Hello Everyone,
Regarding bridge rectifiers I’m hoping someone here can guide me in the right direction. I have two large solar panels that are designed for a nominal 48v DC system in my case for charging batteries. The panels generate about 60 volts each when activated in sunlight. I run the panels in series to produce 120v DC which is required to operate a 60 amp charge controller that charges four 12v batteries running in series to produce 48v DC. The panels themselves require a constant low current 48v DC input to activate. The problem is if I connect a wire from the batteries to the panels to activate them with the 48V from the batteries, the panels immediately generate the required 120V DC when activated which then runs straight back to the batteries through the wire providing the 48v for the panel activation. The same is true if I use a 48v DC wall adapter - the wall adapter activates the panels with 48V DC and the panels respond by immediately producing 120vDC into the adapter output which smokes the adapter within a few seconds. I have seen on the internet some mention of a bridge rectifier preventing “feedback” in a DC circuit. Does anyone know if a bridge rectifier would work in this case to stop the 120vDC from the panels from going back into the 48vDC wall adapter (or batteries) when they are used to activate (wake-up) the panels ? In short I need something in the circuit to allow 48vDC to flow out in one direction to activate the panels but stop the 120vDC coming back in to the 48v batteries or DC adapter.
Thanks Much!

 

hi M,
Welcome to AAC.
Read thru your notes, any chance that you could post a block sketch of the project, a steering Diode looks like a possible solution.
E

 

Cam you provide a link to a description of the type of panel you are using that requires a DC current to activate? I have never heard of such a thing.

Bob

 

No panels that I have heard of require a dc activation current.

A solar controller would require "a low 48v dc supply" ie connection to a battery, to work. Connecting panels to any controller without the battery connection would not produce through current or apparent output voltage, until the battery was connected - is that the issue?

Or maybe it's confusion regarding connecting panels in series to raise the feed voltage to a MPPT controller, vs the parallel connection required for a PWM controller.

Perhaps supply a diagram showing the specific equipment and interconnections involved?

 

hi M,
Welcome to AAC.
Read thru your notes, any chance that you could post a block sketch of the project, a steering Diode looks like a possible solution.
E

Hi Eric,
Thank You for the response and the welcome. The attached is a pic of the block sketch

 

Cam you provide a link to a description of the type of panel you are using that requires a DC current to activate? I have never heard of such a thing.

Bob

Absolutely Bob, thanks for asking. Here are a couple of promo links on youtube. I believe the video from the convention mentions at the end that the voltage feedback is a safety feature. Also attached is a pdf data sheet. Mine are the 500w version.

 

No panels that I have heard of require a dc activation current.

A solar controller would require "a low 48v dc supply" ie connection to a battery, to work. Connecting panels to any controller without the battery connection would not produce through current or apparent output voltage, until the battery was connected - is that the issue?

Or maybe it's confusion regarding connecting panels in series to raise the feed voltage to a MPPT controller, vs the parallel connection required for a PWM controller.

Perhaps supply a diagram showing the specific equipment and interconnections involved?

Hi boostbuck,
Thanks for the response. What you described could possibly be the issue. I will have to test that. My controller is an MPPT 60 amp made by Make Sky Blue. I just now added a diagram to one of the above post that you can look at but I must mention that I have not setup the system per the diagram yet. Reason being that I was looking at the instructions for the controller and it says that for a 48v battery system that the controller wants to have 72vdc to 160vdc open circuit voltage coming from the panels. So the first thing I did was check out the voltage and current coming out of the panels. When I put them in sunlight, an integrated led light comes on and changes from red to green indicating that the panels are working, but no voltage comes out because they are not detecting any batteries. So my next step was to take 5 small 9v batteries wired in series for 45v and clip to the pos and neg on the panels and sure enough the panels instantly kick out about 60v in stand alone or parallel and 120v in series. But there is no voltage coming out of the panels unless I have the 45v going in to them form the small battries so I assumed that the controller wouldn't be getting any power from the panels. I guess my next step is to hook up the controller to a 48v battery bank and see if the panels can detect the voltage through the controller and turn on.
Thanks Again
Manny

 

The spec sheet for the panels describes "built-in MPPT controller" so they are probably behaving as I surmised - the integrated controller will be switched off until a battery is detected. This company is no longer in operation, it seems. I haven't located any info regarding connecting them, sorry.

 

hmmmm.... if the panels incorporate an integrated MPPT controller, then I am guessing they should be connected directly to the battery. You are connecting the output of the MPPT controller (in each of the panels) to the input of the SkyBlue controller. The panels will be determined to provide battery compatible voltages (~48) to the SkyBlue, which is expecting to see panel voltages in the range of 72 volts or more.... ..... ..... this is not likely to work, imo. The SkyBlue controller is superfluous and preventing your panels working, perhaps.

 

... finally(!), you measure the panels in sun at 60v, which would make sense as the panels try to provide maximum permitted battery voltage (for a nom. 48V system) to force current into the batteries.

If I read the data sheet correctly, the panels should NOT be connected in series to raise the voltage, but rather in parallel directly to the batteries (but I'm guessing).

I have NO IDEA what will happen connecting MPPT controllers outputs in series and then to the input of another MPPT controller. No surprises it doesn't deliver power. Given that they are each effectively tracking SMPSs, they might mutually oscillate to death??????

Good luck!