Step Down Transformer / need clarification on required ratings

[JASSMITHUS]

A PCB board circuit that controls a Door Drive Motor in an Elevator for opening/closing the sliding doors (machine room less elevator) currently runs on a Single Phase Supply of about 230 V (Input Range: 100 V - 230 V +10% -15%). The PCB board is connected via cables to the PM motor which runs on 3 phase supply, and an Encorder as well. *Assuming the single phase gets converted to 3 phase within the PCB board.

The main PCB board specs are:
LIN / LOUT: 0.55A/0.85A
PIN/POUT: 126 / 100 W

The PM Motor specs are: 106 V / 94 W / 1.22 A

Problem: The PCB board circuit gets damaged when power supply surge occurs. Even though the PCB circuit has 2 ceramic fuses of 4A each, still the Varistor or other electronic components on the PCB including a microcontroller get damaged. The manufacturing company staff recommends running the PCB Board via a STEP DOWN TRANSFORMER of 230 V to 180 V at 300 VA. Since 180 v is a non standard output voltage, a made to order step down transformer is needed. However the ratings for the transformer are not very clear to me. The lift technician whom I contacted, suggested a 500VA step down transformer instead of a 300 VA. This was costlier as well. However there seems to be some serious questions on the output CURRENT. i.e. How much is required based on the equipment tags/specs and will a step down transformer increase the CURRENT and if so what is the solution, so that the PCB board does not get damaged due to high current/heat? Currently Voltage Stabilizers that are used for home electronics like LCD TVs are not suggested.

Formula POWER = VOLTAGE x CURRENT. I am assuming the below is some where near the truth.

300 VA transformer => at 180 V Secondary would have CURRENT as 300/180= 1.66 A
500 VA transformer => at 180 V Secondary would have CURRENT as 500/180 = 2.78 A

What should be Step Down Transformer Specs based on the equipment tags / ratings given above? 300VA or 500 VA and should output CURRENT also be specified?

Attaching the Power Supply section from an older manual for the door drive as well. Asking for use in India, where supply is usually 230V.

 

[Nigel Goodwin]

As a transformer steps down the voltage, it's steps up the current (and vice versa) - it's what transformers do.

However, I've no idea if dropping the mains to 180V with a transformer will make any difference, presumably the problem is the poor quality of your electrical supply infrastructure?. Also bear in mind, to drop the mains you don't need a full isolation transformer, an auto-transformer should do the job anyway, and cost a lot less.

If you can come across one a Volstab (voltage stabilising) transformer may help - but an old style passive one, not a modern one controlled by electronics. We added them (long ago) to a couple of valve TV relay systems we ran, as voltage fluctuations caused the gain of the repeaters to change - and after the relay was stripped out, we kept the transformers - we found that they were excellent at reducing computer crashes, which were presumably caused by mains spikes.

To avoid an expensive custom transformer, you could also use a Variac instead, and adjust it to 180V.

 

[JASSMITHUS]

Thank You for the tips! Yes the supply here is not steady, fluctuates a lot. Most damages are caused by surges. Anywhere from 220 v to 250V on good days and surge voltage going up to 300 v - 400 v due to distribution faults.

The Variac idea was new to me. Checked and found most have a rotary switch to control the voltage. Like a dimmer. Rotary arrangement might not work in our situation.

Regarding the Voltage Stabilizer, this would have been an ideal choice, cost wise as well as availability. However can't find any that fall in the required range to suppress over voltage surges. Most work in the 90v to 290v range and boost the voltage + or - by 30 V. In this case Undervoltage would not be an issue. However Overvoltage say of 290 V, might get lowered to 260 V. This would still be above the upper range of the door drive and damage it. (Not sure if this assumption is true about stabilizers. These stabilizers seem to have current capacity ratings specified as 1A, 1.5A, 2A, 6A) Some folks suggested that Voltage Stabilizers have "time delays" to protect refrigerator/AC compressors from damage and so might not work well with door drive electronic equipment.

Any idea why a step down transformer secondary might have varying Ampere or dropping Ampere from 1.5A to below 1A with voltage sticking at 180 v? The technician updated that the transformer they got has such an issue. So they are not sure if it would drive the door drive PCB board properly.

 

[crutschow]

Another way to lower the voltage is to get a 230V to 48V transformer of the same output current rating, and connect its output in reverse-phase series with the output of the main transformer.
That will subtract 48V from the output, dropping it from 230V to 182V nominal.
That transformer will actually inject current back into the mains rather than taking current, as it drops the voltage.

 

[ChrisP58]

A PCB board circuit that controls a Door Drive Motor in an Elevator for opening/closing the sliding doors (machine room less elevator) currently runs on a Single Phase Supply of about 230 V (Input Range: 100 V - 230 V +10% -15%). The PCB board is connected via cables to the PM motor which runs on 3 phase supply, and an Encorder as well. *Assuming the single phase gets converted to 3 phase within the PCB board.

The main PCB board specs are:
LIN / LOUT: 0.55A/0.85A
PIN/POUT: 126 / 100 W

The PM Motor specs are: 106 V / 94 W / 1.22 A

Problem: The PCB board circuit gets damaged when power supply surge occurs. Even though the PCB circuit has 2 ceramic fuses of 4A each, still the Varistor or other electronic components on the PCB including a microcontroller get damaged. The manufacturing company staff recommends running the PCB Board via a STEP DOWN TRANSFORMER of 230 V to 180 V at 300 VA. Since 180 v is a non standard output voltage, a made to order step down transformer is needed. However the ratings for the transformer are not very clear to me. The lift technician whom I contacted, suggested a 500VA step down transformer instead of a 300 VA. This was costlier as well. However there seems to be some serious questions on the output CURRENT. i.e. How much is required based on the equipment tags/specs and will a step down transformer increase the CURRENT and if so what is the solution, so that the PCB board does not get damaged due to high current/heat? Currently Voltage Stabilizers that are used for home electronics like LCD TVs are not suggested.

Formula POWER = VOLTAGE x CURRENT. I am assuming the below is some where near the truth.

300 VA transformer => at 180 V Secondary would have CURRENT as 300/180= 1.66 A
500 VA transformer => at 180 V Secondary would have CURRENT as 500/180 = 2.78 A

What should be Step Down Transformer Specs based on the equipment tags / ratings given above? 300VA or 500 VA and should output CURRENT also be specified?

Attaching the Power Supply section from an older manual for the door drive as well. Asking for use in India, where supply is usually 230V.

It's not clear to me why the equipment vendor asks for 180 VAC when, in your first paragraph, you say that the input range is 100 to 230 Volts. That range includes 115, or 50% of 230. 2:1 stepdown auto transformers are quite common and should be readily available.

If you do want 180, then you can use a 230 to 48 isolation transformer with the secondary wired in series with the load. That should give you ~182 VAC.

Note the phasing of the two windings. Test the output voltage before connecting it to the load equipment. If the output voltage is higher than the input, reverse the polarity of one of the windings.

A 100 VA transformer should be adequate. The main thing is for the secondary current of the transformer be greater than the loads input current at 180VAC.

 

[JASSMITHUS]

The door drive has Input starting from 100v - 230v +10%-15%. Correct. This is because the Mfg Company is based in Spain and supplies their products world wide in this closely knitted elevator industry. Most of the drives are mfg in China for our region, though there are 2 plants located in India. I am sure for the more reliable power distribution available in Europe, US, the 100v will work well. Why 180v was suggested- I believe/assume is due to testing done at the local factory under local power supply conditions, as many drives are damaged due to power surges and returned to the factory.

Also Step Down Transformers from 230v to 110v are more readily available here. I have seen multi-voltage Step Down control transformers with secondary voltage as 0, 12v, 24v, 48v, 110v. The door drive company dealer who supplies the product suggested using at 110v based on their other customers using in the same way. However nobody is willing to give all these inputs officially or even give inputs on the specifications of the transformer. Maybe due to liability concerns. The elevator technician who checks at our location seemed concerned on running the drive at 110V supply in India, as he feared it might increase the Current Amperes and added heat might damage the PCB board, affect longevity. We do have distribution Undervoltage and Over Voltage issues here. So what such imbalances would do at 110V Vs 180V or higher volatges is not clear to me.

Using a step down voltage of 48V in series / reverse polarity - is interesting to know. I will see how this could be tested here.

I had the impression 220v to 180v an additional step down transformer had solved the issue.
The only question was ratings of the transformer 500VA, or 300VA or 250VA or 200VA as all these were spoken of. But the concerns on Current Amperes is shaking this assumption. As an end user I don't have much knowledge on electricity/transformers. I do theoretically believe that at same output voltage of 180V, the current would increases in a 500VA Vs a 300VA. I don't know if this should be a big concern or should be ignored.

I am really grateful for all your suggestions and inputs. Cheers!

 

[JASSMITHUS]

Google search for Lin/Lout and PIn/Pout - terms that I didn't understand earlier.
- Lin = live in, Lout = live out. "Pin" and "Pout" typically refer to input power (Pin) and output power (Pout) respectively. This lets me now understand that the PCB circuit really requires:
Input Current = 0.55A
Input Power = 126W (i.e. 0.55A x 230V or 1.15 A x 110V or 1.26A x 100V)
Output Power = 100W = 100VA

Closest Stepdown transformer would be 100VA with 230v input / 180 V secondary output. Secondary Current would be exactly as required by this device i.e. 0.55A.

Now what could break this assumption as I am sure there are other factors I am not considering.
Since Lout = 0.85A
Can I safely assume that a 200VA stepdown transformer with Secondary at 180V and having secondary current as 1.11 A would NOT affect the life of the device, as its already able to handle 1.26A at 100V, the min voltage in the specs.

200VA / 180V / 1.11A - seems ok to use
250VA / 180V / 1.38A - seems slightly higher
300VA / 180V / 1.66A - seems slightly higher
500VA / 180V / 2.78A - now doesn't seem okay!

SUMMARY
Finally the equipment vendor contacted and suggested going for a 180V stepdown transformer either 250VA or 300VA. Better option would be 300VA. Also informed that the current ratings on secondary side reflect its total capacity and higher the VA better the life for the transformer, but the drive would not draw more than 1A - 1.5A and hence no worry of heat/damage or high current flowing through the device.