Limiting alternator current

[Tim22]

this is a bit of an unusual question. I have downsized the start battery for my yanmar 2gm20f to a 35ah Full River 438T. It’s much smaller, and more importantly much lighter than my old battery and seems to work fine. My problem is that it only wants to see 8A max charging. Because of this I want to limit the output of the Hitachi alternator as the alternator goes to the start battery.

The reason the alternator goes to the start is that the House is LifePo4. For the most part I only run the engine going in and out of harbour (20 minutes max) so not worth dealing with LifePo4 charging. Instead, house is charged from solar and start is charged from house via a Victron Orion xs. The alternator has to go somewhere so it goes to the start battery.

i am wondering if I can add a resistor between the alternator and the + start terminal to reduce the current so as not to damage the AGM start battery?

Thanks for your help with this

Tim

 

[Davidasailor26]

The start battery should never be deeply discharged. Since its lead acid it should limit its own rate of charge at high states of charge. I wouldn’t expect you to see more than 8 amps even without changing anything.

 

[Maine Sail]

The battery will limit the charge on its own just like cars.. just take a look at the size of the alt in cars/trucks feeding a teeny tiny batt. For example my vehicle has a 150A DENSO alternator charging a group 24 battery. I last replaced the battery in 2014 / 272,000 miles ago… if you were deep-cycling it then max charge current matters more but start batts should never be cycled.

 

[Tim22]

Many thanks for this clarification. I will leave well enough alone.
Tim