Originally Posted by porkchopsandwiches
Question: with the simple setup of the big solenoid between the bus batteries and house batteries, say you have 4 big deep cycle Trojan batteries for your house bank. Say you have run these down to empty (12.1 volts or whatever it is) and start your bus, let it run for a minute, then flip the switch to close the solenoid so the house batteries connect to the bus batteries. Is there a way to figure out how many surge amps we are talking about with this? Like will flipping all those on at once cause a huge voltage drop in the system and screw things up?
Yes, it will cause the voltage for the entire system to drop the second you flip the switch. On an old mechanical engine, might not be that big of a deal, but on your electronic engine it wouldn't be good at all. That is why they have isolators.
An isolator will:
A) Let the chassis voltage remain at a steady voltage
B) Charge the chassis batteries at their own rate
C) Separate the chassis and house batteries, yet use one alternator to charge both.
D) Charge the house batteries at slow rate(which is what you want if they were discharged slowly)
12.1 house volts is discharged but not that low. Imagine if you left a load on all week (It will happen) and voltage was at 6. Dumping that dead of a battery bank on an alternator will certainly peak the alternator out(shortened life), drop the system voltage way too low (bad for the computer), cause the bus batteries to discharge(something you don't want), and it will probably kill the house batteries as well due to the 100+ amp charge rate you just put on them.
None of that is good. Use an isolator.