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Old 09-21-2013, 12:15 AM   #5 (permalink)
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Join Date: Sep 2013
Location: Oxford, UK
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Black Beast - '02 VW Goff Estate S
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Originally Posted by JRMichler View Post
I had similar thoughts recently when I realized that, with a certain amount of effort, I could get my summer average to 40 MPG.

My idea is a two position alternator switch. Position 1 would be "normal". Position 2 would shut off the alternator. The truck would continue to run off the standard battery. A second deep cycle battery would charge the standard battery through a DC-DC converter with about 14 volt output. The second battery would be charged from a flexible solar panel mounted on my topper and charge controller. I would want the deep cycle battery to be sized for four hours at 20 amps into the standard battery. The solar panel should fully recharge the deep cycle battery in 8 to 12 hours.

I don't think I'll ever do it, but it's a great thought experiment.
I had the exact same idea recently, except that the charged auxiliary battery would also run a couple of small self-adhesive heater pads for engine sump and gearbox - to reduce warm-up times in winter, or in summer come to that.

I'm planning to start with the aux battery and variable input dc/dc converter to see how it works, then add a mains charger for the aux battery. If mpg gains are appreciable I will invest in a roof-mounted solar panel and charge regulator for the aux battery. I'm hoping that simply supplying a slightly higher voltage to the car's normal system (14.8v?) the alternator will 'decide' not to bother putting any amps out, and I will therefore not need an alternator kill switch.

But did you ever make the thing?
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