[RFI] Reducing RFI from Switching Power Supplies

[Roger (K8RI)]

On 9/11/2012 3:55 PM, WD8ARZ wrote:
> Most of the electronics in my home is protected by putting a UPS
> (uninteruptable power supply) between them and the wall outlet.
>
> Avoid the cheap low end low power units. They dont last long, fail
> sooner, and can run hot.
>
> Choose a size from a good vendor that has the capacity to run the items
> it is powering for about 15 - 30 minutes with out AC power.
> Those better models have excellent switching time, larger or multiple
> batteries, run cool, and have excellent filters / suppression built in.
>
> Plus many will adjust to provide the right voltage and 60 cycles needed
> for more sensitive devices, especially computers.
>
> When the UPS is going dead, it switches off giving a clean break to the
> equipment.
>
> So not only do you provide isolation and suppression of a lot of RFI
> from switching power supplies, you also improve the survivability of
> those switching supplies that are still powered on when the device they
> run are off, thus making them vulnerable to power line transients.
>
> Keep in mind that even though a lot of power supplies and electronics
> have built in spike suppression from MOV's (metal oxide varisters),
> those MOV's will no longer be working after several hits, even one large
> event can disable them. Same for those external power strips with spike
> protection built in. The better external power strips will have
> suppression devices that include chokes / filter design, and not just
> mov's.
>
> Ups units are better choices as they have all the mov / filter / choke
> designs in them, but also the battery that absorbs and isolates a lot of
> problems, along with voltage / Hz adjustments.

Remember that these are no longer line conditioners. They neither 
regulate, or filter the output voltage to the loads.  They do have spike 
suppression but they only use the battery to power the inverter inside 
when the line voltage fails.

Line conditioners that generate a true sine wave, where the load 
"always" runs off the battery which is continually charging from the 
power line are available, but rare and very expensive compared to the UPS.

They will likely run about 3 times the cost of a top of the line 1500 
watt UPS.


>
> No, I cant say what UPS units to avoid or to get. That changes so much
> in a short period of time as the models are changing all the time.
>

And it may depend on the model as well.  I've used a range of APC models 
typically in the 1500 VA range with no problems over quite a few years.


73

Roger (K8RI)


> 73 from Bill - WD8ARZ
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