Solar panel and dc motor

Question

I want to run a 130V dc motor 2hp. I have 6 solar panel 120V dc out.

I connected them in series to the motor directly and it runs, but when I check the voltage at the terminal when it is running it read 60V. Where is the rest of the voltage and why not all the volt is use it up?

What can I do to make it run full power?

Second question: Can I attach a dc-dc boot converter at the end terminal of the solar panel and increase the voltage directly without using anything else? What is wrong with that idea?

thank you for your responses. I am trying to run a water pump. I have purchase a mppt unit that has 80v input max, and two lead batteries deep cycle, but I notice that I have to convert the voltage to ac then back to dc and make it 130v. how can I make this work, do I connect the panels in parallel and then charge batteries, have ac inverter and ac-dc inverter, I am not sure if this Is practical at all and how many batteries do I need, can I

Answer 1

Wire your panels like so:

Wired exactly as shown, you'll get

18.5V * 7 = 129.5V
at 
5.9A * 2 = 11.8A
= 
129.5V * 11.8A = 1528.1W

Answer 2

The solar you are using have what is known as a load curve. This simply means that their output voltage and current follow a distinct relationship. You don't say, but the 120V is probably the open circuit (OC) voltage of the panel. Which means how much voltage it will generate with no load. At OC the panel will also not generate very much power.

To get the most out of your panels you need to have a MPPT controller (MPPT = Maximum Power point controller) which is essentially a fancy DC to DC convertor than allows the panel to operate at the point that allows it extra maximum power.

In short, you loading the panel too heavily. In fact it would be a very rare circumstance that you could operate the panels at their maximal point by directly connecting the motor as they have very different characteristics.

As long as you motor is not damaged by running at a low voltage and it can do what you need then this setup may be sufficient and you can get away without any fancy controllers.

Answer 3

The "where have all my volts gone" question is covered already.

"Can I attach a dc-dc boot converter at the end terminal of the solar panel and increase the voltage directly without using anything else? What is wrong with that idea?"

In order for a DC-DC converter to work, it has to draw even MORE current from the source (your panels) in order to pump up the voltage. Even in a perfect world, your net gain would be zero... but the DC-DC converter will ALSO waste some power (heat loss, etc), so your realistic net gain will be a net LOSS. Upshot: you'll have even LESS power to your motor than you have now.

If you're going to run that pump at the full rated 130VDC on photovoltaic, you're going to have to add more panels. Given that you're now reading 60V at the motor, you'll need AT LEAST twice as many panels to get the motor up anywhere near in full sun with perpendicular insolation.

The batteries... assuming 12V lead-acid batteries, you'll need them to store and deliver a total of at least 125 amps per hour to run that pump, probably more than that because the pump motor won't be 100% efficient. Count on twice that. If you're using photovoltaics to CHARGE those batteries, then the photovoltaics will need to supply enough to run the pump motor PLUS enough to charge the batteries. Your sum total power requirement will be more than twice as much as it takes just to run the pump, if the pump needs to run full-time. If the pump is only operated 50% of the time, you could load-switch... charging the batteries while the pump is off, not charging while the pump is running.

So... if the pump needs to run 100% of the time, AND you need to charge the batteries, then you'll need at least FOUR times as many PV panels as you now have.

Answer 4

I'm assuming that you meant the 6 solar panels give 120VDC when they're all connected in series. Not 120VDC each, and thus 720VDC in series. Please edit your question to clarify.

Anyway, the primary piece of information that you're not considering is the rated power output of the solar panels. Your motor is 2HP, which equates to about 1500 Watts. The power capacity of your solar array needs to be at least 1500W. A bit more, actually, to account for losses and less-than-peak sunlight. My guess is the panels you have add up to far less than that.

The reason you're seeing 60V is because the motor is overloading the solar panels. The panels are giving the motor literally every electron they're generating from solar energy. This has the consequence of driving the voltage down as the panels are starved of charge carriers. It's called a "brown out". The same thing happens when to the power grid sometimes. When the power plants can't produce enough energy to keep up with demand, the total voltage in the grid starts to drop, which makes everyone's lights dim.

The answer to your second question is yes. Since you gave no more information about what you're trying to do, I can give no more information than that.

Answer 5

When the motor is running, the internal movement of the rotor creates a negative voltage according to the solar pannels polarity. So your diference of voltage is going exactly where it should; to power the motor.