Charging a (second) lithium battery with alternator? Having issues

Hopefully this is the right forum... feel free to move if need be.

I have a 2011 Tundra Rock Warrior with tow package. As far as I know it has the original alternator which should be a 150A unit. (can't verify though as I bought used)

I'm trying to charge a lithium battery in a fiberglass camper by running power off my alternator.

I had the cables professionally installed -- 2awg cables -- and they run to the back of my unit where they connect to a Victron DC-DC charger that's rated at 50amps. My goal is to pull at or near 50amps.

The problem is that I can only seem to manage to pull 20amps while driving. When I turn on headlights, heater or radio or etc the output drops a few amps. This seems pretty odd.

I've played with all the settings on the Victron unit and think my wiring work is good.

This leads me to believe there may be an issue with the alternator output. I'm trying to figure out if I just need to get a new alternator, if the alternator needs to be modified, or if there is something else in the electrical system that is limiting me.

I get max 13.9V from the alternator as far as I can tell. (max load) Usually runs lower however. Not sure if that's normal. Can't directly measure amps output.

The input to my unit from the alternator never seems to exceed the low 13s, however. (at least in bulk charging mode)

I'm wondering if a ground somewhere might be compromised. The starter battery itself is a year old. Although I did notice it dropping back to like 12.2 after having been at 12.6 after driving.

Any ideas? Trying to do what I can before taking it into a mechanic.

Thanks

 

Update:

A) Took vehicle into shop. Alternator cranks out amps just fine; hits 150A fine. The problem is that it doesn't seem to understand the extra power my DC to DC charger is requesting.
B) No voltage drop from from alternator to back end where power cables are concerned. Negative ground point is fine. Things look good.

Given all this, I've been recommended that I look into this solution, adding a resistor to the alternator that prompts it to put out more voltage:

https://www.tundratalk.net/threads/alternator-voltage-booster.655929/

Does anybody know how hard of a DIY this would be? I don't have a garage or anything.

Thanks.

 

A GM (I used Ford) diode will bump the charge voltage a bit, super easy drop in. But not sure if it'll solve your issue.. which Victron charger are you using?

 

Victron Orion DC-DC Charger 50A.

Actually just ordered voltage booster from https://voltageboosterpro.com/

Didn't realize it was in the engine fuse box at first. Will report back how it works.

 

Yeah I was gonna suggest the resistor, I’ll take a pic tomorrow of the custom one I made