96v at 19 amps vs 72v at 25 amps EBIKE!

Hello, I am running an ebike off an 1800w running watt inverter gen on a trailer... I am planning on DC conversion for the motor to be done through.... It needs to be generator powered as the ebike will be doing 100-200 mile trips, which batteries cant do.

A) 2 1000w, 48V DC PSU in series making 96v at roughly 19 amps.

B) 2 1000w, 36V DC PSU in series making 72v at roughly 25 amps.

I am wanting a speed of 50mph! I feel like option A would get me that speed, yet B wouldn't but would have better torque... I dont really care about torque. I want speed. B I think would get 40mph, maybe 42mph, but higher torque... What do you guys think.

bike4life said:

I am wanting a speed of 50mph!
What do you guys think.

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I think you may be dreaming.

IT doesn’t matter much. Choose the voltage according to the motor Kv and wheel size, for the speed that you want. Or, choose the motor Kv to obtain the desired speed at the voltage that you feed.

The faster the speed, the more watts you will need to overcome wind resistance, and/or hill climbing resistance. So, at some point your generator will need to be bigger for your bike to go faster.

So, two bikes may do the same top speed when fed 72 or 96v, depending of the other factors such as wheel size, motor Kv, aero drag, weight, power... in fact, the one fed 72v may be faster if one or many of those factors are different.

Building an ebike is to design a combination of performance factors, in order to obtain the desired speed, acceleration and efficiency.

What a wasteful fossil-fuelish idea

going to be burning **lots** more petrol that way than just driving an ICE powered vehicle.

Twisted logic publicity stunt

Yep. Logically, a gasser motorcycle would be best for that purpose. Still, many had carried a generator on a trailer for long trips where charging is not available, and to ride an ebike instead of a motorcycle where they are not allowed. So, there is a valid reason for that, even though it is not common.

The target cruising speed of 50 mph pulling a trailer is a problem that the OP might not be fully aware of. Few have the knowledge and willing to spend the time and money to build a good bike for that purpose.

The question is which should I do - 96v or 72v at those amperages!!!

The gasoline is necessary... You folks then would have a battery solution for 200 miles at 40mph?? No...

I will lower my top speed from 50 to 43. Now which should I do, 72v or 96v...

My ebike currently goes 30mph with at 48v battery, and 33-34mph at 54v so that should tell you the windings, kv.

The simple answer to your question is that neither setup will get you at a cruising speed of 50mph unless you've built something of a Velomobile and never get near a hill.
I read a reply that someone stated you need to calculate your motor kv, voltage, and tire size to get your theoretical speed. This is entirely correct. Your motor will spin at a specific rpm per volt and you'll have to use that calculation along with the circumference of your wheel to get "unloaded" speed.
Once your unloaded speed is established you'll need to start dumping watts into the system to overcome your weight and wind resistance (not to mention efficiency losses).
My best guess is that if you can complete this dream and it'll something to the effect of 10,000w to even get near what you are hoping for. With that done, you'll burn up electronics before your road trip is done.
Sorry man. If you lower your speed expectations down to less than 30mph you might be able to pull something off.

bike4life said:

The gasoline is necessary... You folks then would have a battery solution for 200 miles at 40mph?? No...

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I can go 180 miles at 25mph with 3.25kWhr, and could do better if I wasn't running a QS205 for stupid power. At 40mph though... I'd probably need 8-9 kWhr. Yet a velomobile would have >200 miles range with the same battery/drivetrain. A hybrid is complex, and the noise and smell of gas ruin the otherwise peaceful experience of an EV, in my opinion. Better strategy if you really want insane range, is to just improve efficiency as much as you can. Kingfish documented some significant gains with very simple fairings for an upright bike. Probably you could achieve 200 miles @ 40mph with ~6kWhr on an upright bike, or half that capacity with an electric velomobile.

Basically, a trailer is going to add a ton of drag. You'd be better off improving range by spending that weight on battery capacity, and improving efficiency with good aerodynamics as that is by far the biggest thing working against you at that speed.

Can someone tell me the numbers for 96v vs 72v... It needs to be gasoline cause I am not making a velomobile... The inverter generator will sit on a welded basket in the front. I dont really mind the gasoline smell.... Its just i can still call it an ebike and skirt some of the laws with a hybrid. 6kwh of batteries is 2 expensive. My inverter gen is 400 dollars on ebay.

Can 72v at 25 amps go 40mph or do I need 96v at 19 amps

bike4life said:

My ebike currently goes 30mph with at 48v battery, and 33-34mph at 54v so that should tell you the windings, kv.

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It takes about 1800W to go 35 mph, which is mainly due to wind resistance. So, given that all your combinations still only result in 1800W going to the motor, neither will give you the Power to go faster than that, unless you start with a fully faired bike.

If thats the case, how come this.

https://www.gribble.org/cycling/power_v_speed.html

why do these calculators all have much lower wattages. I am not entirely convinced cause i had a really shit battery pack from china that did 30mph, 48v and it had 4s, so thats 10ah right there... I mean, i doubt it was even 2C, only 1C...
I wont need a trailer cause the gen is the tiny inverter ones...

96V @ 45A should get you to 50.


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Volts is speed, but Wh is gas tank
96x19=1824wh - 96V goes faster then 72V but you use up more wh if you go faster.
72x25=1800wh
Then when you ride, you use up wh/mile. The more you pedal the less wh/mile is. How much pedaling do you want to do?

I wanted to go on a long distance ride on my ebike and looked into a small generator of 400W which I would have been able to use 2 dell chargers to charge up a split pack 36V battery, so 18V + 18V in series with series harness. Those dell chargers were cheap, and charged at 20.50V @ 8A and only used 3A each. Look on the label on the charger. Charge specs aren't bad considering full charge is 21V+21V=42V (10S) which is the nominal 36V battery. The gasoline generator was like 1'x1.5'x1.25' and weighed 25-32lbs, cost ranged from $300-$500+ then anytime you want to take a break, you can and you can be in the middle of no where and charge up your bike. You may even be able to hook up the generator to your controller and use 400W. I saw a guy do that with a e-motorbike, motorcycle beard guys on yt, their shtick is buy cheap stuff and see how they ride.

Remember that the generator has specs and your chargers have specs. A charger of 96V and 1A uses less INPUT power then 96V 2A. There becomes a certain point of no return, meaning once you reach a certain wattage, you need change from 120V INPUT voltage to 240V INPUT voltage (Charger). 1500-2000W. Remember the common household outlet can handle 15A, so 120V x 15A = 1800W, thats why when you go to Home Depot, all 120V heaters are rated 1500-1800W. Some if not all gas generators allow you to use 240V, but the nominal rating of your generator is always the limiting factor. 240Vx1A=240W, 240Vx2A=480W, so on a 500W generator, 2A @ 240V, or 4A @ 120V, move up to 800W then its 240V @ 3.33A and 120V @ 6.5A then thats what you base your chargers label of INPUT power on. Remember you have no clue what most outlets are when your gorilla charging, could be a 120V 15A outlet or 120V 20A outlet, you dont want to be popping circuit breakers when you plug in your charger and 20 minutes later its full blast and it trips the breaker and you come back an hour later = wasted time.

E-HP said:

96V @ 45A should get you to 50.


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What about 40mph? Would 72v 28 amps do 40?

bike4life said:

E-HP said:

96V @ 45A should get you to 50.


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Click to expand...

What about 40mph? Would 72v 28 amps do 40?

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It could, depending on air drag, weight, tires...
From 30 mph and up, air resistance is the most important obstacle, and it is an exponential factor. If you have a large frontal area, the difference from 30 to 35 is about half the resistance than from 35 to 40. You can go very fast on little power, but then your bike need to look like a fish.

MadRhino said:

You can go very fast on little power, but then your bike need to look like a fish.

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Yup, like I said, fully faired. And then you don't even need a motor...
https://www.youtube.com/watch?v=jQwpGLCAMm4

bike4life said:

What about 40mph? Would 72v 28 amps do 40?

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No matter what volts or motor KV you have, you can't get around the power required to go that speed, given the wind resistance. Looks like 1000W for 30, and 2200W for 40mph. Exponential, as MadRhino said. 50mph is way off the chart, but close to 4500W (6HP).


Of course if you mean no load speed of the wheel off the ground, or some sort of streamlining, then that's different.

https://www.youtube.com/watch?v=6CFTqHbgsKs

bike4life said:

E-HP said:

96V @ 45A should get you to 50.


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Click to expand...

What about 40mph? Would 72v 28 amps do 40?

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What generator are you thinking of using?

The Honda 2200 watt (sort of a standard) will probably do the 72V at 28A mentioned. Barely. Using 1/3 of a gallon an hour. So that might equal as much as 120 mpg....if you can hit your 40 mph target. For 200 mile range, that's 5 hours runtime. And will use about 2 gallons of fuel.

I ride a BMW R1200, not exactly comparable, but get at least 50 mpg at 60mph. So OK, I will burn 4 gallons vs. 2. But if you want to go 40-50, a smaller displacement motorcycle will likely match your fuel burn.

Why? There are inefficiencies in conversion. Fuel runs an engine, the engine powers a generator, the generator might power the electric engine directly, or worse charge a battery, that later powers the electric engine. The motorcycle in more direct fashion, turns the fuel into distance/range without intermediate steps.

It's likely possible with a clean sheet you could engineer a hybrid motorcycle to do 40 mph at 120 mpg. But to do it with off the shelf components, generator, battery, eBike motor and controller isn't probably possible, especially when you add in the trailer. Unless the trailer is necessary for "cargo", but if you need cargo a motorcycle rack won't carry....then all bets are off.

If you don't have cargo, and like to tinker, you're better off skipping the battery, skipping the trailer. Use a motorcycle frame and engine to drive a generator, that directly (or if necessary via a small battery), powers a hub motor. But this isn't an off the shelf kinda project. And it won't probably beat the fuel efficiency of a standard motorcycle.

yeah im using a honda 2200 inverter clone... basically the same specs / size / formfactor but a chinese knockoff for 1/3 the price

BlueSeas said:

bike4life said:

E-HP said:

96V @ 45A should get you to 50.


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Click to expand...

What about 40mph? Would 72v 28 amps do 40?

Click to expand...

What generator are you thinking of using?

The Honda 2200 watt (sort of a standard) will probably do the 72V at 28A mentioned. Barely. Using 1/3 of a gallon an hour. So that might equal as much as 120 mpg....if you can hit your 40 mph target. For 200 mile range, that's 5 hours runtime. And will use about 2 gallons of fuel.

I ride a BMW R1200, not exactly comparable, but get at least 50 mpg at 60mph. So OK, I will burn 4 gallons vs. 2. But if you want to go 40-50, a smaller displacement motorcycle will likely match your fuel burn.

Why? There are inefficiencies in conversion. Fuel runs an engine, the engine powers a generator, the generator might power the electric engine directly, or worse charge a battery, that later powers the electric engine. The motorcycle in more direct fashion, turns the fuel into distance/range without intermediate steps.

It's likely possible with a clean sheet you could engineer a hybrid motorcycle to do 40 mph at 120 mpg. But to do it with off the shelf components, generator, battery, eBike motor and controller isn't probably possible, especially when you add in the trailer. Unless the trailer is necessary for "cargo", but if you need cargo a motorcycle rack won't carry....then all bets are off.

If you don't have cargo, and like to tinker, you're better off skipping the battery, skipping the trailer. Use a motorcycle frame and engine to drive a generator, that directly (or if necessary via a small battery), powers a hub motor. But this isn't an off the shelf kinda project. And it won't probably beat the fuel efficiency of a standard motorcycle.

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the price of a inverter gen and the fact that electrics means its an ebike by law, so no insurance, registration, and rules... Which is exactly what i need. Its worth the efficiency losses in gold. There is no trailer... The generator will be on the bicycle. I didnt buy it yet, but I might modify the frame with my welder to make it work.

bike4life said:

the price of a inverter gen and the fact that electrics means its an ebike by law, so no insurance, registration, and rules... Which is exactly what i need.

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It's fortunate that there's no law covering 30, 40, 50mph ebikes where you live. :thumb:

E-HP said:

bike4life said:

the price of a inverter gen and the fact that electrics means its an ebike by law, so no insurance, registration, and rules... Which is exactly what i need.

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It's fortunate that there's no law covering 30, 40, 50mph ebikes where you live. :thumb:

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I mean my 30 and 40mph ebikes that i built from batteries, (making this one to get 200 miles range), have never got in trouble with the law. I live in NJ. When your on the shoulder on the highway doing 35mph, 40mph, and the speed limit is 55 and people are doing 60mph, its kinda hard for a cop to notice... Also, in court or what not you would win... Yes mr. police its a 750w ebike, meets the law... Are you going to pull out a clamp meter and do some ohms law trickery to get my true power... Yes it was doing 20mph but I was also pedaling at 15mph, making me go 35... Are they going to say no because wind is the cube of velocity.... They usually dont care and are fine.

so i guess the consenus is to run 72v at like 28 amps instead of 96v at 20 amps?

No, as constantly stated everywhere, the higher voltage will get you higher top speed.

But there is also no "consensus" that you will be able to accomplish your goal.

Do please keep us updated