Using 1500W DC to DC converter to provide the motor with a max constant power...

[Papagino]

Hey guys, I would like to have an opinion from a knowledgeable person in electronic circuit on the following:

A year ago, I was using a 1500 watts DC to DC converter on my Magic Pie 5 to increase Power and eliminate voltage sag when Hub motor was in high demand. I was able to pull 1900 watts Max from the stock Magic Pie with no problems and minimal heat running at 62V @ 31 amps.
Amazing torque and speed...

Unfornutally, these DC to DC converters may overshoot the voltage output when the Hub Motor suddenly becomes in Regen mode, damaging my Magic Pie controller that has a 63V limit.

I am currently designing a new circuit to use this DC to DC converter to prevent this from happening again on my new enduro ebike build.

Here are the specs for the DC to DC converter available on eBay:
(Please see photo)


Specifications:
1, Product Name: High Power DC boost power module.
2, Model: AP-D5060B
3, the input voltage: DC10.5V-60V.
4, the input current: 50A maximum.
5, the input power: 1500W maximum.
6, the output voltage: DC15V-70V.
7, the output current: 30A maximum.
8, the conversion efficiency: 93-97% (efficiency and output voltage and current input related).
9, operating temperature: -20 to 50?.
10, Weight: 1000g

Main feature:
1, high conversion efficiency.
2, the original high-power devices.
3, high-power high-current magnetic sendust.
4, aluminum alloy shell.
5, electronic temperature control with intelligent fan cooling.
6, the input MOS transistor anti-reverse.
7, input undervoltage protection (with LED indicator, adjustable voltage, to protect the battery when the battery power).
8, input over-current protection (with LED indicator).
9, the output adjustable constant voltage constant current even continue.
10, small volume.
11, high reliability and stable operation.
 Main use:
1, high-power solar street driving.
2, large mechanical and electrical equipment supply.
3, various LED lighting constant current drive.
4, and a variety of mobile devices powered car.
5, DIY adjustable constant voltage constant current power supply.
6, solar charging power.
7, for a variety of battery charging.
8, electric vehicles into various motors (motors only the largest category with 350W, 24V input above)

The function of the DIP switch
Output current limiting switch 
Input overcurrent protection switch
Turn lights lock switch
Input undervoltage lockout switch


Here is the circuit that I need your feedback on:
(Also attached)



Usually, N-ch MOSFET have the Source pin connected to Ground, but in this circuit, it is connected to Battery Positive (58V Max) via the power diode D1, would this work, if the voltage at the Drain pin would be at 62V+ by forcing the current to flow through the MOSFET when triggered?

Attached is a photo of my Enduro Ebike build:

Here is my Ebike in action:
https://youtu.be/N3TJ9dg9GLA

Please examine the circuit and provide your thoughts and feedback.

Cheers
Dan

[Bikemad]

Hi Dan,

If you managed an output of 1900W you must have been overloading the DC-DC converter, as it clearly states a maximum input power of 1500W.
1900W Output power @ 97% efficiency would require an input power of at least 1958W (or 2043W @ 93% efficiency) which is 30% (or 36%) more than the stated maximum input power rating. 

I'm not sure what will happen to the the power stored in the inverter capacitors when its output is suddenly shorted directly to its input via the MOSFET. 

I am also not sure how much current the MOSFET will be able to pass with a gate voltage of just 1V. The voltage could still exceed the 63V controller limit during high speed braking if the MOSFET is unable to sink all of the generated current back into the battery.

Even if the MOSFET is able to pass sufficient current, it is also possible that the Battery's BMS might might instantly disconnect the battery if the voltage is too high, which could also result in the death of another controller.

Alan
 

[Papagino]

Thanks Alan for your input.
Those DC to DC converters are pretty rugged and could probably output 2500 Watts in a burst as in can take 50Amp input.
There is a Fan on it and I never noticed actually turn on, as the heatsink on it stay pretty cold.

You mentioned "I'm not sure what will happen to the the power stored in the inverter capacitors when its output is suddenly shorted directly to its input via the MOSFET"...
- That input is also directly connected to the large capacity battery, wouldn't this absorb the load?

Also "I am also not sure how much current the MOSFET will be able to pass with a gate voltage of just 1V"...
- I agree, R2 50k value would need to be calculated in order to bring the voltage around 10V to the MOSFET gate...

"The voltage could still exceed the 63V controller limit during high speed braking if the MOSFET is unable to sink all of the generated current back into the battery."
- Again, wouldn't the battery absorb all this energy when the MOSFET is fully turn on by a proper gate resistor by the 62V zener?

"Even if the MOSFET is able to pass sufficient current, it is also possible that the Battery's BMS might might instantly disconnect the battery if the voltage is too high, which could also result in the death of another controller."
Do you thing this could happen even if the battery pack is 50Ah? I think that even a burst of 70V+ for 30 seconds would not even change the pack voltage
noticeably. Wouldn't you agree? Also, the BMS is programmed to only charge the cells at 90% of their capacity (4.15V)

Do you think of any other way to prevent the MP5 controller from never seeing a voltage higher than 62V?
What about turning off Regen...

Thanks again for your input Alan.

[Papagino]

As a note, the reason I am looking into this option, is that my current setup is using  a 15S 10P @ 2.1 kWh Panasonic NCR18650GA battery pack.
The problem with this current setup is that the battery voltage is sagging a lot. The pack voltage is 62V when fully charge, but as soon as I reach higher speed, the voltage drop to around 53 - 54V at around 20Amps draw on level ground. The DC to DC converter would prevent this with constant voltage/current output by adjusting the input current to maintain it. With a new LiFePo4 large capacity pack, this would not be a problem anymore and the maximum power to the motor would always be available when needed.