LM2596S converter usage?

Is the MX_LM2596S (image) a good solution for providing power to Arduino Mega (+ possibly attached nano) from a nominally 36 V accumulator , lead acid or lithium ion, max voltage around 40V in practice? This is one off hobby project for myself, learning.

I bought the circuit board from DX.com, SKU154907, DC 3~40V to DC 1.5~35V Voltage Step Down Transformer Module , 3.20 USD from China incl. freight (!).
I tried to find out the specifications for the input side capacitors, in vain. The main circuit, black without visible markings in the image, is LM2596S and there is ample information about that in the net. Texas Instruments gives advice e.g. about the properties of the capacitors in their datasheet of LM2596.

I took a risk and connected an accumulator of 38.8V voltage to the input side of the module, adjusted its potentiometer to give 5.0 V (it did …), and connected the output + and - to the 5V and ground of an Arduino Nano. No smoke, and the Nano blinked happily. Then another test, potentiometer to output 7 V from the module, and plus side to the Vin pin of Nano. No problems, blinking ok. Next the connections were moved to Arduino Mega. Good.

But I am still very worried, if there should be protections against voltage spikes from the lead acid battery during connecting/ disconnecting etc. If the capacitor’s voltage tolerance is not high enough (how much needed?), what happens when it fails: short or no connection?

Is this a viable solution and something to improve in it?

What do you think?

mx_lm2596S.jpg

I agree that the difference between 38v and 5v is grounds for concern. You could add a safety margin by clamping the output.

  1. zener - only a help against brief transients. If it burns out it may short the switcher which is probably the least bad result.

  2. Raise switch output to ~7v and stick in a linear regulator with some loss in efficiency.

  3. What me worry? I like magic smoke.

Others may have more clever ideas.

That's weird. Those caps say "35w" where I would expect them to list a voltage like "35v".

I suspect those caps are 35v. It's usually not a good idea to push the voltage rating, as it can result in swift failure. I wouldn't want to push those caps beyond maybe 26v (75%).

There are some other similar DC-DC boards on DX with better caps, for example SKU 126106 which has an input cap marked 50v.

I have a similar board. The capacitors are definitely 35v. In addition the limit voltage for the chip is 40v. 38v is pushing the limits and eventual failure is quite possible. If this is just a brief fun project, I would not worry too much. For a more permanent installation you need a lower voltage or a board with higher voltage specs.

Hi, I agree with joe about some protection, such as crowbar type with a 5.6V zener across the 5V supply, so that it conducts if the supply spikes.

To help you would also place a fuse on the output of the regulator before the zener so that should the zener conduct the fuse will blow, this makes sure that the supply is fully disconnected from the arduino in even of a fault.

There are numerous crowbar protection circuits around if you google, some for low power applications. Not sure how much current the 5V will be supplying.

Tom

tylernt: There are some other similar DC-DC boards on DX with better caps, for example SKU 126106 which has an input cap marked 50v.

Ok, I'll consider ordering that.

[quote author=Joe mcd] I have a similar board. The capacitors are definitely 35v. In addition the limit voltage for the chip is 40v. 38v is pushing the limits and eventual failure is quite possible. If this is just a brief fun project, I would not worry too much. For a more permanent installation you need a lower voltage or a board with higher voltage specs.[/quote] Good to know. I'll use the module until it breaks provided it will not destroy other things (battery, Arduinos).

TomGeorge: Hi, I agree with joe about some protection, such as crowbar type with a 5.6V zener across the 5V supply, so that it conducts if the supply spikes.

To help you would also place a fuse on the output of the regulator before the zener so that should the zener conduct the fuse will blow, this makes sure that the supply is fully disconnected from the arduino in even of a fault.

There are numerous crowbar protection circuits around if you google, some for low power applications. Not sure how much current the 5V will be supplying.

Tom

Ok, thanks. I'll add a fuse and a 5.6V zener. The output current is now about 100 mA, and in the future I guess 200 mA - 300 mA will suffice well.

These regulators do tend to overshoot the voltage when shorted (brief shorts will raise the voltage a couple of volts!)

Another option could be a thermistor, a zener's a good option you might consider using a transistor in conjunction with the zener to take the load off and stabilize the voltage.... but other than that i tend to use 12- 24v supplies, i've never been higher than that and it's all worked flawlessly...

TomGeorge: Hi, I agree with joe about some protection, such as crowbar type with a 5.6V zener across the 5V supply, so that it conducts if the supply spikes.

To help you would also place a fuse on the output of the regulator before the zener so that should the zener conduct the fuse will blow, this makes sure that the supply is fully disconnected from the arduino in even of a fault.

There are numerous crowbar protection circuits around if you google, some for low power applications. Not sure how much current the 5V will be supplying.

Tom

Ok, thanks. I'll add a fuse and a 5.6V zener. The output current is now about 100 mA, and in the future I guess 200 mA - 300 mA will suffice well.

[/quote]

Totally agree with TomGeorge, there are some very fast acting fuse manufactured by 'little fuse', you can easily find them on element14 or RS, however choosing a right value of ampere of the fuse need some expert advice, there is a absolute current limit for Arduino Mega2560 and I believe it varies from unit to units, you want a fuse very close to the limit but not limiting the margin by too far.