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

[power pan]

hello Onleg， mcm5 light could ride up to 35km right?

 

[OneLeg]

10 hours ago, power pan said:

hello Onleg， mcm5 light could ride up to 35km right?

 

yes that is correct.

For those fat tire obsessed people, they might like a installing a chao yang 2.15, which are very elastic and bouncy, so I feel the tire is probably 2.5" wide, it increases friction. I will be honest I did ride lik 56km on day and I was not tired... normally with 30km-40km I would feel tired.

Whilst on a GT16 or probably a 16" chao yang tires are good, I am not sure on the MCM one should move away from the 14" x 2.15 CST tire...

[power pan]

thanks for responding. so, I just wanna confirm why you use 20700 instead of 21700 ? and 3p 16s for the battery configuration ? and could we just use 20s battery instead ? or different motor driver board ? honestly, as an engineer, to design many versions of board is not very good for mess production.

[power pan]

On 5/16/2022 at 11:56 PM, OneLeg said:

yes that is correct.

For those fat tire obsessed people, they might like a installing a chao yang 2.15, which are very elastic and bouncy, so I feel the tire is probably 2.5" wide, it increases friction. I will be honest I did ride lik 56km on day and I was not tired... normally with 30km-40km I would feel tired.

Whilst on a GT16 or probably a 16" chao yang tires are good, I am not sure on the MCM one should move away from the 14" x 2.15 CST tire...

by carefully calculation, I figure out that MCM5 could stuff 64 21700 batteries.... then it could store up to 1184Wh insane battery pack.

[OneLeg]

On 5/17/2022 at 3:36 PM, power pan said:

thanks for responding. so, I just wanna confirm why you use 20700 instead of 21700 ? and 3p 16s for the battery configuration ? and could we just use 20s battery instead ? or different motor driver board ? honestly, as an engineer, to design many versions of board is not very good for mess production.

 

Why NCR20700B? Because it is a 20A battery that will take abuse, and performs amazingly. I am very satisfied, even I have not balanced the pack for a long time.... I have rashed it to the points that I've melted the nickel strips on the pack twice yet none of the cells are damaged of have high internal resistance.

I am quite honestly thinking of upgrading my GT16 to 20700B's once I deall with the vibration issue.

My config is:

16S2P on NCR20700B on the top compartment.... You probably could fit 21700's in there,   Maybe you could use the 21700 VTC6A....

16S2P on VTC6 18650, the reason is that the side compartment has very little room. we had to to some funny arrangement. The trolle handle blocks you from spreading sideways, and also and the cover limits how much you can project outward too....

I am not sure I would recommend buying the gotway BMS (I can look up the part if you want and can post photos...)... I find the Kingsong 16S BMS is way better.

 

 

[power pan]

23 hours ago, OneLeg said:

 

Why NCR20700B? Because it is a 20A battery that will take abuse, and performs amazingly. I am very satisfied, even I have not balanced the pack for a long time.... I have rashed it to the points that I've melted the nickel strips on the pack twice yet none of the cells are damaged of have high internal resistance.

I am quite honestly thinking of upgrading my GT16 to 20700B's once I deall with the vibration issue.

My config is:

16S2P on NCR20700B on the top compartment.... You probably could fit 21700's in there,   Maybe you could use the 21700 VTC6A....

16S2P on VTC6 18650, the reason is that the side compartment has very little room. we had to to some funny arrangement. The trolle handle blocks you from spreading sideways, and also and the cover limits how much you can project outward too....

I am not sure I would recommend buying the gotway BMS (I can look up the part if you want and can post photos...)... I find the Kingsong 16S BMS is way better.

 

 

I'm expert in electronic.. no need their BMS.. 21700 could provide 5000mAh, and the BMS could just use 50A, then enough. 1800W only 30A @ 60V.

[OneLeg]

On 5/21/2022 at 2:31 PM, power pan said:

I'm expert in electronic.. no need their BMS.. 21700 could provide 5000mAh, and the BMS could just use 50A, then enough. 1800W only 30A @ 60V.

Depending on the total number of cells. for 5000mah you would use 10A cells. I would only use 10A cells of on 80 or more cell configs. Even 48 cells with 20A is marginal if you weight around 85kg... On 64 cells with 20A, you can depend on the wheel responding to emergency breaking at high speed after sustained thrashing...

I've yet not had a wheel where I could put enough 21700 to be able to run 5000mha/10A....

BTW, I've bought this BMS :

https://www.aliexpress.com/item/1005003104573871.html?  (the 17S version as it small)

14S, for Powerwall to charge at 48V,  test on demand balancing.

16S for Ninebot S2,  set the max charge to 4V per cell. It normally is a 15S unicycle. I hope I can jam it in.

 

I have some vibration issues to solve on my GT16, the wheel gives me a low voltage warning when I break hard, so I am thinking of rebuilding it with NCR20700B.... It does qualify for those 21700.... The batteries are pretty tight around the L-Column. I placed 10 to ensure that the diamter/lenght of the pack is ok. Eight wise I think putting 2 layers is no issue.... It does seem like I will have to go for the original BMS though... There is no room to put a smart BMS in.

Edited May 23, 2022 by OneLeg

[power pan]

2 hours ago, OneLeg said:

Depending on the total number of cells. for 5000mah you would use 10A cells. I would only use 10A cells of on 80 or more cell configs. Even 48 cells with 20A is marginal if you weight around 85kg... On 64 cells with 20A, you can depend on the wheel responding to emergency breaking at high speed after sustained thrashing...

I've yet not had a wheel where I could put enough 21700 to be able to run 5000mha/10A....

BTW, I've bought this BMS :

https://www.aliexpress.com/item/1005003104573871.html?  (the 17S version as it small)

14S, for Powerwall to charge at 48V,  test on demand balancing.

16S for Ninebot S2,  set the max charge to 4V per cell. It normally is a 15S unicycle. I hope I can jam it in.

 

I have some vibration issues to solve on my GT16, the wheel gives me a low voltage warning when I break hard, so I am thinking of rebuilding it with NCR20700B.... It does qualify for those 21700.... The batteries are pretty tight around the L-Column. I placed 10 to ensure that the diamter/lenght of the pack is ok. Eight wise I think putting 2 layers is no issue.... It does seem like I will have to go for the original BMS though... There is no room to put a smart BMS in.

I've put 5 parallel 21700 8-9-8-9-8 on top container of mcm5 but need some work for the housing. stupid design for mcm5 that's not water proof at all. water could go directly into the control broad along the gap from the pull rods... not like ninebot ( i got 2 A1 and somebody upgraded to 2p15s 21700 without the case of the batteries and even get lighter and up to 60km range)

BTW, you could use 16s in A1/S2 ? nothing went wrong ?

 

[OneLeg]

yeah the mcm is like sieve... I normally carry a plastic bag to wrap it in as soon as it starts raining....

yeah the body the case, could allow for a lot more batteries, the design sucks.... I don't understand your 8-9-8-9-8....

I am starting soon on the ninebot...

My idea of the 16S is to avoid having to charge to 100% so you just charge to 90% when you use the default 63V charger. How is the pedal stability with 21700's. What BMS did you use? what firmware did you use to disable the BMS.

you have photos? so far I am think I have to smash the internal body up to house the batteries and BMS.

[alcatraz]

Fun thread. It's great to learn battery diy on smaller/cheaper wheels.

I just want to warn you that if the wheel doesn't charge reliably you can't really sell/give it away to someone that doesn't know how to do it. 

Also, while you have eliminated some voltage sag, you haven't added any extra power. Take care thinking you're riding a "tweaked" mcm and try to push it. You still have the small motor and control board. Injury could follow the overconfidence. No wheel should be run without a healthy margin to its pickup free speed. You'll notice that that speed is still the same as before.

The V8 I think is dangerous in its stock configuration because the pickup speed is merely 44km/h and you are allowed to set the max at 30km/h. Totally inadequate safety. 

[mrelwood]

 

2 hours ago, alcatraz said:

Also, while you have eliminated some voltage sag, you haven't added any extra power.

I think you kind of have. When the voltage sags, the output power is decreased. Without sag, it is not decreased. So the wheel behaves like it would with a much higher state of charge on the standard battery. Even with a full battery.

 

2 hours ago, alcatraz said:

The V8 I think is dangerous in its stock configuration because the pickup speed is merely 44km/h and you are allowed to set the max at 30km/h. Totally inadequate safety. 

30/44 = 68%. Seems reasonable to me. The V11 is practically the same, in “fancy mode” (55km/h).

[alcatraz]

5 hours ago, mrelwood said:

 

I think you kind of have. When the voltage sags, the output power is decreased. Without sag, it is not decreased. So the wheel behaves like it would with a much higher state of charge on the standard battery. Even with a full battery.

 

30/44 = 68%. Seems reasonable to me. The V11 is practically the same, in “fancy mode” (55km/h).

It's not a huge difference. Your brain will think you've got more than you actually have.

The V8 cuts out already at ~33 km/h on a flat road without headwind (light rider). 

Never get comfy riding with small margins. 

[alcatraz]

My mind gets comfortable quick and starts to relax. Never relax with a small margin. 

What you should aspire for is repeatability. Can you hold this speed/power output in all temperatures, moods, weights, tire pressures etc, year after year?

We tell ourselves yes, and then there's that moment when you hit an average pothole at speed, focused on something else, at a bit too low charge level or temperature. Or some combination of other circumstances. 

That's not a good safety margin then is it?

Edited May 24, 2022 by alcatraz

[power pan]

On 5/24/2022 at 10:33 AM, alcatraz said:

Fun thread. It's great to learn battery diy on smaller/cheaper wheels.

I just want to warn you that if the wheel doesn't charge reliably you can't really sell/give it away to someone that doesn't know how to do it. 

Also, while you have eliminated some voltage sag, you haven't added any extra power. Take care thinking you're riding a "tweaked" mcm and try to push it. You still have the small motor and control board. Injury could follow the overconfidence. No wheel should be run without a healthy margin to its pickup free speed. You'll notice that that speed is still the same as before.

The V8 I think is dangerous in its stock configuration because the pickup speed is merely 44km/h and you are allowed to set the max at 30km/h. Totally inadequate safety. 

 

run safe and keep away from the red line is the key. and all the EUS design is kinda very new... for cost saving...

say if we could use GaN as the power stage, and the control board could be very small, like a business card and with little heat sink.

cost saving is a devil...

[power pan]

On 5/23/2022 at 8:32 PM, OneLeg said:

yeah the mcm is like sieve... I normally carry a plastic bag to wrap it in as soon as it starts raining....

yeah the body the case, could allow for a lot more batteries, the design sucks.... I don't understand your 8-9-8-9-8....

I am starting soon on the ninebot...

My idea of the 16S is to avoid having to charge to 100% so you just charge to 90% when you use the default 63V charger. How is the pedal stability with 21700's. What BMS did you use? what firmware did you use to disable the BMS.

you have photos? so far I am think I have to smash the internal body up to house the batteries and BMS.

could you go to ninebot forum using their APP ? 用户名：数字潘 

I had already posted the photo there.

 

[mrelwood]

On 5/24/2022 at 1:54 PM, alcatraz said:

It's not a huge difference.

No, it’s not huge. It seems normal. That was my point.

On 5/24/2022 at 1:54 PM, alcatraz said:

The V8 cuts out already at ~33 km/h on a flat road without headwind (light rider).

What do you mean by “cutting out”? the top speed of the V8 is 30km/h, enforced with a tilt-back. If someone tries to push beyond the tilt-back, that’s a whole new ballgame, and an irrelevant source of data for any wheel’s safety statistics.

[alcatraz]

3 hours ago, mrelwood said:

No, it’s not huge. It seems normal. That was my point.

What do you mean by “cutting out”? the top speed of the V8 is 30km/h, enforced with a tilt-back. If someone tries to push beyond the tilt-back, that’s a whole new ballgame, and an irrelevant source of data for any wheel’s safety statistics.

 

I cut out at 33km/h on the V8 with a low voltage sag battery. I was stupid back then. Now, I would -never- expect even 1% more speed/power from such an upgrade. Less sag feels better but it gives you no extra speed/power. Which is what my initial point was.

The point is that you don't aim for the edge of the precipice because a wind gust could be the difference of standing or falling. Thinking you got more when you don't is dangerous. Thinking a low lag battery gives you more when it maybe doesn't could result in a high speed crash. Better not push that idea. 

The battery is only one out of a three part system. Upgrading one will not automatically raise the weakest link in the chain.

Amyway. The OP gets my point.

[OneLeg]

On 5/25/2022 at 12:01 PM, power pan said:

could you go to ninebot forum using their APP ? 用户名：数字潘 

I had already posted the photo there.

 

Can you tell me how it feels with the 21700's?

 

 

On 5/24/2022 at 10:33 AM, alcatraz said:

Fun thread. It's great to learn battery diy on smaller/cheaper wheels.

I just want to warn you that if the wheel doesn't charge reliably you can't really sell/give it away to someone that doesn't know how to do it. 

Also, while you have eliminated some voltage sag, you haven't added any extra power. Take care thinking you're riding a "tweaked" mcm and try to push it. You still have the small motor and control board. Injury could follow the overconfidence. No wheel should be run without a healthy margin to its pickup free speed. You'll notice that that speed is still the same as before.

The V8 I think is dangerous in its stock configuration because the pickup speed is merely 44km/h and you are allowed to set the max at 30km/h. Totally inadequate safety. 

 

yeah, my MCM could have been a disaster. The first welding strips were not strong enough, so I did melt them down twice.  But as I have two packs I the unicycle fell forward and then regained balance. it has been rock solid. It is pretty comfortable to even 40-50km rides, with chao yang tires, I don't feel battered.. But in terms of safety I am yet to crashed, out overleaning, or breaking in emergencies (I ride on HK's pavements), and sometimes I have emergency stops (not to hit pedestrians), and I will typically max out at 29km.  I did get at times, some warnings on low voltage...  Yes one bad thing that did happen is that the Gotway 16S BMS PCB's did fail in one of the packs, the wheel ran fine with one pack....

Recently I watched mrelwood's youtube video on charging to 80% vs balancing etc.... and realized that I had not charge the unicycle full for a long time. This time I charge it with another charger that is in my home and ever use. Much to my surprise that unicycle has vastly improved, it seems that my normal charger (charger to 67.2V) has only been outputting 66.0V...    My other charger that actually did balance is also only outputting 66.5 or something, enough to trigger the balancing.

Another thing I find after balancing, that even at low voltages it is not giving any low voltage alarms, also it is feels very beefy at 3x% capacity.... So I am now feeling a lot more comfortable without charging it when it it s below 50%.. I am charging less.... frequently.

As the cells age and resist being charged at 4.2V and possibly drop below 4.09V, I think I want to just charge to 66V and balance manually with an active balancer to maximize the life of the cells. Right now I don't have balancing 16S leads, soldered in, but will add....

 

I agree the stock V8 is dangerous, I find it that if you break hard and you weigh 85kg+ you can fall on your ass, and the wheel will carry on. This happened to my friend and twice the wheel hit a person and he had to compensate them financially. When you ride on the V8, you need to consider its innability for do any serious emergency breaking.... allow yourself space to power break etc... or don't go fast.

Edited May 28, 2022 by OneLeg

[power pan]

for 21700 3p16s, I got at lease 750WH cap. and when I tested the range for up to 45km still the blue-tooth BMS told me 55% left.

mcm5 had weird pedal feeling, it varied from time to time... not knowing the logic. I could say that's a bad design.

[OneLeg]

How did you pack so many batteries in a ninebot....?

Did you also do the 16S config, originally it is a 15S wheel.

What I've been trying to ask you is how firm are the pedals ? any improvement?

Yeah MCM pedals are very V shaped, when I switch to other wheels the pedals feel like the sloping. The pedals can dip a bit if you are in soft mode, you must not wear any heels on this wheel...

[power pan]

On 5/31/2022 at 3:10 PM, OneLeg said:

How did you pack so many batteries in a ninebot....?

Did you also do the 16S config, originally it is a 15S wheel.

What I've been trying to ask you is how firm are the pedals ? any improvement?

Yeah MCM pedals are very V shaped, when I switch to other wheels the pedals feel like the sloping. The pedals can dip a bit if you are in soft mode, you must not wear any heels on this wheel...

I bought 2 3rd party battery BMS and the battery configuration is just as same as original 15s. without the battery case, it could fit into the original place. when I finished, will post pictures in the ninebot forum. but no way to post here or tell me some place for free picture uploading ?

[Tawpie]

6 hours ago, power pan said:

way to post here or tell me some place for free picture uploading

I use postimages.org, no need to create an account if you don't want to

 

[OneLeg]

8 hours ago, power pan said:

I bought 2 3rd party battery BMS and the battery configuration is just as same as original 15s. without the battery case, it could fit into the original place. when I finished, will post pictures in the ninebot forum. but no way to post here or tell me some place for free picture uploading ?

I have created a new thread on the ninebot forum where you can post the photos.

if you look in the box you reply in on the bottom left there is a drag photos or attach files link.

 

I actually think that we should be asking manufacturers to build battery packs using intellingent BMS where we can get per cell voltage and also be able to trigger balancing at any voltage. I think we should tell vendors to shove their suspension and BS and tell them we are going to boycott all new wheel launches which dont' have a BMS that is going to allow us to extend the life of the pack / wheel.

 

Edited June 4, 2022 by OneLeg

[alcatraz]

An intelligent bms is only 50usd retail in China. Wholesale price?

Imagine that it's too expensive for the manufacturers.

It's got bluetooth and it's configurable to balance at any voltage, monitors internal resistance and voltages of all groups. There are two thermal probes. You can connect a separate display to it where it shows you the details while riding.

Edited June 4, 2022 by alcatraz

[OneLeg]

On 6/5/2022 at 6:31 AM, alcatraz said:

An intelligent bms is only 50usd retail in China. Wholesale price?

Imagine that it's too expensive for the manufacturers.

It's got bluetooth and it's configurable to balance at any voltage, monitors internal resistance and voltages of all groups. There are two thermal probes. You can connect a separate display to it where it shows you the details while riding.

Why spend US$50 when later they can sell you the V8 battery pack for around US$250 (in Hong Kong)..... Also why let you switch batteries between the V5, V5F, V8, V8F, V8S.... ? Imagine what a V5F with a 730Whr capacity would do in the market!

Which BMS you you referring to BTW....