Bench power supply to simulate solar panel

ramiws

New Member
Hi,

I would like to simulate a 60cells panel. I have found "PROGRAMMABLE POWER SUPPLY 0-60V/0-3A 180W " for 200usd. Can I simply plug it to the MPPT SCC if it is within the voltage specs?
 

gnubie

Photon Sorcerer
It will usually work. The power supply does behave differently to a solar panel so it comes down to what your tests are checking.
 

DThames

Solar Addict
Not sure what your goals are but you can do it a lot cheaper. An adjustable CC, CV power board should look a lot like a solar panel under a given set of conditions. $5 or so.

What exactly are you trying to research?
 

ramiws

New Member
I am developing own BMS and here in the dark Finnish winter, I need to get the SCC to work "normally" by simulating a solar power source so I can test the communication between the SSC and my BMS. So if I set the power supply to constant voltage and current, the MPPT will be charging the battery according to that power no problem?
 

Craig

Watts are Watts!
Staff member
Moderator
I am developing own BMS and here in the dark Finnish winter, I need to get the SCC to work "normally" by simulating a solar power source so I can test the communication between the SSC and my BMS. So if I set the power supply to constant voltage and current, the MPPT will be charging the battery according to that power no problem?
I think it will work fine as well.
 

DThames

Solar Addict
The solar panel has an equivalent circuit that will look like a fixed voltage power source with a variable resistance in series with that source (the way that I picture it). For any watt output level that resistance will have a value that will limit the current. If you load it too much, a lot of the voltage will be dropped across this internal resistance, making the connection voltage (to the outside world) drop. It is the job of the MPPT to adjust the load to drop the voltage only to the max power point. When you adjust the current limit of the power source you are effectively changing the internal resistance of your equivalent circuit, much like less sun or more sun would do to deliver less or more power at any one moment. So you should be able to crank the current down to zero for dark and up to the max amps of the "panel" for full sun.

Not sure what your output voltage needs to be but I was thinking about something like this.
 

RCinFLA

Solar Addict
It will run but not act like a panel. MPPT will run close to your CV setting on power supply. Some MPPT controllers may oscillate when doing MPPT search because of sharp voltage drop off of CC/CV power supply. If it oscillates puttiing a 0.2 to 0.5 ohm power resistor in series should cure oscillation.

You can make a circuit that looks like a panel but circuit is not for weak of heart. Lot of diodes, heat sinks, and power resistors.

Easiest way is to use a blacked out panel in parallel with power supply and MPPT controller input. Power supply current supplies the equivalent illumination current, up to Isc and Voc of panel. Just make sure the panel has good air circulation around it. As long as you don't wrap the panel in a blanket and not set power supply voltage too much higher then Voc it will not be harmed. It is a little like putting two panels in parallel with one of them blacked out.
 
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ramiws

New Member
Easiest way is to use a blacked out panel in parallel with power supply and MPPT controller input. Power supply current supplies the equivalent illumination current, up to Isc and Voc of panel. Just make sure the panel has good air circulation around it. As long as you don't wrap the panel in a blanket and not set power supply voltage too much higher then Voc it will not be harmed. It is a little like putting two panels in parallel with one of them blacked out.

But would not that blacked out panel suck current ? or because there is a hungry battery the current will flow there. I know that MPPT has diodes to prevent current from flowing back to panels during nights, but if the PS is in parallel to the solar panel on the same terminals MPPT cannot do much. And if the battery is full. Then the current has no where to go except the panel, correct? Would that damage the panel?

I am mainly would like to know that nothing will get damaged, then I can measure and experiment. It is just because I saw a guy on one video plugging the solar panel to multimeter Amps measuring directly, like short circuiting it and he said it is okay because the panel gives voltage or amps. That's why I thought okay a panel is different than conventional power supply, but I do not understand in what way.
 

RCinFLA

Solar Addict
But would not that blacked out panel suck current ? or because there is a hungry battery the current will flow there. I know that MPPT has diodes to prevent current from flowing back to panels during nights, but if the PS is in parallel to the solar panel on the same terminals MPPT cannot do much. And if the battery is full. Then the current has no where to go except the panel, correct? Would that damage the panel?

That is the whole object of putting the blacked out panel in parallel. It represents a stack of series connected forward biased diodes, one for each PV cell in panel, with any shunt leakage current from cells. It will not draw more then cell leakage current until it reaches about 30 vdc (for 60 cell panel) where forward biased series diodes start to conduct. Any ambient light will reduce the appearent cell leakage current from the panel terminals point of view. Slightly above the forward biased diode stack knee is Vmp where most of the current will go to the MPPT controller. Continue to raise voltage without MPPT controller connected and it will draw Isc (minus cell leakage resistance loading current). This is exactly the way the system acts in normal operation. Because the panel is blacked out the power supply current represents the illumination current that would normally be created by PV cells in sunlight.

The only thing missing is the extra panel heating from sunlight that would not have been converted to electricity in normal operation. Panel heating will only be a maximum of Isc * Voc which, because of PV cell efficiency, is only be about 18-20% of heating power it would get if exposed to sun without any load on panel.

Set power supply CV to Voc and CC to Isc. Without MPPT controller connected the panel will heat up by (Voc * Isc ) watts. This is okay as long as panel has some air flow over it and is not wrapped in blanket. It gets about five times that much heating power in full sun when panel is not connected to load. Even when MPPT controller is connected in normal operation only less than 20% of the sun heating power is reduced by electrical loading which is the electrical conversion efficiency of panel. Reducing CC current on power supply below Isc will represent reduced sun illumination current.

In normal operation with full sun in summer climate is not uncommon for panel to reach over 50 degs C. Think of the roof temp of a dark painted auto in mid day summer sun. I know Voc * Isc sounds like a lot of power to dissipate, and it is, but it causes much less panel heating then it would get exposed to full sun. There is a lot of surface area of panel to dissipate heat. Like I said, just don't wrap it in a blanket to prevent some dissipation. A light sheet will block out the light indoors and indoor light won't provide much illumination anyway. You just want to prevent small amount of illumination to make up for some of PV cell normal leakage current. A good suggestion is just place panel behind your workbench. It is shaded from most of room light, enough air flow, and out of the way. If you want you can put a fan blowing air on panel and a temp sensor on panel to make you feel better.

As to your comment about battery. If panel Voc is at least 10%-20% higher then battery voltage only panel leakage current will load battery. If you leave power supply at Voc and you back down CC to low levels, the panel's leakage current will eventually drop the voltage so the MPPT controller will shut down and disconnect. This exactly matches what happens with sun illumination in normal PV outside operation.
 
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rin67630

Solar Enthusiast
I am developing own BMS and here in the dark Finnish winter, I need to get the SCC to work "normally" by simulating a solar power source so I can test the communication between the SSC and my BMS. So if I set the power supply to constant voltage and current, the MPPT will be charging the battery according to that power no problem?
So you are testing the BMS, not the MPPT SSC device?

Do you test on a real size battery or can you scale everything to low power?
 

ramiws

New Member
So you are testing the BMS, not the MPPT SSC device?

Do you test on a real size battery or can you scale everything to low power?
I want the BMS I am developing to control the MPPT SSC to stop charging for example. That's why I need the SSC to be working just as if there are solar panels hooked to it.
 

rin67630

Solar Enthusiast
I want the BMS I am developing to control the MPPT SSC to stop charging for example. That's why I need the SSC to be working just as if there are solar panels hooked to it.
So you could use relatively small blacked-out panels fed with an adjustable constant current source to get the input of your BMS.

You just adapt the shunt value to scale everything to the target dimension. It's easier than to run everything at high amps...
 
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