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


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#1 LosAngeles

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Posted 17 February 2019 - 07:06 AM

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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#2 iowahiker

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Posted 17 February 2019 - 02:29 PM

This is my favorite article on this subject:

 

http://www.truckcamp...and-a-few-tips/

 

The author of this article posted his dislike of generators about the same time as this article but a year or two later purchased a generator so his panel/battery sizes are not excessively large.

 

Your refrigerator is more-or-less twice the size of the refrig in this article.

 

For a 4.3 cu ft refrig, we are ordering 400 watts of solar, monocrystalline, and 300 amp hour lead batteries (150 usable).  Your usable battery is a 20% larger than our order but your refrig is 75% larger.

 

19 volt panels (instead of 17 or 18) and an MPPT solar controller will help.  I wish I could get the next generation 23/24 volt panels to go with the MPPT controller.


Edited by iowahiker, 17 February 2019 - 03:30 PM.

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#3 Happyjax

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Posted 17 February 2019 - 02:55 PM

That is a good write up Hiker:) Thanks

 

LA I don't see how you could be worried much with 200 AH of Lifepo4 batts. It might not hurt to go for a little extra solar though. Driving will help a lot if the install for the truck is good though. Make sure you use heavy gauge wire....don't let anyone get away with 10 gauge..... Go 8 minimum and 4 or 6 if you have a longer run to get to your batteries. Cheaping out on the wire ruins your available amps...

Lots of good write ups here on that very subject....

 

YMMV :)


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#4 rando

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Posted 17 February 2019 - 03:19 PM

Given the size of the fridge you may be a little light on the solar, particularly if you want to be able to have the solar system keep up with the fridge demand.    ~150 W seems to be about right to keep up with my fairly efficient 60L Isotherm fridge you will probably need significantly more for a 200L fridge.   There is also a significant range in the efficiency of these fridges, with the Dometic being less efficient and the Isotherm on the more efficient end.  I don't know where the Novacool falls in this range. 

 

You will also need a solar charge controller, and some sort of battery isolator for charging the batteries from the truck while driving.  This can be a little tricky with lithium due to their higher resting voltage.

 

 Depending on how you envision using shore power, the inverter/charger seems to be a bit oversized.   Typically if you are staying somewhere with shore power, you are staying overnight, so you only really need a charger that can get your batteries up to full in 12 hours or so.  For a 200Ah battery pack, a ~20A charger is probably fine, and it will be much lighter, cheaper and smaller than an 80A inverter/charger.   If you have a good solar system, you may find that you never plug in (we never do). 


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#5 smlobx

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Posted 18 February 2019 - 05:45 PM

LA-
A couple of comments.

Isn’t the Everest a 8.5’ camper? The Cuchara is their 9.5’ camper last time I checked. (I have an Everest).

In my build with their standard fridge we went with 2, 100 amp flexible solar panels and 2, 220AH 6 volt batteries. Through my negligence in not monitoring my fridge (which had been mistakingly turned up to the max on a long trip) I overused the batteries and am now in the process of replacing them with one 100 AH Battleborn battery which is equivalent to what I had. Prior to that episode the set up provided a good balance and never left us without charged batteries.

Since you are installing a much larger fridge and will have the additional storage capacity of a second BB battery I would reccomend considering increasing your solar capacity at least another 100 amps if you have the space on the roof.

Edited by smlobx, 18 February 2019 - 05:47 PM.

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#6 roverjohn

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Posted 18 February 2019 - 06:19 PM

I would make a few changes but, really, JMO.

1.I would ditch the inverter charger for a stand alone sine wave inverter and a smaller one at that.

2. I would suggest a smaller fridge, maybe 3-4 cubic foot, and then make room for a cooler shaped compressor fridge for use as a freezer.

3. I would use glass panels instead of the flexible units. They are more proven, durable, and less expensive if you break one.

They are heavier but I assume you will have a rood lifting mechanism.

4. Finally, the batteries. I would not use the ones you've selected. You are starting from scratch not replacing an existing LA battery. So no need for internal battery management. There are plenty of options out there for MPPT charge controllers designed for lithium iron batteries and they usually have monitoring options so you can skip that too. Buy single cells sized appropriately.


Edited by roverjohn, 18 February 2019 - 06:20 PM.

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#7 rando

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Posted 18 February 2019 - 06:38 PM

I would make a few changes but, really, JMO.

1.I would ditch the inverter charger for a stand alone sine wave inverter and a smaller one at that.

2. I would suggest a smaller fridge, maybe 3-4 cubic foot, and then make room for a cooler shaped compressor fridge for use as a freezer.

3. I would use glass panels instead of the flexible units. They are more proven, durable, and less expensive if you break one.

They are heavier but I assume you will have a rood lifting mechanism.

4. Finally, the batteries. I would not use the ones you've selected. You are starting from scratch not replacing an existing LA battery. So no need for internal battery management. There are plenty of options out there for MPPT charge controllers designed for lithium iron batteries and they usually have monitoring options so you can skip that too. Buy single cells sized appropriately.

 

I would disagree with point 4, unless you are pretty electrically skilled and enjoy electro-tinkering.   

 

If you want your expensive lithium batteries to last, you will still need a battery management system to take care of balancing, cell level over/under voltage protections and thermal cutoffs.   You can buy your own cells, and add your owns BMS (which I did), but this is a non-trivial undertaking and you are on your own if you ever have issues with the system.   For most folks, buying the drop in replacements is the simplest and likely the best option. 


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#8 roverjohn

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Posted 18 February 2019 - 07:43 PM

Rando, It appears to me he is using the BMS in the battery as the charge controller. Am I missing something?

I probably am so I'm asking.

 

If that is the case he's violating a few of my rules of thumb that only apply to me which is why it's an opinion.

1. He's running 2 batteries in parallel when 1 larger would do.

2. He seems to be running 2 BMS when 1 would do.

3. He's combining 2 different functions, electron storage and BMS, into 1 unit, twice.

4. MPPT or nothing

 

The thing is, for me, he's not replacing anything as he's starting fresh so he doesn't need a 'drop in' replacement. If it were me starting from scratch I would make even more changes but I thought he wanted our opinions not a complete redesign. I would eliminate all parasitic draws like Bluetooth anything too but that's a lot to ask anyone now a days. And, I might go with a higher voltage than 12 but that's a different can of worms. I did not see any info at Battleborn about how their BMS works. Without MPPT it would get crossed of the list instantly.


Edited by roverjohn, 18 February 2019 - 07:44 PM.

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#9 roverjohn

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Posted 18 February 2019 - 07:57 PM

I just read the article Iowahiker linked to. My opinion is that there are numerous factual errors so you might want to view it with a grain of salt. Like everything on the interweb including my posts.


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#10 rando

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Posted 18 February 2019 - 07:59 PM

LA will have to speak to his intentions, but a BMS and solar charge controller serve two different functions and are not interchangeable. 

 

You need a BMS (the purpose of which is to protect the lithium cells during charge AND discharge and balance the cells, this is not PWM or MPPT but an on or off system) and a solar charge controller to regulate the power from the solar panels during charging (which could/should be MPPT).   

 

You could buy bare LiFePO4 cells (either cylindrical or prismatic) and wire them up into a battery, but you still need to add the BMS, and you still want to be able to tailor your charge sources (solar, shore power, and truck) to be close to what the lithium battery expects.   I built my own lithium pack, and it is a little bit complicated even having been an EE in a prior life. 

 

Again, for most folks, drop in lithium packs are the way to go - they are more expensive, but they do seem to work well.   If you want to interface with standard appliances and your truck alternator, you really should stick with a 12V battery pack. 


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