I'm having a rather unfortunate problem on my hands.
For my hydroponics I've developed what I call my HydroMonitor, an ESP8266 based system. It's powered by 5V (normally USB), and has an on-board regulator with 100µF cap on the input to bring it down to 3.3V.
For my testing, I've always used USB power, and it works perfectly.
Now for deployment I tried to hook it up to the 12V power supply that also powers the water pumps (3-4W, 12VDC, brushless type). The power supply is rated 2A and I've indeed managed before to draw that much from it for a few weeks on end.
To get from 12V to 5V I wired up a 7805 regulator (on heat sink - necessary to keep the temperature down). Works fine, until I connect one of the two pumps to the same 12V power supply.
When measuring the voltage, I get 12V and 5V readings on the pins of the 7805 and my project where I expect it. But it doesn't work: it appears the ESP doesn't get powered at all.
Conclusion: it seems that somehow these pumps mess up the power supply to such an extent the voltages appear to be there, but the current not. So I'm really wondering what's going on here!
Does that mean a schematic with bits missed out? If so it is useless and we need to see a complete version. One that includes the capacitors that you have put across your 7805 chip.
Do you know how much current the motors draw?
Conclusion: it seems that somehow these pumps mess up the power supply to such an extent the voltages appear to be there, but the current not.
You need to look at the voltages on an oscilloscope to see if the regulator is oscillating.
As said there's 100 µF on the input of the HydroMonitor.
No other caps (none on the input).
No parts missing.
Pumps as said rated 3-4W so that makes 250-300 mA each.
So the question remains: is it normal for bushless pumps to mess up the power supply? I can't find detailed info on this on Google, and I don't have (access to) a scope.
The simple solution is of course to just use a separate power supply but it's; not all too practical.
You need caps on each side of the 7805 regulator, see the data sheet for the manafacature of the device you have used to find the minimum value. If these are not fitted all bets are off.
OK, will try it out. Manufacturer recommends at least 0.33µ on the input, 0.1µ on the output. 10µ should do in that case. It also states "no output capacitor is need for stability" and the input cap "Required if regulator is locate an appreciable distance from power supply filter". In my case there's some 20 cm of wiring in between the two.
Still hoping to get answer to my question: is it normal for bushless pumps to mess up the power supply?
According to the data sheet the capacitors are optional and appear to be only for filtering. But without the caps my regulator didn't work at all the moment the pumps were connected - so obviously these brushless DC pumps mess up the power supply - switching peaks or so? Still hope to egt some idea on what could possibly be the reason for this.
So I connected a 10 µF cap on the input side to smooth it out. The output has capacitors already on the device side - both have 100µF and 100 nF caps. It helped a lot: my devices switched on but one of them had crashed the next morning (i.e. was not responding to http requests). So not stable. The 7805 was pretty hot but not too hot to handle so the heat sink must have been around 50°C, shouldn't be an issue. The 7805 is screwed on tightly with a bit of heat conducting paste in between.
Next: a quick experiment with the caps as suggested in the data sheet (100 nF + 220 nF on the input; 100 nF on the output side - film caps as that's what I have on hand), and also that got the devices to start up. I didn't do stability tests, but went on:
The current configuration: a 12V -> 5V buck converter module. Running for the third day now, so far so good, both devices are stable. So that's a win.
Now if only I could get an idea of what those brushless motors are doing with my power supply I'd be really happy, but it seems I have to wait until I can buy a scope.
Hi,
What is your 12V 2A supply?
What are your brushless motors? spec etc..
A brushless motor will have an electronic control system on board and may be putting high frequency noise on your 12V supply line.
Yes, connected directly using a 12V splitter cable. Two pumps.
Not much in the way of specs available... 6-12V, 4-5W it says on the label. This are cheap made-in-China submersible aquarium pumps. From my searches on how these pumps work I know there is some form of control board; I saw mentions of analog circuits that could be used to operate these pumps; I guess this is the cheapest way so that's most likely what these pumps use.
Power supply is almost certainly of the switching type, again no data sheet or so available. Input 100-240V, output 12V DC. I can't even open it to check the internals, it's totally sealed shut.
Really hope to be able to get the money together to buy a scope... would be very helpful in so many ways, including this situation, but until then I just hope to get a good idea on what to expect from such pumps with regards to my power supply. I hope to not have to go for separate power supplies.
The first attempt was using a 10 µF electrolytic. I still have not much of an idea really what I should be filtering exactly - what frequency/voltage/etc - it did stabilise the voltage enough to make the regulator work, but not perfectly stable.
I was looking also at this image from Wikipedia, which shows decoupling/bypassing as something any type can be used for:
The attempt with film caps (the 100 nF output is ceramic - got those as this value is needed all the time) didn't last long, just to see if it works, and it did. No longer time stability test with that. Maybe I should look into getting some more ceramic caps then. I got a box with like 30 values of film caps, something like that for ceramics would be nice
I was looking also at this image from Wikipedia, which shows decoupling/bypassing as something any type can be used for:
Then if that is what it shows quite simply it is wrong and needs correcting.
Have you read this:- http://www.thebox.myzen.co.uk/Tutorial/De-coupling.html it tells you about self resonance, the point where a capacitor stops looking like a capacitor and starts looking like an inductor and so stops filtering out the interference.
I still have not much of an idea really what I should be filtering exactly - what frequency/voltage/etc
You are doing two things:-
You are lowering the source impedance of the voltage input to the regulator. The motors will have the effect of raising this source impedance.
You are trying to remove very short spikes of under and over voltage caused by the motor. Because they are short then they are a very high frequency.
So that also means I better start replacing some other 100 nF film caps... used those as I didn't have the ceramics yet.
Grumpy_Mike:
You are doing two things:-
You are lowering the source impedance of the voltage input to the regulator. The motors will have the effect of raising this source impedance.
You are trying to remove very short spikes of under and over voltage caused by the motor. Because they are short then they are a very high frequency.
That's the why. I mean, I wonder what exactly those pumps do to the power supply, but I'm afraid that will have to wait until I can get my hands on a scope.
Same accounts for the brushed motors of my peristaltic pumps, so far no issues there but I am getting worried. They should spark and spike. Would it be a good idea to solder a ceramic cap across their connections? Or 10 cm away on the perfboard - basically in parallel to the flyback diode?
I wonder what exactly those pumps do to the power supply,
They are inductive and make the input impedance more inductive. This alters the phase angle between voltage and current and raises the overall impedance. Think of an inductor as a negitave capacitor, it electrically removes some / all of the capacitance you put across the input. This applies to DC because the interference spikes are an AC component of the applied voltage.
Would it be a good idea to solder a ceramic cap across their connections?
Yes. The closer to the terminals the better, even inside the motor like this:-
That was some really interesting reading.
This looks like the ultimate decoupling:
So that'd add inductors to my shopping list... Also makes me consider amending my project to isolate the motors even more from the sensors and so. Going to be a fairly beefy inductor, 20-50 mH based on that article and I'll have to rate it at 5A or even more (and scale the 12V supply accordingly of course). Plenty of space, that's the good thing.
A solenoid I suppose does not need this kind of isolation, lights definitely not (not going to dim LEDs so no PWM), fans probably do as they're usually brushless motors again.
Definitely going to solder some caps on those motors - they may be unnecessary with all the other decoupling but also won't get in the way either. Better be safe than sorry.
(edit) that step-down is a ready made module; it comes with its own caps. I think it's safer to just use a complete module rather than trying to put that on my own board and having to worry about exact component placement and whatnot for those things.
A solenoid I suppose does not need this kind of isolation
Well this is where electronics is more of an art than a science, their is no real way to determine in advance how much decoupling is needed in any one situation. Most engineers err on the risk averse side and would rather put too much decoupling in than too little. A lot depends on the sort of electromagnetic environment it finds itself in.
There are minimum levels of noise immunity a product must reach to receive formal approval for one standard or another, they are all slightly different. But environments exist that have much more interference than these values.
Of course, better be safe than sorry. Decoupling shouldn't ever negatively affect a circuit so can always add more.
Now looking at good values for that inductor - never used those things before so their values have little to no meaning to me. The link in #13 mentions "tens of milli-H" which appears to be a huge value, very big expensive parts for larger currents. Reading a bit more and I see decoupling inductors with tens of micro-H values. Makes me wonder... probably that's an error in that blog, and I need to look at the micro-H range rather than the 1000 times bigger milli-H range.
Basically it is the bigger the better. Things to consider is also the current the inductor will take, the size and the cost.
Some inductance is better than no inductance, so in much the same way as capacitance it is a suck it and see case.
