Help with Water Pump

[salty joe]

I agree, Alec. A modular approach where feeding mode could be added later sounds good. What do you guys say we skip the feeding mode for now?

OK thanks ()blivion, I'll get those little piezos on the way.

Thanks everyone for thinking about this project and all the creative ideas.

 

[KeepItSimpleStupid]

I know we are in favor of skipping the feed mode, including me.

Salty has to "make room" for the possible inclusion of feed mode.

PROPOSAL (OEM adjustible buck regulators - qty = 4)
I do think we need the ability to adjust the output for the tests and in some respects probably a fuller range such as 6 to 22V. For testing, I'd like to propose modifying 4 OEM controllers to be adjustable buck regulators.
Should be easy to do.

QUESTION, assumes feed mode will be added ( Separate or interactive voltage adjust?; fixed or variable)
Joe, can you speculate as to what is needed?

(Fixed using resistors/interactive) is the simplest mode of operation.

Interactive means that the FEED speed has to be set first using a fixed resistor and the NORMAL speed is dependent on the FEED seed setting. The NORMAL speed could have some degree of adjustment (potentiometer).

non-interactive means that you could have two independent setpoint that went from 6-15 volts and another that went from 10 to 22 V.

 

[salty joe]

When the time comes to add feed mode, what I had in mind was to push a button to slow the pumps down for 10-15 minutes, then the pumps automaticly ramp back up to normal speed, with normal speed and feed mode speed both being fixed. If it were a switch that had to be manually activated to get back to normal speed, as much as I hate to admit it, the tank will end up running on feed mode for hours on end.

KISS, when you say leave room for the eventual feed mode, do you mean leave some empty space around certain components or wire in a special plug or what?

 

[KeepItSimpleStupid]

"leave room" basically means to have room for anticipated components or to make an "educated guess" as to what might be required.

"RAMPING UP" is a new requirement, although I can see where this might be beneficial. "ramping down" likely doesn't matter as much. Although, I don't think it's a show stopper.

This is where it would be nice to be able to PWM or Pulse Width Modulate the speed of the motor, but this may be a troublesome area. Alec might have something up his sleave.

The "knowns" at this point is the "timed controller" is relatively simple.

The biggest "unknowns" are:
1. The lowest voltage that the pumps can run at in NORMAL mode
...............a) Hopefully less than 18 VDC
2. "BEST" way to control the speed of the pumps.

This system may be a "prototype" that will go though a bunch of iterations. The best advice I have is to keep it modular at this point.

One thing that I always like to point out is that not all of the optimizations are the same for everybody. Take Solar panels. The cost/W per payback period is likely what you need to optimize for a homeowner. If this were a space application, then the efficiency per kg would be a better optimization parameter.

I designed something once and I panicked when during pulsed testing AC the output was very unstable. In DC testing it was fine. I panicked. The circuit had trouble driving a capacitive load, so I needed a different buffer design. The second part was related to electrically zeroing of the device. I didn't incorporate any mechanical means (potentiometers) for the offset/null adjustments and the algorithm for zeroing didn't work for two reasons: 1) The D/A (Digital to Analog Converter) was not divided down to a low enough voltage and 2) It would not output Zero Volts. <1 mV was not zero.
The second part was not as important as the AC performance. The second part was never fixed.

 

[salty joe]

I was using "ramping up" as a generic expression for getting the pumps back to normal speed. Sorry for any confusion.
Your point on optimization is a good one.

Later today I'm going to order parts to build from Alec 812. That's what I'm going to call it, if it's OK with you Alec.

 

[alec_t]

Alec 812. That's what I'm going to call it, if it's OK with you Alec.

Fine with me.

 

[KeepItSimpleStupid]

Joe:

Will you order f the following parts as well:

(8) 78K 1% 1/4 W resistor
(4) 4K 1%, 1/4 W resistor
(4) 10K, 5% 10-15 Turn trimmer, something like this: https://www.digikey.com/product-detail/en/PV36W502C01B00/490-2888-ND/666515

This will allow you to modify the OEM controller to output voltages from about 8V to <25V and if a 78K is put in parallel with the 78K, the range will be approximately 4.65 to 13V

This should definitely give you the ability to test. I can't write up modification instructions today.

 

[salty joe]

Thanks KISS, I will order those parts.

There are four parts on Alec 812 https://www.electro-tech-online.com/threads/help-with-water-pump.124250/ I'm unsure of.

The varistor (TVS). I found varistors (series tvr) of different values. What value would work?
Is D3 a 3A Schottky?
Is the trip test something I fabricate?
Is the Rsense resistor a 0.22 Ohm resistor?

 

[ronv]

Here is a 24 volt TVS:
https://www.mouser.com/Search/Refine.aspx?Keyword=6251.5ke24ae3

.2 ohm 3 W.

https://www.mouser.com/Passive-Comp...0vo2aZ1z0vnvuZ1z0vl8mZ1z0vo1zZ1z0z819Z1z0z7l5

Trip test could be a push button switch or maybe just a jumper to test it once during build. Up to you.

D3 - Yes, maybe like a MBRS340

 

[KeepItSimpleStupid]

Joe:
Where are you getting most of your parts?

D3 is internal to the FET, not purchased separately.

The Trip test is an ersatz push putton: i.e. an SPST (NO) switch. () indicates momentary. You could use a Tactile switch. Something like this could work: https://www.digikey.com/product-detail/en/EVQ-11U09K/P8085SCT-ND/259570
Lower profile is also available. This is 5 mm = 2.54 * 2 means it will fit on a 0.1" breadboard.

Rsense is a 0.22 Ohm resistor. Yes. At least 3 Watts. This guy should work: https://www.digikey.com/product-detail/en/RWM0410R220JR15E1/RWMA-.22CT-ND/1587884 3 W wire Wound or metal Oxide. 2 W is iffy, Metal oxide resistors will vaporize if overloaded which is a good thing. Make the leads slightly longer in case we need to upgrade to 4 W. I used > (3A)(3A)*0.22

My choice for the TVS: https://www.digikey.com/product-detail/en/1.5KE33CA-T/1.5KE33CADICT-ND/151034 Alec?

 

[alec_t]

@Joe
I think the others have answered your queries.
@KISS
That looks a good bet for the TVS. I have little experience with those animals, which is why I left the type vague. And yes, a 3W sense resistor would probably be better: in the trip state the peak power dissipated in it is ~2W for ~1/2 sec but the average would be well below 2W.

I'm still working on 'Project Speed Control'. In theory it works (the advantage being no supply voltage adjustment is needed), but I want to dig out a 2-phase brushless motor and breadboard it.

 

[KeepItSimpleStupid]

We're not agreeing on a few things:

D3 ronv external; KISS; internal
TVS: ronv: Unidirectional (orientation matters); KISS; Bidirectional (I now think unidirectional makes more sense)

 

[ronv]

Yep, my old eyes. Thought D1 was D3. No D3 needed. However in getting closer to the screen I think maybe D1 should be on the other side of the fuse to protect from the kick if the fuse blows. May not matter cause I think they blow kinda slow, but I don't know for sure. I think the TVS is non functional since there is a diode to ground and one to +24, but I think it makes everyone sleep better. A bidirectional one is okay to. Just look for 24 volt 1500 watt bidirectional.

 

[alec_t]

And now KISS and ronv both agree that the TVS could be inidirectional OR bidirectional . It may well be non-functional but it's belt and braces, and someone way back when thought it a good thing to have.

On the speed control front, I've breadboarded the circuit and it's running as I type this. All components run cool. The BLDC motor is a CPU fan (4-pole, assumed 2-phase). Runs happily at a fixed 12V from max 1800rpm down to 300rpm (and probably could go lower). Starts reliably at low speed. Attached are pics of the current waveform.
View attachment 65991View attachment 65992
Note in the second pic (300rpm) that the current is kept off, following the negative-going edge, for ~60% of the pulse period.

 

[()blivion]

I think we all got scared that this project is what blew up one of Salty's pumps, so we all agreed that a "belt and braces" approach would be preferred.

 

[ronv]

What do you think of the placement of D1??

 

[alec_t]

The anode of D1 could connect instead to the top end of the fuse. But then if the fuse goes high resistance slowly the FET could be damaged by voltage spikes. I guess it's six of one, half a dozen of the other.

 

[KeepItSimpleStupid]

1. Placement of D1 doesn't matter
2. Remove D1 and then use a UNIDIRECTIONAL TVS and the choice and direction of the TVS will matter.

 

[KeepItSimpleStupid]

For giggles, I'm going to throw these out, they are cheap enough ~$8 for 2. 8 ohm 100 W resistors could be used in place of a motor to test the power electronics, Note, they come in pairs with free shipping. **broken link removed**

 

[salty joe]

@KISS-I have gotten most of my stuff from here.
https://www.ebay.com/itm/2-x-IRF320...742?pt=LH_DefaultDomain_0&hash=item3cb9dce2f6
Free shipping on almost everything and they have not made a single mistake.

Thanks Ronv and KISS for the links. Thanks all for the detailed info.

I'm trying to find M1 and I gather it needs to be similar to mosfet IRF3205. IIRC, Rds (on):8m OHM was a critical value. I don't find that under this list of body diodes. Will one of these work?
**broken link removed**

Those giant resistors look pretty cool, KISS. An accurate substitute for a pump? Very cool, it's the plan-thanks.

Alec, the graph of speed control is neat. Does negative going edge mean the ground is briefly disconnected?