Adrian's Bafang BPM Hardtail MTB

[Kepler]

Its amazing how quickly the weight adds up that is for sure. Friction drive is still the weight weenie king.

Adrian, have you considered using a sine wave controller on a friction drive. I have been considering this of late and wonder if it would have much of an impact on the noise of a friction drive.

 

[adrian_sm]

Off topic but hey
______________

Yep. It has been an on going search over the last year. But my desire for keeping sensorless has made the job a truck load harder. I have lost count of the number of suppliers that have promised the earth and failed to deliver. Grrrr.

Still not sure how much it helps on the noise, doubt it will "solve" it. But will definitely help things.

The down side is the higher switching frequencies meaning more switching losses, so is typically a larger and hotter controller.

[EDIT]

For example here is Burtie's FOC runner an 80100 under load
[youtube]2Aqke4sdMoM[/youtube]


And here it is on a think a standard controller but unloaded
[youtube]XVX5T7JkBDA[/youtube]

 

[adrian_sm]

Well I remeasured the idle current on the EB306 controller, in both the on and off states.

On 5s Lipo = 19.5V
On = ~30 mA
Off = ~1 mA

On 15s LiPo = 59.9V
On = ~39 mA
Off = ~6 mA

So I installed the On/Off switch permently, and then I removed the R203 resistor that bleeds down the main battery capacitor. Now on 15s = 59.9V
On = ~33mA
Off = ~0 mA

8)

So now I can safely leave the battery connected indefinitely, and avoid draining the batteries when not in use as long as I turn the controller off. Installing the switch also avoid the need to disconnect the battery cable all the time, and saves the connectors from the spark.

 

[adrian_sm]

I now also have a DC to DC powering my MagicShine headlight. So I took power readings for that too.

@59.5V the input current to the DC-DC was
High = 221mA = 13.2W
Med = 128 mA = 7.6 W
Low = 78 mA = 4.6 W
Strobe = 130mA = 7.7 W
Off = 27 mA = 1.6W

DC-DC off pin grounded = 13mA = 0.7W. Hmph. So much for turning off.

So I still need to be careful with the battery if the DC-DC is left connected.

 

[Kabbage]

Nice Adrian, I hadn't realised you had built a new bike, until you PM'd me today.

I run my BPM code 11(?) at 25A and it seems fine. It is interesting how many of us are ending up on the bafang geared motor, after trying other things. Ben seems to have a few of them tucked away at his place! I hope he never runs out....

I am about to start building a no-CA, stripped back commuter using one of the small Bafang 250w motors like Kepler used. (it may not be enough grunt, but will be an interesting test!). I will post something when my bike finally gets in from the shop - going to build an 'in-the-triangle' elongated LiFePO4 battery like full-throttle's, using Headway 10Ah batteries (38120?).

Anyway, really like the look of yours, I am beginning to feel that this is approaching the 'ideal' setup for most reasonable cases.

 

[adrian_sm]

I have just dialed the Amps down on mine, as it will be more of a gentle commuter, than performance machine. But I did wire up an easily accessible programming port so I can crank things up if the need arises. :lol:

After looking at some statsfor touring type rides, I realised that a low continuous power could be where it's at. So a little 250w hub makes sense, especially if it has a lower drag, no-load current and waste heat.

On another side note, the other day I took my BPM bike for a test ride with my 7 year old down to Auskick, and he started back chatting my "Hey! Your cheating!" That got me thinking how pointless the motor was for me when riding with him, but how cool it would be for him for when we do longer steeper rides. A little 250w geared hub laced in a 20" wheel for his bike would be awesome. Just need a slow wind and low volts to keep the speed in check. What could possibly go wrong ?

 

[-dg]

On the Fighter i am running 40A 18s these days with about 2:1 on phase current to calm down the throttle response a bit. The code 12 seems to handle this fine and rarely hits the CA thermal limiter. The code 10 BPM died on about 30A 18s:

Are you using the stock phase wires for that 30 or 40A? Is that with sensor wires too? Or did you mod the phase wires? Because on my BPM they seem pretty skinny.

 

[Kepler]

Yep, stock phase wires. Not a problem even after 6000km

 

[-dg]

Yep, stock phase wires. Not a problem even after 6000km

Thats a bit of a surprise. The wire charts say those should be toast over 20A. Do you actually run it that hard a lot?

 

[Samd]

I run my Code 10 at 38A in a 26" also, not really that warm.

I think Melbourne has become the hub capital

 

[friendly1uk]

How thick are the wires? I looked at mine and looked away. Same with the inline power connection. It seems woefully inadequate. The wires were not pvc coated though, or even butyl. It seemed like teflon, so you won't melt the insulation easily. However such temps appear to harden copper and in a vibrating environment that is not a good thing.

 

[Glenn_M]

Hi Adrian, nice build.
What freewheel you running there? DNP?
Cheers,

Glenn

 

[adrian_sm]

Yep cheapo DNP freewheel. I only ever used two on my x408 with close to 20,000 km so should be okay.

Would have preferred to get the CST BPM but would have had to ship it in, and just couldn't be bothered when I could pick up this motor locally.

Since I have the battery so easily removable I was toying with the idea of making everything else quickly removable/installable. Then I can use this bike for some pedal only single track work when I feel inclined. At the moment it is only two wheel nuts, two Allen key screws for throttle and grip, a single mudguard bolt for the controller, and a couple of reusable cable ties. All pretty quick except for the mudguard mount screw.

The only other annoyance us not being able to install my rear rack for a kids seat, due to a clash with the disc brakes. I may have to modify the rack to use the disc brake bolt as a mount point instead.

 

[-dg]

How thick are the wires? I looked at mine and looked away. Same with the inline power connection. It seems woefully inadequate. The wires were not pvc coated though, or even butyl. It seemed like teflon, so you won't melt the insulation easily. However such temps appear to harden copper and in a vibrating environment that is not a good thing.

Yeah, I had the same reaction. On the other hand, they do get cooling airflow and a chance to transfer heat to the axle, so maybe they don't get that hot except inside the motor. Still I don't really think the designers had 38A in mind.

 

[-dg]

I run my Code 10 at 38A in a 26" also, not really that warm.

Interesting. I have a code 10 (currently being disassembled and documented by spinningmagnets) and was thinking of trying 30A. How is 38A working out? What voltage also? And are you using phase current limiting? Thanks.

 

[Kabbage]

Would have preferred to get the CST BPM but would have had to ship it in, and just couldn't be bothered when I could pick up this motor locally. .

Amen. Wish BM would get some of them in, but I get the sense his shed its packed high with all the standard ones. I am still amazed that almost all the hubs except the CST take free wheels. Why is that?

The only other annoyance us not being able to install my rear rack for a kids seat, due to a clash with the disc brakes. I may have to modify the rack to use the disc brake bolt as a mount point instead.

It seems that most newer bikes with the rear calipers in the rear triangle handle 'standard' racks no worries; otherwise tioga make a rack variant designed to go over the rear disc... Dunno how you'd go with a child seat but

 

[spinningmagnets]

I am still amazed that almost all the hubs except the CST take free wheels. Why is that?

I don't know about other retailers, but Green Bike Kit is selling the cassette BPM for $230, compared to the freewheel BPM for $124, $106 difference. I'm sure many retailers feel it would be a slow seller and just don't stock it.

http://www.greenbikekit.com/index.php/bafang-cst-bldc-motor.html
http://www.greenbikekit.com/index.php/bldc-bpm-500w-36v.html

 

[adrian_sm]

Usual Chinese economics. It is cheaper and works sufficiently.

 

[anpate]

Nice job Adrian! where did you source your rim, spokes and freewheel from?

 

[adrian_sm]

Ben Moore was nice enough to provide the motor, rim and matching spoke set. But watch out for the killer bunnies when you go to pick them up. :lol:

 

[adrian_sm]

Finally found a SMPS (Switch Mode Power Supply) that can happily drive my headlights from my main battery pack.

I wanted something that:
- will take my main battery DC voltage as the input
- deliver the right voltage & current to directly power my lights
- be water proof
- be relatively small
- only require minor effort to adapt to the bike

These are the lights. I have a couple of similar models. This is a link to one of them: US$35 SingFire SF-90 CREE XML-T6 800lm 4-Mode Cool White Bicycle Lamp

This is the power supply I have found.
US$7 9V 2.2A Power Supply Adapter

- works on voltages from ~27V and up. So no problem for my 15s pack.
- and will have no problem for most ebike battery voltages

The only customisation required is to fit a female connector instead of the male that comes on the SMPS.
Here is a US$4 long cable that has two of the connectors incase you want to try and power two lights.

Alternatively if you are really lazy you could just cut off the male plug, and use the two remaining female plug as an adapter between the lights male, and the SWPS male plugs.
In that case go for the shorter version; $3 - 5.4mm Male to Dual Female Adapter Y-Cable (25cm)

Then modify a standard power cord to hook up to your battery.


Too easy.

----------------------
For the record the charger that came with my lights didn't work with a 15s DC LiPo input.

Either did a replacement charger which looks identical.
http://dx.com/p/replacement-5-5mm-2-1mm-dc-8-4v-1a-power-adapter-supply-100-240v-2-flat-pin-plug-66684

 

[TheBeastie]

Finally found a SMPS (Switch Mode Power Supply) that can happily drive my headlights from my main battery pack.

This is the power supply I have found.
US$7 9V 2.2A Power Supply Adapter

- works on voltages from ~27V and up. So no problem for my 15s pack.
- and will have no problem for most ebike battery voltages

I would of thought this power supply would only work properly on AC inputs?

 

[Tom L]

I would of thought this power supply would only work properly on AC inputs?

The first stage of any AC to DC SMPS is to rectify the AC in to DC. So any AC SMPS will also work on DC as long as you supply it with the minimum required input voltage. Multiply the minimum AC rms rating by the square root of 2 to get the DC volts required.

 

[adrian_sm]

Multiply the minimum AC rms rating by the square root of 2 to get the DC volts required.

And some work at even lower voltages than that, but it will never be shown on the spec sheet.

The one I am using works as low as 27V DC, making it ideal for running from an ebike battery. Not bad for $7.

 

[Tom L]

I noticed that after looking up the published specs on the SMPS you are using. Impressive.