It worked... Then it didn't. Why?

[heirloom hamlet]

Troubleshooting here.
I had been running power tools problem free through my system and changed two things. Now running a track saw and vacuum combo cuts power halfway through an 8 foot rip... every time...and the same cut was no prob before.
The two things I changed to the system:
Added a BMS
Array changed from 3S3P (2.25kw, 113voc, 25a) to 2S4P (2kw, 75voc, 33a)

Initially I thought, oh snap, I should have left the array alone, I need to put it back. But here's the thing.

It seems to be consistent, the cut off, regardless of if the sun is shining or not. Now, I have no idea why the DC array potential output would limit my AC power usage.And then there's
this: The length of time the power is off seems consistent, 20 or 30 seconds, then I can run again.
It hit me that the BMS has restart time delay settings, so it could be a default setting on the BMS is a touch sensitive and is shutting her down as the power pull or heat ramps up.

If it could be the latter, the BMS, any idea which setting to look at first?

 

[DThames]

Just my way of troubleshooting things but if you can put a fan on the BMS (any sort of added cooling) does that change the behavior? If it does, then you know you are on the right track with the cause of the trip.

 

[heirloom hamlet]

Just my way of troubleshooting things but if you can put a fan on the BMS (any sort of added cooling) does that change the behavior? If it does, then you know you are on the right track with the cause of the trip.

I actually did happen to have a fan on it yesterday, and no...that didn't impact the behavior.

 

[Steve_S]

Well, I will hazard a guess on this, the BMS is kicking off during heavier discharge because the cells are diverging during discharge. Some cells will drop voltage faster than others because the internal resistance is unmatched. If the BMS is monitoring the cells and say one or more reach Low Volt cutoff volts during discharge the BMS will drop the line. The voltage on the cells may only drop for a few moments but that would be enough to trigger the BMS to cutoff. This is indicated by the 20/30 second disconnect. Another possibility, although less likely, is a possible out of Temperature range condition but you'd have to be pulling serious amps to warm up the cells to that point.

BTW: Prior to your adding a BMS, it is possible that the Cell Voltages dropped below acceptable levels but continued to discharge as there was nothing to prevent it. As long as such a discharge was not too long or too heavy then you should have no problems. But if this did last long & hard, there is a possibility that one or more cells may have gone below 2.5V (for LFP) cutoff safe zone and could possibly be damaged.

Double check your connections, busbars etc and make sure everything is properly tight and well secured. Take a DVOM and check each cell Voltage "AT REST" with no loading or charging and "settled" for at least one hour. The last step would be to verify each cells' IR (Internal Resistance) if no obvious issues found. Testing the IR is a PITA and there are a couple of threads dedicated to just that.

BE ADVISED, the majority of vendors will sell "Voltage Matched" cells but not Impedance Matched cells which is a time-consuming process that adds cost and can add significantly. Cells which are properly Voltage & Impedance tested usually sell for considerably more cash.

 

[Ampster]

@ecualibrium how did your extension cord problem get resolved? Could this be related? Did you ever get your inverters connected to an electrical panel?
I agree with @Steve_S in sounds like a cell is sagging. I am troubleshooting one now that is sagging a hundred millivolts during discharges. In my case it is not tripping anything but I want to get it swapped out or balanced before it gets damaged.

 

[heirloom hamlet]

@ecualibrium how did your extension cord problem get resolved? Could this be related? Did you ever get your inverters connected to an electrical panel?
I agree with @Steve_S in sounds like a cell is sagging. I am troubleshooting one now that is sagging a hundred millivolts during discharges. In my case it is not tripping anything but I want to get it swapped out or balanced before it gets damaged.

Custom creating the 8awg 125' extension cord did not make an impact. Steve's comments are super helpful... maybe even probable.

I'll do some testing today. But out of the gates this morning, the cells are very matched voltage wise.

I actually have 4 of these systems. It might be worthwhile to simply plug into one of the other LV2424s with a different set of cells to see if there is a performance change.

Question: If @Steve_S is on to something, is my running these tools and triggering the BMS to shut things down to protect the cells only to restart moments later harmful long-term in any way? To anything, BMS, batteries, Inverter?

 

[heirloom hamlet]

@ecualibrium how did your extension cord problem get resolved? Could this be related? Did you ever get your inverters connected to an electrical panel?
I agree with @Steve_S in sounds like a cell is sagging. I am troubleshooting one now that is sagging a hundred millivolts during discharges. In my case it is not tripping anything but I want to get it swapped out or balanced before it gets damaged.

Also, no not connected to a panel yet. I did put on a 30a DC fuse on the positive wire from the array. But I am just running my big boy extension cord to the home for now during building.

This tiny home is permitted and has to have 100a city power supplied. But I think I will wait for the inspector to go bye-bye for good before I run my secondary power to the home, the solar power.

When you guys replied this morning, I was actually in the process of researching exactly how I will do that. I guess I will find the smallest main AC breaker/cuttoff I can and put in (I guess) a 30a breaker, and run the output straight to that in the solar house. Then run 2-2-4-6 from that to the home into a main lug with 6 or 8 spaces, and distribute a few circuits and outlets throughout, where most helpful. Until I dove into this world last fall, I didn't know their were so many ways to skin a cat in electrical design. I thought it was a little more cut and dry. It's making me work and think, which I like.

 

[John Frum]

If your bms is in the high current path you could try bypassing it for a test.
put a small load like a dc light through the bms and the high current load on bypass.
If the light goes off but the high current load works then its probably a cell going low.
if the light stays on then its probably either temperature or over current.

 

[heirloom hamlet]

If your bms is in the high current path you could try bypassing it for a test.

How? I was thinking I would have my wife run the high amperage tools and at the same time I'd be at the batteries with a voltage meter.

 

[Ampster]

Question: If @Steve_S is on to something, is my running these tools and triggering the BMS to shut things down to protect the cells only to restart moments later harmful long-term in any way? To anything, BMS, batteries, Inverter?

I think it it sub optimal to have your BMS triggering a shut down. It also may be symptomatic of an already damaged cell. Could this be one of the ones that went puffy on you earlier?

 

[John Frum]

How? I was thinking I would have my wife run the high amperage tools and at the same time I'd be at the batteries with a voltage meter.

connect the high current conductor to the battery negative terminal instead of the bms.
Just for a test though.
Also notice I updated my previous post.

 

[heirloom hamlet]

Fortunately, I have 2 new cells on their way from XUBA. One to replace my humongous one, and the other a just-in-case. Well, WAS a just-in-case. Now I may have a home for it.
I may change my name to batterykiller on the forum. Maybe @Will Prowse wants to hire someone that works cheap just to break batteries, teardowns and such for the videos. Right now I do it for nothing. I'm real good at it too.

 

[Ampster]

. But I think I will wait for the inspector to go bye-bye for good before I run my secondary power to the home, the solar power.

My experience is they never go bye-bye for good. I know you like to do things your way but is there any risk in doing them to code? That way you don't have to worry if the inspector just shows up.

 

[heirloom hamlet]

My experience is they never go bye-bye for good. I know you like to do things your way but is there any risk in doing them to code? That way you don't have to worry if the inspector just shows up.

Just unnecessary and unwanted expenses and difficulties. The inspector here is contracted, not a government employee. He wont just show up. I've already done what I've done, here for everyone to see. If they say they need something from me in the future and tell me what, I'll say, Oh sure thing, and do it.

 

[Steve_S]

Custom creating the 8awg 125' extension cord did not make an impact. Steve's comments are super helpful... maybe even probable.

I'll do some testing today. But out of the gates this morning, the cells are very matched voltage wise.

I actually have 4 of these systems. It might be worthwhile to simply plug into one of the other LV2424s with a different set of cells to see if there is a performance change.

Question: If @Steve_S is on to something, is my running these tools and triggering the BMS to shut things down to protect the cells only to restart moments later harmful long-term in any way? To anything, BMS, batteries, Inverter?

Technically, no the BMS dropping the Output 'should' not harm the tools nor the BMS, just on the drop side of it. BUT (there always has to be one or more) if you have a Tablesaw turned on, for example, and the BMS drops the line, of course, the saw will shutoff, but the inverter's Capacitors will drain out before the Inverter shuts off. Then all of a sudden the BMS timesout and kicks back on, now you have an Inverter surge (for the capacitors) and IF the saw is still on, then you can expect that surge from that as well. My Tablesaw will pull a full 120V/15A Start Surge for a moment when I start it then it settles down.

Others have threads on Pre-charging for inverter capacitors so reduce/eliminate surge stress on a BMS or battery pack/bank. Also, depending on the BMS your using, there may be various ways to handle that if not built-in. Note, BMS' with such capabilities are at a different level like Orion and similar and so the cost of them reflects it.

Cell recovery is possible IF they were not overly discharged or overcharged. Once you pass 2.0V there is damage, cross 4.0V and the same goes and by then they'll be puffing up. They are not always recoverable and even if they are recovered there may be cumulative issues that will result over time.

 

[Ampster]

Custom creating the 8awg 125' extension cord did not make an impact. Steve's comments are super helpful... maybe even probable.

I wasn't referring to the cord per se, I was referring to the sparking issue. Was it, as someone suspected, simply a matter of bonding the neutral to ground. I am only asking because these issues are a learning opportunity for the community.

 

[heirloom hamlet]

I wasn't referring to the cord per se, I was referring to the sparking issue. Was it, as someone suspected, simply a matter of bonding the neutral to ground. I am only asking because these issues are a learning opportunity for the community.

You know, I have not had the spark one time since grounding each LV2424. I drove two 8' copper rods into the ground six feet apart and connected them with 10awg solid copper.
There is a screw and washer on the bottom of those units with a ground logo by it. Best I could tell, they wanted me to make my connection there for the entire box. The input has a ground plug-in and I saw Will run his output ground wire to that input ground, too.
Haven't seen a spark since, and it was significant, made a pop sound. Also, the BMS' went on in between that spark question and the possible resolution.

 

[GVSolar]

Hi @ecualibrium - I've been following your progress from time to time on the forum - all the way back to the 24v BYDs - and watched your video about A-frame tiny house construction. Great stuff and good fortune. Just curious - originally you were headed to Ecuador - are you there/going yet - or has the virus thing put a damper on all that. best...

 

[heirloom hamlet]

Hi @ecualibrium - I've been following your progress from time to time on the forum - all the way back to the 24v BYDs - and watched your video about A-frame tiny house construction. Great stuff and good fortune. Just curious - originally you were headed to Ecuador - are you there/going yet - or has the virus thing put a damper on all that. best...

Hi. Thank you for the compliments. We were literally hours from closing on the Ecuadorian land and Covid-19 hit new official heights, with more forecasting, amd we pulled the plug. It was enough at the time to scare us about the future. The one thing that we figured could be insurmountable for us was if South America became synonymous with plague.
So, we ate the invested funds up to that point and decided to move forward with the same concept on our land near Savannah. And I started making videos ;-)
I'll get back on track with that soon. It seems the heat has broken a bit here. When you are dangling for your life 30 feet up and doing something extremely difficult in its own right, you would not believe how hard it is to care about setting up cameras. :-D

 

[heirloom hamlet]

I think it it sub optimal to have your BMS triggering a shut down. It also may be symptomatic of an already damaged cell. Could this be one of the ones that went puffy on you earlier?

Sorry, I missed this earlier. No, that cell is holding some papers down on a desk.

 

[Ampster]

You know, I have not had the spark one time since grounding each LV2424. I drove two 8' copper rods into the ground six feet apart and connected them with 10awg solid copper.
There is a screw and washer on the bottom of those units with a ground logo by it. Best I could tell, they wanted me to make my connection there for the entire box. The input has a ground plug-in and I saw Will run his output ground wire to that input ground, too.
Haven't seen a spark since, and it was significant, made a pop sound. Also, the BMS' went on in between that spark question and the possible resolution.

Do the future readers of that thread and post the above in that thread. I learned something from your response and though I have never experienced that spark I now know the solution.

 

[heirloom hamlet]

Technically, no the BMS dropping the Output 'should' not harm the tools nor the BMS, just on the drop side of it. BUT (there always has to be one or more) if you have a Tablesaw turned on, for example, and the BMS drops the line, of course, the saw will shutoff, but the inverter's Capacitors will drain out before the Inverter shuts off. Then all of a sudden the BMS timesout and kicks back on, now you have an Inverter surge (for the capacitors) and IF the saw is still on, then you can expect that surge from that as well. My Tablesaw will pull a full 120V/15A Start Surge for a moment when I start it then it settles down.

Others have threads on Pre-charging for inverter capacitors so reduce/eliminate surge stress on a BMS or battery pack/bank. Also, depending on the BMS your using, there may be various ways to handle that if not built-in. Note, BMS' with such capabilities are at a different level like Orion and similar and so the cost of them reflects it.

Cell recovery is possible IF they were not overly discharged or overcharged. Once you pass 2.0V there is damage, cross 4.0V and the same goes and by then they'll be puffing up. They are not always recoverable and even if they are recovered there may be cumulative issues that will result over time.

How does the "recovery" process go, if possible. Just time and usage? Top balance again, or bottom?

 

[heirloom hamlet]

Do the future readers of that thread and post the above in that thread. I learned something from your response and though I have never experienced that spark I now know the solution.

Sure thing, will do!

 

[tictag]

I had been running power tools problem free through my system and changed two things. Now running a track saw and vacuum combo cuts power halfway through an 8 foot rip... every time...and the same cut was no prob before.

There has been a lot of info about the BMS causing this, the quick test is to see whether your LV2424 actually switches off when the problem occurs. AFAIK, the LV2424 is powered from the battery, no battery, no display. If the LV2424 is staying on, then the likely culprit is that your LV2424 is actually disconnecting the load, maybe a thermal shut-down. Quick to test, and probably is the BMS, just offering an alternative perspective.

 

[Steve_S]

How does the "recovery" process go, if possible. Just time and usage? Top balance again, or bottom?

I have not done it myself but have read up on it when I discovered I had two flaky 174AH cells. (part of the ShunBin mess).
The procedure is not hard but time consuming. First to get the cells down to 2.50V then to slowly bring them up at low Amps and giving them "rest periods" to settle in between, as I recall the instructions said taking a break & rest at every 0.25V which seemed a bit much TBH but I can see some reasoning there due to the chemical reactions going on. There are different posts all over the internet and a lot of speculation as to what is best etc.... I'm sure there are ways to do so but it would really depend on the internal state of the cell in question and just what happened to it. Thing is, is One "recovered" cell worth putting into a good pack of cells ? That's only an answer the risk taker can make, entirely up to the individual.