Yes it gets to a point where you really need to have a better understanding what you are doing in order for us to be able to help you further. I think some time spent reading would be time well spent at this point. here's some more links:
General MOSFET info:
IR - AN-937 Gate drive Characteristics and Requirements for HEXFET Power MOSFETS - rather long winded, but shows a lot of different circuits and resultant oscope traces.
APT - Power MOSFET tutorial
IR - The do's and Don'ts of Using MOS-gated Transistors
Chuck Mcmanis - Understanding MOSFET current ratings
A good, simple, easy to understand writeup on mosfets - if you don't read anything else, read these last two.

at some point in the near future, you will realize that there is absolutely no way that a single MOSFET is going to power your motor with a load on it. When you get to that point, these will come in handy:
IR - Paralleling of Power MOSFETs for Higher Power Output - very long and technical. Took me a few day to get through it. you may want to skip it.
IR - AN-941

once you get everything up and running, but your mosfets keep overheating, read/watch these:
Dave Jones - EEVblog #105 - Electronics Thermal Heatsink Design Tutorial
Introduction to heatsinks and cooling

before you start your PCB design, you might consider reading this:
A Practical Guide to High-Speed Printed-Circuit-Board Layout - I haven't read it, but it is printed out and in my book, wait to be read.
Gound plane 101

you sounded vaguely interested in current limiting; this page has some info on it:
Speed controllers - section 10 - actually I think I already linked to that.

Ok, I just gave you about 1/4 of the things I've printed out and read; I have (2) 2" binders full of information on motor controllers. The stuff I linked to, I think is the best, but there is no end to the information available to you on the internet if you are willing to seek it out and learn it yourself.

 

Another thing is, since most of the circuit is now working, change it from breadboard to a Vero or strip board. Breadboards are not good for this type of circuit. You may be chasing a problem that is being caused by a bad connection or stray inductance from the long component leads or even the 'sockets' of the breadboard. To finalize the circuit transfer what is now working to a strip board with short leads and soldered joints.

 

Please digest section "main capacitor" of this site: http://www.4qdtec.com/pwm-01.html It's describing exactly what we were talking about.

since most of the circuit is now working,

I don't think so. As soon as he puts back in the big motor with 260VDC power supply this thing will catch fire again.

However, it IS a good idea to mount the circuit on a protoboard.

@kandilx
Small summary for you not to get lost:

1. if possible mount the circuit on a protoboard (as suggested by shortbus)
2. minimize the length of all wires as suggested by me and others
3. verify the Vgs signal with an o-scope (as Sgt suggested)
4. if there is excessive ringing (zoom in into the edges) stop here and post the waveform. If it's ok (within the max Vgs ratings of the MOSFET being used) continue with step 5.
5. did you mount any capacitor from the cathode of the motor freewheeling diode to the source of the MOSFET? If not do so. You need one. Voltage rating at least 300VDC better 350VDC. The exact value I would determine experimentally, but I would go for an electrolytic and a smaller low ESR cap of just a few uF.
6. If that's still not enough we look for a snubber for the MOSFET

 

You guys sent me searching again! In the "Art of Electronics" book by Hill. He states and it was always my understanding that a 'snubber capacitor' was only used when switching AC. Where is the energy going when using a cap across the drain and source of a mosfet? It will charge the cap but with the next turn on of the switch that energy will be shorted to ground through the mosfet. Correct?

The snubber caps that strantor referred to are used not between drain and source of a single mosfet but between with dual mosfet or IGBT modules. They are connected between the drain (or collector on a igbt) of device #1 and the link between the source/drain (or emitter/collector) connection on device #2 in the module.

 

You guys sent me searching again! In the "Art of Electronics" book by Hill. He states and it was always my understanding that a 'snubber capacitor' was only used when switching AC. Where is the energy going when using a cap across the drain and source of a mosfet? It will charge the cap but with the next turn on of the switch that energy will be shorted to ground through the mosfet. Correct?

Those IGBT snubber caps I have, I do not intend to put between drain and source of a single low side switch. You could call them "input caps". they would go from the high side of the motor to ground, so they wouldn't short straight through the mosfet, but rather through the motor and the mosfet. this way they negate the effects of incoming battery lead inductance and slow burst discharge rate of batteries. With the freewheeling diode in place, the inductive spike should be rerouted up into those caps and gobbled up.

 

It will charge the cap but with the next turn on of the switch that energy will be shorted to ground through the mosfet.

Yes. It is however possible to use a very small capacitor of a few 100pF directly on the switch to slow it down.

The snubber caps that strantor referred to are used not between drain and source of a single mosfet but between with dual mosfet or IGBT modules. They are connected between the drain (or collector on a igbt) of device #1 and the link between the source/drain (or emitter/collector) connection on device #2 in the module.

Yes, on the power supply of the bridge. Or from cathode of the freewheeling diode to source of the n-channel MOSFET in the OP's case. If you don't put it in you will create the voltage transients caused by the inductance of the wires going to the power supply, batteries in the OP's case.

 

You should also look at Vgs (voltage on the gate, referenced to the source terminal). The gate may very well be "ringing". This will occur if you have any significant distance between the gate driver and the MOSFET gate, with no resistance between the driver and the gate.

The gate driver's ground needs to be connected to the MOSFET's source terminal, of course - and it needs to be a very low-inductance connection.

Posting a photo of your uC, gate driver, MOSFET and load would be helpful.

well i did zoom while testing the output of the mosfet dirver ic here is the image

 

well i did zoom while testing the output of the mosfet dirver ic here is the image

IMO it doesn't look bad enough to turn the MOSFET back on. However, this is without a big load, right. So you should still implement what was said before, twisting the gate wires, keeping them as near as possible to the driver. You can also put a zener diode near the driver with a voltage higher than the output pulse and lower than the maximum gate voltage, let's say 16V to 18V. It can get hot if the negative voltage peak on the gate output is to low.
I'd concentrate on the power side of the transistor (back to where we were before)

 

IMO it doesn't look bad enough to turn the MOSFET back on. However, this is without a big load, right. So you should still implement what was said before, twisting the gate wires, keeping them as near as possible to the driver. You can also put a zener diode near the driver with a voltage higher than the output pulse and lower than the maximum gate voltage, let's say 16V to 18V. It can get hot if the negative voltage peak on the gate output is to low.
I'd concentrate on the power side of the transistor (back to where we were before)

so these "ringings" are not problem then , because the height of one of them is more the the treshold value for the gate and also it is not vertical it is somhow inclined so i was thinking that this may increase the switching resistance ,and btw i have tried to connect the mosfet directly to the gate resistance and without wire same ringings

 

so these "ringings" are not problem then , because the height of one of them is more the the treshold value for the gate

That would be a problem, but I can't see it on the pictures.

and also it is not vertical it is somhow inclined so i was thinking that this may increase the switching resistance ,and btw i have tried to connect the mosfet directly to the gate resistance and without wire same ringings

In your first picture the time is set to 2 or 5us, and it's about the time the gate needs to discharge. Looks ok. I recommend to use a gate resistor between 6 and 10R.

If you provide oscillographs of high frequency signals (like the gate ringing) you need to inform as well where exactly you did measure it. High frequency signals can considerably change depending on the point of measurement, even on the same trace.

Did you implement any of the other recommendations we made?

As suggested before please post a picture of your layout.

 

Did you implement any of the other recommendations we made?

As suggested before please post a picture of your layout.

yes i did 2,3,4&5
but while connecting the capacitor no significant behavior was remarkable
edit: considering point 6 i found what is called snubber calculator in this link http://www.daycounter.com/Calculators/Snubbers/Snubber-Design-Calculator.phtml
i did calculate using first method because i dont understand the second one and using the following values Ipk 100A,rt 1uS, Vrail 260v,freq. 14.4Khz

 

What capacitor did you put in there? Can you post a picture showing the complete setup "driver, MOSFET including heatsink, motor and batteries" ?

did you manage to get a power supply in your university that works up to 260VDC?

If not I would recommend you take your batteries there and do your tests with the battery voltage and the bigger motor but starting with a lower voltage! No point in continuing with the smaller motor. Continue using the mods you made following our suggestions.

When doing your tests, observe the waveforms VGS and VDS and increase the battery voltage step by step, start with e.g. 2 batteries. If possible try to monitor the MOSFET body temperature with a termocouple or something similar while testing.

 

@praondevou - Why do you(or do you?) want the driver wired as in your schematic here? http://forum.allaboutcircuits.com/attachment.php?attachmentid=35611&d=1319388413

According to the data sheets and app notes, Vss and COM are supposed to be kept separate from each other. Vss is the logic side ground and COM is the mosfet ground. They are separate because the mosfet drive side is separate in the IC. It keeps the high voltage spikes from disrupting the logic side and causing false triggering.

 

@praondevou - Why do you(or do you?) want the driver wired as in your schematic here? http://forum.allaboutcircuits.com/attachment.php?attachmentid=35611&d=1319388413

No, I don't want to. It is however possible to do it according to app note AN978.

According to the data sheets and app notes, Vss and COM are supposed to be kept separate from each other. Vss is the logic side ground and COM is the mosfet ground. They are separate because the mosfet drive side is separate in the IC. It keeps the high voltage spikes from disrupting the logic side and causing false triggering.

Yes, they are separate. I didn't want to complicate things by introducing another power supply.
Since the OP is only using 1 low side MOSFET even if there was uncontrolled retriggering there shouldn't be a problem. There is no high side switch to make cross-conduction possible.

@Kandlix

What model was the freewheeling diode again? What shortbus' comment made me remember is that if the freewheeling diode isn't a fast recovery diode then when turning on the MOSFET again (let's say uncontrolled) the diode would still be conducting for maybe a too long time while the MOSFET is already ON. I wonder if this might be a problem.

 

What capacitor did you put in there? Can you post a picture showing the complete setup "driver, MOSFET including heatsink, motor and batteries" ?

did you manage to get a power supply in your university that works up to 260VDC?

If not I would recommend you take your batteries there and do your tests with the battery voltage and the bigger motor but starting with a lower voltage! No point in continuing with the smaller motor. Continue using the mods you made following our suggestions.

When doing your tests, observe the waveforms VGS and VDS and increase the battery voltage step by step, start with e.g. 2 batteries. If possible try to monitor the MOSFET body temperature with a termocouple or something similar while testing.

i still didn't try the big motor all my previous experiments were on the small one i did try 47uF and 100uF and 1uF

later i will try the big one but first i need to make the snubber did you check the edit in my previous post here it again
" considering point 6 i found what is called snubber calculator in this link http://www.daycounter.com/Calculator...lculator.phtml
i did calculate using first method because i dont understand the second one and using the following values Ipk 100A,rt 1uS, Vrail 260v,freq. 14.4Khz"
is these values are ok?
second what should be the max voltage the o-scope can withstand because i ask the lab assistant and does not know so how to know it knowing that the max voltage range is 5v

 

second what should be the max voltage the o-scope can withstand because i ask the lab assistant and does not know so how to know it knowing that the max voltage range is 5v

5V/DIV doesn't mean max input range. It's 300Vp max input voltage. You should be good to go with a 10:1 probe.See the o-scope specs:
GOS-620

Your snubber behaviour will completely change when your make your tests with the bigger motor and under load.
R1 C1 D1 you have replaced by the freewheeling diode of the motor. We are talking about wire inductance.

The main difference between the two snubbers is in how much the capacitor is being discharged. In the case of the rate of rise it will be completely discharged through R2 and the MOSFET while the MOSFET is conducting and it will be charged via D2 when the MOSFET opens. So essentially you have a discharged capacitor from drain to source when you open the MOSFET and a RC when you close it. Power is being dissipated in the resistor.
In general a RCD voltage clamp maintains a voltage on the capacitor lower than the breakdown voltage of the device you want to protect, so the diode is not conducting until the voltage peak reaches the capacitor voltage. After that what would be the additional peak is being cut of. Nothing is done to slow down the rate of rise of the voltage.

The rate of rise snubber R2,D2,C2 could also be modified to change it to a voltage clamp, just by changing it's component values and therefore maintaining a voltage on the capacitor less than VDSmax. In this case I would connect R2 to GND, so I don't depend on the ON-time of the MOSFET.

They all need to be tested under full load and maximum expected DC voltage.

Did you see the computed wattage of the resistor with the values you put in? The high amperage is only present when you start the motor. Use the ampere rating you expect with the motor running and under load. (unless you want to put in a 200W resistor )

Since the wire inductance is unknown you will also need to experiment a little bit to find the appropriate snubber values.

When testing with the bigger motor make sure to monitor the MOSFET temperature, your heatsink may be to small for the amount of power you want to dissipate.

 

5V/DIV doesn't mean max input range. It's 300Vp max input voltage. You should be good to go with a 10:1 probe.See the o-scope specs:
GOS-620

The main difference between the two snubbers is in how much the capacitor is being discharged. In the case of the rate of rise it will be completely discharged through R2 and the MOSFET while the MOSFET is conducting and it will be charged via D2 when the MOSFET opens. So essentially you have a discharged capacitor from drain to source when you open the MOSFET and a RC when you close it. Power is being dissipated in the resistor.
In general a RCD voltage clamp maintains a voltage on the capacitor lower than the breakdown voltage of the device you want to protect, so the diode is not conducting until the voltage peak reaches the capacitor voltage. After that what would be the additional peak is being cut of. Nothing is done to slow down the rate of rise of the voltage.

The rate of rise snubber R2,D2,C2 could also be modified to change it to a voltage clamp, just by changing it's component values and therefore maintaining a voltage on the capacitor less than VDSmax. In this case I would connect R2 to GND, so I don't depend on the ON-time of the MOSFET.

They all need to be tested under full load and maximum expected DC voltage.

Did you see the computed wattage of the resistor with the values you put in? The high amperage is only present when you start the motor. Use the ampere rating you expect with the motor running and under load. (unless you want to put in a 200W resistor )

Since the wire inductance is unknown you will also need to experiment a little bit to find the appropriate snubber values.

When testing with the bigger motor make sure to monitor the MOSFET temperature, your heatsink may be to small for the amount of power you want to dissipate.

i don't get the part you are explaining the difference between the snubber and the diode
but forget about it i will read it again and again until i get it
but which do you think is safer for the mosfet ?

and while testing to get the appropriate value for the snubber is my objective is only to eliminate or minmize the ringings?

third yesterday i did test different resistance vaules and as Strantor said i bought 3 other mosfets now i have 6 and i did connect them in parallel
and the readings are as follows
resistance value in ohm/resistance power in w : one mosfet connected only swtch. time (on/off),all 6 mosfets time(on/off) in uS
4/2:0/1,1/1
5/4:0/1,1/1
15/.25:0.1/0.5,2,2
29/.25:0/0,3/4
80/.5:0/0,+10/+10

the zero value is not absolute but only this time , as it wasn't expected the switching time for some values of resistance is very low and ringings were minimal
all time value expect the zeros were have ringings as usual
this test was done will the ground probe is connected to the ground of the battery and the positive one is connected to the reisitance connected to the output of the mosfet driver ic "1"
so now it seems to me that the mosfet driver can not drive all 6 mosfets , i did think of using a p mosfet to supply the parallel mosfets with enough current is this possible?

 

Yes it gets to a point where you really need to have a better understanding what you are doing in order for us to be able to help you further. I think some time spent reading would be time well spent at this point. here's some more links:
General MOSFET info:
IR - AN-937 Gate drive Characteristics and Requirements for HEXFET Power MOSFETS - rather long winded, but shows a lot of different circuits and resultant oscope traces.
APT - Power MOSFET tutorial
IR - The do's and Don'ts of Using MOS-gated Transistors
Chuck Mcmanis - Understanding MOSFET current ratings
A good, simple, easy to understand writeup on mosfets - if you don't read anything else, read these last two.

at some point in the near future, you will realize that there is absolutely no way that a single MOSFET is going to power your motor with a load on it. When you get to that point, these will come in handy:
IR - Paralleling of Power MOSFETs for Higher Power Output - very long and technical. Took me a few day to get through it. you may want to skip it.
IR - AN-941

once you get everything up and running, but your mosfets keep overheating, read/watch these:
Dave Jones - EEVblog #105 - Electronics Thermal Heatsink Design Tutorial
Introduction to heatsinks and cooling

before you start your PCB design, you might consider reading this:
A Practical Guide to High-Speed Printed-Circuit-Board Layout - I haven't read it, but it is printed out and in my book, wait to be read.
Gound plane 101

you sounded vaguely interested in current limiting; this page has some info on it:
Speed controllers - section 10 - actually I think I already linked to that.

Ok, I just gave you about 1/4 of the things I've printed out and read; I have (2) 2" binders full of information on motor controllers. The stuff I linked to, I think is the best, but there is no end to the information available to you on the internet if you are willing to seek it out and learn it yourself.

now i did bring 3 mosfet irfp460 so total is 6 mosfets in parallel
i'am still studying some of the links you did post and trying the understand more about mosfets

 

now i did bring 3 mosfet irfp460 so total is 6 mosfets in parallel
i'am still studying some of the links you did post and trying the understand more about mosfets

Im unclear on this. Are you saying that you have six irfp460 mosfets in parallel or you have three irfp460s in parallel with three other types? If you meant the latter, I really don't recommend that, because the MOSFET with the lowest Rdson will take the bulk of the current. It is best to have all of the mosfets the same part number and from the same production batch (I.e. Buy them all at the same place at the same time) and match parameters of them. Most important parameter is turn on/ turn off time, followed by Rdson. If you have one MOSFET that turns on slightly before the others or turns off slightly after the others, then if brief periods of time, it will be carrying the full load current, which is not good. It is also important to note, that even with perfectly matched mosfets, once you solder them into the circuit, they may have drastically different turn on/ turn off times due to parasitic inductance in your pcb. This is where Good circuit layout comes into play. Make gate traces all as short as possible and all the same length. Also note that more mosfets is not always better. If you look at the numbers, you may get the idea that it would be best to just throw 20 mosfets into the circuit, but remember that the more mosfets you use, it gets exponentially harder to make them share the load and you have to start derating them by higher and higher factors. The manufacturers recommend that if you are going to parallel more than 4 discreet mosfets, that you start looking into MOSFET modules (expensive)

 

and while testing to get the appropriate value for the snubber is my objective is only to eliminate or minmize the ringings?

First and most important objective is to make sure the peak VDS voltage doesn't exceed the maximum breakdown voltage of the MOSFET, 500V in case of the IRFP460.
The picture in my previous post I found on the internet and is actually not exactly correct. By cutting of the upper peak of the ringing voltage the ringing itself will decrease. But the more you cut the more you need to dissipate in the snubber resistor. I would go with the clamp circuit using it directly on the MOSFET and make sure my voltage stays under the 500V.

third yesterday i did test different resistance vaules and as Strantor said i bought 3 other mosfets now i have 6 and i did connect them in parallel
and the readings are as follows
resistance value in ohm/resistance power in w : one mosfet connected only swtch. time (on/off),all 6 mosfets time(on/off) in uS
4/2:0/1,1/1
5/4:0/1,1/1
15/.25:0.1/0.5,2,2
29/.25:0/0,3/4
80/.5:0/0,+10/+10

I don't understand this data.
You don't need so many MOSFETs if your continuous current is 10A max.
2 would be sufficient (with a heatsink of course)

this test was done will the ground probe is connected to the ground of the battery and the positive one is connected to the reisitance connected to the output of the mosfet driver ic "1"

You mean "to the ground of the battery" or "to the source of the MOSFET" or to the "COM pin of the IR2110". It's not the same thing and it helps us to analyse your results. Start to think of a wire/trace as an electronic component, an inductor.

so now it seems to me that the mosfet driver can not drive all 6 mosfets , i did think of using a p mosfet to supply the parallel mosfets with enough current is this possible?

1. I consider 6 MOSFETs being to many.
2. Did you use an individual gate resistor for each of them?
3. You can build a more powerful driver with a combination of 2 n-channel and 2 p-channel MOSFETs and a few resistors. But I do not recommend to start yet.

I do recommend to start with a lower frequency to turn your motor (not 15kHz). If after changing to 15kHz switching losses in the MOSFETs are too high you can still opt for a more powerful driver circuit.
For now we want to determine if voltage transients are the problem.
You still didn't post a picture of the current setup. I'd like to see distance of 2110 to MOSFET, gate wiring, power wiring, motor and freewheeling diode.