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

cygnusv

Oct 7, 2014
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Hello again from the UK

In preparation for our next (cold?) winter I'm finally hooking our boat's multifuel stove up to provide heat to 2 small radiators and using any excess heat to warm our domestic hot water tank. We live on board all year round.

I've just ordered the back boiler for the stove and have identified a 24 volt Johnson circulating pump. This pump will move 15 litres a minute but this is way too much to allow proper heat transferance. What I'd like to do is this...

I'd like to make the pump speed variable. I know I can do this with a manual pwm controller, but I need something more automatic. If we leave the boat for any length of time when the stove is lit, the stove temperature will vary. Likewise, while we're in bed the stove temperature will drop overnight.

I'd like to optimise all this by fitting some sort of thermostatic controller to the pipe carrying hot water away from the stove that will vary the speed of the pump to suit the heat of the water leaving the stove. The benefit of this is that the system water should not boil and pump noise will be reduced to a minimum.

The pump itself is this one

http://www.asap-supplies.com/johnson-fresh-water-circulating-pump-209614

Can anyone suggest either a suitable circuit (or even a suitable ready made product) that will make this possible?

Many thanks as always, Stu
 

shrtrnd

Jan 15, 2010
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The first thing I'd do, is contact Johnson, and explain your issue, and ask if they have any application data sheets for their pump. You never know unless you ask if the manufacturer has already accumulated data on their products.
What you want to do is going to require interface temperature sensors, probably in a couple locations. It may be that the manufacturer can recommend support information on their product. Some pre-build controller that they, or another manufacturer has already developed for this purpose. I'd try that first, and if nothing is available, work on a do-it-yourself circuit.
 

Alec_t

Jul 7, 2015
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There are plenty of DC motor speed controllers advertised on the net. Most have a potentiometer to set the speed. Perhaps you could replace the pot with a thermistor in series with a trimmer rheostat.
 

CDRIVE

Hauling 10' pipe on a Trek Shift3
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In the event that your only option is a DYI solution you can start Here On Ebay. This particular PWM LISTING includes an external control input option that can be interfaced to a thermostat circuit. Just about any 8 pin uC could handle the Temp to PWM control part of this project. My personal preference is PICAXE

Chris

EDIT: On second thought Alec made a good point. You probably won't need a uC at all. A Thermistor and fixed resistor can probably replace the POT control on any of the listings on Ebay.
 
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Alec_t

Jul 7, 2015
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If you wanted a home-brew solution, here's my offering for a thermistor-controlled PWM speed controller:
TempControlledPWM.PNG

The sim plots show the PWM drive to the motor, and the motor current, as temperature is swept from 0C to 100C.
 
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cygnusv

Oct 7, 2014
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The first thing I'd do, is contact Johnson, and explain your issue, and ask if they have any application data sheets for their pump. You never know unless you ask if the manufacturer has already accumulated data on their products.
What you want to do is going to require interface temperature sensors, probably in a couple locations. It may be that the manufacturer can recommend support information on their product. Some pre-build controller that they, or another manufacturer has already developed for this purpose. I'd try that first, and if nothing is available, work on a do-it-yourself circuit.

Good thinking. We have a bank holiday here this Monday but I have sent an email to them
 

cygnusv

Oct 7, 2014
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In the event that your only option is a DYI solution you can start Here On Ebay. This particular PWM LISTING includes an external control input option that can be interfaced to a thermostat circuit. Just about any 8 pin uC could handle the Temp to PWM control part of this project. My personal preference is PICAXE

Chris

EDIT: On second thought Alec made a good point. You probably won't need a uC at all. A Thermistor and fixed resistor can probably replace the POT control on any of the listings on Ebay.

How straightforward would that be to do?
 

CDRIVE

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How straightforward would that be to do?
It would be quite straight forward but would require some experimentation to select the Thermistor as well as set the Trimpot to calibrate it. All of the Ebay listings utilize a Pot to adjust the PWM but some incorporate an additional External (Voltage Controlled) Input port. You will probably not need this option but I would choose a model that does not have the control pot soldered directly to the board. The models that have the control pot connected via a pigtail & PCB Connector will make your life easier.

The attached circuit assumes that an increase in temp causes an increase in control voltage and an increase in motor speed. Looking at the Ebay listings it's hard to determine whether an increase in control voltage increases or decreases pulse width. That's one of the joys experienced when dealing with Chinese imports. Their technical details usually leave the buyer with a big "?".

Chris

upload_2016-5-29_11-9-21.png
 

cygnusv

Oct 7, 2014
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It would be quite straight forward but would require some experimentation to select the Thermistor as well as set the Trimpot to calibrate it. All of the Ebay listings utilize a Pot to adjust the PWM but some incorporate an additional External (Voltage Controlled) Input port. You will probably not need this option but I would choose a model that does not have the control pot soldered directly to the board. The models that have the control pot connected via a pigtail & PCB Connector will make your life easier.

The attached circuit assumes that an increase in temp causes an increase in control voltage and an increase in motor speed. Looking at the Ebay listings it's hard to determine whether an increase in control voltage increases or decreases pulse width. That's one of the joys experienced when dealing with Chinese imports. Their technical details usually leave the buyer with a big "?".

Chris

View attachment 27138

I've found this PWM control and wonder what you think of its suitability (bearing in mind that I am a novice)?
In the listing it specifically mentions external contols and even shows where to plug it in. Looks simple enough. My next concern is to find a suitable device to clamp onto the hot water pipe to suit.

http://www.ebay.co.uk/itm/6-90V-15A...69230948&tpos=top&ttype=price&talgo=undefined

The PWM description mention the use of 0-5 volt control replacing the potentiometer so has anyone got any suggestions?

Many thanks to all, Stu
 

CDRIVE

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Stu, that description nearly had me fooled into thinking it was authored by an English speaking individual. That is until I reached the description of how to replace the Pot with a 0 - 5V input. It's Pigeon English at it's best. o_O The Input resistance of the control pin would have been nice to know but that would be too high an expectation. That said, the description is detailed enough to get you started and it should work as well as any of the ebay listings.

Regarding interfacing the Thermistor to the hot water plumbing is concerned. I would think a Thermistor package physically designed for plumbing or automotive applications would be the best way to go. Something that looks similar to THIS. Though the dimensions seem overly huge! Perhaps another member can suggest a source.

Chris
 

cygnusv

Oct 7, 2014
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Stu, that description nearly had me fooled into thinking it was authored by an English speaking individual. That is until I reached the description of how to replace the Pot with a 0 - 5V input. It's Pigeon English at it's best. o_O The Input resistance of the control pin would have been nice to know but that would be too high an expectation. That said, the description is detailed enough to get you started and it should work as well as any of the ebay listings.

Regarding interfacing the Thermistor to the hot water plumbing is concerned. I would think a Thermistor package physically designed for plumbing or automotive applications would be the best way to go. Something that looks similar to THIS. Though the dimensions seem overly huge! Perhaps another member can suggest a source.

Chris

Hi Chris
Typically Chinese, innit!! The 0-5 volt confuses me a bit. An initial thought that I had was a screw in temperature transmitter from a vehicle - but where does the 0-5 volt come in?
I know that my lack of knowledge will involve a bit of 'hand holding' but it really is appreciated. Stu
 

CDRIVE

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Both Alec's and my schematic develop the ~ 0 - 5V the same way. The Pots are wired as variable resistors (Rheostats) and the Thermistor is wired in series with the Pot. This circuit constitutes a Voltage Divider. As the Thermistor's resistance changes it produces a voltage change measured from common (GND) and the junction of the Pot and Thermistor. The Pot is used to calibrate the motor speed in relation to the temperature that the Thermistor senses.

Here's the Voltage Vs Temp curve for the Thermistor I simulated. The Pot was set to 10KΩ.

Chris

upload_2016-6-6_9-51-28.png
 

cygnusv

Oct 7, 2014
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Both Alec's and my schematic develop the ~ 0 - 5V the same way. The Pots are wired as variable resistors (Rheostats) and the Thermistor is wired in series with the Pot. This circuit constitutes a Voltage Divider. As the Thermistor's resistance changes it produces a voltage change measured from common (GND) and the junction of the Pot and Thermistor. The Pot is used to calibrate the motor speed in relation to the temperature that the Thermistor senses.

Here's the Voltage Vs Temp curve for the Thermistor I simulated. The Pot was set to 10KΩ.

Chris

View attachment 27255

Thanks for that Chris it's very helpful. I'm looking forward to everything arriving in a day or two. We'll see what happens...

Stu
 

CDRIVE

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Let us know when the parts arrive. some experimentation will be needed.

Chris
 

hevans1944

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Here is a similar, somewhat less expensive PWM controller. The photos do not all appear to be from same product. Note the absence of the metal mounting ferrules at the corners on two of the images. There is also some sort of power semiconductor device mounted near the 3-pin potentiometer connector. The +5 V pin may be voltage derived from a zener diode or a 3-terminal regulator because of the wide range of supply voltages accepted. Both products appear to use multi-layered circuit boards, so it is impossible to trace out, much less compare, circuitry. Hard to beat the price though... if it works as advertised.
 

cygnusv

Oct 7, 2014
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Here is a similar, somewhat less expensive PWM controller. The photos do not all appear to be from same product. Note the absence of the metal mounting ferrules at the corners on two of the images. There is also some sort of power semiconductor device mounted near the 3-pin potentiometer connector. The +5 V pin may be voltage derived from a zener diode or a 3-terminal regulator because of the wide range of supply voltages accepted. Both products appear to use multi-layered circuit boards, so it is impossible to trace out, much less compare, circuitry. Hard to beat the price though... if it works as advertised.

Typically, I didn't see this listing. I've already ordered the other one. Many thanks though. Stu
 

cygnusv

Oct 7, 2014
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Hello again all

I've now got the pump and the controller with the adjustable pot and have bench wired it. As expected, with the knob turned fully anticlockwise I am registering 0 volts. As I rotate the knob clockwise the voltage rises to about 5.1 volts. I now want to match a suitable thermistor to replace the pot. I found -

http://www.ebay.co.uk/itm/0-5-10m-T...hash=item2eebdd8d68:m:mmpK55WgV8IDRzwarcmYuQw

this one. I wonder if some of you might comment as to whether or not it would be suitable? A concern I have is that I would have to clamp the business end onto a 28mm hot water pipe with a jubilee clip or similar.

Any alternate thermistor set up ideas will be much appreciated.

Many thanks, Stu
 
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