newbie question - battery amps vs voltage

With lithium batteries, are they all the same apart from the different amps and voltage you can get?

do higher amps give a longer range on your ride?

and does higher voltage mean higher top speed?

also is the voltage a rough indication of the top speed? I was told 72v battery would be top speed roughly 70kph

Or does it just depend also on what the controller pumps through to the motor?

ive read http://www.ypedal.com/rant/rant.htm ..
so i know..

Volts x Amps = Watts

Volts = Speed, higher voltage means a higher top speed. *( rpm )

Amps = Power, determined by the " controller ", bigger hose flows more water..

edited: still editing it.. to try make it clearer

Watts are the ultimate determinate of range, then you have to calculate aerodynamic and inefficiency loss into the equation.
The best test is a real world test.

Voltage does directly effect top speed, however the faster you go, the more amps you need to sustain high speeds, so a super high voltage with a meager level of amps will get you a low speed.

In layman's terms, volts are like horsepower and amps are like torque. An engine needs a good balance of both to perform well.

And every motor will go a different speed given a different level of voltage. My old geared hub motor would do 18mph max on 36 volts.. my new, and much larger geared motor will do ~28mph max on the same voltage, but it requires more amps to do the same job.

So the better question is.... what are you going for exactly? a certain speed or range?

Watts are horsepower... 745.7W = 1hp, to be exact.

Watt-hours (energy) determines range.

Changing voltage at the motor changes motor speed: higher voltage, higher rpm.

More amps will provide more torque.



Edit: removed landmine. ES remains independent.

both really, range and speed..

between 60-80 kph speed would be fine for me i think..

range.. im not sure what i would need.. at least 30k though 60k would be better... That is 30-60k, on the battery alone. I know range depends on lots of things.. peddling.. hills.. tyres..

i was told by Hyena a 10ah battery would last 30k at 60kph. So I thought doubling the amps might double the range.. but if it increases the torque thats fine also.

so if watts determins range... and watts are just amps * voltage, if you increase either amps or voltage in your battery you should increase range..?

Doubling the amps with the same amp-hour battery will give you half the half riding, but you will be going faster, so not half the range.

Motors act like generators. The faster they turn, the higher the voltage. The amount of current going into the motor (torque) is proportional to the difference between the battery voltage and the motor voltage. The motor stops helping you when the motor voltage and the battery voltage match. Thus, the higher the voltage of the battery, the faster your motor can turn.

Motors have different windings. A "high torque" winding (number of turns of wire in the coil) will give you more torque for the same amount of current, but will also raise the motor voltage for a given speed. You will have high torque with low speed, but it will drop of quickly.

A "high speed" winding will give you less voltage for a given motor speed, allowing you to go faster prior to the speed where the motor no longer helps you.

This is a slight oversimplification, as your actual cruising speed is where the forward force from the tire matches the other forces (air resistance, rolling resistance, and the hill). The force is from the current going through the motor.

hekdude said:

Doubling the amps with the same amp-hour battery will give you half the half riding....

Click to expand...

?

So.. what would be the range and top speed with a 72v battery with 10 amps, 15 amps and 20 amps?

brisbanebikie said:

so if watts determins range... and watts are just amps * voltage, if you increase either amps or voltage in your battery you should increase range..?

Click to expand...

It depends, if you increase your amp limit and you're still crusing at only 10-15 amps, your power usage will stay the same.
If you increase your voltage, your speed will increase, and aerodynamic drag will increase, and you will use more amps as a result. Hence, your wattage will increase due to the higher voltage and amperage.

At 70kph ( 43mph for us 'mericans ), you are going to see a lot of aerodynamic drag. You will want to wear goggles for example!

On 36v, on flat ground, i get about 10 miles ( 16km ) out of each 5 amp hours, drawing around 12amps average the entire time. That's traveling at about 24mph avg. ( 38km/h ).

On say, 72v, you will be traveling almost twice as fast, but drawing quite a few more amps constant due to aerodynamics loss.
Let's say your amps increase by 50% to go that speed, due to aerodynamic loss.

Without the aero loss, you would go 32km on 5 amp hours.
With the aerod ( 50% loss ) factored in, you will go about 24km on on 5 amp hours.

So on 15ah, 72v, you should ( theoretically ) have a range of 72km.

However, a 15ah 72v pack is huge and quite heavy really.

Mind you, these are approximations.

The best way to know is to jump into it and do the tests yourself.

neptronix said:

However, a 15ah 72v pack is huge and quite heavy really.

Click to expand...

do you know the weight differences for 72v 10, 15 and 20 amps?

The prices vary quite a lot.. I was quoted around au $2000 for a 72v 10ah complete kit, 15ah battery: $2500, 20ah battery: $2900

If I can afford it I might go the 20amp option, unless it is way heavier... It seems it would increase range, acceleration and torque..

brisbanebikie said:

neptronix said:

However, a 15ah 72v pack is huge and quite heavy really.

Click to expand...

do you know the weight differences for 72v 10, 15 and 20 amps?

The prices vary quite a lot.. I was quoted around au $2000 for a 72v 10ah complete kit, 15ah battery: $2500, 20ah battery: $2900

If I can afford it I might go the 20amp option, unless it is way heavier... It seems it would increase range, acceleration and torque..

Click to expand...

Depends on if we're talking about lifepo4 or lipo / li-mn here.

The ping batteries are a good example of lifepo4 weight; 8.2lbs for a 36v 10ah pack, double that and you got 16.4lbs or 7.4kg for a 10ah 72v pack, thus a 20ah pack would weight about 14.8kg.

10ah of 36v lipo would be about 6lbs.. 12lbs for 72v, thus 5.4kg .. so 72v 20ah lipo would weigh about 10.8kg.

I'll tell you this though. I don't know how you'd fit 20ah of 72v lifepo4 on a bicycle. It would involve some interesting fabrication. Or maybe a trailer.

Check out some 72v builds on these forums, i suppose.

Perhaps a bit of confusion between amps and amp hours? Both are in the battery specs, so you can end up mixing em up in your mind.

Volts, in general a motor will turn a certain speed at a certain voltage. More volts, more top speed.

Amps, the rate the power flows into the motor determines how quickly you get to top speed, and can affect how steep a hill can be climbed.

Volts x amps = watts which is the horsepower. So more amps or more volts can increase total power.

Here is where it can get complicated in the real world. You can have bikes of the same wattage that perform quite differently because of the different volts or different amps. A 72v 20 amp bike will be different from a 36v 40 amp bike. Then add different motor windings, and it can get even more complicated if one bike has a fast winding and another one a slow one.

Back to the battery itself. It's size is often measured in amp hours, but it also has a spec for the discharge rate that is in amps. The classic way to keep this straight in your mind is the water analogy. Amp hours is the size of a barrel. Amps is how fast you can empty the barrel through a hole in it.

So more amps makes you able to use a controller that pours the power out faster. More amp hours allows you to pour out that power for longer. Because some batteries have a low amp specification, a large size can also allow more power to flow faster. This is why we tend to recomend some batteries in a size at least 15 ah, so you can get 30 amps out of them without wrecking them.

Other batteries can handle much faster discharges, and might be able to put out 30 amps in a 5 ah size easily.


To make your choices start by looking at the kind of ride you will do. Dirt or Street? Hills or flat? Long or Short? Fast or Slow?

Then you determine what motor and controller will do what you want. Then and only then, can you make a battery decision. Once you know the kind of motor, and the amps and volts will get you the speed you want, or the hill performance you want, then you can start looking at what kind of battery will feed that bike.

The typical commute choices are easy. For 15-20 mph, a 300-400 watt gearmotor and a 10 ah battery is usually good. For 20-30 mph, then a 500-1000 watt direct drive motor and 15 ah battery usually does the trick. 15-20 miles of range, or more.

brisbanebikie said:

so if watts determins range... and watts are just amps * voltage, if you increase either amps or voltage in your battery you should increase range..?

Click to expand...

As dogman also pointed out, but I will repeat, with just this in a single post

You are getting confused between amps and amp hours

Regarding my specific batteries ( Nano Tech Lipos )

Each battery is 5Ah

Simplifying things ( ignoring losses etc )
that battery would put out
5 amps for 1 hour
10 amps for half and hour
20 amps for quarter of an hour

Batteries have a C rating...that in this case is 5Ah
My batteries can out put 25C constantly till they go flat

so 5 x 25 = 125 Amps


So Ah is the capacity
Amps is the current coming out the battery...controlled by the controller

More Ah...more range
More amps drawn from battery less range
10

Dear god mate, $2900 for a complete kit. I hope thats built onto one hell of a good bike too, $580 can get you a 9C motor kit from a random bike shop on google in Australia, cheaper if you call up Hyena and buy something similar from him. And assuming from your name your in Brisbane, Australia send me a pm and i can help you build up a Lipo battery pack for a fraction of what is left even building some nice battery boxes and soldering everything together wouldnt cost much. $600 would get you 48V30AH, enough for 40-45km/h and a run time of well over 1hr. you could go to 72V20AH but you would need a new controller from Lyen ~$100 shipped with some extra features and that would get you up to 60km/h. A good charger will cost $300 including power supply. Add another $500 onto that to cover all the little things you might need and you will have a e-bike thats a killer

so if watts determins range... and watts are just amps * voltage, if you increase either amps or voltage in your battery you should increase range..? Yes essentially your right if you mean amps=Ah

brisbanebikie said:

so if watts determins range... and watts are just amps * voltage, if you increase either amps or voltage in your battery you should increase range..?

Click to expand...

Others here have mentioned hills. Just wish to stress how much more power this takes. Beyong amps and volts, ya might keep leg power in mind as a third component in range. If ya assist the motor (battery) to shave off some of the peak loads from accelerations and hill climbs yer Wh/km will drop a lot.
Cheers
Lock

In layman's terms, volts are like horsepower and amps are like torque. An engine needs a good balance of both to perform well.

Click to expand...

Horsepower is a unit of energy like watts.
Torque is a measure of the turning force.
Amps represent the rate of current.

bigisland said:

In layman's terms, volts are like horsepower and amps are like torque. An engine needs a good balance of both to perform well.

Click to expand...

Horsepower is a unit of energy like watts.
Torque is a measure of the turning force.
Amps represent the rate of current.

Click to expand...

HM.. I have classically thought of horsepower as being related to maximum speed.
The combination of amps ( torque ) and volts ( speed ) being classified as horsepower ( watts ) has always been a little confusing to me since internal combustion are rated in torque and horsepower.
The torque levels vary greatly, IE you could have a 200 horsepower honda motor with only 130 ft-lbs of torque.
Or a 100 horsepower diesel motor with 300ft-lbs of torque.

I guess i'm wrong, but i don't understand why amps + volts = horsepower, but cars are rated on horsepower and torque.

I will not refer to volts as being similar to horsepower anymore.

Yep you're definitely getting amps and amp hours confused.
What I told you was in relation to amp hours, which essentially translates into range. With a powerful controller and batteries you don't need the extra capacity to get the current like you do with cheap alibaba special 2C cells.

Bluefang, you aren't privy to the dozens of emails brisbanebikie has sent me, he's after more power than you can get from an off the shelf motor and a long range 48v battery. Your prices are a bit off too, good powerful controllers are alot more than $100 and I doubt you'd get a 15ah 48v battery in this country for that price, let alone one double that size (emtb sell 48v20ah packs for $1000). It's ok for those of us who are experienced ebike DIYers to build stuff ourselves but for a guy like this who is asking these sort of questions it's like a guy walking into a car dealer and asking for a hot rod and them handing him a box of big pistons. What I offer is a hand made, noob friendly plug and play kit. It's deceptively time consuming to modify motor and controllers and hand make batteries, wiring looms etc and I'm not going to do it for Chinese rates.

That said, please don't take the above as a rant

Oww but i wana see some KFF. Sorry i just assumed he was after normal power but going fast, if he is after something more then a basic 9C can do then your price sounds right specially going to bigger controllers Sticking my head in where is doesnt belong lol

Derek

1 horsepower = 745.699872 watts

Hyena said:

Yep you're definitely getting amps and amp hours confused.
What I told you was in relation to amp hours, which essentially translates into range. \)

Click to expand...

yea.. i thought ah was just another way of writing amps...