I need more SPEED!

[mike662]

Hi all! I love my GM 1000W but I need it to go faster, say about 70km/h would be nice (I'll be getting some motorcycle safety gear of course) Torque I don't care too much about. Anyway, I know you can overvolt the system to make the wheel spin faster, but my question is how? Can I rewire the cells in the GM battery pack to go up to 72V or more? Then I assume I'll need to do something with the controller as well but I don't know what. If this is not feasible then I might end up getting a Cyclone 1200W kit (http://www.cyclone-tw.com/order-M.htm). Does anyone know if I can use the GM battery and controller with that kit? Thanks in advance!

[Bikemad]

Hi Mike, reconfiguring your GM battery for 72V is not going to be a simple conversion.
As your pack is made up of 39 4Ah cells (13 groups of 3), the nearest you could achieve would be 70.3V 8Ah, but this would entail major work to reconfigure the pack to a 38 cell pack consisting of 19 groups of 2 paralleled cells. You would also require a replacement BMS board that could monitor the 19 cell groups and a 79.8V charger too!
Because the reconfigured pack would only be 8Ah instead of your current 12Ah, the available maximum and continuous Amps would also be a third less, giving you 13Amps continuous (~980Watts) and 23Amps max (1748Watts).

The GM controller would also need to be replaced, as they will not normally run on voltages above 60volts and the capacitors are only rated for 63V max.

The cyclone motors are brushless, and the the smaller ones have built in controllers, but the larger ones are supplied with external controllers so they should be able to work with the GM controller and battery, but I'm not sure that your GM controller will provide the 25Amps required to produce 1200Watts@48V.

Alan
 

[mike662]

Thanks for the reply Alan! I guess there's no simple solution to this apart from spending more money to buy more stuff. Would you happen to know what the "C" rating of the 48V 12Ah battery is? I would like to know whether or not using the battery with the Cyclone motor and external controller (the 1200W version) would kill my battery.

Thanks so much as always for sharing your knowledge Alan!

[e-lmer]

Mike;

The C rating is the ratio of the max current to the
number of Amp Hours for the pack.

The 48V12Ah pack is rated at max discharge of 35A,
which is just under 3C.

Of course like any machine, running at red-line is
going to decrease the useful life of it.

A good rule of thumb is to run at no more than
80% continuously.  That is 28 Amps for this pack.

Of couse, like anything, Y,M,M,V,

[Bikemad]

Would you happen to know what the "C" rating of the 48V 12Ah battery is?

Mike, GM's specified output for the 12Ah battery pack is 20Amp continuous and 35Amp Max, but the individual 4Ah cells are described as follows:

Maximum continuous charging current 6.5A
Maximum continuous discharging current 10A
Maximum pulse discharging current 40A

So for a 12Ah pack (groups of 3 paralleled cells) I would expect 30Amp continuous (2.5C) to be OK for the cells, so long as the BMS can cope with it.

Providing 1200Watts of power @ 48Volts would require 25Amps, and this current should automatically decrease as the motor's speed increases (even with the throttle fully open), so you are very unlikely to be drawing as much as 25Amps continuous from the pack.

If you were to try and draw too much current, the BMS should cut off the power to prevent damaging the cells anyway.

Alan
 

[mike662]

Ah, thank you gentlemen for clearing that up for me. I've been doing some more research and decided that for now I'll look at getting a new controller and battery. I would like to be able to do at least 60-70 km/h. I do not care too much for torque as I'd rather not rip out my dropouts, but I do want a high voltage for speed. Is a high-voltage, low-amps combo possible? What controller and battery do you recommend? Thanks!

[DirtyGinge]

above 20mph, the wind resistance increases dramatically, you will have to have a lot of sustainable amps handy. I remember right, at 30mph, nearly 70% of the power goes to overcoming wind resistance...even the amp difference between 20 and 25 is surprisingly also you will need about double the ah you use now, as with higher voltage the efficiency reduces

[e-lmer]

Alan;
The GM battery page rated the 48V12Ah pack at
35 Amp continuous.

Any idea why?

[Bikemad]

Elmer, it's actually 35Amp Max not Continuous!

This was taken from the GM battery page:

Max Discharge Current: 35A(12AH)/60A(16AH)
Max Continuous Discharge Current: 20A(12AH)/30A(16AH)

But this is still a lot less than the combined cell rating for the 48V 12Ah pack (13 groups of 3 x 4Ah cells in parallel), which should give a maximum continuous discharge current of 30A, and a maximum pulse discharging current of 120A.

Also, the stated maximum continuous charge current is 6.5Amp for a single 4Ah cell, so presumably the 12Ah packs could be fast charged at 19.5Amps and the 16Ah packs at 26Amps with a suitable charger (provided the BMS can cope).

Alan
 

[mike662]

So I've decided what I'm going to do for more speed. First off, I'm buying some safety gear: dirtbike helmet and gloves, motorcycle mesh jacket with armored chest and shoulders at least, and maybe pants and boots but I doubt it as I won't have anywhere to store it once I get to my destination.

Ordered some of these torque arms along with the epoxy to practically "weld" them on: http://endless-sphere.com/forums/viewtopic.php?f=31&t=29129 Finally found a solution for easy and strong torque arms, thanks Doctorbass!

Ordered this controller (an amazing deal, just read the thread on it to find out more): http://www.dhgate.com/72v-1500w-brushless-speed-controller-for/p-ff808081283845f5012848d41bf455fb.html

Discussion on the controller: http://endless-sphere.com/forums/viewtopic.php?f=2&t=29469&hilit=hua+tong It basically is not programmable but has cruise control, regen, mutli-speed switch compatible, tested with over 100V, $33USD shipped 

I'm looking into getting lipos so I've been doing a whole bunch of reading on those. One person suggested I just attach a 6s (~22.2V) lipo pack in series with my current GM 48V and just put in a diode from the GM pack to avoid damage/setting off the bms. Would this work, or should I just get all lipos?

[o00scorpion00o]

If it's the non Magic Pie motor then you might burn it at 72 volts.

You might get away with it if you turn down the amps but then you won't have decent current.

Get a magie pie external controller motor. On 72 volts you should get 30-35 mph or more on a controller you can set the speed to 120 % for an extra 5 ish mph!

By the way a 1500 watt controller is not that powerful at speeds.

You see you need sufficient torque to allow you to reach 60-70 kph and a 1500 watt controller won't do it I'm afraid, nor will the 1kw GM motor. You will burn it and it doesn't have torque!

The pie is the motor you need and at 33 mph I pull around 2100 watts to maintain that speed and that's before I start to climb steep hills, it's a hungry motor but you got to watch your phase wires that they don't melt, if they start to get too hot you need to replace them with 12g alpha wire ecowire!

For 60-70km you need around 80 volts with the pie and 40 amps that's 3200 kw, and probably 5kw peaks!

Yes the pie will take it and no the normal 1kw GM motor won't!

You also need a battery capable of those kinds of currents, GM batteries are a no no, they are designed for their own kits at stock currents!

You are talking LiPo or A123 batteries and you will pay for the A123 but might be as cheap as 2 GM batteries.

Pm me if you want more info on batteries.

Trust me the need for speed gets expensive!

[o00scorpion00o]

Lol how come I didn't see this post from August?