Thoughts on MSX 100V vs MSP HT

[Dan Hillary]

I have over 2k miles on my MSP (high torque) but have a moderate desire to switch it out for an RS with a high speed c30 motor. Just for the motor's speed characteristics though, I care much less about the LED upgrades and such.

I also just found a mint condition 100V MSX with the smaller 1230wh battery, arriving next week.

I was going to sell the MSX for a profit because I know it's discontinued and in demand, but now I'm wondering if I should just swap its batteries with those of my MSP (giving it the full size 1800wh) and keep the MSX. I'm pretty sure I can do this with no issues since they're both 100v.

I know I'd be giving up the bright, dual headlamps of the MSP, but is there anything else I'd be giving up? The only possible thing I can think of is potential mosfet upgrades that occurred between MSX and MSP, but I'll inspect the main boards side by side to see what that looks like.

Edited March 21, 2021 by Dan Hillary

[Arbolest]

First off, nice find on the 100v MSX! I love Frankenstein-ing (read: upgrading) wheels like this, so your project sounds like fun to figure out properly! 

As to the swapping of parts itself, there are a couple things to keep in mind ...

1) If memory serves, the MSX battery compartments were originally designed for Gotway's then-new 21700-based battery packs, so the MSP batteries MAY fit without issue, however Gotway is also known to put out silent upgrades/changes constantly, so the shell may only fit the original 18650-based packs...  The 18650 packs are just over 1/8" thinner and 1/2" shorter than the 21700 packs, so in the worst case scenario you might need to physically modify the MSX shell to fit the MSP batteries. On the bright side, the batteries usually had 1/4" pieces of foam stuck to the sides as padding, so if you decide not to put those on the MSP packs then you MAY be able to get them to squeeze into the MSX battery compartment if you're lucky (although you still might need to use the MSP side panels to compensate for the added thickness...).

2) The MSX and MSP control boards use the same number and same kind of MOSFETs. The MSX was actually the first wheel that Gotway used those MOSFETs on, so the power-handling and heat-dissipation capabilities should be more or less equal between the MSX and MSP.

3) The MSX and MSP control boards are probably not cross-compatible firmware-wise, so don't try to use the MSP control board in the MSX or vice-versa - the firmware on each board is tuned to its motor, and as you know the motors are not the same.  

4) Also concerning the control boards, the heat sink screw holes might be sliiiiightly off between them, so you may need to drill some new mounting holes... (not sure on this one, it depends on which revisions of the control board you're dealing with)

 

In my opinion, the better option would be to do some extra work and swap both the shells AND the batteries between the MSX and MSP. You could then have your high-speed motor and MSX control board contained within the MSP shell and powered by the larger battery packs you are accustomed to, and you won't have to make any physical modifications to the shell in the process!

 

Anyway, if you decide to go ahead with the Frankenstein-ing and don't have a use for the smaller MSX battery packs let me know! I'm actually trying to get my hands on a few of them for a custom wheel I'm building!

Edited March 21, 2021 by Arbolest

[Planemo]

Theoretically, I don't see a problem with the battery swop. You may have to consider also using the MSP side panels though which I think were wider (?) which I also think may be because the 21700 packs are also wider (?).

I would also be slightly wary of the 4P packs at high speeds. Not saying don't do it, just check voltage drops on the first couple of high speed runs to be sure. Of course we had the MSP HS with the same packs but I am still nervous about 4P 21700's at 40+mph. Maybe thats just me.

Theres no difference in boards that would cause problems with what you are trying to achieve.

Alternatively, you could fit aftermarket packs to the 1230Wh wheel, I have a friend that did this and it works well, extending it to 1860Wh.

[Planemo]

3 minutes ago, Arbolest said:

First off, nice find on the 100v MSX! I love Frankenstein-ing (read: upgrading) wheels like this, so your project sounds like fun to figure out properly! 

You just beat me to my previous reply

3 minutes ago, Arbolest said:

so in the worst case scenario you might need to physically modify the MSX shell to fit the MSP batteries.

I am 99.9% sure that the shells were the same, just the side panels were changed.

[Arbolest]

8 minutes ago, Planemo said:

I would also be slightly wary of the 4P packs at high speeds. Not saying don't do it, just check voltage drops on the first couple of high speed runs to be sure. Of course we had the MSP HS with the same packs but I am still nervous about 4P 21700's at 40+mph. Maybe thats just me.

I don't think there's anything to worry about in terms of using the 4P 21700's at high speed. The 21700s have a roughly 1.5 times higher instantaneous current capability and a lower voltage sag when compared to the 18650 cells, so a 2p 21700 pack should be roughly equivalent to a 3p 18650 pack in terms of available power.

Edited March 21, 2021 by Arbolest
phrasing

[Planemo]

Fair enough, out of interest what particular 21700 cells are you referring to though?

[EMA]

 

26 minutes ago, Arbolest said:

In my opinion, the better option would be to do some extra work and swap both the shells AND the batteries between the MSX and MSP. You could then have your high-speed motor and MSX control board contained within the MSP shell and powered by the larger battery packs you are accustomed to, and you won't have to make any physical modifications to the shell in the process!

agree

21700 batter pack should be a bit wider than 18650, also inner and outer shell from msx are a bit different from msp, not 100% sure if you can swap batteries wo some modifications.

[Arbolest]

2 hours ago, Planemo said:

Fair enough, out of interest what particular 21700 cells are you referring to though?

I was thinking of the LG M50 cells, which I assume are being used in Gotway's 21700 packs (but that IS an assumption, I don't actually know). However, after looking back over the spec sheet for those cells I'm seeing that they really aren't rated for that much more instantaneous current than the LG MH1 (18650) cells that I was comparing them to in my mind. Apparently the biggest thing I was remembering is their lower internal resistance (.04 vs .07) which leads to the much-reduced heat generation and voltage sag at high currents.

So yes, in terms of voltage sag when at high current demands (such as high-speed riding), a 2p 21700 pack is roughly equivalent to or slightly better than a 3p 18650 pack. And with a maximum discharge current of roughly 80 watts per cell for a short time, you're looking at just north of 7,600 watts of output with a 4p pack.

Again, just my opinion, but I don't think there's any need to worry overly much about riding at high speeds with the MSP packs. Have fun with the wheel! 

Edited March 21, 2021 by Arbolest

[Dan Hillary]

Thanks for the input guys; when the MSX arrives I'll open them both up and see about the compatibility. Whatever I decide to do the MSP board with stay with the c38 motor and the MSX board will stay with the c30 motor for sure. I do remember hearing that they widened the MSP side panels, but I had forgotten that it was because of the switch from 18650s to 21700s, so it will be interesting to see if that's an issue or if the side panel holes would line up anyway for trading.

I was reading another topic somewhere that said it's possible to take the 24v headlamp board from the msp and install the brighter headlamps in the MSX, so if I do the trade after all I'll look into that as well.

Edited March 21, 2021 by Dan Hillary

[Planemo]

1 hour ago, Arbolest said:

I was thinking of the LG M50 cells

You've lost me a bit there, I thought M50's were good for just over 7.3A max discharge current each, so at 4P around 29A.

A Sanyo GA is good for 10A, so at 6P it's 60A.

Clearly I'm missing something but to be fair I haven't really looked into the 21700 packs as I've never used them.

[Planemo]

45 minutes ago, Dan Hillary said:

 so it will be interesting to see if that's an issue or if the side panel holes would line up anyway for trading.

The MSP panels absolutely fit the MSX without modification. A friend has done it.

[Arbolest]

44 minutes ago, Planemo said:

You've lost me a bit there, I thought M50's were good for just over 7.3A max discharge current each, so at 4P around 29A.

As to what a given cell is "good for", I find most definitions tend to err on the side of wibbly-wobbly. It depends on a few variables such as (but not limited to) charge level, the length of time for a given discharge, as well as an upper limit on the temperature you're willing to let the cell reach. For instance, the reference material I'm using for my statements on the M50 roughly go along with your figure of 7.3A maximum discharge, but only if you're limiting the cell to a 1.5C discharge rate within a certain temperature range. The material also states that a single cell is perfectly capable of 80W for a burst of 10 seconds which works out to 80W / 4.2v = about 19.05A (which is where I got my 7,600W figure from before)

 

44 minutes ago, Planemo said:

A Sanyo GA is good for 10A, so at 6P it's 60A.

As you pointed out, I used the wrong cell for my example/comparison 18650 pack, which is on me. Apparently Gotway uses the Sanyo NCR GA cell, which is as far as I can tell a much more capable cell in most respects compared to the LG MH1. Again, that's an assumption I can't defend.

 

However, given what the material shows about the M50 cell, I am pretty much certain that a 4P 21700 pack powering one of our wheels will run into voltage constraints (back-emf speed limits) long before it is limited by available current. Otherwise, people riding at 40mph on an MSX's stock 4P 18650 Wh packs would have been running out of power and crashing from the day the wheel was introduced, and that hasn't been happening at all (at least being reported). 

 

For reference, here is the M50 spec info I was looking at:

https://lygte-info.dk/review/batteries2012/LG 21700 M50 5000mAh (Grey) UK.html

Edited March 21, 2021 by Arbolest

[Planemo]

9 minutes ago, Arbolest said:

As to what a given cell is "good for", I find most definitions tend to err on the side of wibbly-wobbly.

Agreed, but I feel theres only a certain amount of wibbly-wobbliness that can be used as an argument though. Theres a lot of wibblyness between (rated) 29A and 60A.

And if we are bringing burst current into it, a GA will hit 18A anyway so is a moot point. Either way, I would certainly rather use 6 cells rated at 10A each rather than 4 cells at 7.3A each to hit the burst figures we are speaking of. YMMV. 

9 minutes ago, Arbolest said:

Otherwise, people riding at 40mph on an MSX's stock 4P 18650 Wh packs would have been running out of power and crashing from the day the wheel was introduced

There were more than a few people who saw big voltage drops with the 4P MSX. The 21700 MSP was even worse. I've not looked for vids of either but I know an experienced 4P MSX rider who has ridden both and the MSP scared the life out of him. And then he overleaned it and crashed. He never wants to ride a 4P 21700 wheel again.

Even at 4P I would rather a tried and trusted GA, which is a solid 10A cell than a 7.3A cell which can allegedly go to 18A.

I think I would need something considerably more substantial to convince me that a 4P 21700 setup is even close to a 6P 18650GA setup, let alone the same.

[Arbolest]

17 minutes ago, Planemo said:

Agreed, but I feel theres only a certain amount of wibbly-wobbliness that can be used as an argument though. Theres a lot of wibblyness between (rated) 29A and 60A.

Agreed. A factor of 2 in terms of rated maximum discharge currents between a 6p 18650 pack and a 4p 21700 pack using the specific cells we've discussed here is pretty big. But like I said before:

1 hour ago, Arbolest said:

However, given what the material shows about the M50 cell, I am pretty much certain that a 4P 21700 pack powering one of our wheels will run into voltage constraints (back-emf speed limits) long before it is limited by available current. 

 

 

25 minutes ago, Planemo said:

 Either way, I would certainly rather use 6 cells rated at 10A each rather than 4 cells at 7.3A each to hit the burst figures we are speaking of. YMMV. 

Totally agree here! I would much rather use the 6p configuration if given the opportunity. Unfortunately, outside of 3rd-party modded battery packs or the one-off shipment obtained by eWheels straight from the Gotway Factory there are no 3P 100v 18650 battery packs available for purchase that I know of. You can either get the 2P 615 Wh 18650 packs, or the 2P 900 Wh 21700 packs.

These are the only two choices @Dan Hillary has. And given the nature of a comparison between two packs with equal numbers of cells like this in a situation a rider might see, you'd better believe that I would suggest the pack with the 21700s over the 18650s. I do so because if they were each forced into a prolonged high-current discharge rate (say 20-Amps or so per cell), the 21700 pack is going to come out of it breathing a lot easier, at a lower (safer) temperature, with more power left in reserve for the next time the rider needs a burst of speed. 

 

45 minutes ago, Planemo said:

There were more than a few people who saw big voltage drops with the 4P MSX. The 21700 MSP was even worse.

That would make sense, as the 4P MSX used the 18650 cells which have a higher internal resistance and voltage drop at high currents. However, I don't know why or how the the 4P MSP would have been worse. The voltage drop at the same high current levels is lower in the 21700 cell than in the 18650 cell, so that doesn't add up on my end... I also say this from personal experience as I never see a significant voltage drop on my MSP HS and I ride it at 40+ mph every day commuting to and from work. That said, just like you stated above, YMMV.

 

39 minutes ago, Planemo said:

I've not looked for vids of either but I know an experienced 4P MSX rider who has ridden both and the MSP scared the life out of him. And then he overleaned it and crashed. He never wants to ride a 4P 21700 wheel again.

I'm unsure of who this experienced 4P MSX rider is, but just to clarify -- when I say MSP in this thread, I am specifically talking about the MSP High-Speed, not the torque version, because that is the version the OP is interested in potentially making. As far as I am aware the MSP HS has a couple more MPH to its name than the 100v MSX did, so I honestly have no idea why riding an MSP would scare the life out of your experienced rider unless they were on a torque-version, which has a much lower top speed. If anything, an MSP HS should have been even more stable and assuring as it approached the MSX's top speed.

 

 

Now, @Planemo, before our exchange gets overly long and/or we completely hijack this thread, I just want to reiterate my position here. All I am saying is that I don't think the OP needs to worry about riding a High-Speed MSP equivalent with a pair of 2P battery packs comprised of 21700 cells. I think they provide ample power for the wheel, and moreover will prove to be a worthy and safe upgrade from the smaller 18650-based packs that are coming in the MSX he bought.

Other than that, I've found our exchange to be rather stimulating and enjoyable. I've taken away a good amount of information from it. You pointed out some misconceptions that I had and I am grateful for the opportunity to learn from it. 

Cheers, and I hope we can split some hairs again soon!