltage - to the R - the resistance of the system, - ignition, lights, line resistances, and battery, to force enough charging current (amps) - I - into the battery.
We do this by using a Voltmeter - many of the more enlightened heh heh) vehicles have a voltmeter on the panel, since in many cases it's the most important thing to know about. If you're not so lucky, you can check your charging voltage in the driveway by connecting a voltmeter on the 0-15V DC scale to your battery. It should read just over 12V with bike not running. When you start the bike, the reading should increase, ideally to 13.8V. In the real bike world, we often have to settle for anything approaching 13 - my '69 Triumph goes about 13, and has never let me down for charging. I use a halogen headlight, but for daytime running only a white truck clearance light under the regular headlight.)
If you're not getting at least 13, you'll have to get in there and twiddle wires. Here's how:
__________ + OUT TO VR | / \ / \ AC IN ______ / \ _______ AC IN \ / \ / \ / |___________ - OUT TO VR
|The way a bridge rectifier is wired - this is the kind in cases of two wires exiting the alternator. This may only be the first stage of an integrated rectifier/regulator unit.|
Less than 20V AC? Click Here
If you're getting >20VAC from the alternator, since 20 X .6 = 12, you should have _some_ charging ability. More than that means a greater capability for your system. Now let's check the DC output from the rectifier.
In the case of the 3-wire alternator, you want to see the same voltage from all 3 possible combinations of output wires. It could be quite high - my SR500 amazed me with open voltages of over 90 VAC! If all three voltages are about equal, reconnect the alternator output wires and do a voltage check at the output of the regulator/rectifier unit. If this closed voltage is less than 12.5VDC, try replacing the unit - the following procedures don't apply to 3-phase/3-wire alternators.(It is of course possible to homebrew a 6-diode rectifier for the 3 phase alternator (see your shop manual), but the off-the-shelf "quick fix" as with the RS Bridge Rectifier isn't there. Am I wrong? Click here to tell me!
This PDC is of a lower voltage than the AC input, and will vary, as will the AC, with engine speed. If the output voltage is lower than that of the battery, the rectifier, because of its "one-way" diodes, will not pass current from the battery to the alternator. If the output voltage is higher than that of the battery, current will pass from the rectifier into the electrical system and battery.
Connect the input wires again (no polarity consideration, since this is AC) and disconnect the rectifier output line. Change your voltmeter to the 0-15V DC scale, and measure the output voltage with motor running at ~1000 rpm.
The DC Voltage will be less than the AC input. But if it's much less than .606 of the AC, then the rectifier needs replacement. Put in practical terms, if you had an AC output greater than 20VAC, but your DC output is less than 12.5, your only hope is to try a new rectifier and/or regulator.
But in either case, you can test your system's ability to make DC output by an inexpensive substitution. They are available, at least on North America, from Radio Shack (TM). All you need is a 4-diode Bridge Rectifier, with a peak voltage rating of 20V and current rating of 10 Amps or more. Your local Radio Shack (TM) has them for less than 5 bucks. (Your location may vary; don't know that they have Radio Shacks, or even bucks, in Karachi or Adelaide, but you get the picture. Any electronic supply store will have something of the sort.)
Connect the AC input wires from the alternator to the terminals marked AC - one to each; no polarity considerations with AC. Start the motor and measure the DC output at the DC terminals, marked + and - on the rectifier. If you get a healthy "open" reading, - over 13VDC, then you can connect the + and - wires to your system - watch the polarity - and check again for a "closed" reading. If your "closed" reading exceeds 13.8VDC, you'll need a Voltage Regulator as well.
This is not said to be funny. In the case of marginal alternator output, you may not have enough excess voltage to require a VR, yet stil have the snoose to keep your lights and ignition working. Especially if you "fudge" a bit on the lights - if you have the output, keeping the lights on may be required to avoid overcharging the battery, but if you don't, you may find that your system will stay above 12.5 VDC with them off, but not with them on.
If you can't get a reasonable system-under-load reading with the lights on, try disconnecting the headlight. If this gets you to a decent charging voltage ( >12.5 ), then the 'lectric goblins are telling you that you don't get to run a headlight full time. (They especially dislike halogens) You can beat this one by installing a law-enforcement-friendly alternative lamp close to the headlight. I've been using "bullet-type" truck clearance lamps, mounted under the regular headlight for years. They have a magnifier in the tip you can point at oncoming traffic, and since I've been using them, have never had a minion do a 180 and make it necessary to give him sob story 3B: Lucas, Prince of Daylight Darkness. And, if you're worried about the safety factor, ie the less bright light failing to deter cage pilots from murder by bumper or door, forget it; you're no less invisible either way; disregard this at your peril.
In most cases, however, your system will be healthy enough to require a VR. If this only applies with your "new" bridge rectifier, then it's choice time. You'll have to find a series or parallel type VR. The only one of which I am aware is the stock Zener diode, supplied through the various manufacturers by Lucas. I'm not presently aware of a part no. or source for a 13.8 VDC series regulator of 10A or greater capacity - I'd appreciate hearing from anyone who's found one. click here to email me
Or you may elect to pop for a "Tympanium" unit. This is an aftermarket integrated unit, using modern solid-state electronics all the way, and works great. I use them myself, Luddite that I am. But I don't in cases in which the alternator output is marginal, since in these cases a regulator isn't even necessary - the question becomes one of whether or not to use the full headlight to keep the charging voltage within reasonable limits, and an RS rectifier is all that's required. Be sure to "heat sink" your new VR when you mount it permanently, since it does its work by converting some of that AC to heat which must be dissipated. (Hmmmmm - how about an electric vest rectifier? Electronic whizzes, take note)
Next, check the system voltage at the battery. If there's any difference between battery terminals and Rectifier output, jump the + and - leads from VR to battery with good quality #16 copper stranded automotive wire. Use appropriate colours - red for + and black for - and be sure to fuse the battery ground.
That's all there is to it! Hope it helped. Lemme know.