Aww, fooey

[Bikemad]

The edges of the groove are like a knife edge, and it is my intention to take a die grinder to those edges and round them off.  I strongly encourage anyone with an MP III to take a look at that area.  I'm confident most axles are similar.

Dennis, my axle used to be the same as yours:


So I removed the sharp edges with a mini drill and mini sanding drum to prevent cable damage too:



Alan
 

[Morgen 3Eman]

Yup, that is just what I did.  I timed how long it took and reported it to GM China so they could do a cost/benefit analysis.  Two minutes total per axle eliminates a very obvious, very destructive, very sharp edge.  Just changing the  sequence and shape of the tooling for machining the slot could completely eliminate the problem with no increase in manufacturing time, and very little change in cost overall.   The radius could be cut by the plunge cut tool.  Pretty trivial delta in cost.

I also recommended that they change the machining of the cover casting of the controller on the MP3.   It is also the heat sink/mounting plate for the FETs in the H-switches.  By machining fins into the surface (instead of just a smooth disk) they could improve the heat transfer into the airstream generated by the fan/disk mounting plate.  (They already machine the surface flat.)  By lowering the operating temp of the FET heat sink , they lower the operating temp of all the components and improve reliability by about double for a 10  degree temp change.  Again, a very low cost manufacturing change with a big impact on reliability .  Their choice of FETs is very interesting.  They are capable of handling over 150 Amps.   But they are only rated at 70 Volts breakdown.  100 Volt versions of the same device are only pennies more expensive.  I'm used to seeing quite high voltage devices used in inductive circuits, relative to applied voltage.

The electrolytic capacitors were chosen also did not have a lot of safety factor for breakdown voltage.  Without seeing the schematics, it is certainly possible they are not being subject to  full DC supply voltage, but selecting a 63 Volt rated cap for use in a circuit  commonly subjected  to 56 Volts is not a plan to have a long life for the assembly.  Maybe I was looking at the 5VDC filter caps.    (No way)

On the other hand, the PC board and wave soldering looked to be very well done.   They really need to pay just a little more attention to detail to dramatically improve   their reliability, and improve their long term profitability. 

I'm pretty sure this all sound very, very anal, but as a retired equipment engineering manager, it is just part of my nature.  I spent decades working to cut the total cost of goods sold, and it is still in my blood.....

On the good side of this failure, I am glad my next controller will have the USB cable built into it.


TTFN,
Dennis

[Leslie]

Maybe a gromet.



?  ? ? ?

 

I don't understand why GM would not find a solution to any of the sharp edge problems all their previous designs have suffered. 

The HBS hubs, the bike falls over once the wires and controller are wrecked, the MP1 and 2 milled wire slot, just cut into the cables attempring to put the motor into the dropouts.. 

Some people when building the bike, leave the cable dangling on the ground, and when they walk the bike, the wheel runs over the draging cable and is pulling nice and tight into those sharp edges. and *slice* arggh.

Running peddels bike upside down with loose cable Awee noooes, cable catches in spokes "crys".  there was even one YT video of a guy testing his hub at full RPM holding his axle with his fingers years ago.


My bike gets built, all controlls, and the stuff get put on the bike and tied into place, I ran one test to see if the hub works. I pull the hub appart, fix all the sharpies and poor solder joints in the controller, and the last thing I do is install my hub and connect it up.  I would not ride ny GM motor out of the box. And would not even bother giving any advice to the contrary.

Solutions

File, sand, all sharp edges on all hubs,







For HBS, thread a garden hose or PVC tube over cables and axle end.  All headaches gone.
Like I did here years ago.




For MP2 removed circlip, use electrical tape to secure wires, and heat shrink and I even finished off with a  fat plastic tie around the axle..



The new MP III issues, I don't own one but am keen to find how people deal with this. Remove cables and use a cheap round metal file to work on the sharp edges. Then set the cable in place with some solid goop.

[Leslie]

Id like to tell all my friends, how to do this, and where to buy electric hubs from, but while all these things continue to go on, I keep my mouth shut and say just go to the internet and type electric bike motor kit and hope for the best. 

I wonder why I come here, as seeing this damage that could be easily avoided at the factory with little effort and cost, just makes me angry and frustrated.

[Morgen 3Eman]

Hi Les,

It may be cultural.  When I visited China a few years ago, I was surprised how important it is to them to get the best end of the deal when buying or selling.  Maybe they simply don't understand that reliability makes profit in the long term, while cheap workmanship makes profit only in the short term.  I know there are a lot of folks in the US with the same short sighted view....

I am building my three-wheeler with a goal of small scale production in carbon fiber, and at the expected price point,  I have to be totally confident that whatever power unit I use is dead solid reliable.  My current experience is not making me real confident....

Of course, you and I are perfectly wonderful, as we spoke of earlier.

TTFN,
Dennis

[Leslie]

It is the same all over.  I see all brands lacking in at least one aspect of the design.  Well for the price I really don't expect much more. But I probably wouldn't want to afford anything flash.

I tried to wind one of these hubs without success, I wanted it to be too perfect.  It didn't help the nylon stator face insulators was melted like ice cream all over the stator.

There are certain steps to take when you first get these kits on the road.. Like the sharpies,  Even check if the controller and charger polarity is correct. It can be that bad. You can test the BMS is working.  One bad sensor connection on a BMS and it is over for the cell.  This is why I prefer not to use the BMS and turn my volts down to 56v.  I seem to not be able to get it so far out of balance it worries me.  After 2 mths of riding the most I've seen a cell go up is 3.56v  and the lowest 3.35v it still had 93% capacity at full charge though.  That low cell I reactivated it.  Charged it to 4v (4.12v) oops and left it for a little while.

I open the hubs and fix all the solder on the controllers.   It might take me a day to go through it all but I do think GM have got the nicest looking hubs and with the work it works for me..

[Leslie]

Yeah as a Bike designer, you buy these bikes and kits and it may end up costng you $1000 and after you do your 3 days work putting them together and checking all the issues that could arrise add another $500.  In the end a lot of people do not see the worth or $1500 electric bicycle..  But as you ride them you understand the goodness the light vehicles and the savings they have to offer.

I went through all of this and more.  I used damned SLA's for 2 years and had to change packs every 6 to 8 mths.  It was costing me $400 AU every 8 mths but I tried to make it work.

After I swallowed that lithium pill, mood stablizer I figured out everyone who moved to lithium was correct and I could never make lead acid pay the way.  I would of spent another $1200 for the life this LiFePO4 pack has got me.  And the weight differences saved me in brake pad, tires and bike stands.  Man I did it hard but I kept at it..

[Leslie]

I even lost a 48v 20ah lithium battery during a flood.  We were about to be isolated on an inland island. Some drunk let my tires down the night before, because I live in Gronkville and I damaged the tires on my towny, and I had to get supplies the next day, so I rigged up a another bike with this 20ah pack and it had no BMS.  Well I couldn't get into town the usual way as all the roads had been flooded out.  I got into town, I must of been 25km ride detour.  Id never travelled this way before.  I missed the turn off and ended up 15km off course.  So I must of ridden 25 kms into town, 35kms almost to the beach and another 15 kms home with a trailer load of supplies using 40 amps continuous controller..  The battery died 5 kms from home. 

It was a rush, as police were closing all the roads down.  I hate myself for it. I prolly would of made it if I didn't ride so hard on the second leg.  I would not of made it home if I spent 10 more minutes at the markets and as it was I had to sneak behind a truck and race through a police road block through 200 meters of water 20 cm deep..  The PIE powered through it all.

[Morgen 3Eman]

Hi Les,

So once again I don't have a clue what you are talking about.  How does one know whether the BMS is working , and how does one turn down the voltage?  Oh, and why would you want to turn down what voltage? 

OZ has really been having strange weather, and it sounds like you were in the worst of it! 

TTFN,
Dennis

[Leslie]

Ok, you test the balance system when it is almost fully charged between each sense wire.  the LiFePo4 GM BMS limits each cell to 3.65v.  If one sensor wire comes loose, this impedes all cell voltages except one, the cell disconnected from BMS can go too high destroying it overnight.

My charger has an adjustor resistor inside it.  It is very agressive at default setting 60v. This makes the process efficient.  I can reduce the charger voltage to 56v for a 16s LiFePo4 system.  The actuall voltage behind the charger-off-latch is up to 65v, I think, its been a while. :-|....  But I can not see this at the plug and this voltage only engages when an uncharged pack is connected.  So the charger has a lot of potential to the pack in bulk mode..

If you watch cells charging they can sit for hours at 3.35v for the bulk of the charge, and then it will moved up to 3.5 - 3.55v in about 30-40 minutes.  When they reach 3.5v they are pretty much charged and then you will witness the cell voltage race up to 3.65v much faster over about five minutes.

You have hours of charge time at 3.35v, 30 mins betweem 3.35v and 3.5 and about 5 mins between 3.55v and about 5 minutes between 3.55v 3.65v and a minute between 3.65 to over 4v cell failure time..  You latch off in that 30 minute window. Say 10 minutes charge can be absorbed at 3.5v withn another 30 minutes with the charger just holding all the cells at 3.5v in float. 

You could put a 60v charger on the cells with no balancer after charging at 56v and all the cells will go out crazy, any where between over 4 volts and 3.5v, it is not a reliable thing over 3.5v with no BMS.

The only reason BMS's are set at 3.65v and some even 3.75v and higher is so there is plenty of head room between full charge cells and one which maybe low.

 .25v is a pretty high resolution circuit under 7% tollerance, if you wanted a BMS to work at .01v, this is .3% tollerance, thats getting a very expensive BMS, you would have a lot more trouble getting them to balance at all and the charge may take forever.  As the BMS works to disconnect the charger to the battery if one cell gets too high to give the BMS chance to burn off the excess voltage..


All my cells stay with in 0.01 balance for weeks by themselves. I pull my resolution from the time factor and internal resistance of the cells being so low, And over a month are lucky to go out by .1v.  You can not fool a series charge on lifepo4. Every cell get equal watts.  The only difference between cells usually is their internal resistance and this is soooo small, unless you have a bad cell.  They self discharge while resting and more so if you use or charge them hard. So it is a good idea to also lower your current and charge more slow.  This happen anyway if you reduce your voltage.

By adjusting to a 3.5v per cell you don't need a BMS but you do have to occasionally balance the cells with a single cell charger..  If one cell gets low and doesnt get up past that 3.35 mark  Most of the other cells will take on that single cells lack of voltage readily, so really .15v over 16 cells is nothing.  If you don't adjust the voltage down with no BMS the fast rise to 3.65v is unpredictable and one cell could rise .

[Morgen 3Eman]

Hi Les,

Ok, wtf are you talking about? I have a 48VDC GM supplied battery and charger.   My charger has a plus and a minus connection.  It apparently puts out around 56 Volts.  Is the other circuitry inside the battery housing?  Am I to understand that each cell is charged independent of the other cells in the string?  Please remember that my battery experience is largely limited to submarine service-  something over 2.15 Volts available at thousands of Amps.   Any recommended reading for my ignorance?

Regarding my replacement controller, the DC supply wires have been routed  and soldered so they will are pushing against the housing, and with the softness of the  insulation and the process of cold flow, I expect there would have been a short across the battery in a matter of months.  I'm going to install a thin sheet of hard plastic insulation on the inside of the housing, and bend the supply wires back within the diameter of the  PC board.     

TTFN,
Dennis

[Leslie]

If you have a 16 cell lifepo4 the top end should be 3.65v *16 cells, this is 58.4v not 56v.

http://endless-sphere.com/forums/viewtopic.php?f=14&t=37047

If your charger is 56v and youre using a BMS then this is wrong or you multi meter is out..

A lot of BMS is just a resistor based switching circuit with channels connected to each cell (sense wires).  When a cell reaches 3.65v its channel switches on a resistor between the cells lowering that cells voltage.  As you should know if one cell is low over a series cell charge or even forced low the other cells will go higher..

Well the BMS works kinda both ways, impedes and energizes cells. a lot of people don't understand how this works.  When the BMS puts resistance between the + and - of a cell it reduces the voltage over this cell by using up energy and current which the cell is more than happy to provide without taking anything much from the acualy charge current..  This voltage reduction over the cell causes the surrounding cells volts to go higher making them abosrb more watts, at the expense of the BMS of the high cell that activated a BMS channel..

[Leslie]

See those resistors.  These are what switch over the cell to limit them from going too high.

The BMS is like a voltage tight rope.  Lose one stablizer cable and it falls over flinging the walker off to its death..  Rather scary if you ask me.

This is a 12 channel BMS.  For a 36v battery.

[Morgen 3Eman]

Hi Les,

If I understand you, correctly, the high wattage resistor string parallels the battery cells, with what looks like an opto-isolated FET to switch the resistor across the cell that is charging more quickly than the others.  That makes some of the charge current to be diverted through the resistor which reduces the charge current for  the actual cell, while continuing full charge current for the rest of the cells in the string.   That is actually pretty clever, and very power efficient. 

My 56 Volt reading was from the battery output terminals after a charge, not from the charger under load.  Thus the "around 56" reading. 

So, when I make my power calcs, I should be using something like 54-56 volts rather than 48 volts in  IV=W to  be more realistic.  Right?  I'm using a Charge/Discharge meter from an Austin-Healey for the current reading.   

TTFN,
Dennis

[Morgen 3Eman]

Hi Folks,

Well, I installed the new controller, mounted the MP3 to the chassis, and took it for a drive.  I don't like the steering,(I'm a long time Lotus owner)  ( I think it needs less trail, ) but the motor accelerates nicely, and the brakes work just fine.  Time to start the body work....

Thank you, everyone, for all the help you have given me. 

TTFN,
Dennis