# Pump on Rheostat/Dimmer



## Guest (Jan 25, 2006)

I'm new here and want to say that I have learned quite allot poking around here. I'm am in the design/planning phase at this time and trying to work out as many details as I can before construction.

The first of what maybe many questions is has anyone put a pump on a dimmer switch? Not being a electric motor guru... I wasn't sure if this would shorten the life of it substantially. I know I could control flow with a valve but I am planning on having a central control area that would allow me to do various things manually (ie lights, mist, fog...). A simple on/off might be adequate but I always like to have options. Or maybe I’m just a control freak! 

George


----------



## defaced (May 23, 2005)

It really depends on the individual dimmer. It will work, and have no harm to your pump, but you may not be able to get the full power out of your pump. This is a design/component issue, so each dimmer, even those of the same model, is going to be different. If you'd like I'll give you the whole "how it works, why this is a problem" breakdown, but it deals alot with the way the circuit is made and involves some thinking. 

Depending on the current pulled by the pump you can use just a regular potentiometer. 

Another option besides a demmer/rheostat is an autotransformer. I don't know if you can find one that's 120vac on both sides, but it will work.



*Never pay again for live sex! | Hot girls doing naughty stuff for free! | Chat for free!*


----------



## Guest (Jan 26, 2006)

Thanks for the enlightenment. I did some more research and I now understand what you are saying. A rheostat is not going to be efficient and generates allot of heat. A potentiometer may not be able to handle the draw of power. The autotransformer is way out of my budget. However, I think I will set up a test (not to expensive) with a dimmer switch. I understand now that it works by cycling the power on/off with each change in current direction. I also have a couple of 120 mm 120 vac fans I am going to test on this setup. Thanks again for your wisdom!

George


----------



## Homer (Feb 15, 2004)

I would not use a rheostat on the pumps. My understanding and experience indicates that starving a motor of the current it is designed to operate at will reduce the life of said motor. These pumps do not have variable speed motors, and are designed to run at consistent current. 

Just my thoughts.


----------



## kyle1745 (Feb 15, 2004)

Homer has a good point... with someone things you can also risk fires and etc.

Most people manage humidity with timed misting and afer some checking you can work out a system that fits.


----------



## defaced (May 23, 2005)

None of those are current limiting devices, they all work by decreasing the voltage supplied to the motor. Usually the problem with controlling a motor is heat dissipating in the controlling device. 

I had another though, an inductor based controler, like a trigger from a drill/saw would work. Now that is a current based device.



*Never pay again for live sex! | Hot girls doing naughty stuff for free! | Chat for free!*


----------



## Guest (Jan 27, 2006)

I put together a quick mockup using a light dimmer and it failed as you knew it would. Low erratic power. So you are thinking that a switch similar to that in a variable speed drill might work. Interesting… I’ll have to go and do some more digging around. Thanks for the idea Defaced. Back to the drawing board.


----------



## Guest (Jan 27, 2006)

Homer said:


> I would not use a rheostat on the pumps. My understanding and experience indicates that starving a motor of the current it is designed to operate at will reduce the life of said motor. These pumps do not have variable speed motors, and are designed to run at consistent current.
> 
> Just my thoughts.


Absolutely! I know of only one manufacturer that produces a "dimmable" (these pumps are DC by the way) pump but these are turbine pumps made specifically for the reef industry and would simply not function in our application. They are made by Tunze, perhaps Tunze makes a traditional impeller pump that can be controlled.
They are a european company so they may have models over there that simply would never sell here in the us.
Although the down side to these pumps are that they are extremely expensive, the cheapest speed controlable model starts at like US$230
From what I have been told you cannot control ac pumps they must be dc.

Matt


----------



## Homer (Feb 15, 2004)

defaced said:


> None of those are current limiting devices, they all work by decreasing the voltage supplied to the motor. Usually the problem with controlling a motor is heat dissipating in the controlling device.
> 
> I had another though, an inductor based controler, like a trigger from a drill/saw would work. Now that is a current based device.


Okay, if you're planning on using a voltage limiting device rather than a current limiting device, I'll change my advice. Replace the word *current* in my previous post with *voltage*. Just remember V=IR (voltage = current x resistance). And, don't forget, if you are using a rheostat on your AC side, most pumps have a transformer. So, changing voltage upstream of your transformer will have effects at the transformer.

Have you ever run your 220v air conditioner on 110 v AC? I'm not going to try it. Have you ever run a 12 volt R/C car on 4 volts? I wouldn't recommend that, either. I may just be over cautious, but I don't see any reason not to be cautious/conservative in this situation.

What you are proposing may work. It will very likely decrease the life of the motor. Regardless, what are you really gaining? Nothing you couldn't accomplish by simply adjusting the flow valve on the pump when you set it up. 

Maybe I'm not understanding your reasons for doing this.


----------



## defaced (May 23, 2005)

You've got it backwards. You can take something of a higher voltage and run it at a lower voltage. So a 120vac air contidioner on 220vac will blow. This is because you are applying too much electric potential (voltage) across the device causing a breakdown in certian components, capacitors come to mind, as do diodes. 

Pumps don't have a transformer in them. They have a coil of wire and a magnet. There is a huge difference. 

A transformer is two coils of wire wraped around a core of some sort, usually iron, sometimes just air. The coils have difference sized wire and a different number of turns, this difference in wire and turns allows the primary side of the coil to induce a magnetice field in the secondary side and thus create an electrical current. 

Small pumps like what we're working with are similar in that they basically consists the primary side of a transformer and a magnet. Again current passing through the wire creats a magnetic field and the change in the magnetic flux interacts with the magnet and movement occurs. North repels North, South repelts South. Because of the shape of the magent and coil a spinning motion occurs. However if you were to take the magnet and the coil and make them flat, linear motion would occur. This is used in Linear Induction Motion roller coasters.

Looking at Faraday's Law of Induction clicky
you can see that Voltage and Magnetic Flux (B field) are directly proportional. This means that if we reduce the voltage, we reduce the B field, and thuse reduce how fast the motor is spinning. This is usually done on fans and such with a multi tapped transformer, in this application that's not cost effective, so other ways of augmenting voltage is necessary. 

Now if we wanted to change the current, one would use Lenz's Law, which says the the movement of a magnetic field causes a current in the wire. Change the current (I propose and inductor) and you change the B field and thus can decrease the speed of the motor. 

The biggest problem simple approaches to change either the voltage or current going to the pump is that too much power is disipated in the controller (resulting in heat) and it fails. 

With a dimmer it doesn't limit the voltage or current, but switches it on and off at some frequency (SCR technology). This is fine for things that have a slow responce to change in current (light bulbs), but a motor will simply not spin fast enough. This is usually due to the poor design or component tolerances inside the dimmer because in theory it should be possible to recreate the whole wave form. This is why if you install a celing fan the directions tell you not to install the fan on a dimmer switch. 

With a drill/saw trigger an inductor is used to limit the change in current going to the pump. This doesn't actually disipate much heat, but it does mess with something called the power factor, because an inductor creates a phase shift between the voltage and the current. In our application power factor really isn't much on an issue, but on large industrial scales it can waste alot of money.

With an autotransformer the incoming voltage is changed using an adjustable transformer. Again these produce heat but they can usually handle alot more power dissipation before they fail.

The last method I can think of to control the voltage to the pump is with a function generator and a transistor. Basically make a function generator that produces a small 60Hz Sine wave. Now take this wave and amplify it to the necessary voltage. Now since the input wave is very low power, one could easily control it with a simple potentiometer. The problem with this means of control is that the person has to build and design the device, and that takes some know how. 

There's your crash course in Electromagnetic Physics and circuit design. I hope you had fun.



*Never pay again for live sex! | Hot girls doing naughty stuff for free! | Chat for free!*


----------



## Guest (Jan 29, 2006)

> You should be able to cut down to the point where maximum pressure for your pump is rated, so a simple ball valve would restrict water, but it would also increase the pressure betweent the pump and the valve. Another way to do it is to take water the pump has pumped and put it directly back into the water rasavoir. This will decrease pressure between the pump and your misting heads and decrease the water flow through the misting heads. I'm needing to do the same thing for different reasons so I'll post on what I did and how it works.


The dimmer isn't a good idea....won't work. Not safe IMHO. Covered by others.

The variable drill switch may work....not sure of the cost factor or the long term effect on the motor or overall safety. Could be interesting approach however.

The direct control of the water is the place to put your attention in my opinion. Easiest approach and most cost effective. (see _defaced_ quote I grabbed from another thread. Just forget the words misting heads and use the same approach)

Also you can control flow...GPH with a simple clamping device on the outlet side. This will give less volume with a higher velocity and back pressure on the pump. The pump may cavitate (slow down) if the inlet is restricted enough. This may have effect on the life of the motor.

Then too you can have a slower flow by increasing the head of your outlet. The higher the discharge opening is from the water line the pump is in the slower the discharge. This is similar to the clamping with the exception you don't have the velocity issue, rather the opposite, volume with slow rate of flow. Again there is back pressure on the pump. IMO not likely to shorten the life of the pump.


----------



## Homer (Feb 15, 2004)

> Pumps don't have a transformer in them. They have a coil of wire and a magnet. There is a huge difference.


If it's a DC motor running the pump, it has a transformer upstream of the motor. Otherwise, you couldn't plug it into the wall. These are what I use. You're right, if it's an AC motor (which would probably be a piston motor or diaphragm motor, rather than an impeller motor used in most of these setups, there is no transformer.

I've built motors, and I've tested motors. I know what a motor is. You are right, it is possible to run the motor at a lower voltage (provided it is enough to spin the windings), but it will shorten the life of the motor. I think we've covered it all above.

It's your money, feel free to spend it any way you like.


----------



## defaced (May 23, 2005)

> I've built motors, and I've tested motors. I know what a motor is.


I did not write my post to be offensive, sorry if it came across that way. I wrote it to be thorough. I agree, a DC motor will need either a rectifier bridge or a center tap transformer + diodes to work on AC mains wiring. I never considered that a pump would be DC, seems wasteful to me. 

No one has yet to fully describe why running a motor at a lower voltage will harm the motor.



*Never pay again for live sex! | Hot girls doing naughty stuff for free! | Chat for free!*


----------



## Guest (Jan 29, 2006)

These are DC, and extremely efficient.
http://www.tunze.com/149.html?&L=1&C=US ... zeprod_pi1[predid]=-infoxunter025
Matt


----------



## Guest (Jan 30, 2006)

I did not realize the pumps we typically use in our aquariums and fountains were DC. There is not a transformer that plugs into the wall so I guess it is within the pump housing itself. I think I will just use a valve and return loop to control flow. I just thought it would be clever to have flow control at a central control center in the vivarium hood. I guess there is not any reason to want to change the flow from your pump once you have it set. It was just an idea… bad one I guess!

Not to change the subject although it is still about speed control. Sort of! Has anyone seen or used this fan setup. http://www.windydayzz.com It looks like it a good idea… but… just because I think it is a good idea, it may not be.


----------



## Guest (Jan 30, 2006)

detrazgw said:


> Not to change the subject although it is still about speed control. Sort of! Has anyone seen or used this fan setup. http://www.windydayzz.com It looks like it a good idea… but… just because I think it is a good idea, it may not be.


Ive got one running on my processor right now.

Matt


----------

