Looking for voltage/advice new build 60v vs 90v

[BionicOnion]

Hello, im developing a recumbent tadpole for my own use, maybe a little bigger than a single rider as i have a little one who im gonna have room for him or a cargo area behind the main rider. I currently have a high power 60v system I'm working on my design with, and I'm wondering if the jump to 90v is worth it. Granted the kwh will scale by 50%, but is the voltage jump really worth the time? I'd ideally like to see 60mph at the almost upper limit, with the majority of time under 45mph. Im hoping with a full wind fairing I won't need a ton of power to do this, but I'm able to pull 200amps without concern on my current setup. Distance won't be a huge issue obviously with the capacity in either system. Has anyone ran both systems or any advice on moving forward?

Thanks in advance and will hopefully be able to make a build thread in a few weeks while working on it

 

[Chalo]

You want to carry a crotch fruit on a 'bent tadpole at 60 mph?

I guess that's one way to reduce the population growth.

 

[BionicOnion]

You want to carry a crotch fruit on a 'bent tadpole at 60 mph?

I guess that's one way to reduce the population growth.

Lol I guess I didn't specify... no. Just want to have that speed capability for my own...idiot moments. Anytime with him would be much more civil

 

[Chalo]

Well, light EVs like to be built for a single top speed. If you give them an excessive top speed, then they run inefficiently most of the time. It's a common request but it never becomes a good idea.

 

[BionicOnion]

Well, light EVs like to be built for a single top speed. If you give them an excessive top speed, then they run inefficiently most of the time. It's a common request but it never becomes a good idea.

Hmm good point. Around my town it'll be under 40-45 pretty much always so maybe I need to rethink motor selection? I was thinking using a mid drive in the back for selecting gear ratio if/when needed

 

[glennb]

You need to crunch numbers. Drag coefficients, required wheel RPM, then power. Voltage is just about irrelevant ... anything above 30V can be used to achieve 60MPH.

But I'd forget about 60MPH, because it'll make the vehicle unpedallable at any speed.

For high speed you don't need a motor at all, just a long enough hill to roll down (and light enough bike and strong enough legs to get you up it).

An 8% grade might suffice if your fairings are good, 10% at the most.

I can't achieve 60 on an upright bike, but 50MPH is easy on what I consider gentle grades, around 9%.

 

[BionicOnion]

You need to crunch numbers. Drag coefficients, required wheel RPM, then power. Voltage is just about irrelevant ... anything above 30V can be used to achieve 60MPH.

But I'd forget about 60MPH, because it'll make the vehicle unpedallable at any speed.

For high speed you don't need a motor at all, just a long enough hill to roll down (and light enough bike and strong enough legs to get you up it).

An 8% grade might suffice if your fairings are good, 10% at the most.

I can't achieve 60 on an upright bike, but 50MPH is easy on what I consider gentle grades, around 9%.

Right so I guess more to your consideration.. I know 90v will give me 50% more range with an identical pack with kwh, so say speeds stay relatively reasonable. Is there any reason to say...stay at 60v vs going to 90? My packs won't care about draw at either, I just know it'll be a lower C rating at 90v

 

[Chalo]

I know 90v will give me 50% more range with an identical pack with kwh,

That's not how it works. Switching from 36V to 48V or 52V at the same Ah of battery tends to give the same range (but with more pep). If you actually use the extra speed available, the range gets shorter.

 

[BionicOnion]

That's not how it works. Switching from 36V to 48V or 52V at the same Ah of battery tends to give the same range (but with more pep). If you actually use the extra speed available, the range gets shorter.

Each of my groups has the same ah, that's what I meant, not just a voltage change. A 3rd pack in series would be 90v at the same ah.. but overall 6kwh

 

[amberwolf]

Some thoughts:

If the packs have a BMS, be very sure their parts are rated for the absolute max voltage the system could ever see, because if any BMS shuts down for any reason it will have that entire voltage across it's FETs.

If they can't handle that they'll fail, and that often means failing shorted, which means the BMS is now permanently stuck on, and cannot protect the cells against anything...and since it was already triggered it means the cells are being damaged right then and there, and will only get more damaged as time goes on becuase you won't know the BMS has failed unless you test for it regularly.



0Regarding total system voltage:
--The higher you go in voltage, the more expensive controllers to handle it become.
--higher voltages mean more potential safety considerations in the electrical system; making sure all switches, fuses, etc are rated for that


Regarding capacity: As long as your total wh is the same, then capaciyt is the same. So if you have 3x 30v packs of some capacity (say, 10Ah for simplicity of math), then youc an have a 30v 30Ah pack (3 in parallel), a 60v 10Ah pack (2 in seires, can't use the third), or 90v 10Ah (3 in series). Only the first and last have the same total capacity, the 60v has only 2/3 of the total because of the pack taht can't be used.

So it depends on what packs you actually have and how many for what total capacites you can get.


Regarding range and performance: It takes a lot more power to go faster above around 20mph for unaero-optimized bikes/trikes; if you know the CdA / etc of your fairing you can punch in numbers into various online simulators and calculators such as those at ebikes.ca to find out how much power it will probably take for various speeds under whatever riding conditions you have.

Because it takes more power to go faster, the faster you go the lower your range will be.


Regasrding voltage vs performance: I'd recommend playing iwth the ebikes.ca motor simulator to show yourself how various system configurations with different voltages behave, power / torque / heating / etc curves on your specific riding conditions, whcih will also help you decide what system voltage to use.





I'll leave ride safety stuff up to you; if you're planning on those speeds at all, I'm sure you'll research the necessary things if you haven't already.

 

[glennb]

You need to spill the beans on where you're at with this project. I gather that the vehicle's in design phase and you already have battery modules in blocks of 30V, but it's insufficient background to sensibly comment on battery design.

How long is a piece of string? Double half of it's length, I suppose. You're battery's much the same.

 

[lnanek]

Yeah, in general, adding packs in series only increases voltage. Adding packs in parallel only increases capacity.

I guess you were hoping going from a 60V system to a 90V system might allow you to use less amps for the same speed and thus get a little extra range, but in general more voltage is used to produce higher RPM since any given motor has a kv rating, which is the RPM per volt. Going even a little bit faster uses a lot more battery, however, due to wind resistance.

If you haven't spec'ed the motor yet, I suppose you could pick one with a kv such that it runs the same speed at 90V as a different motor would at 60V. That might be a way to use the higher voltage for something other than increasing top speed.

 

[E-HP]

The voltage the motor sees is dependent on throttle position, not battery input voltage. From the motor efficiency perspective, it only matters what the motor sees in terms of voltage and current. The battery voltage determines the max voltage the motor will see, but you determine, via your throttle, what goes to the motor at any given time.

Note that higher voltages make throttle control more difficult, since it’s controlling a range from 0v to 90v, instead of 0v to 60v.

 

[BionicOnion]

The voltage the motor sees is dependent on throttle position, not battery input voltage. From the motor efficiency perspective, it only matters what the motor sees in terms of voltage and current. The battery voltage determines the max voltage the motor will see, but you determine, via your throttle, what goes to the motor at any given time.

Note that higher voltages make throttle control more difficult, since it’s controlling a range from 0v to 90v, instead of 0v to 60v.

I didnt really think of throttle response aspect of things. It seems I should do what makes sense most and run the 60 for a while then decide . Maybe 60 will end up meeting my desired usability for 90% of the time and it won't make sense to go higher. I live in a very small town where across town is like 3-5 miles which is brutal on gas costs in the car because of all stop and go. But I also live in Northern pa, so the goal is something usable even in snow, hence the desire for fairings.

I appreciate the responses everyone thank you for your input!

 

[BionicOnion]

You need to spill the beans on where you're at with this project. I gather that the vehicle's in design phase and you already have battery modules in blocks of 30V, but it's insufficient background to sensibly comment on battery design.

How long is a piece of string? Double half of it's length, I suppose. You're battery's much the same.

Glennb, that makes sense. Yes my modules are 8s 67ah. And capable of over 400amps continuous. Depending on many factors, the very large majority of use should be in town/rural so under 45mph. As it sits im sorting a bunch out and going to reuse my 48v 1kw motor that I could get 27mph out of on my... truth be told clapped out used bike I got for I think 20$ lol so I'm hoping for a nicer commute

 

[glennb]

Fair enough.

Rear direct drive Voilamart in 26" wheel? That will be relaced in a smaller rim for the recumbent? If so, yes, 90V is likely the obvious way to achieve higher speeds.

Unlikely 60MPH though, at least without field weakening, beefed up phase wires, and improved heat shedding.

The e-bikes.ca motor simulator is a fantastic tool, worth more than a look.

 

[offGridDownUnder]

so the goal is something usable even in snow

Then wouldn't you design for torque and low-speed handling, rather than very high speed?

If I make a sharp turn on my trike (3d in my sig below) above 20km/hr, I'll be using my shoulder and head to slow myself to a stop. Especially if I'm clipped in.

"Oh, I'll be careful. And I'm a really good rider". Sure. But the others on the road with you won't be, and aren't.

Car drivers can't estimate a fast moving trike, and they will not manage their own driving well to accommodate you. And it's your fault, not theirs. Ask them - they'll tell you.

 

[MxusMick]

My Dad took me for a ride on his bike when I was 3 or 4, he told me not to put my feet in the spokes, guess what happened.

 

[BionicOnion]

My Dad took me for a ride on his bike when I was 3 or 4, he told me not to put my feet in the spokes, guess what happened.

Lol, i guess I could be slightly more clear. I was thinking of a faired unit so if he's in the rear seat he would be unable to put feet or hands in not good places. Looks like I'm stuck at 60v which is probably fine as 95% of my riding will be around my town anyway and under 35mph

 

[lnanek]

You can get cheap plastic mesh to cover your wheels and motor and keep kids safer when seated on the back. I have a half dozen of these zip tied to a rear fender and rack to block any remaining gaps:

https://a.co/d/6gP2SZw

Stopped issues with my kid's blanket dropping from her child seat down into wheels/chain/spokes. Real cargo bikes often have wheel guards to protect passengers as well.

Before the plastic I had cargo nets, but you can push those in, so seem less safe.

 

[PaPaSteve]

Trikes are perhaps the most balance sensitive vehicles on the road.
Adding a child and changing the load balance could upset the handling.
Not saying "don't build"
Am saying be aware of this issue when designing.
I have learned a few hard lessons with trike designs.

Here's a recent thread in recumbent trike forum :

https://www.bentrideronline.com/messageboard/forum/main-category/specialty-discussions/trikes/3035970-best-ways-to-crash-trikes

 

[BionicOnion]

Trikes are perhaps the most balance sensitive vehicles on the road.
Adding a child and changing the load balance could upset the handling.
Not saying "don't build"
Am saying be aware of this issue when designing.
I have learned a few hard lessons with trike designs.

Here's a recent thread in recumbent trike forum :

https://www.bentrideronline.com/messageboard/forum/main-category/specialty-discussions/trikes/3035970-best-ways-to-crash-trikes

I'll definitely take a look later. I sort of figured balance would be important for a few reasons and side to side would seem to be a harder imbalance to sort vs front/back balance. If anything i may be a bit too light in the rear

 

[neptronix]

Maybe you want a hub motor, maybe you want a mid drive.

A very low turn count hub motor would take advantage of this enormous battery since you have a huge amount of amp hours.

What does the bike in question look like and what size wheels does it have.. also.. do you have mountains to climb - or what's your hilliness like?

If you don't live in a mountain state like i do.. here's an approximation of how a Leafbike 3T 1500W hub motor would perform on a bike wit ha 20" wheel ( if you have a bigger wheel, you probably want a 4T instead )

This could climb a 5% grade for a long time w/o overheating.



Motor Simulator - Tools

ps, in this scenario, the motor will take 80 amps or more, and have some very serious acceleration.

 

[PaPaSteve]

I'll definitely take a look later. I sort of figured balance would be important for a few reasons and side to side would seem to be a harder imbalance to sort vs front/back balance. If anything i may be a bit too light in the rear

Consider
Wheel weights and axle weights
For a trike the wheel weights are expected to be 33%
Which puts the axle weights at 66% for the track width and 33% for the single wheel.
Straying too far from these numbers can lead to handling issues.

 

[BionicOnion]

Consider
Wheel weights and axle weights
For a trike the wheel weights are expected to be 33%
Which puts the axle weights at 66% for the track width and 33% for the single wheel.
Straying too far from these numbers can lead to handling issues.

Greatly appreciate any scientific info and ratios. Im hoping to have a faired vehicle similarity to toe cutters, but usable in the snow belt here. My initial thought was hub motors on each front wheel at 1.5kw-2kw range peaking maybe around 5 if I went momentarily stupid, but coupled with a rear mid drive system thats 5-10kw. I'd have the ability to switch between rear, front, and all wheel drive. I've been eyeballing the grin phaserunner for the front wheels to allow easier rolling when in rear drive. I guess my goals are lofty yes, im hoping to eliminate by car unless absolutely necessary im hoping the body drastically will reduce the drag and i still end up with decent range if not beating the snot out of it