Inverters vs wallwarts

I'm setting up a UPS for my computer/comms equipment using an
inverter/charger and battery from Amazon. The equipment draw
is only about 40 watts measured with a Kill-A-Watt, but all
the associated wallwarts use capacitive-input switching  power 
supplies. That means they only draw current at line peaks.

My seat-of-the-pants guess is that the duty cycle is around 10%,
meaning that the average 40 watts is really 400 watts 10% of the time.
That's well within the continuous power rating of the inverter, which
is 800 watts, so it's likely the setup will work as it is.

The question is: Can the peak load be made closer to the average 
load by putting an inductor in the AC line feeding the wallwarts?

If anybody's been through this exercise I'd be grateful for guidance.

Thanks for reading,

bob prohaska
 

On Sat, 25 Jun 2022 02:10:59 -0000 (UTC), bob prohaska
<bp@www.zefox.net> wrote:

>I'm setting up a UPS for my computer/comms equipment using an
>inverter/charger and battery from Amazon. The equipment draw
>is only about 40 watts measured with a Kill-A-Watt, but all
>the associated wallwarts use capacitive-input switching  power 
>supplies. That means they only draw current at line peaks.
>
>My seat-of-the-pants guess is that the duty cycle is around 10%,
>meaning that the average 40 watts is really 400 watts 10% of the time.
>That's well within the continuous power rating of the inverter, which
>is 800 watts, so it's likely the setup will work as it is.
>
>The question is: Can the peak load be made closer to the average 
>load by putting an inductor in the AC line feeding the wallwarts?
>
>If anybody's been through this exercise I'd be grateful for guidance.
>
>Thanks for reading,
>
>bob prohaska
> 
>

You could scope the input current. It may not peak as high as you have
estimated. 



-- 

Anybody can count to one.

- Robert Widlar

bob prohaska wrote:
================
>
> I'm setting up a UPS for my computer/comms equipment using an 
> inverter/charger and battery from Amazon. The equipment draw 
> is only about 40 watts measured with a Kill-A-Watt, but all 
> the associated wallwarts use capacitive-input switching power 
> supplies. That means they only draw current at line peaks. 
> 
> My seat-of-the-pants guess is that the duty cycle is around 10%, 
> meaning that the average 40 watts is really 400 watts 10% of the time. 
> That's well within the continuous power rating of the inverter, which 
> is 800 watts, so it's likely the setup will work as it is. 
> 
> The question is: Can the peak load be made closer to the average 
> load by putting an inductor in the AC line feeding the wallwarts? 

 **  A well chosen choke will do that, but not by much. 

> If anybody's been through this exercise I'd be grateful for guidance. 

 **  PFC corrected  SMPSs were invented for this job. 
       Doubt if you will find such in wall warts. 



......   Phil 

On Saturday, June 25, 2022 at 12:15:48 PM UTC+10, jla...@highlandsniptechnology.com wrote:
> On Sat, 25 Jun 2022 02:10:59 -0000 (UTC), bob prohaska 
> <b...@www.zefox.net> wrote: 
> 
> >I'm setting up a UPS for my computer/comms equipment using an 
> >inverter/charger and battery from Amazon. The equipment draw 
> >is only about 40 watts measured with a Kill-A-Watt, but all 
> >the associated wallwarts use capacitive-input switching power 
> >supplies. That means they only draw current at line peaks. 
> > 
> >My seat-of-the-pants guess is that the duty cycle is around 10%, 
> >meaning that the average 40 watts is really 400 watts 10% of the time. 
> >That's well within the continuous power rating of the inverter, which 
> >is 800 watts, so it's likely the setup will work as it is. 
> > 
> >The question is: Can the peak load be made closer to the average 
> >load by putting an inductor in the AC line feeding the wallwarts? 
> > 
> >If anybody's been through this exercise I'd be grateful for guidance. 
> > 
> >Thanks for reading, 
> > 
> >bob prohaska 
> > 
> >
> You could scope the input current. It may not peak as high as you have 
> estimated. 
> 
**  Yeah,   it more like 20 to 25% . 

  With 50Hz power, 100Hz current pulses are about 2mS duration.



.....   Phil 

On 6/24/2022 7:10 PM, bob prohaska wrote:
> I'm setting up a UPS for my computer/comms equipment using an
> inverter/charger and battery from Amazon. The equipment draw
> is only about 40 watts measured with a Kill-A-Watt, but all
> the associated wallwarts use capacitive-input switching  power
> supplies. That means they only draw current at line peaks.
> 
> My seat-of-the-pants guess is that the duty cycle is around 10%,
> meaning that the average 40 watts is really 400 watts 10% of the time.
> That's well within the continuous power rating of the inverter, which
> is 800 watts, so it's likely the setup will work as it is.
> 
> The question is: Can the peak load be made closer to the average
> load by putting an inductor in the AC line feeding the wallwarts?
> 
> If anybody's been through this exercise I'd be grateful for guidance.

What are the *final* load voltages?  E.g., a more efficient
design may skip the mains voltage and convert direct to
your actual load voltages  E.g., I run a straight 48VDC supply
instead of UPS->mains->48VDC -- because my loads are 48VDC powered.
You might be able to just power your loads directly off a well
chosen battery voltage (and simply *charge* it from the mains)

On Fri, 24 Jun 2022 19:52:53 -0700 (PDT), Phil Allison
<pallison49@gmail.com> wrote:

>On Saturday, June 25, 2022 at 12:15:48 PM UTC+10, jla...@highlandsniptechnology.com wrote:
>> On Sat, 25 Jun 2022 02:10:59 -0000 (UTC), bob prohaska 
>> <b...@www.zefox.net> wrote: 
>> 
>> >I'm setting up a UPS for my computer/comms equipment using an 
>> >inverter/charger and battery from Amazon. The equipment draw 
>> >is only about 40 watts measured with a Kill-A-Watt, but all 
>> >the associated wallwarts use capacitive-input switching power 
>> >supplies. That means they only draw current at line peaks. 
>> > 
>> >My seat-of-the-pants guess is that the duty cycle is around 10%, 
>> >meaning that the average 40 watts is really 400 watts 10% of the time. 
>> >That's well within the continuous power rating of the inverter, which 
>> >is 800 watts, so it's likely the setup will work as it is. 
>> > 
>> >The question is: Can the peak load be made closer to the average 
>> >load by putting an inductor in the AC line feeding the wallwarts? 
>> > 
>> >If anybody's been through this exercise I'd be grateful for guidance. 
>> > 
>> >Thanks for reading, 
>> > 
>> >bob prohaska 
>> > 
>> >
>> You could scope the input current. It may not peak as high as you have 
>> estimated. 
>> 
>**  Yeah,   it more like 20 to 25% . 
>
>  With 50Hz power, 100Hz current pulses are about 2mS duration.
>
>
>
>.....   Phil 

Big supplies are now required to be PFC, namely not pull big current
spikes. Small warts may be exempt.

Even with a simple rectifier front-end, the top of a sine wave is
pretty soft. And it wouldn't shock me if some people skimp on caps.

It's not hard to measure. Or just plug it into the converter and not
worry. An 800 watt converter probably won't notice a 40 watt wart.



-- 

Anybody can count to one.

- Robert Widlar

On 2022-06-25, bob prohaska <bp@www.zefox.net> wrote:
> I'm setting up a UPS for my computer/comms equipment using an
> inverter/charger and battery from Amazon. The equipment draw
> is only about 40 watts measured with a Kill-A-Watt, but all
> the associated wallwarts use capacitive-input switching  power 
> supplies. That means they only draw current at line peaks.
>
> My seat-of-the-pants guess is that the duty cycle is around 10%,
> meaning that the average 40 watts is really 400 watts 10% of the time.
> That's well within the continuous power rating of the inverter, which
> is 800 watts, so it's likely the setup will work as it is.

> The question is: Can the peak load be made closer to the average 
> load by putting an inductor in the AC line feeding the wallwarts?

Yes but only a little, the current phase angle is typically only
about 20 degrees leading so a line reactor will not help much. Most
of the power factor comes from crest factor rather than cos(phi).

It will work better if you put a bridge rectifier before the inductor.
(because now you can use a larger inductor), but now you'll have to
figure out which wall warts actually need AC, and only connect the 
DC-capable ones.

-- 
  Jasen.

On a sunny day (Sat, 25 Jun 2022 02:10:59 -0000 (UTC)) it happened bob
prohaska <bp@www.zefox.net> wrote in <t95qrj$r99$1@dont-email.me>:

>I'm setting up a UPS for my computer/comms equipment using an
>inverter/charger and battery from Amazon. The equipment draw
>is only about 40 watts measured with a Kill-A-Watt, but all
>the associated wallwarts use capacitive-input switching  power 
>supplies. That means they only draw current at line peaks.
>
>My seat-of-the-pants guess is that the duty cycle is around 10%,
>meaning that the average 40 watts is really 400 watts 10% of the time.
>That's well within the continuous power rating of the inverter, which
>is 800 watts, so it's likely the setup will work as it is.
>
>The question is: Can the peak load be made closer to the average 
>load by putting an inductor in the AC line feeding the wallwarts?
>
>If anybody's been through this exercise I'd be grateful for guidance.
>
>Thanks for reading,
>
>bob prohaska

Interesting question, my cheap UPS seems to put out a square wave
I wondered if the flat tops are actually not better for the wall warts
as the charging part is longer than with a sine wave top...
Been working now fine for a year or so with this thing,
comes in almost every day these days with mains company fiddling,..
flashing light bulbs sometimes here too.
To backup for longer times I have a pure sine wave 2 kW converter and a 250 Ah lifepo4 battery..
So I can keep watching sat TV or even cook food.
More than 10 wallwarts on that UPS now, some Raspberry Pi, some USB hubs, some cameras., also
security recorder, monitors... .. audio amp... 4 TB harddisks...
I would personally not bother with a a series inductor...

Jan Panteltje <pNaonStpealmtje@yahoo.com> wrote: 

> bob prohaska wrote: 
> 
>>I'm setting up a UPS for my computer/comms equipment using an 
>>inverter/charger and battery from Amazon. The equipment draw is only 
>>about 40 watts measured with a Kill-A-Watt, but all the associated 
>>wallwarts use capacitive-input switching  power supplies. That means 
>>they only draw current at line peaks. 
>>
>>My seat-of-the-pants guess is that the duty cycle is around 10%, meaning 
>>that the average 40 watts is really 400 watts 10% of the time. That's 
>>well within the continuous power rating of the inverter, which is 800 
>>watts, so it's likely the setup will work as it is. 
>>
>>The question is: Can the peak load be made closer to the average load by 
>>putting an inductor in the AC line feeding the wallwarts? 
>>
>>If anybody's been through this exercise I'd be grateful for guidance. 

> Interesting question, my cheap UPS seems to put out a square wave I 
> wondered if the flat tops are actually not better for the wall warts as 
> the charging part is longer than with a sine wave top... Been working 
> now fine for a year or so with this thing, comes in almost every day 
> these days with mains company fiddling,.. flashing light bulbs sometimes 
> here too. To backup for longer times I have a pure sine wave 2 kW 
> converter and a 250 Ah lifepo4 battery.. So I can keep watching sat TV 
> or even cook food. More than 10 wallwarts on that UPS now, some 
> Raspberry Pi, some USB hubs, some cameras., also security recorder, 
> monitors... .. audio amp... 4 TB harddisks... I would personally not 
> bother with a a series inductor... 

For a personal computer only... I use a Tripp-Lite LC1200. No battery at 
all. I don't recall the last time we had a power failure that lasted more 
than an moment. But there has been flickering. The line conditioner works
great for momentary outages, no messing with a battery. 

Of course that doesn't suit everybody.

 Jan Panteltje wrote:
------------------------------------
>
> Interesting question, my cheap UPS seems to put out a square wave 


** So when rectified is pure DC. 

> I wondered if the flat tops are actually not better for the wall warts 

**  See above.


......   Phil