A Low cost electronic dynamo regulator

A month or two ago a customer sent me a regulator to test. I thought he meant it was a DVR2, but was in fact of the type available cheaply from a good number of sources. This was a 6V Positive Earth unit in a neat cast alloy case, of Chinese origin, but unbranded.

Well I tested it and reported to the customer that it had indeed expired. He said for me to keep it and do what I will with it. So what would any design engineer do? Well I started to open it up and remove the hard black potting compound, little by little. It quickly became apparent that the device was simple in the extreme. The pieced together circuit diagram is shown here, more or less:

circuit diagram of a cheap and nasty dynamo regulator
quick ‘n dirty regulator circuit

To my eye this circuit looks like the sort of thing an inexperienced designer might sketch out as a first stab. Incredibly vague reference setting and low gain suggest poor voltage regulation and wide tolerance variation unit to unit (and against speed, load and temperature variations). SPICE simulation indeed confirms the predictable poor performance. That is to say nothing of fault resilience and reliability. So how does such a design get brought to market? How could meaningful testing have been carried out?

To sum up, buyer beware! Lowest cost and best quality are not often compatible. Buy cheap, buy twice is a more likely outcome (the 2nd purchase being a DVR2 perhaps?). Comments welcome . . .

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