SDR-500VA AC voltage regulator - Teardown - Damage - Repair

[Kiriakos GR]

You may find SDR-500VA this made under 100 brands that no one is honest about it actual specifications, watt sizing.

As you may discover from the pictures bellow the circuit this is technology of 2003, this is the year that cheap 300W UPS they also become popular.
Those ancient UPS they are actually one SDR-500VA (stabilizer circuit) among the UPS backup feature.

The problem starts with newer ACV standardization at 230V for Europe.
Piss poor stabilizers they made to consider 220V  as close to under-voltage limit, and 240V as over-voltage limit, the outcome this is a more frequent  than the normal of relay switching in order this device to offer correction according to what this is programmed to do.

Now any mislead consumer he will consider this basic AC voltage regulator as the savior of his property, and usually the single AC plug at the back (output ) this will be loaded unwisely.

Therefore in a quick summary we have a collection of facts working against this item life-cycle.
a) Wrong programing at voltage detection regarding ACV safe-unsafe limits.
b) consumers will usually overload it.
c) how much trust we can demonstrate to electrical relay quality ? (construction & reliability & longevity)

This is the second unit that I do accept as a gift, mostly because the branded replacement of four relay's this it does bypass the cost of purchase for such a unit as new.
The last question this is of what this unit is good for ?
Well just downgrade the named 500VA at 300 Watt and you may protect the large plasma or LED wide screen in your living room, among with the satellite dish receiver and your DVD player.

This thing is not going to protect any computer PC, or refrigerator, or anything else.             

[Kiriakos GR]

Originally I thought after examining all four relay (they was all at terribly mechanical condition)  that this item will never have a second life.
But by searching at my old PCB collection (BIG wooden box), I did discover one ancient 350W UPS which the PCB this using identical relay (400 Ohm | 12V).

I did solder all four good relay at the SDR-500VA and this came to life.   
Next to follow this is actual tests. 

   

[Kiriakos GR]

SDR-500VA - Electrical tests by VARIAC transformer.

No matter of how much time I did searched online, there is no any detailed product specifications about this AC voltage regulator in PDF (user guide manual) .
By the use of my VARIAC transformer I did manage to discover the all truth about it.

The specific AC voltage regulator, while this using only four DC  relay, this can combine them and deliver seven Steps of correction.
The target voltage output this is programmed to be at 226~240 ACV.
The minimum input voltage for proper operation this is 150ACV.
At 120V on the LCD appears the letter L and this translates as Low limit and the device is unable to operate. 

When input voltage this is at 150V the output this is 235 ACV

Steps of correction due the use of relay 
No1  IN 160V  | OUT 226V
No2  IN 175V  | OUT 233V
No3  IN 190V  | OUT 230V
No4  IN 205V  | OUT 236V
No5  IN 215V  | OUT 226V
N06  IN 235V  | OUT 240V
No7  IN 240V  | OUT 223V

After the discovery of all steps which cause relay activation, I did some load testing with 150W light bulb.
Relay switching was instant between all steps, this works as proof to me that the used lot of relay that I did use as replacements, they are in excellent functional condition. 

[Kiriakos GR]

SDR-500VA this is capable to perform three operations due front panel buttons.
LCD appearance of 230V all times, this is not a measurement, this just serving only as indication that SDR-500VA this is powered on, and the product this is programed to serve at 230V Mains. 

Buttons usage.
1) Input voltage :  This is what it does and you may see the measured input voltage for a period of five seconds, then the 230 math value this return at the front display.

2) Delay function :   SDR-500VA when powered on, this activates the load after of a fixed delay of 6 seconds.
SDR-500VA this includes internal timer for load delay activation.
When Delay button this is activated, the new timer delay setting this now become 120 seconds.
At that mode an countdown starts from the number 120 and when the timer gets down to zero then there is load activation.

This concept of delayed load activation this is planned to assist very sensitive electrical appliances, 120 seconds of delay for load activation, this translates that Mains voltage this has now fully recover and it is stable, because all other loads in the house they are now active and there is no more voltage fluctuation due the startup of other high current appliances. 

In summary
Just remember to never overload this SDR-500VA with more than 350W of Resistive electrical load, and this will serve as basic protection against High and Low AC voltage fluctuations.
It is unfortunate that the quality of internal relay this is anonymous garbage,  the ones which I use as replacements they are branded and they include part code.

In China the price of this item at large quantities starts from 15 USD dollars.
The price of four branded DC relay in retail market, this is equivalent with the price of the entire SDR-500VA.


   

[Andrew-88]

So we have to be thankful at the small dead UPS which served as source of spare parts. 

Another high quality presentation by Kiriakos !!
I would also love to have such a VARIAC !
Thanks.
 

[Kiriakos GR]

So we have to be thankful at the small dead UPS which served as source of spare parts. 

This is more or less the truth, because the risk of getting relay from eBay and you to expect that they will work as you hope so, this is high.
To me this new experience it gave me two portions of pleasure.
a) The voltage regulator got a second life.
b) I did use at the testing process all gadgets which I made for UPS product reviews, among the high quality cables that I got from Germany.
While the idea of UPS product reviews at ITTSB this did not flourish, I am fully prepared for any arrived opportunity in the future.     

[Kiriakos GR]

This is an update  ....

Such products designed and or assembled at 2003, they could not predict that EU Mains voltage standard will change at 240V.
SDR-500VA (230V version) this is adjusted to be triggered at 238~239V so to switch at lower transformer tap.
Today voltage stabilization while this change at 240V, regular voltage fluctuation this is considered at 235~240.

With the default  SDR-500VA (230V version) factory adjustment (PCB potentiometer - trimmer), SDR-500VA (230V version) this is now forced to constantly activate it electrical relay's.
Such frequent and unnecessary electrical relay activation, this is now responsible for electrical relay accelerated wear and failure.

Therefore its not enough to replace any damaged relay at such a product, it is also required a new adjustment, so up to 241V of input voltage, this to considered as normal.
And or 242V of input voltage to become the new preset of over-voltage.

Notes: 
By design, the transformer within such equipment,  this is not equal to isolation transformer.
Some modern made ones are using toroidal transformer instead, there is no additional improvement over the use of metal core transformer.
Toroidal transformer as concept this is used at VARIAC transformers for several decades.   

[Kiriakos GR]

Its true I was motivated to follow this rabbit hole down to it bottom. 

New findings:  The 230V it is natural a volt meter, which it does measuring something at two situations.

a) When AC input button this is pressed = review of input voltage.
b) When output voltage this exceeds 250V of output.

By design with max input of 280AC the output of this thing its at 260V.
This is the capability of the last transformer tap, at the occasion of over-voltage.
It under volts by 20V the input.

At the PCB they are two adjusting pots.
Top pot and or V-out this is for calibration adjustment of the volt meter when this is active, when output is above 250V.
Lower pot this is also for calibration adjustment of the volt meter along trigger adjustment.

More essential adjustment this is the lower pot.
But with out input over-voltage (due VARIAC) there is no chance someone to adjust the top pot, because the volt meter measurement this is inactive.
 
It is in the nature of this transformer taps design, the ACV input and the ACV output to never be equal.

Note: I thought that the top pot was damaged and I did take the all thing apart, I did replace few capacitors and redo soldering ( improvements), and I did discover the new functionality of the volt meter (active only at output over-voltage) almost accidentally.       

THE END..