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Cossack Owners Club |
Written by: Peter Ballard
(As fitted to Ural M61, M62, M63 and M66, Dnieper K750,
MB650, MB750, K650, MT9, MT12)
The Г414 dynamo is designed to operate at 6.5 volts at a
maximum output of 10 amps, thus at a maximum power output of 65 watts (6.5 volts
x 10 amps). Generally it is not advisable to operate such devices continuously
at more than 80% of the maximum output, thus only 52 watts is practically
available. Thus by the time the headlamp and side lamps are on there is no
surplus capacity for any other electrical consumers such as a bright sidecar
lamp, heated handle bar grips etc. The results of overloading are either a
burnt-out armature or a ‘flung’ commutator where the lead solder has overheated
and melted. The field windings however seem to be far more durable being closer
to the cooling air flow over the dynamo casing.
The heat produced by a resistor such as the armature or the
field windings is equal to the square of the current multiplied by the
resistance. Thus it is independent of the voltage! Thus it is possible to run
the dynamo at a higher voltage to increase the power output without necessarily
overloading the armature or commutator. If the dynamo is run at twice the
voltage then the dynamo will produce around twice the power. The downside to
this is that the field windings have to be loaded more. They must now carry more
current for more of the time to excite the armature more to produce the higher
regulated voltage. With the standard electro/mechanical regulator the voltage
from the dynamo output is controlled by switching the field windings on and off
many times a minute. To increase the controlled voltage output the field
windings have to switched on for longer than they were with the lower voltage.
This can be done very efficiently with an electronic regulator that can be
reliable and also absorb less power.
There are many alternators fitted to cars that run at a nominal 12 volts controlled by cheap, reliable, compact and fully encapsulated electronic regulators. These typically run at 14.2 volts. These regulators will easily and safely control the Г414 dynamos at 14.2 volts.
Part Needed – Lucas UCB 100 37672/37647 or equivalent.
At this doubled voltage, the armature and the commutator will
tend to see half the current than before, for the same power output with the
once vulnerable parts of the dynamo having an easier life. So it will now be
possible to run at around 80 to 100 watts continuously with generally less load
on the armature and commutator than before at around 50 watts! The field
windings will run hotter, but are well exposed to the air flow; there is no
evidence of them failing under this increased loading and in any case sadly
there are many unserviceable dynamos around with destroyed armatures and
commutators due to ill advised overloading whilst in standard form, but with
good field windings.
To carry out this conversion, there is no rewiring required
to any of the wiring loom. The rewiring is restricted to the regulator box. The
old 6 volt components on the motorcycle will need replacing; battery, bulbs,
ignition coil, direction indicator flasher unit and maybe the horn but this will
survive at 12 volts. Even ballast resistor can be used with the same
resistance as the original coil to limit the voltage to the coil.
Below there is a circuit diagram and a photograph of the
installation of the new parts in the standard regulator box. The installation is
quite straight forward.
On starting the engine the dynamo will no come on line until
around 2500 rpm or so. After coming on line it will regulate as normal, that is
the red dynamo failure warning lamp will work as it should. The reason for this
is that the dynamo field windings get no voltage supply when you turn the
ignition on, thus the armature will only develop voltage from the residual
magnetism in the field core. The armature thus needs to spin fast to achieve 14
volts at which point the regulator supplies and controls current to the armature
to maintain 14.2 volts. A different regulator and more complex wiring and
‘ignition’ switch can be used to achieve a more conventional dynamo ‘start-up’
mode, but on balance this has not been seen as necessary.
NB
1. As before it is essential that all connections are good
and tight, all earth connections are also good and the battery is in good
condition.
2. Do not be tempted to use a big car battery in the sidecar.
A big battery that has gone flat will demand very high current to recharge,
often a current higher than is safe for the dynamo to operate at. Even at 12
volts, the dynamo will be overheating if you try to draw over 10 amps from it
for more than a few minutes.
I have been running these dynamos at 12 volts with 100%
reliability since 1986 with this system.
3. Check out your dynamo, clean the commutator with fine
glass paper and rinse well with spirit, check the current drawn when run as a
motor at 6.5 volts (manual quotes 6.0 amps maximum).