Help with Water Pump

[KeepItSimpleStupid]

No we don't or at least I don't, but do I agree with it 100% - nope.

The current limiting resistor is different (600) from the datasheet and Pump (520). Earlier, I iterated a calculated a wattage 24*24/600 and 22*22/520. Not sure if it's significant or not and I played some other games too. If the resistor is

I wasn't told the wattage or value of the internal zener. I really want I=(Vdd-Vz)/R and Pmax of the Zener. 520 is 13% less than 600 that's all.

Speculating.

 

[alec_t]

The PDM with C4 removed and 4.7K resistor on Q1 toggled every pump 10+ times.

Good news. The interests of science have been served.

At least we know the pumps toggle with the resistor on Q1. This sounds like it is safer for the pumps.

I've come round to that view, when reconsidering the unknowns about the pump's internal electronics. We've been pushing our luck so far. Going with a steady 4.4A limit, rather than a peaky ~8A, simplifies the design of any supply-voltage reducer that will probably be needed.

If the pump is slightly more apt to stall, that's where the alarm comes in and shuts it down-is that right?

That's right.

No we don't or at least I don't, but do I agree with it 100% - nope.

So should we go for 18V or not?

 

[ronv]

Alec,
Have a look at the data sheet for the part. It has a picture that matches KISS's analysis, except for the resistor sizes, with a suppy voltage of 24 volts. It also has a shut down and retry if it doesn't see rotations in 1 second.
So if it is the same chip that the pump has they aren't as dumb as we think.

 

[alec_t]

So if it is the same chip that the pump has they aren't as dumb as we think.

It would be nice to think that is the chip. But there's a big if. And that brings us back to why did the pump fail if the chip is intended to be used as shown in the datasheet with a 24V supply?

 

[KeepItSimpleStupid]

My take:

We go with the least voltage we can just to reduce power dissipation because there is effectively no thermal sink and that's like a t^4 order (t=temp difference) if I remember right.

Possibly all we need right now is a simple 2N3055 kind of regulator. There are plenty of diodes from 17.3 to 19.8 V so that would give voltages from 17.9 to 20.4. That's a really simple design, I think

So I'm just thinking 18V and 19V; possibly 16 and 17. That's just 4 diodes to get.

OR...

A temporary possiblity is to use a silicon diode. A 25A bridge is easy to come by and that can give us a 1.2 V drop. This, https://www.radioshack.com/product/index.jsp?productId=12678415 Too bad it's WEB only would give us 1 to 2 diode drops depending on the TAP. Two bridges would allow n*0.6 less voltage where n = 1 to 4. At least Joe would be able to try a lower voltage. It could even be permanent, but it would be slightly temperature dependent.

 

[KeepItSimpleStupid]

Well, there is the possibility that the FET was not soldered properly because of the solder blob and it just got too hot. Joe might have been over 24V if my brain is remembering right. He has two supplies and they don't have the same adjustment range.

Two things are that are CERTAIN:
1) Thermally, the pump can't dump heat.
2) The OEM controller needs either a TVS or the HV version of the switching regulator to avoid OEM controller regulator failures.

 

[alec_t]

If it were my power supply I would have had the covers off by now, warranty or not, and added/changed a resistor somewhere around the voltage adjustment pot to bring the volts down . I guess that's not an option for Joe.

Thermally, the pump can't dump heat.

Shame they didn't design it to be water-cooled!

 

[alec_t]

Now the alarm sounds for every toggle even if there is not a pump hooked up and the trimmer is set to max

Check D3 polarity. Also, measure its resistance in circuit, with the meter probes both ways round. If D3 has gone leaky as a result of all the soldering activity around it that could account for the alarm triggering permanently. Look for any solder whisker or other connection between 12V and C3.

 

[()blivion]

No we don't or at least I don't, but do I agree with it 100% - nope.

(0_o) Eh? Yes, no, no, yes... NO WAIT !!!... Yes... (LOL, ignore me.)

Shame they didn't design it to be water-cooled!

Yeah. I had said something about "a good manufacturer would have done it water cooled" WAY back a few hundred posts ago. Some time back in like. . . April?

One thing worth mentioning though is that you really can't let reef aquariums get too hot. Particularly cold water fish as I recall. But honestly that's a bad excuse for not heat sinking the FETS to the water anyway. The pumps make the heat they make, you can't hide it by covering it all in epoxy and hope it won't get out. Doesn't work that way. At least doesn't work out well that way, Q.E.D. burnt pump. /)

 

[salty joe]

If it were my power supply I would have had the covers off by now, warranty or not, and added/changed a resistor somewhere around the voltage adjustment pot to bring the volts down . I guess that's not an option for Joe.

I don't have a problem altering the power supply-other than not having a clue what to change. Yes, I do have two power supplies. One has a min of 20V and the other has a min of 24V.

I'll check out D3 & 12V-thanks.

 

[KeepItSimpleStupid]

Now what? Reverse engineer a power supply?

Joe, you could snap a pic of the solder and component side of the board for starters.

And note any numbering on high pin count IC's and on 4 or 6 pin IC's. That would be a good start.

PS:
Too bad a pump that sits in water isn't water cooled.

 

[salty joe]

Yes, I do have two power supplies. One has a min of 20V and the other has a min of 24V.

I'll check out D3 & 12V-thanks.

I was mistaken-the power supplies are 19.1V-24.1V and 20V-30V. So maybe no need to open them up?

BTW, the alarm problem was apparently due to my not wrapping up the IC. Pins 4, 8 and 9 were not connected together and pins 12 & 13 were not grounded. Odd that improperly connecting the prolong hooks masked the problem. Anyway, I'm going to remove C4 from the other PDM and add the 4.7K to Q1. Final version?

 

[alec_t]

the power supplies are 19.1V-24.1V and 20V-30V. So maybe no need to open them up?

I thought 20.6V was the lowest it (not sure which one) would go? No need to open up the supplies. I was only thinking 'wouldn't it be nice if....'
I'm still dithering as to whether it would be advisable to go for 18V. On balance I think (though there's no guarantee) you will get away with 20.6V, based on:-
1) You've given the pumps a soak test at 20.6V and they've survived; whereas the pump that died was being run at 24V.
2) The Melexis application notes show a 24V system with a circuit virtually identical (apart from the uncertainty of the actual Hall IC) to the one KISS found in the pump.
3) Melexis seem to have cornered the market on 3-pin ICs for 2-phase motor control. Your pump IC is 3-pin so the odds are it's a Melexis one and hence suitable for a 24V system (albeit that 24V gets dropped and held to max 18V within the IC).
4) At 20.6V the pump power dissipation will be a good bit less than at 24V.
5) If you build the Synchronous Pulse Delay (SPD) speed module and it works as it says on the tin (i.e. as it did for the two fan motors I tried) then the speed setting can be adjusted to give a pump power dissipation similar to using an 18V supply for the long term and without wasting power in an external volt-reducer circuit.

BTW, the alarm problem was apparently due to my not wrapping up the IC. Pins 4, 8 and 9 were not connected together and pins 12 & 13 were not grounded.

Glad you've resolved that.

Anyway, I'm going to remove C4 from the other PDM and add the 4.7K to Q1. Final version?

I'd like to think it's the final version While you're at it, R5 and R6 shown in the Mk14 mod are then redundant. If you remove R5 the D5 cathode (right-hand end) should connect to Q1 collector.

 

[salty joe]

I'd like to think it's the final version While you're at it, R5 and R6 shown in the Mk14 mod are then redundant. If you remove R5 the D5 cathode (right-hand end) should connect to Q1 collector.

Will it hurt anything to leave R5 and R6?

 

[alec_t]

No, they can stay (but presumably you won't install them in future PDMs).

 

[KeepItSimpleStupid]

@Alec

I'll put ronv's comment in a different light:

Simulate the Melexis datasheet:

Locked Rotor conditions are detected by the IC
when there is no motion for one second and will
shut off the motor drive for five seconds. Then,
the IC will turn on the drive current for one
second. This sequence continues indefinitely
until the locked rotor condition is fixed. This
feature prevents overheating.

e.g. Motor ON for 1 sec, Motor OFF for 5 sec. Can you simulate Locked rotor for that 1 second?

For one, see if the alarm works?

 

[alec_t]

I've been simulating both free and locked rotor conditions before posting any of the PDM versions. In the latest version the trip operates in as little as 290ms and resets after ~30s (or sooner if the toggle 'on' time is < 30s). So the PDM trip should result in less locked-rotor power dissipation than the Melexis IC would. That's our belt and braces, providing a back-up.

 

[salty joe]

No, they can stay (but presumably you won't install them in future PDMs).

Great, I did not want to go after the existing PDMs again unless I had to. I'll lose R5 & R6 on the following PDMs.

I've been simulating both free and locked rotor conditions before posting any of the PDM versions. In the latest version the trip operates in as little as 290ms and resets after ~30s (or sooner if the toggle 'on' time is < 30s). So the PDM trip should result in less locked-rotor power dissipation than the Melexis IC would. That's our belt and braces, providing a back-up.

That's amazing, it really is. It seems like the last question is how much voltage can the pumps be driven at. Put another way, how much water can I safely move?
It feels like we are very close-I’m hoping my current PDMs end up in service. You guys are tenacious and patient –thanks for hanging in there so long.

 

[alec_t]

It seems like the last question is how much voltage can the pumps be driven at. Put another way, how much water can I safely move?

What you have now (20.6V driving the pumps) looks like the maximum for safety. Hope that shifts enough water. If you use the speed control you should be able to pre-set a max speed lower than the present free-run speed, as well as setting a slow 'feed-speed'.

 

[ronv]

Just my 2 cents:

I think the pump voltage is ok as is because:
1- The lable on the pump states 24 volts.
2- The OEM controller had higher voltage than the current supply
3- The hall IC shows a 24 volt implentation.

I only have 2 thoughts on the original failure:

1- A stall with no current limit other than the motor winding resistance. (200 watts for 1 second is to much)
2- Manufacturing defect.

Joe, Are you up and running now? Or do you still have the alarm bug?