why the DC pump current x voltage doesnt equal to power ??
- Thread starter andydarwin
- Start date
A mystery for sure. I am thinking factory recommends 200w solar panel to drive the pump. Listed as a 'solar' water pump.
I don't see a manual so it would probably be a question for the factory.
https://www.thermalsolarwaterheater...-system-lspi-series-dc-brush-plastic-impeller
I don't see a manual so it would probably be a question for the factory.
https://www.thermalsolarwaterheater...-system-lspi-series-dc-brush-plastic-impeller
sunshine_eggo
Victron's little biatch
LOL...
"FORBID WORKING EMPTY"
"PAY MORE ATTENTION TO (+)&(-)"
"ALL YOUR BASES ARE BELONG TO US!"
Likely a garbage pump with BS ratings.
"FORBID WORKING EMPTY"
"PAY MORE ATTENTION TO (+)&(-)"
"ALL YOUR BASES ARE BELONG TO US!"
Likely a garbage pump with BS ratings.
OzSolar
Whatever you did, that's what you planned.
200 watts of recommended solar makes as much sense as anything.
I've got several solar pumps. Even though thier manuals are written in "chinglish" I've still been able to gather that thier voltage rating has a larger window than thier nominal rating.
Rednecktek
Expert Newbie
It's not just DC motors, I've got a drill press with a 1/4hp motor calling for 6.5a @ 120v...
Well pumps are notorious for this. A 1hp pump calls for 11.5a @ 240v...
Motors all seem to use new math...
Well pumps are notorious for this. A 1hp pump calls for 11.5a @ 240v...
Motors all seem to use new math...
OffGridForGood
Catch, make or grow everything you can.
As was discussed on a recent thread: "just ignore the Hp rating part" = then it all makes sense again. 
BarracudaBob
Harvesting free photons from clean fusion
Resistance = heat = lost power
I'm wondering if those dc motors are actually AC stepper style motors or inductive motors running off an inverter/BDC driver circuit...
It would explain the discrepancy between the 'dc figures' and the wattage (or more accurately the VA)...
Inductive motors don't have their 'voltage curve' (sinewave) and their current curve in time with each other (in AC this is known as the power factor) and this is why the watts doesn't always equal the VA figure in some devices- inductive loads have the curves 90 degrees out of phase- it is this that causes the simple 'volts times amps' to not be as simple as it seems with motors (or any inductive load- capacitive loads have the curves 90 degrees out of phase the other way...)
Most inductive loads like a motor will start out with a PF of about 0.1 to 0.25, usually ending up about 0.5-0.6 or there abouts...
Plugging your numbers into the calculator- 12V x8A= 96W, 96W/200W= 0.48..... very close to that 0.5PF rating....
It would explain the discrepancy between the 'dc figures' and the wattage (or more accurately the VA)...
Inductive motors don't have their 'voltage curve' (sinewave) and their current curve in time with each other (in AC this is known as the power factor) and this is why the watts doesn't always equal the VA figure in some devices- inductive loads have the curves 90 degrees out of phase- it is this that causes the simple 'volts times amps' to not be as simple as it seems with motors (or any inductive load- capacitive loads have the curves 90 degrees out of phase the other way...)
Most inductive loads like a motor will start out with a PF of about 0.1 to 0.25, usually ending up about 0.5-0.6 or there abouts...
Plugging your numbers into the calculator- 12V x8A= 96W, 96W/200W= 0.48..... very close to that 0.5PF rating....
OzSolar
Whatever you did, that's what you planned.
Steppers are indeed used for things like that, but they are also indeed a 'brushless permanent magnet DC motor' (as opposed to the brushed motors like a starter motor in a car or the like...
So yes, I was right in thinking they were actually an induction motor...
So the figures quoted make perfect sense and are quite reasonable...
OzSolar
Whatever you did, that's what you planned.
ConnerLabs
Solar Enthusiast
There is no reactive power in a DC circuit. Volts times amps must equal watts.
Ok I lied. DC circuits can have ripple current that bumps up the RMS current flowing in the circuit without doing any more useful work. But this effect goes the other way, volts times amps works out more than the watts of useful power delivered.
Either the pump has a Mr. Fusion reactor inside or it’s just a typo on the label.
Ok I lied. DC circuits can have ripple current that bumps up the RMS current flowing in the circuit without doing any more useful work. But this effect goes the other way, volts times amps works out more than the watts of useful power delivered.
Either the pump has a Mr. Fusion reactor inside or it’s just a typo on the label.
Actually, it makes a lot of sense to use a stepper style motor- they advance a certain number of degrees for each 'advance pulse' (which is why they are used in CNC stuff- one pulse moves the head/laser/printer/whatever a specific distance for each pulse)- and this remains the same regardless of the voltage (unlike a brushed motor which speed varies according to the voltage)
This allows a simple frequency output from an oscillator to set the flow rate which will remain constant despite the varying input voltage from the panel...
This allows a simple frequency output from an oscillator to set the flow rate which will remain constant despite the varying input voltage from the panel...
Brushless DC motors are electrically commutated and are essentially AC motors driven with DC pulses.
The entire circuit is DC- but if it is as I suspect a inductive motor being driven from a driver circuit (aka an 'inverter') then it has an AC motor at the 'guts' of it... with all the characteristics of an AC motor...
ConnerLabs
Solar Enthusiast
I would call this a BLDC or brushless motor in this context. Same contraption found in computer fans, e-bikes and drone propellers.
True stepper motors have hundreds of poles and spin very slowly for a given input frequency. Also very inefficient and make an annoying whine.
And all motors have back EMF that limits their speed according to the supply voltage. The only way to avoid that (edit: besides field weakening) is to make the motor inefficient enough that voltage drop in winding resistance is large compared to back EMF. That clearly doesn’t apply here since this one is 208% efficient.
Different application, same theory in operation... both steppers and BLDC are the 'same under the hood' in their method of operation so to speak...I would call this a BLDC or brushless motor in this context. Same contraption found in computer fans, e-bikes and drone propellers.
True stepper motors have hundreds of poles and spin very slowly for a given input frequency. Also very inefficient and make an annoying whine.
And all motors have back EMF that limits their speed according to the supply voltage. The only way to avoid that (edit: besides field weakening) is to make the motor inefficient enough that voltage drop in winding resistance is large compared to back EMF. That clearly doesn’t apply here since this one is 208% efficient.
Brushed motors speed varies remarkably depending on the applied voltage, where a 'stepper' motor (using that term to cover all variations here) has a specific speed, set by the control frequency it is being fed from the driver circuit- regardless of the voltage applied to it, the speed remains locked at that exact speed (ie for a pump, a specific L/min flow rate)
ConnerLabs
Solar Enthusiast
This is true for all brushless motors, but the drive also has to supply the right voltage for the frequency, which is to say roughly proportional to the frequency. Too little and the motor stops, too much and it draws lots of current and overheats.
This is for exactly the same reasons that the permanent magnet DC motor’s speed varies with voltage. The physics are the same, the inverter drive is just a glorified commutator. I guess by the magic of PWM it can also function as a variable voltage supply, so the motor can run efficiently at any speed from a constant DC bus voltage.
Stepper motor drives get away with a constant voltage on the motor because they’re inefficient and overheating the whole time anyway. Steppers are never used in any application where efficiency matters.
OzSolar
Whatever you did, that's what you planned.
My solar controller spec sheet mentions BLDC. See post #4. What does BLDC stand for?
BarracudaBob
Harvesting free photons from clean fusion
Brushless DC motors (BLDC) are known for their high efficiency, typically ranging from 80–95%
A Brushless DC Electric Motor (BLDC) is an electric motor powered by a direct current voltage supply and commutated electronically instead of by brushes like in conventional DC motors.
I always thought about them as a brush DC motor without the brushes so less maintenance but similar efficiency
A Brushless DC Electric Motor (BLDC) is an electric motor powered by a direct current voltage supply and commutated electronically instead of by brushes like in conventional DC motors.
I always thought about them as a brush DC motor without the brushes so less maintenance but similar efficiency
OzSolar
Whatever you did, that's what you planned.
What about the L? The B, D and C part are easy enough.
ConnerLabs
Solar Enthusiast
BrushLess (tm) DC motor… 
(seriously, I’m currently designing motor drives for a living and can assure you the L stands for Less)
(seriously, I’m currently designing motor drives for a living and can assure you the L stands for Less)You are getting hung up on my descriptive term rather than looking at the controlling circuitry- which is basically identical in both types ie they are indeed basically the same design in motor, just with two different design goals in mind
BarracudaBob
Harvesting free photons from clean fusion
I was answering a question.
So in a well pump the head pressure lowers the efficiency. Therefore it pulls more current and your resistive losses go up.
The only way to reduce resistive losses is to increase the voltage and lower the current. Or increase the wire gauge which is usually not cost effective.
What I was getting at is that the current curve and the voltage curve in this case are not matched (see the graph I posted before) the peaks are out of alignment by 90 degrees, so when the voltage (remembering that this is technically an AC motor being driven from a DC source) is at its peak, the current is still not at ITS peak yet... so your current and voltage won't match what the plates 'say'... the current at that point is lower than the plates maximum draw, when it is at it maximum, the voltage is lower... but the wattage is higher when the max volts x max amps is used...
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