Warning:
Firstly I don't recommend this to anyone who is not comfortable with electrical work and who has no history of electrical work.So with that out of the way its pretty common that the chargers supplied with our scooters are not really "dialed in" to voltage (you're shocked I'm sure that a charger that you can buy on eBay for $20 wasn't bench adjusted) ... sure someone does some "gross adjustment" but not really careful dialing in (and don't start asking about the accuracy of the 240V supply to your house).
Why?
well as it happens batteries need a particular Voltage to charge, which must be a bit more than the voltage you want them to charge to. It doesn't need to be by much but it does need to be more. Further a reality of electronics is that everything (no matter what) takes some voltage out of the circuit, so even if the charger is supplying 54.4V the BMS will inevitably take a little nibble out, as will all the wires. So its best to tweak the supply to be a little bit over the level of the BMS.Below is a picture of my charger now charging (in the final phase) my 500W mercane which has ridden just a few Km after its last charge (which I noticed wasn't getting up as far as I'd like it to have gotten) on the "other charger" which I keep at work. I've tweaked all my chargers here.
You can see that while the light has gone green indicating (to those who think they are in the know) that charging is complete, the charger is still supplying a small current (for the saturation of cells to 4.2V) which still (because of the voltage) amounts to 7.1W or the equivalent of a modern efficient bulb. All in all the battery has had pushed in about 40Wh, which is pretty consistent with the small running around I did before putting it on charge now.
What did I do
Basically I just carefully opened the charger (mine has screws under the bottom rubber feet) and then identified the "trim pot" and with it plugged in and live adjusted that up to where I wanted it. See this VideoThis basically went very well and I was then able to see good charging voltages and indeed show the difference between what the handlebar volt meter shows and the voltage at the entry to the BMS (using my inline meter)
Job Done
Hope that is helpful to someone.
the cheap bms that the battery has only balances the cells at top voltage and if voltage doesnt get up bms will never balance and will just cut off when first cell reaches 4.2v
ReplyDeleteagreed, but I changed my BMS to an active BMS which (and I've made measurements) does a good job. So rather than apply >yet another< board in there I just went for a BMS that was a modern active type anyway (and one which 3 wire type connections too)
ReplyDeleteif you read this post: https://cjeastwd.blogspot.com/2020/02/difference-in-bms.html
ReplyDeleteyou'll see that the new bms is doing well. Within 3 more charges (and I didn't want to make pulling the battery out my hobby) the post charge voltage on the scooter was showing 54.5V which indicates an average charge of 4.19V. Given that I've never seen evidence of the BMS allowing any cell to go over 4.21V I am confident that this means the pack is now balance charging nicely with the new Active BMS
Can you send me a link to that bms please
ReplyDeleteAnd did you actualy measured the wires if it transfers energy from one cell to another?
Or is it just wasting energy into heat ?
https://www.ebay.com.au/itm/13S-48V-20A-18650-Battery-Li-Ion-Cell-Protection-BMS-PCB-Board-Balance/282524411843
ReplyDeleteI did not measure current along the wires (not enough room to get my hall effect device in there). My thermal camera showed no sign of it being heat. Given the illumination of the LED I believe its doing pulse charge and then measure after a settling time.
I am going to tweak my charger as soon as I get voltmeter (already ordered something similar to yours). Currently on the scooter volt indicator I am getting 54.4v with full charge( this may cause possibly I get 2% less performance on the battery as starting voltage). As you advised it's probably a charger tweak to fix it. In some chargers you can adjust the amper as well the similar way.
ReplyDeleteThanks for the good advice.
Hi Ali
ReplyDelete> I get 2% less performance on the battery as starting voltage
very very doubtful that it would be as high as 2%, even ignoring that the first 2% of battery discharge has the greatest voltage drop 54.4 is about 0.3% of capacity
Do be careful, check your charger carefully as to which side you're working on and be doubly certain you're not tweaking the wrong part. ALSO be very careful with the meter probes, DO NOT short them together (easy to do if you're doing something with the other hand).
Finally got the voltmeter. The reading I got is 54,92-54,98volts. Do you think it's good idea to increase the voltage over 55volts?
ReplyDeletehttps://photos.app.goo.gl/SKxaZMbeZHiPq3x87
Ali, 13 time 4.2 is 54.6, so there is no benefit to going above that by more than a few mV ... as I mention in the video I posted in there I see no benefit of going above 54.9
ReplyDeleteI didn't anticipate you'd bought that meter, which is a good tool, but is not more broadly usable for much else than monitoring power and Wh going into your battery. That is of course useful stuff too, but a general multimeter is still a good tool to conisder getting too. They last for years (all of mine are more than 5 years old, one is at least 30)
Yeah, it's a good coincidence with the meter, was looking for something multifunctional like yours and actually later I noticed it's the same one, can you confirm the voltage on this device is matching with other voltmeters? So, my problem is probably not related to voltage of the charger as mine already have 54.9v(unless the voltmeter shows wrong voltage).
DeleteIn the evening I did a test(might be dangerous and maybe I shouldn't) I adjusted the output voltage to 55.1v and it charged the battery a bit before it went to greenlight, after the greenlight I left it connected about half hour more and in the end it got charged to 54.6 v. I was a bit afraid although BMS doing it's part. Later I readjusted the charger voltage to 54.8v.
https://photos.app.goo.gl/58bjyGL28tK1JuCV6
Do you think it can still be charging voltage issue?
Many thanks
The bms on the we releases charger at 4.25v for each cell
ReplyDeleteIf 1 cell reaches 4.25v the bms will start discharging that cell untill all the other ones Cath up
That's how all the bms-s work
I'm charging mine with 55.5v and the bms stops the charge not the charger
And that's how it should be
I've tested and retested all sorts of bms boards and they all work the same
>I've tested and retested all sorts of bms boards and they all work the same
ReplyDeletewell that's interesting because for a start there is passive and active BMS systems. You are correct however that the BMS is what releases the charging when charging is done. But interestingly when I've tested min it releases (like 0.00A showing on the in line meter) earlier than that. Now it could be because one cell has hit 4.25 but probably not for every cell. 4.25 is a bit of a pointless exersize of diminishing returns and potential for some electrode plating (ie loss of capacity) over time.
That's how a commercial bms works
DeleteStops charge at 4.25v and starts discharging to 4.20v untill all the other cells are the same
Ali I'm unclear what your exact problem is, because everything looks good this end. If I've missed it can you just simply in 2 sentences describe what the problem is, rather than force me to comb through all the above?(and perhaps other posts)
ReplyDeleteThanks. I don't know what is the problem. Just know that with charger at 54.9v battery charges to 54.4v only. Charger at 55.1v then battery charged to 54.6volt. if the voltmeter measures correct and your readings with this voltmeter and other multimeter matches, then it's probably not charger voltage problem I have.
DeleteAli
ReplyDelete>Just know that with charger at 54.9v battery charges to 54.4v
I thought we'd discussed this, its not a problem its just a fact. There will be some parasitic loss between the charger and the cells, humanity has yet to make the 100% efficient thing.
This is less than 1% loss and can be of no significance to the charging ... 54.9 > 4.22V per cell and 4.18V per cell ... if the BMS is actually shutting down (and you now have a tool to measure that by seeing that A falls to 0.00A then you are actually achieving saturation charging and NO PROBLEM exists. If however it does not (which I'd be interested to know then there is possibly an issue that needs examination ...