Do I really need a DC-DC or can I go with a high power alternator?

[Ampster]

A PWM solar controller relies on the solar panel maximum current to limit the current through the device.

Does that mean the alternator will try to put out as much current as the cells will take?

 

[TRAMP]

SMARTPASS 120S

40-289

www.ctek.com

 

[Zjohn]

This would be in conjunction with the main Lead acid starter battery so in theory the pwm drain from the alternator shouldn't cause too much of an issue?
It's a bit beyond my knowledge set but It's interesting to hypothesise about these things..

If you have a lead acid connected first I would say it should work and would surely be more efficient than most of the other solutions. I'd say give it a try with a cheap pwm controller, these are almost free these days anyway

 

[Zjohn]

If you have a lead acid connected first I would say it should work and would surely be more efficient than most of the other solutions. I'd say give it a try with a cheap pwm controller, these are almost free these days anyway

Just make sure that when you first connect the pwm controller to the lead-acid bat, the voltages of the lead-acid and the Lifepo4 are very close. If not there will be a current through the controller that it probably was not designed to handle...

 

[Luk3jay]

Just make sure that when you first connect the pwm controller to the lead-acid bat, the voltages of the lead-acid and the Lifepo4 are very close. If not there will be a current through the controller that it probably was not designed to handle...

This was my conclusion too. the more I think about it, a PWM controller is basically just a transistor switching on/off.
There is nothing to limit current (as mentioned above) so I don't think it would be a good idea. if the alternator could give 80A and the battery could draw 100A, but the PWM can only handle 20A... I think it'll go POP