Quote:
Originally Posted by chopity
You must have a ton of data and knowledge. What would happen if you set your balancer and charger both to 13.8v? Wouldnt you charge slower, but balance longer as it sits there at 13.8v all day balancing? In my head i keep thinking charging at 14.4v will produce more current and charge faster but spend less time in balance mode. Cant seem to shake that thought process. I dont have my own data thats just what i read on other forums. Is the simple answer that theyre able to charge at 13.8v because their ratio of solar to usage is such that theyre fully charged by noon? (also because their bms is not permanently set to 14 or 14.2v)
Separate question. If you were to start over do you think you would go 48v? I full time and have wanted a mini split for years. I keep reading the prices are low and possibly will never be this low again. Was hoping someone would make a direct roof top replacement by now. I read a company is making one but the price will likely be high. Trying to work backwards i almost need to pick the mini split first. Then the inverter and voltage. The hard part is predicting the future. Will 48v mini splits be cheaper? 48v fridge maybe? Right now my fridge will pull 5kw a day on electric mode. Being a toyhauler i need 12v for brakes and 5500w genny. I use a 12v starting battery for the genny and 6vGC2 for the trailer. Thinking about a combo of 12v battery and 48v. But ive read some people who do the combo wish they just left everything 12v. For me i think the mini split will be the decider. If i go 48v air conditioner then that settles it. Are you happy with your mini split? Keep meaning to check out the link in your sig. Out there boondocking have you ever seen a mini split on the roof? My trailer frame is high off the ground. Thought about putting it under the trailer. But it could trap hot air. Yet would be in the shade compared to on the roof. Or do the trailer tongue if i ditch the 12v lead batteries and do a big 12v lithium setup to handle genny, brakes, and mini split. It just seems 48v is more efficient. Cheaper wires. Less amps and big breakers. I havnt priced anything out. More just dreamin!! First step is finding cheap aluminum strut for the roof and maybe do a road trip out to AZ for used panels.
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Yes, if you drop the charge voltage low enough, you will get meaningfully longer charge time. And, if the voltage is above the BMS's balance threshold, you will get more balancing. But, only after voltage hits that voltage (13.8V in this case). Voltage starts rising fairly quickly at 13.8 so the added balancing is probably helpful but not very large.
I did re-balance one of my wayward Lifeblue batteries by putting a current-limited charger on it (5 amps IIRC). That provided over 20 hours of balancing IIRC.
Slowing the charge might be practical for those not using solar or driving from RV park to RV park. Though maybe not if a generator is the charging source. One benefit of LFP is faster charging and less generator time. If the factory BMS does not provide adequate balancing, ..... well, just be sure it does.
For me, it's all about getting everything I can from my solar so stopping charging below 14.3 V is not an option.
Your suspicion that some use solar but don't charge above 13.8V because they have a lot of solar may be the case. Though adding extra solar to charge more slowly doesn't make much sense to me.
And, as I may have mentioned, I do start balancing at 13.4V since I have some wayward used cells. And even my several year old "new" "grade A" Calb cells need a but more balancing than would be provided by Overkill Solar's BMS with default settings. I use this on the used cells ....... its on 24/365, balances at 1 amp at 80 mV delta.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
If extra balancing is needed only occasionally, a trick such as slow charging might be useful. But, IMHO it's not practical for most of us.
Second question .........
I gave up hope on getting a really good roof top packaged A/C using heat pump technology. They all fall short. Most way short. And, my C&H was about $1100 ($1500 with line set & covers and help with getting the flares right and vacuuming the lines). And having a mini split on the rear bumper (fortunately my 2015 Rockwood has a substantial rear bumper .. one of the few good things I can say about this RV) gave me room for another 200W panel on the roof.
My son went with a 240V mini split and built an autotransformer (for under $100). He has an 840 Ah 12V system with 3000W 120V inverter. We looked at 24V and 48V and it didn't make sense cost-wise or reliability-wise. We both camp in remote places so reliability is important.
My system started at 12V and grew over the last 10 years with no good opportunity to go to a higher voltage. I looked at it but quickly dropped the idea. My wires are all short. Batteries are 12" from the busbar and the inverter is 18" from the busbar. Max cable is 1/0 90C on the inverter.
I doubt I would do anything different if I were starting from scratch. I like having the reliability of multiple solar controllers and multiple batteries. I also sometimes carry a spare inverter (the smaller one we started with 10 years ago).
My C&H mini split is 120V so is on a circuit breaker in my 120V panel (which is fed only from my 1800Watt 120V inverter). Mini splits don't like GFI's so I had to disable the GFI in my inverter (I still have two GFI circuits in the RV). The mini split max power in cooling is 1020 Watts. I've never seen it hit this. This is probably in turbo mode under worst-case in/out temperature conditions. Heating is a bit higher, up around 1150 W max (but not experienced yet).
We run the inverter microwave at half power (double the cooking time) if it needs to run at the same time as the mini split is running hard. It only ever runs hard on cool-down and not for very long. Often we can run the microwave on full power (1400W in) while the mini split is cooling or heating. On a recent 8 week trip we only overloaded the inverter once do to the mini split running (though did it a few times by not turning off the expresso machine before putting something in the microwave on full power).
I'm delighted with my $1100 mini split. We camp mostly in spring and fall so haven't needed a lot of cooling and haven't needed overnight cooling yet. But, we use it a lot for heat. The particular unit we have isn't as efficient as some in heat mode (it's EER 15 and SEER 25 in cooling mode and only 10.5 HPFP in heating .. son's 9K Gree is EER 16.5 and SEER 38 and HSPF 15.5 but is heavy) but still is quite usable on solar. We usually have it on until bed time. After bed time the 62F minimum heat setting is too high for us so we switch to propane with a t-stat setting of 50F.
I've never seen a mini split on the roof. The closest one could come to that I think is a bumper mounted outdoor unit and a "ducted" indoor unit that sits on the roof. This isn't off-the shelf stuff but customized to make the factory ducted system work through the 14" opening or an enlarged opening. For people that have a place for the standard wall-mount indoor unit, the mini split is considerably more efficient. In addition, the ceiling ducts in our RVs are very inefficient since the sun beats down on the upper side of all ducts.
My mini split indoor unit is "downstairs" in the fiver so keeps the living area nice and cool. It doesn't do so well up in the bedroom. It heats the bedroom well because heat rises. Some folks do a multi-split with two indoor units, one for the bedroom and one for the living area. The smallest indoor unit that I know of is 6K which is a bit much for an 80-100 square foot bedroom (it will cycle a lot, thus losing efficiency). I think we'd just roll out a pad and some blankets downstairs if we ever need to run the mini split in cool mode overnight.
I don't think 48V or 24V is enough more efficient for that to be a factor. Unless you find a 48V mini split.
I've written the above piecemeal. I might have missed something. Let me know if so. Or any other questions arise.
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