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"Es gibt geniales Zubehör (wie z.B. die Regler-Überwachung von Jörg {...}) und nicht-geniales Zubehör.
- Keks from www.africatwin.de
Introduction
This is a simple device that can be used to monitor the battery voltage in a motorcycle or in a car.
I developed this circuit since I encountered a number of charging system failures that occurred
without a "visible" warning.
Typically, most japanese motorcycles do not have any charge control lamp at all,
and on bikes equipped with such a lamp (Bosch system, e.g. BMW), defects may still occur in a
manner where the "idiot light" may not light up in due time.
The circuit presented here is a simple means to overcome this problem.
The device is used to monitor the battery voltage continuously: As long as this is around
13.6 V (plusminus about 0.8 V), the charging system is very probably working properly.
The circuit itself is of a rather minimalistic design, with only two LED to indicate
the actual voltage range. A red LED is used to signal a voltage that is too
low to charge the battery (usually a sign for alternator failure),
and a yellow one that indicates overvoltage (usually due to a defective
voltage regulator). Thus, it is more a "voltage indicator" than a "voltmeter".
Why only two LED? There are many circuits available that use e.g. three, five or more LED
to indicate the actual voltage. However, all I want to know is if the voltage at
the battery is in the right range to keep the charge up - if yes, I do not want
any control light shining at me: "No messages are good messages" ;-)
The particular design shown here has a number of advantages:
- The voltage display is instantaneous. It is faster than any conventional (analog or digital) instrument! This allows tracking e.g. short "dropouts" easily.
- The 2-LED display is simple to understand. In contrast to this, the display of any analog or digital voltmeter must be read,
understood and interpreted - which would take your mind off the road.
- It is small and rugged. The unit can fit virtually anywhere.
Design
When a (low) voltage is applied, LED D1 simply lights up as current flows
through it; R1 serves as current limiter.
If the voltage that is applied to the circuit reaches some 12 V, the Zener diode
will start to conduct. The current through the Zener diode causes a voltage drop
across R2 which will open T1, and in turn will "cut off" the voltage across LED D1.
At this point, no LED is lit ... which should be the standard condition with a healthy
charging system.
If the voltage increases further (above 14.6 V), the voltage drop across
R4 will be large enough to open T2, which makes LED D2 light up.
Most of the parts are not critical, with two exceptions:
(1) The value of the Zener diode determines the exact voltage limits.
I have come across Zener diodes with nominally 11 V that had only
10.3 V, so you may want to determine its real Zener voltage
before you actually use it.
(2) For T2, a higher β means an earlier onset for LED D2, so you
may need to change R4 slightly (e.g. use 1k5 for a BC547B, 1k2 for a BC547C).
Typically, with the values indicated in the circuit diagram above,
the red LED starts to fade around 12.1 V and is completely off at 12.6 V.
The yellow LED starts to glow at 14.6 V and is fully lit at 15.0 V.
- Note that R1 and R5 are dimensioned for the "old" 20-mA LED.
The device can be soldered onto a small piece of breadboard, or you
may use my PCB layout
(download as PostScript file).
The connections for the +12 V line and ground are directly soldered to the PCB.
On the prototype shown in the pictures I used a length of thin coaxial cable (RG158
or RG174) here, which IMHO looks nicer than two separate cables coming out of the
device; however, most people find it easier to use two-wire cable.
- For protection against vibrations, humidity, dust etc., I placed the PCB in a piece of
plastic tube and sealed it in epoxy resin, fitting an M6 bolt into one end.
Please note that this is an extremely simple set-up. There is
no protection against inverted polarity, and not even a fuse, so you
must connect it to a fused line.
Usage
Function test: When the ignition is switched on, the red LED lights up since the battery is not charged.
After starting the engine the red LED should go off slightly above idle. - There is no such test for the yellow LED.
Normal operation: In normal operation all LED are off. A dim "glow" of the two LED in the darkness
is normal on many Japanese motorcycles and is due to the particular voltage regulation that is used on these
bikes; their charging system creates a rapid sequence of over- and undervoltage spikes, which will cause the
two LEDs to light up dimly in rapid succession.
This phenomenon is not observed with a Bosch system.
Red LED: The red LED indicates that the voltage is too low to keep the battery charged.
With many motorcycles this is normal at idle (in particular BMW airheads, where the red LED
"pulses" due to the pulsating current drain of the ignition. The Bosch charging system starts to work
'reasonably' at about 1500/min.).
However, if the red LED lights up while driving this indicates potentially a defective alternator,
or at least excessive load on the charging system. In case of breakdown you may help yourself provisionally
by switching off all electrical consumers and carefully riding to the next workshop on battery power.
Yellow LED: The yellow LED indicates that the voltage in the electrical system is too high.
In most cases this is due to a defective alternator voltage regulator, or a defective connection
leading to it (hint: ground wire on Bosch systems, connector under the left side cover on Honda Africa Twin).
In this case, the electrical and electronic components of the electrical system are in danger since
the voltage can exceed 40 V: Do not ride the bike in this condition!
In case of breakdown you may help yourself provisionally by disconnecting the voltage regulator
and/or the voltage regulator and carefully riding to the next workshop on battery power.
What else?
Since I keep getting requests about these units, I keep producing them from time to time
and in the different versions shown above. As of fall 2009, over 220 units have been sold
to motorcyclists all around the world!
If you are interested in buying one (or "some" ;-), simply use this page.
This information is provided in the spirit of "open design". The concept is
similar to that of open source software: It is available in "source form". Here,
this means that I am making the design information freely available, and you
may use this information to build your own systems for personal use, free of
charge. However, if you wish to develop some commercial product ("make money with it")
based on the information provided here, I require that you seek a license from me first.
The usual disclaimer: These are things that I did myself on my own
motorcycles. Most of it should also be applicable for other models, but
you do it on your own risk.
