Full-throttle's 2nd - in progress

Hyena said:
What a comedian, as if you'd build anything that looked neat :lol:
Spoken by the Hyena@ inner tube battery pack wrap dude... :lol:

No, but seriously, I don't see any duct tape! With spring/summer here now and all my tape starting to go gooey, I've been thinking about doing some spring cleaning on the bike. Might shave off a pound or two of tape!

Anyway, Full-throttle, I just wanted to write and say that's a kick ass ride! Very clean. VERY MEAN!! :twisted:

Video! Video! Video!
 
Great looking e-bike.
What size tyres are you using?
 
First ride!

Good news: bike tracks well, steering is great, need to tweak the shocks a bit. Motor is great - hits 50km/h on the flats.

Bad news: even taking it easy on the first ride the BMS cut-out prematurely, I think I've used about 5Ah (out of 10Ah - 16 Headway cells) can't tell for sure as the Watts-up lost power at the same time..
Must be the combination of:
1) 1st charge
2) Headways sag in voltage a lot more than my current pack
3) Headway BMS have a reputation for cutting out too soon
4) the new bike is slightly heavier in both overall and rotational weights
5) MAC motor is nowhere near as efficient as the one I normally use

As the result I had the 'pleasure' of dragging my ass for the last 7km or so. I didn't have time to get the gears sorted, so I was stuck wit 44 on the front and the second smallest on the back.

For some reason I can't upload pics at the mo, so I'll ask Mark to post the altitude/speed profiles
 

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Bugger, if it's not the MACs letting you guys down it's the batteries!
I knew about the dodgy BMS's that were kicking around with the headways but I didn't realise they had so much sag. Hopfully you haven't got a dead cell.

What motor were you using before that's more efficient than the MAC ? Was it the bigger bafang ? (350w climber or what ever it's called)
 
full-throttle said:
First ride!

Woo hoo! Congrats.

full-throttle said:
Must be the combination of:
1) 1st charge
2) Headways sag in voltage a lot more than my current pack
3) Headway BMS have a reputation for cutting out too soon
4) the new bike is slightly heavier in both overall and rotational weights
5) MAC motor is nowhere near as efficient as the one I normally use

The headways pack I have sags more than I expected. Essentially I have limited the max current (via CA) to 30Amps, to stop the BMS tripping due to low voltage. The cell test data I have seen all say it is not the cells fault. Could be something to do with the additional resistance in teh construction of the pack somewhere, ie. connections or BMS? This could also explain why I only typically get 9.0Ah out of the pack. I should try to get a cell level voltage reading under load.... Hmmm.

I would love to know where the losses are.
 
So do I!

My other pack is made up of 16s9p 18650 LiFePO4 and I didn't see it sag less than 48V @ 26Amax. Never tripped the BMS while riding either. And the most annoying thing - its one of these V-Power packs. I only bought it because it was the cheapest. Beginner's luck perhaps..
 
I had a ride at lunchtime.


The bike is AWESOME.....well, aside from the fact that I bottom the rear suspension out just sitting on the bike...


Takes off really well. Smooth, responsive. Pulling 40 Amps it goes well (watch those nylon gears).

No controller issues like my Soft-Start 18FET Infineon (My controller's stall protection is ridiculous, you have to ride to 10kmh or it trips, and I get shudders still.....I'm getting a different controller).


Speed is good, no speedo yet, so no numbers.


Brakes (4 pot Avid Codes) are freaking mean.


I can't comment on the handling as the suspension sags under my weight to the point where the steering feels like a chopper, with a real rise over the middle as you steer L to R. This stuffs the handling for me. I've got the 600lb spring Full-Throttle had on my bike, which is fine, but the 300lb one I swapped for is very soft for me.

If the 600lb one is too stiff for you, get a ~450 and we'll split the costs? If the 600 is ok for you, you can have it back.


Bike looks great due to lack of bulk around battery area - mine has bulk up near seat, and towards forks, which I don't like.


I was a bit worried when I saw the original green frame. It was fugly. But when cleaned up and powdercoating, and built up with cool bits, the bike tooks fantastic.

IMO we need to measure all the cells when discharged, and it needs a couple of cycles.


Mark
 
Made the following changes before going home:
1) Checked the cell voltages: all between 3.3 and 3.6V
2) Lowered CC limit on Infineon from 30 to 40A (I did initially prog it to 30 but the shunt must be out)
3) Set LVC to 40V
4) Brought out a by-pass ground terminal

On the way home it all was good and well: Vmin was above 48V, resting between 51 and 52V, Ah was going along quite nicely. Had less than 5km to go, stopped at the traffic light and it was sitting just over 4.5Ah. 300m later - cut-out! So I stopped and bypassed the BMS and continued riding keeping an eye on Watt-sUp, this time the volts were plummeting down - 42.. 41.. 40 then the LVC on the controller started to kick in.

At that stage I've disconnected it completely and pedaled the rest of the way.

Any thoughts guys?

BTW The motor shines @ 30A, I was really enjoying it!
 
Crap.


Have you had a chance to measure the discharged cells?
 
Oh, can you rewire your Turnigy watt meter and measure how much power is going in during charging?


Maybe they aren't getting filled?
 
Were the cells fully balanced before building the pack? It sounds like either the cells are at different states of charge and some are fully discharged before the others or you've got a bad cell with low capacity. The BMS will no way have sufficient shunt current to balance a pack that has cells that are well out of balance. Also some of the chargers out there will stop charging once the BMS has tripped due to a HVC preventing the rest of the pack from balancing properly. I'd recommend checking the cell voltages when the pack is fully charged (charger still running, not after the cell voltages have dropped) and see what they look like. If some cells are like 3.45V or so that's nothing major but if some are only 3.3something then you'll need to get the stragglers charged up somehow.
 
full-throttle said:
the volts were plummeting down - 42.. 41.. 40 then the LVC on the controller started to kick in.
Any thoughts guys?
If your voltage dropped suddenly in the order of 8 volts it sounds to me like more than one crook cell, either that or like cell_man suggested they were well out of balance and not full to start with.
I'd give the pack a full charge and then manually check each cell voltage with a multimeter. Yeah it's a bit tedious but i'll help you quickly diagnose what the problem is.

*Hyena says something under his breath about how good lipo is* :p
 
I feel you. I have a Headway 36V 10Ah pack that had been cutting out after 2.6Ah. I finally got around to replacing the BMS. Same crap as before. I'm going to take it apart again tomorrow and test each cell under load. Its resting voltage looks the same as my E-bikekit battery, but under heavy load (head wind) I'll peek at the CA and it's showing 36.5V compared to 38.5V from my E-bikekit battery under load.
 
Hyena said:
full-throttle said:
the volts were plummeting down - 42.. 41.. 40 then the LVC on the controller started to kick in.
Any thoughts guys?
If your voltage dropped suddenly in the order of 8 volts it sounds to me like more than one crook cell, either that or like cell_man suggested they were well out of balance and not full to start with.
I'd give the pack a full charge and then manually check each cell voltage with a multimeter. Yeah it's a bit tedious but i'll help you quickly diagnose what the problem is.

*Hyena says something under his breath about how good lipo is* :p


It could be.

Some cells were 3.6v and some were 3.3v when we measured them "charged" yesterday.

That could mean the 3.6v cells were topped off, and the 3.3v cells were at 99%.

Or it could mean that the 3.3v cells were at 50%....


There are pluses and minuses about the different chemistries.

Ask Kim how much fun Lipos can be...


Mine only lasted a year, but they were cheap.

They can catch fire if you overcharge, or over discharge - again this seems less of a risk these days.
(Although the Headway cell that Luke burned seemed to go pretty well, it won't burn if you abuse the cell, you have to blowtorch it).

My BMS screwed up due to a failed tab weld, and discharged a headway to 0v. It came back up to 2.5v overnight by itself, then I charged it as normal. They are pretty tough (although I did replace that cell). My brother's headways are over 2 years old now and still going strong, no noticeable degradation. My are 18 months old and same story, same capacity as new, same sag as new.

Lipos are made out of nasty stuff, LiFePO4 less so. Lipos are never going in cars, so you aren't helping that technology advance.

But lipos are lighter, and sag less (although my headways are good enough).


There's something wrong here, it's not normal.

I'd single cell charge all the cells. I have a single cell charger (but I'd need it back soon!!)


But, I am thinking about another bike, maybe RC, with lipos. It won't have enough energy to commute, it'd be just for fun.
 
Thanks for all the feedback,

At the moment dead cell(s) can be ruled out for a number of reasons.

Some cells are 3.3.. and the rest are 3.5-3.7
The charger was still going after 12hrs
Balancing resistors are warm
Pack sits @ 58.2V

So the BMS is working hard to bring the lower voltage cells up.

Mark_A_W said:
Oh, can you rewire your Turnigy watt meter and measure how much power is going in during charging?
I can, but it would be of little use as the energy lost in the balancing resistors would be included.

If after a few charge/discharge cycles it doesn't balance out I might have to charge the strugglers individually.
 
Mark_A_W said:
Lipos are never going in cars

They will be if I get my next project off the ground :wink:

I think all the hysteria surrounding lipo is largely outdated now with the current generation. As Lukes videos showed you've really gotta put them through hell to make them blow up.
Sure overcharging and discharging isn't good for their life span but I think the days of "ZOMG my lipo overcharged to 4.3v, ruuuun, get to the chopper!" are over. :)

Full throttle, you can't rule out a cell as dead just because it's charged up to 3.3v. Ok, well you can rule it out as totally dead but it could be pretty sick and still appear reasonably well hot off the charge. I wouldn't be surprised it you took that fully charged pack at let it sit for a day or 2 and then measured the 3.3v cells to find they discharged a little (or a lot). Take it out for a 3ah spin around the block and then remeasure the voltages or better still hook you voltmeter across one of the lagging cells to measure it under load. My first lithium pack was made from 10ah LiMn cells and it charged up fully to 42v but would only get 5ah range. I'd get off the bike and test all cells to read 3.7v but as soon as I loaded it up 2 of them sagged through the floor and tripped the BMS.
 
I agree, there's a difference between 'dead' and 'sick'.

If they were dead the pack would sag right from the start. Looks more like the strugglers are half-charged and the pack is as strong as the weakest cell.

On the other subject: LiPos are much smaller in size. I was tempted to change chemistry ones or twice during my build.

And since I've started, here are my thoughts of hub vs RC:

The idea of external motor build was slowly baking in my head well before I got my first hub motor. I even started collecting parts for it. Got enough for a one stage reduction and a 3/16" chain.

Pros:
Hub motors are cheap, but so is Turnigy 80-100-B 130Kv
An average Joe can convert an average bike
Quiet
Protected from the elements

Cons:
Physical restriction of the conductor size
Physical restriction of the torque transfer area
Extremely pour heat dissipation
High unsprung weight
 
You could try putting a series resistor inline with the pack and this will allow the shunts to better balance the pack. It can take a very long time to balance a pack that is well out of balance with cells with several Ah difference in SOC. The shunt current of the BMS is maybe only 100mA. It will take 10hours at 100mA to add just 1Ah to the low cells. If it's 5Ah out, it will take 50hours. Running the BMS continuously with max shunt current could get things hot. Better to use a low current charger for this, the lower the better. A 10ohm resistor in line would work and the power rating would depend upon the charger current you are using, 50W minimum for a 5A or 20W minimum for a 2A. If you do not use a series resistor the high cells will hit the HVC at 3.9V, BMS disconnects the charger, the high cell will drop down to 3.8V, the charger is re connected and the process repeats until the low cells come high enough to stop the high cells hitting the HVC.

If you could use a single cell charger on the low cells or bleed some capacity out out of the high cells that would work well. A 1ohm, 5W resistor would pull 3A out of a single cell. If you just apply the charger then go through each of the cells in turn bleeding voltage off the high cells you could quickly get the pack balanced.

If you don't mind pulling the pack apart you could just connect all cells in parallel and charge them all to 3.65V till the current dropped to zero or just connect all the cells in parallel and lave them to equalize. I believe this can take a few days to equalize. I've never used that method, I generally charge them to a fixed voltage.

The typical Chinese supplied BMS is just not capable of balancing a pack that is well out of balance with cells at very different SOC but they will keep a pack safe and relatively well balanced if the cells are properly balanced to start with.
 
Thanks Paul, I didn't think of resistor in series.

It seems better now after a few more hours of balancing, I will avoid riding it to work just yet though.
 
The pack is behaving now - left it to balance for two nights and it was @ 54V after the whole week of no-use.

The camera won't be here for a few weeks.

Fitted the shifter - old Sram LH, its meant for the front mech but the indexing works with 7sp.

Last w/e hit the local singletrack - that was just awesome! Tight stuff is a bit of a workout, but fast open is a bliss no matter how many rocks its got.
 
Two weeks, we can't wait that long if the bike is running. Borrow my little video camera.
minidv-small.jpg


Image quality isn't great, but better it's cheap (similar to this one) and small.

I just clipped it onto the shoulder strap of my back pack, works well enough.
 
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