Alternator delete with lithium and lead acid battery

by Tim Fulton on April 23, 2012

EcoModder forum member, Brucepick has been working on an interesting alternator delete for a while now. He wanted to eliminate the load on the alternator, but didn’t like the idea of just replacing the starting battery with a deep cycle lead acid battery. The downside of doing this is that as the battery discharges the voltage sags lower and lower. The lower the voltage is the dimmer your headlights get, your blower motor slows down, etc.Some speculate that the lower voltage might also negatively effect the ignition system and thus lower engine efficiency. While most have found this is a negligible consideration, Brucepick simply didn’t want to deal with it, so he found another way to go about things.

Brucepick decided to add a second battery. This second battery would be a lithium iron phosphate battery (LiFePo4). The LiFePo4 battery has a higher voltage than a normal lead acid battery. With both batteries fresh off a charger the lead acid would be around 12.7V versus the lithium’s 13.2V. This may not seem like much, but when the alternator in a car is hooked up, it keeps the system voltage at 13.5-14.5V. When you go from that down to 12V, that is a ~15% drop in voltage. The lithium battery helps negate that penalty.

Brucepick’s setup is unique in that he starts his car with the lead acid battery, but the rest of his car runs off the lithium battery. He also has a few switches though, so if he has to travel farther than the lithium battery he can simply switch the alternator back on and run off of the lead acid battery like a normal car would. When he can, he plugs in the lithium battery to go back to running without the alternator.

For more information and a full walk through of what Brucepick has done, you can check out his forum thread.

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