Another Top Balance Screwup

[Hedges]

Low C rate isn't what would cause damage, sitting for a long time at high SoC is what would cause damage.

Charging several cells at a time to 3.6V and then letting them sit while charging others sounds like unequal treatment.
Charging all in parallel to 3.6V seems better.

Why not charge all in parallel to 3.5V or 3.4V? Lower voltage, much less degradation. You have time on your hands, so can sit a long time at 3.4V to let them trickle up.

No reason to get to a high SoC before building a series pack with BMS, at which point you'll use them, get to a lower SoC, and then recharge to some (possibly lower) SoC.

 

[DerpsyDoodler]

So I can charge each battery in the pack at a higher C, since from what I've read in a couple posts in this thread that the battery could be damaged by low C charging for a long period of time. For example if I charge just 1 battery I could put in up to 40 AMPs at 3.2V rather than 1/16 of that which I am doing now.

I wonder if you’re not referring to float voltage settings. To my knowledge slow charging won’t hurt the cells.

 

[cinergi]

I believe he's referring to previous postings and external material showing that you don't want to spend days getting your cells from 3.45 to 3.65 because that's damaging your cells. Once your charging gets past the knee, it won't take that long to hit 3.65 even with 16 in parallel. I wouldn't worry about it. It's a one-time event and relatively short-lived.

 

[Hedges]

I believe he's referring to previous postings and external material showing that you don't want to spend days getting your cells from 3.45 to 3.65 because that's damaging your cells. Once your charging gets past the knee, it won't take that long to hit 3.65 even with 16 in parallel. I wouldn't worry about it. It's a one-time event and relatively short-lived.

Except, he doesn't have a BMS yet.
If he parallel top balances to 3.65, the cells will sit there, possibly for days (ETA of BMS in a week, but who knows?)
So if he does parallel balance them to a high voltage now, should connect in series and then bleed down to a lower voltage.
Even without BMS that should be safe, so long as not deeply cycled, just drawn down to flat part of curve. Then all loads disconnected.

 

[Gazoo]

I have a situation where I don't yet have a working BMS (I had them but long story short they are toast). I received a set of Lishen 270A which were all 3.29v open circuit. Maybe 1 of them was 3.28v. I watched numerous videos talking about top balancing and put them in parallel and put my adjustable 40A power supply at 3.6v open circuit, then connected to the middle of the pack. The supply started at about 28 amps and after 48 hours the power supply is putting out about 25 amps. Obviously this is very low C per cell. This thread is the first I've heard that you could shorten the life of your cells by top balancing them at very low C. I don't think I've ever seen a video mentioning this. In fact I've seen quite a few videos and posts where people are top balancing for a really long time. In a week or so I expect to get a new BMS, but I'd love to do something with these cells in the meantime. What do folks here recommend I do?

1) Keep charging and just be patient - low C won't damage my battery
2) Group into smaller packs and charge them at higher C with my 40Amp power supply
3) Configure them into 16s and connect them to my Sol-Ark which can charge up to 185A@48V while carefully monitoring the cells (I plan to connect a couple of ISDT battery monitors to monitor the cells real time) and then disconnect when the highest cell is around 3.6 (or lower)
4) Something else

Thanks all for your input.

-Keith

I believe there is some misinformation that has been posted regarding this. The majority of us have successfully parallel top balanced cells at very low C rates with no damage. I top balanced my 8 EVE 280ah cells using a 12 amp power supply. Some have done it using 5 amp power supplies.

1) Keep charging and just be patient - low C won't damage my battery

That is correct. Patience is key and you know that so you will be fine.

 

[cinergi]

Except, he doesn't have a BMS yet.
If he parallel top balances to 3.65, the cells will sit there, possibly for days (ETA of BMS in a week, but who knows?)
So if he does parallel balance them to a high voltage now, should connect in series and then bleed down to a lower voltage.
Even without BMS that should be safe, so long as not deeply cycled, just drawn down to flat part of curve. Then all loads disconnected.

I'm not aware of evidence that says disconnecting after hitting 3.65 and letting them fall to a resting voltage of ~3.5 (literally 100% SoC) for weeks (especially at < 25 degrees C) will cause any tangible reduction of cycle life.

 

[Bob B]

If you already have them all parallel, I would leave them that way and charge up to 3.4 or so and wait to charge them the rest of the way til after you have the BMS. Then charge them the rest of the way to 3.65, which should be fairly quick since once you hit 3.4 your are pretty close to the knee.

I don't think we know how long the batteries can be held at 3.65 before some damage starts to occur. I guess from a practical aspect, the take away would be hold them in the upper knee for the shortest amount of time the equipment you have allows.

 

[John Frum]

I'm not aware of evidence that says disconnecting after hitting 3.65 and letting them fall to a resting voltage of ~3.5 (literally 100% SoC) for weeks (especially at < 25 degrees C) will cause any tangible reduction of cycle life.

@Dzl has posted a graph that indicuates storing batteries full accelerates calendar aging.

 

[Bob B]

Rumor around the campfire is that storing batteries full accelerates calendar aging.
@Dzl had a graph.

I think the concern is from warnings from @toms who hates the way top balancing is done by most people.

 

[cinergi]

@Dzl has posted a graph that indicuates storing batteries full accelerates calendar aging.

Found this: https://diysolarforum.com/threads/280ah-cells.10607/page-32#post-166525

95% capacity after 9 months at 100%. Doesn't even get better until you go below 80%. So, I wouldn't worry about a few weeks at 100%.

 

[Bob B]

Found this: https://diysolarforum.com/threads/280ah-cells.10607/page-32#post-166525

95% capacity after 9 months at 100%. Doesn't even get better until you go below 80%. So, I wouldn't worry about a few weeks at 100%.

That chart also demonstrates that is makes a huge difference what the battery temperature is.... the capacity drops to 85% at 50 deg c.

It would really be interesting to know if storage temperature is the more important factor .... what would the loss be if stored at 40% SOC at 50 Deg c?

 

[Just John]

Its this power supply:

https://www.amazon.com/gp/product/B07ML2MP9Q/ref=ppx_od_dt_b_asin_title_s00?ie=UTF8&psc=1

Doesn't look like it using ring terminals?

Unscrew the covers on the banana jacks, it takes ring terminals just fine. If you want to use it to charge the common Lishen or Eve cells with M6 terminal screws, 1/4 inch crimp ring terminals are easy to find and fit great. Use 10 gauge copper wire (not solid, but many fine strands). Sorry for the late reply, but yes I do have that power supply.

 

[Gazoo]

That chart also demonstrates that is makes a huge difference what the battery temperature is.... the capacity drops to 85% at 50 deg c.

It would really be interesting to know if storage temperature is the more important factor .... what would the loss be if stored at 40% SOC at 50 Deg c?

I would also like to know the date of that chart. Although the manufacturers do mention storing at a low SOC.

 

[Just John]

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.

Thanks Will. I just noticed that supply is the same one I just tested at full output, and noticed that it has much better alligator clips and leads than any other brands.

Thread 'Cheap power supply for top balancing (tested and works well).' https://diysolarforum.com/threads/cheap-power-supply-for-top-balancing-tested-and-works-well.19846/

 

[Just John]

I know some of these 10 amp supplies sold on Amazon come with 18awg cables like this one which I believe is the same one @Will Prowse used in the video.

DC Power Supply Variable, 0-30 V / 0-10 A LW-K3010D Adjustable Switching Regulated Power Supply Digital, with Alligator Leads US Power Cord Used for Spectrophotometer and lab Equipment Repair: Amazon.com: Industrial & Scientific

DC Power Supply Variable, 0-30 V / 0-10 A LW-K3010D Adjustable Switching Regulated Power Supply Digital, with Alligator Leads US Power Cord Used for Spectrophotometer and lab Equipment Repair: Amazon.com: Industrial & Scientific

www.amazon.com

They come with alligator clips and banana plugs. Cheap cables and poor connections = low current. At higher voltages it isn't as much of a problem. The higher the voltage the less voltage drop using the same current. It's this 3.65 volt that is a pain.

Anyone can use wire size and voltage drop calculators to see 18awg is not sufficient. I used two feet of 12awg and it worked great but I was still experiencing apx. .2 voltage drop between the terminals of the supply and the cell terminals.

If using 2 feet of 18awg wire with a 10 amp power supply set at 3.65 volts the voltage drop is 7%. Using 12awg wire the voltage drop is 1.75%. That is a huge difference and does effect the current output of the power supply.

It has been proven time and time again using 10 or 12awg cable and ring terminals greatly increases the current output of the power supply when the supply is first set to 3.65 volts and then connected to the cells. There is no need to turn up the voltage of the supply when using better cables and connections and we know what happens when people do that.

Anyone suggesting it's ok to use the cables that comes with the power supply when it's only 18awg cable is making a misleading statement. Will 18awg work? Of course. But it's not recommended.

Oddly enough, that exact power supply has the best alligator clip leads of all the cheap supplies. Not 10 gauge, but better than 18 gauge. "Best" is relative, they only suck, but can actually carry 10 amps.

 

[John Frum]

Oddly enough, that exact power supply has the best alligator clip leads of all the cheap supplies. Not 10 gauge, but better than 18 gauge. "Best" is relative, they only suck, but can actually carry 10 amps.

Anyone got a source for suitable alligator clips or ready made leads with alligator clips?

 

[Just John]

I believe he's referring to previous postings and external material showing that you don't want to spend days getting your cells from 3.45 to 3.65 because that's damaging your cells. Once your charging gets past the knee, it won't take that long to hit 3.65 even with 16 in parallel. I wouldn't worry about it. It's a one-time event and relatively short-lived.

I did some measurements, from 3.45 to 3.65 is around 10 amp hours, from 3.0 to 2.5 is around 5 amp hours. From around 100 amp hours full, 4 cells in parallel takes about 2.5 days using a 40 amp supply. It will start out at 30 to 35 amps, next day about 25 amps, once it gets down to 10 amps, less than 4 hours until it drops under 1 amp. This is using 10 gauge wire and crimped ring terminals. Also assuming you don't have a cat hair on a terminal making you check all the connections!

 

[Just John]

Anyone got a source for suitable alligator clips or ready made leads with alligator clips?

Yes, but Amazon is out of stock at the moment.

 

[Just John]

Anyone got a source for suitable alligator clips or ready made leads with alligator clips?

Here you go, these look like what Longwei ships with their supplies

https://www.amazon.com/dp/B07NWXR4GJ/ref=cm_sw_r_cp_apa_fabc_8HG7S36P2A2Z0B2VF1G7

These look like what most others ship

Amazon.com: Alligator Clip to Banana Male Plug Test Lead Cables (US Stock; Fast Handling) : Industrial & Scientific

Buy Alligator Clip to Banana Male Plug Test Lead Cables (US Stock; Fast Handling): Test Probes & Leads - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

 

[Gazoo]

Oddly enough, that exact power supply has the best alligator clip leads of all the cheap supplies. Not 10 gauge, but better than 18 gauge. "Best" is relative, they only suck, but can actually carry 10 amps.

I was going by the description (Cable Conductor Wire Size: 0.15mm Copper Wire, 18AWG, super flexible

I did notice the alligators look heftier than others. I still believe it's best to recommend ring terminals and at least 12awg cable especially if someone is complaining their supply isn't putting out the rated amps.

Voltage drop is much less at 12 volts (.16 volts or 1.34%) than 3.65 volts (.26 volts or 7%) using 2 feet of 18awg wire. What is the length of the cable that comes with that power supply?