Advice on MXUS Turbo build

[serious_sam]

Yeah im happy with it, the 1500w leaf would be a way better choice motor wise but im gonna use this one until it melts :lol:

Nice!

Correct me if I'm wrong, but what I understand you to be saying is basically the battery is too small, and the motor and controller are overkill.

Basically I just need to run a bigger battery. And figure out how to carry it.

 

[Tolkano]

Yeah im happy with it, the 1500w leaf would be a way better choice motor wise but im gonna use this one until it melts :lol:

Nice!

Correct me if I'm wrong, but what I understand you to be saying is basically the battery is too small, and the motor and controller are overkill.

Basically I just need to run a bigger battery. And figure out how to carry it.

Yeah or you can downsize the motor and controller to match the battery, which is personally what i would do

 

[serious_sam]

Yeah or you can downsize the motor and controller to match the battery, which is personally what i would do

Ok, that's something to think about.

I guess the major advantage to the stealth bomber type bikes is packaging of a big battery pack.

 

[MadRhino]

Many ebike frames are made with the space to fit a lot of round cells and a BMS, but round cells are not a good solution for high power and most end up using RC lipo after some time. Abusing round cells is calling for failure, or dramatic chain reaction fire.

The low C rate of round cells is making them good only for low power, unless you have the space to fit a huge battery. Feeding 200A with round cells does require a lot of connections in the battery assembly, while 4 bricks of high C rate RC lipo with 6 connections are good to feed twice as much. AND, high C rate prismatic cells can be charged in 6 minutes, with much better tolerance to abuse than any round cells.

Think of it like it is explosive substance: in a bag, it is not going to explode but load it in a solid container and you have a potential explosion. Then you will have to significantly limit their use, because it has no room for any abuse, litterally.

People used to be told that round cells are safer, but that was when they were made with safer chemistry. Now that so many round cells are lico chemistry, this is not true anymore. It is quite the opposite, and that is why we have seen so many explosive fires in all sort of toys lately. At the same time, the quality of prismatic cells have improved a lot. It is common now to have some RC lipo survive being charged 4.55v, or discharged 100 C for many seconds without any damage. Try this with round cells, and you’d better dress in a fireman’s suit.

 

[wturber]

I guess the major advantage to the stealth bomber type bikes is packaging of a big battery pack.

That and I think some people just think they look cool. As a moderately old fart, that certainly isn't me. But whatever spins yer spurs. I still find it funny that they call them "stealth bombers." They are neither stealthy nor do they bomb anything. Weird.

 

[wturber]

People used to be told that round cells are safer, but that was when they were made with safer chemistry. Now that so many round cells are lico chemistry, this is not true anymore. It is quite the opposite, and that is why we have seen so many explosive fires in all sort of toys lately. At the same time, the quality of prismatic cells have improved a lot. It is common now to have some RC lipo survive being charged 4.55v, or discharged 100 C for many seconds without any damage. Try this with round cells, and you’d better dress in a fireman’s suit.

These look like something worth considering if you want to draw a lot of amps and not spend a ton of money.

https://www.ebay.com/itm/20-SPIM08HP-3-7V-8AH-LITHIUM-POLYMER-BATTERIES-25C-200A-SUPER-CELLS-24V-36V-48V/173305036284?hash=item2859c8fdfc:g:QXIAAOSw8~5a72gx

 

[amberwolf]

best guess: "stealth fighter" because it's all angular and ugly like the nighthawk f117; "stealth bomber" because it's the bigger version?

 

[wturber]

best guess: "stealth fighter" because it's all angular and ugly like the nighthawk f117; "stealth bomber" because it's the bigger version?

Yeah - probably. Still funny to me though.

 

[MadRhino]

People used to be told that round cells are safer, but that was when they were made with safer chemistry. Now that so many round cells are lico chemistry, this is not true anymore. It is quite the opposite, and that is why we have seen so many explosive fires in all sort of toys lately. At the same time, the quality of prismatic cells have improved a lot. It is common now to have some RC lipo survive being charged 4.55v, or discharged 100 C for many seconds without any damage. Try this with round cells, and you’d better dress in a fireman’s suit.

These look like something worth considering if you want to draw a lot of amps and not spend a ton of money.

https://www.ebay.com/itm/20-SPIM08HP-3-7V-8AH-LITHIUM-POLYMER-BATTERIES-25C-200A-SUPER-CELLS-24V-36V-48V/173305036284?hash=item2859c8fdfc:g:QXIAAOSw8~5a72gx

Wow!
That is making a very cheap battery.
I will buy some for sure.


I just bought those for 143$ each 6s 6 A/h brick

 

[serious_sam]

These look like something worth considering if you want to draw a lot of amps and not spend a ton of money.

https://www.ebay.com/itm/20-SPIM08HP-3-7V-8AH-LITHIUM-POLYMER-BATTERIES-25C-200A-SUPER-CELLS-24V-36V-48V/173305036284?hash=item2859c8fdfc:g:QXIAAOSw8~5a72gx

That's $600AUD shipped to my door for 2x sets, which would give me effectively the same capacity as I had planned with the Sony VTC6 cells, at the same price, but probably 3x the discharge power. Wow

 

[wturber]

These look like something worth considering if you want to draw a lot of amps and not spend a ton of money.

https://www.ebay.com/itm/20-SPIM08HP-3-7V-8AH-LITHIUM-POLYMER-BATTERIES-25C-200A-SUPER-CELLS-24V-36V-48V/173305036284?hash=item2859c8fdfc:g:QXIAAOSw8~5a72gx

Wow!
That is making a very cheap battery.
I will buy some for sure.


I just bought those for 143$ each 6s 6 A/h brick

I've purchased all of my "hoverboard" battery packs from that guy and I think he's a trustworthy source. He dealt with me fairly when one of the ten packs was faulty. I've been seriously considering buying those high amp "super cells" - especially since assembling a pack from them should be pretty straightforward. But they just don't quite fit my cases. So I recently purchased more hoverboard packs to get the storage I want for some long distance riding.

 

[999zip999]

I use a powervelocity 18 fit Bluetooth controller. 80v at 80amps. He's also coming out with bms. I would like to try those cells @ 2p or 3p. I wish they were 20ah. And can be bolted together.

 

[serious_sam]

These look like something worth considering if you want to draw a lot of amps and not spend a ton of money.

https://www.ebay.com/itm/20-SPIM08HP-3-7V-8AH-LITHIUM-POLYMER-BATTERIES-25C-200A-SUPER-CELLS-24V-36V-48V/173305036284?hash=item2859c8fdfc:g:QXIAAOSw8~5a72gx

Just as another reference for people who may be looking at these SPIM08HP 8Ah LiPo cells.

It's possible that the internal resistance is rather high, so there might be a significant drop in voltage when pulling high currents. I found this youtube video where some testing has been done on this type of cell, and the guy quotes 29.9mOhm.

https://youtu.be/9nmDj0Ykn-c?t=150

In my understanding, this is significantly higher than regular RC LiPo, so that's something to consider before buying.

 

[MadRhino]

29.9 mOhm seem too high for any lico prismatic cell. It would be rated 2C continuous with such resistance.

Mine that are rated 25C are ten times lower resistance than that. My 75C are 1.2 mOhm.

 

[amberwolf]

Yeah, I have a 14s 40Ah EIG NMC pack that's entire series resistance is only about 34milliohm, per the CA3's estimate. I wouldn't want the voltage sag of a pack with that kind of resistance *per cell*. :/

 

[serious_sam]

Sure. Like I say, I'm not stating it as fact. It's a youtube video. Can't say how correct or not the methods are.

I just found another video where the guy tests one of those cells and gets totally different results. First he gets 37mOhm, then he changes how the battery is clipped, and gets much lower results (5mOhm then 3mOhm on the same cell).

https://youtu.be/49qel7tlcdc?t=266

 

[MadRhino]

Yep. 3mOhm is what to expect for such a cell rated 25C
Its resistance will change with temperature, so it does need to be measured at various temp to have a realistic figure.

 

[amberwolf]

First he gets 37mOhm, then he changes how the battery is clipped, and gets much lower results (5mOhm then 3mOhm on the same cell).

That makes perfect sense--cotnact resistance can be very high in test setups, and can be much higher than cell resistance. Somewhere around here is a discussion where Liveforphysics and others discuss various methods of testing using low resistance and/or methods that compensate for high resistance.

 

[ridethelightning]

24" is good for light off road, but the best off road bike i rode was running 19" moto rims with shinko sr241s. its like the sledgehammer approach, you can just plow over everything
but you need serious power reserves.

look up es member tumich, he sells sony vtc5a at a very good price and cheap shipping for the patient.
i just got 400 to make a pack, they will do 35Apeak/cell.

extending the wheelbase a fraction would be a good move id say.
i built just such a bike once, for a friend. dh idrive, it had 20s10p25r, cro motor +18"moto, 26mtb front,max-e, zochi 888,
the pack and the cromotor got destroyed in flood. im now rebuilding it slowly, as a barebones off roader.
cause the wheel base was short, especially when climbing logs etc at low speed, it really liked to flip.