Help with Water Pump

[KeepItSimpleStupid]

Label the pumps.

It doesn't matter the order. Everything is in series. Just get (+) and (-) right to the pump. You want two voltages:
1) Across the pump leads.
2) Across the resistor.

For each pump.

U1d

I think Alec is thinking about re-doing the unit to look like post #1110.
Schematic (PDM-Mk12): **broken link removed**

Note that U1d is unused, but it does have it's inputs connected to ground. (can be ground or +12). +12 probably would result is a slightly lower power dissipation.

 

[alec_t]

Glad you enjoyed the break, Joe.

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?

Yes, providing you add the Q3 stage as per the PDM_Mk12 version. Hope you're ok with that. Ronv and I have been trying to get the circuit working better (in theory!) in your absence .

 

[salty joe]

KISS, I don't have any 0.22 resistors. I'll get some ordered.

I have been working with four pumps in a bucket of water. Tonight, 3 of them toggled like they are supposed to. Last night, only one or two of them toggled for more than the initial toggle. The fourth pump ran for the initial toggle, then stalled, then ran for a toggle or two, stalled and so on.

With ground lead of DMM on pin 1 of Q1 and fourth pump running, V at gate - 11.4, V at drain - 0.26, V at source - 0.26. With fourth pump stalled (led on) V at gate - 10.77, V at drain - 0.18, V at source - 0.03.

I took the same measurments from a toggling pump running. V at gate - 11.4, V at drain - 0.26, V at source - 0.26. Same pump at rest (led off), V at gate - 0, V at drain - the numeral one in the far left of the display, V at source - 0.
Thanks.
I don't think I'll have any trouble finding room for the latest mod. If I don't work late tomorrow, I'll fire up the soldering iron.
Thanks.

 

[KeepItSimpleStupid]

0.22 ohm Test

Rsense is 0.22. Just borrow one. You don't even have to remove it from your circuit.

Disconnect (+) of the circuits from the power supply and the pump from your circuits. Leave ground where it is.

Take the top (non ground side) of the resistor and attach to the (-) lead of the pump. Attach (+) to the other end of the pump.

Use the same board/setup to test all of the pumps.

Hopefully, you made Rsense and Ground test points.

 

[KeepItSimpleStupid]

As suspected, it looks like the FET isn't fully on for the stalled pump. So, is the pump that different? That's what the 0.22 ohm test will tell.

 

[ronv]

The drain is only at .26 volts so the FET is on pretty good. The .26 volts across the source resistor would indicate only about an amp. So it would seem there is something wrong between the drain and the pump as the pump should have almost the whole 20 volts across it. Maybe something with the fuse? Do the same test checking the voltage on both sides of the fuse and at the pump. (running and stalled)

 

[alec_t]

@Joe
What was the trimmer setting for those tests in post #1123 ?

fourth pump running, V at gate - 11.4, V at drain - 0.26, V at source - 0.26.

As expected. That means the FET is fully on and the pump current is ~1.2A, which is what Joe measured way back when before we introduced current-limiting.

fourth pump stalled (led on) V at gate - 10.77, V at drain - 0.18, V at source - 0.03.

Not yet explained. FET is not fully on. Current is ~140mA (of which only ~8mA is through the LED). Could the Hall IC in the pump have some inbuilt limiting/protecting feature of which we're unaware?

Same pump at rest (led off), V at gate - 0, V at drain - the numeral one in the far left of the display, V at source - 0.

Nearly as expected. The numeral 1 denotes 'out of range', but I would have expected some arbitrary reading with the pump off, LED off and FET off.

So, is the pump that different?

Or is it the FET that's different? KISS's proposed tests may tell us.

Edit: I'd first check for pump differences by trying them all in turn with one PDM which we know can toggle a pump repeatedly.

 

[ronv]

With fourth pump stalled (led on) V at gate - 10.77, V at drain - 0.18, V at source - 0.03.

This is the troubling one. If the drain is .18 v and the pump is stalled the current limit should have been on for a source voltage of .6 or so. The question I had was why isn't the voltage at the pump .18 volts, I think from a prior post it was 17 volts. Maybe not the same motor. Maybe the fuse "blew" (high resistance) on this one?

 

[KeepItSimpleStupid]

@Ronv. Congats! You get the lecture. .6, etc. should be written with a leading 0. ie .6 as 0.6 The 0 is significant. That was drilled into my head early.

 

[4pyros]

@Ronv. Congats! You get the lecture. .6, etc. should be written with a leading 0. ie .6 as 0.6 The 0 is significant. That was drilled into my head early.

I have not done that since school.

 

[KeepItSimpleStupid]

OK, now a larger dose: https://mathforum.org/library/drmath/view/52352.html

https://www.electro-tech-online.com/custompdfs/2012/10/numbersandstatistics.pdf post has one instance where you can omit the leading zero.

 

[ronv]

Can I get dispensation if I read better than I type?

0.6, 9.6

 

[salty joe]

@Joe
What was the trimmer setting for those tests in post #1123 ?
.

I don't know. I had it at min. but when the fourth pump would not toggle turned the trimmer to max. Sorry, I don't know. How about if I set trimmer to 25 and leave it there for all further testing?

I just got home and am a little wiped out-I will run the pump test that you suggest, KISS (I have an extra Rsense) and the test from pin 1 of Q1 that you suggest RonV tomorrow.
Thanks much.

 

[ronv]

If you can just take the drain, source and gate test on the pump that doesn't run that should do it for me. Just need to make sure the LED is on when you take the measurements. If in fact the voltage at the drain is 0.3 volts or so also measure the voltage on both sides of the pump.

 

[alec_t]

How about if I set trimmer to 25 and leave it there for all further testing?

Ok. We can fine tune it when the other issues are resolved.

 

[salty joe]

The trimmer is set at 25.3K. With the pump stalled (led on) and the ground lead from my DMM on pin 1 of Q1, V at gate is 10.75, V at drain is 0.18, and V at source is 0.03. V across stalled pump is 18.68. Sometimes the pump ran and sometimes it stalled.

I screwed Rsense to the + of power supply, screwed the - jack to the - of power supply, then used a wire nut to fasten + side of jack to other side of Rsense.

I took the V readings at the power supply and also at the pump leads. Pump A registered 16.43-16.62 at the power supply and 16.14-16.37 at the pump leads. The V seemed to be increasing with every pump, so I re-tested pump A and this time got 16.92-17.13 at the power supply and 16.78-17.01 at the pump leads. I don't know if I did this wrong, but the inconsistancy bothers me.

Should I go ahead with the MK12 modification?
Thanks.

 

[ronv]

The trimmer is set at 25.3K. With the pump stalled (led on) and the ground lead from my DMM on pin 1 of Q1, V at gate is 10.75, V at drain is 0.18, and V at source is 0.03. V across stalled pump is 18.68. Sometimes the pump ran and sometimes it stalled.

Let me make sure I understand the pump reading.. Is the meter ground still on on the emitter of Q1 and you measued 18.68 volts on both sides of the pump? Or was the meter across the pump?

 

[salty joe]

Across the pump.

 

[ronv]

Wow. If the pump really has 18.68 volts across it it should be running and drawing more current (higher voltage at the source) What this sounds like is that the leads to the pump are open. Maybe a bad connection around the plug?

If we can understand this one I think it will be time for the mods, but it is actually easier to look at some of these without the current limit and alarm working.

On the other measurement it would be best to just measure the voltage across the resistor. It will be pretty small -- like 0.25 volts.

 

[KeepItSimpleStupid]

Joe:

I think you did it wrong. You should end up with a table like this:

Pump	V(pump)	V(Rsense)/0.22	V(Rsense)
A	16.1	1.13 A	250 mV
B	16.7	1.18 A	260 mV
C	18.5	1.36 A	300 mV
D
E
F

Except you only measure Vpump and Vsense. The other column is a calculated column. I=V/R.
The 250 mV becomes 0.250 for the calculations e.g. 16.1/0.250 or 1.36 Amps. Although we are expecting bigger numbers.

If you "reply with quote", you can see where to replace the numbers.