Electrical System What Works When?

[Ron_CA]

Been looking at class B and have our minds set on an Airstream Interstate. Being new to the RV world I am finding all the switches and which systems work when a little confusing. Also concerning are the posts about battery drain etc.

To make matters worse, the salespeople don't know either. Can anyone help here?

[Protagonist]

Originally Posted by Ron_CA

Been looking at class B and have our minds set on an Airstream Interstate. Being new to the RV world I am finding all the switches and which systems work when a little confusing. Also concerning are the posts about battery drain etc.

To make matters worse, the salespeople don't know either. Can anyone help here?

Welcome to the Airforums! Glad to have you with us.

I've owned my Interstate for slightly over two years, and one thing that has become very apparent is, Airstream Interstates change more from one model year to the next than do most other Airstream models. What's true for my 2012 isn't necessarily true for a 2013, and certainly isn't true for a 2014.

But in general (and simplified as much as I can make it):
You have a chassis battery under the driver's footwell, a Group 49 AGM starting battery. You may or may not have an auxiliary battery under the hood, also a Group 49. The chassis system works everything in the dashboard, plus the retractable step by the sliding door, and the awning.

All other electrical users are powered by the house batteries, typically two Group 24 AGM deep-cycle batteries at the rear of the coach.

You'll also have a 30-amp 120vAC shore-power connection on the driver's side rear quarter panel, and a 20-amp 120vAC propane-fueled generator tucked up underneath between the rear axle and the spare tire.

You may or may not have a 50-amp solar panel on the roof which can trickle-charge the house batteries.

The house batteries and chassis battery are interconnected by means of a Battery Isolation Module (BIM), a relay that allows the two systems to both charge from a single source, but which isolates the two systems when no charging is happening to keep a drain on one system from drawing down the other. That way, if you deplete your house batteries, your chassis battery still has enough juice to start the engine.

There is also an inverter/charger that charges the house batteries (and chassis battery when the BIM allows it) in charger mode when you have shore power connected or the generator is running, OR makes 120vAC power from the 12vDC house batteries when there is no other 120vAC source active, but not both at once.

There is one main disconnect switch that kills 12vDC power from the house batteries. There may be a remote disconnect switch as well that does the same thing from an easier-to-reach location.

Under the dashboard, there is a plug that allows you to disconnect the chassis battery for when you store the Interstate; it's a standard fitting on all Sprinters.

There are 120vAC circuit breakers to shut off AC power.

All other switches throughout the coach are for individual appliances and fixtures, and should be relatively self-explanatory. Airstream only started labeling them for the 2013 model year, though; otherwise you'd have to apply your own labels or memorize them. There aren't that many, though, so memorization shouldn't be too hard.

As for what works when, retractable step retracts when you start the engine, whether you want it to retract or not. It's a safety feature to keep you from driving away with the step extended.

Microwave and rooftop air conditioner only work when you have shore power or generator running. They don't work on the inverter. All the other 120vAC electrical will operate off the inverter, but that's mostly just the televisions and whatever you plug into the wall outlets.

The refrigerator is dual 120vAC and 12vDC. If there is any AC source at all (shore power, generator, inverter) it will default to 120vAC mode. Otherwise it works in 12vDC mode.

Al interior lights, rooftop fan, and bathroom extractor fan are 12vDC, and work when the house battery disconnect is switched on.

Water heater is dual-mode 12vDC and propane-fueled. But it uses spark ignition, not a pilot light, so if 12vDC is off, it doesn't work in propane mode either.

Furnace is 12vDC for the fan, and propane for the heat. Furnace and rooftop AC share the same thermostat, which is 12vDC, so you've got to have both 12vDC and 120vAC to run the air conditioner.

Tank heaters are 12vDC, but don't try to run them off the batteries; they're energy hogs and will drain your batteries in less than 4 hours. Only use the tank heaters if you have shore power or generator running.

Macerator pump is 12vDC and runs off the house system.

[weirdstuff]

Need to find that thread that I'd started a couple months ago, because someone had made a whole chart explaining some of this. Let me see if I can find it....Yes, here it is. David Wile did it. I hope this was the latest version of it.

[73shark]

Don't recall if the chart shows it but the 120 VAC outlet by the rear lounge and the one over the galley are only active when you are on shore power or generator power.

[Protagonist]

Originally Posted by 73shark

Don't recall if the chart shows it but the 120 VAC outlet by the rear lounge and the one over the galley are only active when you are on shore power or generator power.

Knew I missed something…

[Ron_CA]

Thanks everybody. In the middle of work will digest this info later.

[rent]

First of all, hats off to Protagonist for yet another in-depth, but clear explanation of the electrical system.

Secondly, I am a software engineer and consider myself at least above average when it comes to electrical and mechanical matters. However, after lurking here for a few weeks and going thru many posts, I must say, the electrical system seems overly complex.

I wish Apple makes an RV. :-)

Of course, then it would have a completed sealed-off hood, non-replaceable batteries (probably secured by glue), and cost $500,000. But it would mostly "just works" with a reboot taking care of things every now and then...

Sorry, I digress. Anyway, again thanks for the clear explanation.

-alex

[Ron_CA]

Wow, thanks Protag that is quite an explanation and very helpful.

Weirdstuff and 73shark thank you.

[73shark]

Originally Posted by rent

First of all, hats off to Protagonist for yet another in-depth, but clear explanation of the electrical system.

Secondly, I am a software engineer and consider myself at least above average when it comes to electrical and mechanical matters. However, after lurking here for a few weeks and going thru many posts, I must say, the electrical system seems overly complex.

I wish Apple makes an RV. :-)

Of course, then it would have a completed sealed-off hood, non-replaceable batteries (probably secured by glue), and cost $500,000. But it would mostly "just works" with a reboot taking care of things every now and then...

Sorry, I digress. Anyway, again thanks for the clear explanation.

-alex

And you'd have to camp out in line to buy a new one every two years. And there would be no discounts either.

[K9CarCrate]

Permanent subscribe! Thank you Protagonist!

One question, the tank heaters are battery draws, but I was under the impression that it is OK to run the tank heaters while underway driving?

[73shark]

Should be OK as the alternator should keep the house batteries charged..

[K9CarCrate]

73Shark,
Thanks, I'll be putting it to the test this Saturday.

[Ron_CA]

What do you think is the primary reason for the numerous chassis and house battery discharges?

[Protagonist]

Originally Posted by Ron_CA

What do you think is the primary reason for the numerous chassis and house battery discharges?

There are certain components that are always powered up, even when you shut off the house batteries at the main disconnect. Parasitic drains, they're collectively called.

Example: Your inverter/charger might stay on even when the batteries are shut off. Even if you have all of the breakers shut off as well, the inverter/charger still has to power its internal circuits such as the cooling fan.

Ditto for the Battery Isolation Module, which has to be powered up to monitor the charge state on the house and chassis systems and decide whether to connect or disconnect the two.

There may be other parastic drains as well; it depends on which equipment is installed in which model year. Dedicated experimentation will allow you to track down most of them, but even when you know what they all are for your particular unit, you may not be able to do anything about it.

[c21]

Actually, I think the AI has a pretty decent electrical system. 1. The batteries will charge from all 4 sources and 2. they include the BIM which is something many coaches don't include. On my last two rv's I had to install an after-market Trickle-Start so my chassis battery would charge from shore power. Not a problem with the AI. The only change I've made to mine (electrically) is to add an interior propane switch and purchase a portable surge supressor. Happy with mine. :-)

[UKDUDE]

Originally Posted by Ron_CA

What do you think is the primary reason for the numerous chassis and house battery discharges?

Boxster1971 ran some tests last month and determined most of the unwanted draw comes from the Precision Circuits Inc. Battery Isolation Manager (BIM).
See the thread here:

http://www.airforums.com/forums/f240...ml#post1406721

Peter

[Boxster1971]

I agree that AI has a good electrical system. More solar would be an improvement.

Only one with better electrics in my view is the new Roadtrek E-Trek.

[bennu36]

In my 2012 there is a .3 amp drain with everything I can turn off set to off, including the AC main breaker. This is according to my battery monitor I got from the fin folks at AM Solar in Springfield Or. Tri-Metric 2025-RV and wiring harness about $255.00 and well worth it. That drain can drop to about .1 amp from the feed from the 50 watt solar panel on the roof with even a small amount of sunlight. I my opinion if you are going to spend any time at all away from shore power you really need one of these. BTW next week (March 4th) I am having the guys at am solar put tow 105 watt panels and a new controller in I will let you know how that turns out.

[DavisBurns]

We have a 2004 Interstate. We've had some, that is lots of electrical,issues. We installed a Trimetric meter so we know how much power we are using and the battery charge state. All was working fine last trip. While driving, the fridge showed it was drawing half an amp. But we noticed the chassis battery wasn't charging while we were driving. We replaced the BIS relay and a fuse. Now for reasons we cannot figure out the meter shows we are using 2.4 amps ALL the time. We have the main switch turned off. We took out the tv we never use. We took out the radio thinking the precious owner had it wired wrong--but of course that couldn't be the case, since all was well before. We are stumped. We have a front lounge model with twin beds. All the electrical is in the entertainment center behind the driver's seat. We took the top and the mid shelf off so,we could get to electrical stuff screwed to the back of the cabinet-- really stupid place to put stuff you might need to get too. Stumped, flumoxed. Really when the main switch is off, nothing should draw power. Ideas?

[Boxster1971]

Originally Posted by DavisBurns

We have a 2004 Interstate. We've had some, that is lots of electrical,issues. We installed a Trimetric meter so we know how much power we are using and the battery charge state. All was working fine last trip. While driving, the fridge showed it was drawing half an amp. But we noticed the chassis battery wasn't charging while we were driving. We replaced the BIS relay and a fuse. Now for reasons we cannot figure out the meter shows we are using 2.4 amps ALL the time. We have the main switch turned off. We took out the tv we never use. We took out the radio thinking the precious owner had it wired wrong--but of course that couldn't be the case, since all was well before. We are stumped. We have a front lounge model with twin beds. All the electrical is in the entertainment center behind the driver's seat. We took the top and the mid shelf off so,we could get to electrical stuff screwed to the back of the cabinet-- really stupid place to put stuff you might need to get too. Stumped, flumoxed. Really when the main switch is off, nothing should draw power. Ideas?

Unfortunately lots of things are still powered with main switch off. The parasitic load on my 2013 is about 0.4 amps all the time. Your 2.4 sounds very high. Are you sure your Trimetric is properly set for zero current?