soft start for powerhead

[clintyiu]

I read in the other forum that you cannot soft start a powerhead with cheapo capacitor/voltage reduction etc.

So I searched and searched for a soft start module that will work with a single phase shaded pole motor. The only circuit I can find will work with single phase motors but they didn't say whether they can handle shaded pole systems....and they cost a fortune.

If what I read is true then how do those commercial wavemakers provide a soft start feature. Has anyone tinkered with a simple capacitor soft start for their powerheads?

[titus]

Hello,

I wonder how does ramping the supplied voltage from zero to the rated level would work.

[DJ88]

I have been looking into this myself and the voltage is not what is variable. That is why wavemakers are so frigging expensive. They ramp the current up and down for a soft start. Not voltage. I'll find a thread on RC where I was told this.

[titus]

Hello,

<ul type="square"> I wonder what happens when we feed it V(t) = 120 * sin(60 * t) I can only think of changing current by changing the inline resistance, or supplied voltage. Man this is like back to the area where we think about current sourcing amplifiers, tubes or transistors?[/list:u:31a2577a24]

[reefburnaby]

Hi,

I am being a bit picky, but isn't it V(t) = sqrt(2) * 120 * sin(2 * pi * 60 * t) ?

As for soft starting, motors look like inductors and during the initial power up...it looks like a dead short. So, it needs to time energize and create a back emf. Usually, the electromagnetic strength is proportional to the AC current. So, during the inital power surge, the electromagnets are pulling and pushing the stator very hard -- hence the rough start. Once the back emf kicks in, less current flows through the electromagnets and the motor returns to its normal operating point.

So, if you can control the current (i.e. slow down the in rush current), then the motor will start up with less stress. You can use voltage to control the in rush, but the circuit is even more complex. The voltage envelope needs a x^2 like shape to work...rather than x like shape for current control. Another voltage method is by varying the frequency of the AC power supply (VFD), but that's even more complex.

Hope that helps.

- Victor.

[titus]

Hello,

Sorry Victor,you are right I forgot about the peak to rms ratio and I ignored the 2*pi part.

Hey why does it have to be V(t) = t^2 shape instead of V(t) = t? If it is V(t) = t^2, we can do use an op-amp integrator to drive a transistor.

[DJ88]

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quoteHey why does it have to be V(t) = t^2 shape instead of V(t) = t? If it is V(t) = t^2, we can do use an op-amp integrator to drive a transistor.

I Kind of see where you are going Titus. Victor.. why? hmm? Using some form of integrator may work quite nicely. Nothing fancy. I hope I am reading this right.

hmm time to go do some more reading.

If this were possible for a reasonable price you could set up a wave making system where you can vary the output of the PH's could you not? nothing massive but a bit. Great option for a wave maker. Don't shut the PH's off but just slow em down so to speak. As long as you are over the EMF threshold they will spin.

Another application could be using MAG's for closed loop systems. Like what I want to do. Instead of getting the chatter on start up with using a plain old timer, hook them into a "wave maker" of sorts, with an integrator for start up, and then let the switching unit start and stop the pumps for random water flow on a larger scale in the tank.

Anyone agree? Or am I in left field??????

[titus]

Hello,

Well I don't know why it has to be a square function but nevertheless integration would give you a rising and decaying function with time constants that you can easily adjust.

[reefburnaby]

Hi,

Rather than digging in to the equations, lets get some trends.

1) Using a Step response to turn on the power supply. In this case, the current will overshoot and have exponential decay function from its peak current.

2) Using a Ramp response. In this case, the current will be a sort of a step response (not quite...but close). This is what a capacitor or a RC response will do -- which we know that it doesn't work very well.

3) Using a x^2 like/sin function. In this case, the current will change more linearily with time. I am just describing the general shape, but this is what I was referring to as a x^2 function.

Either that...or my wires are really crossed from writing too much.

- Victor.

[ 22 February 2002: Message edited by: reefburnaby ]

[ 22 February 2002: Message edited by: reefburnaby ]</p>

[titus]

Hello,

How about this:
V(t) = 1.414 * 120 * (1 - exp(-t/TC)) * sin(2*pi*60*t)?

This is something we all can do with an integrator-and-dump circuit preceding a transistor current driver. We'll let Darren to actually put it together. images/smiles/icon_biggrin.gif

[DJ88]

Oh titus.. You smart a$$.. lol

I fix your mistakes.. images/smiles/icon_wink.gif kidding.. how about we three get together and figure something out?

I'd love to.. In all honesty the level at which I am learning at in class right now is well belows what I have already studied. I think I might actually get soething out of this.

I should have taken exemptions.. Grrr..

[Gordoe]

If we all agree that powerheads are a shaded pole motor(not sure??) then here is a website that suggests using choke coils.
Universal/Shaded Pole Motors (http://www.tpub.com/ceb/109.htm)

Any input would be appreciated.

gord

[Troy F]

Well you guys are way over my head but from an actual observation when using one of the currently available "high end" wavemakers, there is no such thing as "soft start". Personally, I think that they need the power surge to get them going and without it they'd need to be extremely clean or they'd never get going. My opinion is that the powerheads we use are cheaply made and no amount of fiddling is going to make them quiet and long lasting while doing rapid start and stop applications.

I don't know what cost the components are for the project you guys are thinking about but you may want to look into the Tunze powerheads. My understanding is that they are rampable, put out huge flow rates and are air cooled.

[titus]

Hello Darren,

Sometime after my thesis is good. Whenever that is.

Gord,

I try not to read the article and get too involved in this. But my guess of the choke is just a simple inductor to prevent rapid current spike due to a step function for the voltage input. Yes it'd work but won't provide the level of sophistication of using a controlled current driver.

Troy,

Yeah just as I thought what the commercial hobbyist wavemakers are. But I wonder what the public aquariums use. Isn't that why we started this thread? Oh well it was a while ago so I forgot about it.

Hey I keep hearing these Tunze stuff from time to time. It always seem like they have very neat design. But you are right, powerhead are cheap. I was discussing with John and J&L about the reliability of Eheim pumps, which is supposed to be the best by the way, and me, him, and Precison Marine all agree that there are problems with these guys.

[clintyiu]

It's getting a little too technical for me...
I agree that the powerheads are cheap etc... But everytime the pump starts up the fish in the tank jolts because of the abrupt noise. This is especially bad with bigger powerheads like the aquaclear 5000.

Oh well....maybe I should just get the Redsea wavemaker.

[Aquattro]

Clint, I think you'll find the same problem using the RedSea. It will make your hagen power heads clunk.

[Troy F]

I agree with Brad, I think I have the RedSea Wavemaster Pro. It made both Hagen and Maxijet rattle pretty good. My fish didn't seem bothered but then I never bothered to ask them.

Recently Richard Harker was talking about how it is much more of a concern to have enough flow rather than variation. If you can point the flow of the powerheads so that they hit one another and bounce of the glass creating chaotic flow you'll be much better than intermittent random flow. His words (more or less) not mine, sounds good though smile.gif .

[Aquattro]

Troy, so far I find the Maxijets are pretty silent. They're new though, so that could change in time.

[Reefmaster]

troy
i've come across a couple articles that have said something similar, and i completely agree. i think over the next while we are going to see a huge change in thinking about tank circulation and a trend where rather than three or four large ph's we are going to see 8 or 10 smaller ones which overall will generate better circulation.
shane

[Silverfish]

Hey guys, I am running four MJ's in my 55g and two in Meighans 15g on a Wavemaster Pro. They were loud when I first fired them all up and chattered and stuff but seemed to settle in after a few weeks and became quiet, just a click when they came on. As they became all clogged up with coraline and crap they got loud again, some more than others tho. I might try giving the loudest ones the old "couple o days" vinegar dip to see if that makes a difference.

Troy, I had a conversation a while back with Canadian about skipping the wavemaker and maybe running powerheads two on one side of the tank, two on the other side and simulating a tidal surge that lasts for about six hours. Kind of like what occurs on the reef maybe. I know that after seeing Superfudge's awesome coral growth without the random switching powerheads, just lots of flow, gave me some food for thought.

It would be nice to get rid of the constant noise from these powerheads, but then I would feel bad about not using this pesky expensive wavemaker!!

[clintyiu]

Bruce,

That's exactly what I want to do. Place one powerhead on one side and the second on the other. They will be plumbed so that the outflow comes from the front bottom corners of the tank.

Thanks for letting me know that the redsea pro doesn't really have a soft start. That's is the only reason I would get it. But how can they advertise that it does if it doesn't???

There are variable timer kits that will do the trick.. http://www.rpelectronics.com/English/Content/Items/UK191.asp
All you need here is a cheapo 9/12v powersupply (adaptor), DTDP relay and a nice little box.

clint