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Draining the battery to Zero


SlowMo

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13 hours ago, Sonopanic said:

 ...

BMS of the EUCs are all bad chargers with simple electronics.

The BMS only measures the Voltage of the complete Cells and cuts the power of
the charger. Meanwhile the charger load the battery with full power.
This is oldschool for cheap car battery chargers and really not the way to achieve
1000 cycles.

I hope, there is balancing between the cells, but i doubt it.

 

Imho not - i never verified it but from what i read here the charger (for at least ninebot?) start with constant current and once the maximum voltage is reached the switch to this max fixed voltage and "wait" until the cell balancing (internal from the BMS) is done (the current drops under a certain threshold). And at least ninebot (and KS?) seem to have nice controller chips for the liion cells: 

This should be quite state of the art for liion charging according to http://batteryuniversity.com/learn/article/charging_lithium_ion_batteries . But i never worked through the data sheet of the controller or looked in at the detailed configurarion of it ... @Cranium : do you have detailed pics covering the whole bms pcb? Eventually also from the backside (of the hopefully only double sided and not multilayer pcb)?

for the liion cells in the ninebot e+ battery pack the standard discharge cutoff voltage for 0.2C is 2.5V or for a discharge with 6A 2.75V (according to the manufacturer datasheet linked at the end of above cited post)

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On ‎2‎/‎1‎/‎2016 at 0:08 PM, Sonopanic said:

No !

The battery needs a Minimum

voltage to maintain chemical function.
A Lithium Ion cell with 3,7V should never reach 3,2V or it will be damaged.

The common shut off Voltage is 3,4V.

The good cells can be recharged aprox. 1000x, a harsh undervolting can kill the cell
at once or can reduce the lifetime, so the cell can perhaps only 100x recharged.

I fly multicopter and a great amount of money goes into the battery and the charging.

The BMS of the EUCs are all bad chargers with simple electronics.
The BMS only measures the Voltage of the complete Cells and cuts the power of
the charger. Meanwhile the charger load the battery with full power.
This is oldschool for cheap car battery chargers and really not the way to achieve
1000 cycles.

I hope, there is balancing between the cells, but i doubt it.

 

@Chriull, I think this answers your questions as well but I wanted to focus on what @Sonopanic had posted and re-iterate what you already pointed out.

The BMS on the Ninebot is far from being "simple".

I have taken detailed pictures of the front side of the BMS and figured out to the best of my ability what the BMS does do and what it does not do.  I have posted some of the pictures as well as referenced the spec sheets for most of the ICs and transistors used.  The PCB is double sided and I have no access to the back side so can't follow traces through vias.

The intelligence in the BMS

IMG_20160123_000316.thumb.jpg.e95f654f77

The main protection in the BMS is done using the SH367004 IC.  This IC can and will protect the batteries from overcharging, overdischarging, discharge overcurrent, charge overcurrent,  discharging over temperature, and finally will balance the cells (all functions are handled in the logic module of the IC).  The mechanisms the BMS uses to protect the battery is to control the 3 MOSFETs used for discharging and 1 MOSFET used for charging.  It will either throttle the current or cut it off entirely based on the condition it encounters (handled in the control module of the IC).  It even has a delay module to allow for transients as well as a couple of optional features that can be incorporated.

56a4649d3a878_BlockdiagramoftheSH367004.

Battery specs

IMG_20160121_233330.thumb.jpg.55d77d45f9

EU batteries are different than the LiPo batteries used in the RC world.  The 320Whr battery pack in my E+ uses LG18650MG cells.  Standard charge rate of the cells is 0.5C with a max charge rate of 1C.  Minimum voltage is 2.5V (without damage).  Max discharge rate is 10A.  

More details, spec sheets and pictures of my findings can be found here:

 

 

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On 31-1-2016 at 1:59 PM, SlowMo said:

I have drained the battery of my electric scooter once. There was no warning beep. It just shut off the motor even though the battery was still at around 20%. Yesterday, I was worried about my son's Kahuna wheel when we were on the way back. I was following him and was keeping an eye on the led indicator if it would turn to rapid blinking but it never happened. I was not paying attention to the IPS Zero which was far ahead ouf us and only realized that it was drained to 24% when we finally stopped. My daughter did not complain of any slow motor movent or any tiltback which was a good sign.

if you're a feather weight it seems with the Lhotz you can go below 25% without any problem

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  • 2 weeks later...

Quite a lot of what is being discussed here has been discussed before here: 

Bottom line on how safe and predictable any wheel is at low voltage is simple:

If your BMS handles low voltage, excess current, or any power output "safety" you are going to faceplant one day as the BMS protects the battery - not you - and will cut power, probably suddenly if it sees the need to.

If the wheel's control board handles it (a really good BMS would pass warnings on to the control board for example if one cell went low ) then a well designed board will do everything it can to prevent you continuing. You may still faceplant if you ignore its attempts or over lean when there isn't enough power to hold you up, but that would be down to you.

Regarding the confusion about safe minimum voltages. You need to be careful you are not comparing eggs with bananas! Cells have internal resistance, LiPo cells are damaged if the resting voltage goes much below 3V, LiIons appear to tolerate a bit lower. In practice, below a resting voltage of around 3.4V there is naff all capacity left so it is all a bit academic. Under load, internal cell resistance will cause a voltage drop and resistance gets higher as cells get emptier. That means a battery protection system ideally needs to have a variable warning voltage depending on how high the current flow is at the time. None that I know of do so, as a result the warning, or more often cut off voltage, is an arbitrary figure based on an assumed average current - allowing for the drop due to internal resistance. You can see this on your battery monitor - the voltage goes up when you stop driving the wheel. Since few BMS monitor individual cells and warn or cut off on the lowest, a safety factor is also needed for some cells being lower than others.

Under heavy load, a warning voltage of 2.5V (say) may well be a resting voltage of 3.5V so perfectly OK, but at lower load this would damage the battery. In practice a compromise that protects the cells at a possible cost of reduced range is chosen.

Regardless of whatever protection your wheel has, the deeper you discharge the cells regularly the shorter the life will be.

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On Sunday, January 31, 2016 at 2:53 PM, zlymex said:

For IPS EUCs, because of the BMS is integrated in the mainboard, you get a warning and tilt back when any single cell is low, thus avoid faceplant even if you drain the battery to the last drop. My T260 has been brought for over 17 months and still 85% of its original capacity(Ah) left when I tested using an electronic load the other day.

For many other EUCs(including Gotway and Kingsong), there are no output protection of their BMS. The EUC estimate the battey conditions based on the total output voltage of the series connect pack. Even the voltage of the pack is not reaching to the critical low situation, the voltage of one of the cell may became too low(in a off balanced condition, which theoretically happens all the time). Therefore, riders should take precautions not to let this happen. Namely if you encounter a low battery warning(4 lights flashing together with the two-beep warning sound for Gotway), just stop riding so that not to receive the warning again.

There got to be a weakest cell in a series connected pack. Draining the pack will make this cell to suffer(voltage too low or zero or even reverse-biased) first and become even more weak(increased internal resistance, decreased capacity, more leakage current). If this situation happens frequently, the weakest cell will certainly damaged soon.

I have an IPS T680+, at battery of 100% the app shows 66V

Any idea how low I can go before the cells get damaged?

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On 2016/2/2 at 3:15 PM, Chriull said:

This is me, zlymex, reply to @Jurgen. It must be a bug of the Forum not letting me to reply normally. I have reloaded this page and try three different ways to reply/quote but cannot type in anywhere but here.

I'm unaware of IPS has a T680/T680+.
However, the BMS in most of IPS EUCs are among the best that designed in such a way that rides just cannot harm the batteries in normal ride. Having said that, batteries in a IPS EUC are of average quality that easily become off-balanced if not charged properly.

 

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Hi !

when I get my first EUC ..I was't able to ride so I seat down on my sofa with the feet on euc pedals so it can run against me..and begin to start full discharge.

After some burnout  and some time   one side of the euc shell was a little more hot and battery near to 0% ...

However it never cut-off the power  ..only started move front/back the pedals . every time that it start with  this oscillation I needed to power off euc and tha restart.

When I have learning to ride ..I have discharged euc battery again under 25% because I wanted to know how many km he can do. ...but ..maybe lucky .. no power cut-off.

however now I never ride under 25% battery :)

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LiPo battery review:

I am a Newbie at EC but I have 30 years with LiPo batteries in RC planes and in consumer electronics.  Worked for Sony (who was one of first commercial LiPo battery makers) and now for Amazon (can you say "Prime Air"????).

I suggest everyone go to www.batteryuniversity.com for a crash course in what each battery type can support.  For our 18650 type of "silver sausages" the rules are straightforward and very simple.  Never let a cell go below 3.0 volts and never charge above 4.2 volts.  Nominal working voltage is 3.7 voltsDC.  You can take a 18650 down to 2.5volts per cell.  Doing so generally removes about 30% of your lifetime battery cycles.  So if you want 500-1000 cycles, never go below 3.0 volts/cell.  My rule of thumb when flying airplanes is that when I reach 3.2 volts/cell, my plane gets "sloppy" and I want to land immediately.  When you no longer have "good pickup" on EU, it is time to recharge.  A removal of 10% of battery charge at the bottom end of the battery range costs you 5 times the battery life in a LiPo as taking 10% out of the top of the battery range.

Battery under load.  When you are running, your loaded battery is typically 0.6 volts lower in DC voltage then when you stop and measure the voltage 3 minutes latter.  So if your battery when you get home and get out the meter reads 3.6 volts/cell when cold.....there is a very good chance that while you were under max power, your batteries were at 3.0 voltsDC/cell.

In short: stay out of the bottom end of the battery range and your battery will reward you with long life.   I have set fire to many LiPo in the food packaging containers for rc airplanes.  You can follow my exploits on rc-groups under battery flames.  The silver sausages generally do not explode because of their PTC devices.....but we have had explosions from them when seriously over discharged and then recharged.   There are other types of LiPo coming into the mainstream, but their energy density is less than what the 18650 units have.  They are safer, but they have less "bang for the buck".

I personally believe that every EC should have an active temperature sensor on the center of the battery pack (especially of two layers of cells are used).  When the temperature gets to 65 deg C, you are settting yourself up to "battery runaway".   You should stop and let things cool down.

   tjcooper

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13 hours ago, Makoben said:

TJ, so how do we measure temp and voltage in a simple low cost manner? Like a digital readout permanently mounted on our EU's.

Mike

I used a DC 0-100V / 50A voltage / current -display:

Fujyfpu.jpg

The display used internal wiring directly into battery wires, the white thing attached to charge port is the Charge Doctor (won't show any voltage if your BMS has a reverse protection diode). The see-through case with a red button is the battery for the display (it needs 4-30V input voltage to work, cannot power directly from 60+V batteries).

The display was this one:

http://www.aliexpress.com/item/DC-Car-LED-Red-Blue-Dual-display-DC-0-100V-50A-Voltmeter-Ammeter-2in1-Voltage-Current/1684125289.html

A bit of a pain to install, as I needed to add the quite large shunt next to the mainboard:

gh1lcUl.jpg

But that's only needed for high current measurements, you can simply get just a voltage meter.

 

12 hours ago, Sonopanic said:

I am planning to put a Voltmeter into the casing.

The best way for me, integrate a Meter to a plug for the charging socket. 
 

Unless you have a BMS without a reverse protection diode in charging side, you won't get any voltage readout from the charge port/charging wires, need to wire it to the discharge-side.

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  • 1 month later...

Makoben,

see my description in "how to hop up on petals".  At the end of thread I describe the DROK which can be purchased from Amazon for $15    It takes 5 minutes of wiring and gives you the voltage, current, and total power put into the battery during the charge cycle.  Others reference Doctor Meter (which I had not seen before) which does roughly the same thing.  The advantage of the DROK circuit is that it can monitor charging up to 100 volts DC and up to 100 amps....which we should never do.

   tjcooper

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I always drain the battery until the four leds start flashing. Once they start to flash euc slows down for maybe 2 minutes and then tilts back and stops. I seem to get better mileage with same charge/drain cycles a habit from back in ni cad days. The other reason is mileage. 2-3km's just does not cut it so must drain to get where I want to go. The 170w pack I put in at 1st would only hold 40 minutes charge, after cycling through 5 charge and drains it now charges for 65-70 minutes. Actually got 11km out of it today which is heaps better than the 7 km I first got, but I still think this 170w is a dud as it only does the same as the 130w in my other wheel.

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Dr. Bob,

A micro-fact that should convince you to recharge LiPoly batteries "early and often".  When I worked at Sony the LiPo research people showed their measured data which was a real eye-opener.  A 0.1 volt drop in a LiPo cell at 4.1 volts DC will decrease your battery life by "x" amount.   The same 0.1 v drop at 3.2 volts DC causes about 8x to 10x decrease in your battery life.

This is completely the opposite way the old NiCd and NiMd worked:  "drain them until they are dead" that we used to know in the RC airplane batteries we had.   The "memory effect" on NiCd and NiMd (which is only true if you deplete the battery by less than 10% of its charge) is basically non-existant in LiPoly systems.  The lower the drain voltage, the more the Aluminum plate gets attacked.   So to keep your LiPoly systems running for their full 500 cycles, shut them down as soon as you can and recharge them. 

I have examples for my outrunner airplanes where I would fly until the BEC would cut off the motor and then I would have to restart and "limp" my way back to home plate.  Same size battery on a similar plane that I would only fly 1/2 as long got more than four times the flights (that is 2 times because I only drained half way,  and another two times because I was "kind" to the batteries) until the battery died.  So keep the LiPo cell always above 3.0 vDC and do your recharging as soon as you get home.   Time for a battery to sit in discharge state is also another killer of the battery.   Best to keep it at half full state whenever it is stored.

    tjcooper

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