can someone please explain the charging through the balance wires causes cell bias thing to me? i don’t get how that happens, or how it is functionally different from bleeding cells through the balance wires which is how i thought bms’s work
Consider a 3S pack for simplicity. It will have 4 balance leads. Let’s call them B0, B1, B2, B3. B0 is the battery pack negative and B3 the battery pack positive. To charge the pack, you connect the charger to B0 and B3. As a result, you’ll have current flowing through B0 and B3, but not through B1 and B2.
Now, say that all three cells in the pack are perfectly balanced at 4.1V each.
The C1 voltage is measured between B0 and B1. C2 voltage between B1 and B2. C3 voltage between B2 and B3.
The problem is that since we have current flowing through B0 and B3, there will be some voltage drop on these balance leads. This voltage drop will be added to the voltage readings on cells C1 and C3.
Now, the voltage drop may be insignificant and not a problem. It depends on the length and gauge of the balance wires as well as on the charge current. Higher charge current => higher voltage drop.
With my external charger, I have measured the voltage drop as high as 0.1V when charging just at 1.5A. That is a lot.
Say that you would have 0.1V voltage drop on the leads of our example 3S pack. The voltage reading of C1 and C3 would be 4.2V instead of 4.1V. The balance charger would start bleeding the two seemingly high cells and would bring our perfectly balanced pack out of balance.
For that reason, balance chargers keep the charge wires and the balance leads separate.
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My take on a cell voltage monitor for Xiaoxinag Smart BMS with Bluetooth BLE.
Hardware Cost :USD $10.00, firmware and brief “how-to” on GITHUB. Help available if interested.
This was written for a 10S battery (all of my batteries). This ESP actually has a UI and I think a second or third screen for any number of cells is possible
It only needs 5vDC from ESC and the Bluetooth is fairly robust. You can still use the phone app with this installed. You just can only have one or the other running at once (BT limitation). Some good double sided tape into the side of you enclosure will do the trick. Uses 50 miliamps when running. The number in parentheses is the max cell difference (high-low).
The bars show cell voltages relative difference from mean. Heavily inspired from @janpom and I’ll keep doing it until he patents it and sues me.
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Very nice job. I’m coding noob, could this be implemented in the Firefly Nano (heltec) remote in some way?
@Jamie42
Yeah, probably. I would only activate it when the board is in standstill, however. Furthermore, the OS and hardware are the same, just have to reuse the code on the Nano.
Has anyone ordered from LLT (https://www.lithiumbatterypcb.com) recently?
I placed an order for a 12S Smart BMS on the 9th and haven’t had any updates or responses to my emails (even tried messaging their aliexpress store)
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I purchased from them at the end of last year and wrote a few emails with questions regarding the product that were never answered. From memory it took like 4-6 weeks for delivery to Aus.
A friend ordered from them earlier this year and it took like 2 months for delivery.
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Were you waiting on them to send the order? Or was it just the typical slow/free shipping?
I have no way of knowing if its been shipped that’s all
No idea, i just ordered and waited and eventually it showed up
on the 10s LTT smart BMS , what are the 6 free ports next to the Balence wire for?
I know the Com port/bluetooth port/ and the x2 sesnsor ports + the 2 pin switch port.
but the 6 pin one looks interesting
Pretty sure they are also balance plugs.
darn, No other nifty Open ports with functionalities? always like to learn about the hidden functions.
the 2 pin Switch though - Most switches i know are 4-5 Pin " E-Switches". 2 Pin switch seems like a simple on off, nothing more? does that only work in certain situations/ or BMS setups Ie charge only/discharge?
It only works when you are using the bms for discharge. Also I believe that you need to program the bms to respond to the switch. But I’ve never done it so I’m talking out of my arse really.
thats good > as i want to use it for discharge to test it out.
Attached a Photo to point out the Ports in which im dead keen on knowing what they are for (the yellow)
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Ahh right. No idea what they are for. Maybe for something like a ST-Link? 
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In case anyone is waiting on their order; after ordering on their site I managed to get in contact with them via their AliExpress store where they gave me the tracking number. The BMS was ordered 9/6, shipped from the Netherlands on 22/6 and arrived in the UK on 6/7
Did you order with express shipping? (plus 15$)
I am in need of this BMS, I can order tomorrow but this doesn’t give me too much hope. I need my new battery to be ready on September 1.
That was with regular (free) shipping
Just order one from www.electricskateboarding.co.uk, will be in the post the next day with full tracking, should take about a week to get to you
Yeah I figured out that since I want it soon its better to order it from you.
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