Hello Everyone, First time on AAC, been reading all the posts for many years and it has helped a lot in my education of various circuits. Decided to post because i really need help with a project. Was tinkering with different motors and after some research built a few different pulse motors and BLDC motors. All of which performed very well and spurred me on to build bigger and better. Currently i have a motor with 15 stator coils and a 3 pole rotor (120 deg). Built a simple driver using mosfet and hall ic and it shows great promise. Trying to increase voltage to get more speed but encountered two problems , 1) cant control speed incrementally as there is no speed control and the BEMF\CEMF prevents a full rotation after 36 volts. I am assuming the field isn't decaying fast enough before the magnet reaches the coil and it kicks the rotor back instead of forward at 48 v, at 36 v everything is fine. I think i have to create a alternative path for the field to be depleted from each coil as the pole passes it after being energized. The neons across the coils are meant to arrest the emf and work fine at 36 but are glowing white on higher voltages which indicates that the emf is getting stronger with increased voltage.
Any suggestions on :-
1)how to bleed off emf faster or channel it into a capacitor which then discharges into a lamp or some load?
2) Have not found any MCU that works on 5 phase so need a way to control speed if possible because at this stage it starts at high speed and really wants to take off!!!

Attached crude diagram of current setup (apologies , dont have software to draw proper diags). Any help would be greatly appreciated. I have spent a lot of time and resources on this project and didnt want to abandon it now because of a hurdle which might have a solution out there.

Thank you all and keep up the good work. i would never have learnt all i know in electronics if it wasn't for sites like AAC!!!

 

Currently i have a motor with 15 stator coils and a 3 pole rotor (120 deg). Built a simple driver using mosfet and hall ic and it shows great promise. Trying to increase voltage to get more speed but encountered two problems , 1) cant control speed incrementally as there is no speed control and the BEMF\CEMF prevents a full rotation after 36 volts.

That combination especially the 3 pole rotor is your problem. Even 3phase BLDC motors have more rotor pole s than that. Have you read any of the online papers on how people are doing the 5phase motors?
https://www.google.com/search?q=5+Phase+BLDC+Motor&ie=utf-8&oe=utf-8&client=firefox-b-1

 

H Shortbus, thank you for the response. Yes I have done extensive research on both 3 phase and 5 phase motors .What pole config would you suggest as a start since I have 15 coils and use 3 in a set ? I am not driving the motor with distributed windings as is done traditionally in 3 phase using Allegro or Microchip or any of the other MCU available on the market. Initially to gauge the motors capabilities I prefer to drive it "raw". As per the attached diagram each coil is driven by its own Mosfet which is triggered by a hall . Slight drawback is torque jerk at start up but so far up to 36 volts the motor runs perfectly. I'm concerned about that jerk as I increase voltage hence the need for a crude speed control . Wanted to try some sort of PWM using 555 but the mosfets are triggered by the hall so didn't know where that would feature.
Yesterday I think I figured why it doesn't run on 48v, the rotor passes two coils of a set and kicks back when it reaches the third coil in the same set. Either the field is not collapsing fast enough and has a reverse thrust or the timing needs to have a shorter pulse. Added neon lamps to bleed field and they burn white instead of glowing orange which indicates high emf current? as voltage was around 8 v ac when measured with DMM. Going to tweak timing today to see if that helps.

 

Never had any experience with 5phase. Or for that mater 'salient pole driving' like your talking about. Also I've never heard of just using voltage to make them run faster, the usual thing is to increase to frequency of pulses and leave the voltage alone. You seem to be exploring a whole new way of doing this, that it seems no one else is doing.

But maybe some of the papers/PDFs from this Google search might help you -
https://www.google.com/search?q=bld...ratio&ie=utf-8&oe=utf-8&client=firefox-b-1-ab

Or this one -
https://www.google.com/search?clien....gws-wiz.......0j0i71j33i22i29i30.QB8kuwesfjI