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I have a 1930's car with a Lucas dynamo. Originally it was a 6 volt system but now 12v. This is done without modifying the dynamo. Unloaded, the dynamo voltage can rise to over 20 volts and of course the working voltage is directly related to RPM. At present the 12 volt battery only begins to charge at 2000rpm engine speed. I've been wondering if a MPPT solar controller could work as a more efficient charge controller. Any thoughts on this heretic scheme ?

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  • \$\begingroup\$ If you are operating near the trip point where your load impedance is lower than the source (dynamo), perhaps but that's most likley beyond the current capability of it anyway. Are you regulating to 12 V by modifying the field winding? \$\endgroup\$ – winny Jun 18 '17 at 18:32
  • \$\begingroup\$ Most solar MPPTs are buck converters, so they won't work below 2000rpm either, though they may improve efficiency at higher RPMs. \$\endgroup\$ – Brian Drummond Jun 18 '17 at 19:44
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My best guess is that a solar MPPT controller is not a viable solution. That said - why not consider using a relatively standard buck - boost DC-DC converter?

There are several different types of buck - boost converter circuits readily available via Google. Start by looking up how a SEPIC converter works.

BTW - I think that using the existing dynamo in this fashion is a great way to go.

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  • \$\begingroup\$ Good point ,wimny ..The dynamo has charge control already using "third brush control" which I had overlooked. Electronic regulator schemes disable the 3rd brush and control the field. But is would not be safe to disable and connect in parallel with D+ due to excessive field current. Although a constant (safe) field current with a 3 terminal reg might be ok? All comments taken to heart..I won't be rushing out to buy an MPPT controller to try but might be tempted to experiment if I get one anyway for a solar project..I will also follow up the boost/buck converter idea.. Tk you all for input.. \$\endgroup\$ – Roger Jelbert Jun 19 '17 at 10:56

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