Wiring Question - USB port

[vfxmorley]

Hi there.

I wanted to try seek clarification on something before I do something stupid!

Im wanting to wire up a USB outlet onto my ebike but just want to make sure I do it the correct way.

Ive purchased one of these from Ebay http://www.ebay.com/itm/DC-DC-8-48V...er-supply-buck-step-down-module-/350859745532

The battery im using is 36v running 15Amp continuos. not sure what the peak would be?

My question is this. Should I run something like this http://andersonpower.com.au/lead-double-anderson-sb50-extension-standard-duty-p-453.html directly from the battery, one connector would go to the motor controller, the other to the step down module. I would use standard anderson powerpoles for all the other connections. output of the step down module would be connected directly to a stripped USB cable. Or is there a smarter way to do this?

Also, would Cable that is Twinflex 2.5mm2 (rated to 25Amp) be suitable for this setup? or should I go to 2x4mm2 cable? (rated to 42Amp) for a better safety margin

Thanks for any help

dave

 

[bowlofsalad]

"The battery im using is 36v running 15Amp continuos. not sure what the peak would be?"

I think there is a misunderstanding. I assume you are saying your pack is 36v15a which means the pack puts out about 36 volts and has a capacity of 15 amp hours. What you want to know is the packs C rating is watt hour capacity. To find watt hours for your pack, multiply voltage by amp hours. In this case, 36 times 15 is 540. If your pack has a rating of 1c, then you can draw 540 watts continuously without negatively effecting anything. If you don't have a multimeter and a watt meter, buy those immediately. I recommend cycleanalyst for the watt meter.

I am not entirely sure I understand the rest of your question, I doubt I could adequately answer it.

 

[dak664]

I'd use a one amp self-resetting polyfuse to connect the stepdown converter to the battery, then wires downstream of that can be much smaller. Technically wiring up to the fuse needs to handle the full short circuit current from the battery, so e.g. 30 amp wire and connectors up to the polyfuse, 1 amp wire up to the DC converter, 5 amp wires after the converter (because of the current boost) up to another 1 amp polyfuse, then 1 amp wires to the USB connector. Probably 2 or 3 amps maximum is safe, but at a minimum the jack output should be fused at that level, with either a permanent or self-resetting fuse.

Some USB cables use very fine wire and the specification allows for >1 amp only after recognizing that special power delivery cables have been plugged in http://www.usb.org/developers/powerdelivery/PD_1.0_Introduction.pdf.

 

[vfxmorley]

Hi There.

Thanks for the responses.

the battery is actually 36v11.6AH.

The battery is capable of outputting continuously (without harm) 15amps. So I suppose in my case the "c" rating is approx 1.3c

I will be installing the speedict bluetooth module to monitor and record the power draw/usage

dak664. That ALMOST makes sense. Ill look into what you are saying. The fuse was defiantly going to happen but Ive never heard of a self resetting polyfuse one. One thing I am not clear on, is assuming I split the output of the battery, the voltage and amp input to the fuse or the buck step down will be changing constantly. Is this a bad thing? Its times like these I wish I knew an electrical engineer!

 

[t3sla]

Is your battery in a rear rack and removable.

The specs sound exactly like a 18650 packed EU style rack battery, post a picture of the underside if your battery with the information label

Some of those have fuses built into the battery management system on the discharge side, they aren't cheaply made and have good design.

It's easier to just use this for a cheap USB power solution like this

http://endless-sphere.com/forums/viewtopic.php?p=778921#p778921

 

[vfxmorley]

It is exactly that. Ive had some good dialog with these people, and they have been very helpful to date. I guess the proof will be in the pudding so to speak.

I dont have it in my possession yet, but here is a screen cap of the spec sheet
https://www.dropbox.com/s/icewpxfat1gg175/36v11.6ah_specs.jpg

Also a screen cap of some pictures
https://www.dropbox.com/s/gsqpzbf1jwggrzh/batteryPics.jpg

 

[t3sla]

Ah right, from memory you will have an 18amp peak for a few minutes.

The biggest challenge you face is the controller housing, they are usually very tight.

Also if this is your first build consider a front motor with a waterproof quick release connector.

What are your overall build goals?

 

[vfxmorley]

Im going with an internal Golden motor Smart pie front wheel (26"). I figured this motor was a good compromise on power vs law ratio

I am going to run the Speedict bluetooth "mercury" http://www.speedict.com/ for all the monitoring requirements.

At the moment, Im debating whether I should add the pedelec sensor to the system from the start. I hear the smart pies trigger is very binary when using it. The speedict will allow me to control this a bit better and have a "legal" mode if desired, but I think ill just get going out of the box before I get to knee deep into tuning the system (its nice to have the flexibility though)

Ill be using the bike mainly for commuting to work. so panniers on the back with laptop and clothes. The journey, if I take the long way (which I hopefully will most of the time) will be about 15k. the short more direct route is 5k. So Im figuring, this battery will go hopefully 2 long journeys, but will obviously need to monitor to figure this out.

The bike im going to put it on, is my old single speed mountain bike. Its a great bike (about 11kg) lots of fun to ride, so hopefully it stays that way once I get all this kit on (pic below)

The step down buck converter I was going to install will probably get cable tied to the bottom of the rear rack under the battery. Id the run a long USB cable to the front where my phone will be mounted on the bars and receiving the signal from the speedict. Im going to use anderson powerpoles for connection to everything that I can.

https://www.dropbox.com/s/lber7p0a1tqnxc1/dmBike1.jpg

cheers!