AC Skimmer Question -

[WhatCouldGoWrong71]

I have 2 older (but very nice) skimmers. I’m going to need to put one on a new display soon. I’m thinking the Vertex goes into rotation first.

- Vertex Omega 180
- Bubble King 300

Both are AC powered. Can I take an old school rotary rheostat and make the AC motor variable? Will that do any damage to either motor long term?

So my idea would be to take a HD 6’ extension cord, insert the rheostat in the middle of the cord and plug the skimmer into the cord and the cord into the wall plug.

 

[Quietman]

It's not generally recommended to control AC speed with rheostat. A rheostat is resistance device that drops voltage. Induction motors have to turn at applied frequency. The AC motor is going to draw current to produce its rotation so there's a high chance that the motor will overheat.

Side note: this is also why you have a limitation in how long an extension cord you can run with electric motors (saws, weed eaters, etc). Too long a cord adds too much resistance and the motor overheats as it draws excess current to turn at rated speed.

The proper way to control AC induction motors is with frequency control units. Probably not worth the cost.

 

[Bruttall]

Why not replace the AC pump with a DC variable? OR depending on the size and bioload, make a Venturi skimmer? I'm in the process of building a Venturi skimmer for my heavy bio load 300g, to replace the venturi skimmer I am currently using.

Here's a link to what I have accomplished so far, with some tech info as well.
https://www.reef2reef.com/threads/skimmer-for-300g.1093029/

 

[Pistondog]

I have 2 older (but very nice) skimmers. I’m going to need to put one on a new display soon. I’m thinking the Vertex goes into rotation first.

- Vertex Omega 180
- Bubble King 300

Both are AC powered. Can I take an old school rotary rheostat and make the AC motor variable? Will that do any damage to either motor long term?

So my idea would be to take a HD 6’ extension cord, insert the rheostat in the middle of the cord and plug the skimmer into the cord and the cord into the wall plug.

The rheostat reduces voltage output. An ac motor's speed depends on frequency.
So the rheostat will not vary the pump speed in a controllable manner.

 

[WhatCouldGoWrong71]

The rheostat reduces voltage output. An ac motor's speed depends on frequency.
So the rheostat will not vary the pump speed in a controllable manner.

Thanks. I was curious why I didn’t see this hack before. I wondered because as a kid my house had ceiling fans on regular dimmer dials.

 

[Freenow54]

The rheostat reduces voltage output. An ac motor's speed depends on frequency.
So the rheostat will not vary the pump speed in a controllable manner.

Is there a way to do a DCC application? I have asked the same question of straight voltage control before and see the wisdom of not doing it

 

[Freenow54]

DCC is also called pulse width modulation. Has been used for Years in Industry on 3 phase ( usually mining ) motors. up here by Leasson Canada. It is also used extensively in the model train Industry and probably lots of other applications

 

[Freenow54]

Why not replace the AC pump with a DC variable? OR depending on the size and bioload, make a Venturi skimmer? I'm in the process of building a Venturi skimmer for my heavy bio load 300g, to replace the venturi skimmer I am currently using.

Here's a link to what I have accomplished so far, with some tech info as well.
https://www.reef2reef.com/threads/skimmer-for-300g.1093029/

In the model train industry DCC or Pulse Width Modulation has been used for speed control for years. You could do it by maybe just buying a chip from the many suppliers.