Series II Charging System Questions

[LarryN]

Thinking my battery was dying, I recently took my Alpine to the shop where the battery tested fine, but the generator and voltage regulator looked weak. I elected not to replace anything right away and started poking around in the electrical system. I wound up re-wiring the high-current circuits and repairing several very old splices where the two wires were simply twisted together - neatly done and carefully hidden under about a mile of electrical tape, but very dirty and loose. OK - so now the car has #10 wires from the generator to the regulator and to/from the ammeter and the ammeter is telling a whole different story.

Using the shop manual and a digital voltmeter, I tested the generator (open-circuit voltage rise OK) and the regulator (open-circuit voltage around 13.5v, cut-out voltages looked OK). I adjusted the regulator to 16.3v open-circuit (wires disconnected from terminals A and A1 and tied together). Everything seems to be working fine - the ammeter reading spikes to ~25a for about 15 sec after starting, drops to 15a or so for a few minutes and then steadies at about 5a steady-state and eventually drops to zero. I then connected my voltmeter to the cigar lighter and monitored voltages - charging voltages were around 13.8v at the 15 amp charging rate, 14.5 v or so during the 5 amp charge, and 16.3v at zero (The cigar lighter is tied to regulator terminal A through the common point on the starter solenoid and the ammeter). The load side of the circuit (Terminal A1 which is tied to all other loads through the ignition switch) looks pretty much the same.

Based on the write-up in the manual and the circuit diagram, this sounds like what should be happening BUT the idea of running the electrical system at 16.3v just seems wrong! Even though the current into the battery is zero, 16.3v just seems too high. Even though the voltage drops immediately when load is applied (headlights, etc.), 16.3v open circuit seems high. So, the reality check is : what should I expect to see in the way of voltages and currents in the charging circuit? (Ambient temperature here in Northern California is actually approaching the nominal 68F, so temperature correction isn't a big factor (don't ask me about July and August when the temperatures can bump up around 105F - I'll deal with that when the time comes!).

Thanks
Larry

 

[bobw]

Hi Larry,

I'm not quite sure I fully understand your situation, because if you put 16.3V across a 12 V battery, the current will not be zero. The 16.3V zero current as listed in the workshop manual is open circuit only which means the generator is disconnected from the battery. From your description, it sounds like you are seeing 16.3V with everything connected which is what's causing my confusion. If it's truly the open circuit voltage, then I think everything is OK.

In the wiring diagram I have, the regulator A terminal is connected to the ammeter which is connected to the starter, then to the battery - terminal. The regulator A terminal also has a wire to A1 on the fuse block. The cigar lighter is connected to A2 on the fuse block (A1 through the fuse). That really shouldn't affect the voltage readings much. Cleaning up the wiring was a very good thing though.

Bob W.

 

[LarryN]

Bob:

Thanks for the quick response. The voltage setting for the regulator is made with the load off the regulator (the battery and ignition are lifted from the A and A1 regulator terminals and tied together to power the ignition circuit). The only electrical path out of the regulator then is through the ignition warning light (tied electrically to Terminal D which in turn is tied to the generator output) to the ignition switch and on to the coil - theoretically, this is nulled and should have no current flow once the engine starts.

So far, so good - and, as you note, the confusion arises when everything is re-connected. 16.3v across a 12v battery should be causing a measurable current flow - and I'm not seeing anything on the ammeter. The answer may lie in the generator field current - which is reduced as the load on the system drops. The voltage can be high (16.3v) but the generator is limited in how much current it can produce. I suppose it then depends on the relative impedances of the battery and the ignition circuit - my guess is that the battery looks like a significantly higher impedance than the ignition and therefore draws only a trickle current. I probably should have paid more attention in those electrical engineering classes years ago, but what do you expect from a mechanical engineer?

 

[RootesRacer]

The battery is going to be a much greater load to the regulator and generator than any normal electrical load since its virtually a short circuit to any voltage above the charging voltage of the battery.

The regulator has a built in current limiter, which magnetically drops the voltage regulator output as the current gets too high.

There are 3 specific adjustments to the regulator (charge voltage, Cut in voltage and current limit). In my experience these items really need to be adjusted when connected to a battery since the mechanical gain of the controls is not ideal nor optimized in an unloaded manner.

 

[LarryN]

The later 3-spool regulator does have an adjustment for current limiting. The earlier 2-spool regulator allows adjustments only to the open-circuit voltage and the cut-out voltage. Current limiting in the earlier design appears to rely on balancing the magnetic forces on the armature generated by the field current flowing in one coil and the load current (combined battery charging and circuit load) in the other coil - all neatly complicated by the armature switching a resistor in and out of the field circuit.

I think I may have found the answer in the link below:

http://www.scubaengineer.com/documents/lead_acid_battery_charging_graphs.pdf

This reference shows the charging and discharging voltages vs state of charge at various current draws (stated as fraction of battery capacity) and shows the charge voltage for a battery at 100% charge to be 16.0v for a charge rate of 20% (C/5) of the battery capacity. In my case, the battery is about 50 amp-hrs, so C/5 = 10 amps. I'm seeing currents below 2.5amp, so the system is charging at something like C/40 and I would expect to see voltages slightly higher than the 16.0v. I'm actually seeing the 16.3v limit voltage, so the system appears to be operating as designed.

Thanks to those of you who helped with this question - I appreciate the feedback.

 

[RootesRacer]

The later 3-spool regulator does have an adjustment for current limiting. The earlier 2-spool regulator allows adjustments only to the open-circuit voltage and the cut-out voltage. Current limiting in the earlier design appears to rely on balancing the magnetic forces on the armature generated by the field current flowing in one coil and the load current (combined battery charging and circuit load) in the other coil - all neatly complicated by the armature switching a resistor in and out of the field circuit.

The later regulator may not have a cam adjustment, but the main regulator bobbin field is modified by the current exiting the A and A1 terminals.

As a result of this, the current limit is also impacted by the main regulator voltage setup.

The new japanese regulators available for the generator alpines unfortunately do not have the nice cam adjustment setup, and as a result you have to bend metal spring stops to adjust the voltage output and charging cut it.
It took me a rather long time to get it all adjusted right as it was not even close out of the box.