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Meanwell SMPS power factor

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Mosaic

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Hi All
I am observing that a Meanwell 36V 8.8A PSU has a +90% P.F. vs similar EBAY type SMPS with sub 70% PF.
Is there an easy fix for this given the $$$ difference for a MW PSU?
 

schmitt trigger

Well-Known Member
This means that the higher P.F. units employ an active power factor correcting stage, which the other must be lacking.

In addition to correcting the P.F. these active stages enable true world-wide voltage compatibility, since they perform as a pre-regulator to the output SMPS stage.

In plain English: one gets what one pays for.
 

tcmtech

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Why do you think you need PF correction on such a small power supply? o_O
 

ronsimpson

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need PF correction on such a small power supply?
On one hand I agree with "small power supply" don't need. Example a small TV. There will be only one on a breaker.
On the other hand, the assumption, on lighting, (light bulbs) is that there will be many on the same power source.
At 3:00 am, much of the power draw is street lights.
I can not remember now, I think light bulbs cames under different laws than computers, based on how many will likely be on in a single house.
 

tcmtech

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On the other hand, the assumption, on lighting, (light bulbs) is that there will be many on the same power source.
At 3:00 am, much of the power draw is street lights.
I can not remember now, I think light bulbs cames under different laws than computers, based on how many will likely be on in a single house.
Outside of one's own home power systems what everyone else does is irrelevant being the utility companies have automatic PF control on the HV side of things which nullifies any PF issues they may see. Especially considering the average residential users base load value is usually under 1 - 2 KVA on average where IR loses in their systems are microscopic.
 

Mosaic

Well-Known Member
The cheap ($25) 36V PSUs @ 350W deliver around 0.67PF compared to .98 from the Meanwell PSU. In actual terms the calc works out to about 1.5x the power consumed by the cheap unit compared to the Meanwell for a given output.

Also since the MeanWell has no 115/230 V switch and the cheaper unit does....does this mean the MW unit is compatible with 115 to 230VAC al the time?

BTW I am using a Kilawatt unit to assess the power consumed, PF etc.
 

tcmtech

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The cheap ($25) 36V PSUs @ 350W deliver around 0.67PF compared to .98 from the Meanwell PSU. In actual terms the calc works out to about 1.5x the power consumed by the cheap unit compared to the Meanwell for a given output.

Also since the MeanWell has no 115/230 V switch and the cheaper unit does....does this mean the MW unit is compatible with 115 to 230VAC al the time?

BTW I am using a Kilawatt unit to assess the power consumed, PF etc.
But its not using 1.5x the power.

VA is apparent power not real power and holds no major value in the calculation of the efficiency of a device.
 

tomizett

Active Member
units employ an active power factor correcting stage,
I think #7 above confirms Schmitt's statement earlier.

PFC is generally implemented using a boost converter to step up to 400V DC which feeds a subsequent converter. This gives the double advantage of being able to control the input current waveform and making the circuit operable over a wide range of input voltages - often they'll do anything between 85 and 260 volts or so.

Looking at the circuit board, there are some giveaways that an active PCF boost stage is present:
1. There will be an additional inductor (maybe toroidal or split-core)
2. Often you will see a single 420/450V rated reservoir capacitor, as opposed to two 200V components in a non-PFC unit. The using 2 x 200V caps in series allow the bridge to be configured as a voltage-doubler by the voltage-selection switch.

Hope I'm not repeating too much stuff you already know here!
 

Mosaic

Well-Known Member
Hmm, the Killawatt unit reports 1.5X the wattage being consumed with the low PF unit and shows more amps as well, but similar VA.

The 2 caps in the Meanwell are 150Uf, 400V units

Meanwell Internals
meanwell psu .99PF.jpg

Generic Internals
generic psu .67pf.jpg
 
Last edited:

tomizett

Active Member
At a guess, I'd say that the torroidal inductor with the tape over it is the choke for the PFC boost, and the nearby semiconductors are its associated switches.

They look like good brand caps in that "generic" equivalent, at least.
 

tcmtech

Banned
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Hmm, the Killawatt unit reports 1.5X the wattage being consumed with the low PF unit and shows more amps as well, but similar VA.
Sounds like you or it are reading things backwards. KW value can never be higher than VA value.
 

Mosaic

Well-Known Member
Sounds like it is making Watts = V * (Real Amps + Imaginary Amps).
hard to read wrong...its showing 300+ watts for 200 + VA and a .67 PF
 
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