Tronic's DIY dual Mosfet H-bridge (DSMhb)

Re: Tronic's DIY dual Mosfet H-bridge_

Afaik each transistors ground should be seperated from the others. Afais you've shortcutted them by connecting them to a aluminium cooler bridge together.

Regards
Christian

Re: Tronic's DIY dual Mosfet H-bridge_

hi! the cooling is connected to the drain (center pin).

Re: Tronic's DIY dual Mosfet H-bridge_

i also noticed that if the GREEN led is on (green is the one that is most outside on my board) the motor turns much slower then when the red one is on. when the green one is on the motor slowly moves to the center position, when the red one is on the motor shoots into the center position. is that normal?

Re: Tronic's DIY dual Mosfet H-bridge_

Hi Igor,

I explain in this post, the status led meanings!
post7064.html#p7064

When the motor is centered you should see both lights go out!

And here is another video that shows the status led behavior under normal conditions...!
post7167.html#p7167

About the difference in the speed of rotation for each direction... Is it a wiper motor? Can you post a photo of the motor? If you connect the motor directly to the power source does have difference on each direction?

Regards, Thanos

Re: Tronic's DIY dual Mosfet H-bridge_

hi thanos! i know what the status leds are for.. what i meant to explain is in which of the cases it happens.. so that who knows the board can figure out what components are giving problems.

in my situation both leds are ON in center position. is that normal?

the motor is fine if connected directly to a battery.

i have read various datasheets of the 4905, there appear to be 2 versions. 2-4 V and 10-20V (trigger voltage). do you know what model you sent me?

thanks

cu

igor

Re: Tronic's DIY dual Mosfet H-bridge_

Hi guys!
I have a question..
Can I use the same Battery to feed the 2 H-bridge on the Thanos's DSMhb? Or I must use two battery?

Thanks a lot!

Re: Tronic's DIY dual Mosfet H-bridge_

Yes, you can use one battery for as many DSMhb you want! But depending on the motor rating and usage, it will be discharged more quickly...

One 100Ah car battery can handle well three DSMhb (total 6 motors) and will last for several hours if the motors aren't under constant load (with worm gear mechanism instead of freewheel gearbox!)

Regards, Thanos

Re: Tronic's DIY dual Mosfet H-bridge_

Hi Thanos,

is it available a schematic of your dual Mosfte H-bridge?

Regards,
Alle

Re: Tronic's DIY dual Mosfet H-bridge_

Here it is:

dual_simple_hbridge_schematic.pdf

:

Regards, Thanos

Re: Tronic's DIY dual Mosfet H-bridge_

Thank you very much!

:thbup:

Re: Tronic's DIY dual Mosfet H-bridge_

Hi SirNoName,

I assume you are used the updated layout of the DSMhb1.2 that can be found here:
post7471.html#p7471

And more particularly the one that is shown in this PDF:
download/file.php?id=427

This version is identical to the DSMhb1.2b except from the fact that in the DSMhb1.2b I'm using Terminal Connectors to mount the mosfets to be easy to unscrew and replace them in case they are burned.

The PDF layout is showing correct the orientation of the cooling nose of the MOSFETs that should be in the inner side, back to back on each row, to be able to mount a common aluminum cooling stripe on both two mosfets back. On the DSMhb1.2b layout plans I show on the silk layer the Terminal Connectors orientation and NOT the MOSFETs orientation!!!!!
Can you take a photo of the way you assembled it and show it here, to be sure about the way you placed the mosfets?

Have you tried to decrease the PWM to 17Khz?

And did you tried to test the hbridge manually? You can test the DSMhb1.2 manually with this procedure:
1. Connect the PWM1 line to +5v
2. Connect the M1IN1 to +5v and M1IN2 to Gnd, to see the motor rotate in one direction.
3. Disconnect the M1IN1 from the +5v
4. Connect the M1IN2 to +5v and M1IN1 to Gnd, to see the motor rotate to the other direction.

You can perform the above test with no motors mounted, and just watch the status LEDS light one at a time.
And you can try it on the second half of the DSMhb1.2 by using the rest of the ports (PWM2, M2IN1, M2IN2)


EDIT: The 74HC08 chip is powered from the signal cable (from AMC1.5 for example), not from the motor power source!!!! To be able to do the above tests you need to feed it with +5v also!!!


Regards, Thanos

Re: Tronic's DIY dual Mosfet H-bridge_

Yes they are swapped

Re: Tronic's DIY dual Mosfet H-bridge_

Yes, its rotated, cause I made changes on the placement of the 74HC08 chip. But its fine. It doesn't matter that much on the output, since you can rotate the motor connections too! :lol:

Yes, there are no Pullups as I'm using the internal Pullups of the AVR chip ports!

Funny isn't it? I was wondering too, and thats the reason I placed a few extra holes to connect together the two grounds if needed. To my big surprise, no common ground was needed at all !!!! Actually its bad to let this ground connection happen even through the simulators metal frame!!!!!! And my motors are isolated due to the fact that the joyrider is made from PVC!!
My theory is that the ground reference is created from one of the two direction inputs. For example if the M1IN1 is High (+5volts) then the M1IN2 is Low (Gnd) providing the ground this way. An interesting thing is that if both direction inputs are High or Low, then braking is occurring on the motor!!

Best Regards, Thanos

Re: Tronic's DIY dual Mosfet H-bridge_

Hi Sirnoname

I know that it develops heat too fast sometimes. But with proper cooling (aluminum plates + fan) it can be used for several amperes. I measured up to 12A on my joyrider, under load with the wiper motors, and I was checking it with temperature probe that it was not raised temp above 50 Celsius.

You can place a cooling plate but it should placed only on opposite placed pairs (one IRFZ44 and one IRF4905). I show in the next photo the pairs that you can connect together (circled and colored blue).



On the following photos I show how I connected the aluminum plates, bolted in pairs:





This is the ONLY way that you can connect the cooling plates!!! Any other way will result in short circuit, explosion, or even fire.


Regards, Thanos

Re: Tronic's DIY dual Mosfet H-bridge_

Hi Thanos! how do you do? I would ask you if it's possible to drive mor than 30A in the h-bridge, eventually adding IRF fets, or If I can change the IRF with more powerful ones. It's possible to change only the IRF to drive more current or I must change other components?

I found 2 motors that have 50A nominal current.

Thanks a lot!

best regards
Stefano

Re: Tronic's DIY dual Mosfet H-bridge_

Hi Stefano,

I'm not sure if you could drive the motors you found with DSMhb, as it is now. Igor was trying to drive large 500W motor too some time before by using parallel placed Mosfets in the DSMhb circuit with no luck! He placed up to 12 mosfets per each h-bridges leg, that always smoked the first mosfet in each row for some reason. I think that is a matter of the ON-OFF time difference of the mosfets that become more sensitive as you add more parallel placed mosfets. Thus changes in the gate driving resistors is needed to lower values, that I have no knowledge to calculate. It lies to the ANALOG field of electronics that is beyond my current electronics level...

Maybe this link help you a little:
http://www.mcmanis.com/chuck/robotics/p ... index.html

Regards, Thanos

Re: Tronic's DIY dual Mosfet H-bridge_

Thanks a lot Thanos! I understand.
Do you know a place where i can find a schematic of 50A h-bridge that is compatibile with your AMC Control?
I can make another one more powerful..
thanks

Stefano

Re: Tronic's DIY dual Mosfet H-bridge_

Hi Thanos,
do you have a Picture like this above for the DSMhb1.2b version with the IDC Connectors?. The Layout with the IDC Connectors is a little bit different against the version with the Molex Connectors.
Thanks a lot

Re: Tronic's DIY dual Mosfet H-bridge_

Is there a full schematic of this project. I found detailed board layout images and a simple schematic located at download/file.php?id=842
but this does not show the diodes and other components. I intend to mill this board on my cnc machine as i dont see anywhere to purchase it.

Thanks in advance

Re: Tronic's DIY dual Mosfet H-bridge_

Hi Stefano,

I haven't found any cheap alternate for my DSMhb1.2b yet. But it may worth to modify it with larger mosfets like the IRFB4610. See what Roland ( http://www.simprojects.nl ) said about it:

I upgraded my servo drive system with better MOSFET's and reduced dead-time: dramatic increase in efficiency! I used IRFB4610, (100V 10mOhm) which is a pretty top-line MOSFET for this application, with very fast body diode, to reduce the hard-switching losses. (I discovered that most of the losses in the H-bridge are caused by the MOSFET body diode drop and body diode reverse recovery (due to hardswitching) losses, so this type of MOSFET is specially designed for these kind of applications. There is still some ringing with overshoot on the drains, but 100V MOSFETs should be OK. They also have a huge avalanche rating, so they'll hold. There is one drawback: the switching speed is so fast that there is considerable EMC (electromagnetic radiation) when the system is running. My radio on my lab bench will only give static when I'm flying. (didn't hear the neighbors complain yet, so it may be still OK). Not quite ready for commercial release, but good enough for hobby.

Regards, Thanos