1968 Triumph Bonneville Voltage Regulator Upgrade

| 2/13/2018 12:00:00 AM

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Making sure your charging system is working to full capacity is important on a number of fronts. To begin with, there's the simple issue of generating enough voltage to keep your lights bright. This is particularly important on vintage bikes, which generally have low-capacity charging systems and run low-output headlights, which tend to be dim even with full voltage. And even if your lights are off, there's the issue of generating enough voltage for proper ignition. If you own a decades-old British twin, chances are good you've already ditched the stock ignition points for electronic ignition, a highly recommended upgrade to ensure steady, reliable firing of the spark plugs. However, some electronic ignitions are very sensitive to voltage supply, dropping completely out of circuit if the voltage drops below a certain range. Boyer electronic ignitions, for example, will drop out below 10 volts.

On Sixties and Seventies British bikes, the original Lucas charging system can be prone to failure. By the mid-Sixties, most British motorcycles were using Lucas charging systems with Lucas' silicone diode rectifier for AC to DC voltage conversion and a Lucas zener diode for voltage regulation. Although relatively simple components, after 40-50 years of vibration and exposure, the voltage regulator and rectifier are ripe for replacement. The original-style components are still readily available, but there are better products on the market that deliver superior performance and reliability, like the Podtronics voltage regulator/rectifier we recently installed on Tech Q&A man Keith Fellenstein's 1968 Triumph T120R Bonneville.

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Keith's Bonneville didn't have any particular charging issues, but with a fresh Pazon electronic ignition upgrade, and wanting also to convert to 12-volt negative ground from positive ground, Keith considered it a good move. Adding to the appeal, it's also a relatively cheap and easy conversion. The Podtronics unit was $57 (before shipping), and while we did opt to clip off what became redundant ground lines from the old rectifier to the battery and frame, had we wanted to, we didn't have to make any permanent changes to the original wiring. Keith's bike already had a replacement wiring harness, so we didn't feel bad about altering it in any way as it's not original.

We also like this upgrade because A) it delivers superior performance over stock and B) the only way anyone will know the charging system has been changed is if they lift the seat and see the new Podtronics unit in place of the original Lucas silicone rectifier. On 1968 and up through the mid-Seventies Triumphs the Lucas regulator (the zener diode) is housed in a large, finned aluminum heat sink attached to the bottom of the lower fork yoke. You can leave it in place to preserve your bike's original looks, as we did, or remove it. For the conversion, we isolated the wiring to the zener diode and then tucked it into the headlamp shell.

4/5/2018 8:21:56 AM

Good article. The original Lucas rectifier is a selenium design. Simply replacing that with a silicon bridge is a vast improvement. I did that on my 1965 6T, and several vintage Hondas. MB Mpls

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