Stock set up question: will accessories battery also drain main vehicle battery

[trspaulding]

Hi all-- I've got a 2009 E450 shuttle bus that I'm in the process of converting. There are two batteries currently in a side panel battery box. Next to the driver seat there's a battery cut off for all accessories (double door opener, interior lights, wheelchair lift, etc.) It seems fairly obvious that both batteries are charged by the alternator and that would be a standard set up. However, my question is this: when the vehicle is off, if you were to run the accessories to the point of draining the "accessories" battery would it then start draining the "vehicle" battery?

Is there a way to have both charged by an alternator but to have separate power draws? If so, how can I tell if my bus is set up that way?

Thank you!

[trspaulding]

adding a couple of pics of the battery compartment.

[Sehnsucht]

You are better off adding a set of 'house' batteries which can also be charged by the alternator but then run your accessories and convenience loads without risking draining the starter batteries. How these tie into the electrical system is going to depend on if you want a parallel system or manually switched to tie all batteries together (extra starting amps) or you can even get fancy and have an auto-switching setup. As far as separating the two existing batteries, I'm going to go out on a limb and say they likely cannot be split without some sort of setup like what I just described anyways at which point you're chancing if one battery alone can crank the engine.

[trspaulding]

Thanks. So from what you see (and what I think since the batteries are connected) they are not currently separated and use of accessories could drain both batteries?

Sounds like I'm doing a quick solar set up. Trying to get this whole thing turned around in 5 weeks to do a big road trip.......

[BlackJohn]

Battery date appears to be 10/19, is that right?



How many CCA's are they rated at each?


I am sure you would drain both if engine wasn't running much or at all. How long that would take would require some experimenting if you really want to know. A charger would be handy or another vehicle to boost from worst case scenario.
Not a good idea to drain them very low anyway. Re-charging time is valuable time to be doing other things.


Get a pic of your alternator and any wiring on it. Follow the heavier wire. To the battery box or into an isolator?


Just some thoughts for you. Really like the battery box condition.


John

[magnakansas]

Both your batteries are tied together. your switch just kills power to other stuff to keep from draining BOTH batteries. Your system for the bus and bus engine is likely to need to keep both those batteries tied together untill you do the work the eliminate electrical loads.

what you need/want is called a battery isolater. they make a couple of kinds, one you do manually... it is a really big switch. the other is supposed to be automatic.

the alternator is connected to the isolator,

the switch isolator is connected in such a way in position 1 engine batteries are connected, position 2 engine batteries and house batteries are connected position 3 no batteries are connected

the electric isolator has three connection points, one connection for the alternator, one connection for the engine batteries, and a connection for the house batteries. when the alternator is not putting out power the connection between the house and engine batteries is not there. this keeps from taking power from engine batteries when the bus is parked or "off"

there are variations of these systems but this is the basic idea.

william

[CHEESE_WAGON]

Depends on whether the bus is already equipped with an isolator. An isolator is more or less a 'check valve' for electricity to prevent one system from drawing off the other. And yes, it is possible to set up your system with an isolator to allow the alternator to charge all batteries without having 'house' activities drain the main chassis (engine start) batteries.

I'm with MK on this one, my guess would be there is no isolator currently installed, that both batteries are charged by the alternator, but that the accessories can discharge both.

An isolator is pretty much a must when building a skoolie if you want it to start after sitting awhile, at least when you're using it.