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How to control the speed of a 24vdc pump from circulating water temperature?

skenn_ie

Sep 7, 2009
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Buy a speed/brightness controller (eBay?) that has a pot to control the speed. Substitute a resistive PTC or NTC for the active side of the pot.
 

CDRIVE

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You're a tad late to the party and your comments make it clear that you posted without reading any of this thread except the original post. This thread is three pages deep.

Chris
 

cygnusv

Oct 7, 2014
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You're welcome Stu. Here's some important notes that should receive serious consideration.

(1) The circuit as it's currently drawn has the ability to adjust the control (input) voltage to 0V when the Pot is turned to its fully clockwise extreme.

(2) The circuit I drew assumed that an increase in control (input) voltage produces a longer PWM on time, thus increasing motor speed.

(3) Keeping notes 1 & 2 in mind I drew my pictorials where turning the Pot clockwise will reduce motor RPM because this would be the intuitive direction to increase water temperature.

Earlier in this thread I stated that I have no idea if increasing the control voltage translated into increasing PWM (On Time) that will translate to increasing RPM. That was the post that I commented on deciphering Chinese tech data.

I just went back to the Ebay link and looked at the photo that includes the Pot plugged into the board. Keeping in mind that turning the Pot clockwise to increase RPM is intuitive (except for women:D) my circuit's analog logic may be backward. This is because we never did determine if an increase in control voltage translates to increase in RPM. Looking at that Photo tells me the opposite is true.

So what's the bottom line?

As with all prototyping design nothing should be considered final and permanent unit all experimentation is completed and you're satisfied with the results. This means all connections should be only tacked soldered until final design. Live circuit tests should be done prior to stuffing everything in an enclosure.

I would suggest that you experiment with a with a 12V or 24V incandescent lamp (torch) as a load with the Pot wiring unmodified. Then measure the control voltage between GND (Black) and Pot's wiper (White) while turning the Pot clockwise and counter clockwise while also observing the brilliance of the lamp.

On a final note I would not recommend using your boat's storage cells as a supply for prototyping. They're WAAAAAY to powerful and totally unforgiving if you have an "Oh Sh!T!" moment. A 12VDC wallwart plugged into shore power would be sufficient for experimental prototyping. Even a little 9V battery and low current lamp load would suffice for testing. I guess an LED with a 330Ω series resistor should work for a load too but incandescent lamps respond to PWM better and are more easily seen by the human eye.

Lets us know when you start your experiments.

Alec, take a look at this photo. Assuming clockwise rotation increases pulse width do you agree that this looks like decreasing control voltage increases pulse width?

Chris
$_57.JPG

Hi Chris

I'm so pleased that you and the other guys are prepared tp take the time to help. I really do appreciate your efforts.. I take the point about using a low battery voltage for testing, our domestic battery bank is 24 volts and 225AH - definitely more than enough to destroy the kit if I screw up.
I'm expecting the thermistor to arrive (from Hong Kong) in the next couple of week so in the meantime I'll make up a lamp and buy a PP9. Will report my results for further examination. Thank you
 

cygnusv

Oct 7, 2014
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Hi Chris

Unexpected early reply!

I realised that the pwm works in the 6 - 90 volt range, and I have a 6 volt flashlight with the big rectangular battery. I've wired it up through the PWM and it works! Only thing is that the way the factory have assembled the pwm they've got the black wire and the red wires back to front. I carefully removed the pot's plug, lifted the little plastic plug receiver and spun it round. The black wire is now in the correct place.
Now with the pot turned completely anti-clockwise the bulb is at its brightest and the voltage across black and white wires reads 2.61 volts. With the pot turned fully clockwise the the bulb fades to nothing and the voltage reads zero volts.
Just checked and if it's of interest the bulb is just beginning to glow at 0.11 volts

Does this in any way affect your earlier thoughts about wiring in the thermistor?

Stu
 

CDRIVE

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Do you mean the black wire now goes to ground and the red wire now goes to +5V?
Hi Alec. Hopefully Stu means as shown below. I'm surprised the plug was easily able to be inserted reversed.
$_57.JPG


Stu, I'm almost certain that the heat sinked component on the right side of the photo is a 5V regulator. Your 6V battery supply is too low and why your not reading 5V with the Pot at its extreme CCW position. A 5V regulator needs a higher input voltage then that to properly regulate the output to 5V. No matter though because the 6V input was good enough to determine if increasing or decreasing the control voltage input (0-5V pin) increases or decreases pulse width output. So, if we understood you correctly this circuit configuration can remain as I drew it because the Thermistor resistance decreases with increase of temperature. This will produce an increase in control voltage which agrees with this diagram.

upload_2016-7-1_0-47-55-png.27653

I do find it odd and counter intuitive that turning the Pot CCW increases pulse width and therefor motor RPM. Though I imagine most women would be comfortable with that. :p

Chris
 

Alec_t

Jul 7, 2015
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It's probably not counter-intuitive to the Chinese manufacturer :D. Don't they read from right to left in China?
 

CDRIVE

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It's probably not counter-intuitive to the Chinese manufacturer :D. Don't they read from right to left in China?
Alec, that makes perfect sense. Now when I read head scratching, Chinese tech data I'll just be thankful that it's 'at least' read left to right! :p

Chris
 

cygnusv

Oct 7, 2014
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Hi Alec. Hopefully Stu means as shown below. I'm surprised the plug was easily able to be inserted reversed.




Chris

The plug sits in a small plastic recepticle that has grooves to prevent the plug being fitted back to front. This recepticle was fitted back to front. The plug orientation is determined by its recepticle. So yes - the black connected to the 5V and the red to the GND.
The connections are very delicate so I'm just pleased that I was able to switch it without bending the pins!

So - Just waiting for the thermistor now and I'll report back
 

CDRIVE

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The plug sits in a small plastic recepticle that has grooves to prevent the plug being fitted back to front. This recepticle was fitted back to front. The plug orientation is determined by its recepticle. So yes - the black connected to the 5V and the red to the GND.
The connections are very delicate so I'm just pleased that I was able to switch it without bending the pins!

So - Just waiting for the thermistor now and I'll report back
Forgive me if I seem dense but are you saying that the receptacle is soldered to the board reversed?

International color code acceptance:
Red = Positive (+)
Black = Negative (-)

In order for the analog logic of my Thermistor circuit to be correct your color code must follow this. I also need to know that when you made that lamp test it was wired like this.

Chris
 

cygnusv

Oct 7, 2014
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Forgive me if I seem dense but are you saying that the receptacle is soldered to the board reversed?

International color code acceptance:
Red = Positive (+)
Black = Negative (-)

In order for the analog logic of my Thermistor circuit to be correct your color code must follow this. I also need to know that when you made that lamp test it was wired like this.

Chris

Hi Chris -

It was one of your replies that caused me to take a second look at the board. I corrected the error before the test.

There are 3 stiff wires that come out of the board - the plug fits on these. However, to ensure the plug goes on with the correct polarity there is a handed plastic recepticle that is fitted to these wires before the plug goes on. This had to be rotated to make the black wire sit on the pin marked GND.
Also, when you look at the pictures of the board above, it's very clear that the black wire is on the left. Mine was on the right. I couldn't just turn the plug 180 because it will only fit one way into the recepticle. This was why I had to remove and rotate it.
I always thought that stuff like this was machine assembled, clearly not....

Stu
 

CDRIVE

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Also, when you look at the pictures of the board above, it's very clear that the black wire is on the left. Mine was on the right. I couldn't just turn the plug 180 because it will only fit one way into the recepticle. This was why I had to remove and rotate it.
I always thought that stuff like this was machine assembled, clearly not....

Stu
So you had to un-solder the male receptacle on the board to rotate it?
Whatever you had to do is OK. I just needed confirmation that your measurements were made with Black = GND, which you said it did.

Manpower is dirt cheap in China so it wouldn't surprise me if human hands inserted the components.

Edit: I just read your reply again and realize that you didn't have to un-solder the board connector. If I read it correctly you were able to pull up the plastic body (key) and rotate it without actually messing with the male pins.
Chris
 
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cygnusv

Oct 7, 2014
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So you had to un-solder the male receptacle on the board to rotate it?
Whatever you had to do is OK. I just needed confirmation that your measurements were made with Black = GND, which you said it did.

Manpower is dirt cheap in China so it wouldn't surprise me if human hands inserted the components.

Edit: I just read your reply again and realize that you didn't have to un-solder the board connector. If I read it correctly you were able to pull up the plastic body (key) and rotate it without actually messing with the male pins.
Chris

Confirmed measurements made after correcting the plug rotation. No soldering required thank goodness!

Stu
 

CDRIVE

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Good! Nothing changes... For now...;)

Chris
 

cygnusv

Oct 7, 2014
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My thermistors (incl a spare) have arrived! Less than £2.50 for 2 including postage from Hong Kong! Amazing, and a 2 week turn around.

Anyway. This morning I checked them both to be sure they're working correctly. At room temperature of 21C both are measuring about 10.5K. Dipped into water heated to 65C they both step down quite smartly to about 2.5K. Looking good to start.

In a few days time I'm going to connect a 15 watt load (bulb) to the PWM and connect the thermistor in series to the pot following Chris's drawing above. I'm then going to dip the business end of the thermistor into water heated to various temperatures to get an idea of how hot the water is before I get full output from the PWM.

Has anyone get any views of anything else I should be checking?

One question I do have is - Should the pot be turned fully on or off for the thermistor to operate correctly? In fact will the pot have any impact at all on the range over which the thermistor will operate?

Thanks for the help so far, Stu
 

Alec_t

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Set the pot about half way to start with, then adjust it to get the outcome you want when the thermistor is at the required temperature. If no adjustment gives the right outcome then try swapping the pot and thermistor positions in the circuit.
 

CDRIVE

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Stu, glad to read you have them. Yeah, those Chinese bargains are soooo difficult to resist!

I can't add anything to what Alec suggested because it's exactly what I would have posted... verbatim.

Chris
 

cygnusv

Oct 7, 2014
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In a few days time I'm going to connect a 15 watt load (bulb) to the PWM and connect the thermistor in series to the pot following Chris's drawing above. I'm then going to dip the business end of the thermistor into water heated to various temperatures to get an idea of how hot the water is before I get full output from the PWM.



Thanks for the help so far, Stu

Edited (with apology) It should read 'Cdrive's'

Would it be possible for the part of that same drawing that shows the thermistor connection be clarified for me?
Looking more closely it appears to me that the thermistor wires actually become a bridge within the red wire, but it also appears to show a connection between the red and the white at the pot. Is this the case?
Also showing is a connection between the black and white wires through a 'C1 100n' - what is this?
Clarification of this will help me get it right first time (I hope!)

Stu
 

CDRIVE

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The Pot is wired as a Variable Resistor (Rheostat). When connected in series with the Thermistor the circuit forms a Voltage Divider much like a Pot does when wired as a Pot. The difference here is that the Thermistor replaces or mimics varying (turning) the wiper pin of the Pot. The 100nF Cap is there to filter out any electrical noise that your remote Thermistor may pickup.

Chris
 
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