Adding a 3rd Lithium battery

AJMike · 02-16-2021, 07:32 AM

I currently have 2 Battle Born Lithium batteries in our 2018 Winnebago Fuse and have been thinking about adding a 3rd battery. The two batteries generally are more than enough and I have never found myself lower than about 55-60% SOC in the morning when we are dry camping but have been thinking about being able to run the roof AC for a short time in the middle of the day, and I don't think that 200 AH is really enough for that.

The problem, of course, is that there is no room in the battery tray for a 3rd and I would have to add it separated from the other two or, alternately, find a location where all 3 could be mounted together. BB told me that there might be a balance problem if a 3rd battery is mounted separately from the other 2 but I have to admit that I have no idea what a "balance problem" really is, how serious it might be or what its affects might be. The installer that BB recommended is all for adding the 3rd battery, but then he sells them as well as installs them so he is probably not the best person to ask.

Hopefully someone here can give me some information. This is completely optional - I can do what I do now and run the generator - but my wife really does not like the noise and smell of the generator and if I could find a reasonable way to avoid it for an hour run, then it might be worth the time and trouble. We are almost always dry camping/boondocking so any neighbors we have are usually far enough away that they don't hear the generator but it would also be nice to be able to not use the gen if anyone is close enough to hear it.

I realize it would mean that I would still end up having to add that charge back up, but if necessary I generally do that by running the generator when we go for our late after walk so neither of us has to listen to it and, as I mentioned, we almost always boondock so the neighbors are far enough away that they don't have to listen to the generator either.

Any information would be appreciated.

DavidM · 02-16-2021, 09:20 AM

I suspect that the balance problem that BB is alluding to is due to voltage drop from the third battery to the other two. You can minimize this by using big cable to connect the third one- either 2/0 or 3/0 cable.

But say you used all of the power in the third battery to run the AC- 100 amp hours. 100 amp hours is about 1,200 watts. Your AC probably draws 12 amps at 120V or 1,440 watts. Ignoring inverter efficiency losses, you can only run your AC for about 50 minutes. Doesn't sound worth it to me.

David

Winterbagoal · 02-16-2021, 09:41 AM

Alternately, and as some others have done, and along the lines of David's comments, if you could downsize the A/C draw by going to a lighter draw air conditioner, with less cooling capability, you might get a bit longer use from a 3 battery bank. I have no idea on the how part of this, but I'm sure I've seen 5,000 BTU A/C units used to mitigate the power drain on their battery use. They just don't get the motorhomes frosty, but maybe they could be made more comfortable for short periods?

AJMike · 02-16-2021, 10:01 AM

Quote:

Originally Posted by DavidM

I suspect that the balance problem that BB is alluding to is due to voltage drop from the third battery to the other two. You can minimize this by using big cable to connect the third one- either 2/0 or 3/0 cable.

But say you used all of the power in the third battery to run the AC- 100 amp hours. 100 amp hours is about 1,200 watts. Your AC probably draws 12 amps at 120V or 1,440 watts. Ignoring inverter efficiency losses, you can only run your AC for about 50 minutes. Doesn't sound worth it to me.

David

Well, of course, I would be drawing power from all 3 batteries for the AC, not just the one, and I assumed I could get 90 minutes of AC that way. I am not sure that that is worth the cost either, and it is only a thought at the moment, but I did want to get some information about what "unbalanced" meant and whether or not it was serious.

I have to admit that all of this came about after reading about the new EKKO. The Lichtsinn video said that they were able to run the AC in one of their Class Bs (I think it was the Bolt, but I am not sure) for about 6 1/2 hours on one 315 AH battery before it went dead. There are several issues with that figure for me - first, the Iowa temperatures are not the Arizona summer temperatures, second the interior space to cool with a B is smaller than with our Fuse and third I would not want the battery to go complete dead, but still it did make me think that I might get 90 minutes from such a setup and that might be something to consider.

There is also the issue of having to put that power back into the batteries. In the summer my 400 watts of solar should be enough on a clear day to recharge the 200 AH batteries back to full, but would not do that if I ran the AC for 90 minutes and I would have to get a 2000 watt inverter installed and rewired and somehow get the power to the AC. A lot of "ifs" and "have tos" to consider.

AJMike · 02-16-2021, 10:12 AM

Quote:

Originally Posted by Winterbagoal

Alternately, and as some others have done, and along the lines of David's comments, if you could downsize the A/C draw by going to a lighter draw air conditioner, with less cooling capability, you might get a bit longer use from a 3 battery bank. I have no idea on the how part of this, but I'm sure I've seen 5,000 BTU A/C units used to mitigate the power drain on their battery use. They just don't get the motorhomes frosty, but maybe they could be made more comfortable for short periods?

We never stay here in the southern Arizona heat in the summer, but even in the mountains it is hot enough in July and August to need a lot of cooling to make the interior livable. The current 13,500 BTU unit is not enough to make the inside of the Fuse more than bearable so I don't know what a 5,000 BTU unit might do.

One of the annoying things is that the new EKKO not only has 315 AH in its basic configuration but allows for a second 315 AH battery, uses a stronger AC unit that they have somehow configured to use less electricity and they have 2" of insulation all around. They advertise that you can stay warm in the snow but if it can keep you warm in the snow it can also keep you cool in the heat so it is very appealing. Added to that you can eliminate the generator and get 3 315 AH batteries and that would allow you to run the AC all night, although it would be a job getting the batteries charged the next day.

All of this just got me thinking that perhaps there is something I can do with our Fuse to make it more useful in the summer. At the moment it is all a "what if" kind of project, and the cost would be considerable since it would involve a 3rd battery, a 2000 watt inverter, the re-wiring for the inverter and a soft-start for the AC, and I probably have better things to do with that money. On the other hand we are not getting any younger and perhaps it is foolish to be too thrifty at our age, and whatever it costs would be less than buying a new EKKO.

Don't know.

misteracng · 02-16-2021, 12:10 PM

I think the AC would need around 150AH to run it for an hour straight, but then you might not have enough juice to get through the night, necessitating starting the generator which you are trying to avoid. It seems to be a big project. I think to do this, would really involve moving the entire bank of batteries so they can be together. Some place you could put say 2x 315AH batteries. Also I think you would need an easy start or something to get the AC started, but it can be done. If you have a 2000W inverter, you could install an easy start first and then just see if 2 batteries will meet your needs for a short amount of AC. Perhaps it will not run continuous and you could get a bit more time. Since I think you would need an easy start no matter what, it would not be a waste to install. Then go for a bigger battery solution if needed. I think something like 600AH would be needed to really use the AC for overnight of something.

AJMike · 02-16-2021, 12:27 PM

Based on the responses I am beginning to think that this is just not practical. I believe I could add one more 100 AH battery in the compartment under the dining room bench, but the DC-DC charger is there and there would not be room to add a second battery there without moving the charger.

If I made room for a second battery in that location I have no idea where I could put the charger as it is too hot outside the RV for it to run in the summer and so adding even more batteries would just be increasingly impossible.

If I wanted to use one or more of the much larger batteries, like the Lithionics 315 AH battery, I would have to use the outside storage compartment which would then leave me with no space for our "stuff".

All in all perhaps it is just easier to use the generator for the AC and live with the noise and smell since at least that works and there is no added cost for new parts.

Thank you all for the responses and the good information as it helped me sort out the difficulties in what I was thinking about and saved me what would surely have been a lot of trouble for nothing.

al1florida · 02-17-2021, 12:11 PM

I am not completely sure a 2000 watt inverter will start and run a 13,500 BTU AC. It may or may not. The starting current is probably the big issue. The people I have seen that actually DO run an air conditioner for a few hours have at least a 3000 watt inverter and 600AH or more of battery.

I believe you would find that a 13,500 BTU AC will pull about 10 amps, 1200 watts or about 100amp of 12V DC while running.

So running for 90 minutes would consume around 150AH of battery.

Be sure to ventilate the inverter well in hot weather, it will be generating quite a bit of heat supporting the air conditioner.

As I think you have already written, this may not be a practical project.

Back to the "balance" issue. The longer cable length from the 3rd battery to the first 2 batteries will have some amount of voltage drop. This means you will have an imbalance in the voltages between the 3 batteries.

If your current batteries have #2 or #1 cable between them, and your 3rd battery is only about 2-4 feet away, installing 2/0 or 3/0 cable from the 3rd battery may solve the voltage drop problem.

AJMike · 02-17-2021, 02:23 PM

Quote:

Originally Posted by al1florida

I am not completely sure a 2000 watt inverter will start and run a 13,500 BTU AC. It may or may not. The starting current is probably the big issue. The people I have seen that actually DO run an air conditioner for a few hours have at least a 3000 watt inverter and 600AH or more of battery.

I would think that a 2000 watt inverter would run the AC, but would have a problem with the starting current, so I assumed I would need to install a soft-start or some other mechanism to decrease the startup current. That, I think, would do it.

Quote:

Originally Posted by al1florida

I believe you would find that a 13,500 BTU AC will pull about 10 amps, 1200 watts or about 100amp of 12V DC while running.

So running for 90 minutes would consume around 150AH of battery.

Yes, but that would be long enough. On the other hand I would then be faced with the issue of recharging enough to supply that 150 AH or so. For that I would run the generator, but not while we were in the RV. Most evenings we take a 30 or more minute walk and that was when I was thinking I would run the generator.

Quote:

Originally Posted by al1florida

As I think you have already written, this may not be a practical project.

Yes. I have given up on this project as just being too difficult and too much trouble for the minor savings of not running the generator while we were in the RV.

And I have to admit that all of this thought project came about because I had reviewed the ability of the new Winnebago EKKO to run the AC without having a generator. 945 AH of Lithium battery with a special low power AC, a 2000 watt inverter and a soft-start already installed for the AC (I think. The sales guy was not sure about that, but said the RV could run the AC on the generator, as did the tech at Lichtsinn). All of that made me wonder if I could do the same with our Fuse. I guess the answer is "probably not".

Quote:

Originally Posted by al1florida

Back to the "balance" issue. The longer cable length from the 3rd battery to the first 2 batteries will have some amount of voltage drop. This means you will have an imbalance in the voltages between the 3 batteries.

If your current batteries have #2 or #1 cable between them, and your 3rd battery is only about 2-4 feet away, installing 2/0 or 3/0 cable from the 3rd battery may solve the voltage drop problem.

Maybe, but if I am not going to try to run the AC there is probably no reason for me to add a third battery. As it is we have more than half of the SOC left in the morning, we generally can completely recharge or come close with solar and never actually dry camp/boondock in one location for more than 2 days, so even if it is cloudy we would fully recharge when going to our next location.

And the cost of doing this would have been substantial - $1000 for another battery, $600 for a 2000 watt inverter, $250 for a soft-start and perhaps $500-$1000 for the rewiring and install. That is well over $2000 for not having to listen to the generator for about an hour on some days, and I suspect I can find something better to do with that money.

AJMike · 02-17-2021, 02:42 PM

By the way, exactly what would be the issue caused by the batteries being unbalanced? How would it show itself? Would the batteries not all charge properly? Or would one be at a lower SOC than the others? What would happen if the batteries were not "balanced"?

al1florida · 02-17-2021, 03:21 PM

Quote:

Originally Posted by AJMike

By the way, exactly what would be the issue caused by the batteries being unbalanced? How would it show itself? Would the batteries not all charge properly? Or would one be at a lower SOC than the others? What would happen if the batteries were not "balanced"?

Going from memory, as it has been a few years since I have read about exactly what happens when one battery in a group has a lower voltage that the others.

I believe the battery with low voltage tends to draw down the voltage from the higher voltage batteries. The higher voltage batteries send some of their power to the low voltage battery.

What complicates the RV situation is the lower voltage from the battery on the longer cables is only evident while under a heavy load. The voltage drop is only there under a load. With just a few amps of current flow the voltage won't be noticeable.

AJMike · 02-17-2021, 03:46 PM

Quote:

Originally Posted by al1florida

Going from memory, as it has been a few years since I have read about exactly what happens when one battery in a group has a lower voltage that the others.

I believe the battery with low voltage tends to draw down the voltage from the higher voltage batteries. The higher voltage batteries send some of their power to the low voltage battery.

What complicates the RV situation is the lower voltage from the battery on the longer cables is only evident while under a heavy load. The voltage drop is only there under a load. With just a few amps of current flow the voltage won't be noticeable.

Oh, I see. Then the lower voltage due to the voltage drop would result in a higher current (because of Ohm's Law) and thus would drain the batteries more quickly than otherwise. And, if the voltage drop was relatively large, it might damage the equipment being run as well.

I guess that makes sense.

al1florida · 02-17-2021, 04:15 PM

Here is a link to info about mismatched lithium batteries and their loss of capacity.

https://batteryuniversity.com/learn/...atch_balancing

The article references capacity, not a voltage imbalance while under load.

Marine359 · 02-18-2021, 08:40 AM

Distance between batteries shouldn’t matter as long as your connecting cables are the same length, same material, and same diameter. Voltage drop from one to the next will be the same. 1/0 wire doesn’t cost much more than 2 or 3 gauge if you custom order with ring terminals. May be easiest to connect batteries to covered bus bars.

al1florida · 02-18-2021, 09:07 AM

Quote:

Originally Posted by Marine359

Distance between batteries shouldn’t matter as long as your connecting cables are the same length, same material, and same diameter. Voltage drop from one to the next will be the same. 1/0 wire doesn’t cost much more than 2 or 3 gauge if you custom order with ring terminals. May be easiest to connect batteries to covered bus bars.

Do you mean to say that if the 3rd or more batteries have to be located 4 feet away that you should then lengthen the battery cables that are on the original batteries to the same length as the cables for the new batteries?

I would think you would have to do that if you wanted to keep all the cables the same length.

**creativepart** · 02-18-2021, 09:11 AM

As the RV AC world exists today it’s pretty much required to plug into shore power or a generator to run the AC.

You will find a few that have made this a goal and spent the money to make it realistic for a few hours. So, it’s not impossible.

The reality is with the smaller Fuse motorhome you have space limitations that probably make this impractical.

As more and more people RV and like to camp off grid this could change in the next 5 yrs or less. The new WBGO Ekko has both a more power efficient AC unit and standard lithium batteries and inverter to allow limited AC usage on battery. Optionally the Ekko can have over 600 aH of lithium batteries to make it even more practical.

Marine359 · 02-18-2021, 09:16 AM

4ft is a lot and may not make sense unless you can split the difference and mount a bus bar halfway between the two batts and the one batt. You might find that 2.5ft 1/0 cuts your voltage drop. Sorry, I didn’t use the calculator, but you can by going to: https://www.calculator.net/voltage-drop-calculator.html

al1florida · 02-18-2021, 09:50 AM

Quote:

Originally Posted by Marine359

4ft is a lot and may not make sense unless you can split the difference and mount a bus bar halfway between the two batts and the one batt. You might find that 2.5ft 1/0 cuts your voltage drop. Sorry, I didn’t use the calculator, but you can by going to: https://www.calculator.net/voltage-drop-calculator.html

Excellent solution to matching the cable lengths.

DavidM · 02-18-2021, 09:55 AM

"The new WBGO Ekko has both a more power efficient AC unit...."

Anyone know which make and model A/C unit is in the EKKO?

David

**creativepart** · 02-18-2021, 10:02 AM

Check out The Fit RV YouTube channel. They are WBGO sponsored and are one of the first to get an Ekko. They have done a number of lengthy videos on the model. As I remember they said it’s ducted and more efficient but also less cooling power since the Ekko is a very small Class C. The smaller Ekko has no slide and is a Class C that’s B+ sized.