Puch Maxi Hub motor project.. -help needed

[Rasmus F]

Hi All
I have used some time now searching the forum for answer, only to get more confused.

First of all.. I'm a grown child (44y) from Denmark, and I'm amazed to find so many fantastic people, with more or less crazy projects on this site :thumb:

My beginners project is really simple, or so i thought.
I have an old moped, most europeans know them well as the Puch Maxi, and I thought it would be brilliant to electrify my vintage moped.
From my reading i have found a ground idea of what I want, but need a little help on some specifics before placing the final order.

Im thinking :
Motor: 3KW QS hub motor V3, in a 17" rim. Its about 1.7m/rotation.
Battery: 72v 2100A 156Ah (build with 18650 li-ion, unless someone convince me otherwise)
Controller: Sabvoton Sine Wave Controller 150A (SVMC72150 if that's still good)
Speedometer: Cycle analyst V3
BMS: ?

My problem is that I simply can't figure out the perfect winding for the engine. I'm thinking the total weight with me on it will be 130-150Kg
I'm hoping for 80kpm topspeed on flat road, but thinking the "normal" cruise speed would be more like 40kpm.

The battery I will make from li-ion 18650, and I did some calculation on it but am not sure got it right.
Sony makes this US18650VTC5A 2600mAh 35A 3,6V.
60 of these batteries put together as 20 groupes of 3 would give me total 72V 2100A 156.000mAh, im thinking that would be ok for 150km at 40kph.
What about BMS.. what is my best choice here.

I surely am missing something else.. but let's make this a good start..

/Rasmus

 

[larsb]

your battery calc is unfortunately not correct. each series group can only contribute with it's own 35A current at 72V
60batteries*3.6Volts*2.6Ah=562wh. It will get you something like 15-20km of range at 30-40wh/km guesstimate.
Three parallel battery strings gives max 3*35A = 105A absolute max from your given battery. This current output will quickly kill it but it can do it for short periods.

For the winding a good estimate would be to choose something like kV=14 winding, whatever turn count that is. That should give you the top speed you want at 72V. Hubs are not my cup of tea but i think the 205 will be able to make it without breaking a sweat.

You should play with the motor simulator at ebikes.ca - it's great. I didn't find the 205 motor there but you can input custom motor parameters from QS motor - or someone here will know what motor is most similar to it.

 

[flat tire]

If you want a comfortable 80 kph in a 17" wheel with ~70v you probably want one of the faster windings.

QS motor is helpful and will suggest which winding you need, if you email them with those three numbers: wheel size desired speed and battery voltage.

The ebike simulator does basically have a QS205 (cromotor). But you will need to manually adjust the KV because it's a slow winding.

 

[Dui ni shuo de dui]

BMS: ?

Check the ANT 300A Bluetooth Smart BMS. It works really well, plus you have a little screen so you can see the power draw, the state of each cell, different temperatures, the odometer, the autonomy you have left, etc. Basically you can use this instead of the cycle analyst, it does pretty much the same thing. This will save you a bit of money for more cells in your battery

My problem is that I simply can't figure out the perfect winding for the engine. I'm thinking the total weight with me on it will be 130-150Kg
I'm hoping for 80kpm topspeed on flat road, but thinking the "normal" cruise speed would be more like 40kpm.

Just tell that to QS motors and they will figure out the rest.

The battery I will make from li-ion 18650, and I did some calculation on it but am not sure got it right.
Sony makes this US18650VTC5A 2600mAh 35A 3,6V.

That's an excellent cell choice. Those are amazingly good.
If they weren't so expensive that's probably what I would have used on all my projects. Either those ones or the VTC6.

60 of these batteries put together as 20 groupes of 3 would give me total 72V 2100A 156.000mAh, im thinking that would be ok for 150km at 40kph.

MMmhhh I think your calculation is incorrect.
You have 20 series and 3 parallels.
So, 20 series x 3.6V = 72V
3 parallel x 2600mAh = 3 x 2.6Ah = 7.8Ah total capacity
3 parallel x 35A = 105 A of maximum continuous discharge current.

Your controller needs at least 150A of continuous discharge current. So, 150 /35 = 4.2 P. So you need at least 5 cells in parallel if you don't want to ruin your cells too fast. I suggest you to go even higher, if possible at least 6 cells in parallel. This way, each cell will need to output a maximum of 25Amps, which is already a relatively high output (but these cells are very capable so I guess they will be ok with that).

If you go for 6 cells in parallel, that will give you 6 x 2.6 = 15.6Ah of total capacity. That's not a lot of mileage, I guess something around 30-35 km.
If you want to get more distance, then just add more cells in parallel. Basically the more cells you can parallel the better it will be for you, both regarding max discharge, total autonomy and also cell lifecycles. Only problem here is, of course, that these cells are quite expensive, and you'll need to have enough space to fit them in your frame.

 

[Rasmus F]

That's some miscalculation on the battery..

Now having made new calculations, Dui you recommended using the VTC6 battery, if I understand correctly it's for having more mAh, and the Amp still meets the controllers 150A, correct?

So, I measured out the bike and am thinking I can fit about 3 pack of 120 batteries, total of 360pc 18650.
So new calculation is like this.. 20 cells of 18 batteries. If I choose the VTC6 type with 3,6v 15A, 3000mAh this would give me 74V 54Ah 270A Right ?
And from Larsb's calculation of Wh this would give me 3888Wh and a guesstimate of 150km moderate driving.

Would it be a better option to make the battery 92V instead, to bring the Amp and heat down in the motor ?

That setup could look like this: 26 cells of 14 batteries. Using the same batteri it gives me 92V 42Ah 210A

I'll definitely go for the ANT 300A Bluetooth Smart BMS.. :thumb:

/Rasmus

 

[Dui ni shuo de dui]

That's some miscalculation on the battery..

Now having made new calculations, Dui you recommended using the VTC6 battery, if I understand correctly it's for having more mAh, and the Amp still meets the controllers 150A, correct?

Actually to be honest, I'm not sure anymore that the VTC6 is better than the VTC5A. So you might want to dig a bit deeper here. Anyway, both cells are very, very good so choosing any of them will still remain a good choice no matter what
The VTC6 does have a bit more capacity, but that a bit more complicated than this. I won't go into the details since it is a complicated topic and it would take a while to explain, but basically it's not because you have more capacity that you will actually be able to use it under high discharge rates... So I guess, what I'm trying to say is that it is possible that the VTC5A could actually be better. Try to find some better resource than myself on that matter, I only tried the VTC6 so far.
Anyway, both are good, that's for sure

So, I measured out the bike and am thinking I can fit about 3 pack of 120 batteries, total of 360pc 18650.
So new calculation is like this.. 20 cells of 18 batteries. If I choose the VTC6 type with 3,6v 15A, 3000mAh this would give me 74V 54Ah 270A Right ?

That's perfectly correct.

And from Larsb's calculation of Wh this would give me 3888Wh and a guesstimate of 150km moderate driving.

Yes, I think it will easily give this range, given that your frame is somewhat small and lightweight.

Would it be a better option to make the battery 92V instead, to bring the Amp and heat down in the motor ?

Theoretically yes, but then you'll have a harder time to get a good controller, everything gets more complicated and expensive above 72V.

That setup could look like this: 26 cells of 14 batteries. Using the same batteri it gives me 92V 42Ah 210A

I'll definitely go for the ANT 300A Bluetooth Smart BMS.. :thumb:

I'm not sure you could still use this BMS with a 96V setup.

 

[larsb]

Qs205 50h turn specs:
the 40*3T would fit your specs

 

[j bjork]

The 3T will fore sure get your 80kpm, and some more.
With 4T and 17" I just get 80kpm on a fully charged 20s, but that is with lipos with very little voltage drop. On low charge I probably get more like 70kpm ( I don´t have a speedometer, I have just checked with gps sometime)
If you are building a relatively weak li-ion battery you might not get there. But with your weak controller the 4T may still be the better choice, because you can not feed the 3T motor enough amps to get good performance.

But if you go for a better controller the 3T will probably be a better choice.

 

[Rasmus F]

But with your weak controller the 4T may still be the better choice, because you can not feed the 3T motor enough amps to get good performance.

But if you go for a better controller the 3T will probably be a better choice.

Hi.. So you think the Sabvoton Sine Wave Controller, SVMC72150 is weak ??

 

[j bjork]

A little, but it was better than I thought. It seems like max phase amps are 350, I thought it was 300. For the 4T QS recommend max 300A, and for 3T max 400A. At 350A you will get more torque from the 4T than the 3T. I don´t know how much difference there will be though. If you go for 3T you will get higher top speed, and more power from something like 50-60km/h where the 4T peaks. But a little less up to that.

Here is an example with mxus:
https://www.ebikes.ca/tools/simulator.html?motor=MX4503&batt=cust_84_0.03_20&cont=cust_150_350_0.03_V&wheel=24i&cont_b=cust_150_350_0.03_V&motor_b=MX4504&batt_b=cust_84_0.03_20&wheel_b=24i&bopen=true

This is not what you will get, this is a less powerful motor. The mxus 3T is simular in kv to the qs 4T from what I remember.
If I should guess, I think the difference in torque will be a little bigger. Because 350A is probably a bit much for the mxus 4T. You can play with the numbers a little, maybe try something like 250 phase A to see the difference there.
But the best thing is to try to find the right numbers for the qs motors to compare, but I think I have already asked for that on the forum without response.

About the battery I was a bit fast to judge, I read something about 20s3p. Of good cells, but still 3p.. It seems like the plan is 18p now, so that is a different story. If it is well built it should have low voltage drop I guess