Good idea.I used a SPDT to switch over if I get flick mode
Maybe the pump current is causing a voltage drop in the ground line which is affecting the tidal timer module. I'll play with a sim to see if I can replicate the effect. Enjoy the camping trip, Joe.Oddly, when the pump that toggled and ran the way it's supposed to, the run time (toggle time) decreased from about 14 sec. to about 11 sec.
I must confess I haven't got round to analyzing why/how the pump voltages vary. I'm sure we can take the motor resistance as 2.14Ω, since KISS has actually measured this on a gutted pump. The .22Ω is less certain, as the solder and wiring resistances at the Rsense terminations, in series with the actual sense resistor, could be a significant fraction of that and would result in the trip happening at lower current than designed.2- LED on motor off led me to the low voltage across the pump. Confirmed at 3.1 volts.
This makes me think the motor resistance is lower than we think or there is some other load or the .22 isn't right.
A distinct possibility. Sounds like you've investigated that further than I did. Any suggestions? Someone mentioned many posts ago that we might need to raise the current threshold level if pumps were reluctant to start.3- I think there is a hole in the logic where depending on the FET threshold voltage the motor can be in current limit without tripping the first logic gate
I think you've hit the nail on the head there, Ron. I've now looked into this a bit more. Re-visiting the datasheet for the IRF3205 which Joe is using, the graphs show that for a 'typical' 3205 with Vgs = 4.5 the Vds is ~ 0.2V for a drain current of 3A. In other words the FET isn't fully turned on at Vgs = 4.5V. Even so, it would cause Q1 to pull the U1 input down just below the Schmitt threshold (using your example of the thresholds being 6V +- 1.5V) and trip the latch. So operation is marginal.I think there is a hole in the logic where depending on the FET threshold voltage the motor can be in current limit without tripping the first logic gate
A possibility; but a shorter time would raise the average power dissipation in the FET, which is already pretty high when the trip kicks in.Could just make the time out a little shorter than the fastest cycle time?
For some reason the trip level on U1A was around 3 volts instead of more like 6.2 volts. That's probably the difference in our sims. I used inverters and set the hysterisis based on this data sheet
On my sim the Schmitt levels for the 4093 are 5V and 7V on a 12V supply. As you say, there are differences between our two sims.I think the 4093 model keeps the 5 volt thresholds even when running at 12 volts
1N4148, as far as I know.Don't know what Salty has for diodes.
Ran your sim. That R/D addition certainly brings the cap voltage down quicker, but I didn't find it necessary in my sim. If the trip circuit misses the occasional reset it hardly matters in practice, as it only delays by ~30 sec the next attempts at re-starting a stuck-rotor pump.Take a look and see what you think.
I don't see how it can. The Hall chip in the pump will only allow one coil at a time to be energised.if per chance the pump "wakes up" with both coils on
I've already simulated that, thinking to delay the current limiting slightly. The problem then is that the FET oscillates at a few kHz, the current limit varying +- 0.2A about the mean 2.9A, and there would be a lot of RFI.we may need to add one of Joe's 47Ufd caps from base to ground of the current sense transistor to give it a "kick" to get it started.
On my sim the Schmitt levels for the 4093 are 5V and 7V on a 12V supply. As you say, there are differences between our two sims.
Hmm. interesting. Where did you get your CD4000 collection? I think mine came from Eric, but yours are closer to correct. As close as I could guess from the data sheet they would be 4.8 and 7.2.
Thats cool.1N4148, as far as I know.
I wasn't thinking about the reset as much as the 1 second delay gets shorter when the pump starts the second time.Ran your sim. That R/D addition certainly brings the cap voltage down quicker, but I didn't find it necessary in my sim. If the trip circuit misses the occasional reset it hardly matters in practice, as it only delays by ~30 sec the next attempts at re-starting a stuck-rotor pump.
I don't either. It just seems like it fits with the 3 volts he is seeing across the motor. Guess some more measurements are in order.I don't see how it can. The Hall chip in the pump will only allow one coil at a time to be energised.
I've already simulated that, thinking to delay the current limiting slightly. The problem then is that the FET oscillates at a few kHz, the current limit varying +- 0.2A about the mean 2.9A, and there would be a lot of RFI.
I didn't see the oscillation. What FET are you using?
PS Would you mind sharing your CD4000 files?
PSS what do you think about the 2 diode fix?
Direct from the LTSpice user group on Yahoo (as did Eric, I think; so you should already have the CD4000 collection that I do). Your 4093 model seems the same as mine, but I see you were using the generic LT inverter model rather than the CD40106 model.Where did you get your CD4000 collection?
It does. Which is why C3 is best biased just below the lower Schmitt threshold by R5/R6. The first time is arguably the most important.I wasn't thinking about the reset as much as the 1 second delay gets shorter when the pump starts the second time
I realise now that I was running the sim with a 'stuck-rotor' pump model. I've since made a (albeit crude) free-running pump model and found that C3 voltage then does indeed fail to drop low enough between successive pump turn-on attempts (if their period is less than the trip reset period, without your R/D addition. That seems to be the cause of 'it only toggles once'. Good call.That R/D addition certainly brings the cap voltage down quicker, but I didn't find it necessary in my sim.
It's possible. I'm guessing the 3V (and the other odd voltages Joe found) is more likely due to the FET not switching on fully, so not providing enough current either to operate the trip or get the pump up to full speed. At half speed, for example, the back-emf could still be low enough to allow a current of, say, 1.5A. The twilight zone.It just seems like it fits with the 3 volts he is seeing across the motor
IRFH5207 (don't have a model of Joe's IRF3205). BTW the oscillation frequency with 47u on Q1 base is ~300Hz, not a few kHz as I mis-remembered.I didn't see the oscillation. What FET are you using?
Assuming the lower Schmitt threshold is 5V then by my reckoning any FET which needs Vgs > 5V to give Ids > 2.9A (the current-limiting threshold) won't work reliably in the Mk10 circuit. The 2-diode fix (i.e. another diode in series with D5) would, I think, enable the use of FETs needing Vgs up to 5.6V which might well solve the problem. Adding Q3, on the other hand, would allow for FETs needing Vgs up to 10V or so. It's Joe's call.what do you think about the 2 diode fix?
I just set Vdd to 12V and the model automatically gives 5V and 12V thresholds. I've never tried tinkering with the threshold parameters (Vt, Vh) directly. For this project I just monitored the Q1 collector voltage to assess whether a hypothetical 4.5V or 7.5V threshold would have been reached. Eric's a whizz with sims. A PM to him perhaps if you want to check?Do I need to change anything but Vdd to get the thresholds right?
Thanks Alec. It's amazing that a 3 hr. drive can put you in place where you can see the milky way. No cell phone reception, kids playing in the stream, hiking Cook's Forest, it was nice.Enjoy the camping trip, Joe.
U1d is now redundant (but it's inputs need to be connected to +12 or ground, whichever is convenient).
Very cool-thanks!See what happens when you go away? Lots of activity.
On the left side of U1d, I connected pins 8 and 9 together and ran it between R4 and D5. Are you saying take it away from R4/D5 and send it to 12V?U1d: Only the input (the pin on the left side of the schematic) needs to be tied to ground or Vdd. Your choice, but since it's an inverter, I would tie it to +12 because there would less power dissipation on the output. Very slight to the point it doesn't matter, but since this is going to be running 24/7/365, I'd go with +12.
OK, put a .22 resistor on the +side of the power supply. Hook the pump to the resistor and the – side of the power supply. Measure V by putting black DMM lead on ground and red DMM lead between .22 resistor and pump. Is that right?Joe:
You probably can't measure resistance accurately. I'd guess +-1 ohm. Remember what i suggested?
Take the power supply in series with the 0.22 resistor. Mark it, so you know which one you used.
Turn each pump on.
Measure the voltage across the motor and the 0.22 resistor.
Now you can computer R, to the accuracy of the 0.22 resistor. R=V/I On a relative standpoint, you will be riight on,
“With the ground lead close to the emitter of Q1.
The drain, source and gate of the FET and at the pump.
If you can do it with the pump that runs once then stalls it would give us a good idea.”
I’m guessing the emitter is pin one, which in Q1 goes to ground. So you’re saying hook up a pump that only toggles once, touch DMM ground lead to pin 1 of Q1, then check the V at all three FET pins. Is that right?
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