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Question about battery for Ebike

Posted: Mar 31 2019 5:31am
by Vikingimike01
Hey forum! I'm new here, got sent from a different forum, to ask here too.

I'm planning on building a 5000 watt, hub driven, electric bike. It's a complete kit you can buy from ebay:
https://www.ebay.com/itm/E-Bike-Hi-Powe ... 0995258460

Now, this kit does not include a battery. So I have to get one. I'm not experienced with electrical systems.

I have two main options:

Get 2 72v batteries, that are 15ah, and 30A max output, and wire them in parallel:
https://www.ebay.com/itm/72V-15Ah-Ebike ... 4164384436
This would be the cheaper option by far. And it would be a total of: 72v, 30Ah, 60A max continous output.

Or, get one complete pack:
https://www.ebay.com/itm/72v-30Ah-LiFeP ... 2269099747
This would cost me 300 USD more, because of shipping mainly. And, it would be 72v, 30Ah, but only 50A max continous output.

Now, the motor I am planning on getting needs ~80A, but not sure, if that means peak. I'd be more than enough with 60A though, but just asking, because that option is cheaper, and looks stronger.
Wich one would you guys suggest me to get? Why? Thank you!

Re: Question about battery for Ebike

Posted: Mar 31 2019 8:00am
by dogman dan
Well, the first rule is that amps they say the battery can handle,,, It can't handle that really.. Oh sure it can, as its dying. So the first rule is to keep that battery you spent a fortune on, if it says 50 amps discharge, you better keep it down to 25 amps most of the time. And keep that 50 amps down to a minimum, by using less that full throttle till you are going 15 mph or more.

And your controller in that kit,, it can do 120 amps.. See where this is heading? You simply cannot easily carry enough battery to run that thing, if a 20 ah pack can really only discharge 30 amps or so. You'd need 4 of them, and each one is like 20 pounds or more. Just as a test, put 80 pounds on your bike and try to ride it. Oh,,,, more like 100 pounds, your motor will weigh about 25 pounds.

So how do people do this, with the big motor? A different, more dangerous to use type of battery. RC lipo, same as they use in big drones. Hobby king is a good source. This is more DIY, and requires some education on your part to use, but this type battery can handle 120 amps, from a 15- 20 ah pack. Which will weigh a lot less than 40 ah of the other kind.

Re: Question about battery for Ebike

Posted: Mar 31 2019 9:24am
by 2old
You didn't indicate what your experience is, but if this is your first build, you're in for a big surprise. Only way to be successful is to learn from one of the experts in fast conversions (like Mad Rhino). Better choice is to build a 30-35 mph bike, which can still use normal bike parts, with an inexpensive 1000w, 48V rear hub motor and 52V battery.

Re: Question about battery for Ebike

Posted: Mar 31 2019 10:46am
by MadRhino
This motor is for RC lipo, or a big bunch of the best round cells. Battery need to be able to supply much more than controller setting.

5000w is continuous power rating, meaning it can run non stop for years on a bench when fed 5kw. The peak it can take is very high. Let’s say 20kw acceleration bursts are safe to feed.

Re: Question about battery for Ebike

Posted: Mar 31 2019 12:14pm
by markz
Humans using less throttle is like telling a crack head with a pile of crack in front of them, to not use it all, but just use a small amount.

Vikingimike01
ES member Icecube47 did a whole wack of testing on the Hobbyking LiPo's and the conclusion was that perhaps 10% were duds with testing.
Also, Hobbyking LiPo's are to be derated, you see 40C, its 20C.


dogman dan wrote:
Mar 31 2019 8:00am
by using less that full throttle till you are going 15 mph or more.


Hobby king is a good source. This is more DIY, and requires some education on your part to use, but this type battery can handle 120 amps, from a 15- 20 ah pack. Which will weigh a lot less than 40 ah of the other kind.

Re: Question about battery for Ebike

Posted: Mar 31 2019 1:09pm
by Vikingimike01
Hello! About the batteries, thats the continous output they can handle.

I have experience (Not with electric) because i had a 66cc 2 stroke bike kit before, i went 60km/h on that, but its too much maintenance, and fuel is getting expensive, so I'm selling that. Had it for more than a year. The max output the batteries can handle (The chinese 15Ah ones, that I'd get two of) is "Peak Discharge Current : 75A" And I'm getting 2 of these. Wire in parallel. And then, if I do go with this one, later on I can get a third when I have the money, and wire that in parallel too. That would be pusting 90A max continous. Motor needs 80.

Also. This kit can go up to 95km/h. I'm planning on using it at 40-50 AT MOST. I will most likely pedal to get up to speed. And won't be doing any sick stunts, i like a nice, comfy, slow acceleration.

Re: Question about battery for Ebike

Posted: Mar 31 2019 1:21pm
by donn
Vikingimike01 wrote:
Mar 31 2019 1:09pm
I will most likely pedal to get up to speed.
This I have to see, to believe. The setup couldn't weigh less than 50 kg, likely a good deal more.

Re: Question about battery for Ebike

Posted: Mar 31 2019 1:36pm
by larsb
70A is needed to get you that 5000W at 72V and that shouldn't be a problem for a good 18650 pack of 72V20Ah, they would be 20s8P - many batteries that can do 10A these days.

I'd still buy something else than this kit if you're looking at going 40-50km/h, you'd be better off with a smaller kit.

Re: Question about battery for Ebike

Posted: Mar 31 2019 1:57pm
by Vikingimike01
larsb wrote:
Mar 31 2019 1:36pm
70A is needed to get you that 5000W at 72V and that shouldn't be a problem for a good 18650 pack of 72V20Ah, they would be 20s8P - many batteries that can do 10A these days.

I'd still buy something else than this kit if you're looking at going 40-50km/h, you'd be better off with a smaller kit.
I am not planning on needing all that 5kw. And I'm not going to make a package myself, too much hassle, and yeah... I would rather just buy one done.

I am getting two packs of them wich would make 72v and 60A continous, 150A peak. and 30Ah. I need the power, not the speed. As I'm a big dude, and the place I live is basically like hilly (I live on a mountain kinda)

Re: Question about battery for Ebike

Posted: Mar 31 2019 8:02pm
by MadRhino
Vikingimike01 wrote:
Mar 31 2019 1:57pm

I am not planning on needing all that 5kw.
Nope. You are planning to need much more. You just don’t know yet.

Re: Question about battery for Ebike

Posted: Apr 01 2019 3:09am
by Vikingimike01
Yet. I'm getting an other one of those batteries when i have the money :)

Re: Question about battery for Ebike

Posted: Apr 01 2019 4:13am
by larsb
For hilly riding, fat guy and low speeds a hubmotor is not be the best since only way to gear it down is using smaller wheel. Mid drive would be better in this application.

Then you can buy a motor and adapt the gearing, it's much easier to get it correct since it's your first build.

Re: Question about battery for Ebike

Posted: Apr 01 2019 11:34am
by Vikingimike01
Sorry, I'm not going to get anything other than hub drive. I had enough of chain bullshits FOREVER. Because of my 2 stroke 66cc!!

It will be a 4.0 fat tire bike.

Re: Question about battery for Ebike

Posted: Apr 01 2019 12:58pm
by Chalo
There is nothing wrong with chain reduction, which is used for lots and lots of reliable equipment. You can't draw useful conclusions from shoddy stinking gasbike garbage that should never have been manufactured to begin with. You may or may not need chain reduction to do what you want, but it can be done right.

You have selected the wrong motor, the wrong batteries, and the wrong wheel size for what you're doing. It's the wrong amount of power and speed for a pedal fatbike.

If you haven't ordered stuff yet, don't. Read more and try to make a better match between your performance requirements, your motor/battery system, and your bike.

Re: Question about battery for Ebike

Posted: Apr 01 2019 12:59pm
by larsb
Sorry, I'm not going to get anything other than hub drive. I had enough of chain bullshits FOREVER.
Ok, understood, then go for a belt drive 8)

Or the small wheel hub motor.

Re: Question about battery for Ebike

Posted: Apr 01 2019 2:55pm
by Vikingimike01
Oof. I'm going with the hub motor. The guy told me it will be plenty enough. And, there are good flats where I live, long streets, where there is basically no traffic (Kinda like a dirt road) but when I go to school I'm going up/down the mountain. It's not like a full on mountain, but at least a 30 degree incline.

Re: Question about battery for Ebike

Posted: Apr 01 2019 5:16pm
by Chalo
Vikingimike01 wrote:
Apr 01 2019 2:55pm
It's not like a full on mountain, but at least a 30 degree incline.
No. It might feel like that, but 30 degrees is a 58% grade-- almost twice as steep as the steepest paved streets anywhere in the world.

You will need to have enough power to climb whatever hills you face at more than half of your top speed-- the faster, the better. Otherwise you risk burning up your motor very quickly.

You would be doing yourself a big favor to find a motor that makes a lot more torque per amp than the one you found so far. The 15 year old hub motor I use in my cargo bike makes more than 2-1/2 times as much torque per battery amp as the one in your eBay link. Surely there are many motors available that would make a better match to your riding conditions and to the batteries you're looking at.

Remember, for any given amount of power, the slower the motor's top speed, the more efficiently your bike will climb hills. Better efficiency means more range, but more importantly, less heat.

Re: Question about battery for Ebike

Posted: Apr 01 2019 7:31pm
by E-HP
Chalo wrote:
Apr 01 2019 12:58pm
If you haven't ordered stuff yet, don't.
Reading this and a few other recent threads, it's looking more like the forum isn't being asked to advise on a future decision, but to validate/affirm a decision that's more or less been made, which is fine. Regardless of how sage the advice is, there's something about using your own experience or mistakes to get there, and many folks need to go through that process before skipping to the answer.

Hopefully we get to see the results in a future build thread.

Re: Question about battery for Ebike

Posted: Apr 01 2019 9:02pm
by e-beach
@ Vikingimike01,

Welcome to ES, the worlds biggest e-bike fraternity where we act like frat-boys, albeit with lots of e-bike experience.

You haven't posted anything about the type of bike frame you plan to put your big battery on. I always recommend that e-bikes should have the battery in the triangle of the bike for optimum balance, but with a battery your size, that is not possible.

Where do you plan to put the battery?

As for the kits you posted links to, they would work. I would learn how to monitor the heat to your motor and controller and battery so you don't burn them out accidentally.

The relatively inexpensive generic batteries you posted won't give you anything like the maximum amps you would like to have, especially going up that steep hill. I prefer LiFePO4 for it's stability, but it is not as energy dense as other lithium chemistry's, which is why LiFePo4 batteries are big. The need the size to make up for their relative inefficiency.

If you really want to take advantage of the motor you are considering, you need Li-ion, or Lipo.

Make sure have a safe place to charge your batteries in case of fire.

Also, do not have delusions about e-bike maintenance. e-bikes always need something adjusted.

:D :bolt:

Re: Question about battery for Ebike

Posted: Apr 02 2019 10:58am
by Vikingimike01
Thank you! I am going to carry my thermometer around then.. Just kidding!

But, I'll pedal too. Anyways. Should I get like a temperature sensor or something?

Also. The chinese 2 batteries I'm planning to order are Li-Ion with 60A total continous (150 max)

370mm*125mm*70mm and I'll have 2 of these. Will put like some kind of foam around it. Also it can get quite cold here in the EU sometimes so I don't think the motor will overheat that much. But still don't want it to! :D

I'm getting a 26" fat bike, steel, hydraulic front and back brakes, 4 inch tires, 1080 lumen front light, red generic bicycle back light, and a nice comfy foamy leather seat (That I will make)

Re: Question about battery for Ebike

Posted: Apr 02 2019 8:13pm
by e-beach
I wouldn't worry about a temperature sensor yet. Just get to know your bike and your riding conditions. If your motor or controller are too hot to touch, then they are too hot.

Try to put your battery in the triangle of your bike frame. If it is not possible, then in panniers so the weight is low. If you put your batteries on the rear rack, your bike will be unstable.

Post some pictures when you have it done. Just keep the file size under 512k for easy uploading.

:D :bolt:

Re: Question about battery for Ebike

Posted: Apr 03 2019 6:26am
by marcelo56
attention width of the motor. drop out fat bike = 175mm +/-. your engine 5000 watt = 155mm

Re: Question about battery for Ebike

Posted: Apr 03 2019 8:42am
by E-HP
Vikingimike01 wrote:
Apr 02 2019 10:58am
I'm getting a 26" fat bike, steel, hydraulic front and back brakes, 4 inch tires, 1080 lumen front light, red generic bicycle back light, and a nice comfy foamy leather seat (That I will make)
Might want to check with the vendor about how much clearance you'll have before ordering the rear caliper. I got lucky on my recent conversion to discs, and have 0.5 mm clearance, with a mechanical caliper.

Re: Question about battery for Ebike

Posted: Apr 03 2019 11:04am
by Vikingimike01
Yeah, I'm currently looking for a bike with 155mm dropout.
Or at most 1cm over or under that, but steel frame, so I can bend it a little with a bolt.

Re: Question about battery for Ebike

Posted: Apr 03 2019 11:47am
by Chalo
Vikingimike01 wrote:
Apr 03 2019 11:04am
Yeah, I'm currently looking for a bike with 155mm dropout.
Or at most 1cm over or under that, but steel frame, so I can bend it a little with a bolt.
To my knowledge, the frames in that width range are set up for through-axles. Frames with normal dropouts have mostly 135mm spacing, and 170mm is a relatively common fatbike spacing.

Jacking your frame wider or narrower with a screw thread is a recipe for a crooked frame, because most frames have differences between right and left chainstays that will cause one side to bend more than the other. Have a look at Sheldon Brown's method, because I think it's the easiest way to do it right:
https://www.sheldonbrown.com/frame-spac ... #spreading

After you get the spacing you want, a bike shop can check whether the dropouts are parallel, and make corrections if necessary. This is a very good idea regardless, because many brand new bikes have crooked dropouts.