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  Inside Bonanza & Baron Voltage Regulators





Do you have one of the above voltage regulators that has ceased to be a regulator? If so, and you're the curious type, you're sure to appreciate this outstanding piece of circuitry teardown and analysis by Baron 58 owner Derek dB.



Click HERE to get his PDF narrative.




Here is more voltage regulator schooling from Derek as posted on Beech Talk HERE:


Your vintage Baron has two regulators-- one is in use and the other is a backup. The one regulator in use simultaneously supplies the field current to both alternators. The field current creates a magnetic field inside the alternator which is used to generate output current. The higher the field current, the stronger the magnetic field and the greater the output of the alternator. The job of the voltage regulator is to adjust the field current so the alternator output is at a constant voltage (nominally 28.25V). If more output current is being consumed than is being generated, the voltage drops and the regulator increases the field voltage to keep up with the demand. The same happens in reverse-- if the alternator output current is more than is required by the electrical system, the bus voltage increases, which causes the regulator to decrease the field current.


The left and right alternator outputs get joined on a common bus bar under the nose baggage compartment and this is where the voltage regulator senses the bus voltage. This type of setup is not a true paralleling of the alternators but is instead two separate half systems (a left and a right) tied together. The most efficient half system will drive the bus voltage and the other half will "be along for the ride".


If the half systems are perfectly matched, both alternators will have identical field vs. output curves and will be outputting exactly the same current at exactly the same voltage with exactly the same input field current and the alternators will share the load equally. But if there is any difference in either half system---for example, a higher resistance on one side in the loop from the voltage regulator field, to the alternator, to the bus bar, back to the regulator, or if one alternator is stronger than the other---then one alternator will supply more of the load. This is the case with almost every Baron in existence because things are rarely perfectly matched (one can spend a lot of time getting it close). Because the currents in these loops are large (tens of amps for the alternators and 3 or 4 amps for the field), milliohm differences can result in large voltage changes.


Sometimes, as might be your case, the half system imbalance is so large that one alternator dominates and supplies all of the required current and effectively keeps the other alternator off, which the system senses as a failed alternator (the alternator out light will stay off as long as there is voltage at the aux pin of the alternator; when the alternator output is low or zero, that aux voltage is also low or zero). When that dominant alternator can no longer can keep up with the current demand, its voltage will start to drop, which will cause the regulator to output more field current, which will in turn cause the second alternator to start to output current and take up the load (the added field current will have little effect on the previously dominant alternator because that alternator is at, or is reaching, its limit). This could be what is happening when you turn on your landing lights.


Since the regulator is common to both alternators (both fields are supplied from a single regulator pin), the problem you describe with a single alternator is not likely due to the regulator. I would start looking at every connection in the common bus bar-->regulator-->field-->alternator-->common bus bar loop, (ground connections, too). If everything there is clean, then the next step is to look at your left alternator.


This Baron voltage regulator is typically a Delco PN: 9000591 which consists of very old school components that have likely not aged well. Enter a new solid state version that can be found, the Transpo PN: D591S and shown below. Amazing that the small potted section is all that's required. Look for the D591S on eBay. It holds a rock solid voltage!



Below is an image of the early Baron Delco 9000591 voltage regulator which is supplied in pairs for the early alternator equipped Baron 55s. Also below you will see the Farm & Industrial applications that this same voltage regulator used to serve back in the day. Proof once again that Beech utilized common industrial hardware of the day in many areas of the aircraft!




There are two transistors within the Delco Voltage Regulators shown above which can become tired after decades of service.



Below is an early Baron charging circuit diagram - be sure to note the applicable SNs for it!. Check your Shop Manual for your SN for your specific diagram:




Thanks Derek!





Early Bonanza Delco-Remy Generator Voltage Regulator





Click HERE for an excellent primer on the operation of the early Delco-Remy Generator regulator.

HERE is a link to the Delco-Remy Regulator Service Bulletin from 1953.

HERE is a link to the Delco-Remy Regulator Service Bulletin from 1960.

HERE is a link to the Generator Service Bulletin from 1961


Still sick of 1950's generator and regulator technology and brownouts in your airplane during night ops? Ready to pitch the whole system? Consider the Plane Power ER14-50 generator conversion kit for E-Series Bonanzas



HERE is a peek at an older install manual for the Plane Power ER14-50 conversion kit.




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