Rheostat a Pump?

[fishnu]

I am displaying my ignorance for all to see (opens raincoat). Is it possible to rheostat a pump?

We seem to invest a lot of time and energy in topoffs and flow rates. Mostly these solutions are "binary". Turn it on, turn it off. That is OK alot of the time, and perfectly acceptible for top off solutions.

But another thread here asked about equalizing flow rates between pumps. Most of the solutions I have heard about Rate are using gates and ball valves or changing the pump.

Is there a mechanical or electrical reason why you can't put a rheostat on a simple type of water level meter and turn a pump's speed up and down?

Thanks in advance.

 

[mps9506]

I am displaying my ignorance for all to see (opens raincoat). Is it possible to rheostat a pump?

We seem to invest a lot of time and energy in topoffs and flow rates. Mostly these solutions are "binary". Turn it on, turn it off. That is OK alot of the time, and perfectly acceptible for top off solutions.

But another thread here asked about equalizing flow rates between pumps. Most of the solutions I have heard about Rate are using gates and ball valves or changing the pump.

Is there a mechanical or electrical reason why you can't put a rheostat on a simple type of water level meter and turn a pump's speed up and down?

Thanks in advance.

I don't believe so because they operate on AC power. If you have a pump that operates on DC then yes. I think the Tunze's use something similar to this when you adjust the flow output. the impellar actually slows down.
I don't think it is as simple as a rheostat, but from what I understand the controllers somehow adjust the speed of the impellar and it requires DC to do this.
I'm far from being knowledgeable on electronics though so take this with a grain of salt

 

[framerguy]

I believe it could be done. As an electrician in the navy (over 20 yrs ago, so I've forgotten a LOT) we would rheostat electical motors to run fast or slow. Light and ceiling fans have similar "dimmer" switches but don't know that they would work for this application. I know it won't work for a Korallia because I tried it. It may be best to talk to a local electical shop and ask their advice.

 

[sasquatch]

A quote for you from some electric site lol.
If you attempt this with a standard motor, then you would likely either stall or overheat the motor (particularly the rotor). You are essentially operating the motor in the part of the curve between breakdown and stall. it has something to do with line frequency . Steve

 

[fishnu]

A quote for you from some electric site lol.
If you attempt this with a standard motor, then you would likely either stall or overheat the motor (particularly the rotor). You are essentially operating the motor in the part of the curve between breakdown and stall. it has something to do with line frequency . Steve

We have officially passed my IQ's cruising altitute.:away:

Thanks for the answer!

 

[corrado007]

Seems possible to me, ceiling fans often have adjustable speeds and they operate on AC voltage. I don't recall if I've seen one on a dimmer switch or if they always have a few set speeds. Worth looking into as it would make much of our fine tuning more simple. I'm certainly no electrician so take my opinion with a grain of salt.

 

[KodiakBear]

MPS has it right. Rheostats will only work with DC pumps that rely soley on commutation to produce the torque across the rotor. AC pumps rely on the voltage changes in the field windings (ie frequency). When you mess with the voltage peak values by using a rheostat, the current passing through the windings will compensate to create an equal amount of power. If you have a small Rio 1700 like the one I have, it uses 33 Watts at 115V which means it draws 289 mA of line current at it's rated speed. If I put in a rheostat and reduce the voltage to 100, that current then rises to 330mA. Current produces heat due to various things occuring in the copper (mostly what's called Hysteresis losses). The extra current would cause more heat production, which may be beyond the insulation's ability to transfer the heat. Long story short, you melt the insulation in the wire coil, which shorts out the motor, creates a lot more heat... etc etc. It can get really bad. Now, for very small changes, you might be able to pull it off without a problem... However, is it worth the risk?

 

[KodiakBear]

As for ceiling fans... Most actually have seperate windings installed in them. Others rectify the AC into DC, while others still just over-engineer the insulation for higher currents. It's not something I would try with something that wasn't designed to handle the current.

 

[Scooterman]

The proper way to vary an AC motor would using a VFD (variable frequency drive) it is done industrially all the time but is very costly & not practical. If you want to control flow on a centrifugal pump just use a ball valve on the pump outlet & you can slow or increase the flow.

 

[mps9506]

So are Tunze Streams DC pumps with a transformer? I know the controller is more complicated than a simple rheostat but I'm guessing that must be how the speed is throttled on those pumps.

 

[tbittner]

VorTech is the same way.

 

[Scooterman]

I don't remember quite how the Tunze were made, I remember they had the PH that was inside similar to a regular Magnetic PH so that leads me to believe they are AC but they also had the remote epoxy filled coil & then the last part was the actual controller, I'm thinking being specifically designed to be variable like that It could very well be a simple form of a VFD. If it was DC I don't think it would need that external coil If that is what it was inside it. I should of takes a few reading on them but never gave it a thought until now.

 

[tbittner]

Any more information on this? It IS a great idea! I'm just not sure it's possible with an AC pump though.

 

[Scooterman]

You can do it with an AC pump but you will shorten the life of it dramatically, unless you design it with a FVD of some sort!

 

[tbittner]

Fvd?

 

[tbittner]

I've been reading about this capability in 3 phase motors. You need a 3 phase motor (controller) which can be connected to a PC via an rs-232 port, and a 3 phase pump. Many motors come with auto shutoff in a dry condition. With this combination it's possible to control the rpm of the pump. In fact, that is what they are designed for. They are twice as efficient as the single phase, 115v pumps we currently use which means they use half the electric. Surprisingly, you can buy the controller and the pump that would equal a Sequence Barricuda as far as pumping capability for around $275. For a few dollars more, the motor comes equipped with a flow sensor which will tell the PC what the flow rate is. A program can then be developed to adjust the power being supplied to the pump to keep a constant flow rate.

Amazing stuff!

Most of these require a 240v circuit which all breaker panels can provide. The major downside is, you'd probably have to run different wire.

 

[Scooterman]

Again as I already mentioned, VFD (Variable Frequency Drive) no such thing as a three phase pump but three phase Motor yes & you can control it with the VFD & a laptop or computer via RS232 or these days probably Ethernet by the time you get all what you need your probably better off with a Tunze unless your a commercial operation. Efficient, powerful yes, (you can blow away any reef type pump including the sq), also elaborate, god to know what your doing & will have a cost, If you search RC for FVD I think you'll find one done by a guy named Luke.