2012-06-23

e-bike: wiring diagram

Since my last post about the battery pack, I've been plodding away working on making a wiring diagram for my Switch 100.  Since I plan to make some changes I needed to first work out what I'm starting with.

Here's a 'beta' version of the diagram:

[ Image Removed ]

You can also download a PDF version here:  [ Link Removed ]  I recommend viewing it at 200% size.

It's still beta though, as I want to go over everything again to make sure I have the connections worked out correctly.. there are a couple I'm not certain of.  If you own a Switch 100 (or one of it's many named siblings) and wouldn't mind taking some detailed photos of the wiring on the Brushless Motor Controller, that would certainly help.

I thought I had.. turns out I didn't. -.-

2012-06-12

e-bike: battery build, interlude

Just a quick note:  I've tested the battery pack out on my e-bike.. or rather the eviscerated electronics from my e-bike.. and it works!  Powers the lights, the motor and the LOUDEST gods bedamned theft alarm I've ever had go off right next to me.

That bloody thing is getting modded ASAP. >.<;


Woo!  Next steps will not involve the battery pack, so "part 3 of 3" will be a while.  I plan to rebuild the pack with making it pretty in mind, as I would like to make it visible through the bike's shell.  Those blue cells are just to nice looking to hide. 8)

More later.

2012-06-10

e-bike: battery build, part 2 of 3

Moving on to the BMS (Battery Management System), here's the top-side of the BMS that came with my kit.


And the wiring diagram that EV Assemble ( http://myworld.ebay.ca/evassemble ) emailed me when the kit shipped from China.


(Diagram is copyright EV Assemble and is shown here purely for instructional purposes.)

And these are the connectors that came with the kit, and that were attached to the charger.



I didn't like them.  So I decided to modify all of the connectors that came with the kit, starting with the seventeen sensor wires that would have to be connected to the battery pack.

The sensor wires pick up the characteristic voltage drop that occours when a lithium chemistry battery reaches it's full capacity charge.  When it senses that one of the batteries in the pack has reached capacity, the BMS will drain off some of the current that the charger is pumping into that battery in order to avoid over charging.

(At least that's my understanding of how it works.. please leave a comment to correct me if you know better.)

I picked up a pack of quick connectors at Sayal, drilled a small hole through the metal tang, and then trimmed off the plastic connector where a wire would normally be attached.  I did this because the wires for the sensors are far too small to work with the usual way of attaching these quick connectors.



Then I soldered one of these modified quick connectors to each of the sensor wires.



The next step was building the wiring harness that would connect the BMS to both the charging unit and to the load.. the e-bike.  After a bit of thought I decided to re-use the connectors from the bike's original SLA battery pack for the load part of the circuit, and have a separate connector for the charging part.

Since the load side socket is a standard 3 prong AC connector, I decided to cannibalize a monitor power cable to build the charge side connector.  I didn't want to have two 3 prong AC sockets on the battery pack's casing, as that might get confusing as to which socket was for charging and which was for the load.

Here's what my circuit diagram ended up looking like.

[ image removed ]

EDIT:  I've made an important update to the above diagram!  I had the polarity of the plug going into the e-bike backwards.

EDIT EDIT:  Okay... looks like I may have had the polarity right in the first place.  I've deleted the diagram and will be uploading a corrected version soon, once I've gone over everything and fixed it.

I picked up some Y shaped quick connectors and bolts to use for hooking it all together.  Here's what it looked like with the first wire put together and bolted to the BMS.


Unfortunately I didn't notice until too late that there is a bus wire between the two boards of the BMS which, due to where it's soldered to the pad, gets in the way of the nut used to attach one the wire to the "Out-" pad.  I took apart the two boards to get a look at the problem.. just had to undo the four screws and pull the boards apart, like so.  (I've put a circle around the problem area.)


Fortunately I was able to snip off a bit of the bus' wire and give the nut just enough space to fit.


Having the boards apart made it easier to bolt on all of the wires.


And with the sensor wires plugged in, here's my finished BMS, ready to be connected to the battery and tested.


First step in connecting the BMS to battery is to attach the sensor wires.  First I unplugged the sensor wires from the BMS again.  If they were left plugged in then the BMS would begin sensing the status of the batteries as I went along, attaching them, which would cause it to begin trying to balance the charges of the batteries.  If it tried to do this while only having a couple of batteries connected it could quickly burn out the BMS as it tries to balance charged batteries against batteries that it has no readings for at all.. the ones that have not yet been hooked up.

If you have the sensor wires plugged in to the BMS and you start hooking things up, you will see an LED on the BMS come on, some time around when you're hooking up the third sensor wire, and the BMS will begin to heat up.  If that happens remove the sensor wire you just connected, unplug the wires from the BMS, and carry on.

Once I had the sensor wires unplugged, I connected the "0" sensor wire to the negative end of the battery pack.


Then I flipped the pack over and connected the "1" wire to the negative end of the next cell in the pack.


Then flipped it back over again and connected the "2" wire to the negative end of the next cell.


And carried on along the cell like this, flipping it over and connecting the negative end of the next cell to the next sensor wire.  Be very careful that you don't accidentally cause a short while you are working with the bridging bars.


There we go, all the sensor wires hooked up.  Notice that I've got the battery pack sitting in an enamelled "butcher's tray".  I thought this was a reasonable safety precaution, just in case something shorted out and one of the batteries leaked or even caught fire.

At this point it's safe to plug the sensor wires into the BMS, so I did that, grabbed the power supply and took everything outside onto my concrete patio in order to do a test charge.  I didn't want to try the first charge indoors, just in case of catastrophic failure, leaking acid, flames, etc.


But it worked fine.  Here's the charger, with the Power LED and Charging LED both lit up.


And here's the battery pack and BMS, with an LED or three lit inside of the BMS, indicating that it's balancing the charging between the batteries.


So that's the rough build of the battery pack completed.  Since there were no flames or magic smoke escaping, I brought everything back inside and finished charging the pack.. which only took a few minutes since it seems they were shipped from China with a full charge.

Next step will be to do a load test to make sure the batteries work with the bike and to test their capacity.  So I'll have to partly re-assemble the bike, which is currently in various boxes in my work room.

2012-06-05

e-bike: battery build, part 1 of 3

Started assembling the battery pack.. I might do an Instructables about the process, since I've not been able to find any clear "how to" info online about putting together one of these Headway battery kits.

CAUTION
The batteries come already charged, so keep in mind that you're working with large live sources of electrons.  Be careful!


Tools Required

  1. Phillips Screwdriver
  2. Work Gloves (the plastic spacer blocks have sharp edges)


Step 1
Get two of the batteries and two of the block spacers.


Step 2
Insert the batteries into one of the spacers, making sure you have one positive end (the shiny silver end with venting holes) up and one negative end (the one with a ring of black lacquer) up.  Note:  Be very careful with the negative end, as if you crack the lacquer the electrolyte will leak.  Don't knock it against anything and do NOT over tighten the screw!


Step 3
Press the other spacer on top of the batteries, making certain that you have the tabbed edge and the slotted edge matching on the top and bottom spacers.  Then slide the tabs of a new spacer into the slots on the bottom spacer, making a space to insert the next pair of batteries.


Step 4
When you insert the next pair of batteries, alternate the positive and negative from the first set.


Step 5
Line up the tabs and slots of the next top spacer and press it down into place.  Gloves are very useful for this, and you can also press on the corners of the spacer using the handle of your screw driver.  Be careful not to damage the batteries.  Don't hammer on anything.. just press until it fits.


Step 6
Add another spacer, two more batteries, alternating the positive and negative.



Step 7
When pressing the top spacer into place you can also flip the pack upside-down and press down, gently, on the whole pack to help press the spacer into place.


Step 8
Keep adding batteries and spacers.


Step 9
Until you're finished putting the batteries together.  I went for a simple vertical stack, but I'm sure you could arrange the batteries into other shapes.  My pack needs to fit into a vertical space on the bike, and a vertical stack keeps things simple.  I like simple. :)


Step 10
Now things get a little more complicated with putting the bridging plates between the batteries.


The idea here is to bridge the cells in series, so that the 3.3v individual cells combine into a 52.8v apx. battery pack.  (16 cells x 3.3v apx. per cell)  Then the Battery Management System (BMS) will convert that into the 48v that my e-bike uses.

To bridge the cells into series, here's the pattern I attached the plates in.  The plates up on top of tea candles are for the top of the battery pack, and the other ones are for the bottom side.


The idea is that I'll connect the positive of a cell at one end of the pack, and the negative of a cell at the other end to the charger when charging pack and to the e-bike when discharging the pack.. well.. with the BMS in there to keep things from running wild and blowing things up.

The pattern of bridging plates inbetween the positive and negative connection points of the pack will complete the circuit by linking the positive and negative ends of the individual cells within the pack.

That's the theory anyway.  Time to attach the bridging plates and see the reality.

Step 11
Remove all of the end cap screws from the top of the battery, and loosely screw on the bridging plates.  I'm not screwing them all the way in as I will need to come back and make some changes later when I hook up the BMS, so just enough to make sure the batteries are securely connected is good enough for now.




Step 12
Now remove the screws from the other side, all except the positive and negative which will be used to connect the battery to the charger & bike.  You can roughly see where each of the metal plates will go.



CAUTION
At this point in the construction the risk of accidentally shorting out two or more of the batteries is very high! Be careful when placing the bridging plates!  I let one slip and it landed between the battery ends, briefly shorting them out, sparking a bit and starting to weld itself in place, before I was able to snatch it back out again.. burning my fingers to do it.



Fortunately the batteries don't appear to have been damaged.  The didn't heat up, nothing has cracked, nothing is leaking, the magic smoke didn't escape.  Whew!

Step 13
As a precaution against accidental shorts, briefly hold one of the bridging plates against the battery ends that you intend to attach it between.  This way you can quickly test that there isn't an unexpected short before you start trying to screw it in place.


Step 14
I decided to screw the plates down, lightly not all the way, one side of the battery pack, and then down the other side, to try and reduce the risk of accidental shorts.



Step 15
Check that the batteries are working in series with a multimeter.  53v is pretty close to what I was expecting, so everything looks good.





The next stage will involve hooking the battery pack up to the BMS and charger so that I can top them up, then I plan to connect the pack up to my e-bike and see how she runs.  First I need to make a trip to Sayal to buy some different connectors from the ones that came with the battery pack kit.  They just seem kind of cheap and I'd rather not rely on them.