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The amperage coming from the alternator is determined by the SOC of the battery. Its not computer controlled but charged batteries don't accept current for reasons I can't explain. The house and starter batteries get different current depending on their SOC at the same time. They are not charged sequentially, they are charged simultaneously at the current they will accept and the alternator/wiring/hardware is capable of putting out. When my house battery is fully charged current drops to a trickle as measured on my battery monitor. Voltage remains constant with alternator charging. Keeping the bulk charge voltage on the batteries while driving does not harm the batteries. If it did you would be replacing your starter battery in every vehicle as often as you fill up the gas tank.

My stinger isolator cost about $20 and I'm going on 4 years on my AGM. I've never switched it off while driving. I've been doing this for about 25 years and have always gotten 5-7ish years out of my camper batteries. YMMV.
@afox

I believe what you wrote & the following to be the case;

The PM alternator is controlled by the PM computer to regulate the PM alternator. I have not looked @ the PM alternator, but I suspect it has a regular bolt on automotive regulator. Typically these type of regulators are “D” or “S” or “C”. The PM regulator is logically “C” for computer input. The voltage is kept steady by the computer. The current is increased or decreased depending upon load by whatever magic software the PM computer has (basically the amperage coming from the alternator is being controlled by the computer & the parameters of that is by what loads are being sensed by the computer).

This is a “S” type “sensor”.

@akarmy this would be specifically important to you if you run a Nippon Denso in your RV I do & Vans stoped selling & supporting them. This took me 2 years to research and sort out (I reported the issue on VAF but it never got noticed).

65940





All that being said, the loads “draw” current & I think it is the same for batteries. From what I can detect from my house battery monitor, as my SOC increases the amps decrease & the volts increase.

Cooking a battery while driving is possible, but not probable depending upon the system & battery type & manufacturer’s recommendations, how long you drive, & your starting SOC. In my case “Rolls AGMs” the no time limit voltage (float) is 13.8v & that is above my PM alternator voltage. YMMV



65919
 

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Discussion Starter #42
short answer is YES it is possible

”An Isolator or Voltage Sensitive Relay” can over charge if;

1) A manual system isolator left on too long & too high a voltage (not float voltage)

2) For “smart devices” if they malfunction

3) A manual solenoid has a possibility of “staying on” even if you turn it off (rare, but has happened to me before)
That's what I figured. I'll be getting a dc to dc charger instead.
 

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That's what I figured. I'll be getting a dc to dc charger instead.
For me; If FLA or AGM I do not want a B2B (Lithium definitely a B2B or whatever is needed to keep them happy). I also do not have solar.


My Reasoning;

My direct charging of my AGMs works great & my charge is not being reduced by the B2B magic box. I am diligent to turn on & off my charging system while driving/parked (I have a smart disconnect if I forget while parked). If away on a trip & something malfunctions it is very easy to diagnose & fix (a very simple system that I understand). I prefer simple over complicate & I do not mind monitoring my SOC on my house AGMs. I also believe any equipment can fail, so the less equipment I have the fewer points of possible failures & less to consider when diagnosing the problem.



I have absolutely nothing against B2B chargers if they are “needed”. My perspective for my own design is if it is not needed why would I include it in my build. This is also why I do not have solar (I will someday if it is needed). So far I don’t...
 
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