MurphyGuy
It just needs a bigger hammer
- Joined
- May 20, 2020
- Messages
- 4,129
Hmm.. Lets walk through it..MURPHY! I THINK I FOUND IT!!!!!!!
Take a look at the files for batteries 3, 6 & 8. Make note of the unit current. Then look at battery 5. I had my Pop with me (good 82 year old neighbor who was an electrical engineer). I was showing him the BMS software screens and noted that every battery in our string was showing a unit current of -0.3 except #5 which was showing a 0.5 (positive, not negative like the others). I said, "OMG, Pop, is battery 5 bad?" He said he felt we'd had a bad battery this whole time!
If this is the case, I'm beyond angry because I kept trying to get help from Fortress only to get no answers, straw men, and bad answers and an insult along the way... $35k investment in their products. I cannot tell you how mad I am.
My husband had that Fluke 789 for work. Like I said, he was an electrician for over 40 years. He has lots of equipment and what he doesn't have, my neighbor does. It's just that I don't know how to use it myself and my poor hubby is struggling these days with simple instructions. :-(
We'll continue with the experiment but I wanted you to know I had Pop come over and work with Kevin to eliminate the very small draw the Sol-Ark was still taking though powered off. That adjustment was made right between 3 & 4 pm PST.
The voltage readings so far have been as follows:
2:43 pm 53.27
3:43 pm 53.25
4:43 pm 53.24
5:43 pm 53.23
The draw down is certainly a lot slower than the initial drop we were seeing.
Most of your modules are reading a discharge (negative) current of 0.3 amps, which means they discharging (0.3amps x 53.2 volts)=15.96 watts. Wow, that's actually quite a lot of juice just for a battery to be turned on. Fortress claimed 30 watts and that never made sense.
Since your Bat5 has a positive value (charging), that means that the other batteries are feeding it juice. This would be expected if Bat5 cells were out of balance, but they seem to all be within 0.001 volts of each other at 3327 and 3328. Bat3's cells are 7mV out of perfect balance so it doesn't make sense.. (yet).
Most BMS's do not balance cells unless they are being charged or unless any cell reaches a high voltage level set by the BMS.
Bat5 is being charged at 0.5 amps so (0.5 amps x 53.2 volts) = 26.6 watts charging. But its cell voltages are all in line so where's that energy going?
If you had a bad cell within Bat5 that was bleeding off energy due to an internal problem (short), then I would be inclined to think that one or more cells would have a lower voltage than the rest, but that's not the case. Bat5 is very well balanced at just 0.001 difference. As far as I know, the battery module does not have the ability to suck in energy and deliver it to only one cell out of the 16.
So lets assume for diagnostic reasons that Bat5 has a bad cell.. but not catastrophically bad, just a big bleeder that likes to self drain. So that cell starts to go lower in voltage, which drops the entire pack voltage as a whole, which causes the other 9 batteries to deliver current to Bat5 in order to keep it in line with the rest of the pack.. which the other 9 MUST do.. (laws of physics thing). As that bleeder gets lower in voltage, it goes out of line with the other 15 cells (16 cells total, assuming just 1 is bad). This would cause the BMS to start bleeding down the other 15 to keep the pack balanced. As those other 15 bleed down, the module voltage sinks, which causes the other 9 modules to feed energy to it.
Would be really cool if you had a thermal scope.. you could look at the entire bank and I bet that #5 would be significantly warmer than the others. In fact, I'm wondering if you could feel the difference just using your hand.. but you'd have to know where the BMS resistors are located within the case for that.
So yeah.. you might have a bad module.. but lets not jump to conclusions just yet.
What you want to do now is disconnect it from the battery bank, set it on a table, and take a reading at its voltage terminals. If you can hook up a computer to it and get the BMS info during this test, that would be fantastic.. then we can see WHICH cell is bad because I'm betting it won't attempt to balance the cells unless it has juice coming in. (but it might, not all BMS's work that way). Doesn't matter, if you have a bleeder, it will bleed even if the pack is turned off..
At this point, for diagnostic reasons, I suggest the following: 1) Remove Bat5 from the pack 2) Set it on the table and turn it off. 3) Wait 1 hour, turn it on, give it 10 minutes, then take a voltage reading with the good meter. 4) Turn it back off and let it sit for 24 hours. 5) After 24 hours, turn it on and take a voltage measurement at the terminals. It would be great if you could hook up a computer and get the BMS data too at the end of 24 hours.
If a cell is bleeding, 24 hours should show some results, we can go 48 or 72 hours to get clearer results if needed.
I'll be surprised if Bat5 is the problem, but it certainly could be at this point. That 0.5 amps translates to 638 watt-hours per day of wasted energy because of a bad cell That is significant.