Mr. Lau 48V 15ah Lifepo4

[Toronto_ebiker]

yes, of course lifepo4 is better than SLA. but you might want to check if your battery really delivers the advertised Ah's.
(i once received a 14 instead of 20Ah pack)

btw: lau's tonyyan51 ebay-account just got deleted, and my cheap won auction is thus canceled as well. luckily i didn't make the payment yet. also i don't like the fact that lau uses 1000s of accounts and also has weird specs on his products so I decided not to buy from him (probably a wise decision) and will now head for a ping pack. i should have done so right from the start...
greetings
nicolai

I'm testing battery ah right now with my kettle which is drawing 5.6amp.. I will be testing voltage every 10 minutes... see you in 3 hours 8)

 

[Toronto_ebiker]

What is a safe voltage to take the battery down to without discharging the full battery?

 

[Battboy]

With LiFeBATT it would be 2.5V. (Low Voltage Cutoff pre -set by BMS) I do not know about other brands ?

Don Harmon

 

[Toronto_ebiker]

With LiFeBATT it would be 2.5V. (Low Voltage Cutoff pre -set by BMS) I do not know about other brands ?

Don Harmon

Thanks Don

 

[Ypedal]

You should see a very stable voltage all the way to the end of usable capacity, once you see a drop of pack voltage starting to fall further it's almost done.. 2.5v is as low as you need to go for a full discharge.. from 2.5 to 2.1v is not much power and happens quickly..

 

[Toronto_ebiker]

yes, of course lifepo4 is better than SLA. but you might want to check if your battery really delivers the advertised Ah's.
(i once received a 14 instead of 20Ah pack)

btw: lau's tonyyan51 ebay-account just got deleted, and my cheap won auction is thus canceled as well. luckily i didn't make the payment yet. also i don't like the fact that lau uses 1000s of accounts and also has weird specs on his products so I decided not to buy from him (probably a wise decision) and will now head for a ping pack. i should have done so right from the start...
greetings
nicolai

I'm testing battery ah right now with my kettle which is drawing 5.6amp.. I will be testing voltage every 10 minutes... see you in 3 hours 8)

So it appears that the BMS is cutting power to the battery at 48.4V which doesn't seem right. Here is the graph of the data I collected:

 

[Battboy]

FWIW - You have a BMS from China that is a very "simple" BMS solution. These often shut down the pack when it reaches 45 - 46V because they are designed to only monitor the pack and not the individual cells. This is almost not worth having and for a quick fix you could just disconnect the BMS and measure the Ah discharge of your pack with a Cycle Analyst. Since it is a duct tape pack you can't very easily monitor every cell or even do a proper balance charge by individually charging each cell. I would ask your supplier if they offer a better BMS than what they shipped with your pack and see if you can exchange the one you have and pay for a higher functioning BMS (if they make one) ? Often times the Chinese will have better quality BMS available but they don't let you know because they think Americans just want low prices. It's a cultural thing :lol:

I am not aware of any other fixes - but quite possibly someone like Y.Pedal knows of a way to fix the problem with a better suggestion ? There a a lot of experienced tinkers here who have dealt with these issues before, but I haven't seen any easy fixes for this problem other than to do what I suggested above.

Best,

Don Harmon

 

[rguy56]

Hah! So we meet again Mr. Lau.

He told me he was shipping a replacement charger to me, oh, maybe 5-6 weeks ago, from a purchase I made in spring. I'm still laughing! My belly aches.

Bob

 

[Toronto_ebiker]

FWIW - You have a BMS from China that is a very "simple" BMS solution. These often shut down the pack when it reaches 45 - 46V because they are designed to only monitor the pack and not the individual cells. This is almost not worth having and for a quick fix you could just disconnect the BMS and measure the Ah discharge of your pack with a Cycle Analyst. Since it is a duct tape pack you can't very easily monitor every cell or even do a proper balance charge by individually charging each cell. I would ask your supplier if they offer a better BMS than what they shipped with your pack and see if you can exchange the one you have and pay for a higher functioning BMS (if they make one) ? Often times the Chinese will have better quality BMS available but they don't let you know because they think Americans just want low prices. It's a cultural thing :lol:

I am not aware of any other fixes - but quite possibly someone like Y.Pedal knows of a way to fix the problem with a better suggestion ? There a a lot of experienced tinkers here who have dealt with these issues before, but I haven't seen any easy fixes for this problem other than to do what I suggested above.

Best,

Don Harmon

I have sent an email to the seller with my test results and asked for a working BMS. The seller does carry them and the ones pictures look much nicer then my solder smothered PCB that came with my battery.

 

[Toronto_ebiker]

Only 78% capacity as rated , seems fake nominal capacity.

Take more care when buy some battery from ebay, guys.

I'm not complaining since it was VERY inexpensive and my bike weighs 60lbs less since tossing the SLAs and it also goes way faster .

Hah! So we meet again Mr. Lau.

He told me he was shipping a replacement charger to me, oh, maybe 5-6 weeks ago, from a purchase I made in spring. I'm still laughing! My belly aches.

Bob

mr. lau's a douche

 

[Ypedal]

FWIW - You have a BMS from China that is a very "simple" BMS solution. These often shut down the pack when it reaches 45 - 46V because they are designed to only monitor the pack and not the individual cells. This is almost not worth having and for a quick fix you could just disconnect the BMS and measure the Ah discharge of your pack with a Cycle Analyst. Since it is a duct tape pack you can't very easily monitor every cell or even do a proper balance charge by individually charging each cell. I would ask your supplier if they offer a better BMS than what they shipped with your pack and see if you can exchange the one you have and pay for a higher functioning BMS (if they make one) ? Often times the Chinese will have better quality BMS available but they don't let you know because they think Americans just want low prices. It's a cultural thing :lol:

I am not aware of any other fixes - but quite possibly someone like Y.Pedal knows of a way to fix the problem with a better suggestion ? There a a lot of experienced tinkers here who have dealt with these issues before, but I haven't seen any easy fixes for this problem other than to do what I suggested above.

Best,

Don Harmon

Don.. what's your malfunction ?

I told you at the beginning not to poke your nose in here, you go ahead anyways and wish us all a happy thanks giving... i delete it.. then you post a reply to a technical question you are not qualified to answer and get it all wrong.. i delete it again..... now this ? wrong again...

Grow up .. or get out...

The BMS in most of these chinese packs are all the same model to an extent, most of them DO monitor cell level voltage ( or paralell groups of cells ) and not just " pack voltage " ...

 

[dogman dan]

Yeah, Don, even a dope like me knows that was wrong. But there is good reason to question whether any bargain pack bms even works. As for not delivering the amp hours, would you want to discharge a cheap 18650 pack any farther than that? ( 70%) I wouldn't! Even thought the bms is monitoring each 3.4v cell group, there is what about 20 or so cells in each group? I'm nervous enough with 4 cells in each group in my Ping v 1.0. Now that the weather cooled off I'm tripping the bms more than ever and I really don't like it! I want to ride that bike like it has no lvc and never have to find out if it works more than a few times a year.

We don't doubt you have a superior product, Don, but we can't afford it, and if we ride 700 watts or less, we don't need it. A lot of folks are riding these bikes shorter distances, just on the weekend and evenings. Guys like me that do serious commuting, want it to be as cheap as possible. If I wanted to spend big bucks, I'd buy a new car.

 

[Toronto_ebiker]

Don,
This is my thread and your opinions (right or wrong) are welcome.

Here is a data sheet on the 18650 and by the looks of the chart the battery have 80% capacity until they are cycled more times. I will keep on cycling the battery every day and post the results.

http://www.valence.com/sites/all/themes/valence/pdfs/18650e%20Cells%20Data%20Sheet.pdf

 

[dogman dan]

Well, yeah, my ping, which now has 1700 flawless miles on it, only had about 2/3 of its normal capacity on the first few charges. But anecdotal evidence seems to be that at higher discharge rates, like 20 amps and above, the mr lau packs seem to put out a lot less than 20 ah. Your chart seems to show voltage going off the cliff so it is most likely good that your bms stops it there. Better safe than sorry with that many cells in the pack.

 

[Toronto_ebiker]

I ordered some 18650s single cells from ebay is anyone interested in testing them out? I don't have the proper equipment to test single cells.

 

[Toronto_ebiker]

Update:

I discharged the battery again with the same result as last time. I tested each BMS lead from the battery and here was the result:

49.8
46.6
43.4
40.3
37.1
34.4
31.2
28.0
24.9
21.7
19.0 <<<<<<<<<< 2.7
15.8
12.7
9.5
6.3
3.1

Looks like one of the groups of cells isn't working correctly/yet. Teh good cells average 3.1-3.2 volts so the battery has lots of life left, but the one bad grouo is pulling the battery down. I have contacted the seller and they told me to charge the battery without the BMS for 30 min then reconnect the BMS. does this sound right?

 

[Ypedal]

Better yet would be to get a single cell charger, http://www.voltphreaks.com and charge up the low group independantly..

overcharging the whole pack to get the one low group up will not solve your problem..

 

[Toronto_ebiker]

Better yet would be to get a single cell charger, http://www.voltphreaks.com and charge up the low group independently..

overcharging the whole pack to get the one low group up will not solve your problem..

Is there a solution that does not require spend extra $$$. I have a precision 2 amp benchtop power supply 0-30v, could I use this to charge up the low group?

 

[Ypedal]

If you can set it to Constant Voltage around 3.5 to 3.7v, then yes.

 

[Toronto_ebiker]

If you can set it to Constant Voltage around 3.5 to 3.7v, then yes.

At what voltage should I disconnect the group at? The other groups are sitting at 3.1-3.2V? Sorry I'm a little new to battery packs so I appreciate your help and speedy responses!

 

[Ypedal]

At the 3.4v mark the cells have about as much(capacity) as they will take, but can safely be taken up to 3.7, even 3.9v without much harm.

I'd set the supply to 3.6v or so for about a half hour and then let it rest for a while to see if it drops back below 3v on it's own.. if it does you likely have one cell in the group pulling the voltage down..

 

[Toronto_ebiker]

At the 3.4v mark the cells have about as much(capacity) as they will take, but can safely be taken up to 3.7, even 3.9v without much harm.

I'd set the supply to 3.6v or so for about a half hour and then let it rest for a while to see if it drops back below 3v on it's own.. if it does you likely have one cell in the group pulling the voltage down..

Thanks again... This might just be a balance issue. that cell group tested at 3.4V when the battery arrived.