# dummy load for testing



## skooler (Mar 26, 2011)

Jamie EV said:


> Provided I can get my DIY motor controller working, does anyone know of an easy way to test it while I look for the perfect motor?
> 
> What's a good choice for a dummy load? I'm looking for about 600 amps....


An EV???

Seriously though, 600Amps is a lot.

How long do you need to test for?


I have seen cooker hob elements submerged in oil/water used as a dummy load but I'm not sure how long that would last.

Cheers,

Mike


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## Ziggythewiz (May 16, 2010)

The standard bench load in the Curtis manual is a string of lights. Obviously it would be difficult to make one of those up to EV power levels, but it should be an easy place to start for low power testing.


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## Jamie EV (Oct 3, 2012)

Ziggythewiz said:


> The standard bench load in the Curtis manual is a string of lights. Obviously it would be difficult to make one of those up to EV power levels, but it should be an easy place to start for low power testing.




I guess my concern is that I want to test the ability for the DIY controller to handle load while keeping cool, not exploding, not spiking. 

My mosfets in theoryh should be able to deliver approx 560 amps and 600 max volts. 

I guess my question is what is the safest and best way to test this without a motor.


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## Jamie EV (Oct 3, 2012)

Well if I had a 120 volt pack and I had 100 watt bulbs, I'd need 720 of them lol! I could light the city.


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## frodus (Apr 12, 2008)

You really want an inductive load though.

Just wait on the motor and test then, that's the only real world test you should do.


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## Jamie EV (Oct 3, 2012)

What if I use a 12 volt deep cycle battery with 10 x 100 watt bulbs? Would that be the same as 83 amps? That's a start...


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## Siwastaja (Aug 1, 2012)

Resistive load is easier to drive and saves you from the voltage spikes inductive load (motor) gives. So it's not a very good test.

OTOH, you can still see the spikes caused by your DC bus inductance. (Make the large-current carrying + and - wires as short as possible inside the controller, and place them close to each other, not forming a "loop", and connect a small plastic capacitor (about 1 µF 1000V) on the DC bus as near the switching element as possible, and larger electrolytics next to it.)

IMO, the best way to avoid burning your expensive MOSFETs is to use the actual motor with a test load and carefully ramp up the voltage by adding more batteries, monitoring Vgs and Vds with an oscillosscope all the time. This way you can see the spikes before they are too much for the FETs.

Coming up with a mechanical test load can be a problem too. Of course you could just install it in a car and drive it along a straight road with no other traffic and have a friend look at the scope. This would be relatively simple with no extra work, as you will install it in your car anyway.

We are going the dynamometer way, building two controllers and connecting two motors; OTOH, we have regen.


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## Salty9 (Jul 13, 2009)

Jamie,

Microwave oven transformer cores can be used to make inductors. I'm don't know what inductance you need but I would do a Google search for "diy MOT inductor"
http://diygallery.de/DIYsites/inductor.htmlhttp://diygallery.de/DIYsites/inductor.html


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## PStechPaul (May 1, 2012)

Remember that incandescent light bulbs have about 10:1 resistance change as they achieve full brightness, so they are much different from a motor load. You might want to make a low current version of the controller with one MOSFET and test it on a motor that runs at about 50 amps, such as a starter motor. And you might also try a 120 V AC/DC universal power tool motor like a circular saw which will have inductive voltage spikes similar to what you might expect with an EV motor. They are typically 2 HP or so (1500W) so they will draw about 15 amps normally and up to 100 amps at start-up. You can also lock the blade to test for overload conditions.

Once you have determined that your controller can handle this sort of load, you can be fairly confident that 20 MOSFETs in parallel will handle 20 times the load. You will probably burn up a few MOSFETs during your initial testing, but much better (cheaper and safer) to do so one component at a time.


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## Jamie EV (Oct 3, 2012)

I guess based on the responses that i AM to expect mosfet burnouts.


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## smpavlik (Mar 28, 2011)

I used few kettles in parallel to have a resistive load. This is good as a start point but not completely true as Siwastaja said. 




Jamie EV said:


> My mosfets in theoryh should be able to deliver approx 560 amps and 600 max volts.



Unfortunately MOSFET can not operate under high voltage with full load. It must be in safe area. For example, you have 600V/100A MOSFET, your battery voltage is 100V, the FET can deliver ONLY 15A 10mSec single pulse. If you want 500A, you need at least 33 FETs in parallel! 

If I'm not mistaken, Kelly 96V,400A controller has 7 ultra-low resistance FETs per shoulder. 
What kind and how many MOSFETs do you use?


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## PStechPaul (May 1, 2012)

Yes, the safe operating area is based on the fact that there will be a period of time where much of the operating voltage will be present as well as much of the peak current, and that translates to a lot of power. Since the current and voltage are not evenly distributed in the MOSFET during switching, there will be hot spots, so there is a maximum peak power, perhaps 10 times the rated power. So at 100V and 15A, you can have 1500 watts. Actually probably about half that, since the full voltage and current can never be present simultaneously. If you run at the maximum ratings of 600V and 100A, there can be 30kW for a few microseconds, plenty of time to do permanent damage. And it's even worse with an inductive load. You can see this effect if you run a simulation.

http://en.wikipedia.org/wiki/Safe_operating_area
http://www12.fairchildsemi.com/an/AN/AN-558.pdf
http://www.irf.com/technical-info/appnotes/an-1155.pdf
http://www.aosmd.com/res/application_notes/mosfets/Power_MOSFET_Basics.pdf


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## dougingraham (Jul 26, 2011)

Jamie EV said:


> What if I use a 12 volt deep cycle battery with 10 x 100 watt bulbs? Would that be the same as 83 amps? That's a start...


10 x 100 watt bulbs on 120 volts would be pulling a little over 8 amps. The effective resistance once the bulbs are glowing white hot is 14.4 ohms. When cold it might be 2/3 of this or around 9.6 ohms. If you tried to use that on 12volts it probably wont even visibly glow. I would expect around 1.25 amps. So 1.25 amps times 12 volts divided by 10 bulbs is 1.5 watts per bulb. Probably not what you had in mind.


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## Jamie EV (Oct 3, 2012)

PStechPaul said:


> Yes, the safe operating area is based on the fact that there will be a period of time where much of the operating voltage will be present as well as much of the peak current, and that translates to a lot of power. Since the current and voltage are not evenly distributed in the MOSFET during switching, there will be hot spots, so there is a maximum peak power, perhaps 10 times the rated power. So at 100V and 15A, you can have 1500 watts. Actually probably about half that, since the full voltage and current can never be present simultaneously. If you run at the maximum ratings of 600V and 100A, there can be 30kW for a few microseconds, plenty of time to do permanent damage. And it's even worse with an inductive load. You can see this effect if you run a simulation.
> 
> http://en.wikipedia.org/wiki/Safe_operating_area
> http://www12.fairchildsemi.com/an/AN/AN-558.pdf
> ...




So let me see if I am to understand this correctly. My 600V 35Amp Mosfet can not switch both 600v AND 35 amps at the same time. Seems fair.

How about 16 of them in parallel? So a cumulative 560 amps? Would that take some of the heat off?


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## Jamie EV (Oct 3, 2012)

So I guess I have to read my component's data sheet and find out the safe SOA. Down the rabbit hole I go...


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## Salty9 (Jul 13, 2009)

http://endless-sphere.com/forums/viewtopic.php?f=30&t=40948&p=599153&hilit=derating#p599153

has a good discussion about derating MOSFETs. In particular BigMoose in the second post lists references worth reading,

The rabbit hole might be deeper than you thought.


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## PStechPaul (May 1, 2012)

Look at your thread: http://www.diyelectriccar.com/forums/showthread.php/my-first-pwm-79775p4.html
where I noted that the MOSFETs you have chosen have a very restrictive SOA. It might only be safe to switch 3 to 15 amps per device at 100V, so your parallel bunch of 16 will probably allow safe switching of only 50 to 200 amps or so.


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## Jamie EV (Oct 3, 2012)

PStechPaul said:


> Look at your thread: http://www.diyelectriccar.com/forums/showthread.php/my-first-pwm-79775p4.html
> where I noted that the MOSFETs you have chosen have a very restrictive SOA. It might only be safe to switch 3 to 15 amps per device at 100V, so your parallel bunch of 16 will probably allow safe switching of only 50 to 200 amps or so.



well hell...I'll check that out.


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## Jamie EV (Oct 3, 2012)

I looked at the fairchild sheet and tried to make heads or tails of it and failed. 

I am unsure of what the crucial variables are for determining the SOA.

Sorry Paul. I know you're trying to dumb it down for me, lol.


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## Jamie EV (Oct 3, 2012)

oh wait I see it.

Ok I see that at 100 v, the amps are restricted to about 10 amps in 10ms pulses. (Am I reading that correctly?) 

So in theory, if I had 16, at 100v, I might be able to switch about 160 amps....maybe more with sinking. Not an auspicious beginning to my plan. Still I guess they could be my experimenter's mosfets. Give em a try and see what I can get out of them before moving to something more substantial.

There's also the question of what the voltage and current required to power them is and how much to do 16 of them. If I'm not mistaken, most micro controllers do about 200mA gate output...


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## jehan12413 (Feb 4, 2010)

I have used 316L stainless Tig welding rods for a resistive load in the past. Just take the rod and wind around a bolt to make a tight coil then stretch out after removing the bolt. They're cheap and you can hook as many as you need in series or parallel or combination for any voltage/current. Mount on fireproof board because when bright red they give off A LOT of heat. I never tried submerging in liquid.


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## Jamie EV (Oct 3, 2012)

I have a couple of treadmill motors. Perhaps I could start out with one, then wire the second in series...or parallel. See how that goes.


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## smpavlik (Mar 28, 2011)

Jamie EV said:


> oh wait I see it.
> If I'm not mistaken, most micro controllers do about 200mA gate output...


This is very optimistic assumption. Most of micros have not more than ~10mA output capability. One power MOSFET easily can have 10nF gate capacity. 16 have 0.16 uF and you have to recharge them! There are 2 scenarios if you connect the batch to a micro output directly:
1. if the micro has current limitation, you l'll have a gentle slope and huge local power dissipation while switching. Result - all MOSFETs will burn almost immediately.
2. if the micro has no current limitation, you'll have huge current through a micro output while recharging the monster capacitor. Result - the micro output will burn out. 

You need to use a MOSFET driver like this 
http://www.irf.com/product-info/datasheets/data/irs2186pbf.pdf
Don`t forget to put a resistor in series with gates to limit current.


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## Jamie EV (Oct 3, 2012)

smpavlik said:


> This is very optimistic assumption. Most of micros have not more than ~10mA output capability. One power MOSFET easily can have 10nF gate capacity. 16 have 0.16 uF and you have to recharge them! There are 2 scenarios if you connect the batch to a micro output directly:
> 1. if the micro has current limitation, you l'll have a gentle slope and huge local power dissipation while switching. Result - all MOSFETs will burn almost immediately.
> 2. if the micro has no current limitation, you'll have huge current through a micro output while recharging the monster capacitor. Result - the micro output will burn out.
> 
> ...




That's what I was afraid of. (although Arduino claims 200 mA or so I'm told)...

I'll check that one out.


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## Jamie EV (Oct 3, 2012)

Hey now THAT's the driver I need. So I guess a microcontroller could trigger that driver, and THAT could power a string of mosfets...or IGBTs...that's what I was looking for.

Now would you isolate the PWM from the driver....or the driver from the Mosfets? 

I'm thinking opto-isolate the PWM from the driver and then have the driver sit on the board with the mosfets ready to slug it out with the ripples.


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## Jamie EV (Oct 3, 2012)

http://www.ti.com/lit/gpn/ucc27322
???


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## Jamie EV (Oct 3, 2012)

Does the IRS2186 have it's own pulse generator? In other words, is it it's own PWM source? Or is it simply an amplifier for the MOsfets?


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## smpavlik (Mar 28, 2011)

Jamie EV said:


> Does the IRS2186 have it's own pulse generator? In other words, is it it's own PWM source? Or is it simply an amplifier for the MOsfets?


No. This is driver only. Or amplifier if you want


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## smpavlik (Mar 28, 2011)

Jamie EV said:


> http://www.ti.com/lit/gpn/ucc27322
> ???


You can use this or similar for low-side MOSFET if we talk about a simple PWM controller for brushed DC motor. If you build a controller with regen or for BLDC/ACIM motor you should have a half-bridge or even 3 of them. So you have low- and high-side MOSFETs. Gate and source of the last one is under high voltage so you need to use either opto-isolated driver or one that I mentioned ( many similar available). The IRS2186 can handle bridges up to 600V

In case of half-bridge be better to use a driver which has both low- and high-side output because many of such ,first, has a circuits to prevent to open both low and high FETs at a time and , second, have a small delay to open a low side which can handle pass-through current.


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## Jamie EV (Oct 3, 2012)

smpavlik said:


> You can use this or similar for low-side MOSFET if we talk about a simple PWM controller for brushed DC motor. If you build a controller with regen or for BLDC/ACIM motor you should have a half-bridge or even 3 of them. So you have low- and high-side MOSFETs. Gate and source of the last one is under high voltage so you need to use either opto-isolated driver or one that I mentioned ( many similar available). The IRS2186 can handle bridges up to 600V
> 
> In case of half-bridge be better to use a driver which has both low- and high-side output because many of such ,first, has a circuits to prevent to open both low and high FETs at a time and , second, have a small delay to open a low side which can handle pass-through current.



OK I'm sold.
Where to attain IRS2186?
I'm really trying to avoid using a microcontroller as I thing it's unecessarily complex for a PWM circuit. 

I was thinking of this one. 200 ma output, dual output. Fed into an IRS2186 and then fed into a MosFet array. Sink the hell out of it all and schottky the output and pray.

http://www.ebay.ca/itm/5-x-TL494CN-...ltDomain_0&hash=item2c6321ddbd#ht_2543wt_1043


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## smpavlik (Mar 28, 2011)

Jamie EV said:


> Where to attain IRS2186?


For a simple PWM you need only low-side FETs so it could be either single low-side or dual low- and high-side driver. For 16 MOSFETs I think you need at least 4A output. Check Digikey. There are a lot of such IC. Select few drvs then check eBay for them. There it could be cheaper


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## Jamie EV (Oct 3, 2012)

smpavlik said:


> For a simple PWM you need only low-side FETs so it could be either single low-side or dual low- and high-side driver. For 16 MOSFETs I think you need at least 4A output. Check Digikey. There are a lot of such IC. Select few drvs then check eBay for them. There it could be cheaper



A low side FET driver with 4 amp output? (What about opto-isolation? Many say I need that.


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## smpavlik (Mar 28, 2011)

Jamie EV said:


> A low side FET driver with 4 amp output?


Yes, at least. For 16 gates it would be 0.25A per a gate capacitor. Not too much  



Jamie EV said:


> What about opto-isolation? Many say I need that.


It depend on your schematic. If you want to isolate a battery( and motor with MOSFETs) from control circuits, deferentially you need it. But then you need 2 power supplies - one for the opto and second for the control circuit. This make sense if you use a micro and other complicated stuff.
No need in your case.


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## Jamie EV (Oct 3, 2012)

smpavlik said:


> Yes, at least. For 16 gates it would be 0.25A per a gate capacitor. Not too much
> 
> 
> 
> ...


I have a couple of buck boost converter/voltage regulators. I can use one for the logic and one for the driver/mosfets. SO seperate power, I wonder if I could diode the outputs of the pwm and just keep the driver on the FET board and if it goes , it goes. No great loss. 

I was thinking of actually having separate boards for PWM and for driver/FETS. Just to isolate power supplies. I wonder if I could run the gate driver off of the accessory batt straight. I believe it's rated for 12 v...


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## Jamie EV (Oct 3, 2012)

Hey as luck would have it, my old ATX power suply has a TL494 in it. Thanks for the idea Paul! Also it's got an abundance of resistors, caps etc.


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## PStechPaul (May 1, 2012)

Jamie EV said:


> OK I'm sold.
> Where to attain IRS2186?
> I'm really trying to avoid using a microcontroller as I thing it's unecessarily complex for a PWM circuit.
> 
> ...


That's a very good price for five of these ICs. But there may be additional shipping and international tarrifs, so watch out for that.

Actually, a microcontroller such as the PIC16F684 can give you a PWM drive and a control input with only a properly bypassed 5 VDC power supply and the signal from the throttle pot. It's a 14 pin DIP (or SOIC-14) and costs about $1. I can supply the code to get you started, and all you need is a programmer like a PICkit 3. Or a PICkit 2, and I have an extra one I'll sell you for $30 which is about 1/2 price.

If you are serious about building a PWM for a vehicle you WILL need more than the TL494, and the PIC can provide everything you need. It's a lot easier to build the hardware with all the bells and whistles and then program the PIC as you add the features.

Hoping and praying and massive heatsinking will not make your parallel MOSFETs reliable if you exceed the SOA. The damage occurs too quickly for the heat to be transmitted through the substrate and tab and the heat sink. The weakest MOSFET will be destroyed first. If you are lucky, it may short out and save its comrades, but it will supply full voltage to the motor and the current will probably be enough to vaporize the leads. Then its buddies will take turns letting out the magic smoke until you have a real mess.

The IRS2186 is available from DigiKey for about $3.40/1:
http://www.digikey.com/product-detail/en/IRS21864PBF/IRS21864PBF-ND/1300606

It's a good half-bridge driver with 4A gate drive but you really don't need the high side unless you want to do dynamic braking or regen. You CAN do that with the PIC, not the TL494.

A good low side driver is the TI http://www.digikey.com/product-detail/en/UCC27321P/296-13672-5-ND/509704 which has 9A drive and also about $3.28.

Isolation is not absolutely necessary but for an EV it's a good idea. In that case there are some high speed optoisolators such as:
http://www.digikey.com/product-detail/en/HCPL0501R2/HCPL0501R2CT-ND/3041742
It's about $2 in an SOIC-8 package and has about 500 nS propagation delay. The driver will then provide about 50 nS rise/fall gate drive. You may find you actually need to add a bit of delay to avoid overshoot and inductive spikes. You will need a good scope to see these transients, at least 40 MHz and 100 MHz or better is ideal.


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## Jamie EV (Oct 3, 2012)

I know what yhou're saying guys. I know the TL494 is not ideal, however I have to start somewhere and learning bit by bit is probably better. I'm stubborn too.

Perhaps I will go the PIC route eventually but right now, I'm just trying to grasp the basics. I take to heart that the MOsfets are not really ideal for the full amperage you suggest. That's why I'm wanting to make the PWM modular to the driver and the Fets. Hopefully, they won't all go together with some sort of isolation. 

Maybe I'll opt for better IGBT later too like you suggested. I'm still stoked to see if I can make a smaller controller. Pretty awesome fun actually!


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## Shah (Oct 25, 2012)

Hi Jamie and other participants of this thread.

I am extremely interested how you get on because i am in the same boat only slightly further along (i think), i have been playing with the IRF2186 for a couple of weeks.

I encountered a problem i could not understand, after an exhaustive search in my off time i found this thread mentioning the device. i joined so here i am hoping that someone will have enough knowledge to guide me.

Background, i am trying to make a small buck converter (1 kW) to show my son the speed control concept using PWM. Something we will use later on our cart.

I tried another converter and accidently burnt my motor . long story short, i am now making a buck converter to ensure i do not go above the voltage rating of the motor.

My problem is that since i am new to the Highside driver i am not able to understand why it wont simply work. I have in my opinion made the bootstrap arrangement to cater for my frequency. In my PWM code for my arduino, i am making sure that there is no short out period, ie the highside and lowside are never on together. There is a time in the waveform where they are both off and this is the cause of my problems.

The VS pin (floating return) seems to be about 2.65V above COM, which means that when both fets are off the VS supplies the load. it heats my poor chip. now the problem goes away if i switch on the driver before i connect the load....i have no idea why.

i removed the pwm signal and am manually switching each side on and off. The mosfets are turning on and off without a problem and as expected but VS is also supplying the load. i have added an LED on the output to show me whether the VS is on and where the current is going. 

The cct diagram (for just the driver) is as follows. PWM is going to be supplied by my program in the arduino, i will basically control current and let the pwm drive the output voltage until the programmed maximum.

PS. to make a dummy load you could potentially take the approach i have used before to test some generators. i have drawn it on the same page with my cct diagram so that i did not have to attach many files.


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## Shah (Oct 25, 2012)

dummy load was used to test 1.4MVA diesel generators, lots of arcing, current value not fixed (varied about 15%) because it was 400Vac and each time the arc struck the ionization would have an impact on the resistance of the path. 

Wont be a problem with DC....i think.


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## PStechPaul (May 1, 2012)

There are many application notes that describe the operation of the bootstrap circuit, as well as design criteria and pitfalls. Here is one that seems fairly thorough:
http://www.fairchildsemi.com/an/AN/AN-6076.pdf

Looking at your circuit, when the low-side MOSFET is turned on, the 22 uF bootstrap capacitor is charged through the diode and the two 1 ohm resistors and within three or four time constants it will reach almost 12V. With these components it will take about 100 uSec. When the low side MOSFET is turned off, it will be essentially floating, but Vb will be at about 12V. When you turn on the top MOSFET, it will conduct and the voltage of Vs will rise toward 12 VDC. Thus the other side of the charged capacitor will make Vb rise, and since it is used for the high side gate drive, it will be sufficient to drive the top MOSFET on full. As long as the gate current and the current used by the gate driver circuit in the IRF2186 is small, the 22 uF capacitor will hold the Vb voltage at nearly 24 volts, or 12V above Vs, to keep the high side MOSFET turned on.

As long as the duty cycle remains within certain limits, the charge pump action will maintain the gate drive voltage above Vs and the HI and LO inputs will drive either MOSFET on solidly. However, you need to be sure that the MOSFETs can drive the load solidly, and the 12V supply must also be solid. 

The level shifters in the IRS2186 and the logic circuits for the high side driver should not supply appreciable current to the load as you seem to experience during dead time, but it may be best to maintain drive to either top or bottom MOSFET for at least 50 uSec and dead time should be only 1 or 2 uSec. Also make sure the load is not excessively inductive or capacitive, and look for possible high voltage transients that may wreak havoc during switching transitions.


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## Vehikelfranz (Feb 13, 2012)

Maybe, this is not the correct place for my answer,
but, for wiping away Your fear from programming a
small microcontroller, i want to show You one of my very first
programs i wrote for an ATtiny 13 in BASCOM:



$regfile = "attiny13.dat"
$crystal = 1200000
Config Portb.0 = Output 'Pin5 PWM0a
Config Portb.1 = Output 'Pin6 PWM0b

Config Timer0 = Pwm , Prescale = 1 , Compare A Pwm = Clear Down , Compare B Pwm = Clear Down

Config Adc = Single , Prescaler = Auto , Reference = Avcc
Start Adc

Dim M As Byte
Dim N As Byte
Dim Ad_2 As Integer
Dim Ad_3 As Integer

Do

Ad_2 = Getadc(2) 'Pin3 ADC2
Ad_2 = Ad_2 / 4
M = Ad_2

Ad_3 = Getadc(3) 'Pin2 ADC3
Ad_3 = Ad_3 / 4
N = Ad_3

Pwm0a = M
Pwm0b = N

Loop

End


That's all......... and this gives two !! PWM-Channels
to an ATtiny13! There are a few things in these lines that are not 
perfect, no integer is needed, word is enough, 
but this is exactly as i typed it those days and it works.
and give the output of one channel to a TC4451, then you can even
drive big IGBTs with this.

Some time ago, i started with a TL494 and was happy at first

i found the schematic there:
http://www.atx-netzteil.de/pwm_mit_tl494.htm

but as soon as You want to add extras it will be much easier
with some controller. (Paul also already mentioned this)


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## Vehikelfranz (Feb 13, 2012)

here You can see this absolute primitive IGBT-Controller in action:
7805 ; ATtiny13 ; TC4451 ; a 1200V 500A -IGBT
and a few capacitors plus resistors......
nothing more! 
A microcontroller does not make it complicated,
it makes it easier!

http://youtu.be/SfnGKJG5Nkg

have fun!


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## Jamie EV (Oct 3, 2012)

smpavlik said:


> No. This is driver only. Or amplifier if you want


 I have a couple of 1458 TC operational amplifiers I'm wondering if those would work as drivers I'm not really sure to be honest


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## PStechPaul (May 1, 2012)

Jamie EV said:


> I have a couple of 1458 TC operational amplifiers I'm wondering if those would work as drivers I'm not really sure to be honest


An OpAmp can be used as a driver but it won't do the job nearly as well as an IC designed for the purpose. If you keep taking shortcuts and trying to use parts you may have on hand or can get for cheap, you are likely to get disappointing results and possibly destroy your MOSFETs or IGBTs or damage the motor. If you mostly want to learn about electronics in general there are numerous tutorials and fun projects you can build, but you should invest in some decent test equipment so you can so what's going on. If you just want to make a DIY PWM motor controller you need to determine the final specifications and then design, build, and test the various modules and circuits that will eventiually be combined to do what you want. 

There have been many good suggestions for you to run with but it seems like you are always adding new possibilities to the pile without fully understanding what you have already tried. I have made the mistake of trying to use components that I already have (in huge quantities), and usually it has resulted in my spending more money and time than it would take to purchase just what I needed. As mentioned, I made a three phase motor controller that powered a specially wound FHP IM, and I made the erroneous assumption that I could drive logic level MOSFET gates directly from a PIC, and I may have even used 1K gate resistors. It did work, briefly, but soon enough some of the MOSFETs blew up. Lesson learned. You might as well benefit from my mistakes and the experience of others to avoid such problems and quickly advance to something that works well. There's plenty of room for tweaking and improvement after that milestone.


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## Vehikelfranz (Feb 13, 2012)

The quality of an IGBT or Mosfet-driver is defined
by the speed of switching and the current it can
deliver for these short moments.
every microsecond counts in this case,
those drivers are disigned for this purpose, use them 
and it should work.They have to kick the gates
to the position You want them to be as fast as possible.

in these short switching times, every gate-capacity is 
like a shortcut at first, and so there are really curents
of a few amperes when switching larger FET or IGBTs.
this is also the reason why the power-supply for the
driver is so important, and at these speeds even the 
inductivity in electrolytic capacitors is a problem.
it is absolutely normal that the driver is much more
complicated and expensive than the power-stage itself.

one thing that made a lot of trouble for me in the
beginning is that those drivers (i prefer TC4451 at the
moment, but there are many similar ones) 
have a serious problem with over-voltage.
It is not good to supply them direct from the 
motor- power-source. those problems are gone since
i supply the driver via optocoupler and DC-DC-Converter.
I killed more driver ics when testing at 12V than 
at 400V..... ;-)


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## Jamie EV (Oct 3, 2012)

PStechPaul said:


> An OpAmp can be used as a driver but it won't do the job nearly as well as an IC designed for the purpose. If you keep taking shortcuts and trying to use parts you may have on hand or can get for cheap, you are likely to get disappointing results and possibly destroy your MOSFETs or IGBTs or damage the motor. If you mostly want to learn about electronics in general there are numerous tutorials and fun projects you can build, but you should invest in some decent test equipment so you can so what's going on. If you just want to make a DIY PWM motor controller you need to determine the final specifications and then design, build, and test the various modules and circuits that will eventiually be combined to do what you want.
> 
> There have been many good suggestions for you to run with but it seems like you are always adding new possibilities to the pile without fully understanding what you have already tried. I have made the mistake of trying to use components that I already have (in huge quantities), and usually it has resulted in my spending more money and time than it would take to purchase just what I needed. As mentioned, I made a three phase motor controller that powered a specially wound FHP IM, and I made the erroneous assumption that I could drive logic level MOSFET gates directly from a PIC, and I may have even used 1K gate resistors. It did work, briefly, but soon enough some of the MOSFETs blew up. Lesson learned. You might as well benefit from my mistakes and the experience of others to avoid such problems and quickly advance to something that works well. There's plenty of room for tweaking and improvement after that milestone.


 will strictly speaking I haven't taken any shortcuts yet because I haven't begun


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## Shah (Oct 25, 2012)

Just an update i managed to figure out how to remove that 2.65v from my Vs. It seemed to be a startup deal....if you have the low side on in the start, the driver will startup ok and behave normally. But if you have the high side on and very little load(like in the mA region) then it will screw up and have a floating voltage on Vs pin. My startup sequence was the issue. 

Anyway, paul i didnt take your advice and i wasnt careful. I hooked up a very small buck converter to the output and there were some transient spikes and i have lost 4 mosfets and 1 driver. I will need to protect my driver cct. Lucky I hadn't connected my micro processor.

I still have a question. What's wrong with using a NMOSFET driver with a floating power supply to run the highside mosfet? Aside from another power source. I have been thinking why can't I just use a separate battery and wire it up like I would a lowside fet. I would have to insulate the high side driver so even if it was floating dangerously high there would be very little chance of shorting. I would use optos to get the control signal in.


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## PStechPaul (May 1, 2012)

A separate floating supply, such as a DC-DC converter, is perfectly OK, but you will need one for each leg of the bridge. Thus a three-phase bridge needs three converters. And you also need a separate high-speed optocoupler and MOSFET driver for each of the high side devices. Why go to all that trouble and expense when you can get everything in one inexpensive IC?


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## MPaulHolmes (Feb 23, 2008)

I use a 200amp inductor & several strands of 12 gauge resistance wire (from ebay) in series as the "motor". I stick the wire in a water bath, and you can get lots of power out of it, and the oscilloscope readout looks a lot like it's driving a motor.

Here's a 3.3kw test with resistance wire & inductor:
http://www.youtube.com/watch?v=ijVLeixj2pM


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