Hello! We have a 2500w PV system with grid support. Over the last 2 years I have noticed our Classic 200SL showing Batt Over V message at a lower max voltage than before. Our repurposed Chevy Volt LiOn batteries (6 x 50ah, 48v) were installed in 2019. They have a custom BMS with a 13a shunt, and there is no mod-bus or Xanbus connected to either the SW4048 or the Classic. As new batteries (rather than salvaged) their quoted voltage range was 38-49v, but we have kept batteries in a narrower range. Initially we were able to charge batteries with PV or the SW up to 48.0v, but now the Batt Over V shuts down charging somewhere around 47.4v (both from PV or SW charger). Absorb is set to 3 minutes at 48.0v, and Rebulk is set to 47.0. Can the Classic somehow sense that charging is being shunted by the BMS, which is happening sooner due to battery wear and tear? Or is the SW sensing batteries are at capacity and then triggering the Classic to stop charging? Am I missing a setting somewhere that would allow for higher charging? Thanks!
Have you calibrated the cables voltage drop from batteries to Classic ( and inverter ) to make sure they are both reading the same voltages ?
In the Classic there is a place to do that in the Tweaks menu.
You would want to do the calibration for the top voltage and charge.rate around absorb setting.
Larry
Not sure exactly what you mean about the Classic knowing the charging is being "shunted" by the BMS ?
The Classic should not show "over voltage" unless it goes over the set point by some amount, that amount I can't remember exactly but it would be more than 1 volt as I remember.
Do you possibly have battery temperature sensing connected and enabled for this battery ?
Is the Classic reading close to the correct value ?
Also, a short over-voltage should not hurt anything.
Hello, and thanks for your replies. I have adjusted the Classic voltage for cable loss through Tweaks. It was initially off from battery voltage by 0.2v but has stayed fairly stable since then. I checked it with no loads active and while the Classic was in resting phase. When there are bigger active loads and/or batteries are charging, the Conext battery monitor and the Classic voltages differ by 1 volt or even more. I will double check cable loss today.
The BMS is connected directly to one of the 6 batteries through its positive terminal, and then it has another line that connects to the negative lug. I assume that in event of overcharge, the BMS would bypass the batteries and route the charging current back to ground, up to 13a. I'm not sure if the impedance would change or if there would be some other way the Classic would sense that overcharge had happened, despite being at a voltage lower than Absorb. I may be way off on that.
Batteries do have a temperature sensor, but it's connected to the Conext Battery Monitor rather than the Classic. Even with relatively high loads and/or charging, the battery temp seems to stay fairly constant.
One thought I had was if battery terminals, which I tightened a little during the first few months, could have loosened since then.
Thanks again.
Quote from: jwb on December 12, 2022, 09:13:18 AM
Hello, and thanks for your replies. I have adjusted the Classic voltage for cable loss through Tweaks. It was initially off from battery voltage by 0.2v but has stayed fairly stable since then. I checked it with no loads active and while the Classic was in resting phase. When there are bigger active loads and/or batteries are charging, the Conext battery monitor and the Classic voltages differ by 1 volt or even more. I will double check cable loss today.
The BMS is connected directly to one of the 6 batteries through its positive terminal, and then it has another line that connects to the negative lug. I assume that in event of overcharge, the BMS would bypass the batteries and route the charging current back to ground, up to 13a. I'm not sure if the impedance would change or if there would be some other way the Classic would sense that overcharge had happened, despite being at a voltage lower than Absorb. I may be way off on that.
Batteries do have a temperature sensor, but it's connected to the Conext Battery Monitor rather than the Classic. Even with relatively high loads and/or charging, the battery temp seems to stay fairly constant.
One thought I had was if battery terminals, which I tightened a little during the first few months, could have loosened since then.
Thanks again.
Did you use a Fluke meter to measure voltage ?
boB
Quote from: jwb on December 12, 2022, 09:13:18 AM
Hello, and thanks for your replies. I have adjusted the Classic voltage for cable loss through Tweaks. It was initially off from battery voltage by 0.2v but has stayed fairly stable since then. I checked it with no loads active and while the Classic was in resting phase. When there are bigger active loads and/or batteries are charging, the Conext battery monitor and the Classic voltages differ by 1 volt or even more. I will double check cable loss today.
The BMS is connected directly to one of the 6 batteries through its positive terminal, and then it has another line that connects to the negative lug. I assume that in event of overcharge, the BMS would bypass the batteries and route the charging current back to ground, up to 13a. I'm not sure if the impedance would change or if there would be some other way the Classic would sense that overcharge had happened, despite being at a voltage lower than Absorb. I may be way off on that.
Batteries do have a temperature sensor, but it's connected to the Conext Battery Monitor rather than the Classic. Even with relatively high loads and/or charging, the battery temp seems to stay fairly constant.
One thought I had was if battery terminals, which I tightened a little during the first few months, could have loosened since then.
Thanks again.
I don't understand your BMS set up or shunt setup .
A bms like I think about monitors and balances individual cells in a single battery.
Only sensing one battery isn't the best because every battery ( in your parallel string ?) could have different voltages . That is unless you have some kind of smart BMS that will adjust the current in each individual battery to keep the voltages of them close to the same.
Larry
I think our BMS is not smart, but more like a "Chernobyl switch" that only prevents overcharge rather than making sure the parallel batteries are coordinated. I use a generic multimeter rather than a Fluke to check voltage. Is Fluke the standard? I probably need to shut the system down, pull out all batteries, and check voltage on each one after they have been disconnected. Maybe one or more of the batteries is degrading faster than the others and limiting max voltage. Thanks again for your replies.
Quote from: jwb on December 12, 2022, 02:58:52 PM
I think our BMS is not smart, but more like a "Chernobyl switch" that only prevents overcharge rather than making sure the parallel batteries are coordinated. I use a generic multimeter rather than a Fluke to check voltage. Is Fluke the standard? I probably need to shut the system down, pull out all batteries, and check voltage on each one after they have been disconnected. Maybe one or more of the batteries is degrading faster than the others and limiting max voltage. Thanks again for your replies.
Flukes are well known for their accuracy but they are a bit pricey.
The Kaiweets on Amazon have been reviewed by a few electronics experts and tested and received good words for accuracy .
This model is is selling for around $25 with coupon on Amazon . Their other smart model is even a bit nicer . They have some decent ac/dc clamp on meters too.
So if you have generic meter meaning those cheap ones from like Harbor Frieght or other places - an upgrade would be nice. I had an older digital meter that I thought was half decent and when I got the new Kaiweets I noticed how far off it was on voltage. Not a big deal on a lot of things but if you start wanting more decimals on individual lithium cells or battery packs it makes a difference.
https://www.amazon.com/gp/product/B07SHLS639/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
This is the one that I got last year and I like it .
https://www.amazon.com/KAIWEETS-Multimeter-Electrical-Capacitance-Temperature/dp/B09GF2FZVY?ref_=ast_sto_dp
review of above - I think he also reviewed the other one I linked too.
https://youtu.be/tiDYCNnkGGo
Larry
Fluke meters are pretty much the standard but not absolutely necessary.
It's just that you should be able to trust a Fluke meter. Even the Harbor Freight meters are pretty good for measuring battery voltage.
As long as you have lithium batteries, it might be a good idea to compare the meter you have with another meter or two just to see if they agree well. Especially at around the battery voltage you are using.
If you can compare to a Fluke then you would know how good your meter is and then you can pretty well trust it.
boB