My 48v pack show 55.2v fully charged on SW900, should I worry?

Debunker

100 mW
Joined
Mar 9, 2017
Messages
47
Hi lads, I just finished my 2nd charge after dropping to 45.5v the pack, cause tomorrow I plan a large ride, and now the LCD SW900 shows a charge of 55.2v.
Suposetly the charging should stop at 54.6. I remember the first time I charge them right away with multiple re-plugging to allow BMS to level the cells, and the final voltage was 54.8 or so, the cells are 21700 (unbranded), not 18650, so my guess is that may be normal... or is not?

I can't really give them a quick ride right now, I just press the accelerator with the wheel lifted to allow it to spin the motor and burn a few watts, but there's almost no consumption without resistance.
 
What does a voltmeter read on the battery output?

How many series cells (or groups) are in the pack?

Which lithium version is it (LiFePO4, or not)?

What does your charger label say, in it's entirety?
 
Debunker said:
Hi lads, I just finished my 2nd charge after dropping to 45.5v the pack, cause tomorrow I plan a large ride, and now the LCD SW900 shows a charge of 55.2v.
Suposetly the charging should stop at 54.6.

Check the output voltage of your charger. You may need the adjust it.
 
54.6, 4 amp, Made in China... those are the only indications besides the input voltage and a warning.

No way to adjust anything, it's the charger that comes with the pack.
I don't have multimeter, the SW900 seems accurate, at least it displays the same every time, but it may be not.

Is it so bad if it charges the pack just a little higher? I got extra careful with my first e-bike, that was stolen btw, branded samsung cells, always charging at 80%, a full charge to balance pack every 15 charges etc... and after 2 years it loss significant performance, so for this one I decided to buy cheap unbranded pack and treat it like the shit it is, but of course I don't want to damage it that early.
 
Debunker said:
I don't have multimeter, the SW900 seems accurate, at least it displays the same every time, but it may be not.

Consistent doesn't equal accurate. Buy even a $10 voltmeter if you're going to own an ebike, and if you need help diagnosing an issue.

Most generic chargers that come with packs can be adjusted with a potentiometer inside the unit, however, with no voltmeter, not possible.
 
I am using the LCD3 on my ebikes. They have a voltmeter readout too, and do they all read the same? No. You should use a voltmeter you trust to find out what's really happening, but i think it's just inaccuracy in the displays,,

The way most inexpensive chargers work, they count on the battery BMS to limit each cell group to 4.20V max, Most do not have trimpots and are usually a little below the target voltage with good QC, but I've received two that were too high by ,2 volts.

Actually, I received one that was a 52V when I thought it was a 48V, Lunacycle, back in their Happy Hour Days shipped me a 52V charger when I ordered a 48V. The label said 48V but fine print said 58.8, Used it for a year before I found out, A good BMS saved my bacon.
 
E-HP said:
Debunker said:
I don't have multimeter, the SW900 seems accurate, at least it displays the same every time, but it may be not.

Consistent doesn't equal accurate. Buy even a $10 voltmeter if you're going to own an ebike, and if you need help diagnosing an issue.

Most generic chargers that come with packs can be adjusted with a potentiometer inside the unit, however, with no voltmeter, not possible.

Cheap voltmeters often don't completely agree with my Fluke meter either. $5-$10 doesn't buy a lot of calibration, I guess. But they're much truer than the cheap panel voltmeters or wattmeters I use for onboard monitoring, or the KT displays I've installed.
 
Debunker said:
I don't have multimeter,
If you want to know what voltage the battery, charger, etc., really is, get one--even a cheap one is at least a second check you can make on things from whatever your system tells you, and you can use them to troubleshoot your stuff, too, which you cannot do without one, unless you just like buying new parts to swap things out one at a time on a system until it starts working again. ;)

the SW900 seems accurate,
Compared to? If you have no other readings to compare to, you can't really judge it's accuracy. ;)

Until you check it with something else, you can't know if the SW900 is correct or not, either.

No one else can tell you if it's right, or if your battery is ok, etc., without a comparison measurement, which you have to do with a different device (the multimeter is the simplest way to do that).

Once you have a measurement, we'd also need the details on the battery itself (chemistry and number of series cells / groups) to tell you if the voltage you read is low, high, or just right for it. If you dont' know what that is, then you can just post a a link to the sale page you bought it from, as that typically has this info.
 
The vendor says 13 serial 5 paralel 21700 cells and BMS voltage cutt of on 54.6v and 39v.

So, if the SW900 is right, the BMS has failed.
 
Debunker said:
The vendor says 13 serial 5 paralel 21700 cells and BMS voltage cutt of on 54.6v and 39v.

So, if the SW900 is right, the BMS has failed.

If the SW900 is right, the charger has also failed.
 
This is why you need that multimeter, so you can verify first if there even is a problem, and then to troubleshoot it if there is one.
 
There are some bms that start balancing at 4,25V. Charging stops at 55.25 but after some time voltage drops to 54,6V. Lion max V is 4.2, so the bms overcharge cells
 
The multimeter finally arrives at my home, but I am unable to test the charger...

I can test the battery and it shows the exact charge that the SW900 shows, wich is concerning cause that would mean that the charger is overcharging them + the BMS don't give a damn.

When I try to test the charger itself, the multimeter goes nuts showing diferent voltages (about 39v maximum) and not stabilizing any time. I put the multimeter in 200v DC, should I swich it to AC? videos say it must be at DC for both testing the battery and the charger.

If I can't get a propper reading I will try to overcharge the battery again to show the vendor that the LCD + the multimeter shows its overcharged and ask a refund cause neither the charger or the BMS are working, but I honestly prefer not to to it if there is something I am doing wrong.

Edit, I try to measure it with AC insted of DC, and the result is the same, from 0 to +70V (instead of 39) and nothing stable... if seems that the charger is just puting out burst.
 
The voltage coming from your pack is dc and the voltage coming from your charger SHOULD be dc too. I would definetly suggest taking a photo of it and asking for a refund.
 
I've had chargers that wouldn't really turn on unless they were hooked to a battery, making it harder to probe with a meter, esp if the plug has a lot of shielding around it.
 
I finally managed to get a reading (I just drill 2 little holes to the charging port and stick the moltimeter thingys trough them while charging)

The carger puts out 55.3v

Is it in ''normal'' range or should I ask for refund?

[youtube]https://youtu.be/fXpBM0BQ8ns[/youtube]
 
Debunker said:
The carger puts out 55.3v

Is it in ''normal'' range or should I ask for refund?

Open it up. There should be a little blue rectangular component with a tiny brass screw on top. That will adjust the output of your charger within a narrow range (like a volt or two). Dial it down to 54.6 or lower, and you're all set.
 
Chalo said:
Debunker said:
The carger puts out 55.3v

Is it in ''normal'' range or should I ask for refund?

Open it up. There should be a little blue rectangular component with a tiny brass screw on top. That will adjust the output of your charger within a narrow range (like a volt or two). Dial it down to 54.6 or lower, and you're all set.

Holy shit thank you. I didn't found it at first cause they put a big mess of hotglue just over it, the piece in mine is white and the dial is plastic, I managed to tune it to 54.6/7v, curiously, any less than that causes the charger to plug in/out of current with audible clicks when not plugget. The bastards overcalibrated it and put a mass of hotglue on the piece to cause a fire inside an american house, its a clear sabotage and a casus belli... CIA will know about it.

(I'm actually in Spain)
 
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