Increasing power on a Prokit 901, questions.

[jan-norway]

Hi everybody

I have a GM prokit 901 and a 36V 12Ah LiFePO4 battery bought in april this year. Probably one of the best decisions I have ever made:D  We have recently moved to a place that is slightly more hilly so I have been thinking about increasing the power a little bit and maybe the range aswell. I have learned alot by reading this forum over the last months but I am still confused about a few things. Especially the electric part. It would be great if someone would have the time to answer a some of my questions / correct or confirm my current understanding!

I've read that the GM controller I have is limited to 15A. This means that my bike is running on max 36V * 15A = 540W. If I buy a 48V battery I would get 720W. And if I buy a 36V 16Ah battery I would get improved distance but not power due to the 15 A limit. Correct?

On the GM website I find the following info about the LiFePO4 batteries :
Max Discharge Current: 35A(12AH)/60A(16AH)
Max Continuous Discharge Current: 20A(12AH)/30A(16AH)

Are these numbers correct? This means that without the controller limit of 15 A max, my 12 Ah battery system could give me 20A * 36V = 720 W continuous and 36v*30A=1080 Max. I guess this would make a big difference in performance. And if I get a 36V 16 battery the numbers would be 1080W continuous and 2160 Max (if controller and wires could take 60A?)

Regarding the max discharge current. How long is this discharge, seconds, a minute, a short hill?

I don't need a strong powerbike, but a slight increase would be great. I guess the easiest way to achieve this is to buy a 48V battery giving me 720W without changing/modding the controller in any way (also no need to change controller settings). I could then carry the 36V I currently have as a spare for long rides. I understand that this would probably ruin the leds on my throttle as they are made for 36V (if I don't build some extra functionality).

Another option would be to buy another controller or modding my existing one. I don't have any experience with soldering so I am not sure if modding is a smart way to go. I have found this post from Alan http://goldenmotor.com/SMF/index.php?topic=4072.msg23115#msg23115 . However, I don't understand 100% what is gained here or if this would be a good approach for me. By altering the amplifier does the Amp limit double??

If I bought a 36V 16Ah battery, and had a controller which settings were 30A continuous and 60A Max discharge, and then changed to use my old 36V12Ah battery without changing the controller settings, would then the BMS in the last battery make sure that the 36V12Ah battery would be running within its safety sone? Or could possibly a Cycle Analyst be used to change max Amps on the fly? I'm not sure if it is clear what I mean here, I want to know if the BMS is always making sure that the battery is working within its limits or if some other agent is necessary?

If I buy another controller, the Lyen is mentioned on this forum, is it plug and play or do I have to fix alot of wires and stuff? Would this be a good way to go? My current controller often gets really hot, If another controller stayed cool it would one less thing to worry about.

I don't need higher top speed ( have 700C wheels so it already runs at around 40 km/h) so I'm leaning towards buying the 36V 16A battery from GM and using my old one as a spare/backup if I could get passed the 15 A limit.

I would really appreciate any comments and suggestions

Thanks for the help!

Jan

[jan-norway]

I forgot to write that I have a BAC-281P external controller.

Jan   

[Bikemad]

I've read that the GM controller I have is limited to 15A. This means that my bike is running on max 36V * 15A = 540W.
The actual current seems to vary, some users have measured up to 30 Amps while others have measured as low as 10.

If I buy a 48V battery I would get 720W. And if I buy a 36V 16Ah battery I would get improved distance but not power due to the 15 A limit. Correct?
Yes, a higher voltage pack will produce more power and a higher speed, but your range would be reduced if you ride at a faster speed because of the increased wind resistance.
As you say, more Ahs will only give an improved range.

On the GM website I find the following info about the LiFePO4 batteries :
Max Discharge Current: 35A(12AH)/60A(16AH)
Max Continuous Discharge Current: 20A(12AH)/30A(16AH)

Are these numbers correct?
The maximum current rating is controlled by the BMS, but I have a feeling that the continuous rating is just a recommended maximum continuous current which the cells should be able to cope with, rather than a physical limit imposed by the BMS.

This means that without the controller limit of 15 A max, my 12 Ah battery system could give me 20A * 36V = 720 W continuous and 36v*30A=1080 Max. I guess this would make a big difference in performance. And if I get a 36V 16 battery the numbers would be 1080W continuous and 2160 Max (if controller and wires could take 60A?)

Regarding the max discharge current. How long is this discharge, seconds, a minute, a short hill?
This seems to vary according to the cell manufacturer. Some suggest 5-10 second bursts max., while others say up to 30 seconds.

I don't need a strong powerbike, but a slight increase would be great. I guess the easiest way to achieve this is to buy a 48V battery giving me 720W without changing/modding the controller in any way (also no need to change controller settings). I could then carry the 36V I currently have as a spare for long rides. I understand that this would probably ruin the leds on my throttle as they are made for 36V (if I don't build some extra functionality).
My 36V throttle LEDs are still running fine and are regularly powered by my 51.8V LiPo pack which starts off at 58.8V. The throttle control gets noticeably warm during use and the three LEDs stay on continually, but they seem to have survived OK so far.
If you want the gauge to actually work with the 48V battery, you will need to fit a resistor into the gauge supply wire as per this post.
If you connect a small switch across the resistor, you could easily set the gauge for either 36V or 48V operation.


Another option would be to buy another controller or modding my existing one. I don't have any experience with soldering so I am not sure if modding is a smart way to go. I have found this post from Alan http://goldenmotor.com/SMF/index.php?topic=4072.msg23115#msg23115 . However, I don't understand 100% what is gained here or if this would be a good approach for me. By altering the amplifier does the Amp limit double??
I have not been brave enough to try changing the incredibly tiny components on the circuit board, so I opted to increase the shunt instead.  If you're happy with a small increase in current I think it can safely be achieved without overloading the controller. However, I wasn't happy with a small increase, so I greatly increased the shunt for even more power, which eventually killed the controller after I increased the size of the shunt a little bit too much:


If I bought a 36V 16Ah battery, and had a controller which settings were 30A continuous and 60A Max discharge, and then changed to use my old 36V12Ah battery without changing the controller settings, would then the BMS in the last battery make sure that the 36V12Ah battery would be running within its safety zone? Or could possibly a Cycle Analyst be used to change max Amps on the fly? I'm not sure if it is clear what I mean here, I want to know if the BMS is always making sure that the battery is working within its limits or if some other agent is necessary?
As I mentioned earlier, I think the BMS only controls the absolute maximum current rather than the continuous current, so the Cycle Analyst could be used (with the correct installation) to restrict the current if required.

If I buy another controller, the Lyen is mentioned on this forum, is it plug and play or do I have to fix alot of wires and stuff? Would this be a good way to go? My current controller often gets really hot, If another controller stayed cool it would one less thing to worry about.
The Lyen Controllers will be fitted with different connectors (some or possibly all), but your phase wires coming from the motor may need to be upgraded to handle the increased current.

I don't need higher top speed ( have 700C wheels so it already runs at around 40 km/h) so I'm leaning towards buying the 36V 16A battery from GM and using my old one as a spare/backup if I could get passed the 15 A limit.
I would suggest increasing the shunt very slightly (use a single leg from an LED (or a piece of wire from a resistor) of ~0.5mm diameter) to see how much difference it makes with your existing pack, but please don't increase the shunt as much as I did!

My original MPI with the shunt mod was regularly drawing up to 60 Amps, and continued to do so for almost 12 months. It was only after I further increased the size of the shunt that the controller finally gave up and admitted defeat.

I mainly use the Smart Pie at the moment, but the MPII that I fitted to my other bike back in April when I blew the controller (also with a modded shunt) still draws a maximum of nearly 60 Amps and has never let me down.

I can only really comment on my own experience, where I have found the shunt mod to work reliably, as long as I've kept the maximum current below 60 Amps.
Unfortunately, there are times when I can no longer resist the immense temptation to further modify the controller for even more power, and this is usually when my problems begin.

I wonder if hypnotherapy could be used to cure my current addiction?
                                                                                               
Alan
 

[jan-norway]

Thanks alot for another great reply Alan!

This might be a stupid question, but does the controller software settings regarding max amps still work after the shunt has been modified?

By the way, I got a reply from Goldenmotor that they don't sell 36V 16Ah batteries. The information I found about this battery on the website must be outdated.  They also said that the BAC-281 controller should be 30 A.

Thanks from snowy Norway,

jan

[Bikemad]

Hi Jan,

The software should still adjust the current, but in larger increments than before, but I haven't actually tried reducing the current as I have always been trying to obtain more, not less.

I see what you mean about the battery, I just checked the site, and it appears that the 16Ah rack pack battery is now only available in 24V format.

The description for the BAC-281P says 36V/50A, but I have not heard of anyone getting anywhere near 50 Amps from that controller without actually modifying it.

Do you have any means of measuring the actual current being used by your controller?

Alan
 

[jan-norway]

Thanks again Alan! Sorry for answering so late, but I have been visiting my parents for a week.

I currently have no means of measuring the actual current being used by my controller but I certainly see the use here   I have been thinking about buying the CA but lately I have been dreaming about building a full suspension e-bike. We'll see I have alot of time, but money is another issue. The shunt-mod you suggested sound like a fun and cheap project. Guess I might give it a go some time this winter. If I have understood it correctly it just requires soldering equipment and a leg from a LED. Should be doable!

Bought an 1800 lumen bike-light/headlamp off ebay the other day though. Looking forward to it big time. The sun sets so early in Norway now.. 
However, after ordering I found a 5600 lumen and wanted that instead. Just the way it is I guess

Jan