Originally Posted by DLindy
Iíll get the DC ammeter. Good idea. Where would I find the right wire to test the amps? Is it coming out of the alternator? Or coming in to the house batteries? To test it without the lithium connected can I just hit the house battery disconnect? Do alternators fluctuate a lot? Or if I see 30 amps several times in a few minutes that should tell me? I plan on getting another battery so I probably should test it again after I get the 2nd battery? Thank you!
You have to start with somewhat discharged batteries so there will be a significant load on the alternator. So disconnect from shore power and leave all of the lights and fans on for the better part of a day to draw down the battery.
Ideally use the wire coming from the batteries to measure the alternator charging current, which runs through the coach's BIM and then connects to the chassis alternator. But like my MH you may have several wires connected to the battery and it probably isn't obvious which is that one.
First measure the current through each of the wires. Ignore the small gauge ones. This wire has to be pretty big, probably at least #2. Note the current in each wire.
Then start the engine, wait a minute for the chassis electronics to fully turn on the alternator and measure again. You should see one of the wires jump 20 or more amps. That is the one.
Another way is to measure the current from the lug on the alternator. But that also includes current to operate the chassis which with modern electronically controlled vehicles can be significant. So shut off the use/store switch, start the engine, measure the current from the alternator, then open the switch and measure again. The difference should be the charging current from the alternator to the coach. You can confirm this by finding the wire at the coach battery that has similar current.
Sorry for this long detailed explanation. What sounds simple to do gets complex when dealing with a MH where you can't trace the wires because they head off into the unknown.