Raising the Bridge...Automation with Arduino: Failure reconciliation

RE: Raising the Bridge...Automation with Arduino: Failure reconciliation

robogary — Thu, 25 May 2023 13:55:00 GMT

The photo is really helpful. The stalled motor current is likely more current than the h bridge can handle long term. If the pwm output motor rms voltage is lower , the rms stall current is lower. You can get an idea of the motor resistance by checking the dc motor leads with an ohmmeter. Stall current is the max volts applied to the motor, divided by that resistance. You could try resistors in series with the motor to limit stall current to 2 amps or less. The motors will automatically slow down as load increases, giving them a speed droop feature

RE: Raising the Bridge...Automation with Arduino: Failure reconciliation

colporteur — Thu, 25 May 2023 00:28:33 GMT

I had put further troubleshooting of the issue with the L293D until I had some spares. I received L293D driver chips this week. My thought was to replace the chip in the problem modules to determine if it was the cause of the failure. Then I would repeat some tests to see what lets the smoke out of the chip.

Changing the integrated circuit

DIDN'T RESOLVE THE ISSUE!

Crap! What did I overlook in my testing? Back to the meter. I struggled with the specification sheet. Something wasn't right.

I confess I am not the sharpest tool in the shed when it comes to electronic gardening. My electronics career forked into System Administration in 1996 so some of the stuff in memory is rusty. I had used the L293D modules in two other projects with success. The failure this time came as a surprise. I take it as a failure on my part when I let the smoke out of components when I am building something, So I work real hard to keep the smoke in.

My problem with the driver chip was the two supplies VCC1 & VCC2. I hate the VCC references in the spec sheet. One supply powers the chip and the other is used by the chip to power the load. On the module PCB there are inputs, VCC is 5V for the chip and Vin is the motor supply. You can see this on the module image on the left.

A meter reading of the modules Pin 16 VCC1 is 12V. Meter meting of Pin 8 VCC2 is 5V. Wait a minute the values are reversed. After much consternation and nashing of teeth I discovered I must have put the chip in backwards???

The screen shot on the left is the orientation of the L293D chip from a picture on the website and the two modules on the right are what is installed. Note the position of the red circles that show the chip orientation key.

Putting the chip in backwards is something that can happen but here is the kicker, I never removed the chips. They were installed backwards when I received the modules.. The two modules on the right image are installed and working. The three L293D modules I thought I had damaged had the L293D chip installed backwards also. That is five modules delivered from the supplier with the chip installed backwards.

With the chip in the correct orientation the voltages at the power pin begin to make sense %v is where you would expect it. With the chip in the correct orientation the modules work. No parts replacement required.

I did discover measuring the voltages at the motor points with no load appears to work but slightly lower. With a motor load attached the voltage sinks. I can only speculate the two modules that are working is because the load is not that great.

My actions didn't cause the failures. I now have five L293D spare integrated circuits.

RE: Raising the Bridge...Automation with Arduino: Failure reconciliation

colporteur — Mon, 24 Apr 2023 23:44:16 GMT

I have order some replacement components for the L293N & L298N.

If you are squeamish about seeing devices destroyed than I recommend you drop following this post.

In the interest of learning, I plan to sacrifice at least one of each of the component in a recreation of what I believe caused failures.

RE: Raising the Bridge...Automation with Arduino: Failure reconciliation

robogary — Sat, 22 Apr 2023 02:27:30 GMT

wow- I've had pretty good luck with these bridges, it could be luck or the way I use them.

#1 - I usually fuse upstream from the H bridge in case of accidental short (short term instantaneous current) , and long term current (overload current).

It could be the motor current overloads the bridge.

#2 - I dont slam the H bridge full FWD, or full REV with full PWM. First have PWM duty = 0, enable the FWD or REV and increment the PWM duty to 1023 (or is it 255?) in a quarter second or so, or whatever accel/decel you want. To stop, first reduce the PWM duty from the set value to zero, then turn off the FWD or REV bit.

I have used these IBT-4 50A bridges in some projects , and they have been running for years.

https://www.amazon.com/H-Bridge-High-Power-Single-Channel-Semiconductor-Refrigeration/dp/B07PM76KJG/ref=sr_1_1_sspa?crid=1N78ZSPXO8QN7&keywords=H+bridge&qid=1682129796&sprefix=h+br%2Caps%2C785&sr=8-1-spons&psc=1&smid=A2P6NQ66D5K6F0&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUEyMUFCMVA3QVBSN01XJmVuY3J5cHRlZElkPUEwNTEzMDgyMUJQQkVIRFVMR0wwVCZlbmNyeXB0ZWRBZElkPUEwMzA4NDU0M01NSk5QMjRUOE1UUiZ3aWRnZXROYW1lPXNwX2F0ZiZhY3Rpb249Y2xpY2tSZWRpcmVjdCZkb05vdExvZ0NsaWNrPXRydWU=

RE: Raising the Bridge...Automation with Arduino: Failure reconciliation

scottiebabe — Fri, 21 Apr 2023 12:11:39 GMT

Apparently this is common, people are blowing up 3-d printers! if the driver broad was designed correctly I wouldn't expect it too...

[embed:1a31843e-3f91-4c61-9d55-056575b1c5e8:ee4b2ffb-1e1c-4d74-b908-a4540b476a30:url=https%3A%2F%2Ftwitter.com%2FMAYERMAKES%2Fstatus%2F1632795296601128971&sanitizedEmbedCode=%3Cblockquote%20class%3D%22twitter-tweet%22%3E%3Cp%20lang%3D%22en%22%20dir%3D%22ltr%22%3EWhy%20you%20should%20not%20move%20your%203d%20printers%20axis%20by%20hand.%20Demonstrated%20by%20killing%20an%20led%3A%3Ca%20href%3D%22https%3A%2F%2Ftwitter.com%2Fhashtag%2F3dprinter%3Fsrc%3Dhash%26amp%3Bref_src%3Dtwsrc%255Etfw%22%3E%233dprinter%3C%2Fa%3E%20%3Ca%20href%3D%22https%3A%2F%2Ftwitter.com%2Fhashtag%2Felectronics%3Fsrc%3Dhash%26amp%3Bref_src%3Dtwsrc%255Etfw%22%3E%23electronics%3C%2Fa%3E%20%3Ca%20href%3D%22https%3A%2F%2Ft.co%2F2DmgAmG73W%22%3Epic.twitter.com%2F2DmgAmG73W%3C%2Fa%3E%3C%2Fp%3E%26mdash%3B%20MAYER%20MAKES%20%F0%9F%A6%86%20%28%40MAYERMAKES%29%20%3Ca%20href%3D%22https%3A%2F%2Ftwitter.com%2FMAYERMAKES%2Fstatus%2F1632795296601128971%3Fref_src%3Dtwsrc%255Etfw%22%3EMarch%206%2C%202023%3C%2Fa%3E%3C%2Fblockquote%3E%0A%3Cscript%20async%20src%3D%22https%3A%2F%2Fplatform.twitter.com%2Fwidgets.js%22%20charset%3D%22utf-8%22%3E%3C%2Fscript%3E%0A]

Source mayermakes

RE: Raising the Bridge...Automation with Arduino: Failure reconciliation

shabaz — Fri, 21 Apr 2023 03:29:40 GMT

The other elephant in the room is that these driver boards are not very good. They have a lot of caveats, and if you're not sure of the code or the motor or supply connections are likely to change, then these are not the modules to use.

These ones look much better, and are cheap, and are a bit more modern:

They use a Toshiba chip (TB67H450) which, being more modern, is more efficient, won't get as hot, has various protections built-in, including that there's no risk of the shoot-through, so if the code is faulty, there's no problem. Plus it has over-current protection.

Also, the boards you're using look like they have a very small capacitor. The one in the photo has a larger one, but even then, it is built down to a cost like all these cheap boards are, so if it were me, I'd be desoldering the capacitors and adding better quality ones, since they are essential for protecting the chips from inductively caused spikes. An example on the Newark website would be this one: https://www.newark.com/united-chemi-con/elxz350ell101mf15d/aluminum-electrolytic-capacitor/dp/23K4236

It has fairly low ESR for an electrolytic, and is a good price, and would probably be a lot better than the one on the board. Also, you could solder a ceramic capacitor across the two pins of the electrolytic. Something like this: https://www.newark.com/kemet/c1206c105k5racauto/cap-mlcc-aec-q200-x7r-1uf-50v/dp/91Y9113 on sale currently, just $0.03 USD.

It is surface mount but large, so you'll easily be able so solder that (tweezers help but not essential, it could even be temporarily held in place with a tiny amount of glue before soldering).

If you did all that, you'd have something that is more rugged for a variety of scenarios.

RE: Raising the Bridge...Automation with Arduino: Failure reconciliation

Gough Lui — Thu, 20 Apr 2023 23:42:56 GMT

"At one point I prevented the arm from rising. I also noticed the module LED’s come on when I pushed the arm back down. The L298N didn’t work after that. Did the action of preventing the arm from rising or pushing it down, smoked the chips. I’m just not sure?"

Yes, that could certainly have hurt the module.

Depending on the module's current capability, when you stopped the arm from rising, the motor current may have risen to a much higher level (i.e. the stall current) compared to the normal operating current. This may have overstressed or overheated the bridge. Depending on your power supply, you may be able to have a protective current limit to prevent over-stressing the bridge, but keep in mind, if there are large capacitors then they can also provide a short burst of current during anomalous operation that can hurt the bridge. If your motors are brushed, incorrect brushes or carbon dust may cause spikes of current as the commutators cross the split-ring and that can cause a transient short circuit and back-EMF spike that might hurt the chip. Snubber capacitors are likely to be recommended in that case.

As for moving the motor when it is powered off, it will be working as a generator and creating back-EMF. Many drivers are MOSFET based and the body diode will conduct this back EMF to the voltage rails. As this is not regulated, if you did it quickly enough, you may have generated enough voltage to fry things upstream (e.g. an Arduino's output) thus that may later cause damage to future modules as they're not outputting properly. At worst, it may have stressed input ESD protection diodes which may cause early failure of inputs/outputs on an IC. But if there is a beefy capacitor and you were not too vigorous, then you may have survived this one.

Jan's suggestion regarding dead-time is absolutely important for many types of drivers with no integrated prevention. Your code should NEVER enable the bridge in such a way that it would short out the supply as that is a quick way to failure.

- Gough

RE: Raising the Bridge...Automation with Arduino: Failure reconciliation

Jan Cumps — Thu, 20 Apr 2023 20:43:13 GMT

Do these drivers have deadband / shoot-through prevention?

That's typically the aspect that goes wrong in H-bridge designs.