AVR vs Step-Down Transformer

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AVR vs Step-Down Transformer

Unread post #1 by joey81 » Wed Jan 15, 2014 11:27 am

For the same capacity (3KVA, for example) a step-down costs about twice as much as a servo-type AVR. Therefore, for economic reasons, the latter is more attractive.

Question is, what is the difference between the two in terms of performance? They have the same power ratings so in my mind the performance should be the same. But I've heard many times that the step-down is better when it comes to powering our amp-hungry tools. Why is this so?
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Re: AVR vs Step-Down Transformer

Unread post #2 by willyfernando » Wed Jan 15, 2014 11:52 am

I think the raw state of power of a Transformer can supply the unpredictable surge or spike of a power tool especially those Hi-current motors. During start up you notice how your light bulbs slightly dim or flicker? This I think is dangerous for those electronic circuits of those fully electronic AVR step-down units. There were AVR transformers that were coil wounded and with basic electronic parts that can handle motor start up. I was fortunate to get one during the 90's at a surplus store in Angeles. It was used by the US servicemen during the 70"s and when i tested it it was true to it's claim. It can handle +/- 5% fluctuation. I still have it and a 7KVA step down w/c powers my US power tools. We have a member by the name of JoJoD18 who is an electronics expert. Maybe he can help shed light on this subject. :thumbup:
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Re: AVR vs Step-Down Transformer

Unread post #3 by joey81 » Wed Jan 15, 2014 12:02 pm

Lets say the AVR is the toroidal type with a servo arm that goes around toroid.
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Re: AVR vs Step-Down Transformer

Unread post #4 by imcnovicio » Wed Jan 15, 2014 12:27 pm

It is better to have tried and fail rather than having not tried at all and play it safe. Keep on trying never give up.

“Give me ten thousand Filipino soldiers and I will conquer the world.”
― Douglas MacArthur
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Re: AVR vs Step-Down Transformer

Unread post #5 by JojoD818 » Thu Jan 16, 2014 7:35 am

every one misses the real issue with AVR's 100/110 output.

the thing is, the VA rating of the winding (toroid or EI) is for a 220V/240V output, halve that and you also halve the VA output of it.

so, in layman's terms, an AVR with a 5KVA rating will (theoretically) output 5KVA of power for a 220V equipment, however, using the 100V tap only provides 2.5KVA of theoretical output power.

in contrast, a step-down is a fixed purpose driven transformer that is meant to take 220V in and output 100V (or 110V) and whose VA rating is based on the fixed input and output parameters.

HTH

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Re: AVR vs Step-Down Transformer

Unread post #6 by JojoD818 » Thu Jan 16, 2014 7:48 am

joey81 wrote:For the same capacity (3KVA, for example) a step-down costs about twice as much as a servo-type AVR. Therefore, for economic reasons, the latter is more attractive.



Hi there!

Please read my previous post. If you think you are saving money by getting an AVR instead of a step-down, you are not my friend.



Question is, what is the difference between the two in terms of performance? They have the same power ratings so in my mind the performance should be the same. But I've heard many times that the step-down is better when it comes to powering our amp-hungry tools. Why is this so?




The simplest answer is that a step-down can take the beatings due to saturation, while an AVR will try to correct the surge and increase it's output voltage to compensate for the sag when a power tool is turned on. This will put the servo motor or the relays if it is a relay-type into overdrive and work like crazy. This also poses a small danger by exposing a power tool to increased voltage after it's motor has settled and up to speed.

IMHO, for 100V, 110V, or 120V equipments, especially those involving a motor such as those in our power tools, I would highly recommend a step-down instead of an AVR.

IF it is however unavoidable and you need to use an AVR's 100V output, please bear in mind that the maximum VA rating you can load it will be

AVR VA rating / 2 X 70%

this should give a small headroom for startups and should avoid the magic smoke from coming our of your AVR.

Remember, once the magic smoke comes out, it is very hard to put it back in. :lolno:

Cheers

Jojo
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Re: AVR vs Step-Down Transformer

Unread post #7 by J03L » Thu Jan 16, 2014 9:07 am

JojoD818 wrote:every one misses the real issue with AVR's 100/110 output.

the thing is, the VA rating of the winding (toroid or EI) is for a 220V/240V output, halve that and you also halve the VA output of it.

so, in layman's terms, an AVR with a 5KVA rating will (theoretically) output 5KVA of power for a 220V equipment, however, using the 100V tap only provides 2.5KVA of theoretical output power.

in contrast, a step-down is a fixed purpose driven transformer that is meant to take 220V in and output 100V (or 110V) and whose VA rating is based on the fixed input and output parameters.

HTH

Jojo


Thanks Sir Jojo..

Ito ata yung inixplane sakin ng taga davao electrical sales.. di ko lang masyado ma gets.. natandaan ko lang is pag avr dapat raw x2 or x3 ang watts equivalent. So they prefer step-down xformer.
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Re: AVR vs Step-Down Transformer

Unread post #8 by willyfernando » Thu Jan 16, 2014 2:05 pm

JojoD818 wrote: If you think you are saving money by getting an AVR instead of a step-down, you are not my friend.


The simplest answer is that a step-down can take the beatings due to saturation, while an AVR will try to correct the surge and increase it's output voltage to compensate for the sag when a power tool is turned on. This will put the servo motor or the relays if it is a relay-type into overdrive and work like crazy. This also poses a small danger by exposing a power tool to increased voltage after it's motor has settled and up to speed.

IMHO, for 100V, 110V, or 120V equipments, especially those involving a motor such as those in our power tools, I would highly recommend a step-down instead of an AVR.

IF it is however unavoidable and you need to use an AVR's 100V output, please bear in mind that the maximum VA rating you can load it will be

AVR VA rating / 2 X 70%

this should give a small headroom for startups and should avoid the magic smoke from coming our of your AVR.

Remember, once the magic smoke comes out, it is very hard to put it back in. :lolno:

Cheers

Jojo



Well said Sir Jojo, well said.
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Re: AVR vs Step-Down Transformer

Unread post #9 by JojoD818 » Thu Jan 16, 2014 5:03 pm

Incidentally, galing ako kanina ng ACE diyan sa may SM Annex, from the looks of their step down I would say they're somewhat overrated.

Since we are using these for power tools, when using commercial and locally purchased step downs, please do add some headroom, a 40% headroom would be my recommendation. SO if you have a 2000VA step down tranny, try not to exceed a total load of 1200VA only to prevent any problems.
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Re: AVR vs Step-Down Transformer

Unread post #10 by J03L » Thu Jan 16, 2014 6:54 pm

Pano na lang yung triton 3 1/4 router ko sir?

Kaya nyo po ba gumawa ng step-down transformer sir Jojo? if ever sayo na lang ako kukuha :thumbup:
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