Author Topic: New Battery Specifications  (Read 11379 times)

Offline Bikemad

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Re: New Battery Specifications
« Reply #15 on: July 05, 2016, 12:02:12 PM »
A full refund sounds like a very good result to me, and you don't have to break any laws by posting it back either. ;)

If your dropouts have broken, I presume you must have an alloy frame and didn't have any torque arms fitted.

Did it damage the wiring from the motor when the axle spun, and can the frame be repaired easily?

Perhaps you can post some pictures of the damage as a warning to others.

I am surprised that it is only charging to 4.0V per cell, I would have expected at least 4.1V, if not the maximum 4.2V.
Have you measured the voltage output from the charger while it is charging?

It might be worth checking the 13 cell group voltages to see how well balanced they are.

Alan
 

Offline Bedmountain

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Re: New Battery Specifications
« Reply #16 on: July 05, 2016, 08:31:17 PM »
Hi Alan

I have an alloy frame. I had torque arms fitted to both sides...

The gear hanger snapped and the axle came out of the other side dropout as well.



I guess the gear hanger is designed to be the weakest point to save damage to the frame which seems to have only suffered cosmetic damage.

There were 4 separate areas where the wires were stripped bare. I've repaired all these and the motor seems to be turning under throttle ok.

As always - I'm going to ask a daft question but how do I measure the voltage output from the charger? - Thanks Alan
 

Offline Bikemad

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Re: New Battery Specifications
« Reply #17 on: July 05, 2016, 10:13:42 PM »
Hi Ben,

I'm surprised the axle has spun with two torque arms fitted. I suspect something may not have been tightened up quite as tight as it possibly should have been.

Do you have any pictures showing how the torque arms were attached to the frame before the axle spun loose?

You can usually check the open circuit output voltage of the charger by measuring across the two output terminals on the charger's connector plug, but be very careful not to short the two terminals together!  :o
If your charging plug has a central pin and an outer cylindrical collar similar to this:



Then I recommend using a short piece of drinking straw over the centre pin to ensure the meter probes cannot touch each other or accidentally short circuit the two contacts together. One probe goes inside the straw (usually the positive probe) and the other goes outside of it.

To check the charging voltage with the battery connected, simply insert your meter probes into the two contacts on the battery's power output connector while the battery is charging, and the reading taken from there should be approximately the same voltage as the battery itself.
At the very end of the charge, the voltage on your battery should be 53.3~54.6V dependant upon the charger voltage and/or the BMS maximum voltage settings (whichever is the lower).

There will be a very slight voltage drop across the battery's BMS as the output voltage is being switched via MOSFETs, but if good quality MOSFETs have been used, then the difference should be minimal (but definitely nowhere near as much as 2.6V even with poor quality MOSFETs  ;)).

Alan
 

Offline Bedmountain

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Re: New Battery Specifications
« Reply #18 on: July 09, 2016, 12:19:15 PM »
Hi Alan

Unfortunately I don't have any pictures of the torque arms fitted. They were probably on upside down, wrong way round and inside out.

I checked the output of the charger and got a reading of 54.3V

The battery output voltage when on the charger is 52.8V

Offline Wklatt

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Re: New Battery Specifications
« Reply #19 on: July 09, 2016, 01:34:59 PM »
One thing I learned was that the big nuts loosen up after an initial installation. Seems the high torque on start up and regen works them back and forth. I had to tighten mine several times before they would remain tight. I still check them regularly, but they seem OK now.
Walter

Offline Bikemad

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Re: New Battery Specifications
« Reply #20 on: July 09, 2016, 05:23:11 PM »
I checked the output of the charger and got a reading of 54.3V

The battery output voltage when on the charger is 52.8V

Ben, the voltage reading for the charger output appears to be within 0.5% of the expected voltage, but this lower than expected reading may be due to the accuracy of your multimeter (cheap multimeters are usually accurate within ±1.0%).
If the charger output was calibrated absolutely spot on @ 54.60V, you could still have a voltage reading (on a cheap multimeter) anywhere between 54.05V and 55.15V and still be within the meter's specified tolerance.  ::)

The 1.5V difference between the charger output and the battery output will be partially due to the slight voltage drop across two different sets of MOSFETs, one set on the charger input and the other on the battery output.

The main voltage difference is most likely due to the accuracy (tolerance) of the individual cell maximum voltage settings for each of the 13 balancing modules within the BMS, but it could also be slightly lower if some of the cells were not quite 100% fully charged.  ;)

If you were to leave your battery on charge for at least 24 hours to ensure precise cell balancing and a full charge has been achieved, it's possible that the battery output voltage reading (measured while still on charge) might even increase slightly.

It is very unlikely that an expensive and highly accurate BMS has been used with that battery, so you may have to simply accept that the output voltage of 52.8V is all that you are going to get.  ;)

52.8V is ~4.06V per cell, which should make the cells in your free battery last quite a bit longer.   ;)


One thing I learned was that the big nuts loosen up after an initial installation. Seems the high torque on start up and regen works them back and forth. I had to tighten mine several times before they would remain tight. I still check them regularly, but they seem OK now.


Walter, most people don't understand quite how much torque is actually being transmitted through the two 10mm flats on the axle. If the axle nuts are not properly tightened they can work loose very quickly.

I measured the stall torque on my modified Magic Pie and calculated it to be around 93Nm. If this force is exerted on a 10mm deep dropout the lateral force acting upon the end of the dropouts by the edges of the flats is probably around 950kg (475 kg on each end of the axle).
To visualise this amount of torque, if you were to place a 130mm long 10mm spanner onto the flats of the axle, you would have to apply a force of 73kg (160lbs or 11.5 stone) on the opposite end of the spanner to produce 93Nm of torque!



So Ben was lucky that it was only the hanger for the derailleur that broke and not his frame dropouts. If the dropouts in the frame had been deeper, then it might have been a different outcome.

I was never able to measure how much torque was produced with this much power:



But the torque was enough to easily flip the bike over backwards when trying to pull away from a standstill on the level.
Fortunately, I had steel dropouts on my bike and the axle nuts were tightened very tightly indeed, and the dropouts survived the huge amount of torque even without any torque arms fitted.   ::)

The torque developed by your Smart Pie will obviously be a lot less than my modified Magic Pie (and a bit less than a standard Magic Pie) but it still has to be transmitted safely to the frame (or forks) through the dropouts.

Alan
 
« Last Edit: July 02, 2017, 06:55:33 PM by Bikemad »

Offline Bedmountain

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Re: New Battery Specifications
« Reply #21 on: September 21, 2016, 09:30:45 AM »
Hi guys - quick update on the dodgy (but free) triangle battery pack...

For the first 50 miles or so it was just about behaving ok - although I was experiencing the occasional cut out near the end of my 16 mile commute.
I went on holiday for a couple of weeks and when I used the bike for the first time back I didn't get more than a couple of miles before the cut outs started.
Just went for a test run today and within a mile I'm getting cut outs and my cycle analyst is showing minimum voltages of around 11-17v.

Not sure if it's the BMS or the controller cutting the power. Any ideas as to what is causing such an extreme voltage sag? Could it be simply the poor quality of these cells?

Offline Bikemad

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Re: New Battery Specifications
« Reply #22 on: September 21, 2016, 04:15:01 PM »
Hi Ben,

If you are using this battery with your MP5 motor, then it will probably be the battery's BMS that is cutting the power completely, as the MP5's controller does not cut off the battery power under load, it simply reduces the motor power when the battery voltage reaches the minimum set voltage to prevent the battery voltage from falling any further.

The 11-17V figures on the CA are probably just the generated output voltages from the motor when the battery's BMS has isolated the battery from the controller and the Cycle Analyst.

If you increase the Undervoltage protection value (V) setting in the controller to 46~48V (which should hopefully be higher than the battery's BMS Low voltage cut off) it should prevent the BMS from cutting off the power completely when the cells are struggling under heavy load.

You should find that the motor power will noticeably reduce after a long trip instead of the battery cutting out, and the lowest recorded voltages on the CA should never be any lower than the controller set minimum voltage.



If you find that it still cuts out completely at the end of your 16+ mile commute, it will probably be the BMS cutting out because the voltage of one or more groups of paralleled cells is being pulled down too far under load.  :(

Reducing the Battery drawn current (A) setting on the MP5 should also help to increase the range of this poor quality battery pack.

Quote from: Shenzhen K E technology co., LTD
Quality
We are professional Electric bike battery supplier on aliexpress, We have perfect production process and all kinds of scientific management tools to control the quality,such as Six Sigma,PFMEA,CP,SPC and so on.The battery is brand new and every single item you buy from our company has been completely tested before shipping , after several times of testing , so we can guarantee the quality.

I notice that they don't guarantee the quality as being; good, as specified or even acceptable, so perhaps the "perfect production process and all kinds of scientific management tools to control the quality" are simply needed to ensure that "after several times of testing" the quality is consistently poor and unable to match the stated specifications.


Alan
 
« Last Edit: July 02, 2017, 06:54:14 PM by Bikemad »

Offline Bedmountain

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Re: New Battery Specifications
« Reply #23 on: September 21, 2016, 04:43:32 PM »
Hi Alan

Thanks, as always, for your advice. I'll have a try with amended settings.

I'm considering attempting to build my own triangle pack. I have read a lot around it but I'm still worried any cells I buy will not be as specified so I could end up with a poor end product anyway.

Anyway - thanks - for the time being I just need it to cover 16 miles without me having to push/carry it. I'll let you know how I get on....

Cheers
Ben