10 KWh of Batteries - 126 lbs. Total Weight - Less than 2 CF Volume

[pdavitt]

I have noticed a growing trend, on this site and others, toward higher amp hour lithium battery banks and larger solar arrays. From a weight and size perspective, putting 400-600 (12V) amp hours in a large RV is doable. But, what about smaller RVs or more amp hours? There have also been discussions about the lack, in prime destinations, of available sites with electrical hookups. This lack, is one driver towards longer lasting and more self-sufficient electrical systems.


While designing an electrical system for an Expedition Vehicle, I discovered these batteries when looking for the highest energy density, lowest weight, commercially available products. They are Victron Lithium HE NMC (LiNiMnCoO2) 24V/200AH and only weigh 63 lbs. apiece, which is about half the weight of a similar sized LiFePO4. The dimensions are 14" x 14.25" x 7.5". They also require a Victron Lynx Ion BMS to operate.


I thought with everyone starting to hibernate for the Winter, and the fact that more Lithium based batteries are coming into the market; that it might be an appropriate time to start a discussion about the optimal battery system for a RV. The only two negatives I see with the Victron HE batteries are one, they are not 12V and, two, they require a proprietary Victron BMS. The cost per KWh is comparable to LiFePO4 batteries.


Just to put things into perspective, this battery bank has the same power rating as 800 AH of 12V batteries.


Below are photos of my 48V/200AH battery box and the inside of the BMS:


Look forward to the discussion,
Pat

[dbj216]

Wow, this is going to be interesting for me. I'll be a student as I'm still in the lead acid age along with my fancy rotary telephone and 35mm camera.

I recently read a thread about a lithium based battery pack for a boondocking Airstreamer. Cost to acquire and install was in the $2500 range not counting a couple of solar panels to help keep the batteries charged when the sun shines. I think that's what I read.

I'm guessing the investment in these high tech batteries is spendy. But the energy density is amazing compared to my old lead acid ones. Life is a major consideration too. Spending a couple of thousand every 6 years would be prohibitive for many folks.

We have an "off grid" house being built in our neighborhood. Solar is nice, but... it has limitations. I think pumping water out of our deep well is our biggest electrical energy user. I wonder if the home will have some type of high tech batteries in the basement to keep the place going on cloudy winter days like today, or 12" of snow on the solar panels like last week. The home will likely use propane for a heat source for air and water.

Colorado museums have examples of "miner's log cabins" to look at. A door, a window, a bed, a fireplace, and a table. That's about it. But it is "off grid". No electricity required.

David

[wulfraat]

Yes those are great batteries with a very high storage density / KG.

I chose to use regular Victron lithium 12v batts in my setup as the ones above were 24v, which would have required an additional DC-DC converter for a 12v nominal trailer system. I forget but I think maximum throughput on the victron dc-dc converters was only 20AMPs or so... just barely enough to run the furnace.

My 600ah of 12v lithium weigh in at 225lbs. Technology is advancing rapidly, and in 10-15 years when my current batteries need replacing I can only imagine what the options will be

[pdavitt]

Originally Posted by dbj216

We have an "off grid" house being built in our neighborhood. Solar is nice, but... it has limitations. I think pumping water out of our deep well is our biggest electrical energy user. I wonder if the home will have some type of high tech batteries in the basement to keep the place going on cloudy winter days like today, or 12" of snow on the solar panels like last week. The home will likely use propane for a heat source for air and water.
David

David,


Yes, it is "spendy". The two batteries and BMS were around 10K. In this case, weight and space overrode cost.


I live in a full size, off-grid, solar powered house. At this time I don't think Lithium's are the answer for houses. I have two 48V industrial, traction (fork lift) batteries that store a usable 40Kwh apiece. They are flooded lead acid but are a bit heavy for RV use; they weigh 3,300 lbs. apiece.


Pat

[pdavitt]

Originally Posted by wulfraat

Yes those are great batteries with a very high storage density / KG.

I chose to use regular Victron lithium 12v batts in my setup as the ones above were 24v, which would have required an additional DC-DC converter for a 12v nominal trailer system. I forget but I think maximum throughput on the victron dc-dc converters was only 20AMPs or so... just barely enough to run the furnace.

My 600ah of 12v lithium weigh in at 225lbs. Technology is advancing rapidly, and in 10-15 years when my current batteries need replacing I can only imagine what the options will be

You are correct that energy storage technology is rapidly advancing.


I went totally nuts with my system, I have a 48V/5000VA Victron Quattro Inverter/Charger and the system is AC centric. I use a 50A 120VAC to 12VDC Power Supply for my DC Loads. Below is the schematic for my system.


Pat

[wulfraat]

Yes very nice. I did now think about a 120v->12v converter. I think that makes a lot of sense for an AC centric system.

[pdavitt]

Originally Posted by wulfraat

Yes very nice. I did now think about a 120v->12v converter. I think that makes a lot of sense for an AC centric system.

If you are interested in a detailed description of my system it is contained in two articles I wrote for Truck Camper Adventure magazine. The URLs are below.


http://www.truckcamperadventure.com/...system-part-1/

http://www.truckcamperadventure.com/...system-part-2/


Pat

[mythbuster88]

Originally Posted by pdavitt

You are correct that energy storage technology is rapidly advancing.


I went totally nuts with my system, I have a 48V/5000VA Victron Quattro Inverter/Charger and the system is AC centric. I use a 50A 120VAC to 12VDC Power Supply for my DC Loads. Below is the schematic for my system.


Pat

How you draw that schematic?

[pdavitt]

Originally Posted by mythbuster88

How you draw that schematic?

I used Microsoft Visio. It's easier to learn than Autocad, and a lot cheaper.
Pat

[aswell]

Originally Posted by pdavitt

David,


Yes, it is "spendy". The two batteries and BMS were around 10K. In this case, weight and space overrode cost.


I live in a full size, off-grid, solar powered house. At this time I don't think Lithium's are the answer for houses. I have two 48V industrial, traction (fork lift) batteries that store a usable 40Kwh apiece. They are flooded lead acid but are a bit heavy for RV use; they weigh 3,300 lbs. apiece.


Pat

Read your two "Mad Scientist" articles, and bookmarked for future reference. A lot of work, and a lot of good reference material. As a former low-voltage systems designer (home/office automation), I know enough to know that you know your stuff. Thanks for sharing your experience...

So, I am curious about the statement above, "At this time I don't think Lithium's are the answer for houses." Is that view based primarily on cost per Kwh as compared to older battery technologies?

[pdavitt]

Originally Posted by aswell

So, I am curious about the statement above, "At this time I don't think Lithium's are the answer for houses." Is that view based primarily on cost per Kwh as compared to older battery technologies?

Yes, it's a matter of economics, especially with off-grid systems. When weight and space are not a consideration, Lithium's loose out economically.


My home system is 6+ years old and the specific gravity of the electrolyte is still within new battery specs. Takes monthly maintenance but it is worth it.


Pat

[guskmg]

My system that lewster designed a few years ago is serving me well. 800 watts on the roof and 600 AH Lithium batteries. It sure is nice to spend a 4 day week end off grid with all the conveniences. The compost toilet with urine plumbed into the black tank is a real plus. Now all I have to do is remember to drain the combined tanks. Also, on my trailer I eliminated 4 lead acid batteries up front and put the Lithiums under the rear bed. That really improved the tongue weight situation with the Hensley hitch.
guskmg

[pdavitt]

Originally Posted by guskmg

My system that lewster designed a few years ago is serving me well. 800 watts on the roof and 600 AH Lithium batteries. It sure is nice to spend a 4 day week end off grid with all the conveniences. The compost toilet with urine plumbed into the black tank is a real plus. Now all I have to do is remember to drain the combined tanks. Also, on my trailer I eliminated 4 lead acid batteries up front and put the Lithiums under the rear bed. That really improved the tongue weight situation with the Hensley hitch.
guskmg

Lew does great work and if I was looking for a retrofit of an existing RV that's who I would go to. I'm looking beyond the existing towards the future. I believe 48V Systems will become the norm as we go forward.
Pat

[switz]

Our 600 amp hour 12Vdc Lithium battery weighs in at 168 pounds. We feed it sun energy from nine 100 watt panels on the roof of our 31' Classic. We have a 300 amp hour lithium at 84 pounds in front of the street side wheel well under the sofa on our 23D. Is is about the same form factor of the two original lead acid batteries and weighs about 8 pounds less. We feed it with five 100 watt solar panels on the 23D roof.

[pdavitt]

Originally Posted by switz

Our 600 amp hour 12Vdc Lithium battery weighs in at 168 pounds. We feed it sun energy from nine 100 watt panels on the roof of our 31' Classic. We have a 300 amp hour lithium at 84 pounds in front of the street side wheel well under the sofa on our 23D. Is is about the same form factor of the two original lead acid batteries and weighs about 8 pounds less. We feed it with five 100 watt solar panels on the 23D roof.

Sounds like you are into this stuff big time. That is quite a setup on both trailers. I would submit that you have about reached the practical limits of a 12V battery system on your 31 Classic. The wire, fuses and/or circuit breakers must be quite large or doubled up. Would love to see a schematic.


The system I designed is going in a 10' Cab-over, flatbed truck camper. Going to be interesting.


Pat

[pdavitt]

Come on guys. What do you think?


Pat

[wulfraat]

I think it will be a long long while before the US RV industry moves away from 12v systems... but again, for your application (mostly inverted 120v usage) your setup is perfect and ideal.

[pdavitt]

Originally Posted by wulfraat

I think it will be a long long while before the US RV industry moves away from 12v systems... but again, for your application (mostly inverted 120v usage) your setup is perfect and ideal.

Thanks.


For Airstreams and smaller RVs, I agree, but not for the reason you might think. The issue is not the batteries, but getting enough solar charging capability on the roof to support the more powerful batteries. I was able to fit 1400 watts of solar on top of a 10' cab-over truck camper. Mainly because it had a 7.5' x 14' basically flat roof and a non roof mounted AC. I calculated it would take about 1,200 watts of panels to properly charge the 10Kwh of batteries.


The reason I mentioned Airstream above is because of the aerodynamic shape, especially all the roof curves and the multiplicity of roof mounted devices. The Airstream design is iconic and I don't see them changing it to put a bunch of solar panels to the roof.


I just noticed something funny. The spell checker on Air Forums doesn't think "Airstream" is a correctly spelled word.



Pat

[rmkrum]

Originally Posted by pdavitt

Thanks.
-------------------snip---------------
I just noticed something funny. The spell checker on Air Forums doesn't think "Airstream" is a correctly spelled word.

Pat

Slight thread misdirect: Actually the spell checker that complains is usually on your local device. Both my iPhone and PC complained until I added the word to the local dictionary, and the iPhone finally learned it...

[pdavitt]

Rich,


Thanks for the heads-up. I am a retired Systems Architect/Engineer; just goes to show that knowing a lot about big things leaves something to be desired.


Pat