8fun kit performance

[FJJ]

Hi,

After the freezing weather clearing up I've had a good chance to test out my new 8fun kit (build described in http://www.pedelecs.co.uk/forum/electric-bicycles/10313-8fun-conversion-new-carrera-subway-hybrid-bike.html ) and I notice that it doesn't seem to have a huge amount of power compared to my old 24V Urban Mover...

I attached the throttle and it runs at about 16mph unloaded (e.g. on the work stand or upside down) I can get about 13mph out of it on the flat but this substantially drops off if there is any gradient), thats without pedalling. On 'high assist' there is nowhere near as much power as I got from my Urban Mover on 'high assist'. Battery life does seem good though, after 15 miles there was just one LED out.

Could it be poor power connections, or maybe the gauge of the included cables is too small? The power connectors are using bullets are they maybe not up to the job??

The controller is the potted one so doing anything to it is not really an option!

Thanks,
F

 

[NRG]

I would have expected the unloaded wheel speed to be around 20mph, what is the battery voltage? On some controllers theres a link/wire that needs to be removed to get the full speed....cant recall the thread where this was mentioned...or if your controller would have this. Did the motor come pre-laced into a wheel? Just trying to eliminate a motor ~ wheel mismatch in RPM...

 

[FJJ]

I would have expected the unloaded wheel speed to be around 20mph, what is the battery voltage? On some controllers theres a link/wire that needs to be removed to get the full speed....cant recall the thread where this was mentioned...

Hi NRG, it's a 36V 9Ah bottle battery. The controller doesn't have any obvious external jumpers / switches etc that may need linking / unlinking and as it's filled with silicone like potting compound I doubt anything could be changed internally.

 

[NRG]

OK whats the measured voltage fresh off charge? Did the motor come pre-laced into a wheel? Just trying to eliminate a motor ~ wheel mismatch in RPM...

 

[FJJ]

It was charged yesterday after a ride and it's now reading 41.7v on my multimeter. The motor was supplied by 8fun pre-laced into a 26" wheel.

 

[Deleted member 4366]

How many amps does it say on the controller?
Did you take the end-plate off the end of the controller to see it full of silicone or can you just see it from the outside? Is it possible to get at the shunt, which is normally at the opposite end to the wires?
The speed restriction (when available) is a pair of single wires, normally 3 or 4 inches long, that are connected together via a single connector.
Does it climb hills as good as your Urban Mover or is it gutless?

 

[x332race]

I have recently fitted an 8fun motor to a Marin Mount Vision and I have achieved speeds of around 17-18mph on the flat (measured by gps) This slows on hills depending on gradient. Something does not sound quite right with your kit.

 

[FJJ]

How many amps does it say on the controller?
Did you take the end-plate off the end of the controller to see it full of silicone or can you just see it from the outside? Is it possible to get at the shunt, which is normally at the opposite end to the wires?
The speed restriction (when available) is a pair of single wires, normally 3 or 4 inches long, that are connected together via a single connector.
Does it climb hills as good as your Urban Mover or is it gutless?

Hi d8veh, it says rated to 6A; 13A max. It's actually just a gasket at the other end so I can get at what appears to be the shunt - pics attached.

It does appear to be a bit gutless, hill climbing ability doesn't seem as good as the UM was.

Thanks for the help folks

 

[Scottyf]

Same controller as my old kit. Best to add some solder to the shunt to help it up to 15-17amp.
An as d8veh says check the speed wire loop. I would suspect it's the low amp controller not dishing out enough power for your needs.

 

[Deleted member 4366]

13A max is the problem. I suspect that they've down-graded the controller for the lower rated bottle battery.
Start by adding solder up just the leg of the shunt to the bend. Be careful that blobs don't fall through the pcb and form on the underside, so It's best to turn the controller on its side. It would be better if you had some sort of watt-meter so that you can see exactly the effect. Try and get a bit more power than your Urban Mover. The speed of your new bike will probably be about 17-18mph and won't go any faster regardless of power. Only the acceleration and climbing power will be improved. Don't be greedy and go for too much - I wouldn't solder more than half the shunt because it will put too much strain on your battery.
Let us know how you get on.
Don't worry when the motor makes a bit more noise. The fact that it's quiet now seems to indicate that it's running low amps.

 

[NRG]

yep, 13amp is not enough and you can solder the shunt in stages to drive up the current but it wouldn't really account for the very low speed. The battery should be around 42v hot off the charger so you are more or less there...either the controller has been setup incorrectly at the factory, the throttle is not outputting enough voltage to the controller or they have laced a low RPM motor into the 26" wheel...

 

[wurly]

I would have thought the rpm will be 185. It will be the last 3 numbers on the casing. I have one on my wife's bike running on 36V, it tops out at 14-15mph.

 

[FJJ]

It's pretty gutless on both throttle and pedelec so I don't think it's the throttle. I'll have a look at the markings on the motor tomorrow and have a look at soldering the shunt to give it a bit more erm...grunt.

Thanks for all your advice folks, much appreciated.

 

[NRG]

The throttle and Pedelec inputs are separate, on some controllers like the LDZS ones the throttle is a couple of MPH faster so it still may be worth checking the output voltage. The gutless feeling is to do with the low amps, the low speed may be due to a low input voltage from the throttle. It's worth checking.

 

[Scottyf]

If you have a speedo you could try test how fast the no load speed is and report back. This should give us an indication of what the potential problem is.

However I know having that controller on my 250w build that it wasn't enough. An I'm 26 and fairly fit. To the point where the added weight and type of riding I was doing it would slow me down. Unless I slowed down with it and let it take over more of the effort.

There will be some simple fixes we can do to help you on your way. Do not lose hope just yet...

 

[NRG]

16mph unloaded in the first post....



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[x332race]

Sorry but I am a bit of an ignoramus when it comes to things electrical....what is the "shunt" and why does adding solder help?

 

[FJJ]

Looks like it is a 185rpm motor, despite the big green "26" sticker on the hub...

I will drop them an email and see if it can be exchanged for a 201rpm one - fingers crossed!

Pic attached showing the model number.

 

[flecc]

Sorry but I am a bit of an ignoramus when it comes to things electrical....what is the "shunt" and why does adding solder help?

A shunt is a high precision resistance which allows large currents to pass through it. Often in the form of a metal rod or bar, the small voltage drop across it allows large currents to be accurately measured and therefore controlled. In the photo below from a previous post by a member, the shunt rod is in the foreground, marked as sensor, and extra solder (arrowed) has been added to one end to reduce the resistance across it. This increases the permitted current measure (click to enlarge):

 

[x332race]

A shunt is a high precision resistance which allows large currents to pass through it. Often in the form of a metal rod or bar, the small voltage drop across it allows large currents to be accurately measured and therefore controlled. In the photo below from a previous post by a member, the shunt rod is in the foreground, marked as sensor, and extra solder (arrowed) has been added to one end to reduce the resistance across it. This increases the permitted current measure (click to enlarge):

Thanks for that!