260v Dirt Bike 2021

Energy is energy, if your battery is 2kWh, you can't draw more out of it than that. Decreasing amperage could decrease resistance related losses and give you a small range boost, but the difference would probably be negligible over a well designed 72v system. 260v is more dangerous, time-consuming, and expensive.

cheapcookie said:

Wouldn't there be less current draw?

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Yes, but so what. If you ust take the same battery and divide it into 4 65V packs and put them in parallel required for the same power at 4X the current. With the packs paralleled at the cell level the battery will be under the same stress, but will arguably be more than 4X less likely to fail and it will be much safer. All components will be more readily available and cheaper (excluding the salvage type stuff from electric cars).

cheapcookie said:

Longer range for the same amount of kwh?

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No. The only advantage of running such a high voltage is that you can use smaller gauge wire on your power mains. That tiny weight advantage doesn't hold a candle to the multitude of advantages of running a lower voltage.

The 2018 Redshift MXR’s electric motor runs on 350 volts and makes ~37kW. On a 65V battery pack that is 570A from the battery assuming for arguments sake 100% efficiency versus 106A for a 350 volt battery pack. The engineers at Alta plainly believe the higher voltage is a better solution as do the engineers at every major car manufacturer across the globe.

The great thing is that everybody is free do do what they think is best. I fail to see how the reliability of a battery pack built from X cells is in any way dependent on the series/parallel configuration. If a single cell fails you have a problem regardless of how you have connected those cells. Automotive manufacturers aren't afraid of 96S battery packs. The Porsche Taycan battery pack at full charge is 835 volts. Sure high voltages are dangerous, has anybody in the world been electrocuted by a EV battery?

You're comparing professional, multi-million dollar projects to a DIY build. For someone building a motorcycle in their garage, the danger of high voltage electrocution can be very real, especially if you are new to the hobby. 260v is lethal.

I'm not saying you can't build a 200+ volt system in your garage, just that the risks are a lot higher.

kiwifiat said:

Sure high voltages are dangerous, has anybody in the world been electrocuted by a EV battery?

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Not yet, maybe.
But if EVs become more common, I am sure this will happen.

I would not want to ride a vehicle with more than 100V under my butt-
and I am experienced with electricity-have been doing all the 230V installations in my house myself.

But with my house I am not riding around, and risking crashes...

TorgueRPM said:

You're comparing professional, multi-million dollar projects to a DIY build. For someone building a motorcycle in their garage, the danger of high voltage electrocution can be very real, especially if you are new to the hobby. 260v is lethal.

I'm not saying you can't build a 200+ volt system in your garage, just that the risks are a lot higher.

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No Argument that high voltages can be fatal. If you don't know what you are doing or have contempt for the dangers do not build a high voltage dirt bike.

What are the objective risks and how do you assess them? Fatalities in the USA seems to be a reasonable basis. In a recent CDC report I read it was indicated that fatalities in the USA from electrocution average around 400 per annum. This report:
https://www.ghsa.org/sites/default/files/2021-03/Ped%20Spotlight%202021%20FINAL%203.23.21.pdf
on pedestrian fatalities in the USA indicate that 2,957 fatalities occurred in the first 6 months of 2020. It seems then you are more than 14 times more likely to be killed taking a walk than you are to be killed by electrocution in the USA.

In my opinion the risk of being electrocuted is by far the least of my concerns when out riding. Other motorists and my own skill or lack thereof are the major drivers of risk. I had a bad accident in 2019 that resulted in multiple busted ribs, punctured lung and concussion but the high voltage battery pack in my scooter was still securely bolted to the frame. To have affected an electrocution during the accident would have required a monumental effort of Mr Bean-esque stupidity especially in light of the fact that during an accident the rider is usually thrown from the bike.

Yeah the risk of electrocution for the average person isn't that high, but the average person isn't building a 260v battery.

I think Zeros are Crap, having owned a 2015SR and getting to ride it all of three times (isolation faults that the dealer knew about when they sold it to me, and that Zero also knew about and didn't reveal - I had to go through the BMS log myself), but it seems that if the OP wants a dirt bike with KTM-like build strength and Zero power, he should be looking to transplant a Zero drivetrain into a KTM. Just saying...

Just a thought here. I also believe that its unrealistic for a hobbyist to do a high voltage build. However, I think there is a clear argument that mileage WOULD be better with high voltage.

With low voltage and high amperage more HEAT is created, is it not? Heat is a loss factor, energy that's being lost to the atmosphere and not being used to power the vehicle.

With a high voltage system it's easier to control these losses and hence deliver higher efficiency. While we may be talking only 5%, as others have mentioned, making a 300v battery is not inherently more difficult. So if you're designing the system from the ground up, why not use HV.

Due to the ease of LV, it is certainly the direction I will be taking on my build.

In high voltage systems, the efficiency gain you get by using higher voltage is often offset by the efficiency loss of using a transmission with a higher speed motor. The space used up by a transmission/gearbox is also often better used to fit a bigger motor or more parallel cells, both of which can increase efficiency if the battery or motor are at their limit already.

Are you talking about two configurations with the same motor constant?

Personally, i treat all packs as if they were 400v and find it easier to stay safe then to beef things up and cater to more heat dissipation and production.

Yes I was talking about similar motor constants. If aiming for the same rpm, using a slow wind motor with high voltage isn't necessarily better than a fast wind motor with lower voltage, because all else being equal, the phase to phase resistance will be higher on the slow wind motor. Another trade off. A 70s bms is also going to be pretty expensive.
I think treating all packs as if they are dangerous is a good move. I melted the end of a wrench and burned my hand shorting a 64v pack.

TorgueRPM said:

I think treating all packs as if they are dangerous is a good move. I melted the end of a wrench and burned my hand shorting a 64v pack.

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:thumb: That is solid advice, plenty of auto mechanics have injured themselves by shorting 12V lead acid batteries with metal watch straps, spanners, and screw drivers.