Sram Battery

[motrax]

I have a bike with a Sram ematic hub. I do not have a battery. I wish to use an after market battery. The Sram hub has an inbuilt controller. There are two fat wires and one thin one from the battery to the hub. The fat ones are obviously the feed wires but what would the third one be for?

 

[vfr400]

I would say that there's a 95% chance that your plan won't work due to handshaking between the controller and battery, which a dumb battery won't be able to to.

You can test for that with any voltage source that matches somewhere in the range of normal battery voltage (22v-29v for 24v battery and 31v-42v for 36v) and can supply at least 1 amp. You can use a lab power supply or a battery charger. You can get chargers for £10 on EBay, which is cheaper than spending £200 on a battery that you can't use.

If it doesn't work, you can sometimes strip the controller out of the hub and use an external one. Personally, I'd prefer to chuck all the electrics and start again, but, to add insult to injury, these hubs sometimes have special torque resistance arrangements that prevent a normal wheel or motor.

Good luck. I hope you get the 5%.

 

[motrax]

vrf400. Thanks for the reply. I will work something out. The question is: what signal goes between the controller and the battery. Is it just a simple voltage or is it more complex?

 

[vfr400]

vrf400. Thanks for the reply. I will work something out. The question is: what signal goes between the controller and the battery. Is it just a simple voltage or is it more complex?

It could be anything from a remote switch to full comms asking about state of charge, etc. I don't know that system.

If a controller is connected to a battery by only two wires, then you can use any battery of the correct voltage, but when there are more than 2, you can't.

 

[crown7]

I have a bike with a Sram ematic hub. I do not have a battery. I wish to use an after market battery. The Sram hub has an inbuilt controller. There are two fat wires and one thin one from the battery to the hub. The fat ones are obviously the feed wires but what would the third one be for?

Did you ever succeed in getting this SRAM system up running?

I just brought myself in the exact same situation by recently bricking the electronics inside my battery, so I am now in the same boat as you. Definitely the hub needs communication from the battery controller, as I see a one-line-communication interface chip connected to one of the three wires going to the hub.

That leaves me searching for either bad battery to scrap the electronics from, a replacement battery-controller, or, the more sophisticated solution: understanding of the communication, but I guess that later requires a functioning bike to learn from.....

 

[saneagle]

Did you ever succeed in getting this SRAM system up running?

I just brought myself in the exact same situation by recently bricking the electronics inside my battery, so I am now in the same boat as you. Definitely the hub needs communication from the battery controller, as I see a one-line-communication interface chip connected to one of the three wires going to the hub.

That leaves me searching for either bad battery to scrap the electronics from, a replacement battery-controller, or, the more sophisticated solution: understanding of the communication, but I guess that later requires a functioning bike to learn from.....

Another option would be to rip out the electronics and use an external standard Chinese controller and pedal sensor. I think the gear shifting is done by reversing the motor, like the 2-speed Xiongda does. In that case you need a controller that has the wires for a reverse switch so that you can shift manually. Alternatively, you might be able to get a controller and LCD as a spare part from Xiongda. They're normally very helpful. Their controller has the automatic reverse function, though I always found it better to shift manually.