Reason for Starter Cable

[Arbee]

I've read my initial post on this a dozen times. Initial thread

I must be stupid because I don't understand the answer. What I'm not is a troll--or at least I don't intend to be.

I called the manufacterer...they have an answer that makes no sense to me.

So I am reposting--not because I am unhappy with the answer I got and wish the world were different when it can't be, but because I don't understand--here goes:

Either of these Renogy Dc-Dc chargers with MPPT https://www.renogy.com/dcc30s-12v-30a-dual-input-dc-dc-on-board-battery-charger-with-mppt/ or https://www.renogy.com/dcc50s-12v-50a-dc-dc-on-board-battery-charger-with-mppt/ (30 amp and 50 amp respectfully) comes with a cable that plugs into the product to let it know if the vehicle engine is (of course the other end of the cable is connector to vehicle circuits that energize only when the engine is cranked.) Just to bring everyone up to speed this one device in 30 or 50 amp variety charges a starter and house battery from both a solar panel and the vehicle's alternator.

According to Renogy, this cable need not be used on vehicles that don't have smart alternators:

Still further, I understand that smart alternators exist to not give vehicle (i.e. starter) batteries more power than needed to allow an ICE (internal combustion engine) to use less fuel, and perhaps also make the starter battery last longer---ok, maybe the first if the second reason.

Why would this wire not need to be connected for vehicles with standard (i.e. non smart) alternator charging? You see I could get why either of these DC-DC/MPPT devices would want to know the vehicle is cranked regardless of the type of alternator under the hood so as to not let the house battery be energized by the starter battery unless the engine (i.e. alternator) is simultaneously operating and charging the starter battery (the answer the Renogy rep gave me before the call was cut off and I was 10th in que when I called back.) But I don't understand why this ignition wire is requried for just smart alternators.

Thank you. Mr snoobler...if this rehashing offends you I am sorry. I is NOT my intent to piss anyone off---just to understand.

FWIW, either of these Renogy products will prioritize charging the house battery over the starter battery when the vehicle is off and the solar panel is collecting energy, but will prioritize the batteries in the reverse order if the vehicle is cranked.

 

[snoobler]

When you RTFM, you saw the different voltage of smart vs. non-smart alternators. This is that crap charging algorithm we touched on that undercharges batteries for small fuel efficiency gains.

You have to instruct the charger to behave differently due to different charge sources. On a dumb system, the resting voltage is too low to trigger charge, so it doesn't need to know it's on. On a "smart" system, operational voltage can be much lower, so you need to signal the charger that it's okay to charge when the voltage is lower than a "dumb" system.

 

[Arbee]

When you RTFM, you saw the different voltage of smart vs. non-smart alternators. This is that crap charging algorithm we touched on that undercharges batteries for small fuel efficiency gains.

You have to instruct the charger to behave differently due to different charge sources. On a dumb system, the resting voltage is too low to trigger charge, so it doesn't need to know it's on. On a "smart" system, operational voltage can be much lower, so you need to signal the charger that it's okay to charge when the voltage is lower than a "dumb" system.

Got it. Understood now. Sorry if you said this prior and it didn't click. It makes sense now. Thank you. I won't ask this again. Page 17 in the manual.

 

[snoobler]

I think we've touched on it before, but not in the same context. It was a legit question, and I had to think about how to explain it because without my prior knowledge of Honda charging systems, I would have had the same question.

Please don't be scared of me.