89 mid cabin paralleling solenoid

[mrrudely]

I just installed a 100ah lithium battery to run my 1000 watt inverter
I installed a Victron 30amp dc/dc non isolated charger to charge the lithium battery
The dc/dc charger is powered by my starboard agm start battery

On a 3 hour trip (around 3000rpm) with a fully charged lithium battery no issues.
After 3 days on a mooring occasionally running the generator to charge things we
returned home. I am fairly sure the lithium battery was not fully charged.
About half way home the engines started dying, they were not getting enough
from the alternators, the gauges at the helm both read just under 12v
I disconnected the dc/dc charger and things returned to normal.

The charger puts out 30amps (or consumes) it was set to trigger at 13.4v I now increased it to 13.8v

Why the problem and why both engines were affected is a mystery to me.
Is it possible that the paralleling solenoid automatically connects the two batteries when the engines are running
and one battery is low?

[BobCT]

My understanding is that the paralleling solenoid is only engaged for starting.

[mrrudely]

That's my understanding as well
But something is not right
Both batteries were being drained
I think the dc/dc charger is the culprit
But why both batteries?

[prowlersfish]

How do you have the DC to DC charger hooked up? Has a battery switch been hooked up to the batteries and is it on all? Recheck all your wiring.

[mrrudely]

still trying to figure out what happened
I just replaced the port starter motor
the old one was in such bad shape it was not rebuildable
does anyone know if it is possible that a short in the starter motor
could drain the battery so much that the alternator could not keep up?
that would explain why the engine died and the battery went dead in the middle of a trip
thx
rr

[prowlersfish]

Yes it's possible. If stayed engaged it would draw more than the altnator could put out. Was it burned up?

[mrrudely]

can't say if it was burned up
I did not see all the parts when it was broken down
the parts I did see suffered from major corrosion

I am now thinking both engine problems at the same time was just a wierd coincidence