What does "AH" stand for and its purpose?

[lifeupjimbob]

Looking at batteries on the web and on here i can see People in the form talking about batteries such as;

72v 20AH or 72V 10Ah ect..

Does :72v mean rang/distance? and 10AH=power?

I really want to build a ebike which can only go 15 miles in distance, 20 miles at the most but at the same time i would like it to go 40mph on a flat road, when i say flat road i basically mean a family owned 40 acre field of land.

(My Bike will be used on the following)

...Flat field grass
....not going to climb hills
....40mph speed
...15-20 miles max distance
....My weight 65kg
....bike weight when completed 40kg

Going to use "LiFePO4" 100% not going to use normal lipos, im not experience enough

 

[dogman dan]

Well that's a lot of quiestion, so I may not be able to answer it all. The first thing you should do, is go to Grin Cyclery's website.
Justin has written a very good explanation of the basics, and put it there in the FAQ type pages.


Right now, just a few short version defenitions for you.

AH is amp hours. it's a way to describe capacity based on voltage. so 10 ah of 12v is half as much capacity as 10 ah of 24v.

Watt hours is the way to describe capacity, in a way so voltage does not matter. 100 wh of 12v is exactly the same capacity as 100wh of 24v.

Amps x volts = watts. Amp hours x volts = watthours.

To have 20 miles of range at about 20-25 mph will generally require about 800 watt hours.

To get to 40 mph, with common hubmotors requires 72v, and a 40 amps controller.

72v 10 amp hours is about 800wh, so you need a 72v 40 amps controller, and a 72v 10 ah battery.

Here is the catch 22. Most of the affordable lifepo4 batteries need to be much larger than 10 ah to crank out 40 amps.

So you may need to consider a much larger battery, or modify your desires to about 30 mph.

Battery is where the money goes. Got money?

 

[made_in_the_alps_legacy]

Ah is a convenient information which, linked to Voltage gives you an idea of energy stored :
V x A = Watts (power)
V x Ah = Wh (watt x hours : energy)
The "true" unit for energy should be "Wh"

The reason I see, talking about Ah, is assuming the voltage does not dropp that much during use, and you "pull" a known current from your battery (like the rated current of your controller for example) :

you would just need to divide those Ah per the current you actually use, to have a conservative guess how many hours you could run at this pace.

 

[dnmun]

riding in grass and dirt is much harder than riding on a smooth asphalt surface. there is no need to consider a high voltage pack unless you need high speeds. 36V would give you a lot of range at reasonable speeds.

Ah is the unit of stored charge. when it is delivered to the motor at a specific voltage and rate then that is used to perform work and it is considered energy in the form of Wh watt hours.

 

[spisska]

Have a look at the info at ebikes.ca for more detailed information, but here's the quick and dirty:

* Volts -- voltage will primarily determine the maximum speed at which the motor can turn. The higher the voltage, the faster it can go.

* Amps -- the amount of current, which primarily determines the torque of the motor.

* Watts -- the amount of power being consumed. W = V * A, so a typical e-bike configuration of a 36v battery at 20 amps has a maximum draw of around 1,000W.

* Watt-hours -- a measure of battery capacity that describes how much power can be consumed over time. E.g. a 1 kWh battery can deliver 1kW for an hour, 500W for two hours, 250W for four hours, etc.

* Amp-hours -- a different measure of battery capacity that describes how much power can be delivered over time.

Note that these are all related to each other. Add batteries to your pack, and you increase both voltage and amperage, which by definition also increases the potential WH and AH of the pack.

That said, if I were you, I would very carefully examine your speed goals. Getting just about any bike frame to 20 or 25 mph is no problem. But you can't get around physics, and pushing a bike to 40 mph creates a lot of very dangerous complications.

For one thing, you'll need a lot of juice to hit that speed -- 72V at 40A at the minimum, I'd think, and that's going to be heavy. Second, any forces on the frame (like going over a bump) are going to have a much, much greater effect at 40mph than they would at 25mph. Very few bike frames are specced to go 40 mph while carrying an extra >=25 kg or so.

At that speed and carrying that weight, your frame might just snap, and that would leave you in a very bad way.

Also, have you thought about how you're going to stop? Standard caliper brakes are not going to give you safe stopping distance, and you'll need a better brake system.

For a practical example, my bike's built off a heavy steel beach cruiser, weighs about 45 kg, and tops out at around 30 mph. It feels absolutely safe up to around 25 mph, but frankly, 30 is terrifying, even on smooth, flat pavement.

 

[meanunclebob]

The thing that confuses me is that they don't seem to be consistant across "technologies". Of course I could have misread or misremembered but I could swear that the same ah rating does not mean the same usable power (without killderating the battery) on different battery chemistry.

 

[parajared]

I think it's silly that companies advertise their AH ratings. This one has a zillion ah, this one only has 5ah, who cares; what we really care about is watt hours, how many watts you can send to the motor for how long.

Just to clarify: a 36 volt 10ah pack and a 72 volt 5ah pack are the exact same amount of availible energy and should get you exactly the same distance if your power consumption stays the same.

 

[lifeupjimbob]

Just reading through these comments makes me understand that im certainly talking to the right people for the job in hand, so im extreamly grateful for all the great comments and reply's from the ebike community on Endless-Sphere.

Actually makes me feel safe knowing that people will take time out just to answer these question to a newbie

Personally i can peddle a bog standard bike up to 25mph pretty easily without a motor, do it most days but now that my knees are wearing out with age im just wanting something with a little more power, something to take me out of my comfort zone.

my Budget for a battery is around $500

Thank you to (meanunclebob)... (spisska)....(dnmun).... (made_in_the_alps_legacy)..... (dogman) ...(parajared)
and to everyone else for being so cool with answering question.

Thanks guys

 

[e-beach]

Just reading through these comments makes me understand that im certainly talking to the right people for the job in hand........

Hey lifeupjimbob!

Personally i can peddle a bog standard bike up to 25mph pretty easily without a motor, do it most days but now that my knees are wearing out with age im just wanting something with a little more power.....

A motor will give you more power, but standard bicycles are not designed to go much faster then that. If you want to go faster you will have to modify your bike for safety so your frame doesn't crack apart while you are riding.

my Budget for a battery is around $500

You probably won't be going 40mph on $500 worth of LiFePO4, at least not for long distances because your 40 mph setup would have to be high voltage and low AH for that money. Also your battery chemestry "C" rate probably wouldn't be high enough to handle the amp draw of your controller. It could kill your batter rather quickly....consider lower speeds or consider a different battery chemistry....RC lipo maybe. I run on LiFePO4 because it suits my lifestyle, but it is low "C". RC lipo adds to the "vertical-learning-curve", but can be handled safely if you are diligent. Be sure to charge it someplace where smoke and fire won't do any damage in that rare event something bad happens.

http://batteryuniversity.com/learn/article/what_is_the_c_rate

 

[dnmun]

this guy had some cheap batteries but he may have sold them:

http://www.ebay.com/itm/181148272576?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

 

[lifeupjimbob]

i don't really have any ambitions to run the motor for 15 miles straight at 40 mph,If anything i would probably Just want push the bike to 40mph for about 7 seconds then smoothly take over with some peddling when i decrease the speed back down to 25mp , its just a way of getting a tiny bit of fun out of the build as its only going to be used on private land.

Im going to be using a specially design e-bike frame made of steel, the frame on its own may weigh around 11kg but once all the items are put together on it, im guessing it would be around 40kg, but then my own weight would be 65kg

So
65Kg=143lb
11kg=24lb...

Total (167) in Pounds
Total (76)in kg

The controller i was thinking of getting was either this




I can get a 48v 20ah from here made up http://www.ebay.co.uk/itm/48V-20AH-Portable-LiFePO4-Li-ion-Rechargeable-Battery-for-Electric-BIKE-Scooter-/131166070542?pt=UK_sportsleisure_cycling_bikeparts_SR&hash=item1e8a1b670e

If i do go for a 72v 10ah then i will contact the actual factory it's self instead of worming through dodgy over priced middle men, which sadly seems to be most of the Chinese ebay sellers

what do you all think of that controller ?

 

[lifeupjimbob]

Does anyone know the stealth's battery & controller set up?

i hear its a 72v 18ah, is that correct?

 

[Ykick]

Can't think or offer much about any product choices until we at least know what country, currency, shipping and laws you're subject to?

Is it too much to ask that you update your location with at least Canada, UK or ???

 

[brumbrum]

just to add to the soup of information, you maybe better off getting a geared motor rather than a direct drive motor if you want to still use the bike as a bike. Pedalling against the magnets of a direct drive motor is not too pleasant. Saying that, finding s geared motor that will take the power to get to 40mph unassisted is probably going to be difficult due to the stress on the cogs in the motor. the 6T Mac motor maybe capable... with 72v. ??


btw, Lyen controllers would be pretty bullet proof for your need.

 

[lifeupjimbob]

"Can't think or offer much about any product choices until we at least know what country, currency, shipping and laws you're subject to?"...

Great so How do i fill out my location on this site?

 

[brumbrum]

"Can't think or offer much about any product choices until we at least know what country, currency, shipping and laws you're subject to?"...

Great so How do i fill out my location on this site?

User control panel tab, and then profile

 

[lifeupjimbob]

Thats actually a very interesting point brumbrum!

Something very similar was said on Here a couple of months ago about the peddling being extreamly hard when the motor was off, that must of been what your talking about.

I heard that the mac and geared motors are prone to damages more, is that true?

 

[brumbrum]

If i was going to get a geared motor that was going to be used for lots of amps and volts it would be a MAC motor. They are built with strong inner cogs and you can upgrade the phase wires on purchase that will handle the power you want. They are also easily serviceable and you can get all the spare parts needed if problems occur. you have to take into account the wires coming from the motor as most are only capable of handling so much power and can be quite thin. You could end up up frying standard wires on a motor if you put 40 amps through them.

 

[teslanv]

Thats actually a very interesting point brumbrum!

Something very similar was said on Here a couple of months ago about the peddling being extreamly hard when the motor was off, that must of been what your talking about.

I heard that the mac and geared motors are prone to damages more, is that true?

A Direct Drive HUb has the fewest parts to break. No Gears so to speak. Just wiring that may melt if it gets too hot. Geared hubs on the other hand have clutches and usually plastic/nylon gears which wear out over time. And mid drive systems - even more parts to break...
DD hubs are the only motor that has the ability to "regen" or pump power back into the battery when stopping, but this feature is also a negative when no power is flowing to the motor, are what cause the "cogging" or resistance when you pedal without any power hooked up.

 

[brumbrum]

Also, if you are using for off road purposes, i have found that the thin hall wires become a failing factor(in my experience) as they snap and disconnect easy. best to solder them direct from controller to motor rather than use connectors. i got fed up of hall wires snapping due to such thin wires and i now run with a sensorless motor and controller that does not use them. But that is another story. regen is a waste of time in my opinion as the power gained back into the battery is minimal.

 

[brumbrum]

the mac motor will also give amazing torque/acceleration compared to a DD motor.

If you have the money...

Torque raptor frame, down hill forks and compatible crank. Hope Tech hydraulic brakes and large discs. Mac 6T motor with uprated phase wires which is laced into a top quality fat rim which the mac seller can supply. 12 fet lyens controller and a 72v battery. Battery chemistry would be Lipo, though some knowledge is needed to make and there are lots of wires involved. Maybe go for a Lifepo pack that you know will fit in the raptor frame, maybe a triangle shaped battery pack with most AH you can get. Just my 2 pence worth. It all comes down to budget. some will spend spend spend, many believe in 'the thriftier the better'. You could just buy a scrambler motor bike for same price.

 

[lifeupjimbob]

I May actually try and do that, seems very logical!

have any of you drilled holes into your motor covers to help with air cooling?

 

[brumbrum]

I personally would want to keep my motor water and mud tight, especially in the UK. Maybe different for those living in hot dry deserts.

 

[e-beach]

A very little application of the throttle will alleviate any cogging in a DD motor....I mean a really slight application....almost nothing.

 

[lifeupjimbob]

what if i used a "48V 5kw Brushless Motor Controller"
with a "26' Rear Wheel Motor for Electric Bike 1500W"
Running on a "48V 20ah battery"

would that be a bad idea?