----- Original Message -----
From: "Brown, Herb" <BRown@ida.org>
To: "Military Vehicles Mailing List" <mil-veh@mil-veh.org>
Sent: Wednesday, October 04, 2000 2:55 PM
Subject: [MV] Voltage Regulators
> Anyone out there familiar with old voltage regulators and able to describe
> their operation on a 1945 MB?
>
Old regulators possibly, 1945MB not really, but a regulator is a regulator.
> What I have concluded so far follows: I have 3 solenoids (voltage
> regulator, current regulator, and cut-out) inside the regulator system.
>
Yup.
> The
> voltage regulator is normally closed, and opens the generator field
circuit
> when voltage exceeds some threshold (probably 8 volts).
>
Yup, but, the current regulator is also closed and the two sets of contacts
are essentially in series. The field is not completely opened but a high
wattage wire-wound resistor is placed in series with the field when either
contact opens to drastically reduce the generator (dynamo) output.
> The winding for the
> voltage regulator coil comes from the generator armature and goes to
ground.
> It appears that the other side of the voltage regulator points connects to
> the points of the current regulator solenoid.
>
Yup. So the voltage regulator is set, often by an involute cam on the
armature spring blade, to just open when the generator voltage reaches a
prescribed average maximum.
> At this stage my knowledge of the circuitry breaks down for both the
current
> regulator and the cut-out. I am getting continuity to ground just about
> everywhere, even when I open up the points. Can this be caused by the 8
> volt pass condensers?
>
Unlike the voltage regulator bobbin being wound with probably a thousand
turns or so of fine enamelled wire, the current regulator is wound with only
some 5 or so turns of very heavy wire about 10 AWG or 12 SWG. This winding
is in series with the generator output and when the current flow is
sufficiently high the produced field pulls the associated contacts open
putting the field resistor in circuit again.
It is possible but unlikely the suppression condensers (capacitors) have
gone short, most likely, as you are dealing with very low ohmic values, you
cannot read them on your meter, especially if the generator is connected as
its windings will be probably well under 1 ohm.
>
> Due to these continuity readings, I am having difficulty following the
> circuit path. For example, it is not clear to me where the other end of
the
> current regulator points connect with the wiring to the generator
armature.
> It is my perception that the current (out of the regulator system) drops
as
> the battery gets fully charged; however, it is not clear to me how this
> arrangement actually regulates the current.
>
All the devices are only relays but wound and connected in such a way as to
operate on specific voltages or currents through their windings.
The cut-out simply disconnects the generator from the battery when the
generator output falls below that of the battery, at low revs or stationary,
as the battery would try to discharge heavily through the generator trying
to drive it as a motor.
The voltage regulator and current regulator operate under different
conditions. The voltage regulator will operate alone when the battery is
lightly loaded and fully charged to limit the generator voltage to that of a
fully charged and charging battery. With no control the generator voltage
keeps rising with revs to many times that of the maximum battery voltage,
and would ultimately boil or explode it.
The current regulator will operate when the battery is not well charged
and/or the main lights are on making a heavy current demand, it limits the
current supplied by the generator to a safe level, independently of voltage
and protects the generator from burning itself out through a serious
overload demand.
Both regulators will oscillate rapidly when operating as they effectively
pulse the generator by alternately connecting the field full on (too much)
to almost off (not enough), you will note the needle of the typical dash
ammeter is noticeably vibrating when the regulators operate, they are not
linear devices but make an average by the alternate all or nothing method.
This causes some sparking at their contacts so the capacitors are fitted to
both to minimise contact arcing and to reduce the RF interference hash so
generated.
Some very early UK regulators only had two devices, the cut-out bobbin and a
combined voltage/current bobbin where the few turns of huge current sensing
wire were wound over the fine turns of the voltage sense coil so either
would operate the contacts, this does not allow accurate control and was
largely superseded by the onset of WWII.
> Finally, once I hook up everything, what are the specifications I should
be
> looking for to verify that the system is working properly, or that I have
a
> problem?
>
Using the meter see that the battery gets to 14.2V - 14.5V (7.1V - 7.25V for
a 6V system) absolute max with a fully charged battery and the engine
turning at a good speed for charging, typically 2000 rpm will do.
With the installed ammeter or a suitable one hooked in with heavy wire, let
the battery discharge a fair bit with the engine at idle, say main lights on
and brake lights too, then turn the lights off and rev the engine, the
ammeter should indicate x amps which should be the same as the dynamo
maximum output spec. It will fall back as the battery charges so you have
to be reasonably on the ball, its a crude check but without some very
special, very high load, variable resistors its all you can do.
I have no idea what the MB generator is specified at for maximum current but
as a 6V light vehicle I would expect around 15A max. typically.
Richard
Southampton - England
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