E-Bike Upgrade

[campbell1987]

Hi all, I have this E-Bike

http://www.greencarsite.co.uk/4sale/00124-mountain-bike.htm

I have just finished building a new battery pack for it from old 18650 laptop cells, It originally had a 36v NiMh pack but i replaced that with 2 x 20v packs @ 40v/15AH

Its working great now but it is a heavy bike and with such a low power motor the bike hasn't got much torque and struggles on the hills so i was wanting to upgrade the motor or maybe even add a second hub motor to the front wheel if possible but not sure which would work best,

Also i have a KU65 controller so was wondering is it possible to mod it in any way to make the bike faster, Also thought about upping the 2 battery packs from 5S to 6S so it would be 48v but don't know if the motor could take that without burning out,

If i need to buy a new motor id like to go for something with lots of power/speed for pulling up hills so 48v or 72v would be good but im not fully clued up on all the types out there so thought here was a good place to start,

 

[Alan Quay]

For good hill climbing you need around 20amps at 36v.

The KU65 will deliver 15a to the motor if the battery can keep up. This can easily be upped by soldering the shunt.

My guess is that your home made battery is not giving as much current as you need. What cells are you using, and how many?

 

[Nealh]

For speed more volts are generally needed along with a higher wound hub, more amps will give extra torque for climbing along with a lower wound hub. For a reasonable all rounder you will want to look at about 17 -22amps with a 230 - 260 rpm motor for 36v @250w. Something of this nature should see 20 mph and a bit more with pedalling.
How fast do you need ?

 

[campbell1987]

@Mike Higgins
This is the first pack i made so didn't want to splash out on good cells then destroy them using the spot welder i made, I built the packs using a job lot of old laptop batteries with all different makes and models of cells, each pack has 7 cells in parallel then 5 packs of 7 in series giving 2 x 21v @ 15AH, I wanted to make a bigger pack but was limited by the battery box size, I got a new rear seat post mounted rack for adding more but it is also limited by weight to about 10 - 12kg

Also you mentioned soldering a shunt to the ku65, Can you please explain how this is done or provide a link, Searched the forum and cant see anything on it,

Lastly is it possible to up the voltage to 48V or will this damage the hub motor, I think the ku65 can take the voltage just not sure about the wheel,

 

[campbell1987]

@Nealh
20Mph should be fine, I live at the bottom of a mountain so there are lots of hills here so i think i need more amps, Also can anyone suggest a good source for good quality cells, Lithium Ions or LiPO4, Obviously the cheaper the better..

 

[Alan Quay]

@Mike Higgins
This is the first pack i made so didn't want to splash out on good cells then destroy them using the spot welder i made, I built the packs using a job lot of old laptop batteries with all different makes and models of cells, each pack has 7 cells in parallel then 5 packs of 7 in series giving 2 x 21v @ 15AH, I wanted to make a bigger pack but was limited by the battery box size, I got a new rear seat post mounted rack for adding more but it is also limited by weight to about 10 - 12kg

Also you mentioned soldering a shunt to the ku65, Can you please explain how this is done or provide a link, Searched the forum and cant see anything on it,

Lastly is it possible to up the voltage to 48V or will this damage the hub motor, I think the ku65 can take the voltage just not sure about the wheel,

Ok, so 5s is a nominal 18v. Since you have two, you have a 36v battery. This will measure 41-42v fully charged.

Assuming your cells are 2ah and perfectly balanced, then you have 14ah.

Most can handle 2c, so your battery has the potential for 28a. I doubt it will perform so well in practice. There will likely be a voltage sag, reducing power. (i.e watts).

Before you do anything else, you need some way to measure the current. Search eBay for 'rc watt Meter'. Little blue thing, goes between battery and controller.

Soldering the shunt: Apply solder to approx. 1/3 of the shunt resistor, reducing resistance and fooling the controller into giving more current. You need your watt meter to verify results, and do a bit at a time.

48v probably won't damage the motor, but it will mean that the low voltage cutout (Aka LVC) won't work on the controller, so you will need to manually monitor battery voltage, or use a BMS.

If I were you, I'd do the current mods first, and play with volts later. Most de-restricted/shunt moded systems with decent battery will get you too around 18mph +. Sounds like you need more torque than speed.

Hope that helps.

 

[campbell1987]

Thanks Mike, Ill buy the rc watt meter then try that, Also just to be clear the ku65 isnt the original controller, The original one failed so i replaced it,
http://www.pedelecs.co.uk/forum/threads/powerpac-electric-bike-limp-mode-fault.17267/
I'm no expert on this stuff but i think the ku65 is 48v and the old one was 36, could be wrong though,

Ill post back results after i do tests,

 

[Alan Quay]

....
I'm no expert on this stuff but i think the ku65 is 48v and the old one was 36, could be wrong though....,

Probably a 36v ku65. If it was a 48v the the LVC would cut it out at (IIRC) 41v.

 

[campbell1987]

Yeah pulled it out last night to do the shunt mod and it says on it 24v/36v... I thought it was 48.. I also added thicker wires from the battery to carry more current and then tested it again, Haven't received the rc watt Meter yet but its definitely a lot better on the hill i tested it on but i still think its lacking in speed.....would it be possible to have a 328 rpm bafang bpm2 48v 500w front on bmsbattery, could i add that with its own 48v battery mounted on rear and use it once up to about 15mph to get more speed?? also might help on the hills a bit, I know the 201 rpm would be better for torque but i think with 2wd it would have plenty of power, Also seen people use brushless hub motors as generators so if i was only using the front wheel to power the bike would the rear be charging the battery or would the controller stop this?? If it would could you run wires from motor to battery to bypass motor controller with a switch to enable and disable charge mode and charge battery... Be like free energy.. ;-)

 

[trex]

you can only have regen with direct drive (gearless) motors - these motors weigh a ton and not efficient at climbing hills.
The BPM motor is a good idea but not sure about putting 500W on the front wheel though. There's probably not enough friction to keep the wheel on the ground.Plus you only get at most 80% of what your battery can supply out of the motor. The first step may be to get a better battery.

 

[Alan Quay]

......so if i was only using the front wheel to power the bike would the rear be charging the battery or would the controller stop this?? If it would could you run wires from motor to battery to bypass motor controller with a switch to enable and disable charge mode and charge battery... Be like free energy.. ;-)

No no no no no.

Your battery almost certainly won't power both motors, so you will need another battery, and controller. And another throttle of some kind. By the time you've spent out on all that, you may as well buy a half decent second hand MTB and start again.

As far as low top speed goes, have you got the limit wires connected? that would limit you to 15mph regardless of shunt soldering/battery limitations.

Normally its two single grey wires, joined externally to the controller.

 

[KirstinS]

I overvolt a ku65 to 48v but without a shunt mod

It makes my 250w motor fly

Your battery is simply not up tot ask. Laptop cell are not able to give enough amps 0.2c is standard

I harvest them and use in booster batteries (11.1v) to get from 36 to 48 volt nominal

They don't last long. Maybe 6 months , maybe less before at least one series goes

More torque and Speed will be got from a decent battery than anything else at this stage

Also make sure the Speed wires are not connected as others have said. Mine are white not grey. But they are the only single wire with a connector on a ku65

 

[KirstinS]

Ok, so 5s is a nominal 18v. Since you have two, you have a 36v battery. This will measure 41-42v fully charged.

Assuming your cells are 2ah and perfectly balanced, then you have 14ah.

Most can handle 2c, so your battery has the potential for 28a. I doubt it will perform so well in practice. There will likely be a voltage sag, reducing power. (i.e watts).

Before you do anything else, you need some way to measure the current. Search eBay for 'rc watt Meter'. Little blue thing, goes between battery and controller.

Soldering the shunt: Apply solder to approx. 1/3 of the shunt resistor, reducing resistance and fooling the controller into giving more current. You need your watt meter to verify results, and do a bit at a time.

48v probably won't damage the motor, but it will mean that the low voltage cutout (Aka LVC) won't work on the controller, so you will need to manually monitor battery voltage, or use a BMS.

If I were you, I'd do the current mods first, and play with volts later. Most de-restricted/shunt moded systems with decent battery will get you too around 18mph +. Sounds like you need more torque than speed.

Hope that helps.

You sure about that c rating Mike. I think laptop cells are usually 0.2c ?

I built a 44.4v 12ah pack once and the sag was horrible. Fine on Flat but any serious load and voltage just collapsed

And that was on 200w bike

 

[Alan Quay]

No, not sure. The ones I have salvaged seem to be ok at 1C, and I have pushed them to 2C in my power drill, although I agree you get a lot of sag.

 

[campbell1987]

Lot of replies there.. Thanks all.. Ok i have already got the speed restriction wires disconnected, Also i thought 18650 cells were around 2C each, I will try redesign my pack a bit to see if it helps any, I got a few more good cells so was thinking maybe 2 x 6S to get 48V and this time and instead of 7 cells per pack ill use 12 so it can pull more current, I'll put 1 24V pack in the original battery box and the second on a rear seat post mounted rack.. Also if this new pack doesn't work out and i need to invest in a good battery for it which would be best?? Im guessing LiFePO4 but the price of them is a bit much when im tryin to make a 36/48V 15-20AH pack so i think lipo maybe the cheaper option,

 

[KirstinS]

I I usually look up the specification of batteries I harvest. They are usually 0.2c standard but some times it says to a maximum of 1c

Cheers

 

[campbell1987]

Ok so i rebuilt the battery using heavier cables so now it can draw more current, Now i have 2 x 24v packs 25AH each, also I have done the shunt mod, I was messing with it yesterday and connected one of the 24v packs then applied the accelerator while holding the bike in one spot to see the power difference, Now i think i have damaged something in the controller as the red lights come on my display and show full battery but no drive when accelerator is applied,also i can see scorch marks near the big resistor beside the shunt on the ku65, Would anyone know what might be the problem? Would i need a new controller or can it be repaired?

 

[KirstinS]

Any photos of the controller ?

It might be a blown cap, possibly

My KU65 has 63v caps but I am aware that some have 50v caps. It seems a bit random which you get looking around here and on ES

Can you see what the writing is on the side of the "big resistor" ?

 

[KirstinS]

Have a look here

http://www.pedelecs.co.uk/forum/index.php?threads/Ku65-cap-question-and-amp-rating.19550/

Might help

 

[KirstinS]

Also do you get anypower at the wheel ? I presume not