are streams DC or AC?

[jnb]

Just want to know - are stream pumps AC or DC? This is from a certain thread...

Beyond what the others have stated, I just wanted to add that Tunze streams are not true DC pumps it turns out. They are merely low-voltage... but still AC. There has yet to be a mfg that has a true DC 'stream' style pump. I wish someone would too.

 

[hahnmeister]

I think Resun has a true DC prop driven powerhead... but its crappy from what I have heard...
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Aquabee has DC pumps, but they are just pumps, not prop-driven/stream style.

I am also shocked that there arent more DC pumps. I am considering trying a 7400/2 as a threadwheel pump though. It may not be DC, but I can still control the speed... and if it doesnt work out, I can just swap out the impeller. My question about the 7400/2 is... how large is the outlet/inlet. It appears to have a decent size volute, so the air capacity should be nice and high, but not so sure on the inlet/outlet.

But yeah... the lack of DC pumps has me shaking my head as well. In particular, with skimmer pumps, where normal AC pumps encounter all sorts of demons (startup sputter, extra heat, noise, speed/slip problems, power factor loss, etc) that DC pumps would be immune to.

 

[rvitko]

They are DC, the old design had an AC output transformer and the driver had a bridge rectifier that converted this to DC. New units (6101 for example) are straight DC input.

DC pumps are much more expensive unless they are direct drive, like a blower motor, with an electomagnetic armature.

The 7400/2 is 25m inlet and outlet. They don't work well as a needlewheel pump, we have tried it and they tend to choke on the air and rattle a lot.

 

[hahnmeister]

Yeah... direct drive is the way to go otherwise the electronics to control the motor can get pretty expensive. But the advantages of DC pumps for skimmers would seem to outweigh the expense, if that much at all. Considering how much good needlewheel pumps cost after the retrofit... and they still arent even all that great, converting a DC shaft driven pump would seem a better option.

 

[rvitko]

The problem is that our shaftless drive system doesn't handle air bubbles well, the impeller gets lifted out of position by air and rattles. I am also not sure how a needle wheel would run with changes in speed. I would think the ideal is a recirculating AC needle wheel pump being fed by a variable DC pump.

 

[hahnmeister]

The problem with AC pumps as needlewheels is that when the needlewheels get to a certain size (esp with 'threadwheel/meshwheel' types), they have startup problems, or 'sputter'. The larger needlewheels are desirable though because when the pumps are pumping the air/water mixture, they 'slip' because they were made for water, and their power factor drops. This causes them to heat up, get calcium buildups faster, etc. A pump that is otherwise efficient when pumping just water can take on completely bad characteristics as a needlewheel. The best way to counter this is with a larger needlewheel... the larger impeller making up for the easier spinning through air/water and helps bring that power factor back up. The problem is that before the pump takes in air, the needlewheel can be too large for the pump to handle, so it sputters out. DC pumps have a continuous and more constant torque curve as the pumps start, so they dont have this 'sputtering' problem. DC pumps also dont have a power factor like AC, so the efficiency drop when going from water to water plus air doesnt happen.

The speed is nothing but a good thing... most needlewheels spin at 1800rpm max. Being able to go up to 4000 or 5000 rpm really increases the output, and makes the bubbles even finer.

If nothing else, Im surprised that there isnt more out there for 'wave control' if nothing else. The tunzes are sweet, dont get me wrong, I love my 6100s, but after all this time that they have been out, there have been little other entries into this segment.