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Old 03-02-2017, 08:35 AM   #17 (permalink)
DieselJan
Less waste = better FE
 
Join Date: Feb 2017
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Quote:
Originally Posted by Stubby79 View Post
I'd not recommend that, unless you have a separate battery for starting the engine. You might shut off the car with just over 10v in the battery, and not have nearly enough juice left in the battery to get it to start again. So, either a separate starting battery, or a supercap and some circuitry to charge it higher than the 10v it would get from the deep cycle battery.

DJ: Nice, well-thought through mod you have done. I was considering something a bit more simplistic to do a similar job, but with a proper schematic in front of me to follow, I could more easily just duplicate your work and tune it to my needs. Love the idea of tricking the alternator to put out less than full charging voltage. Thanks!
Hi Stubby 79
Yes I also wouldn't recommend discharging to 10V, but that is what I thought you asked from your question. I don't think going lower than 13V or so will have any significant gains anyway.

You asked for something more simplistic, see attached. It is essentially the same circuit. This is the first concept I thought of, but realized that I would have to change the Penlight battery periodically.

In this circuit you add more diodes in pink area to increase the voltage you want the battery to normally run at. Not decrease as in more complex circuit.
The regenerative input from break light doesn't have any delay to stay on. You can add a capacitor in parallel with relay coil to get some delay. The capacitor size will depend on your relay, so you will have to experiment with that.

I can't really quickly think of something simpler for you.
The only downside would be periodic battery changes, so I would recommend the more complex circuit for long term hassle free driving.
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