Technical Information Pages for the Restoration of the heavy military bikes BMW R75 and Zündapp KS 750.
Monthly available on our website.
H - P Hommes
© 2013 h-p hommes
Problems with the Generator?
The generator brings
When I accelerate, the light becomes brighter.
But when I drive for a certain time, then the battery is empty!
When I ride without light I have a full battery.
Where is the mistake?
When battery, generator and the power plant
are in order, then this may be due to a too high power consumption, when the
light is switched on.
The generator brings a maximum output of 50/70 watts.
When I assume that the battery is fully
charged at 8 amps, a longer trip with light should be possible without problems.
Since the 50 watts are only generated at a
certain speed, it may be that the battery is empty after some driving time in
spite of a working generator.
The reason for this is mostly the use of bulb with too high a voltage.
Correct items are.
Headlight 25/25 watt bulb
Parking light 1,5 watt (This light was not turned on during normal driving like today)
Rear light 3,0 watt
Sidecar light 1,5 watt
Sidecar rear light 1,5 watt
So electricity consumers with 25+3+1,5+1,5 = 31 watt are connected.
Today consumers are often increased in the wattage:
The head light has a 35/35 watts, the rear light has 5 watts or even 10 and as for parking lights three 2 watts bulbs are used.
This results in at least 46 watts. This
means that the generator always has to bring full power, just to operate the
When the generator brings less at a low engine speed, the battery must supply the missing power.
But the battery gets almost no charge current and is slowly sucked empty.
With the correct light bulbs a normal driving is possible and a 25-watt bulb with a good reflector also brings sufficient good light.
It is also important that the governor is set correctly
Electronic governors without adjustability always bring too little power.
This permanently dim light of the headlights indicate this.
Adjustable governor you can get in our shop order no. 3170
The information that I found always says
more or less, that this battery is not suitable for our bike because the
charging by the generator destroys the battery within a short time.
Unless, the battery is not charged by the generator but externally by a suitable charger.
On this subject I found the following article:
The gel battery is sensitive to excessive charging voltages.
Therefore, a battery charger which operates with constant current or constant
power charging, can drive the voltage too high to adjust the current. This is
not good for the gel battery. Usually it is not clearly visible if the charger
drives the voltage too high or not . Therefore you should make sure that the
charger contains a reference "also suitable for gel batteries". These chargers
will limit the charging voltage or work with a charging curve which does not
raise too high a voltage. The gel battery should not produce gas as there is
actually no refilling possibility. If, however, the charging voltage is too high
the gel reacts and will cause a damage to the battery.
For lead-acid batteries or NC battery a too high charge voltage is also not optimal but can be compensated by refilling water.
A car charger is just like charging by generator usually
unsuitable for the gel battery because the currents of these devices are too
Too high currents heat the battery. This changes the end-of-charge voltage.
It makes sense to use gel batteries as stationary batteries which are provided with a suitable charger via the power grid.
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