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.

 

[HadesOmega]

More voltage more power less heat because for the same amount of power at a higher voltage compared to a lower voltage and and higher current. If you want more power go with a higher voltage if you want more range go with a lower voltage with higher amphour rating. Ultimately in the end it is how much you twist the throttle is how far you will go. Power = Volts x Current

On my build I am going from an 84V battery to a 72V battery because I have a bunch of 72V chargers already. It works better for me logistically. Also I am prioritizing range over power. I only need about 15KW for what I am doing with the bike. So I'd rather have it go farther than faster.

 

[halg]

I am posting this for anyone who might come across this later while planning a build.

I asked my contact at siaecosys if there were 96 volt EM260SGTP controllers. He said yes and they were $261 which is $10 more than I paid for the 72 volt version.

This does not change things for my current build. It is more of a trail bike than a motocross bike. However, if I were building a bike that needed high power, I believe I would go to 96 volts. [edit]This requires more planning and precautions such as choosing high voltage safe components, etc. So, if you are looking for an easy plug and play style kit I would not recommend it. However, if you are someone who is willing to spend the time to search down and spec and design the appropriate components yourself I believe it is worth considering.[/edit]

 

[DonCox]

Thank you Halg. I will check with Siaecosys about the 96V model. But I still want more power for the street conversion, I am considering the Fardriver ND961000, or 1200. I figure 96V over 72V is a 33% increase in power, and if I go to 500A over 400A it is another 25% increase, 600A over 400A is 50% more power. I want to get to 100MPH fast...
I got from a friend a Stark battery box , and I am going to use it for the battery. It will be a 26S15P battery. This build is on a 2023 KTM Dike 790 bike. A brand new bike without the motor. The motor was used for a AFT Flattrack twin. I have most of the fairings off the Marlboro bike, and I hope to end up with that look.

 

[halg]

Wow. That will be cool...and fast! Yeah I don't think the EM260 can take you there maybe an EM550 if you are trying to stick with votol. I had a fardriver on a bike I bought for my nephews for christmas and it seemed to work fine too. I have no experience with these larger controllers (or much experience at all yet really). blacksheep engineering chose an ND961800 and went to 28S I believe. Seems like a lot to me but I think he chose to overbuild a bit.

That will be a cool project. Please keep us posted. What happened to the varg battery? Did it go bad and someone got sent a new one? What is it like inside? Are they rebuildable?

I purchased a surron ultra bee and was disappointed to read that their batteries are potted with glue or epoxy so they are nearly impossible to rebuild.

 

[DonCox]

A friend know someone who had a defective Stark battery replaced. He purchased it and removed the batteries. He said he got about 350 good cells and used them for another project. He gave me the box, and left over parts. I can build a 2 wide 21700 cell battery inside. My goal is to fit 410 cells back in. 26S16P or actually 2 times 26S8P, so I can charge with 2 chargers. But I may only be able to get 2 time 26S7P groups in there. I will do an article on the battery build as it goes. I have 72V test batteries, and I will get it running with 72V Votol controller at first.

 

[Theo]

A friend know someone who had a defective Stark battery replaced. He purchased it and removed the batteries.

Well, you've said that you have worked with 120KV on CT scanners and you surely sound like someone who knows what he's doing, but let's remind everybody that opening such a battery can easily kill the person who does it if this person doesn't have the knowledge and skills or makes a mistake.
Also buying a battery from Amorge for those builds is one thing, since as far as I've understood it comes to the buyer assembled, while putting cells and cases together is pretty dangerous, too.
I just don't want anyone to underestimate the risks involved.

 

[DonCox]

Well, you've said that you have worked with 120KV on CT scanners and you surely sound like someone who knows what he's doing, but let's remind everybody that opening such a battery can easily kill the person who does it if this person doesn't have the knowledge and skills or makes a mistake.
Also buying a battery from Amorge for those builds is one thing, since as far as I've understood it comes to the buyer assembled, while putting cells and cases together is pretty dangerous, too.
I just don't want anyone to underestimate the risks involved.

Very true Theo. I have experience, and still have to be very cautious. I have had a few accidents with building batteries and repairing them. Everyone do be cautious, and use safety equipment, Googles, gloves, apron, And as a word of caution, Lithium fires cannot be put out by normal fire extinguishers. You must submerge an "on fire battery" in a water tank. So a good idea to have one near where you work, and a device to grab it and pull it into the water. I speak from a friend who had this happen.