Will PWM pumps run at full speed without the PWM signal?

Thread Starter

339

Joined Jun 1, 2021
19
I am making an indoor fountain with an old 800 L/H AIO pump. Will the pump run full speed without the signal, like fans? if so, can I hook a potentiometer to the 12v adapter to adjust the height of the stream?
 

LowQCab

Joined Nov 6, 2012
1,308
Maybe.
What kind of a Controller did the Pump come with ?
Do you have all the Specifications for the Motor and the PWM Circuitry ?
Is the PWM Controller separate from the Pump-Motor ?
Can you get inside the Pump-Motor,
modify it,
and then insure a perfect re-Sealing of the Housing ?
.
.
.
 

Thread Starter

339

Joined Jun 1, 2021
19
Maybe.
What kind of a Controller did the Pump come with ?
Do you have all the Specifications for the Motor and the PWM Circuitry ?
Is the PWM Controller separate from the Pump-Motor ?
Can you get inside the Pump-Motor,
modify it,
and then insure a perfect re-Sealing of the Housing ?
.
.
.
It's controlled by motherboard with a 4 wire header. I don't want to crack the pump open.
 

ThePanMan

Joined Mar 13, 2020
127
You can always use a valve to control the flow. If you're restricting the flow excessively you can use a Tee to let the pump run without making it work too hard while some of the flow can go to the height you desire.

Now, will your pump run at full speed where it was formerly controlled by PWM? Yes. PWM is Pulse Width Modulation. Assuming you can vary the PWM from 0% to 100% - ask yourself this - what is 100% PWM? Is it not 12V all the time? So what's the difference between PWM @ 100% and 12V unrestricted?
 

LowQCab

Joined Nov 6, 2012
1,308
You can always use a valve to control the flow. If you're restricting the flow excessively you can use a Tee to let the pump run without making it work too hard while some of the flow can go to the height you desire.

Now, will your pump run at full speed where it was formerly controlled by PWM? Yes. PWM is Pulse Width Modulation. Assuming you can vary the PWM from 0% to 100% - ask yourself this - what is 100% PWM? Is it not 12V all the time? So what's the difference between PWM @ 100% and 12V unrestricted?
100% PWM can also be Ground.
 

ThePanMan

Joined Mar 13, 2020
127
100% PWM can also be Ground.
Standard understanding of PWM is that the top of the square wave (metaphorically speaking) is the positive voltage. Yes, it COULD be the negative leg, but generally PWM isn't thought of that way. But I understand what you are saying.

In the vein of this thread, 100% PWM is the same as the full supply voltage (respectively speaking). Therefore if the TS pump motor runs at 100% PWM it should also run on full supply voltage.
 

ThePanMan

Joined Mar 13, 2020
127
Can I connect a potentiometer to VCC and GND of the pump?
That's probably unlikely. The pot will act as a voltage divider, meaning it has to be able to handle the load of the pump and as a load itself it must be rated in watts to handle that much current. Suppose you have a 10K pot: At 12 volts, that pot will draw 1.2mA and 14.4mW. That's not a small pot. While 14 milli watts is not a lot, most trim pots I've ever worked with are too small to handle that much power.

Now, the load: Suppose it draws (and we don't know exactly what that amperage is) suppose it draws 2 amps. That's 24 watts. If the pot is tuned to 90% of the range, 90% of 12V is 10.8 volts. Your pot has to drop 1.2 volts that's going to pull 20 watts through that pot. It's going to burn up. So - no, you're not going to find many pots that can handle that much power.

As I suggested before, consider water valves to control the flow. That'd probably be my approach.
 

ElectricSpidey

Joined Dec 2, 2017
1,961
Why not just use PWM?

You could build a simple PWM module that could drive the pump with a 555, and in turn you can control the 555 with a pot.

Just keep in mind that the PWM signal might need to be 5 volts just as all PWM fans are, and higher voltage could damage it.

Simple build...regulator...555...few other parts, plus the pot.

Look up Noctua white paper for more info on the PWM specs.
 

MrSalts

Joined Apr 2, 2020
712
I am making an indoor fountain with an old 800 L/H AIO pump. Will the pump run full speed without the signal, like fans? if so, can I hook a potentiometer to the 12v adapter to adjust the height of the stream?
You can but it would not work nearly as well as pwm. When controlling power delivered to the pump with a pot, the drop from full power to half power requires the pot to heat up from the other half of the power (the power not used by the pump). In PWM, at half power, the power is literally off for half the time and on half the time. No energy needs to be absorbed or lost - there is simply no power consumed for half the time.
 

Thread Starter

339

Joined Jun 1, 2021
19
Why not just use PWM?

You could build a simple PWM module that could drive the pump with a 555, and in turn you can control the 555 with a pot.

Just keep in mind that the PWM signal might need to be 5 volts just as all PWM fans are, and higher voltage could damage it.

Simple build...regulator...555...few other parts, plus the pot.

Look up Noctua white paper for more info on the PWM specs.
Should I pull pin 4 high and floating, low and floating, or high and low?
 

shortbus

Joined Sep 30, 2009
8,952
Should I pull pin 4 high and floating, low and floating, or high and low?
Pretty sure the pump would work like a PWM computer fan does. Read this - "Pulse-width modulation

Pulse-width modulation (PWM) is a common method of controlling computer fans. A PWM-capable fan is usually connected to a 4-pin connector (pinout: Ground, +12 V, sense, control). The sense pin is used to relay the rotation speed of the fan and the control pin is an open-drain or open-collector output, which requires a pull-up to 5 V or 3.3 V in the fan. Unlike linear voltage regulation, where the fan voltage is proportional to the speed, the fan is driven with a constant supply voltage; the speed control is performed by the fan based on the control signal.

The control signal is a square wave operating at 25 kHz, with the duty cycle determining the fan speed. 25 kHz is used to raise the sound of the signal above the range of human hearing; use of a lower frequency could produce an audible hum or whine. Typically a fan can be driven between about 30% and 100% of the rated fan speed, using a signal with up to 100% duty cycle. The exact speed behavior (linear, off until a threshold value, or a minimum speed until a threshold) at low control levels is manufacturer dependent.[9] " From https://en.wikipedia.org/wiki/Computer_fan_control#Pulse-width_modulation
 

ThePanMan

Joined Mar 13, 2020
127
I am making an indoor fountain with an old 800 L/H AIO pump.
I must confess my ignorance but what is an old 800 L/H AIO pump?

Here's what I'm thinking: A centrifugal pump can be valved and the flow can be adjusted via that valve while the pump runs at full power. Dead-Heading it is like putting your hand over the opening of a vacuum hose. The motor speeds up but isn't doing any work because no air is flowing. The same would be true of the centrifugal pump. But if it's a positive displacement pump then you would need two valves - a control valve and a waste valve.

Trying to control the level of water flow by means of varying the output of the pump will likely be less accurate and more problematic than having the pump apply its full power and metering that power with a valve or valves. With the valves you'll always get consistent control. With PWM or any other electronic means, as the pump motor is slowed its output will drop dramatically. Just a guess here but it will probably drop by the square of X value. - - - Let me put it this way: If the motor is pumping 3000 GPH at full speed and full voltage and you cut the electrical power to 50% you won't get 1500 GPH you'll likely get more like 750 GPH. And if you try to go even slower the pump efficiency will continue to drop off exponentially. Not so with valves.

OK, sorry - I'm pushing valves. To state the obvious; 'You can do it any way you wish'.
 

Tonyr1084

Joined Sep 24, 2015
6,452
I must agree. Running a motor at half voltage won't result in half the output, it will put out something less. Probably much less. You need to not think in terms of volts or amps but in terms of watts.

Assuming your pump motor runs on 12 volts and draws 5 amps - that's 60 watts. At 6 volts the amperage will be lower. You won't draw 5 amps. If you did then that would be 30 watts, but the reality is that the inductance of the motor will change things up on you. I'm certainly not an expert on motors, but I'm fairly certain that if you run a 12 volt motor at half the voltage you won't get half the work (moving water). I'm thinking the valving method offered by @ThePanMan sounds pretty good.
 

ElectricSpidey

Joined Dec 2, 2017
1,961
These pumps are used in water cooled CPU systems, and are designed to run with PWM, and it doesn't matter if 50% duty cycle doesn't equal 50% water flow.

In a computer temperature feedback is used to control pump speed, in a fountain a simple adjustment of the pot will do the same.
 
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