Noob power circuit design question(s)
Hey all, I've wired up a ESP32 with a relay to control a pump and heater combo; the SS Brewtech FTSS pump and heater to be exact. I have the relay successfully switching in response to elements in the BrewControl interface, so the software side and 'non-power' circuit aspects I have working fine. For the power supply, I have 12v 10a DC. The factory provided power block for the FTSS is 12v 8a (or 12v 3a for just the pump without a heater). The pump has a sticker on it clearly indicating 12v.
It was my, likely naïve, initial understanding that matching voltage to a device was the important part and as long as one didn't exceed the max load for the power supply (and wire size) in current draw, all should be OK. Well, one pump I've fried already 😛 It became quite hot when feeding it directly from the power supply and seized within several minutes of running. I experimented with adding an 8ohm/50w resistor to limit the current down around 1.5a, and this seems to work but I'm realizing YMMV when learning electrical engineering from youtube 😉 What I don't understand is; 1. Why does the pump still function under far less than it's rated 12v? I measure the voltage across the resistor at 5v. 2. What would explain the first pump frying when being fed its rated voltage? It seems obvious there was too much current, but I don't understand the mechanics of why the device would draw more than it 'needed'. After all, I have the ESP32 feeding off the same power supply with only a voltage regulator 12v->5v but no current limiting resistor and it's fine.
As a follow on question, when I wire the heater, is it possible it will become hotter than designed given a 12v 10a power supply vs the factory 12v 8a supply?
Thanks in advance!
Motors can run with less power than rated... their output torque (and therefore pumping power) will be reduced accordingly. In fact, this can be a great way to control flow speed: if you use a PWM output from BruControl, you can purposely reduce pump power and flow.
Links, photos, schematics would help... BUT my first question would be: were you pumping liquid or running it dry? Many pumps need to have liquid running through them for cooling or to keep the motor "in check" so to speak (though this is more typical of AC motors).
Thanks for the response! Yep, I was pumping room temp water for testing. The pump had never been run dry. I've attached a pic of the panel. Sorry, it's a bit of a rat's nest but I don't have any education in electrical schematics so they would probably end up full of notation errors and ultimately more confusing.
On the attached panel image, there are two 12v 10a power supplies since I'll eventually be powering 2 pumps and 2 heaters. Each heater can draw at least 6a so I'm wiring one supply per heater/pump combo. The power supply on the right breaks out on the terminal block on the right to power one pump, one heater, and the ESP32 + 2 one wire probes and relay board. The pump simply plugs in the dc connector on the far left (the one slightly out of frame). Each power supply has a negative terminal bar on the left (the two vertical ones); the rightmost being the one feeding back to the negative terminal on the right power supply. This is all before I added the forementioned resistor of course.
Here's a link to the pump; FTSs | Pump - Ss Brewtech
One thing I found yesterday is that the power supplies measured closer to 12.1v out of the box. I've adjusted this down to 11.9v. Would 0.1v over tolerance be enough to cause problems?
No - that pump should not burn up at 12.1V, let alone 15V. Manufacturer defect for sure.
Your heaters are DC?
One thing I potentially see for the future... you need wires that can carry the 10A out of the power supply. That should be 18 or 16 AWG at smallest. Not sure yours, but they look possibly undersized.
Yes DC. The heater is just a big flat resistor I suppose, that wraps the cone of a conical. Here's a picture; FTSs² Heating Upgrade Kit | Chronical Fermenters & Unitanks - Ss Brewtech
This panel build is for the cold side of my home brewery. I figured it would be good training before I tackle my hot side. It's certainly conceivable that the pump failing was a coincidence. I'm glad I sanity checked this stuff or else I would have over-designed and probably ended up with more issues.
The wires on the dc side are indeed 18 awg.
Update; I tried the new pump with the resistor out of the circuit and it works fine. It appears the old pump really was just defective to begin with. Boy did that lead me down the wrong path in thinking. Wired the heater and it also seems to work fine. Left the system running overnight on one fermenter, full of water ;), and it's holding a target temp reliably.
Thanks for the help and clarifications!
OK good. Yes, you do not want that resistor in there... just wasting power.
If you connect the pump to a PWM output of a MOSFET (or UniShield driver), then you can reduce power via PWM.