# Atmega running at 15Khz + A 9A Mosfet agte Drive(13v)UCC37322P + N Channel Power Mosf



## ashkar_malik (Mar 18, 2012)

which mosfet should be used to drive 2HP pmdc 48v motor
and free wheeling diodes for the controller,how much capacitance should be used??? kindly help me


----------



## ashkar_malik (Mar 18, 2012)

Are 4 gate drives and 16 irfz44n mosfets are enough or irfp250n are better


----------



## ashkar_malik (Mar 18, 2012)

please reply soon


----------



## Ziggythewiz (May 16, 2010)

There are a few threads about building controllers, search for Open ReVolt and you can see what they use.

Not many of us are controller experts, so you may have to be patient to wait for a response from someone who knows.


----------



## Arlo (Dec 27, 2009)

ashkar_malik said:


> which mosfet should be used to drive 2HP pmdc 48v motor
> and free wheeling diodes for the controller,how much capacitance should be used??? kindly help me


 IM interested in this.
Its not just about numbers for how much capacitance you should have at least 2 different type of caps something for the fast spikes and something for the slow spikes. I'm not an engineer but a friend explained it to me like this. 
You need different levels of defence one for the nukes one for the hand guns one for the torpedo's etc. He recommended 3 types of caps.

In my brushless controller I have used 2 ATM but I will plan for a third one when I build the finished product. Whats the max voltage you want to charge to? And whats the FET size you plan to use??

I would love to work with you so I can make a cheep diy brushed controller to have the Kids help me build at a drag race hi school program I volunteer at.


----------



## ashkar_malik (Mar 18, 2012)

Thanks for your reply,
But I am trying to make my own Speed controller so I just need help about my problems,
Please tell me how to calculate the capacitance required for a 2Hp @48v DC motor and does 55v mosfets would be sufficient to fun a motor @ 48vDC


----------



## Arlo (Dec 27, 2009)

ashkar_malik said:


> Thanks for your reply,
> But I am trying to make my own Speed controller so I just need help about my problems,
> Please tell me how to calculate the capacitance required for a 2Hp @48v DC motor and does 55v mosfets would be sufficient to fun a motor @ 48vDC


So what batteries are you using? The reason I ask is you will only be able to charge to 55v absolute MAX for using a 55v mosfet you are better off using 75v mosfets so you can charge to say 65v and under load still have 50-55v usable voltage. I asked what mosfets you are using for this reason.
There was a thread about calculating caps on a BLDC controller over on endless sphere and all the calculations seem to go out the window when used in the real world. Remember the caps are protecting the mosfets from the spikes of the inductance of the motor. So every motor is different. 
If I was you I would get ~1000uf of electrolytic and something around a 1uf film cap as close to the fets as possible. I used 1 uf for every mosfet...
Ceramics close to the mosfets would be a good idea. As well do you have a scope to see if its working ok?

One other thing is if you have mosfets a margin over the max voltage you are going to run you will have a better buffer for spikes that the caps are not absorbing!


----------



## ashkar_malik (Mar 18, 2012)

Battery:-12x4 38Ah each
MOSFETS IRFZ44N
Brushed motor 2hp PMDC @48v
And how to connect these caps with each mosfets please help me with that.


----------



## Electroddy (Dec 29, 2009)

Ashkar: I THINK that you MAY have problems with those mosfets. I personally do not like to use a mosfet at more than 2/3 rated voltage, as there is no room for voltage spikes. I replaced the IRFZ44V mosfets on my controller after I spiked them by unintentionally causing REGEN with a BRUSHED motor. 
I later figured out that is was a combination of the load pushing me downhill, and my easing in on the throttle, giving just enough current to energize the field without powering the motor. 
A possibly better FET may be PSMN6R5-80PS,127 by NXP 80V 100A 210Watt 6mOhm. Looks like I should have used these myself.


----------



## ashkar_malik (Mar 18, 2012)

That was a good suggestion and I do understand the problem that would be caused due to improper matching of MOSFETs.
PSMN6R5-80PS,127 these dudes looks good


----------



## PStechPaul (May 1, 2012)

You should use the safe operating area graphs to determine the suitability of a MOSFET for the application. See the datasheet:
http://www.nxp.com/documents/data_sheet/PSMN6R5-80PS.pdf

This is determined by the peak wattage that could be expected during switching. This MOSFET shows that it should handle 50 amps at 50 volts, with a 100 uSec square wave, but only 3 amps at 1 mSec. IMO it is best to choose a device with twice the supply voltage, so these 80V devices may be OK for a 48V system, but if battery voltage could be 54 volts the transients could exceed the rating. A 100V device may be a better choice. It is relatively easy to protect agains overcurrent and overheating, but voltage transients can be very fast and hard to detect, and yet inflict catastrophic failure.

TCS diodes are very good for voltage spike protection. And snubbers are also good, usually placed across the Drain-Source of the MOSFET or across the load.


----------



## Arlo (Dec 27, 2009)

ashkar_malik said:


> That was a good suggestion and I do understand the problem that would be caused due to improper matching of MOSFETs.
> PSMN6R5-80PS,127 these dudes looks good


 No those have a fairly hi rdson (for the voltage) which meens you will have heat in the mosfet from the internal resistance.

These are a good budget 100v mosfet we use for a lot of e-bike controller hop ups http://www.digikey.com/product-detail/en/IRFB4110PBF/IRFB4110PBF-ND/935978

Here is a 75v fet with about 1/2 the rdson you posted
http://www.digikey.com/product-detail/en/IRFB3077GPBF/IRFB3077GPBF-ND/2354085
There is a whole page of fets in the TO220 package on digikey to choose from that are decent. You should look at thermal resistance and the safe operating area among other specs as well.


----------



## Electroddy (Dec 29, 2009)

Arlo; I was the one to originally suggest the NXP PSMN6R5-80PS,127 MOSFET. I blew up 10 of the IRFZ44s that came OEM in my controller. I looked at pricing as well as performance. the NXPs that i suggested are better performance wise and slightly less cost wise. That said I went with some IXYS IXTP70N085T FETs. They are slightly better than the IRFZ44s but not as good as the NXPs. But again they are good for the purpose.


----------



## ashkar_malik (Mar 18, 2012)

That was a nice amount of Knowledge  thank you friends for your help,
Another Question.- How much voltage and current should be opted for schottky diodes????


----------



## smpavlik (Mar 28, 2011)

ashkar_malik said:


> How much voltage and current should be opted for schottky diodes????


No need to put additional diodes. Power MOSFET has an anti-parallel diode as a part of its structure. As usual the diode has same voltage and current rating as the MOSFET.


----------



## ashkar_malik (Mar 18, 2012)

but why are then motor controller circuits uses schottky diodes with mosfets


----------



## PStechPaul (May 1, 2012)

ashkar_malik said:


> but why are then motor controller circuits uses schottky diodes with mosfets


I think this is because Schottky diodes are faster and have lower forward voltage losses than the MOSFET body diode. Less losses may boost efficiency. The improvement may be marginal at motor PWM frequencies (~15 kHz). Most Schottky diodes are fairly low voltage (<60V) but some higher voltage types are available.


----------



## smpavlik (Mar 28, 2011)

ashkar_malik said:


> but why are then motor controller circuits uses schottky diodes with mosfets


Schottky has two main advantages compare to a regular diode. One is a low forward voltage drop which leads to lower power dissipation in forward direction. Second advantage is very fast recovery time, which is a period when the diode switches from conductive to non-conductive state. Obviously, this leads to lower reverse power dissipation and higher switching frequency. 

But as usual, you have to pay for that: Schottky has relatively high series resistance and as a result it has comparable forward voltage drop under high current. Other problem is relatively low reverse voltage ratings and higher reverse leakage current which significantly increases with temperature. Even worse, exceeding the maximum reverse voltage may irreversibly damage the diode (short circuit), in contrast to a regular diodes, which are conduct to reversible breakdown (Zener for example)

Conclusion: there's no technical or economical reason to parallel MOSFET with an ext Schottky for current higher than 50-100A. Unless you really need high switching frequency and you have big pocket  
For lower current it makes sense, but...


----------



## ashkar_malik (Mar 18, 2012)

So what is the end result! weather to use those diodes or not???


----------



## smpavlik (Mar 28, 2011)

ashkar_malik said:


> So what is the end result! weather to use those diodes or not???


I would not use them. You have a micro which has full knowledge when a diode should conduct. So just open MOSFET at that time and you'll get a result much better than Schottky: voltage drop and recovery time are close to zero. If you don't want to have a headache with software, forget the solution. An embedded diode will serve good too.


----------



## ashkar_malik (Mar 18, 2012)

Thanks smpavlik for your advice


----------



## ashkar_malik (Mar 18, 2012)

CHECK MY SCHEMATIC AND WHAT ELSE MORE SHOULD BE IMPLEMENTED IN THIS CIRCUIT?


----------



## smpavlik (Mar 28, 2011)

1. Not good idea to short VCC with S1 
2. LED D1 and D6 reverse biased. Not work


----------



## smpavlik (Mar 28, 2011)

ashkar_malik said:


> CHECK MY SCHEMATIC AND WHAT ELSE MORE SHOULD BE IMPLEMENTED IN THIS CIRCUIT?


UCC is rated 3 A. It would be enough to drive all FETs with one UCC. 
Series resistor is pretty big. Peak current is only 0.7A, you may increase it up to 3A having R=5.1 Ohm. Also you can connect all gates together. 

More important. You use PWM with inductive load so voltage spikes will be huge. You have to anti-parallel the motor with a diodes rated for the same current as FETs. The schematics doesn't have regen. If you need it (I believe yes), put there a half-bridge and hit two targets - have FET's embedded diodes as ananti-parallel diodes and regen option.

More improvement
Mega8 has internal RC generator which is good enough for you application. You can save 5 cents on a crystal. 
I would use switch mode supply instead of 7815 and connect it to a main power. And connect 7805 to its output


----------



## smpavlik (Mar 28, 2011)

My bad. Didn't realize you want to use UCC37322P which is rated for 9A, so 1 Ohm series resistor is enough having FET gate resistance 1.3 Ohm

Should you use half-bridge, put there UCC27200 which is 120-V Boot, 3-A Peak High-Side/Low-Side Driver


----------



## ashkar_malik (Mar 18, 2012)

I am using a PDIP gate drive and its thermal power disipation is only 500mW,so I think it will drain only 30mA,Am I right with that or what???


----------



## PStechPaul (May 1, 2012)

According to the datasheet the device can dissipate 650 mW in the PDIP package. It is also rated at 600 mA maximum continuous and 9A peak. I think you are confused about the ratings and the way the device is used. It delivers a pulse into a capacitive load (MOSFET gates), and the faster the rise and fall time, the higher the current, but the duration is only 50 nSec or so. Thus the power dissipation may be as high as 9A*15V or 135W, but for 15 kHz the duty cycle is only about 0.000001% or about 180 uW. Your wattage figure is based on 15V*30mA=450mW. 

I realize you are a beginner and are trying to learn, but it may be better to buy a PWM controller rather than play around with circuits which involve quite a lot of available power and catastrophic failure can be dangerous. Good luck.


----------



## ashkar_malik (Mar 18, 2012)

PStech paul Thanks for your clarifications ,And I think Catastrophic failure are more favorable to watch how miscalculations might show you real fireworks


----------



## ashkar_malik (Mar 18, 2012)

Another question,How to do regenerative breaking most efficiently with minimum loos of power,I was planing to use car alternator on the wheel would that provide enough power to charge up the battery


----------



## smpavlik (Mar 28, 2011)

ashkar_malik said:


> How to do regenerative breaking most efficiently with minimum loos of power,I was planing to use car alternator on the wheel would that provide enough power to charge up the battery


Bad idea. You have a motor and that's enough. You just need to increase voltage like it's done in boost converters. Also, it's good idea to monitor gate driver voltage and main voltage. And absolutely necessary to monitor current. The current monitor must provide, first, a feedback to a micro for PWM adjusting, and , second, must be able to limit/cut off peak current independently.


----------

