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Old 02-17-2019, 01:08 AM   #1
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Question How is this for a power system? Solar vs battery balance?

How is this for a power system? Solar vs battery balance?

Hi all

Have owned a couple RVs, and now designing (with Hallmark) a 9.5’ Everest pop up truck camper.

How is this for the balance of 200 watts of solar and 200 amp hours of (probably Lithium) batteries?

I’m aware that the Lithium are very expensive, but they can be run down to 90% depleted without any damage….. plus they last many times longer than wet cells, so in the really long run, probably (hopefully) no more expensive. The Battleborn batteries (likely get these) have a built in battery management system that makes sure the battery can be used (or discharged) at temperatures as low as -4°F. However, the battery will not accept a charge below 25°F. The BMS also makes sure they dont over charge or under charge.

Planned system:

Propane for stove…. and Truma Combi. (hot water and air.)
(of course 12v needed to run the Truma Combi too)

7.2 CU side by side. 2 way compressor. Novacool RFS7501 fridge.

Maxx fan.

Interior LED lights.

Solar System: 2 X 100 Watt Soft Panels on roof.

Xantrex 817-2080 Freedom XC 2000, 2000 Watt Pure Sine Wave 12 Volt Inverter/Charger

Victron BMV 712 Battery Monitor w/ Bluetooth Lifepo4 Ready

2 (two) x Battleborn 100 amp hour (each) Lithium

Other occasional loads:
Small microwave. Blender. computer maybe.

We camp 4 seasons…. sometimes below freezing. Sometimes higher altitudes. Sometimes in cloudy Pacific NorthWest. So the ability to discharge the Lithuim 90% with smaller bulk and weight has advantages.

We mostly boondock. We prefer the quiet.
Occasionally we stay someplace for 2 nights, but often drive around a bit, to explore, each day (so the F350 would also help charge up the batteries)

Thanks for any and all thoughts.

J.
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Old 02-17-2019, 10:17 AM   #2
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Given your intended usage, I suspect that 200W on the roof won’t be enough, at least in some locations and during some parts of the year. Batteries sound interesting, but not sure that double the usable capacity of a standard dual 6 setup will be sufficient to overcome this. Have you done the math to add up actual planned amps of usage vs realistic input from intended panels? Jon Vermilye’s input on this would be valuable for you. I’d love to see you pull together a system that works as you want. Best regards, S
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Old 02-17-2019, 10:56 AM   #3
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I just reviewed the Battle Born Battery website. Those are some expensive batteries, close to a grand each. I am not sure you could recover the cost of those puppies.

I was also surprised that they only offer 12 volt batteries. These sound more useful as a house battery on a motor home or a trolling motor. The AGM manufacturers offer six volt. Does the fact that you can fully drain the battery mean you only need one?

The AGM can be discharged to 80% and has a very fast charge rate. Not sure of the charge rate on LiFePO4. An AGM can be found for as little as $370 for a pair, a long life span on a LiFePO4 would have to be triple in duration.
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Old 02-17-2019, 11:05 AM   #4
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Originally Posted by fudge_brownie View Post
I just reviewed the Battle Born Battery website. Those are some expensive batteries, close to a grand each. I am not sure you could recover the cost of those puppies.

I was also surprised that they only offer 12 volt batteries. These sound more useful as a house battery on a motor home or a trolling motor. The AGM manufacturers offer six volt. Does the fact that you can fully drain the battery mean you only need one?

The AGM can be discharged to 80% and has a very fast charge rate. Not sure of the charge rate on LiFePO4. An AGM can be found for as little as $370 for a pair, a long life span on a LiFePO4 would have to be triple in duration.
The fact that you can pretty much fully drain Lithium batteries, time and time again, means that if you are camping and it is very cold at night, and the furnace really drains the batteries by running much of the night.... if you wake up to really drained batteries... you dont need to replace them. AGMs or other regular batteries will likely be damaged, and will have their lifespan really shortened.

Supposedly Lithium last 5 to 10 times longer than AGM... plus are smaller and weigh less than similar capacity of AGM or similar.

That is one of the big advantages of Lithium... you just dont need to worry about them at all. That would be really nice.

Yes they come at a price premium but the science indicates that they'll last a long, long time. (of course time will tell more)
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Old 02-17-2019, 11:21 AM   #5
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Trojan is a terrific resource for battery and maintenance information. I only became aware recently that they have a line of lithium deep cycle batteries.
https://www.trojanbattery.com/trilli...hoCA3QQAvD_BwE
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Old 02-17-2019, 01:01 PM   #6
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Originally Posted by gbaglo View Post
Trojan is a terrific resource for battery and maintenance information. I only became aware recently that they have a line of lithium deep cycle batteries.
https://www.trojanbattery.com/trilli...hoCA3QQAvD_BwE
cool! I did not know that these new models existed from Trojan.

https://www.solarpowerworldonline.co...-battery-line/

just a bit more than Battleborn, about $1,000 Trojan vs about $900 for the (i think) similar one from Battleborn.... Trojan may well be worth the extra $.

J.
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Old 02-17-2019, 02:40 PM   #7
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The small size of these RV-market lithium batteries is annoying for applications where more than about 80 amp-hours @ 12V of usable capacity is desired. They are so light that they could be made in a package the size of two GC-2 lead-acid batteries, without being too heavy to lift. The other obvious option would be the classic configuration of two "6-volt" modules in series; LFP batteries for nominally 12-volt applications have four cells in series, so modules with two cells in series would work.
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Old 02-17-2019, 03:08 PM   #8
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Originally Posted by Brian B-P View Post
The small size of these RV-market lithium batteries is annoying for applications where more than about 80 amp-hours @ 12V of usable capacity is desired. They are so light that they could be made in a package the size of two GC-2 lead-acid batteries, without being too heavy to lift. The other obvious option would be the classic configuration of two "6-volt" modules in series; LFP batteries for nominally 12-volt applications have four cells in series, so modules with two cells in series would work.
Battle Born does make a 100 amp hour, 12v GC-2 sized battery designed so that two fit the standard golf cart battery box (they charge an extra $100.00 for the size). Of course you would need to change your wiring to go from 6V per battery to 12V, but 200 amp hours you can treat like 400 amp hours that weighs 48 pounds is awful tempting.

The only thing I don't like is that after talking with the Battle Born factory folks at the Big Tent this year I discovered that they "strongly" suggest moving the batteries to a warmer storage area if you are expecting to subject them to less than 4°F. I'm not all that interested in going back to removing batteries if I decide to stay at home for a winter.
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Old 02-17-2019, 03:41 PM   #9
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Originally Posted by Losangeles View Post
...

How is this for the balance of 200 watts of solar and 200 amp hours of (probably Lithium) batteries?

Solar System: 2 X 100 Watt Soft Panels on roof.

2 (two) x Battleborn 100 amp hour (each) Lithium
...
Having great batteries that you can pull 180 Amp-Hours out of is only half the story. You need to replace those 180 AHs (plus usual conversion losses) somehow, before you can pull another 180.

With 200 watts of solar fixed-flat to the roof in mid-winter you will be lucky to make 50 AH per day. And thats assuming clear skies, no shade, etc. That's 3+ days to a full battery.

You may want to consider a port and a portable panel in addition to the above. Something you can aim at the sun can give you better than triple the output of a flat panel in the winter. (For reference, I measured about 25 watts from my 150 watt panel in mid-January at noon in Denver, with the panel flat, and 75 watts with it aimed at the sun.)


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Old 02-17-2019, 03:45 PM   #10
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Originally Posted by Vermilye View Post
...
I'm not all that interested in going back to removing batteries if I decide to stay at home for a winter.
At least I could lift those 48 pounds - compared to my 70 pound (each) AGM's.
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Old 02-17-2019, 05:55 PM   #11
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Another advantage of Lithium batteries is they charge much faster than a lead battery, and they are not harmed if you only do a partial charge. Lead batteries tend to do better if they are fully charged vs a partial charge.
Lithium batteries also maintain 12V over their discharge cycle, which is why having a battery monitor would be important so you can really see what is coming in and going out of the system. The standard systems in RV's that look at battery life do so by measuring voltage, so with a lithium battery the voltage doesn't really drop, so those type of systems are next to useless
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Old 02-17-2019, 05:59 PM   #12
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Quote:
Originally Posted by alanmalk View Post
At least I could lift those 48 pounds - compared to my 70 pound (each) AGM's.
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Actually the 100A 12V GC2 batteries offered by Battle Born Batteries only weigh 31 lbs
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Old 02-17-2019, 10:12 PM   #13
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Originally Posted by Vermilye View Post
Battle Born does make a 100 amp hour, 12v GC-2 sized battery designed so that two fit the standard golf cart battery box (they charge an extra $100.00 for the size). Of course you would need to change your wiring to go from 6V per battery to 12V...
Right - 100 Ah @ 12V in one box is the main product and Battle Born has nothing at 6 volts and nothing larger - but then you still have two battery modules, each with a complete 4-cell BMS, connected in parallel (which you never want if you can avoid it). What I'm suggesting is either
  • one big box , or
  • two boxes, each with only 2 cell levels (so nominally near 6 volts)
... either way, it would be the same total size, weight, and capacity, with half of the BMS complexity and no module-level parallel connection.

LifeBlue offers larger "12 V drop in" batteries, similar to the Battle Born product but in 100 Ah, 150 Ah, 200 Ah, and 300 Ah sizes.

Victron also offers up to 300 Ah @ "12 V" in a single package, with internal BMS and a line of external monitoring and control products. Victron as an extensive product line, so one could put together an all-Victon system including charger, solar charge controller, inverter, and monitor, with everything communicating. It wouldn't be cheap.

All three of these brands are available from AM Solar, but I'm not suggesting (or discouraging) this particular source.

If someone wanted a package specifically configured for their application, they could buy polymer- or metal-cased individual cells of the desired size (or the desired size in combination) from a supplier such as CALB, install them in a battery box, connect them in series, and attach a BMS.
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Old 02-17-2019, 10:28 PM   #14
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ALithium batteries also maintain 12V over their discharge cycle, which is why having a battery monitor would be important so you can really see what is coming in and going out of the system. The standard systems in RV's that look at battery life do so by measuring voltage, so with a lithium battery the voltage doesn't really drop, so those type of systems are next to useless
Lithium batteries of all chemistries drop in voltage as they discharge, but not as steeply as lead-acid. These lithium iron phosphate (LiFePO4 or LFP) cells have a nominal voltage of 3.2 V per cell, so three cells isn't enough and four cells in series are used, resulting in a battery nominal voltage of 12.8 V. Discharged voltage may be high compared to a 6-cell lead-acid (depending how low you are willing to go in each case), but fully charged voltage is also high - typically 14.5 V or more. As recent discussions in this forum demonstrate, high system voltage in an RV can be problematic.

Cell voltage (not overall battery voltage) is used to monitor lithium ion batteries - that's how every electric car works. Yes, counting charge in and out is a good way to estimate remaining charge, but you can't depend on it; "empty" and "full" are still determined by the lowest and highest cell voltages.
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Old 02-17-2019, 10:39 PM   #15
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Actually the 100A 12V GC2 batteries offered by Battle Born Batteries only weigh 31 lbs
That makes sense - four 100 AH plastic-cased cells typically have a total weight of 13.2 kg or 30 pounds. Electrical connections and the BMS (monitoring and disconnect for high and low voltage) add to that.
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