84.2 volts vs. 100 volts

[CarlW]

Electrical stuff is not my thing but I would like to get a better understanding of the basics as it relates to EUCs  I can get that the higher the wattage of the motor translates to more torque and/or higher speeds.  The larger the watt hours of the battery apparently gives more energy at your disposal for longer rides and a reserve for peak demands to avoid a cut off.  Could anyone give me a basic overview of how the different voltages used in EUCs impacts performance.  Clearly the more powerful wheels are using 100 volts these days.  What can they do better or more efficiently than an 84.2 volt wheel?  Is there a direct correlation between large diameter wheels that requires the higher voltage to power them effectively.  Does voltage have any impact on the temperatures of wiring and the control board?  

Edited June 5, 2021 by CarlW

[Tawpie]

tl;dr 100v enables more speed. Larger diameter wheels are more stable and comfortable at high speed. Speed requires exponentially more power so battery capacity and instantaneous power delivery must grow accordingly.

Here’s my explanation of speed and 100v vs 84v…

Larger diameter wheels go further on each revolution so you’ll typically see them go faster… but they trade speed for torque. The longer lever arm from the motor to the tire is a mechanical disadvantage for torque. The large diameter does help a lot with absorbing bumps and other imperfections in your path making for a smoother and generally more stable ride (larger diameter gyro effect is in play stability wise as well).

As to heat, that’s all about losses in the path the electrons take from inside the battery to the motor windings. More power = more heat given the same losses, and 100v wheels generally utilize more power. The components, wires, heat sinks, air flow etc. should be designed to accommodate the higher power dissipation. All that gets played against unit cost but there is plenty of design margin so you won’t have heat problems (wink wink).

Edited June 5, 2021 by Tawpie

[Ben Kim]

eWheels really needs to fix this 84.2V nonsense because it is complete miseducation of the general public. it’s 84.0V (20S * 4.2 = 84.0)

[Camenbert]

51 minutes ago, Ben Kim said:

eWheels really needs to fix this 84.2V nonsense because it is complete miseducation of the general public. it’s 84.0V (20S * 4.2 = 84.0)

In fact it's the whole EUC industry that mislead about voltage.
Everywhere else a 20S is call 72V and not 84V, because it's the nominal voltage that matter.

[meepmeepmayer]

The short version is: a higher design voltage (like 100.8V instead of 84V, 20% more) gives you a higher max speed (20% more) with practically no downsides. In fact, wheels even seem to be more efficient at speed at higher voltages.

That's why everyone is going towards higher voltages (e.g. the V12 is 100V, coming from the 84V V11). There's little reason not to do it. Not much else to it.

It doesn't have to do anything with tire diameters or so, I think.

12 hours ago, CarlW said:

Does voltage have any impact on the temperatures of wiring and the control board?

In theory, you could exchange less current for a higher voltage for the same result, and current is what heat up the electronics. So you could have thinner cables etc. But all the parts are too thin/small anyways, so in practice it makes no difference with our EUCs.

[bracky72]

Voltage x amperage(current) = wattage

 

So increasing the voltage allows you to reduce current flowing through the system to get equivalent wattage. It’s high current that heats wires and stresses the system.

Edited June 5, 2021 by bracky72

[RockyTop]

While voltages do make a difference it is more about the setup. A 12 volt motor could out do a 100 volt motor no problem. First we have to work with what we have. If you take a motor that is normally using 84 volts and set it up with 100 volts it will go faster. As long as everything is within the limits we are OK. ( there is a limit) Most of the time we are doing the same amount of work and the motor is getting the same amount of energy. The jump in voltage is not a big deal. 

The big bonus is that we can use smaller components to do the same amount of work. A 12 volt setup that would over power the standard 100 volt wheel would take much larger components. The wheel motor wires would have to be 13 mm thick. All of the electrical components would have to be larger. If you look at electricity like plumbing, the size of the pipe is like the size of the wire. The voltage is how fast the water moves. If the water moves slow the pipe needs to be bigger the flow the same amount of water/work. 

[Ben Kim]

6 hours ago, Camenbert said:

In fact it's the whole EUC industry that mislead about voltage.
Everywhere else a 20S is call 72V and not 84V, because it's the nominal voltage that matter.

if you want to get super granular, even 72V is incorrect in many cases since nominal voltage on many of these cells is ~3.6V not 3.7. 

[drader]

Keep in mind many of the 100v wheels are 4 packs in parallel, and the 84v wheels they replaced were 6 packs in parallel. The 6P would be able to deliver 50% greater current... but if your electronics really just come down to watts then the 100v version probably has an efficiency advantage, as well as being better able to avoid voltage sag. I think the Tesla cars are around 350-375 volts, but Porsche and the industry are moving to 800v citing “Lower weight, higher efficiency and faster charging”. You can use less copper in the motors since you are dealing with less current to do the same job, and avoid heat in charging for more efficient energy retention.

[Camenbert]

1 hour ago, Ben Kim said:

if you want to get super granular, even 72V is incorrect in many cases since nominal voltage on many of these cells is ~3.6V not 3.7. 

3.6x20=72 dont you think?

[RayRay]

On 6/4/2021 at 8:12 PM, CarlW said:

Does voltage have any impact on the temperatures of wiring and the control board?

IMO, this is the important part of the question. (I will now repeat things already said on this thread...)

Power (watts) is a product of volts and amps, so higher voltage is being used to offset higher amperage.

To balance 'cheap wiring' vs. 'not overheating', we tend to get the former because we are guinea pigs.

(About 10-20% of our forum discussions address this while giving a 'basic overview' of how euc's work.)

Edited June 6, 2021 by RayRay

[KenO87]

so is there any reason to not use higher voltage? I've heard that at lower speeds, lower voltage is more efficient

[Eucner]

1 hour ago, KenO87 said:

so is there any reason to not use higher voltage? I've heard that at lower speeds, lower voltage is more efficient

There is a reason. At the low speed the power consumption is also low and efficiency plays very little role. At higher speeds wind resistance increases in the power of two, meaning much greater power need. The efficiency starts to count.

[meepmeepmayer]

@EucnerVery good point! Never heard of any efficiency advantages of lower voltage designs, and that explains it. If they exist, they play no role anyways.

So, a higher voltage is for all intents and purposes "just better".

[KenO87]

@Eucner you say there is a reason? But your answer sounds like, there's really no advantage to a lower voltage.

[Eucner]

If you want to go as far as possible without charging, a low speed is the king. Low voltage matches well will low speed giving even more distance. Very few of us have patience for this. When choosing a wheel, the voltage is only one parameter. I wouldn't put too much emphasis on it.