Using a benchtop power supply to simulate solar panels?

[jdege]

I have a pair of Epoch 100Ah 48V batteries, to power my boat, and an Epoch 460Ah 12V battery to use as a house bank.

I also have 16 BougeRV 100W flexible panels that I've not yet mounted on my boat.

My plan, over the winter, is to experiment with MPPT controllers, and to see how everything goes together.

Unfortunately, I can't experiment outside, so connecting the panels to the controllers and the controllers to the batteries is out.

What I'm thinking of doing is to connect the controllers to the batteries and to feed power into them using a benchtop power supply.

I mean, a panel can provide at most 5A at 20V, and I can configure the power supply to provide that. Or any lesser power, to test limited light, etc.

I could then see how the MPPT controllers behaves, and how the battery responds.

Any reason that won't work?

 

[zcskywire2]

I could then see how the MPPT controllers behaves, and how the battery responds.

Any reason that won't work?

There is nothing that would prevent that from working. There should be no issue with charging the batteries via mppt controller using a bench top power supply.

However this wouldn't nessiarally give the results you would be looking for. The main issue is that a DC supply and a solar panel behave very different. The behavior of a power supply will not come close to the behavior of an actual solar panel. The voltage and current of a solar panel can move orders of magnitudes faster than most bench top power supplies. The response curve of a power supply and a solar panel are also very different as you let the voltage on a solar panel rise to the open circuit voltage the current will go down, where as on the bench top supply the current will be maintained. What this means in effect is that the mppt controller should just always lock in at the maximum voltage and current set on the power supply.

 

[jdege]

The other side of this is is there a way I can measure exactly what's coming out of a solar panel?

Measuring open circuit voltage in trivial, but can I put a load tester on it and see what kind of power and current I get?

 

[zcskywire2]

The other side of this is is there a way I can measure exactly what's coming out of a solar panel?

Measuring open circuit voltage in trivial, but can I put a load tester on it and see what kind of power and current I get?

You can and I have, but you will likely need quite a large capacitor across the load bank terminals. As I mentioned the solar panels can change voltage and current extremely fast. Pretty much any electronic load can not keep up with the changes in voltage and current. This will cause the control loop in the electronic load to mess up as it can not compensate for the fast changes. For the solar panels I used, I put a 10000uF cap across the terminals of my load bank to stabilize them. The large capacitor absorbs the voltage spikes from the panel and smooths out the dips, allowing the electronic load to stabilize. Now I can't tell you if that will be enough capatiance for you, it depends on which electronic load you are using. Just make sure to buy a high enough voltage rated capacitor for your panel with headroom to spare.

Also understand that capacitors are dangerous especially at the voltages and capacitance we are talking about. Always make sure that it discharged properly. To disconnect a panel properly, turn off the load, disconnect the panel, then put the load back on to ensure the capacitor is drained. It is also recommended to have a decently high resistance resistor across the capacitor to drain it and prevent and charge from building when you do not intend for it to.

 

[jdege]

Another possibility would be to connect the panels to a high current resistor. From that I could measure voltage and calculate current.

 

[Hedges]

Panel is approximately a current source and a resistor in parallel.
If your power supply has CV/CC operation, you just need a suitable high wattage resistor. That might be one or more electric radiators.

Set the power supply for 20V max, 5A max.
Connect it in parallel with a 4 ohm resistor. 20V/4 ohms = 5A.

A 120V 1800W space heater draws 1800W / 120V = 15A
120V / 15A = 8 ohms.
Connect two, 1800W heaters in parallel. Switch on and thermostat all the way up.
That should emulate 100W PV panel in full sun.
Reduce max current to emulate less sun.

 

[MakeMePower]

I have not done the resistor trick, but the mppt I have played with cycle over and over unless they are at their max current, since the psu drops the load when going over the max current limit set. i believe the mppt's need to see a voltage drop to lock the voltage, they do not behave remotely similar to a solar panel

 

[efficientPV]

Why stop at 4 ohms, make it 100. Really, 4 ohms is exceedingly high resistance to simulate a solar panel with a power supply. With 4 ohms the max you will get into the controller is 1A. Fine if the intention is to simulate 15W panel. The voltage will become so low with 1A that it won't operate in MPPT mode. Some resistance is needed to isolate the capacitance of the power supply from the charge controller. Hopefully, it won't oscillate much. Set supply to about 22V, add 0.5 ohm to 1 ohm resistance, and set the current limit on the supply.

 

[Hedges]

You're right, linear resistor doesn't make a good model. Scratch that!
Forgot we need a non-linear resistor, exponential current flow of a stack of diodes.

 

[tinyt]

Looks like this programmable power supply can do it, together with their virtual control panel software.


Additional page:

If I win the lotto I can buy it to play with it.