Jump to content
OneLeg

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

Recommended Posts

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?

Share this post


Link to post
Share on other sites

Do I see problems with your plan? Too many to count.

Replacing cells or building a battery pack from scratch is a lot of work, and has countless danger scenarios and fire hazards, since you are working with live high discharge li-ion cells. Are you 200% sure your skills and experience warrant for doing something like this? If you were familiar with the dangers I’d think you’d have mentioned something about your experience level. You did not, so I can only assume.

Are your soldering and spot welding skills at a level that you’d trust your life in them even after the wheel has been shaking and tumbling for a few thousand miles?

”If I replace them all”... If you replace one cell to a different type, you replace all of them.

I can’t comment wether the cells you mention would be even suitable for an EUC. Besides discharge rates at least the internal resistance is a crucial factor.

DIY battery packs are not cost conscious if you put even a slightest value for the countless hours it’ll take to make them.

Share this post


Link to post
Share on other sites

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.

 

Share this post


Link to post
Share on other sites
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.

Share this post


Link to post
Share on other sites
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.

Spoiler

Chinese.png.0315ca12248fa54a70ceb8eed8b0893f.png

English.png.b61274630fd60bfa7c9a9cb0fd6acdb0.png

Above for English reader

Source link

 

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.

Spoiler

18650.thumb.png.c2ae9a41beaa4ca1a7a849c50b24c571.png

1406819416_18650Eng.thumb.png.812cdc1524def71c64de64b0f23d1949.png

 

Source link

21700.thumb.png.bbbf0d5d854c1ae4b359f790d5c58c76.png

264737752_21700Eng.thumb.png.6d1fa4ed760c0231ba5057adaa2a85a1.png

Source link

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

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites

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.

  Reveal hidden contents

Chinese.png.0315ca12248fa54a70ceb8eed8b0893f.png

English.png.b61274630fd60bfa7c9a9cb0fd6acdb0.png

Above for English reader

Source link

 

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

 

Source link

21700.thumb.png.bbbf0d5d854c1ae4b359f790d5c58c76.png

264737752_21700Eng.thumb.png.6d1fa4ed760c0231ba5057adaa2a85a1.png

Source link

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. 

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites
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

Share this post


Link to post
Share on other sites

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...

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites

I don't know what you are wanting to do with the mosfets? There is no need to touch the motherboard.

Share this post


Link to post
Share on other sites
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.

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


×
×
  • Create New...