Solar project thoughts.

Work2,
Beautiful! Good thing we've had lots of sun lately on the west slope. Give a progress report down the road once you have a trip or 2 under your belt.
We have so many 100 foot trees on the property it's difficult to find a sunny winter spot for more than a couple hours per day. This eats into our charge time. Our tinky, by comparison, 200w array has only 2 things going for it: it's lightweight and has few distracting gauges and dials to worry about.
Again, nice job on the install.
jefe

The project is complete!

The bank has been assembled in the generator compartment. 24 CALB 3.2v/100AH cells producing a combined 600AH @12v



I have been testing the last few days. Everything has been working properly. Yesterday was the first test of actual available stored AH. The battery monitor tracks amps used. Solar panels not engaged.

Among things tested through inverter:

Air Conditioner uses just under 100AH
Fridge on AC mode uses about 30AH
Hot water heater on AC mode uses 135 AH

I played around with each for a while and ended up plugging in a 900 watt space heater and leaving the fridge and lights on as well for almost 4 hours to finish test before dark (which it didn't)

I installed a microair soft start on the air conditioning unit. As described in their literature the inrush starting amps dropped with each use as the unit programmed. The unit starts easily with a 2800 watt inverter.

Results were impressive. Charging the battery bank to a very conservative 13.6V and discharging to a safe 12v the 600AH bank produced right at 600AH before the inverter shut down to programed LVCO. This was more than I expected given the charging voltage I selected.I could get more with a higher charging voltage but without BMS this is where I feel safe. I could also get more with a slower rate of discharge or discharging farther although the added benefit is slim and not warranted IMO.

As a practical matter I don't anticipate using the battery this far down often, but does give a nice range in the event of multiple cloudy days or camping in the woods for a while where shading cuts solar production.



We are planning a trip south for the winter and I'm sure I will have more to learn as we start using it daily.

HMS Beagle wrote:
I understand you will not be using a BMS routinely. How often do you think you will need to check the cell voltage, and how often rebalance?

I will check often at first. From what I have read from people using these batteries for some time now I can't find anyone yet that has needed to rebalance unless they are adding cells to their system. Like any battery with multiple cells no two cells will be exactly "balanced" or equal. The important factor is that no cell is outside it's safe usage zone on both the high and low ends. Other than that concern lies with a cell failing and as it dies dragging other cells along with it. On this issue again I haven't found anyone who has experienced this. One long time electric car conversion company who uses these stated they have never seen a cell fail.

When assembled in P/S configuration the voltage in the parallel wired cells are balanced or maybe a better term averaged along the parallel stings. So having 2 batteries configured 3p/4s I will simply be checking the 3 in parallel 4 times per battery to see if the grouped cells voltage is similar to the others. This is all a BMS would be doing as far as monitoring. To monitor cells at an individual level they need to be run in series and a separate BMS required for each string in series. I would need 6 BMS to achieve complete cell level monitoring/balancing. In the configuration I am running the BMS would be monitoring/balancing each parallel string in series, so I would need 2 BMS.

A problem with BMS systems I have seen is their fairly limited shunting capacity. One I studied maxed to 1 amp shunting ability per "cell". Not sure how that would help control a cell being charged at 2-3x that amount, not to mention 3 cells in parallel.

At least for now my solution is to keep charging and discharging levels far away from the cause of all failures I can find to date, over and under voltages. Fortunately some quality chargers and inverters are fully programmable to control charging and discharging cut-offs with exact voltage levels.

There has been much interesting reading chasing this project for a while. The only thing I am sure about is there is much more to learn.

I understand you will not be using a BMS routinely. How often do you think you will need to check the cell voltage, and how often rebalance?

Quick update.

Finally started bottom balancing the cells. In this procedure each of the (24) 3.2v/100AH cells is discharged to 2.5 volts, allowed to recover to around 2.8v and then again discharged to 2.65v. Each cell should recover to around 2.7v. At that point cell voltages are compared. They should all be within a couple hundredths of a volt from each other. At that point groups of 4 in series are charged together and again voltages compared. I start with a relatively low charge limit and slowly adjust up to ensure no single cell will be charged past the manufacturers safe limit of 3.65. My actual final limit will probably be in the 3.4v max per any cell staying well below the margin of safety while charging. There is very little energy to be gained by trying to may out charging capacity.

nickmgray wrote:
Very interested to see the final results. I've actually been doing some research of my own forand stumbled upon these same batteries yesterday.

Are you able to upload the kayout/diagram again? The link in the first post doesn't seem to work for me. I'm still in research mode, so I'm quite interested to see what the schematics for your install look like.

Thanks for the interest, here you go. The batteries will be 'wired' as shown on first page image not 4s6p as shown here.

I got the solar charge controller up and running today. The inverter will be next. The cells still need bottom balancing and assembly. That will take a couple days or more.

Very interested to see the final results. I've actually been doing some research of my own forand stumbled upon these same batteries yesterday.

Are you able to upload the kayout/diagram again? The link in the first post doesn't seem to work for me. I'm still in research mode, so I'm quite interested to see what the schematics for your install look like.

Thanks Jim! It's been a fun project. Can't wait to get back on the road.

Looking really good! Class A work and craftsmanship!

Jim

Dry fitting into the generator compartment without batteries. All cabling can be measured, built and checked for fit now to solar charge controller, inverter and house 12v.