Yesa

[Ypedal]

what's with the tiny coppr tabs ? vents ?

And the blue BMS leads, is all that solder used to conect the cells from tab to tab.. or is that just to hold the leads ?

I found it strange that my pack had 10 x more solder used than required.. i wonder if they get paid by the LB for using as much as possible for indication of productivity lol..

 

[Storm]

The batteries are spot welded together by tabs, the solder only holds the wires.

The copper squares are vents.

A few weeks ago Yesa changed their website and for while I hadn't been able to contact them on the Email address we had previously been communicating (sales@yesa.com.cn) I thought it was possible Yesa didn't want to help me repair my battery pack that had a shorted cell ie 0.00v and my other cell that had a broken tab.
I recently checked their new webpage and found a similar address (sales@yesa.com.hk) which worked as I received a reply, I'm pleased to inform you they are sending the two replacement cells. They quickly replied and as usual seem to want their batteries in working condition. They always seem proud of their batteries!!

 

[BiGH]

My last email to sam was 8 days ago - so far no response

I'm thinking of investing in a bunch of single cell chargers and making an adaptor harness for the pack - this would be great as it would allow a maintence charge once a month to keep cells in balance.

commuting is going well its just those two dodgy cells are either not being charged right (full charge only takes ~2 hours on a 47v 3a charger)

 

[BiGH]

i was also a victim of the email problems.

I just received a call from Sam @ yesa and i'm impressed. I'm in the process of modulating the cells at the moment, and will report back soon.

The cell that was a bit low before has come up in voltage a bit in comparison to the other cells.

at 22ohm its going to take a while to discharge the cells to the right voltage.

 

[Freddyflatfoot]

Good to hear that Sam has contacted you again.
Hope the cells comeback and then all will be good!
Looking fwd to your results.

 

[GGoodrum]

First of all, I believe the BMS is probably cutting off at something lower than 2.9V. Wasn't that the "resting" voltage? Under load, that is going to drop to a lot less, so it sounds like the BMS is doing its job.

Instead of mucking around with trying to drop the voltage of the higher cells, you really need to try and charge these indiidually, and see if it really is just an out-of-balance condition, or if you might have a "stressed" cell(s). What I've found is if an a123 cell has been abused, the most it will hold after a charge is somewhere between 3.35 and 3.45V. healthy cells should have a resting voltage, about a half-hour off the charger, of at least 3.5V.

Until you get to the bottom of this, I would not use this pack at all, and certainly not down to BMS cutoff. This is how you kill cells.

-- Gary

 

[Beagle123]

Aren't those cells supposed to be really safe? Why can't you take the bms off, and just watch the voltages with a voltmeter. It seems like the BMS may not be doing a good job of protecting your batteries. I like the idea of knowing the voltages of each cell so you can see any potential problems.

If your problems persist, maybe you should consider dismantling your cells, charging and testing each individually so you can dump the bad ones. Then you can reassemble your pack, and charge with individual chargers so its always balanced.

 

[GGoodrum]

He already has access to measure each cell voltage. I think the BMS is fine, based on his measurements after it hit the cutoff. Like I said, a resting voltage of 2.9V means it was probably below 2.5V under load, so the BMS did its job. The bigger question remains, why are the cells so out-of-balance?

 

[BiGH]

i've equalised the voltages of the 12 cells in the pack (took ages as only rigged up temporary stuff).

And i've chucked it on charge. its taking quite a while to charge which is a very good sign. Looking forward to checking invidual voltages at the end of it.

Im going to definately invest in some single cell chargers - that will make this process better, and also be useful later on if / when i get a dewalt pack.

 

[Beagle123]

Yea that sounds good. I still think you should check your voltages after a ride. Then you'll know if any cells lack capacity compared to the others. Once the cells are balanced, go for a reasonably long ride and check the cell voltages. I think this is a great test because discharging the cells in series insures that you're drawing exactly the same amount of current from each cell. If one has less capacity than the others, it will deplete faster than the others and have a lower voltage. I think you'll know if the cell is uacceptable, and you cn replace cells as needed.

I was considering buying a pre-packaged battery pack like yours, but I decided against it because I wanted the ability to replace cells. I think all of our battery solutions involve a decent amount of DIY. If the guy who sold you the pack could sell you individual cells, I'm sure you could keep it going well for a long time.

But at this point in time, I think the best insurance for your batteries is having the ability to to test and replace cells. (my opinion)

Please let us all know the results.

 

[BiGH]

Hey

yeah i'm going to keep a very firm focus on the individual cell voltages. I'm going to do my commute today, which drains them fairly well.

 

[BiGH]

ran the bike until cutoff today - got longer out of that pack 6.7ah - i didn't charge that cell fully, its just too dificult and time consuming by using the drain other cells to X voltage.

I'm going to order some single cell chargers. I now understand and highly reccommend to anyone with single voltage (pack chargers) ie that run at 36v or whatever, should go and get a set of single cell chargers, as they may / will be necessary for proper ballancing occasionally.

 

[Beagle123]

I don't think you need a whole set of chargers. YOu could charge with your regular charger then use one charger on each of the low cells.

 

[BiGH]

oops your right -

i just said that for ease of balancing. I'm only ordering two myself

i blame the heat lol

 

[BiGH]

another update - Yesa sell single cell chargers!

I'm going to wait for further info tomorrow (Sam's not in the office today).

and get a load of single cell and full pack chargers (save on postage).

 

[Storm]

I have recieved the replacement cells from Yesa, fast post as usual and well packed.

After removing the old cells I opened one up with my rotary tool to see what was inside... hmmm, I love pulling things apart.

 

[Ypedal]

No sparks of flames when you opened it up ??? :lol:

Cool pictures. thanks !

 

[Malcolm]

Wearable batteries anyone? Just sew a couple of cells into the lining of your jacket, add a few dozen LEDs and you could be the star of all the kids' Christmas parties

 

[cerewa]

I used my Yesa pack today for the first time (outside of very short tests).

I found out first-hand that a brief short-circuit doesn't ruin the pack. Yesa's site seems to indicate that the BMS's have short circuit protection. It's still able to make an impressive spark and "pop" noise.

I never realized you can check cell voltages using the little connector on the pack; I will have to try that.

EDIT: I tried checking the voltages. I'm not sure if I'm using the correct method though, especially for checking the first cell on the positive-pole end of the pack. the other problem I'm having is that the power output connectors seem to be providing less than the full voltage of the pack at 22.6V , while the charger connectors show 26.5V.

I was trying to fully discharge the pack per Yesa's suggestion and found out that it takes quite a while. I was not running the pack very hard, just riding around in circles, but it actually took me something like an hour and a half of boring riding-around to run the battery down, AFTER having ridden 20 miles pedaling hard+lightly using throttle.

 

[BiGH]

got my 2nd shipment from yesa

very pleased. Got 2 single cell chargers and 2 36v chargers. Sam's customer service skills are really coming into their own. he's helped a lot. charging up my single cells to ballance the pack - should be great. ready for the meet tomorrow!

edit: looks like two cells are REALLy out of balance.

 

[BiGH]

after modulation i was able to get 7.7ah out of my pack before the first cutoff - a good increase from 6.6. Going lighter on the throttle after cutout was good though - i was pulling 1500w+ at time of cutoff (40kph uphill + extreme headwind)

 

[recumbent]

Are you getting more range from better charging technics, you think? Or do the cells need to settle-in the first few cycles.
Thanks for keeping us in the loop BTW.

 

[BiGH]

to be honest it could be a bit of both.

I did find that the inital capacity went from 6.1ah to 6.7ah based on just normal charging.

To get it to 7.7ah it required my single cell to be charged separately (i have to find out what was causing the problem).

These packs are rated at 12ah though... so getting 7.7 ah out of a pack isn't ideal 10 would be what i would have expected.

as a side note, even tho the BMS tripped, the voltage sag was fairly intense (i was hammering the pack) so going gentle on it might get another amp hour out of it.

i'm fairly happy with the yesa cells, however they do sag a bit which is a problem for the bms boards.


what would be great is a board that monitors indiviudal cells, then reduces the throttle signal until the cells are on the good side of their cutoff point (if this happens at all). This would stop the bms's from cutting out then having to be reset under high loads

 

[Ypedal]

what would be great is if the time was taken to properly test the packs before they ship from the factories..

The chinese version of testing seems to be " Does it work ? ,yes, no."

Of all the packs i've seen on this forum from FalconEV, Yesa, Aten? Point1, etc.. not a single one works as it should.. with quality BMS and charger...

It's a damn shame..

 

[fechter]

what would be great is a board that monitors indiviudal cells, then reduces the throttle signal until the cells are on the good side of their cutoff point (if this happens at all). This would stop the bms's from cutting out then having to be reset under high loads

Yes, that would be good.

Overcurrent could trigger the same response.
If the BMS had an opto-coupler with and open collector output to interface to the controller, it would be easy to adapt to almost any controller.