Would I be crazy to think that I need 1200amp hr's worth of Lithiums (4 X 300 each battery) to run one AC all night along with fridge and smaller loads? I am not much of a solar/installation guru so I thought I'd ask those of you who done this. Seems that lithium battery prices are all over the place. Ampertime on Amazon has their version for $700 while Battleborns are 2300. I guess I need help designing this thing. connecting and wiring this is not an issue for me. It's more of how do I separate the charging of the lithiums from the starting batteries, isolating the generator 12v charging circuit and the like. Marie is pushing me for the tax credit but when batteries are close to 10k for what I want, the $950 worth of tax savings is really not worth it. She has the stigma that the government should not get the $950... I have plenty of roof space for solar panels. Seems like most of what I need to charge off grid will be in the 900watt capability in terms of solar panels.
1200 amp hour could run a 12k btu inverter heat pump all night with no problem, on high with the unit compressor at max will draw about 9 amps @120vac or 90 amps at 12vdc per hour. Wattage is voltage x current so basically its 1080 watts if you have 1200 amp hour storage at 12vdc thats 14.4kwh which will run that ac unit for 13.3 hours BUT you can only use 80% of that 14.4kwh to keep your batteries safe so you can run the ac for almost 11 hours without damage to the batteries. Anything you add to the circuit will reduce that amount of time of course.
You can build your own and save a fortune, I've built 3 sets of batteries and this one in my house for my solar generator is 30,720 watt hour and cost me about $3600, the only problem is waiting on them from China, the batteries are B stock batteries but the way I have them programed should last the rest of my life. The BMS's safeguard the system, all the little red wires looks tacky but its important to monitor LifeP04 batteries. You can configure them in series and parallel to make any voltage you want 12V 24V 48V. When we put solar on the roof of our rig I will change out my inverter to Growatt 3kw inverter charger all in one system just as I have in our house. These 2 units power the AC heat pump in our bedroom and the other does all the refrigeration in our house, if we ever loose electric we will have a cool or warm place to live and refrigeration for our food plus it saves us on our electric bill.
That's really cool! I don't know much about building my own or fear some lithium meltdown taking out my coach with us in it while we sleep. I am intrigued by it though. I also see that the battery manufacturers show only 4 can be connected in parallel. I would like to do a minimum of 6 300ah batteries but seems they don't support that. Probably their BMS system?
There are guys that post on you tube about building lifep04 batteries, its not that hard and the BMS will protect you at all times. I use Daly BMS with bluetooth, I can see the state of my batteries anytime I'm in the house, the same would work for your coach. If you really want to be safe and have the last for years only charge them to 90% and discharge them to 25%. This will insure your safety and they will last for over 5000 cycles. Check out this guy and look for his battery builds.
I have watched Will Prowse before. He is the guru on this stuff. Thanks for the link. Makes me think server rack batteries might be a nice cleaner installation for my coach. Need to see if they come in 12v variety and maybe stack them to get 20kw worth of power. Next question is how do I connect them to my new and unopened Magnum MSH3000 watt inverter and add solar, battery isolators and such. Much to learn. Wiring up sub panels and such is easy as he described. I just need to learn the charging aspect and incorporating this in an old lead acid based wiring system.
If your magnum is unopened try and return it, Growatt is all in one, a 6kw 220vac inverter, solar charger, battery charger when plugged into the grid and cost $1299 from Signature solar. Also you can buy the wifi dongle ($50) and you can monitor batteries, inverter and solar panels from anywhere in the world from your phone. If you where to go with a 24 or 48vdc system you can still power the coach with a 24-48vDC to 12vDC converter this will make all your wire sized much smaller if you go with 24 or 48v. If you want to keep the magnum then you will have to purchase a MPPT solar charger and another DC to DC converter to charge the lithium batteries from the alternator, lithium batteries have different charge characteristics and you just can't charge them from an alternator.
On lithium battery subject, almost all the lithium batteries are made in China, if you buy a battery made in USA it more than likely has China batteries in it. I buy Calb batteries, they are made for aircraft and have a heavy duty case around them. Here is a picture of a battery I built for our Airstream Interstate when we owned it.
I will be doing the above down the road but now we are involved with a major project rebuilding the salon slide.
In my defense, you opened the post with “would I be crazy”.
It for the most part is technically possible as Jack has outlined. Before spending that kind of effort, what is your intended use and purpose?
Plans for extensive boondocking?
Plans for boondocking where you can’t run the generator?
Just don’t like the generator running at night?
Don’t like the generator while traveling?
Here are some fundamental points to consider.
What does one AC draw on your coach? Jack’s estimates are a bit low from what I remember the Dometic split units drawing. That number impacts your run time. Also calculate an 85 or 90 percent efficiency on the conversion from 12VDC to 120VAC.
I don’t think you can install enough solar on the roof to recharge the batteries in a day of boondocking to carry you through the next night. So either you will plug in to a pedestal, run the generator, or charge with the alternator while driving. If the plan is to use the alternator, there is a lot of thought and execution needed to make the alternator survive.
Seriously consider a higher voltage system than 12V, all the way up to 56V if you are really intent on this. The wire diameter and voltage loss is significant at 12V. The voltage drop with even 4/0 wire at the charging currents you will use is enough to cause inaccuracies in the charge cycle. I say this based on my own system of 1000 aHr, Magnum 2812, and NEW 4/0 cabling. When the charger is putting out it’s max of 125 amp, there is about a .3V drop at the batteries. So what you say. The Magnum reads the charge voltage at the inverter charger not the battery. Also, when using a heavy amp draw (over 300 amps) on the batteries such as the 120 water pump and oven at the same time, the voltage at the inverter will drop below the LBCO even though the voltage at the bank is well within the limits I am comfortable with. Again, this is due to voltage drop in the wiring. Yeah, I know, I have done the calculations and the actual is more than the calculations. I have new wiring, new lugs, and clean connections.
A higher voltage system with a dedicated alternator minimizes these challenges.
My .02
Richard and Rhonda Entrekin
99 Newell, 512
Maverick Hybrid Toad
Inverness, FL (when we're home )
if indeed you decide to do solar......the offer is there to come out to my place, we can put it in the extra bay in the shop and use the scissors lift to do the roof work. i know you have an impressive array of tools, but i have hydraulic cable crimpers that make nice ends on any size even way past 4/0 cable. i am no solar or lion expert, but i do have a rolling leather couch and lazy boy in the shop to watch you figure it out.
the offer is there...
tom
2002 45'8" Newell Coach 608 Series 60 DDEC4/Allison World 6 Speed HD4000MH
Jack, I had a feeling you would suggest returning the Magnum. It may be easier to sell it as I got a good discount on it at $1875. When looking at Will's video it was clearer than mud that I would be best served by a higher voltage server rack battery and separate inverter that would link things together much easier.
Richard, yes, on all the above. Hate the generator running while driving, hate the noise at night (Where/if it even can be run) and yes, We realize there's not enough solar that would charge the batteries. I even went as far as thinking that adding a second or replacing the alternator with something more Lithium friendly but it may be easier to do a DC to DC converter. I agree the Dometics are hard core power hungry users and that a higher voltage system would make things more efficient. I was looking at the new Honda 3000watt fuel injected gas inverter generator coming out. Perhaps installing that in the engine bay to deal with the battery charging and second AC use might be the ticket while relegating the 17.5kw generator for all coach power when sitting still? Would it be sacrilege to remove 17.5 kw generator in favor of a smaller lighter unit such as the Honda? I thought of that too but hate the need to carry another fuel source other than diesel. I appreciate you "Guy-ses" (New York pronunciation) help and ideas. I may look at returning the Magnum. It is still sitting in my entry unopened since it arrived...
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