High Power yet light option?

[DaveThomasPilot]

I frequently take my 16s with me in my airplane.  It's doable (much better than the foldable bike I used to lug) but smaller and lighter weight option would be better.  This summer, we were just too loaded to take the EUC with us, so it had to stay home.

I don't do long rides.  So, lots of battery capacity just means more weight.   The 800 wH battery in my 14C is about 3x what I need, range wise.

But, I do want a high power motor for safety and hill climbing capability.  Cost isn't much of a factor.  Reliability is most important.

Any suggestions?

Thanks!

 

[dmethvin]

The power is in the battery, and the battery is heavy. A high power motor is only useful if it can get that power from the battery. You could change the 16s4p configuration in the 14C battery pack to 16s2p and add some filler to take up the remaining space, but it would reduce the margin of safety at lower battery levels. Still, it could be an option if you ride gently. I have no idea whether the battery reduction surgery is possible but ewheels does sell a replacement pack if things go wrong: https://www.ewheels.com/product/king-song-840wh-battery-pack/

[DaveThomasPilot]

Quote

"The power is in the battery, and the battery is heavy."

Well, only to the extent the battery limits maximum available current (versus wiring, connectors, motor windings, and thermal constraints). 

A higher voltage battery (at same internal resistance)would likely have less impact on maximum available instantaneous power (required battery current is inversely proportional to battery voltage).  But, the additional series cells would add to the battery internal resistance, so maybe the large capacity is the only way to get there.

Do you know for sure that the battery what limits maximum power in the lower weight wheels?

Thanks,

Dave Thomas

 

[niwrad]

on paper the Mten3 is the lightest EUC.

Also remember cutting the battery in half also reduces its peak power output by half as well

[DaveThomasPilot]

Yeah, I was thinking Mten3.  Maybe I'll try buying a used one.

Yes, reducing the parallel cells by a factor of 2 will reduce its peak output power by about the same.  But, probably the motor itself is the limiting item, not the battery.  

It would take a heck of a lot of internal battery resistance to limit power.

[niwrad]

Just now, DaveThomasPilot said:

Yeah, I was thinking Mten3.  Maybe I'll try buying a used one.

Yes, reducing the parallel cells by a factor of 2 will reduce its peak output power by about the same.  But, probably the motor itself is the limiting item, not the battery.  

It would take a heck of a lot of internal battery resistance to limit power.

it's not internal resistance that limits battery output, it's how much heat they can handle. Cutting it in half but asking for same amount of power means double the heating of the battery, at the very least since internal resistance heating increases at the square of the current according to Ohm's law. For typical 18650 cells, each series set can handle up to 10 Amps before they are at risk of a runway thermal reaction. The motor actually doesn't really have that many limits and can easily be run at much higher power. I double the power into a motor and it just simply got hot but otherwise worked fine 

[DaveThomasPilot]

So, does the Mten3 have a problem with overheating?

The thermal mass of the batteries must be huge.  So, it would take tens of seconds (if not minutes) for them to get hot enough to be an issue.

I should have clarified--I want the extra power for safety margin of overleaning, pot holes, etc.  I have no desire to ride u a long steep hill like Marty :-)

[niwrad]

I dont have any EUC, but I DIY an electric bike kit, so I know generally how electric motors and batteries work now.

It's difficult to gauge the battery temp since they are often sealed, but it's not like an overheated motor where it'll simply get hot, but could literally catch on fire and explode. Definitely want to be extra careful if you plan on using half a battery pack but asking the same amount of power. 

Also this will cause the batteries to degrade more quickly in either case

[DaveThomasPilot]

I have no plans to cut the battery pack in half.  I plan on selling the 14c to get something not only lighter but hopefully smaller.

Back to the Mten3--does it have a problem overheating?

 

[neurokinetik]

1 hour ago, niwrad said:

on paper the Mten3 is the lightest EUC.

Also remember cutting the battery in half also reduces its peak power output by half as well

Lightest EUC is the IPS i5. Not all that powerful, though.

Edited September 28, 2019 by neurokinetik

[comp_2]

I have the MTen3 and also the Kingsong KS16S.  The MTen3 is easy to handle because it is so light.  Easier, I would argue, than the Kingsong.  But it can be a less stable than the Kingsong and lacks the shutoff when you pick it up, so it needs to be powered down when picked up.  For easy of use and 'portage', the MTen3 is great.  Pity you can't borrow one to see if you like it.  Or if money isn't that big a deal, buy it and when you have the room, use the Kingsong.  Otherwise, take the MTen3.  And if you really don't like it, it could always be sold to recoup some of the money. 

[DaveThomasPilot]

That sounds like a good plan, comp_2.

I'm in no hurry.  I figure some MTen3 will get the "need for speed" and want to sell it for one of the new, fast, big wheels.  

If not, I'll put in an order at EWheels.

[comp_2]

The MTen3 is not slow or under powered, but I would not want to go really fast on it.

[alcatraz]

I'd maybe use a 14 inch wheel in your case with a high voltage like 84V ~ 2000w peak power. Ensure your battery cells are rated for high discharge. High capacity sometimes means slow discharge.

Power means weight. Heavier motor and heavier battery.

14inch wheels have less speed but they can go up the climbs just as easily as the bigger wheels. 

By ensuring your cells are high current cells and using a 14inch high power wheel I think you can maximize the power/weight ratio at the expense of range.

[alcatraz]

A V8 is only 13.x kg and 16inch. It can peak 2000w. It's certainly no power monster, and has a few watts less than a 16S but it's supet weighy efficient.

I recently made a custom battery and the wheel really livens up significantly. The original battery is strained because the cells are operating at their peak discharge rates. It influences the quickness of the power. By choosing the best cells you can have a very reactive V8 16 inch 2000w wheel at 13.x kg.

[DaveThomasPilot]

Good point on choosing different cells for the battery, Alcatraz.

Power tool batteries are optimized for maximum current rather than capacity.  I have a project where I used a power dock for DeWalt 20v batteries.  But, I made my own batteries using different cells, since I had no need for the high current capacity but energy capacity was important.

 Identical form factor cells were available that had much higher energy capacity.

I could do this in reverse for a EUC battery.  Use highest current capacity cells without regard to energy capacity might result in a smaller and lighter battery with sufficient range for me. 

Sigh, another project.