Why not 96 volts instead of 72?

[halg]

I am planning an electric conversion and have read a lot here and endless-sphere so thank you to everyone who has provided information in both places. I'd be lost without it!

I have read that most of @DonCox builds use 72 volt batteries (often as 20S12P) and it seems like a popular choice. @fmxxx666 went slightly higher and electro & co bump things slightly as well to 76v.

Based on my calculations, the difference in watt hours between 26S9P and 20S12P are pretty small (only a couple hundred watt hours). But, 26S has the obvious benefit of requiring less current for the same power and all the good stuff that goes along with that. Edit: Here is an example at amorge of a comparison of 20S10P and 26S7P which shows the watt hour difference between those two.

The main reason I can see to consistently choose 72v are that the controllers are cheaper. But, at $273 for an EM260 $535 for an ND96850, I would not see that as a large part of the equation. Especially since it would help alleviate some of the heat build up. I would think any power/torque curve difference the higher voltage would introduce could be managed with different sprocket gearing.

Why is 72 volts chosen so consistently especially by people like @DonCox who are clearly very knowledgeable and experienced at this.

Are 96 volt batteries more expensive? Am I wrong about simply using the sprocket gearing to move the power down with 96 volts? I feel like I'm missing something b/c 72 volts is so popular.

I'll be sticking with 72 on my first build since it is a KLX400 which I got free and has a bad motor and isn't a great fit with its non spar frame. So, it will be a budget build for my first go. But, I'm wondering in general and obviously thinking I'll try again on another bike.

Thanks!

 

[fmxxx666]

So I would say 72v is the most common as most (plug and play) motor controller sets run on 72v.

And most ppl try to do their builds on a budget so 72v will give you a good enough power output by keeping the costs manageable.

Additionally (at least here in Germany where I live) 80v is the barrier (in a work environment) where you have to have a special license to work on „high current“ equipment as it begins to get more and more dangerous after that.

I talked to a guy who had a 72v MX bike with qs138 70h v3 motor and a 72v 60a amorge battery (using Samsung 50s cells) and he was quiet disappointed with the performance on the MX track. So he sold his complete build in the end and said if he ever gonna do something again he will go with more current and higher performance cells.

This in the end made me go the route with 22S (81,4v) and the best performing cells I could afford (Molicel p45b)
I was pretty soon sold to the features of the EBMX X9000 controller and the max supported volts is 22S if it would have supported more I may also would have went higher than 22S

 

[DonCox]

The answers are in most of your statements. First of all the guy that was underwhelmed with the bikes performance, was running the wrong batteries. Samsung 50S do not supply the current in the 20S12P configuration. Maybe 16 or 20P you could get the current for the performance. That is why we use the Molicel P42A and P45B cells. I run 300A most of the time on the moto track, and 400A when needed, but that has some power at 400A. I'm not a Pro rider, but 400A is powerful.
The components at 72V are more common and less expensive. All of my build are at 72V, but I am doing a KTM Duke 790 next for the street, and I am going to 96V with a higher current battery, 500-600A, probably 24S16P maybe 18P. I know I will need more for range, but we will start with that. I want to get 100mph
But the main reason for 72V to this point, is that I have been using Votol EM 150 thru 260SGTP controllers, and they are only 72V. I just got a Fardriver small controller for a Razor MX500 upgrade so I can learn the Fardriver software. Cost of the higher voltage 3Shul CL1000 or CL1400 is very high, and they have had reliability issues.
Also lower voltage components are more common and less expensive as well as a lot more charger options.
There is no high level decisions on the higher or lower voltage. We all know for the reasons you guys stated, Higher voltage is better, and more efficient, and dangerous, like you said in Germany, there are rules. KTM had a hard time getting American dealers to take on their Freeride because of the higher voltage. They didn't want to service that voltage.
When I was working (I am retired) I worked on CT Scanners, with 120,000volts (120KV) on the XRAY side of the machine. That is scary voltage...

 

[halg]

Thanks for the replies. The safety thing is what I was missing. With the 96 volt fardriver controller I linked earlier it doesn't seem like cost/availability are as big a deal assuming a 96 volt battery is not inherently more expensive than a 72 volt given an approximate same number of cells. I also imagine these things are constantly changing and evolving like everything else and what was available two years ago may be different than now.

After lots of reading and several years of experience I've become comfortable enough to work/service my house electrical panel. I'll apply the same logic to researching higher voltage DC systems and what safety precautions are appropriate and make a decision on that if/when I design my next build.

It really does seem like going higher voltage with its benefits for reducing stress and increasing efficiency makes a lot of sense. But safety is nothing to dismiss for sure.