Substitute methods for determination of battery cell health:
Options
softdown
Solar Expert Posts: 3,824 ✭✭✭✭
Lets say your name is Dave. You are assessing a hospitals battery bank deep in the Mongolian jungle. Your voltmeter and specific gravity meter were both lost by the airline. Or somewhere else along the line.
Do not despair. There are other ways to determine bogus cells. Your infrared temperature sensor will show bad cells. Their charging temperature will lag behind the healthy cells. You may also remove the caps and watch for cells that are not bubbling under charge while the healthy cells are bubbling away.
For that matter...cells that require much less water are also indicative of poor cell performance.
Do not despair. There are other ways to determine bogus cells. Your infrared temperature sensor will show bad cells. Their charging temperature will lag behind the healthy cells. You may also remove the caps and watch for cells that are not bubbling under charge while the healthy cells are bubbling away.
For that matter...cells that require much less water are also indicative of poor cell performance.
First Bank:16 180 watt Grape Solar with FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
Comments
-
If it is a hospital, I would think they have an internet connection or at least someone with a smart phone and decent data plan.
I do not need to go there as I can see the battery bank on the web from my home on Outback and Schneider electric combox systems.
Probably other makes of systems also."we go where power lines don't" Sierra Nevada mountain area
htps://offgridsolar1.com/
E-mail offgridsolar@sti.net -
Guess I failed to consider using the internet to solve my various battery issues.
First Bank:16 180 watt Grape Solar with FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries -
softdown said:Lets say your name is Dave. You are assessing a hospitals battery bank deep in the Mongolian jungle. Your voltmeter and specific gravity meter were both lost by the airline. Or somewhere else along the line.
Do not despair. There are other ways to determine bogus cells. Your infrared temperature sensor will show bad cells. Their charging temperature will lag behind the healthy cells. You may also remove the caps and watch for cells that are not bubbling under charge while the healthy cells are bubbling away.
For that matter...cells that require much less water are also indicative of poor cell performance.
Or the exact opposite.
I always have more questions than answers. That's the nature of life. -
Definately agree! Most all battery failures are cells using too much water! It is often an early warning of loss of capacity.
Hey Marc! I promise to send some business soon!"we go where power lines don't" Sierra Nevada mountain area
htps://offgridsolar1.com/
E-mail offgridsolar@sti.net -
Good point. A cell that is overheating is indicative of the worst kind of battery failure. I was referring to weaker cells....not catastrophic cells.Marc Kurth said:softdown said:Lets say your name is Dave. You are assessing a hospitals battery bank deep in the Mongolian jungle. Your voltmeter and specific gravity meter were both lost by the airline. Or somewhere else along the line.
Do not despair. There are other ways to determine bogus cells. Your infrared temperature sensor will show bad cells. Their charging temperature will lag behind the healthy cells. You may also remove the caps and watch for cells that are not bubbling under charge while the healthy cells are bubbling away.
For that matter...cells that require much less water are also indicative of poor cell performance.
Or the exact opposite.
First Bank:16 180 watt Grape Solar with FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries -
Weaker cells also can use alot of water. It is a clue that the battery bank is on its way to being recycled.
There are many types of battery maladies. Many!"we go where power lines don't" Sierra Nevada mountain area
htps://offgridsolar1.com/
E-mail offgridsolar@sti.net -
In the end, you have somewhere around 6 to 24 or more "identical" cells... Generally, every cell should perform the same as every other cell (water usage, charging/discharging voltages, specific gravity, temperature)--You are looking for cells that are behaving "differently" from the rest (cold/hot, bubbling too much or not enough, specific gravity higher/lower than rest of cells, etc.). That will (usually) be your first indication of a failure.
-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset -
Or you could say "In the beginning, you have somewhere around 6 to 24 or more "identical" cells." No longer true at the end. Almost every battery I have recycled was fine except for one bad cell.
First Bank:16 180 watt Grape Solar with FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries -
Does anybody else find that the weaker cell always seems to be the one in the middle, in a 3 cell battery?Mate, VFX 2812, FM 60 & MX 60, 2 Full River AGM 400 6v, 1400 watt Solar Array, Yamaha 3000iSEB inverter gen
12 volt Flojet water pump
off grid summer home in northern Ontario -
Mine use very little water.
I top them off every three to four months. 64 Trojan L16 RE-Bs' 6 volt 375 AH.
About 5 or 6 gallons.Ranch Off Grid System & Custom Home: 2 x pair stacked Schneider XW 5548+ Plus inverters (4), 2 x Schneider MPPT 80-600 Charge Controllers, 2 Xanbus AGS Generator Start and Air Extraction System Controllers, 64 Trojan L16 REB 6v 375 AH Flooded Cel Batteries w/Water Miser Caps, 44 x 185 Sharp Solar Panels, Cummins Onan RS20 KW Propane Water Cooled Genset, ICF Custom House Construction, all appliances, Central A/C, 2 x High Efficiency Variable Speed three ton Central A/C 220v compressors, 2 x Propane furnaces, 2 x Variable Speed Air Handlers, 2 x HD WiFi HVAC Zoned System Controllers -
It has been my experience that batteries in series never perform the same as each other. People talk most about parallel banks. I sell a LOT of 2v x 24 battery banks in my business.BB. said:In the end, you have somewhere around 6 to 24 or more "identical" cells... Generally, every cell should perform the same as every other cell (water usage, charging/discharging voltages, specific gravity, temperature)--You are looking for cells that are behaving "differently" from the rest (cold/hot, bubbling too much or not enough, specific gravity higher/lower than rest of cells, etc.). That will (usually) be your first indication of a failure.
-Bill
Most often I see a variation in the middle-to-negative end of the strings. In the past when I worked for Sun Edison, I dealt with only very large FLA's. Now, it's only AGM's from Concorde and Fullriver for me - and it's the same thing.
The pattern is identical. I cannot put my finger on a cause (but I would love to know!):
- The manufacturer spec's a charging voltage. Typically between 2.4v to 2.47v.
- Measuring individual cell voltage in a 24 battery series string will invariably show numbers WILDLY varying from this.
- But the bank voltage is right on the money at 58.8v for example.
- I have measured this on a new system during the break-in period.
- I have measured this on a 10 year old battery bank with 79% of original capacity.
When discussing this topic with some well known and respected engineers in the industry, I get answers like:
"If you could measure the cell voltage in 6v and 12v batteries you would see the same thing."
Yes, I understand how and why cells can/will have different resistance than other s called "identical" cells.
Yes, I understand how that changes with age, temperature and sometimes orientation. (yes!)
But I cannot wrap my head around a cell that draws a particular current, depending upon its position in the string. I have done this in the field enough times to know it is true.
Been around for awhile, but I suspect that there are smarter folks here than I am. I would love someone to help me understand the dynamics of this.
I always have more questions than answers. That's the nature of life. -
Maybe someone can also answer "why is there so much emphasis on series over parallel when they both have imbalance and the latter is less damaging and easier to fix?".
Middle of the pack sounds like a heat issue.I am available for custom hardware/firmware development
-
I am not sure I understand why series cells go "different"... My suggestion would be more charging towards 100% SOC and equalization... Basically, you have to "over charge" the full cells so you can charge the less than full cells.
I always wondered if a per cell Battery Management System would be the answer... But since flooded cell lead acid batteries are relatively cheap, and do alright with "moderate" equalization once a month or so--It seems that usually takes care of the issue of cell to cell balance.
There are folks here that rotate their batteries because the cells near the positive end of the bank (or it could be the negative end) seem to have lower voltage/state of charge and shuffling the batteries once per year works for them.
Why series vs parallel batteries... If you have a cell go open or shorted, it is very easy to see it when monitoring the string voltage (one series string). If you have two or more parallel strings, then a weak cell is much harder to see during normal operation and maintenance (with the advent of relatively cheap DC Current Clamp DMMs--It is much easier to check each string is carrying its share of the current--open and shorted cells (and bad cable connections/corrosion) stand out very easily when checking current.
The other couple of reasons:
--More cells to check specific gravity/water levels (each parallel string is another set of cells to check)
--More maintenance, more connections to check
--In theory, with three or more parallel strings, each string should have its own fuse/circuit breaker to prevent internal bank short circuits from starting cable fires
--Lead Acid batteries are temperature sensitive--If you have one string hotter than the other, that string's voltage will drop and accept more charging current (and get hotter, etc.).
--Current Sharing from my experience with computer power supplies--The string with the lowest resistance will carry the most current (charging/discharging)--So you don't always get equal current sharing between string. Turns out if you have one string that is hogging all of the current, that string can overheat the wiring/battery post connections and fail--Then the next string with the lowest resistance will carry more current--etc.
My two cents--One series string is "best"... Two parallel string is OK, and I would suggest three parallel strings in about the useful maximum--Unless you have no other choices (many parts of the world, you only have a few sizes/types of batteries available and you have to make do.
-BillNear San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset -
One can add a 4x 12V equalizer ($60 on ebay) to address some of the series voltage balance issue.
> a cell that draws a particular current, depending upon its position in the string.
I don't understand this question. Everything in series draws exactly the same current. Volts and watts can vary.I am available for custom hardware/firmware development
-
Regarding parallel:
When a lead acid battery is fully charged, it draws very, very little current. At absorb voltage, it is 0.05 amps or less of the C/20 rating for Concorde AGM's. This checks in the field - I typically see 1/4 to 1/2 amp per hundred amp hours of battery bank, at absorb voltage when the batteries reach 100% SOC.
With batteries in parallel, yes of course they will charge a different rates, just as they do in series. Sometimes a lot different, other times very little difference. But the "full" batteries draw almost no current while waiting for the other batteries to catch up. So "over charging" them is of little consequence in many systems, because it simply means that the full batteries are sitting at the absorb voltage a bit longer than the others. On industrial projects with a charge rate of 100% or 200% of the C/20, the time lag between batteries reaching full charge is very little. On PV projects with their inherently low charge rate, I most often see 1-3 hours. (In general, I see PV battery banks sized for 15% to 20% average daily DOD)
With Concorde AGM's, a 4-6 hour equalization at 2.58v per cell, will often bring parallel batteries back in line with each other.
For series strings:
I have yet to see a string of 24, 2v cells that are all at the same voltage during bulk/absorb. I sometimes see some of the cells at a higher voltage than "the maximum" voltage published by the manufacturer. With 57.6v applied across the string, it doesn't seem logical that each and every battery will see exactly 2.4v because of differences in individual battery resistance. In general, all of the batteries in a string do not die at the same time, but the overall battery bank life still meets the projected lifespan.
Bill, I too have wondered if a simple battery management system could extend the working life.
I do not pretend to have all of the answers - more like a lot of questions based on field observations!
Marc
I always have more questions than answers. That's the nature of life. -
Doing some testing right now of advanced technology. I would say the reason there is not a BMS for lead acid is a risk reward scenario.
Lead acid is inexpensive and not worth the risk of having a BMS system start a fire. Some of the crazy ideas I read about are even more proof of why this will not happen soon.
And then there is the fact that if a lead acid system is designed and used right from the start, they often last for 10 years and are extremely safe.
Imagine a good lawyer in court against Surrette, Trojan , or US battery asking, "if you have been building these this way safely for 75 years and made this change to BMS you are liable for the house that burned down". Maybe even punitive damages for doing something stupid like this to a known good design."we go where power lines don't" Sierra Nevada mountain area
htps://offgridsolar1.com/
E-mail offgridsolar@sti.net -
http://www.ebay.com/itm/Battery-Equalizer-HA02-4-X-12V-Used-for-Lead-acid-Batteris-Balancer-Charger-/122138833727?hash=item1c700ab33f:g:ZIwAAOSwLF1X3ksV Here is a Chinese model for $75. There is a used 12/24V American model for $89. The schematic makes it look like it could work in principle. However....trying to use it on eight 12 volt batteries looks a bit sketchy to me. That is a lot of wires running around.jonr said:One can add a 4x 12V equalizer ($60 on ebay) to address some of the series voltage balance issue.
> a cell that draws a particular current, depending upon its position in the string.
I don't understand this question. Everything in series draws exactly the same current. Volts and watts can vary.
OK....found the $60 model here: http://www.ebay.com/itm/Battery-equalizer-HA02-used-for-48V-lead-acid-batteris-Balancer-charger-battery-/262134620720?hash=item3d0870e230:g:C8cAAOSwo0JWQD01
The Cooper Bussman's costs at least twice that and are relegated to the 12/24V battery range. In fact, my study indicated they tend to be voltage converters in the 12/24V range.
Think I need a reputable testimony before trying this strategy. This unit may be a fire hazard at this point in time.
Those wires appear to be about 16 AWG. That seems counter-intuitive considering the high amps and low voltages of DC battery environs. Would not take a lot of DC 12 volt current to set a 16 AWG wire on fire. Imagine the 2 volt current.
First Bank:16 180 watt Grape Solar with FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries -
One of the problems with the new battery technology BMS is it is very challenging to build one that can surge 100 amps on a 48 volt system when loads come on. It is a really hard to watch the battery surge for the load and the charge source just trickling. Unacceptable to me. Several other things that are being worked on to make this safe but mum is the word."we go where power lines don't" Sierra Nevada mountain area
htps://offgridsolar1.com/
E-mail offgridsolar@sti.net -
Every single device plugged into any electrical system may be a fire hazard, much less so when you don't locate it adjacent to flammable materials (and yet we still have electric blankets and incredibly complex cars in the garage). If someone is worried about it, add fuses. Or equalize once in a while and live with lower bank life (a result of "WILDLY" different cell voltages).
At one point, someone on this forum reported multiple users of such devices and good results.
There seems to be some confusion about series balancers like the HA02 needing to handle high amps - they aren't in the load path.I am available for custom hardware/firmware development
-
It is the internet! You are free to do as many not so intelligent things as you want.
Keep in mind that "someone on this forum" will not be there when you do something not very intelligent.
Warning flags go up when I hear E-bay BTW. A great source opened boxes of unknown quality and dubious design."we go where power lines don't" Sierra Nevada mountain area
htps://offgridsolar1.com/
E-mail offgridsolar@sti.net -
We can love, or hate, Ebay. Yet it is hard to argue with the fact that it is a known source of finding stuff that often seems virtually impossible elsewhere. Do I want to go through a new sellers rig-a-ma-role check-out process for a $19 trinket? Probably not.
While some "flags" pop up when Ebay is mentioned, for others "$$$$$" pop up when other names are mentioned. Now I am going to look for a titanium jock strap. A stray bullet may hit me this time of year....
First Bank:16 180 watt Grape Solar with FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries -
Dave Angelini said:Doing some testing right now of advanced technology. I would say the reason there is not a BMS for lead acid is a risk reward scenario.
Lead acid is inexpensive and not worth the risk of having a BMS system start a fire. Some of the crazy ideas I read about are even more proof of why this will not happen soon.
And then there is the fact that if a lead acid system is designed and used right from the start, they often last for 10 years and are extremely safe.
Imagine a good lawyer in court against Surrette, Trojan , or US battery asking, "if you have been building these this way safely for 75 years and made this change to BMS you are liable for the house that burned down". Maybe even punitive damages for doing something stupid like this to a known good design.
Dave, I hadn't looked at from that perspective. I have tended to think the other way around:The BMS is to avoid fires with Lithium systems - it never dawned on me to flip that around.
Yep, I see 8-12 years as a pretty standard service life on well designed systems for off grid systems with gel, flooded or AGM as long as the designer knows how to deal with the specifics of the product chosen.
Marc
I always have more questions than answers. That's the nature of life. -
The BMS does many things but it's main job is to allow the 98% to 2% range of the battery and then the safe charge back-up.
I think people who are offgrid and long for the maintenance free aspect will find they are going to have to give-up something, especially people who have difficult loads.
Hard to beat an XW inverter and a big flooded or AGM with the right cabling. It is only one of the things that lithium needs work on.
They also will have to learn how to read a warranty that is very complicated now for early adapters.
I think the key point is whoever builds the BMS had better be right there legally with the battery manufacture. Otherwise in a failure they will blame eachother and the owner will never get warranty let alone damage to the system or structure. That is why I warn people about E-bay and the heart of a power system being compromised. Great fun at a test bench with a fire extinguisher but very dangerous in someones home with a family.
Oh yea... the fire extinguisher had better be a cart with wheels to roll the burning inferno outdoors.
"we go where power lines don't" Sierra Nevada mountain area
htps://offgridsolar1.com/
E-mail offgridsolar@sti.net -
One reason a suggestion for a separate solar+controller+battery shed (and even a second generator shed) can make sense.... If there is a fire, it is away from the residence and can help to limit the amount of damage (lose a generator rather than the entire off grid power system and/or home). And don't under estimate the dangers from smoke and "smoke damage"...
-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset -
Well, there should not be a fire if all the electrical is done right in metal boxes/conduit and one manufacture has listed the whole system.
I almost always think of battery sheds as second best. They are often hot/cold, people do not go in there unless there is a problem so the early warnings of a problem are lost. I like an attached garage or a perimeter equipment room on the house. Nice conditioned space that is large enough for changes in the future and a central smoke detector.
The other way is too condition the space in your shed or shipping container.
I just did a system last year in a 10 foot shipping container that we insulated and drywalled and shipped to Guatemala. The whole system including the solar panels and ground array was in the container. It went thru customs without problems and was prewired/tested 95% so a handyman could connect it in a day + the time to build the groundmount. Part of the array sheltered the container from sun and a mini-split kept the temp/humidity in the sweet spot.
Can we get some rain from you folks in southern sierra?"we go where power lines don't" Sierra Nevada mountain area
htps://offgridsolar1.com/
E-mail offgridsolar@sti.net
Categories
- All Categories
- 243 Forum & Website
- 150 Solar Forum News and Announcements
- 1.4K Solar News, Reviews, & Product Announcements
- 191 Solar Information links & sources, event announcements
- 919 Solar Product Reviews & Opinions
- 256 Solar Skeptics, Hype, & Scams Corner
- 22.5K Solar Electric Power, Wind Power & Balance of System
- 3.6K General Solar Power Topics
- 6.7K Solar Beginners Corner
- 1K PV Installers Forum - NEC, Wiring, Installation
- 2.1K Advanced Solar Electric Technical Forum
- 5.5K Off Grid Solar & Battery Systems
- 438 Caravan, Recreational Vehicle, and Marine Power Systems
- 1.1K Grid Tie and Grid Interactive Systems
- 652 Solar Water Pumping
- 829 Wind Power Generation
- 626 Energy Use & Conservation
- 626 Discussion Forums/Café
- 303 In the Weeds--Member's Choice
- 91 Construction
- 124 New Battery Technologies
- 108 Old Battery Tech Discussions
- 3.8K Solar News - Automatic Feed
- 3.8K Solar Energy News RSS Feed