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Fear of the Dark, Part 2:
Electronic Voltage Regulator
Cameron Lovre

As anyone who's ever tried to do anything useful can attest, there's often more to the task at hand than one might initially expect. And as you may or may not remember from an earlier article, we've been experimenting with some new-to-us lighting equipment. This started with upgrading the headlights and then progressed to the installation of one fog and one driving light (Cibié "Tango") on a Volvo 122.

To get an idea of what these lights could do, we ran one (the fog) and then the other (the driving) over several days (nights, actually) and learned that (as usual) this project would not be without some glitches.

The first problem was that the lights consumed more power than the original generator could supply. No big deal; we installed a 55 amp Bosch alternator and matching voltage regulator. This nicely kept the battery from going dead, but immediately led to the new problem: Blown Bulbs. After several E-mails back and forth with people who know this lighting stuff better than I do, it was decided that though the amperage supplied to/consumed by the aux lights was correct, the voltage was not adequately limited by the Bosch Voltage Regulator.

The problem we had was that immediately after starting the car the alternator/voltage regulator end of things was recharging the battery at voltage high enough that the bulbs in the aux lights would promptly blow. (This phenomenon, I'm told, is a Voltage Spike -- something I hadn't really thought of, but which made sense when someone else explained it.) So we grabbed the Voltmeter and checked; it indicated a peak of roughly 14.9 volts after startup, gradually decreasing to what we'll call the "engine running average" of 13.5 volts.

Of course, starting the engine -- especially in the cold weather -- drains some juice from the battery. Then, the alternator and voltage regulator recharge the battery during the first several minutes of running; thus the higher voltage shortly after startup. Simple enough.

The confusing part (for me) was that all of the fuses had remained intact. The master fuse in line between the battery + terminal and the relays hadn't blown, nor had either of the inline fuses between the relays and each of the lamps. This reinforced the Voltage Spike Theory. Too many amps, not volts, would have blown the fuses. Too many volts allow the bulbs to sacrifice themselves and save the (much cheaper) fuses. Hmmmm.

Before learning the Voltage Spike Theory, though, I began by installing and blowing all six of my spare bulbs. Just wanted to be sure something really was going wrong -- and it's very entertaining at $6+ each. After this exercise, I was presented with three possible solutions:

1) Avoid turning on the aux lights until the voltage has stablized at a level low enough to avoid ruining bulbs (likely 5 to 10 minutes after starting the engine). This idea had no appeal.

2) Install something called a Zener Diode between the + terminal on the alternator and ground (this would act as a voltage "dump") to limit the maximum available voltage effectively supplied by the alternator.

3) Install an adjustable voltage regulator.

Of these, I chose Option #3 because it was the most reasonable approach overall: a simple replacement exercise has more appeal than adding more components. OJ Rallye carries an adjustable regulator that easily accepts the OE wiring terminal end and has the same spacing between the mounting holes as the OE Bosch unit. The difference size-wise is that the new unit is much shorter overall than the old Bosch unit. Installation was a simple remove-and-replace procedure followed by about 90 seconds spent adjusting the voltage output of the new regulator.

The regulator offers a small screw on its underside for adjustment: turning the screw clockwise increases the available voltage. We had previously noted that the bulbs didn't blow when the charging system was operating at or below 14.2 volts. Opting to err on the side of caution, we adjusted the new unit to allow a maximum of 13.8 volts.

The result has been excellent for two reasons: 1) we can turn on the aux lights immediately after startup and the bulbs don't blow, and 2) regardless of what electrical loads we place on the charging system as a whole, the operating voltage remains rock steady. This stablization is the most reassuring aspect of the swap -- the system voltage tops out at the predetermined setting, regardless of what the electrical load is. We're getting 13.8 volts, period. This should prevent any more problems associated with Voltage Spikes.

So if your relic Volvo has been fitted with lighting equipment or other electricity consuming doodads, the first thing to do is upgrade to an alternator. If you choose a Bosch (which I think is the best one, for whatever that's worth), opting for the adjustable VR will allow you to control the maximum voltage within the charging system as a whole and will offer protection for the more sensitive electrical gadgets.

(Thanks to OJ Rallye, Daniel Stern and Phil Singher for thoughts about electricity and how to reason with it. Thanks to OJ Rallye for the dandy new VR!)

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