378TS coach vehicle battery isolation

[stokkeland]

I am back with my new-to-rv questions on electricals - a 2019 Georgetown 378TS.
I been doing some testing on how long my coach batteries would keep the inverter/fridge and some lights running, looks like the bank of 4 lead acids (i think it is) is providing at more than 24 hours.
What concerns me is that it appears the vehicle (start) battery also seems to be dropping at the same rate the coach ones are.
I was under the assumption that there was isolation between, or at least some type of smart-system in place to avoid draining the vehicle if the coach happens to drain completely.
I have a "boost button" to use the coach batteries for starting, so that indicates there must at least be some sort of isolation, intent of it anyway.

Anyone know what the "normal" way is?

I looked through the diagramming i could find, but I didnt see anything on this particular subject, nor did i find other posts on it in my searches.

any hints be appreciated

[stokkeland]

I havent looked around to find it - but from some more googling, this post anyway, i am guessing i have a "BIRD" or similar, or something that keeps the batteries connected until the volatege goes below a certain point.. so to test if it works, i probably have to do a 36 hour test ad run it quite low

[bubbles]

Originally Posted by stokkeland

I havent looked around to find it - but from some more googling, this post anyway, i am guessing i have a "BIRD" or similar, or something that keeps the batteries connected until the volatege goes below a certain point.. so to test if it works, i probably have to do a 36 hour test ad run it quite low

I have a 2012 GT 378 and it doesn't have an inverter or a residential fridge but I think the newer 378's may be same as my vintage for chassis and coach battery interconnect. What controls battery switching is a battery control center (BCC) box typically mounted on the bulkhead in the coach batteries area. The chassis and coach batteries are only tied together for charging and emergency start purposes. Charging is from either shore power/genny/engine alternator. Shore power and genny charging is via the converter and alternator charging is from the engine driven alternator. Emergency start is via actuating that switch and provides coach battery power to start the engine. In all cases the same interconnect relay is utilized (within the BCC). When charging is from shore power or genny charging to the chassis battery will not take place till coach batteries are at a preset charge level. Conversely, when charging is from the alternator charging to the coach batteries will not take place till chassis battery is at a preset charge level. Now, if these scenarios are not applicable to the newer 378's someone should chime in with the corrections. Here is a drawing of my BCC.

[stokkeland]

Awesom thank you - yes I do have a BCC by the battery bank, that drawing is probably not far off.

[camaraderie]

I'm still puzzled by the voltage drop in your engine battery. May I ask what voltage it started at and what voltage it dropped to over what period of time? Any dashboard items in use (GPS/Radio/DVD, Lighter plug chargers etc.) in use during that time?

Also...on your 4 battery house bank. What readings are you using to determine the fridge is OK for 24 hours? I'm pretty sure only 2 of those batteries are dedicated to the inverter & fridge and the other two are for the rest of your 12V system...but I could be wrong. In any event actual before and after voltage readings for EACH battery will tell the story.

[stokkeland]

I did not actually write it down - in my next test i will. I have a Fluke RMS so it is pretty accurate, I am pretty sure that I started around 12.46V after I unplugged shore power, 20 hours later I was at 12.25, if I put some extra load on it, like running water so the pump kicked in i saw 12.17 at that time (from top of my head).
As far as I know nothing was on up front, i have not taken the time do do full disconnect and measure usage tests.
I believe all 4 coach batteries are in parallel but i need to confirm that - over the next couple of weeks when I get a moment I will do some better tests and check these things out, then wake this thread back up with some more accurate findings, I will also try to figure out if my BCC looks like it is similar to that drawing - so stay tuned.

[ScottBrownstein]

Standard Georgetown has all 4 in parallel. BCC couldn't handle two house banks anyway. Your data sounds just like mine. You can get a good 24 hours on inverter...but little more.

[camaraderie]

Originally Posted by stokkeland

I did not actually write it down - in my next test i will. I have a Fluke RMS so it is pretty accurate, I am pretty sure that I started around 12.46V after I unplugged shore power, 20 hours later I was at 12.25, if I put some extra load on it, like running water so the pump kicked in i saw 12.17 at that time (from top of my head).
As far as I know nothing was on up front, i have not taken the time do do full disconnect and measure usage tests.
I believe all 4 coach batteries are in parallel but i need to confirm that - over the next couple of weeks when I get a moment I will do some better tests and check these things out, then wake this thread back up with some more accurate findings, I will also try to figure out if my BCC looks like it is similar to that drawing - so stay tuned.

I'm thinking all is fine and you're just settling out on the engine batt after being in use. Dunno if you're batt center has a spillover function to keep the engine batt charged once the house is full...but you can easily check that when you've been plugged in overnite. If not... TrikLStart is an easily installed product that will keep the engine batt topped off from the house when they are on float.