Benefits of DC pumps

[mussel and hate]

Ok Bean animal, you win. The Korallia low voltage AC pump doesn't really exist and therefore isn't within the scope of the OPs question.

Well played...

 

[dread240]

It is done all the time... That is how many VFDs work.

The VFD takes an ac Voltage at 60Hz, rectifies it, then feed it to an inverter to create a sinewave at the desired frequency.

You have it somewhat backwards

There are several types of AC motors, but in general using resistance to speed control any of them (Lets ignore universal motors) is not effective due to severe loss of torque causing phase slip and therefore heating issues. That said, some small desk fans, blower motor, etc use an autotransformer, or a triac and a resistor to do just that (cause loss of torque and phase slip) to give some degree of speed control.

A universal motor (a motor with an armature and brushes) is a different beast... but lets ignore it simply because it has no place in our hobby.

Resistors:
Large "variable speed" DC "traction" motors in industrial applications (to power underground track equipment in coal mines, street cars, rail locomotives, etc) use huge banks of resistors to vary speed. The speed controller drops in or pulls out banks of resistors to change the speed by varying resistance in series with the motor. The resistor banks are often used in dynamic braking systems (both regenerative and rheostatic).

In any case...

I have been using a few DC pumps for several months. While the motor itself may be a bit more efficient, the losses in the power supply abd speed controller (switch mode in my case) pretty much cancel the savings. That said, I am happy with the pumps and would rather have the wasted heat in the controller and PSU instead of the field windings, core and magnets.

and to show no bias, bean most of the information posted in here is in regard to brush driven motors. Resistance plays no factor at all in an inductive motor (like our pumps where we excite a stator around a magnet and the magnet just floats in the middle with no external excitation) The only way to vary the speed or control on those is to alter the frequency to the stator (which is where the VFD's come in like you mentioned)

I only wanted to point this out though to avoid somebody thinking they can go get a dimmer switch or something and run their 120v ac korallia through it lol. This stuff confuses alot of people, even myself many many times :lolspin:

 

[dread240]

I'm confused, fairly sure i posted this before the other post but mussel... if we are nitpicking even certain pumps, a DC pump is still safer then an AC pump, even if we're considering 12v

12vdc = 12 volts, that's all there is, nothing hidden
12vac (RMS which is what everything is rated for) = 17v peak which really leaves you with a 34v peak to peak sine wave. This has other underlying problems as well

I'll also quote a journal published by the department of physics from university of illinois

Another interesting point to consider is that in addition to acting like a resistor, the epidermis acts like a capacitor if placed in contact with a piece of metal (the underlying tissue is like one plate of a capacitor and the metal surface is like the other plate - the dry epidermis is the less-conductive material or "dielectric" in between) . In cases of electrocution by a DC voltage source, this capacitive property has little importance. But if the electrocution is by an AC source, the epidermis's natural resistance is "shorted out", allowing the current to bypass that part of the body's resistance and making the body's total resistance much lower.

-Tamara


Reference: R. Fish & L. Geddes, Medical and Bioengineering Aspects of Electrical Injuries, c2003 Lawyers & Judges Publishing Company, Inc.

Basically with the polarity and intensity never staying consistent with AC voltage, you cannot build up the protection barrier even against lower source ac voltages. Think of a metal oxide varistor breaking down and then trying to reoxidize 50-80 times a second... it's not going to happen, as the time period isn't long enough to provide full protection.

Totally unrelated to all of that though, and just food for thought with hybrids and various other products in the real world these days, don't confuse any of this with what I fear the most... which is high voltage DC systems. It will lock you into it and kill you in seconds. These hybrid's on the road with their high voltage battery packs I can really see taking a few lives over the next few years when uneducated and uninformed people start working on these things :-\

 

[ksed]

I couldn't really say if there are higher voltage DC pumps for the hobby though I'd be surprised if there were. I was just dispelling myths regarding AC vs DC. There are some low voltage AC pumps though. The Koralia controllable are 12V AC for instance.

Brushless motors possess superior longevity and a brushless DC motor is just a brushless AC motor with an inverter and rectifier. Not all DC motors are brushless btw.

If you're using AC power from your wall plug an AC motor will be more efficient. Conversion to DC requires you to give up some electricity as heat. If you're running your DC pump off of solar panels and batteries then that would be pretty efficient.

Are all or majority of Brushless DC motors a AC motor with an inverter and rectifier?

 

[ksed]

I think I found the answer: Basically a brushless motor is a sinusoidal motor or hence AC motor, but is able to accept DC or AC current to run the motor.



AC vs DC Brushless Servo Motor
By John Mazurkiewicz,
Baldor Electric
Brushless motors are similar to AC motors since a moving magnet field causes rotor movement. Brushless
motors are also similar to PM DC motors since they have predicable linear characteristics.
Is this why the brushless is sometimes called AC brushless and sometimes called DC brushless? It is the
method of driving or powering the motor from which the name AC or DC is derived. The method of driving
the motor will result in different effects (i.e. different torque delivered even from the same motor!).
Torque developed
Torque developed by a brushless motor depends on the control technology used. A simplified way to
determine the type of control is to look at the feedback scheme. DC uses Hall sensors for feedback,
whereas AC uses resolver or encoder for feedback. Each of these control methods has its strong points
and advantages, which have to be reviewed to determine which is best for an application.
By applying a constant current to one winding of a three phase motor, a torque is generated. Since the
winding distribution is sinusoidal, torque is not distributed evenly as the shaft is rotated through 360
degrees. As shown in Figure 1, the resulting torque generated is a function of the shaft angular position.
Thus, current into a single winding generates a torque that is described by:

 

[barjam]

I don't know about reef hobby pumps but brushless DC motors for rc vehicles work via a speed controller which more or less is a computer circuit that senses motor position and turns the magnets on/off super fast to control the speed.

On a oscilloscope I suppose this would look like an ac signal but wouldn't reverse polarity as far as I know like AC does.

 

[reefer91]

Bean, any word from the pipeline about external control in the near future? This is the biggest potential advantage I believe of these pumps, return and skimmer applications.

 

[BeanAnimal]

It is my understanding that the new pump may have an external control input, but I am not sure what the topology is going to be.

 

[reefer91]

Thanks man! I will be patiently waiting haha.

 

[alton]

If you listen to Thomas Edison, DC was much safer than AC, remember the electric chair used AC not DC. George Westinghouse almost lost his bid to push AC because of the electric chair. Anytime you can get voltage below 50 volts it helps and since most DC pumps in the aquarium industry do this, it becomes much safer.

 

[BeanAnimal]

Thomas Edison was a well documented cheat, thief, liar and crook that often took credit for the work of others and lied about the dangers (and benefits) of both alternating and direct current. His end game was to win electrification contracts using his DC current power grid by slandering the acv system developed and sold by George Westinghouse... That reality in itself does not make either AC or DC safer

 

[NeilFox]

Thomas Edison was a well documented cheat, thief, liar and crook that often took credit for the work of others and lied about the dangers (and benefits) of both alternating and direct current. His end game was to win electrification contracts using his DC current power grid by slandering the acv system developed and sold by George Westinghouse... That reality in itself does not make either AC or DC safer

Very true Bean. Edison used to go around electrocuting Elephants and the like. Edison liked to use the term "westinghousing". Edison actually designed the first electric chair to Westinghouse a condemned prisoner. By all accounts it was a gruesome affair that took nearly an hour. Edison basically quit the electricy business after that due to the bad press. Many electric chairs used dc current. Both will kill with equal efficiency.

 

[cherubfish pair]

I got a 6095 tunze from the wife for christmas, and I love it. There's a few differences though that aren't mentioned on here

AC pumps have a brake feature, and are also prone to starting in reverse more common. This means cycling them fast for detritus removal or that pulsing flow to make your corals REALLY sway will shorten the life of the pump considerably.

While it is true what atreis said about the safety of ac blowing you back, the other side of the equation is the voltage behind it. My pump runs at a max of 24VDC, compared to my 120v AC going to the korallias that are already in there. Your skin acts as an insulator against voltage, and it's generally accepted that anything over 50v can overcome your skins insulation properties. DC current also only flows in one direction, it's ground to complete the source (not any path to ground like an ac pump) and considering each pump has it's own + and - leads right next to each other, chance of amperage to you is slim to none unless the cable is shorted and you stick your hand in. That's not the case with ac powered objects in the tank which can ground through you to the floor and subsequently to earth.

There's other benefits to this new pump though aside from that, but you actually get that on all the nanostream pumps now. It's the same footprint as my korallia 1400 and 750, however it's mounting options and angles are vastly superior (I used to think the korallia's gave good aiming where you want to put the flow, and I was totally wrong once I saw a tunze)

The controllability is a big point though. You simply can't make ac pumps do this type of work without some SERIOUSLY expensive hardware behind it. I priced VFD's to put on ac pumps, and it just wasn't cost effective by any means

I got a Tunze 6095 for Christmas also. Would switching the pump on/off with the controller shorten the lifespan less than ramping up and down, "pulsing"?

 

[alton]

Thomas Edison was a well documented cheat, thief, liar and crook that often took credit for the work of others and lied about the dangers (and benefits) of both alternating and direct current. His end game was to win electrification contracts using his DC current power grid by slandering the acv system developed and sold by George Westinghouse... That reality in itself does not make either AC or DC safer

I just thought it was funny that over a hundred years later we can still brew up an arguement of which is better or safer Ac or DC

 

[pfoxgrover]

Steve,

I use both the DC-10000 and the DC-5000. I have been happy with both, but ran into some problems with the DC-10000. Waiting for it to be replaced right now.

To answer your question: The spec power:flow ratio are derived from power measured AFTER the controller and therefore do not take into account the losses in the power supply or driver. When those losses are accounted for that 98W is closer to 130W The pump is still great. It has a speed control, feed timer, etc.


Hope that helps.

What went wrong with the DC-10000?
I noticed the difference in wattage between the DC-10000 and the Water Blaster HY-10000. Do you think the water blaster has a more honest rating of their wattage or do you think it really uses 30 plus more watts?

Thanks,
-Paul

 

[Mark Elliott]

Guys, (apologies to any ladies here) I have a couple of Eheims in my sump as return pumps that probably need replacing. I use two smaller pumps so I don't worry too much if one fails.

For about the same money I could use two waveline dc5000. I'd run them at less than 100% but variable output isn't really an issue for a return pump.

So, assuming the wavelines will use less electricity does anyone have a view as to reliability ease of maintenance, stuff like that? I'd hope they'd run cooler and less calcium carbonate would precipitate on the moving parts but does anybody actually know?

Thanks

Mark

 

[mrcoberg]

Speed wave 1320ghp DC pump

Speed wave 1320ghp DC pump

I have went thru 2 transformers now, One on a Jebco and one on a Speed wave. Pump . They use the same controller and transformer. Does anyone know where to buy a factory made transformer 120 VAC / 24VDC for these pumps???

 

[pfoxgrover]

I have gone through a ton of power supplies for Jabao pumps. For my Dct pump it helped to not run them on the highest seeing. Fish street sells them for $15 to $25 dollars and the shipping time is pretty good.you may have to ask them for the part if you can't find it on the site.

 

[outssider]

ebay sells 24v power supplies up to 10 amp....10 amp should be plenty....

http://www.ebay.com/itm/AC-100V-240...hash=item4d40a0cc0c:m:mZ4Ble8qza4zeAF1uBXikxg

 

[h3dgehog]

I decided to use a DC return pump for one big reason....

I am not the most diligent water changer who tests the NSW before making the change. So the parameters of the NSW and display tank water can sometimes differ. By having a DC return pump and changing water via sump, I can ease the NSW from the sump into the display tank.