Wow that is a fun idea :D
Another Top Balance Screwup
- Thread starter Luthj
- Start date
To be fair, you did talk about cranking up your PS higher than 3.6 for a parallel top balance because you're impatient and said something about that being an advanced tactic or something
I don't remember which video it was. But it stuck with me and led me down the dark path (despite being advanced with this stuff).Getting these 280Ah cells to full for the first time is a *bitch* ... and I've taken to the tactic of putting them in series with a BMS, charging until HVDC, and then finishing with a top balance. Because, from the factory, they're arriving at 40-60% SoC (for the most part) and that's a hell of a long time to top balance, especially with the crappy cables that come with these power supplies.
Some of the confusion is just how these power supplies work. You have to set the voltage BEFORE you connect. Some of the mistakes are from people setting the voltage after the connection.
I'm constantly impressed by how elusive the flat voltage curve is for people here. They think their batteries aren't charging so they increase the voltage to get more amps blah blah blah. And to be honest, I was shocked the first time I experienced the flat curve even though I knew about it. Even after dealing with it multiple times, it still messes with my head. It's truly something to behold.
I wouldn't say you have a responsibility, but you do have the reach and audience and power. A new top balancing video that stresses all these points might be helpful. And never ever mention any advanced techniques.
Maybe Top Balancing Video and Instructions should include an extra step.
This extra step would include checking voltage drop on cables and terminals. This was eye opening to me after only dealing with high voltage for years. I found the crappy cables with my Rider Power supply make a big difference, that the Riden RD6018 has voltage drop on the battery terminal of 100mv at 18 amp, and I needed to clean oxide off the cells (10mv). Finding these issue and fixing really changes the charging experience.
This extra step would include checking voltage drop on cables and terminals. This was eye opening to me after only dealing with high voltage for years. I found the crappy cables with my Rider Power supply make a big difference, that the Riden RD6018 has voltage drop on the battery terminal of 100mv at 18 amp, and I needed to clean oxide off the cells (10mv). Finding these issue and fixing really changes the charging experience.
At some point we are moving into advanced knowledge territory. I know EEs who (through lack of experience) have trouble understanding DC circuits with batteries and power supplies without drawing a circuit diagram (mmm superposition).
There is a small number of people who get into a hurry, make assumptions (you can't stop people from doing that), and make mistakes. Its the very nature of DIY. Thankfully LFP are very forgiving, and total meltdowns are basically unicorn events.
There are cell level disconnect boards, which could be used to protect a parallel charged bank.
I am a big fan of series charging, and then using a single power supply (and/or resistor bleed method) to take care of any low/high cells. But this requires a level of understanding/experience that many do not have. Plus every time you have a newb connecting and disconnecting leads, there is a risk of an accidental short.
Again I would like to point to the outcome of the subject of this thread. With a stiff compression fixture the cells are performing nominally after 5 cycles, and will be used in an off grid cabin somewhere. I have advised that they stick with 3.45-3.50V to reduce any future balance issues, and that the pack not be places on top of any flammable materials due to the slightly increased risk of internal shorting as the cycles pile up.
Despite gross abuse the cells did not catch fire, and with 50W of input power they did not get particularly hot either. Now if the charger had been capable of 500W? The cells may have vented, but its hard to say.
There is a small number of people who get into a hurry, make assumptions (you can't stop people from doing that), and make mistakes. Its the very nature of DIY. Thankfully LFP are very forgiving, and total meltdowns are basically unicorn events.
There are cell level disconnect boards, which could be used to protect a parallel charged bank.
I am a big fan of series charging, and then using a single power supply (and/or resistor bleed method) to take care of any low/high cells. But this requires a level of understanding/experience that many do not have. Plus every time you have a newb connecting and disconnecting leads, there is a risk of an accidental short.
Again I would like to point to the outcome of the subject of this thread. With a stiff compression fixture the cells are performing nominally after 5 cycles, and will be used in an off grid cabin somewhere. I have advised that they stick with 3.45-3.50V to reduce any future balance issues, and that the pack not be places on top of any flammable materials due to the slightly increased risk of internal shorting as the cycles pile up.
Despite gross abuse the cells did not catch fire, and with 50W of input power they did not get particularly hot either. Now if the charger had been capable of 500W? The cells may have vented, but its hard to say.
FilterGuy
Solar Engineering Consultant - EG4 and Consumers
Wouldn't the BMS trip before the current goes to zero?
John Frum
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Since you are measuring at the terminal just set the bms to trip at 3.625 and set the charge voltage to 3.65 that way there will still be some current when the bms trips.
Bob B
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I saw the video linked below for the first time today .... and I have changed my opinion somewhat and think it is probably the reason we have so many threads about top balance taking so long ... and damaged cells during top balance.
Even though @Will Prowse did mention several times that these cells were at a high state of charge .... that if they were at a low state of charge that they should be placed in groups of 4 to get them to a high state of charge first .... that not getting to a high state of charge first, it could take a long time. ......
I think the NEWBY take-away from this video would be ..... just take my commodity 280 ah cells out of the box, connect them in parallel, and they should be top balanced in a couple of hours .... Oh, and if it isn't going fast enough just crank up the voltage a little bit.
At around 4:40 in the video, Will committed the cardinal sin of adjusting the power supply voltage while the power supply connected. He didn't mention that the crappy leads that come with these cheap power supplies will limit the current you will get. If you make leads with 10 or 12 gauge wire and connect with ring terminals on both ends, the current will come up with no boosting of the voltage. We have to tell people over and over again ..... ADJUST THE VOLTAGE WITH THE LEADS DISCONNECTED AND DON'T TOUCH IT AGAIN. If using good leads, the voltage of these power supplies will normally drop when connecting the leads.
These are the top 2 things that there are so many top balance threads and screw-ups.
Sorry for a somewhat harsh post, but I think Will needs to take this video down and re-do it with some of the ideas on this thread.
Even though @Will Prowse did mention several times that these cells were at a high state of charge .... that if they were at a low state of charge that they should be placed in groups of 4 to get them to a high state of charge first .... that not getting to a high state of charge first, it could take a long time. ......
I think the NEWBY take-away from this video would be ..... just take my commodity 280 ah cells out of the box, connect them in parallel, and they should be top balanced in a couple of hours .... Oh, and if it isn't going fast enough just crank up the voltage a little bit.
At around 4:40 in the video, Will committed the cardinal sin of adjusting the power supply voltage while the power supply connected. He didn't mention that the crappy leads that come with these cheap power supplies will limit the current you will get. If you make leads with 10 or 12 gauge wire and connect with ring terminals on both ends, the current will come up with no boosting of the voltage. We have to tell people over and over again ..... ADJUST THE VOLTAGE WITH THE LEADS DISCONNECTED AND DON'T TOUCH IT AGAIN. If using good leads, the voltage of these power supplies will normally drop when connecting the leads.
These are the top 2 things that there are so many top balance threads and screw-ups.
Sorry for a somewhat harsh post, but I think Will needs to take this video down and re-do it with some of the ideas on this thread.
DerpsyDoodler
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Think he might recreate the video?
Just edited the video and took out the advanced option. If a beginner were to follow something that I stated "Beginners do not attempt!!!" in the video, and vocally stated by me, then I do not feel bad for them over charging their packs.
If someone is an advanced user and understands voltage drop on the leads and other factors that determine how these cells balance, they can crank the voltage like I do all the time.
How I just edited the video will allow beginners to only know one method. Set voltage, attach leads. Wait till current drops to nearly zero or .1A.
Simple method and they can't screw it up.
No I am not going to recreate the video.
Hedges
I See Electromagnetic Fields!
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Overlay a note, "Do NOT adjust like this, it can kill your battery!" with a circle/slash over his hand
Hedges
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Me? I would just use a supply with remote sense.
But that's because I like to spend small bucks on equipment that used to be big bucks.
Don't believe me? Just watch! ?
But that's because I like to spend small bucks on equipment that used to be big bucks.
Don't believe me? Just watch! ?
No not true about the leads. If you buy a good power supply with thick leads that can handle ten amps, it should be fine. If someone does not understand current capacity of a conductor, and they are building a raw cell battery, then they need to study the basics first.
I try to make this stuff as simple as possible, but I am not going to a do a full blown lecture about conductor sizing in every single video.
How the video is set now will ensure that people will never screw it up.
Give it a few hours for the edits to update. That segment of the video will be removed forever. I do not feel bad for having that section in because I stated that beginners should not attempt that.
I cannot add an overlay to the video any longer. That was an option a few years back, not anymore. I will add a note to the description. I could add a "card" but it would be hard to see.
haha! Yeah, that is the proper way to do it. Is there a cheap supply with a remote sense?
This is the updated description. What do you guys think? And the video edits are now live:
Hedges
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One out of two ain't bad?
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That's why I buy old boat anchors. Didn't happen to need low voltage high current, but I have 4x HP supplies (quad & triple output) some up to 50V and some up to 7A. I used those to power my analog board designs without the problematic custom 10-output switching board someone else designed. For instance, quad output 50V @ 1A supplies gave me +/-100VDC. The old HP supplies cost me between $50 and $200 each.
What you use is probably best for demo to DIY crowd. I didn't spot any modest price remote-sense supplies when I looked to suggest for the other members. Probably out there somewhere, though.
Hedges
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Except, anybody here is probably getting reject cells which were yanked from testing with random SOC, probably need balancing.
I was thinking about my idea of assemble and charge series pack with BMS, then top individual cells. That is a new approach, and don't want to have to disassemble. If assembled with tall enough grub screws, leads for the supply could be put on top.
