Evening all,

FTP, so excuse any rubbish formatting.

TLDR: I have an issue at the moment where a BLDC driver i am making isnt drawing anywhere near the current it requires from a battery.

so i have 3 half-bridge set up running a 3 phase BLDC motor, you know the type...

I have code written up an verified to be working for the arduino, and its suppose to turn on the respective logic-level mosfets for each phase depending on the motor position (i can use the hall sensors or BEMF as i have a couple sets of code).

The logic-level Fets state i can use the 5V from arduino digital pins to turn on the Fets, allowing current through to turn the motor.

HOWEVER.If i use a lead acid battery, it only draws about 0.5A into the circuit (fair enough ,its only rated for 1.05A initial), but i do get resistance if i manually turn the wheel whilst the driver is running. If i use the battery i want to use (ebike/hoverboard battery - stated below), then it doesn't draw at all, whereas i know these are working as i can pull them right off and plug them into their proper devices, and they work (hoverboard and e-scooter), and they work no problems. i have multiples of each battery i can use.

now, ive looked at the devices ive pulled these from and had these batteries working, and confirmed charged. the main boards and ebike controllers have the v+/v- from the batteries connecting straight to the high and low sides of the gates, so i know that they should work.

thinking it is an issue with how im controlling the Fets?

Any ideas how i can resolve this to draw what its meant to be using?

Thanks to all who can help me...im stumped on this, i may be an amateur, but i know my stuff, or not as it seems!

see attached for schematic, excl. all sensor components.. excuse my appauling use of the software, still learning it.

components used are:
Hoverboard BLDC Motor - 350W BLDC
only working source - Lead acid battery - ''6fm3.5'' - 12V/e.5Ah - 1.05 initail current (stated) -http://images02.cdn86.net/kps01/M00/6A/4A/wKiAiVWZ5sLPAerCAA2ljvtaRgc979.pdf
desired Hoverboard Battery pack- 36V/3.4Ah/122.4Wh - (basicly 7x 18650 cells)
desired ebike battery pack - 36V/3.4Ah/144.4Wh - (basicly 10x 18650 cells with BMS)
Logic level Mosfet - RFP30N06LE - https://www.sparkfun.com/datasheets/Components/General/RFP30N06LE.pdf

 

I may be wrong about this, correct if I am. You have a hoverboard motor, hoverboard battery, why not use the hoverboard controller? Even if your putting it in an Ebike, why reinvent the wheel?

 

Yeah, i agree. in fact, i will be doing that with one set of the parts as part of a toy for my children.

i just wondered if i could do it to be honest, and see if i could put it to use

 

Your high-side N-FETs need a gate voltage higher than Vcc to turn them on.

When they turn on, the Source terminal rises to Vcc, to get the correct V-gs, this implies a voltage higher than Vcc.

Investigate using gate driver IC's- with gate boot-strapping circuitry.

The Aurduino I/O pin is not very good for driving a MOSFET gate at any decent frequency; the gate looks like a large capacitor that needs to be charged and discharged rapidly, it requires high currents during the transients.

 

Yeah, i agree. in fact, i will be doing that with one set of the parts as part of a toy for my children.

i just wondered if i could do it to be honest, and see if i could put it to use

Do you know there is an 'old school' way of doing this? But it requires a BLDC with Hall sensors. https://www.onsemi.com/PowerSolutions/product.do?id=MC33035 If you do a search for that part you can also find an Application Note that walks you through using it.

 

Your high-side N-FETs need a gate voltage higher than Vcc to turn them on.

When they turn on, the Source terminal rises to Vcc, to get the correct V-gs, this implies a voltage higher than Vcc.

thanks for the reply! So, its safe to say that if i have a supply of 36V from the battery to the high side, i need to apply minimum 36V+V(gs) to the gate of the respective fet?

https://www.onsemi.com/PowerSolutions/product.do?id=MC33035 If you do a search for that part you can also find an Application Note that walks you through using it.

thanks for that... ive just spent a few minutes browsing the data sheet and some pre-built boards with this IC, looks promising, may invest in a couple to simplify some projects. However, i would like to eventually create the drivers myself. 'Thrill of the chase' type thing.

plus I'm learning so much!

 

Yeah, i agree. in fact, i will be doing that with one set of the parts as part of a toy for my children.

i just wondered if i could do it to be honest, and see if i could put it to use

Also, i need to re program the GD32 chip on it, aannddd i cant afford the £75 for the GD-Link USB interface chip. ST links are cheap and work, but not with GD devices.

it gets speed and direction instructions from 2x accelerometer daughter boards via UART, which i simply dont have the ability to de/encode directly on. however, i planned to re-program the GD32 to use a simple potentiometer to determin speed like a foot/twist throttle. hence the chip.

if i could use an arduino to read 2x Pot~s and encode the inputs from them both to UART and send to the board, then fantastic, but i dont know what specific protocol that the GD uses unfortunately.