AC vs DC Pumps. Which Run Hotter?

[ca1ore]

And I am saying that if an AC pump is doing less work (gph) it is using less power.

I can confirm that the AC PanWorld 200 that I use as my main pump draws less than it's fully rated max of 290 watts. I run it against a significant amount of head pressure (about 15'). DC pumps I tried, regardless of whether more efficient or not, proved anemic against that pressure.

FWIW, I always run my AC (and DC where possible) pumps externally so that at least some of the heat generated ends up lost to the air rather than the tank water.

 

[1jwampler]

AC vs DC Pumps. Which Run Hotter?

Something people are forgetting and some mentioned about is power factor.

AC motors do not have a PF = 1. DC motors MAY have a PF close to 1.

Consider this, if you have a DC motor, you still have to convert AC to DC, which will reduce the PF. Unless you have Active PFC, you do not have a PF = 1, AC or DC.

What does this mean? In terms of energy savings, you save more on AC motors. Why? Our electric meters are designed to measure WATTS not Volt-Amps. Something drawing 100 va will be billed 70 W (estimated PF = 0.7 of AC motors)

Heating: You will heat less with AC motors. Same reason above. 70 W dissipated.

All of this is moot if you are calculating W/GPH. Thats is all about motor design, nothing to do with PF.

I am a EE but not in power electronics. I learned this stuff years back from a course in power electronics. Feel free to correct if I am wrong, but back up your statements.

Why would you think a brushless DC motor would not have a power factor? Every time you change poles there is no draw I.E. power factor. Lightly loaded inverters (aquarium DC pumps) often reach .6pf at 60hz sampling.

The above said not many people run their DC pump at full load (100%) which not only is the benefit of a DC pump without power factor but enhances the benefit with PF. This is exactly opposite with AC, once load is enough to eliminate freewheeling PF gets very close to 1 (I have never seen 1.0 with a single phase AC motor on a scope). This is why every sane application of AC motors (when considering power draw) uses 3 phase


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[1jwampler]

I can confirm that the AC PanWorld 200 that I use as my main pump draws less than it's fully rated max of 290 watts. I run it against a significant amount of head pressure (about 15'). DC pumps I tried, regardless of whether more efficient or not, proved anemic against that pressure.



FWIW, I always run my AC (and DC where possible) pumps externally so that at least some of the heat generated ends up lost to the air rather than the tank water.

Agreed I too run panworld for my WC system in the basement to the 1st floor, but not for efficiency of power but efficiency of plumbing I get over 20gpm out of 3/4 pipe, where I would need 1" maybe 1.25" to get the same from an L1, not to mention $450 vs $260 for a pump that runs less than 3 minutes per week


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[LXXero]

Where did you see that? I didn't see any of that information when I bought my SP4, and I don't find it on their web site or in the instructions/specifications.

it actually says it on their website too:

http://www.fluvalaquatics.com/ca/saltwater/aquarium-pumps/series/sp-series/

at the bottom it says


* SP4 and SP6 only

 

[sleepydoc]

I can confirm that the AC PanWorld 200 that I use as my main pump draws less than it's fully rated max of 290 watts. I run it against a significant amount of head pressure (about 15'). DC pumps I tried, regardless of whether more efficient or not, proved anemic against that pressure.

FWIW, I always run my AC (and DC where possible) pumps externally so that at least some of the heat generated ends up lost to the air rather than the tank water.

Agreed I too run panworld for my WC system in the basement to the 1st floor, but not for efficiency of power but efficiency of plumbing I get over 20gpm out of 3/4 pipe, where I would need 1" maybe 1.25" to get the same from an L1, not to mention $450 vs $260 for a pump that runs less than 3 minutes per week


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I think that has more to do with the pump design than the type of motor. If you tried to replace your panworld with a MagDrive 12 you wouldn't be very happy either.

Running pumps external will always heat the water less, but how much less depends on the design of the pump. The Panworlds are designed to be external and have a casing designed to dissipate heat. Many of the convertible pumps are not as efficient at dissipating the heat.

 

[sleepydoc]

it actually says it on their website too:

http://www.fluvalaquatics.com/ca/saltwater/aquarium-pumps/series/sp-series/

at the bottom it says


* SP4 and SP6 only

Thanks! I totally missed that page when I was looking (actually I had to look kind of hard to find it even when I knew it existed.)

 

[1jwampler]

I think that has more to do with the pump design than the type of motor. If you tried to replace your panworld with a MagDrive 12 you wouldn't be very happy either.

Running pumps external will always heat the water less, but how much less depends on the design of the pump. The Panworlds are designed to be external and have a casing designed to dissipate heat. Many of the convertible pumps are not as efficient at dissipating the heat.

Yep completely concur, the impeller design on an A/C pump (no freq drive) is much like a car without a transmission, you have to pick one gear ratio suited best for the application. Panworld/Blueline have a low ratio, which means for their power consumption, they don't have a lot of flow, but, when you put a load in front of them they have a distinctly higher torque multiplier against the pressure. If power efficiency is not your concern they are awesome with maintaining similar flow, through a manifold no matter the position of the valves.

 

[d0ughb0y]

my tank is now running at or slightly below ambient now with DC return pump instead of above ambient when I used AC pump.

Data collected by reeftronics.net

 

[LXXero]

my tank is now running at or slightly below ambient now with DC return pump instead of above ambient when I used AC pump.

what pumps are we comparing here out of curiousity?

Something people are forgetting and some mentioned about is power factor.

AC motors do not have a PF = 1. DC motors MAY have a PF close to 1.

Consider this, if you have a DC motor, you still have to convert AC to DC, which will reduce the PF. Unless you have Active PFC, you do not have a PF = 1, AC or DC.

What does this mean? In terms of energy savings, you save more on AC motors. Why? Our electric meters are designed to measure WATTS not Volt-Amps. Something drawing 100 va will be billed 70 W (estimated PF = 0.7 of AC motors)

Heating: You will heat less with AC motors. Same reason above. 70 W dissipated.

All of this is moot if you are calculating W/GPH. Thats is all about motor design, nothing to do with PF.

I am a EE but not in power electronics. I learned this stuff years back from a course in power electronics. Feel free to correct if I am wrong, but back up your statements.

i was pretty much trying to say similar earlier, since residential power isn't usually billed for PF, a pump with a PF of 0.6 is going to cost less to run than an equivalent pump at closer to 1.0PF at the same given VA. Commercial power is another story, since they often ARE charged for excess PF and then you have more reason to care, or go 3-phase, etc...and indeed it applies the same with the heat, all the more reason you do need to really look at wattage as opposed to just VA, since the PF is actual important when we're talking about AC motors.

however, i think another thing to consider is, a DC pump might have a PF closer to 1, but it also might draw less power at a given GPH - if that's the case, it may even out somewhat.....so you end up getting charged nearly the same, one is higher VA but lower PF and thus lower wattage that way, and one is lower VA, but higher PF, and using a more efficient DC drive, thus still lower wattage....that kind of thing.

My killawatt thinks the PF is 0.6 on my fluval sp4. I don't know if that's accurate or not, but it's saying 66 watts, and it's rated at 88w max, I tend to believe this is true.

 

[d0ughb0y]

what pumps are we comparing here out of curiousity?

from eheim 1262 to jebao dct 4000.

see
http://www.reefcentral.com/forums/showpost.php?p=24636068&postcount=21

I ran the eheim in a bucket full of fresh water overnight, this time indoors, and the water was quite warm, I'd say at least 85F maybe higher. The pump is running unrestricted though, running at max power.

I'm going to switch my skimmer to one with dc pump as well.

I am sold on dc pumps, so currently working on a diy dc pump controller for BLDC pumps like crossflow/gyre/dct/dcs pumps.

I have analyzed the jebao dc controller circuit and imho, it is quite well designed. I monitored the signal on an oscilloscope and logic analyzer and the waveforms are very clean.

FWIW, I have used the eheim for 8 years, but I would not go back to using AC pump.

 

[LXXero]

from eheim 1262 to jebao dct 4000.

see
http://www.reefcentral.com/forums/showpost.php?p=24636068&postcount=21

I ran the eheim in a bucket full of fresh water overnight, this time indoors, and the water was quite warm, I'd say at least 85F maybe higher. The pump is running unrestricted though, running at max power.

I'm going to switch my skimmer to one with dc pump as well.

I am sold on dc pumps, so currently working on a diy dc pump controller for BLDC pumps like crossflow/gyre/dct/dcs pumps.

I have analyzed the jebao dc controller circuit and imho, it is quite well designed. I monitored the signal on an oscilloscope and logic analyzer and the waveforms are very clean.

FWIW, I have used the eheim for 8 years, but I would not go back to using AC pump.

I think the 1262 is one of those pumps where it's probably putting out more heat than it has to for most loads people use it for - basically, it's a pump with a lot of torque and can handle more head @ a given GPH than some other pumps rated around 900GPH but if you're not taking advantage of that extra head, it's probably just excess heat to water. that's my guess anyway. it's always been considered a high wattage pump for the GPH it pushes. basically just saying, don't knock all AC pumps as running hot! I have a feeling the fluval SP series would put out a lot less heat, anyway!

i have been following your one thread about those jebao controller mods, definitely got me interested, those types of mods are definitely within my ability, have done a fair amount of surface mount rework myself. I was actually close to getting one of the jebao/waveline pumps for this tank i'm building now, but I opted for the fluval sp4 as a reliable AC pump and figured I'd eventually retire it as a backup pump if I ever get a DC pump. I'm kind of holding out to see if neptune labs ever puts out their COR pump or whatever. i still just hear too many failure stories with DC pumps. at least you still probably have a 1262 around as a backup pump!

BTW, have you managed to determine the PF on your jebao pumps? Would be interesting, given we're having a bit of discussion of Watts vs VA and PF calculations.

 

[alton]

from eheim 1262 to jebao dct 4000.

see
http://www.reefcentral.com/forums/showpost.php?p=24636068&postcount=21

I ran the eheim in a bucket full of fresh water overnight, this time indoors, and the water was quite warm, I'd say at least 85F maybe higher. The pump is running unrestricted though, running at max power.

I'm going to switch my skimmer to one with dc pump as well.

I am sold on dc pumps, so currently working on a diy dc pump controller for BLDC pumps like crossflow/gyre/dct/dcs pumps.

I have analyzed the jebao dc controller circuit and imho, it is quite well designed. I monitored the signal on an oscilloscope and logic analyzer and the waveforms are very clean.

FWIW, I have used the eheim for 8 years, but I would not go back to using AC pump.

I have never used an Eheim, but I can tell you with Mag pumps a eight year old mag pump will use twice as much energy as new mag pump and create twice as much heat because of it. I had the issue with one on my skimmer. Wait 8 years and come back to let us know how the DC pump is doing on energy usage plus if it is still pumping the same volume?

 

[1jwampler]

what pumps are we comparing here out of curiousity?




i was pretty much trying to say similar earlier, since residential power isn't usually billed for PF, a pump with a PF of 0.6 is going to cost less to run than an equivalent pump at closer to 1.0PF at the same given VA. Commercial power is another story, since they often ARE charged for excess PF and then you have more reason to care, or go 3-phase, etc...and indeed it applies the same with the heat, all the more reason you do need to really look at wattage as opposed to just VA, since the PF is actual important when we're talking about AC motors.

however, i think another thing to consider is, a DC pump might have a PF closer to 1, but it also might draw less power at a given GPH - if that's the case, it may even out somewhat.....so you end up getting charged nearly the same, one is higher VA but lower PF and thus lower wattage that way, and one is lower VA, but higher PF, and using a more efficient DC drive, thus still lower wattage....that kind of thing.

My killawatt thinks the PF is 0.6 on my fluval sp4. I don't know if that's accurate or not, but it's saying 66 watts, and it's rated at 88w max, I tend to believe this is true.

You are billed for watts which is v/a over time PF is the time. I.E. 60 cycles per second, V x A = watts if all 60hz is the same "A". PF is more complex than just time, but, easy to figure is the % of time at highest A. This is why the SP4 says 88 watts but draws 1 amp max or 120va, this is a PF of .73. Utility will bill for 88 watts for 120v/a at PF .73. If your PF were 1, this would be 120 watts.

As I brought out in my prior post to the "EE", a DC brush motor would have a PF of 1, but, an aquarium pump, is driven by a controller and pulsed just like an AC motor and also has a PF. This is why they are more efficient, even with the power supply overhead. RPM is driven for the flow, not by utility power frequency. So at a given output, the DC pump controller pulses just like AC, but unlike AC, it's frequency changes to meet the setting without a restrictor, like a valve.

 

[ksed]

Correct and understood. Basically when a pump is not driven at 100%, (in a AC application reduced with a valve) the DC is more efficient, but lets say we are running the pumps at full capacity the energy saving is minimal at best?

You are billed for watts which is v/a over time PF is the time. I.E. 60 cycles per second, V x A = watts if all 60hz is the same "A". PF is more complex than just time, but, easy to figure is the % of time at highest A. This is why the SP4 says 88 watts but draws 1 amp max or 120va, this is a PF of .73. Utility will bill for 88 watts for 120v/a at PF .73. If your PF were 1, this would be 120 watts.

As I brought out in my prior post to the "EE", a DC brush motor would have a PF of 1, but, an aquarium pump, is driven by a controller and pulsed just like an AC motor and also has a PF. This is why they are more efficient, even with the power supply overhead. RPM is driven for the flow, not by utility power frequency. So at a given output, the DC pump controller pulses just like AC, but unlike AC, it's frequency changes to meet the setting without a restrictor, like a valve.

 

[1jwampler]

Correct and understood. Basically when a pump is not driven at 100%, (in a AC application reduced with a valve) the DC is more efficient, but lets say we are running the pumps at full capacity the energy saving is minimal at best?

Running at 100% assuming same quality, impeller, etc, the A/C pump should be more efficient due to the parasitic loss in the inverter (DC power supply) and controller.

For example Blueline/PanWorld impellers have a smaller bite to maintain flow at high head pressure, most tanks are not 12-20 ft above the sump. So, kind of like running your car in 2nd gear down the highway at 70mph, going up a hill won't require much pressure on the gas peddle, but, your tank will empty much faster than shifting to 6th. The reason I bring this up, is all of the DC pumps I'm familiar with are geared toward flow, not pressure, which is the resistance to flow.

 

[ksed]

Absolutely agreed. A lot of people are misunderstood of the benefits of DC.
Take a look at the Ecotech thread . They would like to run a DC pump at 100%. I mention in there that if you don't have a purpose of reduced flow just use an efficient AC pump.
http://www.reefcentral.com/forums/showthread.php?t=2515313&page=39

Running at 100% assuming same quality, impeller, etc, the A/C pump should be more efficient due to the parasitic loss in the inverter (DC power supply) and controller.

For example Blueline/PanWorld impellers have a smaller bite to maintain flow at high head pressure, most tanks are not 12-20 ft above the sump. So, kind of like running your car in 2nd gear down the highway at 70mph, going up a hill won't require much pressure on the gas peddle, but, your tank will empty much faster than shifting to 6th. The reason I bring this up, is all of the DC pumps I'm familiar with are geared toward flow, not pressure, which is the resistance to flow.

 

[1jwampler]

Absolutely agreed. A lot of people are misunderstood of the benefits of DC.

Take a look at the Ecotech thread . They would like to run a DC pump at 100%. I mention in there that if you don't have a purpose of reduced flow just use an efficient AC pump.

http://www.reefcentral.com/forums/showthread.php?t=2515313&page=39

IMHO why not overbuy for current needs and use DC to adjust down, you get the immediate energy benefits of a smaller pump and the ability to adjust flow up for:
1.) A bigger tank
2.) Another tank on the same sump
3.) More accessories like reactors or algae scrubbers
4.) 20x tank size through the sock(s) after maintenance.

And I'm sure lots of other stuff I didn't write.

I also have what is likely a false hope that a 3100gph pump running at half speed/power may last twice as long


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[gcarroll]

IMHO why not overbuy for current needs and use DC to adjust down, you get the immediate energy benefits of a smaller pump and the ability to adjust flow up for:
1.) A bigger tank
2.) Another tank on the same sump
3.) More accessories like reactors or algae scrubbers
4.) 20x tank size through the sock(s) after maintenance.

And I'm sure lots of other stuff I didn't write.

I also have what is likely a false hope that a 3100gph pump running at half speed/power may last twice as long


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Twice as long? What's that, a couple years or so?

 

[LXXero]

Twice as long? What's that, a couple years or so?

haha ouch.

yeah that's the other thing with DC pumps, many are too new to have a proven track record. and there are failures (even the ecotech thread has a big thing going on right now about L1's overheating and crapping out)

not that AC pumps don't fail either but at least many have been around long enough now that we know the difference.

 

[d0ughb0y]

Running at 100% assuming same quality, impeller, etc, the A/C pump should be more efficient due to the parasitic loss in the inverter (DC power supply) and controller.

FWIW, the MOSFETS used in DC motor driver typically have RDSon way below 100 milliohms. For my 50watt pump, its 30 mohm. x2 is still less than 0.1 ohms. running at 1.5a, the heat loss is only 150 milliwatts, negligible compared to total power. I have run the DC pump full speed and the FETs were cool to the touch. Again, based on empirical data and not just a conjecture.