Need help with Low voltage protection circuit

[truclacicr]

FWIW, R5 in the original circuit on page #1 provides hysteresis.

[Dima Abramov]

Hello i want to utilize this circuitry to put in to Power Tool adapter makita batteries -> other brand tools. The power tool draw can be constant 25-30 amps with peaks reaching up to 100 amps. So in this case IRF9540N from schematic is not a good choice because it would generate too much heat. Is there a better drop in replacement option? Something like PSMN1R2-30YLDX with 2.64 mΩ RDS for rough estimate .

[greg1985]

Re: Need help with Low voltage protection circuit

Just got my boards back from JLCPCB
IT works perfectly. though see if you can spot the error (on my part).




Yes I forgot to join a copper area to a network.

Hi. Nice project. Thank YOU for making this. Can You send me gerber file or pcb? I want to order from JLCPCB too. Thanks again for this project.

[flinx]

Re: Need help with Low voltage protection circuit

if anyone cares here is a video of the device being tested under load to cut off.
https://youtu.be/tkce2S1gxYA

[flinx]

Re: Need help with Low voltage protection circuit

Alright!

I hooked the dustbuster and circuit up to a 15v somewhat adjustable switching power supply that can put out 40 amps and set it for 16v.

It started up just fine and ran fine. I dropped the voltage as low as I could but not low enough to hit the cut off I set.

Voltage did not dip too much when it started up (that I could tell). I did not have an amp meter on it, but I know it pulls at least 11 amps.

After about maybe one minute my thermal camera showed the mosfet was 172° f\78° c and I shut it down since I don't have a heat sink on it.

[flinx]

Re: Need help with Low voltage protection circuit

SO...

I got sidetracked by a project that I have been waiting a month for (stupid Post office).

I finally hooked up the dustbuster to it, reset the shutoff voltage for 13 volts, and... My control head for my power supply couldn't handle the load. My power supply has a maximum current limit of 15 amps.

When I hook everything up to the dustbuster and turn it on my PS resets. I did some poking around and checked the resistance of the motor. it's .59 ohms. Which means that at 16 volts it pulls about 27 amps cold start. Then it settles in at a comfy 11 or 12amps.

So I have to hook it up directly to one of my switching power supplies that can handle that amperage.

[flinx]

Re: Need help with Low voltage protection circuit

So how does it perform using noisy load such as Vacuum motor?

I have not tested that yet.

[budm]

Re: Need help with Low voltage protection circuit

So how does it perform using noisy load such as Vacuum motor?

[flinx]

Re: Need help with Low voltage protection circuit

I setup a test where I powered a purely resistive load of 4ohms which pulled about 7.5amps.

Using my thermal imaging camera I measured the temp of the mosfet at about 120°f 49°c. for about 5 minutes. Well withing the 175°c 347°f operating temp. I have the capability to test it to 10.5a resistive maybe 21a for a few minutes.

the whole thing was in free air with fans blowing about.

I did run in to an issue and it may require some tweaking of the hysteresis settings and resistors. If you turn off power to the circuit and the voltage that is powering it is below the upper level cutoff voltage the device won't power the mosfet.

My test setup is a bit janky and I need to devise something better that won't follow over, burn down, and sink in to the swamp.

[eccerr0r]

Re: Need help with Low voltage protection circuit

Honestly though they beat us into our heads not to omit bypass caps but the PSRR of a lot of well designed analog circuits it's not critical to include them,..

[budm]

Re: Need help with Low voltage protection circuit

Just got my boards back from JLCPCB
IT works perfectly. though see if you can spot the error (on my part).




Yes I forgot to join a copper area to a network.

So it works pretty well and no oscillation due to no filter cap for IC VCC and Ground?
Good Idea that you made separate board for MOSFET so you can scale up or scale down as you like.

[eccerr0r]

Re: Need help with Low voltage protection circuit

dammit hope I don't get spoiled by kicad having built in schematic-layout compare...hopefully reduces the chances of a mismatch when the pcb comes back.

and I really should get my grid tie inverter project finished, been lazy because of frustrations of not getting it fully single sided so I can etch my own board...nevermind needing to write firmware and ordering mosfets for it, as well as add *sigh* jumpers. Other issue being the board is huge, like 6"x9", really need to put it on a diet.

even made my own homemade ferric chloride with old nails...

[flinx]

Re: Need help with Low voltage protection circuit

Just got my boards back from JLCPCB
IT works perfectly. though see if you can spot the error (on my part).




Yes I forgot to join a copper area to a network.

[eccerr0r]

Re: Need help with Low voltage protection circuit

btw the 393 version I think I chose R2 poorly. It needs to be a lot lower, else the gain will be really bad. Probably 20K is good for it too.

[flinx]

Re: Need help with Low voltage protection circuit

ok full travel the hysteresis pot changes the voltage .45v. nice.

[flinx]

Re: Need help with Low voltage protection circuit

I got my 36v power supply yesterday, got it all hooked up to the control head and was able to make some more detail measurements.

It takes a bit of fiddling to dial in but I have it currently set to turn off at 18.02 volts and back on again at 20.68v. A spread of 2.66v.

The hysteresis does have an effect but it will take a bit more fiddling to figure out exactly how. When it is adjusted the cut off has to be re-adjusted. this is not a big deal and after I can test it under load I can decide what is the best voltage spread.

I may just determine that voltage and hard set it on the board with some resistors instead of a pot.

I will have to try the 393 circuit when I get my bench cleaned up.

[eccerr0r]

Re: Need help with Low voltage protection circuit

did someone have too many lm393's?

Redesigned from scratch but once again NOT simulated/tested and YMMV if this actually works. This should work down to a bit above 5 volts limited by MOSFET selection and then the reference. Power draw is about a quarter of the the previous design, though I think I'm really pushing it without detailed calculations, and may be running up the limits of the amplifier.

IMHO LM358 is better suited for the task, but if all you have is a LM393, all you have is a LM393.

[budm]

Re: Need help with Low voltage protection circuit

No need to have B- and OUT - so far apart, move them to be closer as possible so less resistance and so you can have room for more copper plane for more heatsinking area since you are not using through hole MOSFET which you can use bolted down heatsink.
BTW, you should also add bypass cap.

[eccerr0r]

Re: Need help with Low voltage protection circuit

Looks like a lot of whitespace...

You should use a cheap 1-turn pot for the hysteresis control, the resistor in series already compensates for most of the invalid region...

[flinx]

Re: Need help with Low voltage protection circuit

just for S&G's I decided I would make an SMD version.

After accounting for thermal vias and the ability to add a heat sink the resulting circuit board is no smaller than the first one I made.