Yeah man, I got it, thought I’d post succeses with the failures after that haha:joy:
1 Like
It’s mentioned in the initial post.
@Skaterboy58 has used it in his external charger: https://www.electric-skateboard.builders/t/external-bms-and-charging-box/79444
5 Likes
Inspired by this idea, upgrading my first (only working) build. 2/5s lipos in here with a plug for balance cables and a plug for charge leads.
Continue with my balance charger but don’t have to unplug and open up Tupperware boxes anymore. Still keeping it cheap though, $4 mini paint tray enclosure
7 Likes
When charging one 12s battery with two balancer chargers, do i need to split the pack into two 6s packs or can i leave them as 12s with only the balance leads split and one of the chargers pushing power into the pack? or how does that work?
1 Like
I put loop key mid pack between the lipos
2 Likes
You don’t need to split it if the balance chargers are not on a common ground. You must not power them from the same DC power source, otherwise you’ll short out your battery over the common ground and you don’t want that!
If you have two independent power sources, i.e. two independent cables going into the wall socket, it should be OK.
To be safe, be sure to check with your multimeter there’s no continuity between the two ground wires of your two balance chargers.
1 Like
So what you’re saying is i can cheap out on a BMS and a 8amp charger by just buying two imax’s? holy fucking shit, imma go out and buy a 14 pin connector then.
And two imax’s
1 Like
That’s correct. It gets a bit tedious though. I have had exactly that setup with two iMaxes. Doing all the wiring anytime I needed to charge the board annoyed me. I’m much happier with a brick charger and a BMS. The price difference actually isn’t that significant.
1 Like
I’d argue it’ll be more convient since i’m properly gonna buy a 14 pin connector that’ll be able to handle roughly 5-8 amps and then it’s just plug in press 2 buttons and go. Also i don’t think i’ll be carrying the setup much around but if i do i’d still rather carry 2 imax’s then a heavy as fuck power prick, i’ll get more amps out of the imaxs too.
The iMaxes will definitely be bulkier and heavier than a brick charger with a matching power.
With brick charger you just plug one end to the wall and another to the board. It can’t be simpler than that.
With iMaxes, you’ll have two devices to plug into the wall and you’ll have many wires to plug into the board. If your battery is 12S, you’ll need a 13 pin connector for the balance leads and two 2 pin connectors for the charging wires. You don’t want to charge over balance leads. That would bias the voltage readings on some cells.
1 Like
Fair enough, i just feel like it’ll be easier with my build, cause yesterday I realised my battery pack only just fit in the top mount enclosure. lets just leave it here. Also I like general idea about balance chargers.
this is IMO the single biggest benefit of external balancing. I can often fit a whole nother P or S group by ditching the BMS. untill they get tiny like the Flexi. even that takes up some space, and often my builds have zero space left over.
I do charge through the balance leads, and there is a bit of bias but no more than a few hundreths of a volt when I checked manually. gone about 800 miles on that board and the cells still perform well and balance within .03v.
It’s not cheaper than a brick charger for the first battery, but you can have several battery configurations and charge with the same charger. I have 5s packs in a 10s board, and 6s packs in a 12s board and charge them both from the same charger (different plugs though). The 6s scooter also charges on the Imax.
I put my switches between the two halves to separate them. when separated, they can be charged on a duo charger, but if you forget, poof. so now I only ever charge one half at a time out of an abundance of caution and lack of working duo chargers
needless to say, if I build a battery for someone else’s go-go- gadget, it gets a BMS and brick charger on delivery unless they say otherwise.
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.
3 Likes
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.
20 Likes
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)
2 Likes
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.
1 Like