Lighting Variac (auto-transformers) vs Frequency regulator (VFD) questions

[Groff]

Hey folk,

2 part question. Have no where else to ask in this forum, so I hope the electrical guru' here might shed a light (pun intended).

- I've seen DIY LED dimmers in a local craiglist sort of website. Are these safe to use? What do I need to know about these?

My main question though, is the following. Everyone knows (or should) there are two type of speed controls for fans and motors. There are the voltage regulators and frequency regulators (VFD).

Freq regulators are cheap and lightweight, but really suck as they create loads of hum and shorten the life of your fans and motors - for lights I have no clue. Variac are much more expensive and heavy, but reduce the voltage without affecting the equipment. Absolute zero hum, and no distress to the motor. This is how I effectively have an almost zero noise exhaust. I put an extremely oversized 10" filter, fan and ducting on a variac at 1/5th the power and I still have negative pressure, but virtually no noise.

I suspect that exhaust fans with variable speed control or thermostat use VFD due to their pricing and no apparent added weight. Anyone care to confirm or deny this?

My question is the following. Is it safe to run variac in series? Lets say

Mains -> Variac [HASHTAG]#1[/HASHTAG] -> Variac [HASHTAG]#2[/HASHTAG] -> Exhaust fan

What about VFD's? If an exhaust fan uses VFD to reduce speed, can I still use a Variac before it?

Mains -> Variac -> fan win VFD

I'm asking because I have a pretty hefty variac and I want to connect a second fan and filter to the room. The idea would be to run a sealed room, and also have a backup exhaust. So fan#1 would pump back into the room while filtering smell, while fan#2 would exhaust out the room but only kick in if temperature rises above my set mark.

 

[BigSm0]

Hate to see a thread go unanswered. The sad part is there has probably been a thousand hits and not a single reply.

Sorry Groff I can't help here.

 

[Groff]

Hate to see a thread go unanswered. The sad part is there has probably been a thousand hits and not a single reply.

Sorry Groff I can't help here.

Yeah, I figured it's not an easy question .. Thanks anyway @BigSm0

 

[BigSm0]

I have bought a few fan speed controllers and they only work partially for a week or so then it's full on or full off. I'm sure it's the non variable speed fan. I just gave up lol.

 

[Groff]

I have bought a few fan speed controllers and they only work partially for a week or so then it's full on or full off. I'm sure it's the non variable speed fan. I just gave up lol.

Yeah, I went cheap and bought a speed controller with thermostat (and a nice probe to set over the canopy) … you set minimum and max speed, when temp go over and above, the fan kicks into the max speed. Then there is a medium speed, and when temps go low, the fan would go into minimum speed.

Sucks big time, and the hum it produced was soooo loud I couldn't bare the though of a neighbour knocking at my door. After some research I ordered a ready-made variac speed controller. You set it manually and it just goes fantastic, zero hum and zero damage to the motor. I've had it on for 3 years now on 1/5th speed … it has a 5 way position switch… Virtually silent and still negative pressure. Possibly the single best investment I made, supersized fan, filter and variac.

 

[2Stoned2Care]

Yeah, I went cheap and bought a speed controller with thermostat (and a nice probe to set over the canopy) … you set minimum and max speed, when temp go over and above, the fan kicks into the max speed. Then there is a medium speed, and when temps go low, the fan would go into minimum speed.

Sucks big time, and the hum it produced was soooo loud I couldn't bare the though of a neighbour knocking at my door. After some research I ordered a ready-made variac speed controller. You set it manually and it just goes fantastic, zero hum and zero damage to the motor. I've had it on for 3 years now on 1/5th speed … it has a 5 way position switch… Virtually silent and still negative pressure. Possibly the single best investment I made, supersized fan, filter and variac.

You got a link @Groff for the variac bro ?.i bought a plug in fan speed controller but you are right the hum drives me mad so i want something alot better than that

 

[BigSm0]

You got a link @Groff for the variac bro ?.i bought a plug in fan speed controller but you are right the hum drives me mad so i want something alot better than that

Stand in your tent and when you get warm unzip the door just a little and blow as hard as you can.

 

[Groff]

You got a link @Groff for the variac bro ?.i bought a plug in fan speed controller but you are right the hum drives me mad so i want something alot better than that

Sure, this basically what I have. You can choose the right one for your fan(s) from the drop down menu.

http://www.ebay.co.uk/itm/130591386...me=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649

Stand in your tent and when you get warm unzip the door just a little and blow as hard as you can.

hahahah, yeah, the would be the ultimate DIY

 

[dankle]

You can still use a variac before a fan with a built in speed controller. I would bet you can also use two variacs in tandem, as they seem to mecheanically throttle the flow of electricity, so setting both variacs to 60V would likely give you 30V output.

Small variacs are avaialable for 35-40 dollars on ebay and worth their weight in copper.

 

[wayward1]

@Groff or anyone. Do you know if that variac will work with the td 350/125? This area of hardware seems to confuse a lot of people. Me included!