Will a Battery Isolator relay also protect the Tow vehicle alternator?

[rickst29]

Originally Posted by Rob Culver

Hi Wavery,
Do you know what kind of charge rate you're getting from the Tow Vehicle to the TM in amps? I'm sure that would depend on how depleted the lithium battery was to start with. I assume also that in most cases the alternator would not provide high enough voltage to top off the last 10 to 20% on the battery so that's another advantage of having a DC to DC charger.
I haven't tried mine yet but if the tow vehicle can provide 15 amps or so then it might not be worth it to have a charger if it charges only at 20 to 25. And probably wouldn't want to charge faster than that because then it would require an upgrade on the wiring in the tow vehicle, TM, or both.
So do you know what rate your Tow vehicle charges up your TM batteries?
Just curious.. Thanks.

'Waverly' has solar panels. When traveling in daytime, they probably provide enough power to run the fridge (and support other smaller loads in the TM) with even a bit of extra for his batteries.

Let's review the situation from the tow vehicle:

An 80% charged LFP battery pack has resting voltage around 13.3 volts, and the Tow Vehicle needs to provide more than 13.4 to further charge that battery. Under the hood, the Silverado probably runs at about 13.5 volts. When zero amps flow through the skinny and long wires along the "trailer battery charge" power path, it will have 13.5 volts. But as soon as significant current (and power) begins to flow, the voltage seen atr the battery terminals falls below 13.4V. The Silverado, without a booster, is unable to send significant into LFP batteries when they are already at moderately high SOC.

A DC->DC booster overcomes that limitation, by presenting higher voltaqe to the battery terminals when the trailer batteries are "NOT YET FULL".

- - -

A good DC->DC "boosting charger" protects the vehicle alternator from overload in two ways: #1, it should not be configured to attempt pulling more than about 15A under any circumstances. (Buying a uncontrolled "bigger one", more than about 20A maximum capability, is a waste of money - it will only melt the bargman cable.) #2, if the alternator struggles to maintain high voltage under the hood, the Booster sees low voltage, it shuts down. (In good DC->DC devices, you can configure that value.)

15A is less load than running the headlights. If the alternator can't handle that "additional load", is was probably about to die anyway -- just from engine and accessory loading issues, and inability to handle low voltage (from the truck/SUV battery) after running the starter of truck.