I'm trying to plan out a dual battery setup and I just wanted to make sure I understand that our alternators are considered fixed voltage?

variable are after 2000 generally?
temperature compensating are for diesel?

from FSM

The alternator output voltage changes with temperature - it is right there at the last spec in the image you posted.

Lead acid batteries require different charging voltages depending on temperature...

-Charlie

After reading a lot more on the subject, yes 100% agree. The D4D prado was supposedly the first Toyota to have "the alternator output voltage drop to approximately 13.5 volts when the temperature under the hood reaches its predetermined level"

even though the FSM is not exactly that I have to think the 3rd gen alternator is classified under the "temperature compensating" type.

setting up a dual battery system is kind of hard. I have a lot to learn about DC automotive systems.

To me they are all temp compensated. It's just where the voltage regulator is located.

Internal with a thermistor imbedded in the regulator or external and a battery temp sensor under the battery. I don't remember seeing a temp sensor in a externally excited alternator.


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Yeah, this. The temperature sensor is built into the regulator on the alternator. That Prado D4D might just be the first to put the temp sensor on/near the battery itself.

-Charlie

Why is this important to your dual battery set up ? I'm asking because I'd like to know. To my knowledge most guys just throw in dual batteries and wire it up with few other fancy things. Never saw anyone worry about the temperature changing their voltage.

Chrysler and jeep have a battery temp sensor. My 94 Dodge Ram with the Cummins has a battery temp sensor and the alternator field (voltage regulator is in the PCM) is controlled by the PCM.


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@kolelt

because I attempted to do a cheesy dual battery setup last year for a 10 day road trip. figured as long as I could keep sandwiches cool I would be happy. it actually worked ok but only lasted for 7 days.

this is what I did


so Now I'm trying to plan something that will keep things cold without fail. The problem is I want the battery in the back, the engine bay is cluttered enough and I really don't want to mess with stuffing another battery under the hood. I would also like the ability to add solar maybe, not sure yet. have a friend with a sailboat up in bayfield WI and they run their chest freezer off wind and solar. it's really cool and works great. head out in lake Superior and just sail without having to run a generator.

This is the magic box I'm thinking about using, I like it because it handles exactly the plan I wanted to follow. DC to DC charging is a bit more complicated and I still don't know all I should know about it.

https://www.redarc.com.au/smart-start-bcdc

also, I don't think the original intent toyota had was for us to run dual batteries and so... there is a lot of extra things to consider if your going to do it. IMO.
https://www.redarc.com.au/alternator...xed-alternator