custom battery

[Tomek]

Hi all,

I'm playing with the idea of building my own battery pack - as part of a plan to build a whole custom unicycle based on microworks parts (learning from lessons of others on this forum such as @DebboR http://forum.electricunicycle.org/topic/1881-another-30kmh-microworks-and-battery-upgrade/  or  @mokwichi http://forum.electricunicycle.org/topic/2035-tg-f-5-500w-motor-upgrade/).

Most likely (because of the design idea I have for my custom shell) I'll be limited to two packs of 16 cells, so I really need good performing batteries. I have narrowed down my choices to:

• LG 18650-HG2 3000mAh 20A http://www.nkon.nl/rechargeable/18650-size/lg-18650-hg2-button.html
• Samsung INR 18650-30Q 3000mah http://www.nkon.nl/rechargeable/18650-size/samsung-inr-18650-30q-3000mah.html (my pick so far)
• Samsung INR 18650-25R http://www.nkon.nl/rechargeable/18650-size/samsung-18650-inr18650-25r.html
• Sony Konion US18650VTC5 http://www.nkon.nl/rechargeable/18650-size/sony-us18650vtc5-flat-top.html

All are rated at 20A (or more), but I can't find much info on internal resistance, which is critical to determine the voltage drops at high discharge rates and thus proneness to BMS shutdowns. (@Jimicycle's post explains it very clearly how internal resistance (impedance) can be calculated in practice http://forum.electricunicycle.org/topic/2079-30-kmh-on-a-350w-motor/?page=2#comment-23835)

Do you guys have any (other) battery recommendations?

btw. I'm also considering using this or similar BMS http://www.aliexpress.com/item/High-quality-60v-bms-10A-16S-smart-bms-60v-lithium-pack-PCM-3-7v-li-ion/32481689184.html, as my battery will either need to be very slim, or have an unusual shape, making it impossible to use the typical unicycle BMSes to which cells are fixed directly. Waiting for the specs from the seller, as they don't give much on the page.

 

[esaj]

dampfakkus.de lists the internal resistances for at least some cells, here's a few examples

http://www.dampfakkus.de/akkutest.php?id=592  3000mAh LG INR18650HG2  20 milliohms NMC (20A)
http://www.dampfakkus.de/akkutest.php?id=507  2500mAh LG ICR18650HE2  21 milliohms  NMC (20A)
http://www.dampfakkus.de/akkutest.php?id=608  3500mAh LG INR18650MJ1  37 milliohms NCA  (10A)

http://www.dampfakkus.de/akkutest.php?id=490  2500mAh Samsung SDI INR18650-25R  18 milliohms NMC  (20A)
http://www.dampfakkus.de/akkutest.php?id=586  3000mAh Samsung SDI INR18650-30Q 18 milliohms NMC  (15A)
 

Although the internal resistance isn't the whole story... as you can see, 25R and 30Q from Samsung both have internal resistance of 18 milliohms, yet the 30Q is recommended "only" for 15A, so probably some additives etc. also play a role? From what I've read, NCA chemistry has been suggested as more safe and robust chemistry for electric vehicles over NMC (for example, Tesla uses NCA), but not sure what it is exactly that makes it more safe (at least it's said to handle vibration and physical shocks better?).

Personally I went with LG MH1's for the custom packs (3200mAh "version" of MJ1), as it was slightly cheaper (still over 200€ per 16S pack with spot-welding assembly and BMS). Dampfakkus doesn't list internal resistance for it, but someone had tested the cells and found it to be between 34 and 36 milliohms per cell.

[Tomek]

thanks @esaj

1 hour ago, esaj said:

25R and 30Q from Samsung both have internal resistance of 18 milliohms, yet the 30Q is recommended "only" for 15A,

From what I've read on some battery forums Samsung is overly cautious with the rated current, and in fact their cells perform better than the higher rated cells of e.g. LG HG2 vs Samsung 30Q

[Jimicycle]

Anyone knows reliable sources in USA?

One of the problems is that not sure whether the spec for a battery is real or not.  Some supper ones marks 6500mAh or even 9800mAh .   Both Am and Eb have many such batteries, do not know whom I should trust now. 

[Tomek]

just a thought... is there a good reason why we shouldn't put a really big capacitor between the battery and controller to prevent shut downs from high current draw spikes?

[esaj]

1 hour ago, Tomek said:

just a thought... is there a good reason why we shouldn't put a really big capacitor between the battery and controller to prevent shut downs from high current draw spikes?

AFAIK, you wouldn't put it in between (in series) with the battery and controller, but in parallel... probably it would also have to be very large not to discharge completely in an instant if the BMS cuts out and the current draw is high. But could be wrong... also I cannot say if and what other effects it might have.

EDIT: This might also be a problem: there were only three supercapacitors I could find from Digikey (just the first page I encountered which listed supercapacitors) that could handle the voltages used in most wheels (above 67.2V)... the cheapest costs over 1000€ a piece, and the dimensions are 14.448" L x 9.251" W x 3.110" H (367.00mm x 235.00mm x 79.00mm). Doesn't state the weight, but probably also heavy. Lifetime 1500 hours @ 65 degrees Celsius.

[zlymex]

On 2015/12/29 at 1:27 PM, Jimicycle said:

Anyone knows reliable sources in USA?

One of the problems is that not sure whether the spec for a battery is real or not.  Some supper ones marks 6500mAh or even 9800mAh .   Both Am and Eb have many such batteries, do not know whom I should trust now. 

They are fake. The largest for 18650 cell is 3600mAh so far.

[zlymex]

All 4 batteries will do, make not much difference.

The internal resistance from the specs(if they have any) is measure by AC method. Although related, it's different from DC internal resistance that more applicable to EUCs.

The BMS from the link rated 10A, a bit small. I would choose 15A making a total of 30A. Also it may not be slim if you put it on top of the batteries as there is an aluminium heat-sink/protector.

[Tomek]

another battery dillema: to shunt or not to shunt the low voltage and over-current cut off... with powerfull cells it shouldn't matter, and battery packs catching fire because of one malfunctioning cell is also a serious concern. do you guys know if quality wheels (ks, gotway) have entirely removed these protections or replaced them with something else?

[esaj]

If memory serves, at least some versions of Gotway (MSuper 2? Others?) have the discharge protections entirely removed. Don't know about King Song.

[zlymex]

On 2016/1/22 at 2:22 AM, Tomek said:

another battery dillema: to shunt or not to shunt the low voltage and over-current cut off... with powerfull cells it shouldn't matter, and battery packs catching fire because of one malfunctioning cell is also a serious concern. do you guys know if quality wheels (ks, gotway) have entirely removed these protections or replaced them with something else?

Gotway(MSuper 2 MS at lease) just shunt the output protection. Actually there is No output protection on the BMS(The mainboard has a lo-batt warning but it's base on the total voltage, not individually).

There is no output protection circuitry in a KS-18A 64 cell pack either but there is a fuse instead. This is also the way I made my own battery packs.

For IPS EUC, there are 17 sense wires(actually there are 19) from the battery directly to the mainboard. If there is a lo-V problem for any cell, the pedals will tilt and red LED flashes forcing the rider stop without power cut off. This is the best way AFAIF but with added complexity.

In this case(shunt and no low voltage protection), one must take his own care to ensure the safety of the batteries. 

[Tomek]

@zlymex what fuse do you use? i think i'll do the same as you. i havent seen any reposts on this forum about battery damage (fires?) resulting from over discharge in shunted BMSes, so that's somewhat reassuring. btw. doesn't IPS have the whole BMS on the main controller?

[zlymex]

On 2016/1/24 at 5:19 PM, Tomek said:

@zlymex what fuse do you use? i think i'll do the same as you. i havent seen any reposts on this forum about battery damage (fires?) resulting from over discharge in shunted BMSes, so that's somewhat reassuring. btw. doesn't IPS have the whole BMS on the main controller?

I use Panasonic NCR18650B the most. They are good in uniformity and large in capacity(3.4Ah). I bought a lot single cells before.

Edit: I use these batteries for external mainly. I did use them for internal once(for my MSpuer2) but there are existing internal packs for large current thing. These NCR18650B are not good for large current and cannot be used as internal pack alone.

[Tomek]

@zlymex wow, nice supply

I was actually curious what fuse you're using though...

[zlymex]

On 2016/1/24 at 7:47 PM, Tomek said:

@zlymex wow, nice supply

I was actually curious what fuse you're using though...

Automobile fuses

 

[Tomek]

@zlymex are't they rated for 24V max? and isn't 15A not too little? i was thinking 50A or more for myself (it's after all mainly for a short circuit protection)

[esaj]

8 minutes ago, Tomek said:

@zlymex are't they rated for 24V max? and isn't 15A not too little? i was thinking 50A or more for myself (it's after all mainly for a short circuit protection)

Not that sure about the fuse voltage-rating, I don't think there can be a strikethrough at these low voltages (ie. the electricity "jumping" across gap), maybe it's related to the amp-rating (if the fuse is calculated to withstand a certain power, not amperage, then the current at which it blows would be different for different voltages).

50A sounds pretty large for 16S1P, I don't know if you plan to add more cells in parallel though. Of course you can be pretty sure it won't blow by accident during riding at least if it's 16S1P  

[THA]

Amps are what burns fuses, not volts, f.ex. trucks (24V) uses the same fuses as cars (12V). And think about fuses at Your home, they all about amperes, 230V as well as 400V (380) are all the same. Keep in mind P = UI and U = RI - so when volts increase, if the power remains the same, current decreases, resistance increases (thinner cords). That's the reason why electricity transferred rather higher volts than higher amps (for longer distances especially).

[Tomek]

@THA @esaj, agree about the principle with voltage and fuses, but for some reason the automotive fuses do have a rating of 24V or sometimes 42V, so there must be some factor at play...

and about amperage: with an 800W motor you may get peaks of 2000W+, which @60V would give 33A, even if split over two packs, if one pack fails at a peak, you don't wont the fuse of the other one blow when riding.

I'd rather skip the fuse if it can cause a face plant, the very thing I'm trying to avoid by shunting .')

[esaj]

32 minutes ago, THA said:

Amps are what burns fuses, not volts, f.ex. trucks (24V) uses the same fuses as cars (12V). And think about fuses at Your home, they all about amperes, 230V as well as 400V (380) are all the same. Keep in mind P = UI and U = RI - so when volts increase, if the power remains the same, current decreases, resistance increases (thinner cords). That's the reason why electricity transferred rather higher volts than higher amps (for longer distances especially).

I was thinking more along the lines of passing, say 10A through the fuse at 12V or 60V:

P = UI  =>  12V * 10A = 120W, 60V * 10A = 600W

Of course only some part of that power is dissipated in the fuse itself (would have to know the internal resistance or the voltage drop over the fuse).

 

Just now, Tomek said:

@THA @esaj, agree about the principle with voltage and fuses, but for some reason the automotive fuses do have a rating of 24V or sometimes 42V, so there must be some factor at play...

and about amperage: with an 800W motor you may get peaks of 2000W+, which @60V would give 33A, even if split over two packs, if one pack fails at a peak, you don't wont the fuse of the other one blow when riding.

I'd rather skip the fuse if it can cause a face plant, the very thing I'm trying to avoid by shunting .')

Personally I'd probably go the same route as you, use way overrated fuse that won't burn without short circuit.

About the voltage ratings, this is what Wikipedia had to say:

Rated voltage[edit]

Voltage rating of the fuse must be equal to, or greater than, what would become the open circuit voltage. For example, a glass tube fuse rated at 32 volts would not reliably interrupt current from a voltage source of 120 or 230 V. If a 32 V fuse attempts to interrupt the 120 or 230 V source, an arc may result. Plasma inside the glass tube may continue to conduct current until the current diminishes to the point where the plasma becomes a non-conducting gas. Rated voltage should be higher than the maximum voltage source it would have to disconnect. Connecting fuses in series does not increase the rated voltage of the combination, nor of any one fuse.

Medium-voltage fuses rated for a few thousand volts are never used on low voltage circuits, because of their cost and because they cannot properly clear the circuit when operating at very low voltages.^[8]

 

So actually it could "jump" (arc) through the fuse at higher voltages. Don't know if 60V is enough though.

 

[dmethvin]

The spec sheet for Littelfuse brand fuses says at least some of them are rated for up to 58 volts, so you're not pushing them too far past their rated max voltage.

[Jed]

Hello members,yesterday I go trail climbing with my ks18".its extremely difficult with a lot of tree roots on the ground.

one thing l don't understand is that my ks18" when climbing some nice hill without any tree roots or extreme," but a bit high". when l stop and climb again the pedal beginning to rise high n high n high till can't lean anymore to the front.its been this situation for two times since l bought this ks18".the battery still got level 9.do anybody been this situation before?

[esaj]

8 minutes ago, Jed said:

Hello members,yesterday I go trail climbing with my ks18".its extremely difficult with a lot of tree roots on the ground.

one thing l don't understand is that my ks18" when climbing some nice hill without any tree roots or extreme," but a bit high". when l stop and climb again the pedal beginning to rise high n high n high till can't lean anymore to the front.its been this situation for two times since l bought this ks18".the battery still got level 9.do anybody been this situation before?

Don't have a KS, but it could be that the temperature of the mainboard is rising with the power needed for climbing, and it starts to warn about that. Does it go away if you stop for a while or turn it off for some time?

[Cloud]

24 minutes ago, Jed said:

Hello members,yesterday I go trail climbing with my ks18".its extremely difficult with a lot of tree roots on the ground.

one thing l don't understand is that my ks18" when climbing some nice hill without any tree roots or extreme," but a bit high". when l stop and climb again the pedal beginning to rise high n high n high till can't lean anymore to the front.its been this situation for two times since l bought this ks18".the battery still got level 9.do anybody been this situation before?

When the pedals are rising, is the wheel also beeping?

also get off the wheel and let it tilt back all the way. Does it then start to tilt forward?

if the answer to both questions is yes, then this is the overheating tiltback. 

How much do you weigh again? How steep was the hill? How long was the hill?  Did you frequently ccelerate and brake? Connect to the app and see what the temperature is when this happens. Should say around 68-70C

you need to stop and wait/ or turn it off for a few minutes to let it cool then start again. For best results without waiting too long, let it cool for at least 4 minutes

 

[Jed]

35 minutes ago, esaj said:

Don't have a KS, but it could be that the temperature of the mainboard is rising with the power needed for climbing, and it starts to warn about that. Does it go away if you stop for a while or turn it off for some time?

@esajYes it go away after awhile.normally pedal rise is because shortage of battery but my one still full!a lot of things l never knew.thanks!