Help me kill my alternator - it is stubborn and won't die

[Daox]

It really only works well if you run off a deep cycle and basically never turn the alternator back on (except for regen situations). If you turn the alternator back on in normal driving it is going to turn on at pretty much full blast and that will hurt your fuel economy.

[teoman]

Very elegant solution indeed.

What kind of mpg gain will you get from this? I am assuming here that it will be more significant than your older car since the 2014 is more electronic and has a slightly increased power consumption.

Liters / 100km or hour (or gal/mile) units would be much appreciated.

[Stubby79]

I was intending on continuing down this path as well...I picked up a cheap charge controller from ebay for a couple of bucks...it will switch on a relay when the voltage gets too low, and switch it back off once it reaches another voltage. It's adjustable. The point of it is if you aren't watching closely and your battery gets drained, it will kick the alt in automatically for you and save you from needing a jump start.

[teoman]

You could modify the system just a little bit and feed it 9V or so so you charge the batteries faster.

[Daox]

Originally Posted by teoman

Very elegant solution indeed.

What kind of mpg gain will you get from this? I am assuming here that it will be more significant than your older car since the 2014 is more electronic and has a slightly increased power consumption.

Liters / 100km or hour (or gal/mile) units would be much appreciated.

The rough calculations I did show that disabling the alternator reduces engine load by ~8%. I expect a 5-10% gain in fuel economy which is what the ecomodder wiki page shows to be historically true for most alternator delete mods.

[teoman]

So in the range of 0.3 l/100km or 0.3l/hour

%10 on a car that gets 10mpg would be impressive.

[Daox]

Disaster struck last night. My dc-dc converter got toasted I am pretty sure. The input voltage range for it is only 10.8-13.2V. Well, I think my switch (which actuates with almost no physical input) got bumped or jostled and the alternator turned on bumping the voltage up to 14.4V. Then, it got turned back off which exposed the dc-dc converter to more than 13.2V as the battery voltage slowly fell. And, while it can take a 100ms spike at 18V (which I had hoped would be enough), it stopped working. So, I am thinking that I have two choices:

1) Create a protection circuit so the dc-dc converter never sees above 13.2V.

2) Use a different dc-dc converter.

I'm partial to #1 because I bought two dc-dc converters just in case I fried one. However, I'm thinking #2 may be a better option. A voltage divider will not work for the spread of voltages I'm looking at. I did the calculations. I'm not aware of any other simple circuit that can keep the voltage to the dc-dc converter in the necessary range. I'm not looking to make this complex.

On the upside, this would have happened anyway once I figured out the regen side of things because that would have been intentionally turning the alternator on and off. So, the dc-dc converter has to be able to handle this scenario if I am going to go through with that phase of the modification.

[teoman]

Add diodes to its input.

[Daox]

Not a bad idea. Lets do the math though. The alternator's max output is about 15V. We have to drop 15V down to 13.2V. That would take three .7V drop diodes which would create a 2.1V drop. But, lets say I'm now running on the battery. The lowest my battery voltage to the dc-dc converter can be is 10.8V. With the diodes in place, that means my battery voltage can't drop below 12.9V. If it does, the dc-dc converter won't work anymore. 12.9V is higher than the resting voltage of a 12V lead acid battery, let alone a loaded one. So that unfortunately won't work.

[teoman]

Then get a voltage converter to feed your voltage converter.