Why isn't "node charging" through the balance leads more common?

I had suggested a rectangular connector to replicate the JST connector for simplicity, but node charging through the balance leads requires up-sizing the balance leads at each cell, and then re-terminating both JST connectors and possibly up-sizing the charger balance leads back to the charger PCB. The technical ability and commitment would therefore seem to open up better, non-rectangular options -- namely (if using proper multi-conductor cable for the charger side) ubiquitous circular connectors, from cheap commodity DIN connectors to expensive locking industrial and mil. spec. connectors.

Positive locking (with confirmation) and extra quick mating/unmating is desirable:
Primer on circular connector locking mechanisms
1/3 bayonet is nice because it does not require high force (90-130N) normal to the receptacle, and instead cams the plug into the receptacle with leverage. Bayonet also provides both audible "click" and tactile locking confirmation.

Affordable & lightweight plastic construction is desirable.
The 1/3-turn bayonet Souriau UTS series offers 7 #20 gold-plated contacts for 18AWG wire/8mm cable in a size 10 shell, but only rated for 250 mate-unmate cycles.
The new Souriau UTGX is still plastic, but includes a metal mating nut rated for 500 mate-unmake cycles.

More advanced would be combining multiple node chargers into a single connector.
2x 6s node chargers would still require 2x 7 balance leads = 14 contacts. The 250-cycle UTS series offers a 14 #20 for 18AWG wire in a size 12 shell.
3x 6s node chargers would still require 3x 7 balance leads = 21 contacts. The same UTS line offers a 23 #16 in a size 18 shell.

Is durability a concern? Being rated conservatively for industry, everything (force, resistance) is guaranteed to remain in spec for that cycle count, but usable for much more.
I can't find a rating for JST, but being a board connection, might only be in the tens of cycles.
Real XT-series (60, 90, 150) are rated for 1000 cycles, but fakes are ubiquitous and rarely result in complaints.
Still, the upgrade to the 500-cycle UTGX is likely worthwhile.

If longer cycle life is desired, it seems there aren't any better options for plastic 1/3 bayonets. Lumberg/Lutronic Quicklock for 16AWG wire/13mm cable is rated to 1700 cycles, but they're latching quick connects requiring high normal force to insert and lock, and only confirm with an audible click. But they are probably easier to mate blindly.
Plastic LEMO 3B push-pulls for 16AWG wire are rated for 5000 cycles, but those are expensive and not available.

Does anyone have experience with these circular connectors, to provide insight/comparison?

spinningmagnets said:

BMS's are the cause of a pack death "often enough" that it's a reasonable risk to run a battery pack with no BMS.

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Agreed.

spinningmagnets said:

3) assemble a balance charge system like Teklektik. A 14S pack would have 14 small 4.1V chargers to individually charge each cell (or possibly only 7 chargers, with two separate 7S harnesses on the pack)
4) if you add 14 tiny cheap digital voltage readouts, you can clearly see when you need to take the time to do a "balance charge". It might only be once a month...

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Well, you're sort of describing a simple node charger here, except only one charge current and end voltage would be possible, monitoring is cumbersome, points of failure are increased as every individual charger has to convert AC, etc. And as I understand it, every cell would need two charge leads, so 2n for the pack, rather than n+1 with an RC node charger. That would become a real problem when selecting connectors, as a 6s pack would require 12 contacts rated for 8A, etc.

Re: 4), the whole point of node charging would be that every charge is a balance charge. This would mitigate some of the disadvantages of running naked RC LiPo.

DogDipstick said:

Little more complicated answer, it would be a super long time to charge any good pack at the amperage that connectors can handle without overbuilding, reliably, and safely.

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If you just added two more heavy gauge wires to that setup, that would work fine - because the balance leads carry almost no current. Only the top and bottom wires carry anything significant. Even if they are N individual chargers.

Which, of course, is why balance connectors are wired the way they are.

JackFlorey said:

If you just added two more heavy gauge wires to that setup, that would work fine - because the balance leads carry almost no current. Only the top and bottom wires carry anything significant. Even if they are N individual chargers.

Which, of course, is why balance connectors are wired the way they are.

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Are you referring to node charging each individual cell through the balance leads? Or traditional bulk charging with trickle balance through the balance leads?

fatty said:

Are you referring to node charging each individual cell through the balance leads? Or traditional bulk charging with trickle balance through the balance leads?

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Specifically I am saying that from the battery's perspective - those two are identical.

JackFlorey said:

fatty said:

Are you referring to node charging each individual cell through the balance leads? Or traditional bulk charging with trickle balance through the balance leads?

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Specifically I am saying that from the battery's perspective - those two are identical.

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*If the pack is balanced...

JackFlorey said:

fatty said:

Are you referring to node charging each individual cell through the balance leads? Or traditional bulk charging with trickle balance through the balance leads?

Click to expand...

Specifically I am saying that from the battery's perspective - those two are identical.

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I don't think we are talking about the same thing. Are you saying a 6-channel, 8A/channel node charger puts 48A through only the top and bottom 26AWG balance leads?

serious_sam said:

*If the pack is balanced...

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Even if it isn't balanced. It's very rare, for example, for one cell to take full charge current and the neighboring one to take zero. That's the only case in which you'd see full charge current through a balance lead. More often cells are somewhat out of balance, and the difference in individual cell current is the current you see through the balance leads. (Difference, not sum.)

fatty said:

I don't think we are talking about the same thing. Are you saying a 6-channel, 8A/channel node charger puts 48A through only the top and bottom 26AWG balance leads?

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No. In that case you would see a maximum of 8 amps through the top and bottom leads. Any intermediate lead will see only the difference in charge current between the two adjacent cells. In a balanced pack this will be zero; in an unbalanced pack you will see some current. But as I mentioned above, you will not see 8 amps in the intermediate leads unless the pack is truly horrendously unbalanced. (i.e. some at 0% some at 100% charge.)

JackFlorey said:

serious_sam said:

*If the pack is balanced...

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Even if it isn't balanced. It's very rare, for example, for one cell to take full charge current and the neighboring one to take zero. That's the only case in which you'd see full charge current through a balance lead. More often cells are somewhat out of balance, and the difference in individual cell current is the current you see through the balance leads. (Difference, not sum.)

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The problem is that you don't need much deltaV to get 8A.

Say your group has an IR of 10mOhms.

0.01x8=0.08V

serious_sam said:

The problem is that you don't need much deltaV to get 8A.

Say your group has an IR of 10mOhms.

0.01x8=0.08V

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True. But I absolutely guarantee your balance wires + connector do not have a resistance of less than 10mOhms. That limits current as well. Which is fine - because the primary charge current is always carried by the top and bottom leads.

serious_sam said:

The problem is that you don't need much deltaV to get 8A.
Say your group has an IR of 10mOhms.
0.01x8=0.08V

Click to expand...

JackFlorey said:

True. But I absolutely guarantee your balance wires + connector do not have a resistance of less than 10mOhms. That limits current as well. Which is fine - because the primary charge current is always carried by the top and bottom leads.

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I've never seen a node charger. How do they work electrically?

fatty said:

I've never seen a node charger. How do they work electrically?

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I've never heard that term either, but from his description, it's a series chain of chargers such that each cell group has its own charger. So a 10s battery pack would have 10 4.2 volt chargers in series, with the junction between each charger connected to the balance leads (which are connected to the junction between each cell group.) That way each charger charges each cell group separately.

JackFlorey said:

serious_sam said:

The problem is that you don't need much deltaV to get 8A.

Say your group has an IR of 10mOhms.

0.01x8=0.08V

Click to expand...

True. But I absolutely guarantee your balance wires + connector do not have a resistance of less than 10mOhms. That limits current as well. Which is fine - because the primary charge current is always carried by the top and bottom leads.

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100mm of 24AWG has about 8mOhms.

Even if you tripled my previous example to 30mOhms, you'd still only need 0.24V deltaV to push 8A.

Basically, it just wouldn't be safe to produce/sell an 8A "balance lead" node charger. Because there'd still be the odd case of needing to bring an unbalanced pack into balance. Then kaboom.

You could get away with a custom build for a vigilant user. But even then, we all make mistakes. The risk is too high. If you were going to custom build, then replace the balance leads with something that could take the full 8A.

Just get a bunch of isolated DC-DC step down converters and wire it up

https://www.murata.com/-/media/webrenewal/products/power/datasheet/hph-12-30-d48.pdf

https://endless-sphere.com/forums/viewtopic.php?f=10&t=30112&start=50#p514589

wire.rat said:

Just get a bunch of isolated DC-DC step down converters and wire it up

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DC converters, like power supplies, do not have the safeties and monitoring that proper chargers have.

spinningmagnets said:

[Cellpro 10S]

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Cellpro 10S is discontinued and only charged at 4A maximum in node charging configuration.

serious_sam said:

Basically, it just wouldn't be safe to produce/sell an 8A "balance lead" node charger. Because there'd still be the odd case of needing to bring an unbalanced pack into balance. Then kaboom.

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Agreed -- this appears to be why this is not common and likely why many node chargers have been discontinued. But the BC168 8A is still for sale, and even updated for 4.35V LiHV.

fatty said:

serious_sam said:

Basically, it just wouldn't be safe to produce/sell an 8A "balance lead" node charger. Because there'd still be the odd case of needing to bring an unbalanced pack into balance. Then kaboom.

Click to expand...

Agreed -- this appears to be why this is not common and likely why many node chargers have been discontinued. But the BC168 8A is still for sale, and even updated for 4.35V LiHV.

Click to expand...

Bottom balance p-groups first (as needed). I use either a 1.5A or 1.2A charge with a 6S charger with my experimental 10S split pack (5S3P) paralleled for first bottom balancing, then bulk charging (or balance charging) or top balancing if even needed with a 6S charger. This is how i first bottom balance my experimental 10S3P pack before bulk charging. With BMS top balancing the discharge rate is only 0.40A (if even that much). Bottom balancing is the way to GO.

Being a BMS can balance the p-groups with resistance discharge so too you can use 22 awg JST balance leads to charge appropriate p-group(s) to equalize all p-group voltages before bulk charging. IMO, it's worth the extra time; especially with 30Q cells that are prone to self-discharge. Even if some cells suffer from self-discharge their potential capacity isn't diminished. Just because some cells may leak it doesn't mean they have any less capacity potential when first bottom balanced to equalize p-group voltages before bulk charging.

If a 2S-8S Balance Charger was available a 16S (split pack) could be bottom balanced before bulk charging.