Sakura Woes

[neptune]

I met a disabled guy today, pushing a Sakura bike. The LBS told him the motor was kaput, but I am not sure they know what they are talking about. It is in my shed at the moment . I cant find a model number on it . It is a step through with rear hub drive, and V brakes. It appears to be a 36 volt Lithium battery , fitted behind the seat tube. In the bottom of the battery compartment is a male 2 pin plug which is meant to plug into the battery. These pins have broken free and are flapping in the breeze.
A quick multimeter test shows 38 volts on the battery socket where the charger plugs in, but no volts on the output socket. I am wondering if a fuse has blown inside the battery box, but why ? Does anyone know what model the bike is? The owner says it is about 4 years old. Do I have to buy a new battery compartment to sort the pin problem? Any advice welcome.

 

[Waspy]

Is this it?

lithium battery electric bicycle TDR028Z-13 Supplier & Manufacturer

4 years is quite old for a battery, is it not?

In the FAQ on that link, they say they supply replacement batteries.

A new budget priced e-bike might be a better option than a new battery.

Where was the bike purchased originally?

 

[shemozzle999]

Hi Neptune,

Can you id it from their website?

http://www.sakura-ebike.com/category/electric-bicycle-3996-156e/1

 

[Deleted member 4366]

I think this is the part you want.
e-bike discharge plug, 4 pin discharge connector for ebike-Greenbikekit.com online store for electric bicycle components-GreenBikeKit.com

 

[Geebee]

If the pins that it plugs are into have broken away they could have shorted to the frame which would blow any fuse in the battery box, can you open the battery, sounds a bit like there is nothing to lose.
Fix the connector before refitting,

 

[neptune]

Hi guys and many thanks for info.Whilst out riding my own bike, I suddenly realised that the keyswitch is on the battery box. Swiched on, and now getting 38.5 volts out.Doh!. Further investigation will follow. Bike looks generally in fairly good condition, too good to scrap. Will keep you informed of progress, or lack of it.

Update. One thing I have notices is that the bike is just as a easy to wheel backwards as forwards, unlike my old Powabyke, which is very hard to wheel backwards, as it turns the motor.
I did a bodge to bypass the broken connectors, so I can now connect the battery to the controller.
From a standing start, if you open the throttle, you can hear the motor run, albeit not very energetically. However it does not move the bike. So it sounds like a problem inside the hub, and that the LBS was right after all. Having talked to the owner, the battery is probably on its way out, as its range is down to about 4 miles. it is not looking very promising at the moment.

 

[Deleted member 4366]

From a standing start, if you open the throttle, you can hear the motor run, albeit not very energetically. However it does not move the bike. So it sounds like a problem inside the hub, and that the LBS was right after all. Having talked to the owner, the battery is probably on its way out, as its range is down to about 4 miles. it is not looking very promising at the moment.

Plenty of reason to be optimistic. Open up the battery and get it properly balanced before you condemn it.

The motor may be running backwards, especially if someone's been fiddling with connectors. If it has a bolt-on side, it might be worth taking it off to look inside. It could be rust that's jamming the clutch disengaged. If the clutch is ok or you can't get the side off, try the 36 different phase/hall sequences to see if you can get it to go forwards.

 

[shemozzle999]

Another link to Sakura bikes:

electric bicycle, electric bicycle direct from Jiangsu Hi-Tech Lion Vehicle Industry Co., Ltd. in China (Mainland)

And these people might have spares but you need to identify the model first:

http://www.northwestpoweredcyclecentre.co.uk/Spares And Accessories.aspx

 

[neptune]

@d8veh . I have had no experience with lithium batteries, but if the cells were out of balance, wouldn`t the battery management system take care of that? The rear hub does have a bolt on side, so I will probably strip the hub later in the week.
I know that you can not always rely on the word of non technical people, but the owner says that the bike was always as easy to push backwards as forwards. Could any sakura owner confirm this please?
When the motor is running, [but not moving the bike] all the battery lights stay lit, so the battery is not suffering massive voltage sag.

 

[shemozzle999]

Pictures might help.

 

[Deleted member 4366]

@d8veh . I have had no experience with lithium batteries, but if the cells were out of balance, wouldn`t the battery management system take care of that?

Depends on the BMS. It seems to be a common problem that batteries go out of balance if not used for a while and most people chuck them then without finding out why they have a lack of capacity.

 

[Synthman]

Depends on the BMS. It seems to be a common problem that batteries go out of balance if not used for a while and most people chuck them then without finding out why they have a lack of capacity.

I think my battery is slightly out of balance, the BMS doesn't seem to have a balancing function. I know how to open it and measure the individual cells, but what is the method for charging/discharging each cell so they sort of match the others?

 

[Deleted member 4366]

You need a voltmeter to check the cells/cell-groups first to see what's what. You can either bleed the high ones down or charge the low low ones. You can get really cheap cell balancers that will do up to six cells that bleed down, or use a torch bulb (try 4.5v) to do single ones. To charge up individual cells, you can use any 5v charger, like a phone or USB charger, but you must keep an eye on the voltage so that you don't over-charge. You can also use one of those very cheap 3 cell lipo chargers from Hobbyking or Ebay to do up to three at a time.

Whatever way you do it, you need to get to the balance leads that go from the cells/groups to the BMS. If you're lucky, there'll be a multi-pin connector that you can disconnect from the BMS to measure/charge/discharge. You may have to get hold of the matching connector wired with flying leads to charge/discharge cells.

 

[jazper53]

I met a disabled guy today, pushing a Sakura bike. The LBS told him the motor was kaput, but I am not sure they know what they are talking about. It is in my shed at the moment . I cant find a model number on it . It is a step through with rear hub drive, and V brakes. It appears to be a 36 volt Lithium battery , fitted behind the seat tube. In the bottom of the battery compartment is a male 2 pin plug which is meant to plug into the battery. These pins have broken free and are flapping in the breeze.
A quick multimeter test shows 38 volts on the battery socket where the charger plugs in, but no volts on the output socket. I am wondering if a fuse has blown inside the battery box, but why ? Does anyone know what model the bike is? The owner says it is about 4 years old. Do I have to buy a new battery compartment to sort the pin problem? Any advice welcome.

I did notice this one on gumtree

Electric bike for sale in Worthing, West Sussex | Bikes, & Bicycles for Sale | Gumtree.com

 

[neptune]

Sakura-Final Report.
First the battery. I weighed the battery pack today- it weighs 22 pounds, or 10 Kg. So I think it is probably a lead acid battery, although I have not opened the box. I decided to have a look inside the motor hub today. Removing the rear wheel is a bit of a pain. There is no plug and socket to disconnect the wires, so I had to disconnect them at the controller. To do this you need to remove the bottom from the controller housing. One of the screws is behind the chain wheel, so out with the crank puller. I had to deflate the rear tyre to get the wheel out past the rear mudguard. Once I had the wheel on the bench, I needed to remove 6 Allen head screws to remove the hub side plate. They were very tight, and take a very small size allen key. I loosened them first by gripping the screw heads with a pair of pliers. I also removed three philips screws near the axle. This turned out to be a bad move, as this secures the freewheel to the hub side plate.
The freewheel is of the ramp and roller type, and once I had reassembled it, it worked OK. The actual hub problem turned out to be the gears. It looks to have a double reduction arrangement, and the gears, which are nylon, are so worn that they slip. The owner has decided he does not want to spend money on it, so I have put it back together.
One thing I did notice about this bike, is that it is a stepthrough frame , with only one tube between bottom bracket and headstock. With all the weight at the back, this gives handling that can best be described as "flexible".