I am available for custom hardware/firmware development
One other note for anyone considering Unistrut (not telestrut). DON'T use the unistrut solar end clamps, mid-clamps, or angle brackets. I tried them, but found third party solutions better engineered and less expensive. For example the Unistrut mid-clamps did not have as much meat to overlap onto the panel as say, the ProSolar clamps.
I haven't followed this thread, but isn't the idea of a balancer (bypass or active) to allow exactly this? Ie, you can safely continue charging because no more current will be applied to the cells that are at 3.65V
Thanks for the update.I am not sure that your balancers are useless. It looks like your battery is badly out of balance and it will take a while for the balancers to balance it.The way to stop the situation where you are having some cells at 3.38V and some going over 3.65V is to reduce the SCC (charge controller) bulk voltage and float voltage to around 54.1V (3.38*16) and wait for the balancers to balance all the cells to within 0.05V. When this has occurred increase the bulk and float voltage by 0.2V and wait for the balancers to do their work. Keep slowly increasing the bulk and float voltage until you reach 57.6V(3.6*16). This can be done over several days. I hope you have your Cellog 8 connected to your SCC to stop it charging if any cell voltage goes higher than 3.65V.It is a shame that Hobbyking is no longer selling the version of the Turnigy 300W that I bought. My charger is functionally the same as the Junsi iCharger 206b which is still available. There is a 10A version, the 106b and a 30A version, the 306A. The two units you bought will be just about useless for discharging the cells as the maximum discharge current is ~1.5A-2.0A at 3.2V.Simon
cow_rancher said: How about listing your sources of supply for your Unistrut 3rd party parts?Is telestrut just not Unistrut with sizes that telescope into one another?Rancher
There are various games a manufacturer can play with specs for a charge shuffling (aka active) balancer. For example, say it's rated at 6A. But 6A at what differential between two cells (charge moves faster with a higher V differential in capacitor type designs). Continuously or intermittent? And of course if the low cell is several hops away from the high cell, then the effective rate is much lower. Once one cell reaches max voltage, charging needs to be limited to this unknown effective rate (not the rated amp rate). Do that and no cell will over-voltage up to the point where all cells are at max voltage. A cell at 3.65V being charged at 5A with charge being shuffled away at an actual 6A *will* decrease in voltage.If a charge shuffling balancer doesn't have cells voltage balanced after no load or charging for 4 days, then I think it is defective. It would only take a failure of one unit.Someone should put these balancers on the bench and get some real specs.
LostinSpace said:I gave the balancers 4 days to balance the pack with no charge coming in. Maybe I should have waited longer, I don't know.I had first tried reducing SCC on this latest foray to get the cells balanced as you are suggesting. I can't recall exactly but I think I did start at around 54.1. Then when any cell went full I stopped and let the balancers do their work (did not wait anything near 4 days though). I was able to slowly increase the voltage, and did this several times. But finally it reached a point where some cells would immediately hit 3.65 while others lagged in the 3.3x range. Again, resting the pack with the balancers still not equalize the charge.
I now watch the meter through all these exercises and NEVER let a cell go over 3.65. ;>
I am strongly disposed toward charging and testing each cell individually at this point. So if the chargers I bought don't cut it I will swap them for a Junsi unit.
By the way, when measuring internal resistance of a cell, is that performed at full charge? Documentation is not clear on that.
It is really easy to connect the cellog 8 up to your Midnite.
This is the best way to get your system up and running. How were you planning to do the capacity test and balance the battery using the Junsi unit?
I wouldn't use the Junsi unit to measure the internal resistance. The apparent resistance of the battery is affected by how much current you are drawing/supplying, the temperature and the SOC.
Even though all the cells are 3.6 volts, they are not balanced. But I suspect that you know that. If I were to use the bank that way, I would use the balance boards because as the cell voltages diverge the boards will protect the cells with slightly lower capacity from getting over charged. Then the bank can be charged until the individual cells reach 3.6 volts.If the cells were balanced at 3.55 to 3.6 volts then no balance boards needed and absorb could be set to 55.2. Have you considered charging all the cells in parallel?Rick
LostinSpace said:Thanx for holding my feet to the fire on this one. Today I programmed my cellogs to close the output relay if any cell exceeds 3.60, or if pack voltage exceeds 28.5v (half of 57v). The trick will be to get my Midnite Classic charge controller to stop charging on the proper external input. The Classic has two Aux ports, but only one of the two can be programmed for INPUT, and I'm already using it for a WizzBang Jr.; a device to track power usage and SOC. So I am going to take this up with the Midnite people. Ha. This topic almost wraps back to the original reason I made the post
... yesterday I individually charged 16 of the 32 cells to 3.60.
Today I put the array back together, and this afternoon will put a moderate load on (standup freezer) and see what happens. No balancers.
I did measure the cell voltages after sitting overnight and they are running from 3.487-3.564 (77mv dif).<
I was actually going to ask you how your charger does capacity testing. Does it have a dedicated feature that will cycle the battery and report an AH number? If not it occurred to me that you could simply time how long it takes each cell to go from, say, 3.45 to 2.8, and compare the results across all cells to at least get an idea about relative capacity.
Or you could discharge all cells at a fixed current rate and calculate AH?
karrak said:Yes my charger tells you the total Ah on the display and also logs the cell voltages and Ah every two seconds. I would have thought that the units you bought would have showed the total Ah on the display?Discharging at a fixed current rate and measuring the time it took for the battery to drop to 2.5V would be one way to calculate the battery capacity. A word of warning, you must have some way of terminating the discharge when the battery voltage gets to 2.5V otherwise the cell voltage will keep going down to 0V which will damage the cell.Simon
@LostinSpace I think the best way to go would be to discharge the full bank connected in series/parallel about 15 amp hours. Then check cell voltages under charge. Rick
Raj174 said:I think the best way to go would be to discharge the full bank connected in series/parallel about 15 amp hours. Then check cell voltages under charge. You want to see them around 3.4 volts without the highest going over 3.55. Then connect them all in parallel. Let them balance for a few hours, then use a 3.65 volt charger connected positive on one end to negative on the other to slowly bring them up to 3.6 volts. Be sure to check cell voltage while charging to make sure the cells with the charger clips are not rising too fast. If they, are then move the clips to lower cells. If you have buss bars, it may not be an issue. I am sure there are other ways to do this. I really can only tell you what has worked for me. Simon may have a better approach, maybe he will chime in.
Well here is today's news. After leaving a load on overnight I found the cells within a 20mv range this morning, centering around 3.35x.I disconnected the load, then charged all day from the solar, going through a bulk, absorb, and float cycle. At the end of the cycle cell voltages were more than 100mv different, from 3.401-3.531 (see photos).The charge controller was set to go absorb at 55.2 (3.45v). One nice thing is that at float no cell was in the 3.6+ danger area.