Help with Water Pump

[4pyros]

As I said a few weeks ago it is a strange motor arrangement.

 

[()blivion]

I taped the magnet to the bottom of cardboard. Hoping it's a good enough pic. Thanks all.

Ohhhh! nicely done Joe, Just one question. If you were to roll it along the bottom of the cardboard would it "flip the grains" twice... or four times per full rotation of the rotor? If two times, then it's a two pole magnet, if four... well then obviously it would be a four pole magnet. But you don't have to answer this. Based on just that picture I'd say it almost has to have only two poles. Which would jive well with the driver theory me and KISS have proposed so far.

In case anyone is interested... Click this to see my simulated version of KISS's schematic for these pump controllers.

You have to change which FET is turned on and which is off by manually moving the slider on the right side that says "resistance".


Edit:

As I said a few weeks ago it is a strange motor arrangement.

Indeed it is.

 

[alec_t]

Looking at the pic of the rotor I see two dark lines at the left end of the grey cylinder. They seem to be ~ 60° apart, so perhaps a 6-pole rotor?

 

[alec_t]

@ronv
The LF150 PTC limiter in your post 523 looks a promising candidate. Rotor lock (11A) would trip it in ~ 2 sec according to the spec. Not clear how long it would take to reset itself?

In case adjustment of the trip time is useful, here's a first draft of a proposed current-limited driver module for a single pump. I think it takes KISS's concerns into account, but I may have missed something. Criticism/suggestions welcome.
@Joe
Don't build this yet .

Circuit operation:
A 12V enabling signal from the timer circuit (not shown) charges slow-start cap C1 to turn on M1. If M1 current exceeds ~2.8A the voltage on sense resistor R3 turns on Q1 and C3 starts to ramp down as it charges via the trimpot. Q1 also pulls M1 gate down to restrict the M1 current. If the current falls below 2.8A Q1 switches off and the gate voltage rises again. If Q1 is on for ~1.5 sec C3 voltage drops to the lower Schmitt threshold voltage of inverter U1a, U1a output trips U1b, and U1b output pulls M1 gate low via D4, thus turning off M1 and hence Q1. M1 stays off until C3 voltage rises to the upper Schmitt threshold voltage of U1a (~ 7 secs). The C3 charge/discharge cycle repeats providing the 'Latch' switch is open. If that switch is closed then on the first occasion that U1a output goes high it latches Q1 on via R7 and M1 is held off until the latch is reset manually. U1a output provides an alarm-driving output to warn of a rotor-lock or other over-current fault.

 

[()blivion]

Humm.... I'm prolly missing something, But if Q1 turns on/shorts, dumping the gate charge, wouldn't the sense resistor have less than trip current right away? Then wouldn't it also turn Q1 back on right away, thus causing the system to oscillate?

(It's *WAY* past my bed time, been up all night here.)



Edit:
My (meager) simulations show that it doesn't actually oscillate like I though at first, but rather it simply holds at constant current (IE basic current limiting). C3 never discharges, The inverters never get tripped, the alarm never goes off, M1 never gets turned off. So those sections of the circuit appear useless currently. Also note I can't do inverters that are Schmitt triggered or that are 12V capable, as well as Schottky diodes at all with the falstad simulator. So I had to play things by ear a bit.

 

[alec_t]

it simply holds at constant current (IE basic current limiting)

That's what was intended . Q1 collector sits at ~3V while there is limiting.
If you can't sim Schmitt circuits then that probably explains why you don't get the results I found. Non-Schmitt gates don't work in this configuration; there needs to be hysteresis.

 

[alec_t]

Have just come across this explanation of 2-phase BLDC motor operation :-
http://bldcfan.100webspace.net/
The circuit looks very similar to what I think must be in 'our' pump, even if the coil layout is different and the rotor/stator are 'inside out'.

 

[salty joe]

I turned the rotor one full turn and the filings started out standing up, then they laid down, stood up, laid down and after one full turn stood up.

 

[alec_t]

So, it's a 2-pole rotor, as guessed in a post above.

Here's a sim based on the circuit I linked to in post #547. Weird as it is it seems to work (albeit the sim resistor values are probably way out).

 

[KeepItSimpleStupid]

Both body diodes are verified forward biased in the UP direction in both of our schematics.

so the polarities are backwards in our schematics and, I guess, the MOSFET appears to be N channel.

The PCB is definitely single sided. Some black Epoxy potting material is on about 1/3 of the back side.

 

[4pyros]

Have just come across this explanation of 2-phase BLDC motor operation :-
http://bldcfan.100webspace.net/
The circuit looks very similar to what I think must be in 'our' pump, even if the coil layout is different and the rotor/stator are 'inside out'.

Looks like the right driver. I cant see a two pole motor working efficiently.

 

[KeepItSimpleStupid]

I remember seeing this somewhere and I found it again: https://www.simplemotor.com/hemotor.htm

 

[ronv]

Current Limit

Alec, Might want to remove D5. Again, we can't be sure what the starting current needs to be. 3 amps may not be enough.

 

[ronv]

Both body diodes are verified forward biased in the UP direction in both of our schematics.

so the polarities are backwards in our schematics and, I guess, the MOSFET appears to be N channel.

The PCB is definitely single sided. Some black Epoxy potting material is on about 1/3 of the back side.

Any chance the gate resistors are like the example Alec gave or are they definately like your picture?

http://bldcfan.100webspace.net/

 

[salty joe]

Thanks. You guys are the best.

 

[KeepItSimpleStupid]

What if they are bipolar transistors? The "body diode" is the E-C junction with C being the tab.
Basically can't tell too much with bad parts.

@ronv
The OEM switching regulator is a 3 Amp model.

 

[ronv]

The OEM switching regulator is a 3 Amp model.

The datasheet I looked at gives 4.2 - 6.9 amps at 25C or 3.5 to 7.5 over the temperature range. Do you have a different one?

It also has a thermal shut down, but that would be slow.

 

[KeepItSimpleStupid]

I don't really see it in here: https://www.electro-tech-online.com/custompdfs/2012/06/lm2576-2.pdf It says guaranteed 3A output.
Remember that there are fixed versions of this regulator too.

I think the OEM 24 VAC transformer says 24 VAC at 1.5 A, 35 VA or something close.

 

[KeepItSimpleStupid]

Any chance the gate resistors are like the example Alec gave or are they definately like your picture?

They are connected as they are. What they are is unknown. Not even sure which way power connects. I'm guessing where the coils went too. There is a pic that salty joe took. You can almost deduce the circuit from that.

 

[alec_t]

Alec, Might want to remove D5. Again, we can't be sure what the starting current needs to be. 3 amps may not be enough.

You may be right. Easily done. However, I would have thought that even 3A would get the motor started, albeit somewhat sluggishly perhaps. Looking at the LM2576 datasheet again I see that the chip current limit varies from 6A to 4.5A as the (output transistor) junction temperature rises, so the OEM controller can't provide the ~11A t=0 current that the motor winding theoretically draws. Perhaps something like 5A might be a better limit to aim for?
I've realised that the circuit I posted relies on the FET M1 having a low turn-on gate threshold voltage whereby the gate voltage is below the Schmitt lower threshold when the FET is current-limiting. It can be modded by moving C3 and adding a PNP transistor (Q2) so that Q1 turns on Q2 which in turn allows C3 to charge positively rather than negatively. This makes the choice of FET less critical. If anyone's interested I'll post a revised circuit.

@Joe
Can you guestimate how long it takes your pump, in water, to get from 0 to max speed? <0.5 sec?, < 1 sec?, ....?