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Testing solar inverters PV input without solar pannels for testing purpose


jovani

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Hello everyone, i need your help, there is any way to test solar inverters PV input without solar pannels? In the building where i have my repair shop i'm not allowed to install solar panels, and i need some help on how to do this only for testing purpose of mppt's and solar inverters pv input.  I'm thinking to buy a high voltage adjustable power supply 0 - 200 v DC / 0 - 5 Amps, would this be helpful to simulate panels? Thanks!

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Just a thought. I was at a small factory complex and saw a trolley, on wheels that held 3 panels. They pushed the panels out of the shop into the sun in the morning and pushed back into the garage at night. Rather clever, I thought.

You will need a decent voltage to test, depending on MPPT specs, so you might have to connect panels in series/parallel to test but 3 panels should cover most MPPTs..

 

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2 hours ago, FixAMess said:

Just a thought. I was at a small factory complex and saw a trolley, on wheels that held 3 panels. They pushed the panels out of the shop into the sun in the morning and pushed back into the garage at night. Rather clever, I thought.

You will need a decent voltage to test, depending on MPPT specs, so you might have to connect panels in series/parallel to test but 3 panels should cover most MPPTs..

 

It could even be an option to use just a single smallish-size panel, or 100-250W panel, and combine it with a PV Voltage booster, such as the type from Microcare here Microcare SVB350 Single-Phase Solar Voltage Booster – Sustainable.co.za.

If that could work, it would make for a smaller-size trolley or test rig, and I mean if you go even smaller like with a 50W panel, you could almost hang it in the window. I do like the thought though of testing with actual solar panels even just to demonstrate more vividly to the customer that it works. 

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On 2024/06/25 at 5:39 AM, jovani said:

I'm thinking to buy a high voltage adjustable power supply 0 - 200 v DC / 0 - 5 Amps, would this be helpful to simulate panels?

Yes, it think it would, but it would have to have some sort of current limiting capability. Otherwise, the MPPT would just keep taking more and more current until something tripped. Or you could put some sort of high power resistor in series, but that is also a nuisance as it would be very bulky and would get very hot when the MPPT was operating. A 100-200 W incandescent bulb might work, and gives a visual indication of power drawn. As it is, that power supply might be expensive, bulky, and might waste a lot of heat.

The power supply would have to be isolated from earth, and be able to withstand hundreds of volts with respect to earth. Most power supplies would meet that criterion.

Actual panels would be a nuisance for testing, not always having enough power to start an MPPT, can't use at night or in heavy rain, etc.

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55 minutes ago, jovani said:

Yes it will work below link 250v 5A with current limit capability so no need for resistors to limit the current. Also <0.5% ripple that is important when simulating pure dc source. Bit more expensive even 500vdc 2A available. You won't really need more than 5A for testing purposes.

https://www.aliexpress.com/i/1005003706493808.html

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16 hours ago, jovani said:

Do you think they would work?

As TaliaB says, yes, I think that they would work well. The 250 V model might be better. Probably no need for a series resistor if they just switchmode lower power, as it appears that they do, avoiding all that heat.

If you found that you did need a resistor, then 40 ohm 300 W would be enough for the 200 V model, or 50 ohm 300 W for the 250 V model.

15 hours ago, TaliaB said:

You won't really need more than 5A for testing purposes.

Agreed.

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15 hours ago, TaliaB said:

Yes it will work below link 250v 5A with current limit capability so no need for resistors to limit the current. 

I see a number of suggestions for the PSU for 200V. I come from a different angle. 

Why not buy a voltage stabiliser that can adjust from 230V AC up to around 260V AC. Remove the servo motor and circuit and use the box with variac. Add a full wave rectifier with a 1000 uF 400V capacitor. Wire this through a LM338 5A regulator and resistor optional as a current limiter. The current can be limited via 5 way switch and resistors. The LM338 will self regulate output if the temp rises. Input voltage can be adjusted from 5-260V.

Just a basic indication and electronic guys can fine tune the circuit. 

Any reason why it will not work? 

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On 2024/06/28 at 10:15 PM, Scorp007 said:

Any reason why it will not work? 

Yes! Generally, a variac is not isolated (I suppose some might be). This circuit must be isolated from ground/neutral.

This circuit will have a horrible power factor, and you'll need some sort of inrush current limiting for the giant 1000 μF capacitor.

On 2024/06/28 at 10:15 PM, Scorp007 said:

The LM338 will self regulate output if the temp rises. Input voltage can be adjusted from 5-260V.

? The LM338 can only regulate 32 V. I don't like the idea, sorry.

If these power supplies are proper power factor corrected switching types, the losses will be manageable (though still probably many tens of watts). 

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5 hours ago, Coulomb said:

Yes! Generally, a variac is not isolated (I suppose some might be). This circuit must be isolated from ground/neutral.

This circuit will have a horrible power factor, and you'll need some sort of inrush current limiting for the giant 1000 μF capacitor.

? The LM338 can only regulate 32 V. I don't like the idea, sorry.

If these power supplies are proper power factor corrected switching types, the losses will be manageable (though still probably many tens of watts). 

The variac as an adjustable transformer does the voltage control. 

The LM338 is used purely as a current limiter with no connection to the neg supply so it does not see 32V at all. The volt drop over the series resistor on the output provides the ref for the chip. 

Then after many yrs I learnt we all look at the 32V max input for this range of regulators but in fact this 32V refers to the delta between input and output. 

If the input is 45V the output cannot be adjusted for lower than about 13V.

Having said the above this method then fails the most important test that the supply is not isolated as it is actually an auto transformer. 

Edited by Scorp007
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10 hours ago, Scorp007 said:

The variac as an adjustable transformer does the voltage control. 

The LM338 is used purely as a current limiter with no connection to the neg supply so it does not see 32V at all. The volt drop over the series resistor on the output provides the ref for the chip. 

Then after many yrs I learnt we all look at the 32V max input for this range of regulators but in fact this 32V refers to the delta between input and output. 

If the input is 45V the output cannot be adjusted for lower than about 13V.

Having said the above this method then fails the most important test that the supply is not isolated as it is actually an auto transformer. 

Yes, it cannot be stressed enough that PV- and PV+ must NEVER be grounded / earthed. In the high voltage type MPPTs this will always lead to inverter damage. 

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3 minutes ago, BritishRacingGreen said:

Yes, it cannot be stressed enough that PV- and PV+ must NEVER be grounded / earthed. In the high voltage type MPPTs this will always lead to inverter damage. 

Would it be OK if one had to use say a 110/220V transformer of 5A rating between the variac output and the AC/DC rectifier before wiring to the LM338 ?

Now we talking of cost higher than what a purpose built power supply would cost. Stupid suggestion from the start. :)

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18 minutes ago, Scorp007 said:

Would it be OK if one had to use say a 110/220V transformer of 5A rating between the variac output and the AC/DC rectifier before wiring to the LM338 ?

Yes, in fact there is a lot of suppliers of 220/110 step down transformer modules on the market, mainly for consumers buying eg. USA sewing machines from Amazon etc. 

But yes that will add about R700  to your BOM.  Even more if its 1kW needed. 

Edited by BritishRacingGreen
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16 hours ago, Scorp007 said:

The LM338 is used purely as a current limiter with no connection to the neg supply so it does not see 32V at all.

If it reduces the current to zero, then there will be hundreds of volts between the input and output.

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