H-bridge get's boiling hot! What can i do?
Botdocter
Posts: 271
My parallax propeller robot control board has an onboard h-bridge.
But when connected to my 12v motors (2), it get's really hot. I put my finger on there and it whas not enjoyable....
I'm afraid that i will burn it. Is there a way to restrict the outgoing power?
What can i do to cool it? A fan maybe? I thought about a aluminium cooling plate, but i can't mount it on the chip.
But when connected to my 12v motors (2), it get's really hot. I put my finger on there and it whas not enjoyable....
I'm afraid that i will burn it. Is there a way to restrict the outgoing power?
What can i do to cool it? A fan maybe? I thought about a aluminium cooling plate, but i can't mount it on the chip.
Comments
I believe the h-bridge can handle 2,5 amps per channel. I only tried slow speeds. Can that be the problem?
http://www.st.com/stonline/books/pdf/docs/7616.pdf
The motors shouldn't be drawing more that 2.8A each or you're asking for trouble. Can you connect one of the motors directly to the battery and measure the current? See how it acts under no load and also if there is a load on it. Worst cases will be when the motor starts and under a stall condition (no movement). It sounds like you don't have things sized quite right and may be using motors larger than are recommended for that H-bridge.
Robert
RC-car motors are available in a wide range of amperes. Even up to 20Amperes but still small in size!
If you haven't bought a Multimeter with a 10A range then it is the right time to do so now. And then simply measuring the amperes.
In my Opinion a Multimeter that can measure AC and DC millivolts to 400 Volt and AC/DC microampere up to 10A is a must if
you work with electronics
I'm using this one
http://www.dealexcel.com/ut61b-digital-multimeters-acdc-r-f-c-t-duty-cycle-usb_p367.html
beside two other multimeters.
Lot's of measuring functions,
Volts, AMperes
Ohm-Meter
Capacity-Meter
Even Dutycycle
backlight, and even a USB-connection to your PC to log measurings
If you can afford $54 I would recommend this one
best regards
Stefan
I'm thinking about buying external motor controllers. Wich one should i use? I think 10 amps should be enough right?
Hi Botdocter,
I agree with Leon on this. You need to look on the side of the the motors you are using, to see what the nameplate rating is and then markup that number up 150%. By doing this, then you can size what motor controllers are needed for what you need to do. This prevents any overcurrent problems and I do this as an electrician with all types of motors.
I found these brushed ESC's. Apart from the current, Are they usable with the propeller? And will they turn the motor both ways? Or just forward and no back?
http://hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=9090
http://www.parallax.com/StoreSearchResults/tabid/768/List/0/SortField/4/ProductID/584/Default.aspx?txtSearch=robot+control+board
You got a pluggable connector for Vin, for Motor A and Motor B
At all three connectors you can insert probing cables to measure the current.
It doesn't even matter which probe is connected to what as long as your meter is switched to measuring amperes and you
connect the amperemeter as "INLINE"
Examples
Vin-gnd----black probe of meter ---meter itself
red probe of meter ---- gnd of Powersupply
Vin-Plus----black probe of meter ---meter itself
red probe of meter ---- lus of Powersupply
the only difference that makes is that the sign of the current flowing is inverted.
Or you cut or unsolder one of the cables
from
- powersupply
- motor
and INSERT the multimeter there. This means the whole current have to flow through the multimeter
If all of this is should be new to you I highly recommend to learn the basic concepts of electricity
(I mean a bit beyond "electricity makes motors spin and LED light up") especially how to measure voltages and how to measure currents.
The current consumed by the board itself will be 0,05A or 0,1A. The motor will take 2, 3, or 6 A so the current to the board doesn't matter
best regards
Stefan
I will come to it in the next few days.
I accually gratuated in electronics ; ) Allthough that has been years ago...
Thanks again!
PS: I found these brushed ESC's. Apart from the current, Are they usable with the propeller? And will they turn the motor both ways? Or just forward and no back?
http://hobbyking.com/hobbyking/store...idProduct=9090
the link doesn't work. If it is a electronic speed control for R/C-vehicles it expects a standard servo-signal on the inputside.
best regards
Stefan
So if the esc receives a normal servo signal, it will work right? It will turn both ways?
turning the motor forward baclward depends NOT on th einputsignal but on the inner circuitry of the ESC.
For Airplanes with E-Motor or helicopters one direction is enough.
It needs to have a H-bridge to change the voltage's polarity. A Single MOS-FET that does PWM is not enough.
I would like to comment on your style to build projects
You bought the controllerboard and connected to possibly much to big motors. That's why the H-bridge gets so hot.
Now you searched in the internet for a controller that can do a lot of ampere and is still cheap (this turnigy thing)
Putting together components in electronics is a bit more complicated than plugin in a USB-device to a PC.
USB has a few standards and EVERY USB-device has to fullfil one or all of these standards (USB 1.0 USB2.0 USB3.0)
That's why it works plug and play.
Microelectronics is almost NOT standardised or let's say there are standards but a lot of different ones.
For example a serial interface can be TTL-level or V24 = +- 12V) RS232, RS422, RS485 variing baudrate, parity bits, stopbits, inverted logic levels, hardware flow-control.
So you have to check if components that should be interfaced can be configurated to equal parameters and if they work on the same electrical standards.
In your case you have to measure the current of the motor under maximum load.
If you know this value you can choose a suitable motorcontrolling H-bridge.
best regards
Stefan
Is it possible to boost my h-bridge? With a few mosfets maybe or can i use the existing h-bridge in another way?
with a maximum current (under mechanical load of the motor) of 2A. Depending on the weight
of your vehicle this might be suitable or too small.
There might be still a chance if your actual motors are really oversized and you do NOT
need a high rpm on the wheels of your robot. Is it a robot? How big? weight? How fast should it move?
If you can tell these details it might be possible to use a smaller motor with a gearbox to
translate the high rpm of the motor to something usable for wheels.
If you take a look into RC-cars - even 50 mph fast R/C-racers have two tooth-wheels to translate
the rpm DOWN (not up)
What I can see from the picture of the board in the manual is that the propeller-chip
is connected directly with the H-bridge.
boosting an electronic device itself is almost impossible. Except maybe installing a liquid cooling-system
which is much more effort than using a bigger H-bridge. Adding big MOS-Fets would mean to add
extra circuitry to get back from a high voltage PWM signal with changing polarity to a signal
motor enable and a signal direction, to drive the input of a bigger H-bridge.
by the way
It is always good to give an overview about:
- Your project: what do you want to do IN THE END
- your programming skills
- your knowledge about electronics.(maybee by describing your most comlicated circuit that you have finished successfully)
Doesn't have to be a 10 page report but 2-5 sentences per item
with a rough classification like
expert,
advanced hobbyist,
moderate experienced hobbyist,
newbee
This will help the forum-members to give you understandable advice.
best regards
Stefan
I tried to measure the current taken by the motors but somehow when i put a ampere meter in between the motors won't turn. @?!??
The board is powered and does what it has to but somehow when the motors start turning the program crashes and the propeller is non-responsive.
When i apply the power without the meter in between everything works fine!
At it's max. It uses 2.4A. When starting it draws less. It doesn't come over the 2.4 ampere ever.
congrats ! Well done that you measured the maximum current.
that is the most important and guiding to the solution value we need.
To check the maximum current is so common for this kind of application that
nobody even mentioned it at the beginning of this thread.
I want to introduce you to a semi-professional way of working on your project.
Therefore I have some guiding questions that you should answer:
Where can the usermanual to for the Propeller Robot Control Board (PRCB) be found?
if found - download it
Which is the chip on the propeller controller board that controls the current of the motors?
Do a search on the internet for the datasheet of this chip.
read the feature section of the datasheet.
Then give an answer to the question: "Can these 2.4 Ampere Motors be driven with the propeller controller board?"
What happens?
I have done exact all these steps. I could tell it to you directly. But I don't want you to beg me for my fish. I want you to learn fishing yourself.
best regards
Stefan
And it should be able to take 2.8A continuous. And 7A peak.
So why is it getting so hot?
Guiding questions: How is electric power calculated? Which values do you need therefore?
What says the datasheet about these values?
What says the datasheet about the thermal behaviour of the chip?
best regards
Stefan
I=U:R
For the answers in you post: we both know wat the datasheet says.
Do i reallly have to type it out? Oh wait... I did allready in my former post.
It does't answer my question though!
I want yo thank you for your help but is it nescecairy to treat me as a kid?
I know my way around electronics. If there is something i don't know i will ask.
Power: P = R * I²
Ron = 0.3ohm
P = 0.3Ohm * (2.4A)² = 1.73 W
Datasheet Thermal Data
PowerSOI20 Package:
62°C/W Maximum Thermal Resistance Junction-Ambient Mounted on a multi-layer FR4 PCB without any heat sinking surface on the board.
62°C/W * 1.73W = 107.3°C
best regards
Stefan
Leon is right on about measuring the current of the motor 'itself' when connected to a power source. The power source should be just like the one you want to use, probably a fully charged battery pack. With that you need to test it several different ways: No load, during startup, under load, startup under load, etc. to find out exactly what it does draw.
If you are making these measurements while connected to the H-bridge without do the basic motor tests first then you're pretty much just wasting time and effort.
I posted a link to the datasheet for the H-Bridge chip on the board. It is supposed to have thermal limiting built-in (although I prefer not to push it) and what may be happening is that you are exceeding the capacity of the chip which is causing it to heat up too much and start to shut down. This may limit what you are pulling through it so you might only be seeing what it is letting through instead of what it actually wants to use....
When you asked about beefing up the H-bridge it is easier to bypass what is on the robot control board. At that point you are better off just using a USB Propeller Proto board and connecting that to a different H-bridge driver. You can either use a standard H-Bridge where you can control the direction and provide the PWN for the speed in each direction. Or, you can get one with some smarts on board that has an input the same as a continuous rotation server where pulses of about 1ms are full speed one way, 1.5ms are off, and 2ms are full speed the other direction. Values in between make the motor go in the appropriate direction at a slower speed. Those pulses should be repeated approximately every 20ms. You're still controlling an H-Bridge but instead of driving it directly you use use one pin.
If you really want some good information on testing motors for use with H-bridge drivers and also the R/C controllers start looking up information on Battlebots. For that we did push things to the limits (and well beyond) but that was only meant for 3 minute matches. With so many motor options out there everyone had to test the motors to see what they would draw and figure out if they would work with each controller. I personally witnessed several cases where that wasn't done and watched motor controllers, wiring, and motors all go up in smoke and flames....
With a bit more research and testing I'm sure it will all fall into place for you!
Good luck on your project.
Robert
this is new to me. And you catched me on not following my own advice.
Read the datasheet carefully and completely.
Do you think the resistance of the H-Bridge keeps the current down
or does the non dissipative protection of the H-bridge limited the current already?
Do you know if the H-bridge can be driven a long time when ithe overcurrent protection is always active?
best regards
Stefan
It should have the lowest current free running without a wheel attached. It should draw more with the weight of the robot running on a flat surface. It'll draw even more going up an incline. It will draw even more pushing against a wall. It will draw most with the wheel unable to turn. Also ensure the robot has the weight that is expected for it to run, if this includes batteries, cameras, and other items then either bolt them on or place equivilent expected weight on so you will be measuring usual conditions.
And as Leon said, motor to battery with the meter in series to provide the least resistive path.
This next comment may be for Leon or anyone else that has experience. I haven't done this, but I'd assume he could deliver less power, and thus current to the motors if he used PWM to drive the duty cycle to the motors. Sure this would equate to less torque, but should mean less current passing through the H-Bridge. Though the downside is that it may be a bit tougher on the H-Bridge (depending on the implementation), and switching frequency could make it even hotter or cause it to premeturely fail. If it would work then it would be relatively easy to implement in the propeller. Anyone tried this?