bought an electric bike without battery, appreciate some battery buying advice .

HI My name is John. I'm 65, disabled because of emphysema , ex electrician. Just bought a second hand Powabike ( cambridge) in very good condition, but came without a battery.

I 'm looking for ideas of what to buy to get the bike up and running. This is my first foray into e bikes, so treating it as a leaning experience.

The previous owner had fitted a 3 terminal female cooker plug to the power input and was using the bike with a battery that he had converted to match the female cooker plug by fitting a male plug to the battery and carrying in the saddle bag.

I saw the bike working before I purchased it, the reason it didn't come with a battery is because the owner wanted to use it on another e bike.

 

.From what I understand the motor is 24v, but the battery he was using was 36v, apparently he has been using this setup for around 8 months and everything was fine.

 

Do I need to get a 24 v battery, or a 36 v ?

 

I'm not looking for maximum range, so what sort of Amp hour should I be looking at , something like 10Ah?

 

I also need the left hand brake lever if anyone can advice on where to get one of these, second hand would be fine.

I'll enclose a photo of the bike if possible.

 

I would be very grateful for any advice.

Thanks, John.

Hi John, it's a Powacycle, Powabyke is another make so best to avoid any confusion.

 

The original Li-ion batteries for these were actually 25.9 volt though nominally 24 volt. Their controllers could handle 36 volt so you could buy either.

 

On a nominally 24 volt battery they are limited to the legal maximum assist speed of circa 15 mph, but on 36 volts they can run to much higher speed, up to about 22 mph in favourable circumstances.

 

Any e-bike battery of those voltages will be ok since their controller isn't very demanding of current.

 

You can buy the specific lower voltage battery for it from Powacycle, but they are rather expensive and you'd have to swap back to the original connection arrangements:

 

Here's the link, scroll down to the Cambridge model for the batteries and charger.

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Edited May 29, 20196 yr by flecc

Hi John, it's a Powacycle, Powabyke is another make so best to avoid any confusion.

 

The original Li-ion batteries for these were actually 25.9 volt though nominally 24 volt. Their controllers could handle 36 volt so you could buy either.

 

On a nominally 24 volt battery they are limited to the legal maximum assist speed of circa 15 mph, but on 36 volts they can run to much higher speed, up to about 22 mph in favourable circumstances.

 

Any e-bike battery of those voltages will be ok since their controller isn't very demanding of current.

 

You can buy the specific battery for it from Powacycle, but they are rather expensive and you'd have to swap back to the original connection arrangements:

 

Here's the link, scroll down to the Canbridge model for the batteries and charger.

.

.

Thanks so much for your fast response Flecc, much appreciated.

I was aware it is a powacycle, just typed the wrong thing!

Thanks so much for your fast response Flecc, much appreciated.

I was aware it is a powacycle, just typed the wrong thing!

 

An added note John. I'm assuming it had a lithium battery since there are few of their old NiMh batteries still in use. I mention it since the chargers are different for each type, so if changing a new charger is needed as well.

.

Yes ,it did have the lithium battery.

I don’t have either a battery or a charger yet.

The original batteries via Powacycle are very expensive, I’m still researching alternatives.

Thanks for your help, much appreciated.

https://bga-reworking.co.uk/product/insat-li-nmc-ebike-battery-10ah-24v-36v-48v/

Try this one if its back in stock they sell out fast cheap and cheerful has 1 year warranty ships tax free from Germany

 

 

www.pswpower.com/ven.php?cargo.2018-9d-q1nb

You can buy those batteries on Aliexpress and EBay. They're standard batteries, not specific to Powacycle. You must make sure that the polarity is correct before you install it. If it's wrong, it's a two minute job to swap over the terminals. Search for silver fish battery, then check the dimensions. They normally come with the locking strip, so a longer one is OK as long as you don't need the seat in its lowest position.

 

You can run with 36V, which will give 50% more power and speed compared with 24V, but there is a downside. Your motor controller is programmed to cut off power when the 24V battery goes below 20V to protect it from damage and fire risk, and any battery level indicators you have are also calibrated on the basis of 29V being full and 20V being empty. If you use a 36V battery, the cut off needs to be at 30V. You therefore need a meter of some sort to tell you what voltage your battery is at. That can be included in an LED control panel or a throttle with battery indicator LEDs. If you don't have either of those, you can wire in a voltmeter. Bear in mind that any of those devices already fitted will indicate incorrectly. If you wait for your 24V LED control panel to indicate that your 36V battery is flat, you'll be looking for a new battery because it won't accept a charge at that level.

 

There's one other potential problem at 36V, which affects any 24V bike that doesn't have a control panel with 3 or more levels of assist. You get maximum power as soon as you start to pedal. That's OK with the low power at 24V, but it can be a inconvenient with the higher power at 36V.

Edited May 30, 20196 yr by vfr400

Thanks for the link peter.c. Unfortunately they appear to be out of stock!

Thanks for the information VFR400, that's exactly the sort of information I am after as I'm keen to learn as much as I can about e bikes.

So, I have now learnt that things are not straightforward with substituting a 36v battery for a 24v battery.

 

You mention :'If you wait for your 24V LED control panel to indicate that your 36V battery is flat, you'll be looking for a new battery because it won't accept a charge at that level. '

Does that mean that if I was to run a 36v , or indeed a 24 v battery below a certain level it would render it unusable? I have had experience of trying to recharge flattened batteries in the past, initially it seemed that the battery would not accept a charge with the standard charger, but when I used a slightly higher voltage for a few seconds, it seemed to kick start it into action, and then would accept a charge using the nominal charging voltage.

 

As I'm new to ebikes, now I have learnt some of the potential issues with using a higher voltage than standard, I think I will go with a 24 v.

 

Now onto another problem I need to find a solution for:

 

As I mentioned, the previous owner of the bike was using a 36v battery fitted in a saddlebag and connected to the bikes existing wiring using a kettle lead.

It appears that the socket that the original battery plugs into has been removed .

I would like to replace this socket to enable a standard sized battery to plug into the socket as the designer intended.

Anyone know what the name of this socket is?

Also, what is 'Silver fish'? I presume it's the style of the battery?

 

Thanks for all your help, very much appreciated by this newcomer.

When you buy the new silver fish battery, it'll come with the locking strip and base-plate. Alternatively you can buy any battery you like and run the wires through, like the previous owner did.

 

Lithium battery cells charge to 4.2v and can be discharged down to 3.0v. You have 10 groups in a 36v battery and 7 in a 24V one. there are two control systems for discharge, which are the motor controller and the battery management system. The Controller is normally set to cut off at 3.1V per cell and the BMS at around 2.9V per cell. The BMS only allows charging when the voltage is above 2.5V per cell for all cells, so if one drops below that voltage, the battery is dead. The control by the controller is pretty reliable, but I've found that many BMSs don't shut off at all, even though they're supposed to.

 

Discharge voltage is not linear. It takes a lot of charge to go from 4.0V to 3.9V per cell, but virtually none to go from 3.0V to 2.9V and even less to get down to 2.5v. basically, the battery falls off a cliff when it gets to 3.1v per cell and accelerates downwards, so as you approach the danger zone, you run to it faster and faster.

 

A 36v battery will be perfectly OK as long as you have a voltage measuring device attached to it like this one, then make sure you're near home when it gets to 33V because there's not much left.

 

https://www.ebay.co.uk/itm/Waterproof-Car-Boat-Car-Motorcycle-DC5V-48V-LED-Panel-Digital-Display-Voltmeter/233122332845?hash=item36472c80ad:m:mOSNiJPUEEHuocBb98esbWg

Excellent explanation , totally understand about about the non-linear discharge curve.

I just wasn't aware of the perils of discharging below a certain level rendering the whole thing unusable though.

So that now explains why it has 4 wires, I presume the 2 larger gauge wires are for the motor controller, and the 2 thinner wires are for the battery management system?

As you can see in my enclosed photo, the previous owner has joined the wires in just 1 pair ! which I presume means there will be no battery management control?

 

So, If I were to buy a new Silver Fish battery it would come with a base plate that engages with the battery base?

No. The battery management system is inside the battery and the two power wires go through it as well as supply the power it needs. Inside the battery are lots of wires, but only two come out of it and go to the motor controller. i suspect that those other two wires are for lights or something like that.

 

As I said, the batteries normally come with the lock strip, base plate and charger, like this one, which is the narrow form, like the photo of your bike above shows. You have to check the fore and aft dimension in your frame to confirm that it's correct.

https://www.ebay.co.uk/itm/36V-10ah-500W-Silver-Fish-Electric-bike-Lithium-Battery-with-20A-BMS-and-Charger/183606519079?epid=25023775803&hash=item2abfcd2527:g:tYcAAOSwQqJbm4ti

 

This one is the more common size 100 mm (fore and aft) x 75 mm (side to side). A charger with the right connector is £9 last time I looked.

https://www.ebay.co.uk/itm/36V-10AH-Electric-Bicycle-18650-Lithium-Battery-Pack-250-350W-E-bike-Silver-Fish/173758130347?_trkparms=aid%3D555018%26algo%3DPL.SIM%26ao%3D1%26asc%3D20140122125356%26meid%3D889744ac3f3945cfae61beee9e9a70b8%26pid%3D100005%26rk%3D1%26rkt%3D12%26sd%3D173758235564%26itm%3D173758130347&_trksid=p2047675.c100005.m1851

I will remove the controller side cover later to see if I can see where the 2 additional wires are coming from, as you mention, they might be for lights.

 

The first battery link you supplied looks perfect for my requirements and I believe it will fit in the space I have ( i need to check later on). I appears that the battery base will screw directly onto the bikes frame too. Just need to check which of the discharge connectors I need.

 

Your help is very much appreciated!

 

btw, do you own a Honda NC30, I wondered if your username relates to you having one? I ride a Ducati.

NC24 with the exhaust on the other side to NC30, plus NT700V and BSA Rocket Gold Star replica.

Nice collection of bikes in your stable. I've always been impressed with those little V4's.

The Goldie was my era , would struggle to kick it over now though lol.

Have ordered the battery possibility suggested by vfr400:

 

36V 10ah 500W Silver Fish Electric bike Lithium Battery with 20A BMS and Charger . I made an offer to the vendor of £180 which was accepted, so saved £20 there.

 

I have now traced the pair of wires emanating from the junction box that join in with the 2 supply wires from the battery. They go to the headlight, which also contains something ( don't know the name ) which I presume is some indication of battery level.

As the indicator of the battery level is designed for a 24 v battery I think I might as well remove the headlight and utilize the wiring which feeds through the frame to supply a DC5V-48V LED Panel Digital Display Voltmeter . I do have one of those 'Lezyne' L.E.D cycle lights which I can use in the unlikely event that I will be riding at night.

 

Can anyone help me with the purpose of the wires ( that have been snipped off ) on my right hand brake lever, they look as if they might be used to switch the lights on/off when the brake lever is used, is this correct?

 

The Wuxing brake levers missing wires are/were for brake sensor cut off.

Re your new battery check the output polarity is correct with a meter before connecting it up, it has been known for them to have wrong polarity wired up.

Thanks for your fast reply Nealh, much appreciated.

 

Is the brake sensor cut off an essential part of the system, or can the bike still work properly without?

 

I shall definitely check the ouput polarity of the battery before fitting!

You'll know whether you need a brake sensor when you start riding the bike. Some older bike's motors run for about two seconds after you stop pedalling, which is not very convenient when you want to slow down to go round a corner. You only need one brake switch. If there are two, they're in parallel, so either one will stop the motor. See if there's one on the other brake.

 

If your pedal assist only has one power level that gives maximum power whenever you pedal, you can add a switch in parallel to the brake switch to disable the motor power whenever you want. That will help when you need to ride slowly.

Thanks for your explanation vfr400. So it's not a brake light switch as I suspected it might be ,but a feedback to the motor control electronics?

My understanding of the 'Pedal assist' function was that there were 'Torque sensors' which calculated how much input torque is being applied to the crank and then amplified this input torque with the electric motor- ie, the more harder you pedal the more power is applied to the motor. Is this only available on more sophisticated bikes and possibly my bike is just a basic start to pedal and full power is applied?

Pedal assist is either cadence predominantly used with hub motors and only requires gently activation for operation, though the Suntour system on Halfords Carrera Crossfire uses their own torque system.

The other is as you mention Torque assist and predominantly used on crank/mid drives and multiplies the input of the user, though with both systems the you can find both sometimes on crank or hub drive.

 

Bafang bbs mid drive uses cadence as does a few other copies.

Tongsheng TSDZ uses a torque system as do all the main oem players like Bosch, Shimano & Yamaha etc ,etc.

 

Kits are available to convert hubs to torque assist if you feel you want to try one.

O.K I believe I now understand the function of the brake switch, thanks to your explanation. It cuts out the power to the motor as soon as the brake is used ( via an internal micro switch I presume, as no micro switch is visible).

 

I have now traced all the wires in the junction box and know mostly where they all go . There are quite a few wires in there, didn't realize e bikes were so complex!

 

There is one pair which has connectors which can be joined together. The connectors were apart when I opened up the junction box. From previous experience I would hazard a guess that the reason for this is to give a choice. Disconnected = one state, or connected = a different state. Anyone know, or could hazard a guess as to what they might be?

Thanks for the detailed information Neilh, very interesting.

I have whilst tracing the wiring, noticed an induction pick up fitted to the frame and corresponding metal pieces embedded in the crank chain wheel, which presumably is used to measure the speed of rotation of the crank, similar to the system which is fitted to motorcycle wheels for A.B.S systems.

 

There is a 'cut out switch' fitted to the handlebars btw.

Blue wires could be speed restriction, throttle restriction, self-learning (detect hall and phase sequence in a new motor) or cruise control (dangerous without brake switches). In all cases, leave them disconnected for now.