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MCM5 (Light) 900W/67.2V using 20700 20A batteries


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I want to know if anyone sees any problems with what I am trying to do. My MCM5 is a 130Whr version (2200mha 16S) on the side panel battery pack.

I want to replace the batteries with Sany 20700B 4250mah/20A batteries. (732Whr in theory if I replace all 60 cells) The reason for this is for the battery to be able to discharge quicker. I weight about 87kg and find a big difference in the responsiveness of the 20A battery packs.

I understand that physically the side panel the batteries it may not fit, however I see @Traveller else has already done it.  On the LHY16S version 2 board (the big flat one), I don't see anything limiting the AMPs like other generic BMS do.

For the top battery pack I've yet not figured out how I am going to put 20700 batteries into it and whether it feasible. I have to take the MCM5 apart.

As I don't have an existing battery pack to savage I don't have the BMS board.  I think it is the LHY16S version 1 board. If anyone can tell me where I can source our or anyone has a dead battery pack I take one from it would be great.

How will the mosfet handle going from a theoretical 600A discharge to a 960A discharge rate? Do I have to replace those?

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Thanks for your concern, I am concerned too, so they are being manufacture by a electronics pro, that works reparsing everything and anything day in day out for the past 20 years. The packs will be  inspected with a FLIR infrared camera.

Manufacturing,, testing, inspection, burn it, safety runs safety measures have been figured out.

 

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5 hours ago, OneLeg said:

Thanks for your concern, I am concerned too, so they are being manufacture by a electronics pro, that works reparsing everything and anything day in day out for the past 20 years.

While that doesn’t yet give credit for experience in high voltage li-ion battery handling (the same phrase could be used to describe me), that is somewhat a relief to hear. At least the soldering should be good then.

If you go on with the plan, I’d still ask for him to be sure to take enough steps to make the battery pack water tight.

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6 hours ago, OneLeg said:

I want to know if anyone sees any problems with what I am trying to do. My MCM5 is a 130Whr version (2200mha 16S) on the side panel battery pack.

I want to replace the batteries with Sany 20700B 4250mah/20A batteries. (732Whr in theory if I replace all 60 cells) The reason for this is for the battery to be able to discharge quicker. I weight about 87kg and find a big difference in the responsiveness of the 20A battery packs.

When did you purchase yours ? If recently then you should be able to upgrade to 84V B) But then again, you'll need to purchase the 84V main board, BMS & charger too.

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i donno what is with the recent hype for 20700/ 21700 battery, until today not even one did a real life comparison. Theorectically if you have a 18650 with 4250mah & a 20700/ 21700 with 4250mah, the range will be more or less the same.

mine was advertise 67.2V(170WH) with 1500watt motor. i did check with the seller & he did confirmed that it is able to fit 80pcs of 18650. Ordered the battery but still haven't arrive yet.

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18650.thumb.png.c2ae9a41beaa4ca1a7a849c50b24c571.png

1406819416_18650Eng.thumb.png.812cdc1524def71c64de64b0f23d1949.png

 

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21700 is almost double the price of 18650 & you don't have the space to store 80pcs of them !

 

Hmm, i donno how these Taobao shop calculates the WH, few offer 1300WH for mcm5. May be they are able to cram in 5P or 6P in there :P

3.4AH x 3.7V x 20 cell x 4p = 1006.4WH

3.4AH x 3.7V x 20 cell x 5p = 1258WH

2.8AH x 3.7V x 20 cell x 6p = 1243.2WH

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We recently opened a 1500W unit and only saw the 2 packs totally 60 cells... mind you we didn't open the other side.... but all the cabling didn't show any signes of a 3rd battery pack...

On the 1500W there is no room to put 20700 or 21700 cells... I think the max is 3.5A x 3.6V x 20S3P = 756Whr.... 

IF they used 21700 it would be lighter and could be setup with 5A 3.6 x 60 = 1080Whr... but they don't. It would also would lose weight.

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  • 2 weeks later...

I think the motors are different in between the 1500w and 900w mcm5 so you wont need packs of 20 cells as you wont need 84v.  You will need packs of 16 cells.  I think there would be enough room in the top location for 20700 or 21700 cells as the spot is made for 20 cells and you will only be putting in 16.  You will be able to recover the original bms of the original top pack  of 130wh so you will only need one bms.  I just purchased a generic 16s bms from AliExpress and have had no problems.  As others have said it is a lot of work.  

I was aiming for about 400wh to keep weight down whilst ensuring maximum amps which is why I went for 21700s.  For maximum battery size you would be better off with 18650s as you will be able to fit 2p in the side location where as with 21700s you can only fit 1p.

Option 1 - total 2p 16s Sanyo 20700B 4250mah/20A batteries = 244.8wh x 2= 489.6wh total

Option 2 - 3p 16s Sanyo NCR18650GA 3500mAh 10A = 201wh x 3 = 603wh

Option 3 - Maybe somehow you can get 3p in the side pocket and 1p in top pocket as 1500w motor somehow gets 4p20s.  This would give you max 804wh if you stick with all 18650 if you went with 20700 in the top bay you could get 850wh.  

On 12/10/2019 at 2:02 AM, yuweng said:

When did you purchase yours ? If recently then you should be able to upgrade to 84V B) But then again, you'll need to purchase the 84V main board, BMS & charger too.

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English.png.b61274630fd60bfa7c9a9cb0fd6acdb0.png

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i donno what is with the recent hype for 20700/ 21700 battery, until today not even one did a real life comparison. Theorectically if you have a 18650 with 4250mah & a 20700/ 21700 with 4250mah, the range will be more or less the same.

mine was advertise 67.2V(170WH) with 1500watt motor. i did check with the seller & he did confirmed that it is able to fit 80pcs of 18650. Ordered the battery but still haven't arrive yet.

  Reveal hidden contents

18650.thumb.png.c2ae9a41beaa4ca1a7a849c50b24c571.png

1406819416_18650Eng.thumb.png.812cdc1524def71c64de64b0f23d1949.png

 

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21700.thumb.png.bbbf0d5d854c1ae4b359f790d5c58c76.png

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21700 is almost double the price of 18650 & you don't have the space to store 80pcs of them !

 

Hmm, i donno how these Taobao shop calculates the WH, few offer 1300WH for mcm5. May be they are able to cram in 5P or 6P in there :P

3.4AH x 3.7V x 20 cell x 4p = 1006.4WH

3.4AH x 3.7V x 20 cell x 5p = 1258WH

2.8AH x 3.7V x 20 cell x 6p = 1243.2WH

If yours is 67v I can't see that it would be a 1500w motor.  Even if it is the same motor then you would also need to change the control board to put in 80 cells as the voltage is different.  

 

On 12/9/2019 at 6:37 PM, OneLeg said:

I want to know if anyone sees any problems with what I am trying to do. My MCM5 is a 130Whr version (2200mha 16S) on the side panel battery pack.

I want to replace the batteries with Sany 20700B 4250mah/20A batteries. (732Whr in theory if I replace all 60 cells) The reason for this is for the battery to be able to discharge quicker. I weight about 87kg and find a big difference in the responsiveness of the 20A battery packs.

I understand that physically the side panel the batteries it may not fit, however I see @Traveller else has already done it.  On the LHY16S version 2 board (the big flat one), I don't see anything limiting the AMPs like other generic BMS do.

For the top battery pack I've yet not figured out how I am going to put 20700 batteries into it and whether it feasible. I have to take the MCM5 apart.

As I don't have an existing battery pack to savage I don't have the BMS board.  I think it is the LHY16S version 1 board. If anyone can tell me where I can source our or anyone has a dead battery pack I take one from it would be great.

How will the mosfet handle going from a theoretical 600A discharge to a 960A discharge rate? Do I have to replace those?

Also board is not going from 600a theoretical.  The cells are in series so 10A cells in theory put out max continuous 10A and 20A 20700s put out max continuous 20A.  I have seen up to 50A from my modified battery pack through the AP instantaneously when doing pendulums or just starting out accelerating hard.  After that settles way back to 10 amps or so. 

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I have just had another look at my photos of the battery compartment.

https://imgur.com/a/udToFxs

Looks like you could fit 2p 18650 in the top compartment and 2p 18650 in the side compartment.  Gives you 800wh even in 16s if you use 3500maH 18650 cells.

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Thank you.

1. BTW make sure your generic BMS does not have mosfets, original Gotway does not have any

2 . Where did you plug the BMS cable from the new pack  on to the motherboard?

I have taken photos of my MCM's battery slots and the motherboard.

https://www.dropbox.com/sh/uymym2tko903xlu/AAAtoDGWv5CBdZgrJklz4vFpa?dl=0

3. I think the top location if you remove all the pad the has enough space for the Sanyo 20700B's.

This means that there is space at the top location be able to configure it with 16S2P and 16S1P on the side location.  In my calcualtions that would give 734Whr. In some places the rate the 20700B as 20A.

4. Do you know what the mostfet model/part number. Seems the mosfets are not visible and are under the board.

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On 12/20/2019 at 1:55 AM, Traveller said:

Oh that is how they can configure 800Whr.... that is an interesting option but you would be using 10A batteries..... maybe my 48 x  20700B option is better though only 734Whr/20A

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It seems that the top location can't take the 20700 if inserted the same way as we have to do  4 x 20mm + 2 BMS.... that is close to 83mm... and the space is only 76mm tall... So the batteries battery pack must go in sideways... I still have to measure how much does it stick out by...

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The top pack cells don't need to stack on their diameter - they can be offset in a pyramid type stack on their 45 degree.  Width would be 73mm and height whatever the space height is - 76 would be fine.  The pack would just be a bit longer however there should be plenty of length.

I just made a y joiner cable for both the battery charge (JST connectors) and discharge cables  (xt60 connectors).  I just charged one pack and then charged the other and then knowing they were both at the same voltage I could then join them with the "y" joiner.  

I am not concerned about my generic BMS as I also have the original manufacturers battery pack in parallel so if the generic bms shuts down then the manufacturers battery pack will take over.  I have flattened the battery completely once and the tilt back worked at low voltage and there was no cut out.

There is no real advantage to using higher than 10A rated cells if you are going to put in two packs of 2P16S.  That will deliver 20 amps per pack continuously (40A) and bursts of probably up to 60A which is more than the motor can draw.  Each 18650 cell can deliver 10A so in parallel two cells can deliver 20A and then two packs can deliver 40A.  Note that a 60A burst x 60V is 3.6kW which is more than the 900w motor can draw.  I was only adding one pack of 21700 cells in series to keep weight down so needed 20a capable cells - 20A plus existing 10A for 30A continuous rating with bursts say up to 45A or 45 x 60=2.7kW.  

If you want absolute maximum capacity then use 5000mah 20700 10A batteries in top bay in 2p16s = 576wh plus 3500mah 18650 10A batteries in side bay 2p16s =403wh grand total 979wh.  

Both packs will require their own BMS however you could use one from the original pack which won't have cut out.  Some people will say that mixing 20700 and 18650 packs is not the greatest idea however as they are in parallel with their own BMS then personally I think it is ok.  As others have stated earlier in this thread it is a lot of work and you are dealing with a lot of energy if you get it wrong.  I am not a battery engineer and accept no liability.  As you have stated you will be employing a qualified technician you probably don't really need to understand much more than what cells you want to use and then the technician should be capable of doing the rest for you.

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  • 3 months later...
On 12/23/2019 at 10:14 AM, Traveller said:

.  

Both packs will require their own BMS however you could use one from the original pack which won't have cut out.  Some people will say that mixing 20700 and 18650 packs is not the greatest idea however as they are in parallel with their own BMS then personally I think it is ok.  As others have stated earlier in this thread it is a lot of work and you are dealing with a lot of energy if you get it wrong.  I am not a battery engineer and accept no liability.  As you have stated you will be employing a qualified technician you probably don't really need to understand much more than what cells you want to use and then the technician should be capable of doing the rest for you.

Sorry for the late reply...

Here is my progress, getting batteries has been a big problem due to the wuhan virus and only got them 2 weeks ago. I have cycled them all through an Opus charger.  I think my photos speak 1000 words.

https://pixhost.to/gallery/dnNUX

I sourced both original BMS boards and bout 64 x Sanyo 20700b 4250mha (20A discharge) To begin with the made a pack 4S8P, brick shaped battery. At least it helps demonstrate that the battery fits in the top compartment. After we got things sorted we are building the side battery, 32 cells. It shows that you can't put 20700 batteries in an 84V as you can't put 2 extra batteries.

I want to test performance and pedal stability with one pack then I will install the top one.

But first we the electronics workshop must finish! so slow.

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  • 5 weeks later...

So we finished. The maximjm 20700 batteries we could put in the MCM5 was 48.

https://pixhost.to/gallery/tVNFy

This is the side panel battery pack. We built a 32 cell pack and then it was too tall to be able to close it. So we had to remove 16 cells. I can't figure out a way to put 32 x 20700 batteries there... Some have suggested modifying the side panel of the mcm, use heat to expand it but it would need to be at least 2cm bigger...
 

https://pixhost.to/gallery/AEZBr

This the top battery bank. To begin with I ran with this this 32 cell pack.

If you look at the photos, there is a 4P16S config wiring was wrong as I didn't give my electronics guy  the split PCB BMS, he was going split the side battery PCB and solder it... After we clarefied it made the upper brick and fits well.

With the 32 cell I acelerated fast the motor is able to drop the voltage where the stated battery capacity would drop to 10% and it would beep with low battery. With 48 batteries it is much better.  Both the 900W and 1500W  version of the MCM5  use a the same 60V motor. The power the motor draws makes me believe that is it bigger than 900W.... I have gone up very steep hills and seen it draw 4000W...

1. For those out there with 84V MCM5,  you can't put 20700 batteries in the 84V version, as the top compartment won't take 40 x 20700.... maybe the side panel could take 20 x 20700. Still you would have to mix cell types and it would not be good.

Riding it feels aggressive and fast, like a KS-16S, I have not pushed it above 30km/hr, and I don't see much of a point going faster unless I have a full face helmet... I feel it would be better if the MCM5 would have less powerful motor, it really can draw a lot of juice.

Next is to get shorter L columns to raise the pedals....

 

 

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  • 3 weeks later...

Hi OneLeg,  If you are using the gotway app and gotway BMS to measure the power you should be aware that it tells lies.  I have replaced my original generic bms with a new bluetooth bms so I can measure current from both the original battery and my new battery.  The gotway app overstates the current output massively.  I can't remember exactly the factor but it really isn't drawing anything like 4000w.

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Yes those are the numbers I get regardless of the app I use.... I really is a beast, when you ride it is feels aggressive and like it can way way faster than what I am pushing it. I set max speed at 30KM/hr

BTW is your BMS wired on the discharge wiring too?

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  • 2 months later...

Yes it is not app related.  It is a lie from the mother board.  My BMS is just on the discharge wire of the additional battery that I built.  I have the original 170wh battery in parallel with  the 260wh battery I built.  The Gotway bluetooth app says it is putting out say 50 amps and at the same time the additional battery BMS says it is putting out say 10 amps.  Impossible for the original battery to be putting out 50 amps whilst my additional battery with higher capacity is putting out only 10 amps.  If this was true then the original battery voltage would drop quicker than the larger additional battery which is impossible as they are in parallel.  The current essentially must be proportional to their capacities.  - original battery 170/430 of total amps and additional battery 260/430 of total amps.  Real current at this moment must be more like 18 amps -1200w.

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  • 2 weeks later...

My little experiment is great. I love the breaking power my MCM5 has. I've done 1600km so far on it but recently riding up and down some steep hills some of the batteries have died and have taken the pack out for repair and replace the dead cells.

I've bought a V8 used ( 4000km) and i've come of backwards 3 times in 2 months because it just couldn't deliver the power. So I am buying Sony VTC6 (3000mha,20A) batteries and doing the same to what I've done to the MCM5...

 

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  • 8 months later...

So my MCM now has a 32 x Sanyo 20700B (top compartment) and 32 x Sony VTC6  on the side....

It is a beast, dependatable, can climb, can break fast, accelerates well.... i really have under voltage alarms...

The unicycle really needs 64 cells to drive that motor....

Also I recommend the MCM5 V1 over  V2 as it has more torque, but you still have the low pedal issue...

I would like to see the 84V with 64 x Sony VTC6, is like....

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11 hours ago, OneLeg said:

Also I recommend the MCM5 V1 over  V2 as it has more torque, but you still have the low pedal issue...

My MCM5 "V2" came originally with what look like a V1 MB (white connectors) and it was definitely more powerful than the newer MB with colored connectors I installed since.

Thank you for the input, that's a confirmation of what I was felling. Big deception by the lower torque.

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Just saw this thread & can't help it to say that if I had access to parts & expertise as easily, I'd likely go the 100v route. It would likely be the only 100v MCM5 in the world & for sure, it'll be super fun. I bet it'll out torque (& out climb) any wheel period. It'll be the bestest skatepark wheel evar!

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100V why?

Unless you get yourself a controller that can do 100V.... which you could get from a monster. However then you have to drive the motor which is 60V, so you would have to find 14" 100V or 84V motor...

Then you would have the issue of getting batteries into the body. Right now doing even 2P16S with 20700's is a challenge.... you would not be able to use 20700 on a 24S/48S on the top slow. Also on the side panel there isn't room for 48 cells so you should have to reduce the total number of cells to 24, so overall you would have less cells (a total of 48). I presently have 64 in mine 858Whr and oodles of torque.

 

Edited by OneLeg
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