# Blowing MOSET with small homemade controller (10 A max, 120 V)



## peggus (Feb 18, 2008)

Your diode should be in parallel with the field, not the mosfet. And the way you have it drawn the mosfet is not even in the circuit, the field goes straight from 120V to gnd.

Oh, and your gate driver circuit isn't working either, there is nothing to turn off the gate and the turn on will be really poor with a high side Nfet driving it.

Lycka till.


----------



## jockepocke (Nov 24, 2009)

peggus said:


> Your diode should be in parallel with the field, not the mosfet. And the way you have it drawn the mosfet is not even in the circuit, the field goes straight from 120V to gnd.
> 
> Lycka till.


Why have the diode in parallell with the field? Would that not just by-pass all current when either reversing or going forward, so that no current is flowing trough the field? 

Also, the mosfet should be in the circuit. The gnd is actually 12 V gnd, and no current can flow from 120 v to ground with just one connection to ground. The ground connection is to allow the PWM generator (connected to 12 V) to turn on/off the big MOSFET that in turn control the field current. Any current going to 12 V gnd must come from +12 V, that is the MOSFET gate. Or am I wrong somewhere? 

In my testing I managed to make the circuit control another circuit with a separate power supply, just as will be the case in the car - just at higher power. 

Thanks for answering!


----------



## alvin (Jul 26, 2008)

It looks like you have the drain side of the mosfet is grounded. It should be source to the same ground as the gate voltage. there should be isolation from the 555 to the mosfet. optoisolator, mosfet driver, and dc to dc converter. Also the diode goes from drain to positive 120v. A mosfet should be derated alot so you should parallel a few of them. Maybe this is right . I hope it helps. Here is a link that might help.
http://robots.freehostia.com/SpeedControl/SpeedControllers.html


----------



## peggus (Feb 18, 2008)

Here's a back of the envelope drawing of what you need. The diode is there to give the energy stored in the field somewhere to go after the mosfet turns off. Otherwise it gets upset and zaps things.
Note that 12V here has to be referenced to 120V gnd or the mosfet can't turn on. You must NOT use your cars 12V, use an isolated DCDC to provide the 12V for your field controller.


----------



## jockepocke (Nov 24, 2009)

peggus said:


> Here's a back of the envelope drawing of what you need. The diode is there to give the energy stored in the field somewhere to go after the mosfet turns off. Otherwise it gets upset and zaps things.
> Note that 12V here has to be referenced to 120V gnd or the mosfet can't turn on. You must NOT use your cars 12V, use an isolated DCDC to provide the 12V for your field controller.


Ok, thank you all a lot guys, although it does seem very complicated to fix this - especially as the field current must flow in the opposite direction when reversing (and all current will then pass trough the diode and I will not have any magnetic field to drive my car...) 

And having to use a DC-DC makes things far more expensive and/or complicated... Am I right that the DC-DC thing is for safety (not ground the main battery pack)? This is however not as dangerous as it might sound as the controller does limit the current supply to the field to max. 10 A, and I will use a proper fuse. 

I will probably just go with resistive load as before. The best would obviously be PWM, but I cannot afford (and do not have the knowledge to build a proper one, obviously) right now... I am though going to scavenge the PWM controller to use with the 12 V motor cooler fan (it is just one direction so diode should work good here). 

Next question then: Anyone who knows if you can put relays in series to break higher voltage? In theory this should work - if they are shut off at the exact same time...


----------



## peggus (Feb 18, 2008)

Don't give up, you're almost there, and blowing things up is the best way to learn. Or at least the most entertaining way.

For reversing you don't reverse the diode, just the field coil so no, the circuit doesn't change.

You can put relays in series for breaking higher voltage but it's not recommended.


----------



## major (Apr 4, 2008)

peggus said:


> For reversing you don't reverse the diode, just the field coil so no, the circuit doesn't change.
> 
> You can put relays in series for breaking higher voltage but it's not recommended.


Or use an H bridge


----------



## peggus (Feb 18, 2008)

major said:


> Or use an H bridge


Shhhh, don't add more confusion


----------



## alvin (Jul 26, 2008)

If you want reverse. You will need an H bridge like major said. You need a different chip than 555. Get a mc33033 chip it will do the trick. Read the data sheet and application note an1078 for instructions.


----------



## peggus (Feb 18, 2008)

reversing contactor is far easier


----------



## major (Apr 4, 2008)

jockepocke said:


> I am connecting the PWM to the field supply of the controller (in that way it will not protest, and I can also limit the current to max 10 A),


Hi jock,

Doesn't your SepEx controller have user settable parameters which you can adjust to get the field weakening you desire?

Secondly, I see a problem inasmuch as you say you are using the controller field supply to power a PWM circuit in series with the field. The controller output to the field is likely a PWM in the first place. You cannot run 2 PWM circuits in series without a large filter between them.

Peggus has helped with the basic PWM circuit. But even when you get that sorted out, I fear you will still have problems using a PWM source for your PWM. 

Good luck,

major


----------



## jockepocke (Nov 24, 2009)

major said:


> Hi jock,
> 
> Doesn't your SepEx controller have user settable parameters which you can adjust to get the field weakening you desire?
> 
> ...



I can control the output, but not in the desired way. It is supposed to to be at 10 A up to 2000 RPM, and then about 2,5 A from 2000 RPM to 7000 RPM, kind of like shifting gears! The controller cannot control the field current according to RPM value (although I asked them to do this, and they said they could - turns out they misinterpreted me and only limited RPM to 7000). 

Without this function I can keep any constant speed up to nominal speed (nominal field) OR accelerate to max speed with reduced field. I cannot maintain constant speed above nominal speed and below max speed. 


You are right in that the controller uses PWM, but doesn't it have capacitors to filter the square wave and give a smoother DC current? I am afraid you are right though... 

Is there a way of measuring wether the controller actually gives a square wave, of if it does filter it? I do not have an oscilloscope at home, but I may may may be able to borrow one at school, I know that they have one. The controller frequency is 7,9 kHz.


----------



## major (Apr 4, 2008)

major said:


> Doesn't your SepEx controller have user settable parameters which you can adjust to get the field weakening you desire?


Hi again jock,

Is this the controller you have? http://www.elektrosistem.com/xtra/53 - News PHOENIX ING.pdf It says there: 
- Parameters adjustment by programming terminal.

Have you accessed the unit with a programming terminal? It could be you simply don't have it set up correctly. List up the field parameters you have set and maybe we can get it working so you don't have to monkey around with external band-aids. I have a concern you'll damage the controller doing that.

major


----------



## major (Apr 4, 2008)

jockepocke said:


> You are right in that the controller uses PWM, but doesn't it have capacitors to filter the square wave and give a smoother DC current?


No, it would use the field inductance to do this.


----------



## jockepocke (Nov 24, 2009)

major said:


> Hi again jock,
> 
> Is this the controller you have? http://www.elektrosistem.com/xtra/53 - News PHOENIX ING.pdf It says there:
> - Parameters adjustment by programming terminal.
> ...


It is that controller (or actually it is T62, that is not in the PDF, but the only difference to T61 is that it handles 120 V). I did buy the programming terminal and keyboard, so I can program all the listed parameters! 

I have tried many many different setups, but I have not gotten good results with any of them... I will list the settings as soon as I can though. Elektrosistem have not been able to help despite having a mail conversation with them. 

What I know in my head is that for now the settings are: 

Max. acceleration current: 200 A (motor can handle 300, but 200 was enough and does save batteries)
Max current at max voltage: ~150 A
Min braking current: about 30 A
Max braking current: maybe about 70 A
_Braking end max current (- not sure what this does actually)_: maybe about 100 A
Acceleration: about 45/50
Deceleration: about 35/50 

max. field current: 11 A (had to be higher than nominal) 
nominal field current: 10 A
Reduced field current: 7 A (I choose this as it gives me a top speed of about 50 km/h, and as I cannot keep constant lower speeds this suited well). 
rotor level - field max current: I think I set this to somewhere about 70 A now, but I have tried several settings
rotor level - field min current: Maybe I am mixing this up but I think it is set to about 300 A or something. Also tried many different settings. It has to be higher than "rotor level - field max current". 
Forward speed reduction: 100 % (i know that driving is driving forward in the controller software - I have not mixed up the field wires)
Backward speed reduction: 33 % 
Creep speed: 8 (this is the least value I can have, tried higher once, but car started jerking and could not be still...)


----------



## major (Apr 4, 2008)

jockepocke said:


> It is that controller (or actually it is T62, that is not in the PDF, but the only difference to T61 is that it handles 120 V). I did buy the programming terminal and keyboard, so I can program all the listed parameters!


Hi jock,

Maybe we can figure this thing out. Please post the actual parameters you have set and also the motor nameplate data. Is it possible for you to post or send me a pdf of the manual? Every maker of controllers seems to use different terminology and then these guys talk in Italian to boot.

major


----------



## jockepocke (Nov 24, 2009)

major said:


> Hi jock,
> 
> Maybe we can figure this thing out. Please post the actual parameters you have set and also the motor nameplate data. Is it possible for you to post or send me a pdf of the manual? Every maker of controllers seems to use different terminology and then these guys talk in Italian to boot.
> 
> major


I can send you both the manual and motor specification sheet (I got it from ABB), but how? Can you send me your email please? 

Thank you all!


----------



## major (Apr 4, 2008)

jockepocke said:


> I can send you both the manual and motor specification sheet (I got it from ABB), but how? Can you send me your email please?
> 
> Thank you all!


Sent to you on a PM.


----------



## major (Apr 4, 2008)

major said:


> Sent to you on a PM.


That was fast  Give me some time to look it over. 

I'll be back


----------

