In really hot climates the under hood temps soar of my '97 Jeep Grand Cherokee 4.0 liter straight six. The engine doesn't overheat, but because it gets so hot under the hood, the Battery Temperature Sensor does it's thing and pulls back charging voltage to about 13.2V - this, whilst maintaining voltage, doesn't really adequately recharge my Optima AGM battery. After turning off the engine and allowing it to stand for a bit, I found its resting voltage to be about 12.5 to 12.3V when a fully charged Optima AGM should give a resting voltage of about 12.7 to 12.9V.
So I had a battery that was really only about 1/2 charged and wouldn't give its maximum possible powering time for running a 12V TV, or a Notebook PC or GPS some lights etc. The "constant and higher draw" stuff runs off a second Optima Blue Top AGM and is charged via "12V to 12V" Battery Charger that works whenever the engine runs. It charges at the correct charging voltage for AGM's of 14.4V .
So what I did was cut and solder in a 40 Thousand OHM 1 watt resistor into one of the leads to the Battery Temp Sensor. Easily removed, cut spliced in, soldered, sealed with Heat Shrink, and double wrapped and replaced. It took a bit of research, a bit of experimentation and a bit of substitution..... but I now have an alternator that charges the Primary battery at 14.4V and a primary starting Optima that has a resting voltage of 12.8V.
I'm happy with that little bit of custom engineering and thought I'd share it with you people out there.
P.S. I've obtained another sensor and lead assembly so that in case of failure or need to return to standard specs in cold/cool climates it's a 5 minute job to change it out.
Any and all comments gratefully accepted.
So I had a battery that was really only about 1/2 charged and wouldn't give its maximum possible powering time for running a 12V TV, or a Notebook PC or GPS some lights etc. The "constant and higher draw" stuff runs off a second Optima Blue Top AGM and is charged via "12V to 12V" Battery Charger that works whenever the engine runs. It charges at the correct charging voltage for AGM's of 14.4V .
So what I did was cut and solder in a 40 Thousand OHM 1 watt resistor into one of the leads to the Battery Temp Sensor. Easily removed, cut spliced in, soldered, sealed with Heat Shrink, and double wrapped and replaced. It took a bit of research, a bit of experimentation and a bit of substitution..... but I now have an alternator that charges the Primary battery at 14.4V and a primary starting Optima that has a resting voltage of 12.8V.
I'm happy with that little bit of custom engineering and thought I'd share it with you people out there.
P.S. I've obtained another sensor and lead assembly so that in case of failure or need to return to standard specs in cold/cool climates it's a 5 minute job to change it out.
Any and all comments gratefully accepted.
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