House battery charge duration question

[bankerhill]

When off of shore power, how long should the house batteries on my 2017 AI Grand Tour be able to run the refrigerator and freezer if nothing else in the coach is on?

Seems like I get about 10-12 hours now before the batteries drop below the point where the 12 volt system auto shuts down...

Thanks.

[FlyFishinRVr]

Originally Posted by bankerhill

When off of shore power, how long should the house batteries on my 2017 AI Grand Tour be able to run the refrigerator and freezer if nothing else in the coach is on?

Seems like I get about 10-12 hours now before the batteries drop below the point where the 12 volt system auto shuts down...

Thanks.

With full house batteries, mine easily last 10hrs, and that's including running interior lights, water pump, charging up tablets and phones, and even running the Fantastic fan for a few hours. When it's time to break camp and move on, they're usually around 12.2 - 12.3v.

What's your voltage when you unplug/turn off the motor?

[bankerhill]

12 to 12.5 volts is what I have at the point that I unplug, so to speak. Both times this has happened was end the end of a long drive that day to stay in a hotel on the way back from a 3000+ mile trip on the last day. So all that I should expect is 10-12 hours?

[FlyFishinRVr]

Originally Posted by bankerhill

12 to 12.5 volts is what I have at the point that I unplug, so to speak. Both times this has happened was end the end of a long drive that day to stay in a hotel on the way back from a 3000+ mile trip on the last day. So all that I should expect is 10-12 hours?

12 to 12.5v is a huge range. According to the Lifeline spec, that's the difference between 60% Depth of Discharge (DOD) and 30%, respectively.

Let's assume the best and say you're starting at 12.5v. That's already 30% discharged. If you look at my numbers, let's take the worst case and say I end up at 12.2v, which is 50% discharged. If my batteries started where yours did and I take away that 30%, mine would end up at 80% DOD, or around 11.5v, which would be very bad for the long term health of the batteries.

It looks to me like your house batteries are starting the evening already low, and you can thank the combination of the BIM and Atkinson solar controller for that. They aren't letting your batteries get past 12.6v because of how the two operate together (not well). This is a BIG reason why I replaced the Atkinson with a Renogy MPPT controller. The Renogy (or any programmable solar charge controller) will keep the batteries fully topped up (I've set mine to Float charge my house batteries at 13.4v, so as I'm driving if I'm getting any sun at all on my panel it will keep them there) vs. 30% discharged, meaning I can last through the night with no problem.

In the end, given your starting point of 30% (or more) discharged, I'm not surprised your house batteries are dead in 10hrs. You never said if your propane switch was on or if your Fusion was only "sleeping" vs. forced off, and both of those are relatively big current draws (about 1A each, so 20A over 10hrs, or 1/4 of your total battery capacity!) so they will really shorten your battery life as well.

There are two ways to fix this: add more batteries, or replace the bits that are keeping the existing batteries from being fully charged as you drive. Those bits are 1) the solar charge controller, and 2) the Battery Isolation Monitor (aka BIM). I've replaced #1, and will likely replace #2 this winter. I live in California where we get a lot of sun, so #2 is less of an issue for us (meaning I rely a LOT on the solar to keep my batteries fully charged vs. relying on the alternator), but it could definitely be a problem if I was driving in cloudy conditions all day so that's why it's on the list.

I hope that helps.

[bankerhill]

That's great info, Fly. I am traveling with the propane switched to off. How do you force the Fusion system to be totally off?

[uncle_bob]

Hi

A little more information:

Lead acid batteries should only be discharged to the 50% level. At normal temperatures that is about 12.0 to 12.1V. Zero charge is around 10.5V. Full charge is up around 12.7V. All of this is with nothing going on (no charging, no discharging for an hour or so). When charging, the batteries should get up to around 13.7V. Batteries that run down below 12V on a regular basis wear out quickly. They loose capacity and may actually fail.

Throw on top of this the fact that people have reported the built in monitor panels to be inaccurate by significant amounts. If your panel is off by 1/4 V, that is a really big deal. The "correct" voltage is what you get at the battery terminals with a multimeter. It's worth checking once, just so you trust your panels.

Next gotcha is temperature. If it's hot out and the batteries are hot as well, move all the voltages above down about a half volt. If they are cold (as in down towards freezing) move all the voltages up by a half volt.

Charge time is tricky. You get to about 80% charge fairly quickly. Getting to 100% takes longer. Best bet is that 8 to 10 hours will get you to 100% from normal discharge levels. Working this out from voltages is tough. Running a current shunt based setup is much easier.

No, it's not easy ....

Bob

[FlyFishinRVr]

Originally Posted by bankerhill

That's great info, Fly. I am traveling with the propane switched to off. How do you force the Fusion system to be totally off?

Long press of the power icon. This will put it into what I call "sleep 2", which is the best you can do. It will still draw power (how much is a current topic of debate), and the only way to truly cut power to the unit is to install an external switch. There's a thread on this forum where we've kicked around some ideas on the best way to do this, and at least one person has done it with good results.

My current guess is the Fusion is drawing about 500mA/hr, so overnight even when "off" it's still pulling about 5A out of the batteries over a 10hr period. While that's not a lot, as you've seen, every little bit helps (or hurts) when you're off the grid.

[MISGM]

Note: 1st time on forum; so please excuse if I somehow screw up this attempt

I am interested in the detail for switching out the Atkinson and BIM....especially where I have to switch out standard display unit.

BTW I have a 2018 AI GT but that selection is not available yet during registration

[VAtom]

Originally Posted by FlyFishinRVr

There are two ways to fix this: add more batteries, or replace the bits that are keeping the existing batteries from being fully charged as you drive. Those bits are 1) the solar charge controller, and 2) the Battery Isolation Monitor (aka BIM). I've replaced #1, and will likely replace #2 this winter.

Fishin,
I liked your approach to the Renogy and plan on doing your mod this winter.
Have you tracked down a replacement BIM that is superior to the Precision Circuits? I have been unsuccessful.

[Wesair]

I've noticed that the volts registered on the internal control display bounces around depending on what power is being used. i.e. the furnace fan will pull the volts down but they will then increase when the furnace fan turns off. Would a voltmeter at the battery be a better measure? Does a voltmeter at the battery register its overall capacity or would it also vary up and down depending on current use?

[FlyFishinRVr]

Originally Posted by MISGM

Note: 1st time on forum; so please excuse if I somehow screw up this attempt

I am interested in the detail for switching out the Atkinson and BIM....especially where I have to switch out standard display unit.

BTW I have a 2018 AI GT but that selection is not available yet during registration

Welcome to the forums and congrats on the new Interstate!

I have a thread detailing how to swap out the Atkinson for a Renogy MPPT solar charge controller, which you can find here:

http://www.airforums.com/forums/f240...roller+to+mppt

I chose this solar charge controller and remote control panel because it is a "plug and play" replacement for the Atkinson. You do have to get creative with mounting the remote, but it uses the same Cat 5 cable that's already there for the Atkinson.

Re. the BIM swap, I haven't done that yet, but when I do, I'll be using the Blue Sea ML-ACR model 7622. This should allow the house batteries to charge via the alternator much more completely and easily vs. what we get with the BIM. No more arriving at your camping destination with a house bank that's already 20-30% depleted!

With these two changes you should be able to boondock comfortably every night, provided you drive for at least an hour during the day, regardless of the weather. You won't be able to run your A/C or microwave without using the genset because of the limits of your batteries and the inverter, but a few more mods will allow that as well. It's just a matter of time and money.....

[uncle_bob]

Originally Posted by Wesair

I've noticed that the volts registered on the internal control display bounces around depending on what power is being used. i.e. the furnace fan will pull the volts down but they will then increase when the furnace fan turns off. Would a voltmeter at the battery be a better measure? Does a voltmeter at the battery register its overall capacity or would it also vary up and down depending on current use?

Hi

A voltmeter on the battery will give you a better idea, but not a perfect picture. The numbers we talk about for voltage on a battery are for a battery at rest. Charging or discharging the battery stirs things up a bit. It also can warm the battery up. Both of these things impact the voltage.

The real answer is to use a good shunt based integrating current meter monitor. Even that is not perfect, but it's better than a voltage based approach.

Bob

[FlyFishinRVr]

Originally Posted by VAtom

Fishin,
I liked your approach to the Renogy and plan on doing your mod this winter.
Have you tracked down a replacement BIM that is superior to the Precision Circuits? I have been unsuccessful.

See my post above. The Blue Sea ML-ACR model 7622 is what I plan to use.

[amirm]

Side comment: if you ever convert to Lithium, you get a "coulomb counter" that measures how much power has been put into the battery or taken out. This will be your battery gauge. You will no longer worry about battery voltage as a measure of how full it is (and its attendant inaccuracies).

[Sebtown]

I've been using a simple volt meter on my T1N house battery for the last 5 years trying to understand my battery capacity. I finally ordered a shunt based Trimetric 2030RV which arrived today. I am hoping this will allivate some of my battery consumption anxiety.

[rmkrum]

You will find it makes more sense to measure current in and out of battery as well as voltage. More precise view of state of charge

[uncle_bob]

Originally Posted by rmkrum

You will find it makes more sense to measure current in and out of battery as well as voltage. More precise view of state of charge

Hi

.... just be sure that the current shunt is in the right place in the circuit and you get things calibrated properly. It does not matter if it's called an integrating current meter, a coulomb counter or a BMV. They all look at the current over time and try to figure out the battery state. It's still not perfect. Batteries self discharge and they will not catch that. They also change capacity with temperature and I've never seen one that puts this into the % charged math.

Bob

[TayaraTravel]

Prior to our last trip, we doubled (200w) our solar panels; kept the same SunExplorer charge controller. The extra solar helped by going into the evening with more battery charge than before. We found we can stay one full night off grid if we are careful. We conserve power by shutting off the freezer, just running the refrigerator. (Maybe not possible in earlier models of Interstate). We are careful to shut off the LPG switch. With these measures, we typically reached morning with 60% or so still left in the batteries.

[Sebtown]

Hey uncle_bob. Thanks for your imput. I double checked my installation and spent time to properly program the Trimetric. I know it is not a perfect solution but having a guesstimate of battery percentage full is, for me, still better than relying solely on a volt meter. I also like the Trimetric's ability to read amperage and wattage use of my 12volt fixtures and appliances. I'll see how helpful it is on my next outing.

[uncle_bob]

Hi

The real answer to the battery issue is modifying your habits. That's what takes you from dead in a day to off grid for a week. Doing that with "feedback" is a *lot* easier than doing it based on guesswork.

Enjoy !!!

Bob