[oil pan 4]

Just incase I am able to install more solar capacity then what the 10 amp genasun can handle I am experimenting with a way to rig a 15 amp Morningstar MPPT lead acid controller for LiFePO4.
You might be thinking "I should just use this 15 amp Morningstar for my lead acid battery instead of the lithium specific 5 amp genasun". True, only thing is the price difference between the 5 amp LiFePO4 genasun and the Morningstar sunsaver tristar is at least $140. The price difference alone would pay for most if not all the solar panels you could put on your car.

The main reasons you do not want to use a lead acid charge controller on a LiFePO4 battery is the cell equalization and temperature compensation.
Equalization is when the battery voltage goes up to like 15.2 Volts or more once every 4 weeks or when battery voltage drops below 11 volts at rest.
Temperature compensation is where more volts are added to the charging voltage for lower temperatures. Lead acid batteries benefit from this, LiFePO4 batteries only ever want steady 14.2 volts all the time, hot or cold.

There are 2 ways I am going to try and accomplish this.
#1 this Morningstar has a switch to disable equalization, so leaving it off solves half the problem right there.
#2 get the charging voltage right. I may be able to just set it for gel batteries (14.0v even) or use the sealed batteries (14.1 volts) setting and forget it.
But then there is the pesky temperature compensation.

Lucky for me this Morningstar has an optional remote temperature probe for the battery.
I believe this temperature sensing element is a thermistor. Which means it has a fairly high resistance value that changes a lot with temperature.

Temperature compensation as stated by Morningstar on this unit is about 2 millivolt per degree F. Doesn't seem like much.
But this part of New Mexico has a about 120'F temperature difference between the coldest winter nights and hottest summer days.
This charge controller shouldn't hurt a LiFePO4 battery with active temperature compensation, but I like to be thorough. Plus the gel and sealed voltage wont quite get the battery up to full charge on a hot day with temperature compensation.

So I what I am going to do is get the remote temperature sensor, measure its resistance at 70'F and stick a resistor equal to that value in the remote temperature sensor terminals. Then resell the probe on ebay, since I wont need it for anything else.
If I can lock in the 14.1 volt sealed battery setting all the time that would be perfect.