A Question of Balance

[Kingfish]

Do you have a balancing charger of any sort?

Never.

When I first got into the hobby I had LiFePO4 with a BMS. Then I converted to LiPo and bought the blinkies because I already had a charger. Then I upgraded to Meanwells S- and SP-units. And now the HRP-600 series. I've left my packs connected and topped off from time to time. The only problem I had ever was on the first trip to California when I ran into a windstorm and drew the pack down to the LVC mark. That killed off 5 bricks.

I don't want to go through that again. And the Blinkies take too long. Can't get a Battery Medic cos they're on backorder. Can't source a reasonable BMS without falling back to cumbersome technology that doesn't support 15S. I am left with only Balance as an option. It's not rocket science; just simple math, yes?

• A cursory review of JST-XH connectors suggests that the leads are 22-18 AWG, with the majority of posts leaning 18 AWG. Once source suggests that 18-guage wire can handle 18A @ 12V.
• Most bricks can handle 2C charge, and if they are 5Ah, then we're looking at 10Ah. If each cell was max'd out to 4.3V, that would be 4.3 * 10 = 43Wh.

Am I on the right path?

~KF

[neptronix]

Oh dear.
You need some kind of balance charger. Not just because they are great at balance charging and all that , but because they can also be used to analyze batteries too.
The factory balance is absolutely horrible, so each pack needs to be balanced from the get go.
A 1010b+ would be great since you could do double duty on those 5s packs.

The leads are about 24awg at the battery themselves. They would hopefully act like fuses if you connected significantly misbalanced packs to each other.

4.3v/cell will drastically shorten their life span for a small capacity gain. Don't recommend it.

[Kingfish]

You're misreading what I am explaining:

For calculations, I presume the worst. I do not charge to 4.3V/cell; I use 4.3V as the worst-case to determine potential maximum current

I have zero-interest in purchasing something I consider not meeting my requirements; the iCharger was ruled out long ago. That would be a step-backward when We need to focus forward.

Back to the engineering solution:
43Wh/1h = 43W. Closest overrated Resistor is 50W. Went to TheFind and sourced a few out of curiosity more to understand what industry uses a 50W resistor.

What is the relationship of resistance to current? If I want to slow the flow and yet dissapate safely, is this a 1:1 relationship?

Little help plz, KF

[Kingfish]

Found this thread: Spark avoidance and precharge resistor which points to "No Spark" Resistor.

Looks like this can be accomplished with a whole lot less complexity, like maybe a 2W 50 Ohm for safe and sleepy throughput.

Still reading, KF

[number1cruncher]

KF - Do you have any CellLog8s or other trusted monitors? Or DVM, buts that's just a hassle. If the cells are within .05V, packs within -+1V, it would be okay to hook up without a resistor.

Do you have any 24V meanwells? Maybe charge each pack to something like 23.4V (3.9v per cell) and see what the cells look like. If similar you're good to go.

I both admire and respect your decision not to use a balance charger. I only use mine to charge ALL the other crap in my house not ebike related. Like the nicad cheese grater. It had a wall wart that did not perform right. Sat in my attic for 5 years before its resurection. My $30 turnigy fixed it. Sold my wife on the benfits of the ebike hobby.

If not for the bike, maybe everything else around the house I recommend: http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=15167 (out of stock atm) and http://www.sureelectronics.net/goods.php?id=59 (wow, these have got a little pricey). The 12V DC supply comes in handy for a multitude of tasks, but I digress...

Good luck and have a safe journey along the Left Coast!

[Kingfish]

KF - Do you have any CellLog8s or other trusted monitors? Or DVM, buts that's just a hassle. If the cells are within .05V, packs within -+1V, it would be okay to hook up without a resistor.

Do you have any 24V meanwells? Maybe charge each pack to something like 23.4V (3.9v per cell) and see what the cells look like. If similar you're good to go.

I both admire and respect your decision not to use a balance charger. I only use mine to charge ALL the other crap in my house not ebike related. Like the nicad cheese grater. It had a wall wart that did not perform right. Sat in my attic for 5 years before its resurection. My $30 turnigy fixed it. Sold my wife on the benfits of the ebike hobby.

If not for the bike, maybe everything else around the house I recommend: http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=15167 (out of stock atm) and http://www.sureelectronics.net/goods.php?id=59 (wow, these have got a little pricey). The 12V DC supply comes in handy for a multitude of tasks, but I digress...

Good luck and have a safe journey along the Left Coast!

No cellLogs. I have an S-350-27 CC that I think can be turned down pretty far, but that's a good idea - just zap them individually before connecting

Left Coast: No doubt about it. I've often heard some particular cities described as being like a bowl of granola: Remove the fruits and nuts and yer left with a bunch of flakes Maybe that's why I always ate Cap't Crunch with Crunchberries...

Checkin' fer cavities KF

[Kingfish]

Balancing Plug

I’ve gone ahead and drawn up this little schematic just for grins. Essentially it shorts all the positive pins together, equalizing the potentials between the cells. With two or more these can be tied together in prior to attaching to the parallel cable.



The only thing missing is a fuse or micro-breaker.

What about an inline LED, one in each direction: The LED would light up until the potential is equalized.

Full of ideas, or at least full of something…
~KF

[Kingfish]

bump.

Also another question; forgive me ~ I am a noob:

Would you leave the balancing cables attached whilst in use? I am not talking about the entire pack, just the 6-to-1 bundles.

Thanks, KF

[number1cruncher]

bump.

Also another question; forgive me ~ I am a noob:

Would you leave the balancing cables attached whilst in use? I am not talking about the entire pack, just the 6-to-1 bundles.

Thanks, KF

Any packs hooked to the 6-to-1 can not be series connected to each other, otherwaise you get KFF. Is this what you are asking?

[Kingfish]

bump.

Also another question; forgive me ~ I am a noob:

Would you leave the balancing cables attached whilst in use? I am not talking about the entire pack, just the 6-to-1 bundles.

Thanks, KF

Any packs hooked to the 6-to-1 can not be series connected to each other, otherwaise you get KFF. Is this what you are asking?

Yes, exactly, thank you

I will need to re-strategize my thinking on how to maintain this in the field.

FWIW, I recently checked my extra reserve pack; this was actually the original pack, though after the road trip last year I cycled the batteries out with the “new” batteries and have been running those for close to a year. Anyway – this pack has seen more abuse and was last charged some months ago, although every cell was still within 0.03V within the 5S1P unit, and 0.08V between the high and low of all cells.

Am I worrying too much? KF

[rhitee05]

Unfortunately, I don't think there's a simple passive circuit that you can hook up to balance your cells. If there were, I suspect GGoodrum/Fechter would have been all over it a long time ago... If you just hook up a string of resistors along your 5S pack, one across each cell, the cells will just discharge individually with nothing to guarantee they end up balanced. That's why the BMS uses a transistor to actively control the current and balance the pack.

If you don't have or want to invest in something that will actively balance the pack, my suggestion would be to use your Meanwell to fully charge each one to your normal charge voltage. You should check the voltage on each cell, so if it's all you have a DVM will work if tedious. Like dogman said, I think +/- 0.05V is fine, so I wouldn't be surprised if the cells end up within those limits on their own. If not, you can manually use a resistor to discharge a little from the high cells. Then I think you'll be fine to just connect them together, either permanently or with a pigtail.

If you can't exactly match the individual cell voltages, I think it's a little safer to connect them at full charge rather than near midpoint. My reason is that the voltage/charge curve for LiPo is fairly steep here. That is, there's not a lot of energy stored between 4.2V and 4.15V as the surface charge dissipates. There is a lot of energy stored between 3.85V and 3.8V. Less of an energy difference means that it'll be easier for the cells to equalize after you connect them.

If you want to be really cautious, build up one of those parallel pigtails with resistors between each pack on the balance leads. Something like a garden-variety 1k 1/4W resistor will be fine. If you plug the packs into that first, the resistors will allow the packs to slowly equalize. Let them sit like that for a little while, then you can plug them into the real pigtail without resistors. I think this method should work even with packs that are fairly out-of-balance since the resistors will limit the current even if the cells are substantially different - you'd just have to let them sit for a while.

[Holocene]

Uh, bulk-charge the pack with the Meanwell. Until you can source a Battery Medic, you can top balance individual cells with a cell-phone charger. Limit balance charge rate to Max 1 amp through the little balance leads.

[Kingfish]

Uh, bulk-charge the pack with the Meanwell. Until you can source a Battery Medic, you can top balance individual cells with a cell-phone charger. Limit balance charge rate to Max 1 amp through the little balance leads.

I sourced a Battery Medic yesterday from A Pro Hobbies. Actually the call it a "3in1 2S-6S Lipo Medic System - Discharger / Balancer / Voltage Meter".

I also have the Battery Medic Booster kit from TPPacks which I plan to integrate with the above device for improved performance.

It's the best that I can hope for at this point
~KF

[Spacey]

Are you referring to parallel balancing?
If so, this is what i have my 5s packs plugged into:



And then the charge/discharge leads are all plugged into parallel harnesses too.
They are thusly, for reasons of charging, balancing, and discharging, large 20 amp hour packs. The cells keep each other even, and the pack voltage as a whole keeps itself even too.

The only thing that can throw them severely out of balance is if there is one cell in the parallel pack that is super wonky. In that case, i disassemble the pack and cycle each one to find the weak pack.

Trying to find these plugs that are for 8 cells i.e 9 wires... nowhere sells them

[scoot]

ProgressiveRC will make you a custom one pretty inexpensively if they don't stock it. EP Buddy is another supplier that may do so it as well.

[neptronix]

Good link, kingfish. Let me know how that battery medic works for ya.

Maybe the ones hobbyking sells are the rejects that weren't calibrated so well. You never know...!