I am mostly past my other time-draining matters, and I am back to focusing on my battery/inverter/microwave power issue.
This is very long. My apology. It is a brain dump about most of the points from previous exchanges. If you have the patience for my list, I will value your thoughts.
I also want to say how much all of the previous comments, related thoughts and education I’ve received are appreciated. Even 2-3 years ago, I would never have gotten my solar system built without DIY Solar Forum help. Thank you, thank you.
I’ve done some of the suggested testing. More to come.
Here are the initial results.
All of these tests today have the microwave running at an +/- 140 amp (level 6 on the inverter microwave) for the “load.”
Basic Tests Suggested – There is no line loss without a load for the 3 batteries I can reach to test. There is, however, 0.07-0.08v line loss through the 250-amp breaker I use as a switch to the inverter. That surprised me, as I expected more from your comments. Also, I was surprised that the oldest 200 Ah battery (the old-style lithium cells, round probably, but it is encased) was showing 0.02-0.03 v more power than the two newer batteries with the new-style cells. Not only is #3 two years older, but it is also the furthest from the busbar of those tested with the 3rd longest 4/0 cables).
Source ----------- No Load – Load
Battery1----------13.21v-----12.94v
Battery2----------13.22v-----12.94v
Battery3----------13.22v-----12.96v (Surprising, because longest cables of 3 tested)
Battery4--- (Not able to test)
Busbar out ------13.20v-----12.88v
Breaker out -----13.19v-----12.81v
- To a point someone made, all 4 batteries are individually wired to a master busbar and from there to the inverter. Someone told me to do it that way. Is that part of my problem?
Battery Types – Yes, they are different. The newest are Ninthcit 280 Ah battery cells received a couple of weeks ago; and the other 200 Ah Ninthcit cells (I think I recall) are 2 -1/’2 years old, or so.
The other 2 batteries are a huge mistake I made with my first LiFePO4 buy in 2019. I bought 3 crappy “BTR” 150 Ah Chinese batteries – that was before I found the DIY Solar Forum for help.
In late 2020, while on the road in Arizona, all three BTR batteries failed. I was dead with my RV power. I bought a couple of sears marine deep cycle batteries and limped along without a solar system, essentially. Then, with DIY help, I began to understand and I bought the older Ninthcit cells with Dally BMS installed.
Months later, with help from here, I finally tore apart the failed batteries and learned the problem was that the cheap BMS units had failed, not the cells.
Then 6-8 months after that, I received an offer from BTR (fulfilling their “guarantee," kinda’) for one of their new 200 Ah batteries. I accepted. It is now my battery #3. It is the one encased and I do not know what the cells OR the BMS are inside that battery. But it does work. No doubt the BMS is the cheapest available, and even worse than the cells. Please note that several times I have disconnected that crappy BTR battery and just run with the 3 batteries that I know are good. It makes no difference with the inverter shutting down.
BMS Types – Three of the four BMS units are (essentially) Overkill Solar 4s 120 amp units. When the original BTR batteries failed, I studied on this forum and got assistance here, too. I rebuilt one of the 150 Ah original-to-me BTR batteries. I purchased 3 faux-Overkill Solar BMS units directly on AliExpress. They were recommended here by several people who argued they were manufactured at exactly the same place in China as Overkill’s. I believe that those units are as near to Overkill’s as possible, just 2 years older. The newest BMS I bought directly from Overkill (feeling a little guilty) and I reserved one of the Chinese cheapies for rebuilding the encased BTR battery with a new BMS when I have a chance. I concede they may be slightly different than the new Overkill, but I’m betting not much.
Battery Cable Lengths -- In the back of my mind, I kinda’ understood the “longer-battery-wires = more resistance.” It seemed common sense, but I’d never looked it up and wasn’t absolutely sure given my limited knowledge. Thank you for the wire length suggestion. I’ve now tested three of the batteries and as you see from my numbers, there doesn’t seem to be that much loss between no load and load with the microwave running. I cannot reach the furthest away battery with the longest battery cables without a major project dismantling everything in the small solar/battery/etc. compartment in my RV.
I'm just not up for that huge project right now. I am confident you are correct about line loss with the long cables. To the best of my then knowledgte, I kinda’ considered that when I wired the batteries. The choice was either long cables, or don’t wire in the last 150 Ah battery because of the space. I chose wiring in that extra battery because I knew it had a good BMS and the cells tested OK and balanced.
As for rewiring and making the cables all the same length, it would cost about $300 for the additional 4/0 cable + lugs. The cost/benefit? My guess is the payback for the small voltage gain from one of the four batteries will take a long time. And, honestly, I don’t have an extra $300 right now to buy cable and make a test. So, I’ve taken that off the table in my mind. Plus I’d have some very long, very heavy excess cables with no place to go in my already very small solar compartment space.
The Microwave – First, I‘m now able to use it just fine with no problems when I set it at level 6 or below. If in daylight with solar charging, I’ve used it a few times at level 7. But, I have learned the unit has a pretty heavy demand for power, to be sure.
While it “ain’t easy” for me, I have figured a way I can take the microwave to the compartment where the batteries are located and with a trick for added reach, I can plug it directly into the back of the inverter. That is a test I am eager to try! I just need to recruit some help getting the heavy microwave out of it’s mounting inside the RV to the outside compartment. At my age, I just don’t have the strength to do that alone without high probability of pain and potential body damage.
Anyway, I’m surely not in a power crisis. I just cook things a little longer in the microwave at the lower levels, Easy enough. I started this discussion because I was interested in learning the “why.”
I think what I‘ve learned so far is that, as I kinda’ anticipated, it is an electrical “rabbit hole” with endless possibilities.
Yet there is one interesting new “wrinkle” I just happened to notice.
A couple of days ago when I was connected to shore power, I was microwaving at “Level 7” on my unit when my icemaker kicked on. Immediately the microwave hiccupped . . . it didn’t stop or shut down, but I was really wondering because of the sound change and internal light flicker. The Icemaker uses 8-10 amps when freezing ice. Again, this was not inverter power, this was 30-amp shore power.
It got me thinking. I am now wondering if all my issues are because of my RV’s internal 120 volt wiring? I realized that the microwave, my icemaker, my residential refrigerator, my air fryer, other power outlets plus a couple of charging cords AND the bathroom outlets are all on the same “kitchen” circuit in the power panel.
FYI, my inverter is wired directly through my 3-way switch to my RV’s power panel via about 23-24 feet of new 8/2 outdoor weather-resistant Romex-type wire that I installed. The RV’s original 120v shore power wiring uses 10/2 interior Romex.
Now since I know the microwave is sucking deep for power even when shore power is connected, I’m wondering if at least part of my rabbit hole problem is that there is so much wiring connected on the kitchen circuit? Even if appliances are not running? Many connections? And quite a bit of accumulated/collective wire distance.
So, I’ve begun wondering if it might solve part of the problem if I run cable – it would have to be something like an 8 AWG heavy duty extension cord -- from one of the 120 volt receptacles on the back of the inverter directly to a new receptacle with a dedicated new breaker for only the microwave and air fryer, and possibly the always-on residential refrigerator? I never use the microwave/air fryer at the same time. I’m also guessing it might slightly reduce the 3-4 amp drain of the residential refrigerator because of the direct connection . . . or does it work that way? It sure would eliminate a lot of connections through the RV’s old power panel and wiring.
When I get help to move the microwave near the inverter and plug it in directly, the test of that should be very, very telling. I am eager to know that result. To me, it now seems key? Or am I just kiddin’ myself?
Again, thank you for your time and knowledgeable comments and suggestions.
I honestly don’t know how to express how much I value the help.
jesfl
