48v Solar Controller

[tuberider]

I have 4- 12v 100w flex panels and want to put them in series for 48v. I have a blue sky 3024 controller and contacted Blue Sky but they said it will only support 24v and I don't want to series parallel them. I tried it anyway and the controller worked great for a few months but quit. Is there a solar controller out there that will take 48v and convert it to my 24v batteries.

[grjfield]

I am learning this myself. Why are you wanting to series the panels to 48 volts when you have 24 v batteries? If you series/parallel them to provide 24 v wont you amps double up? (a good thing?)

[Electric Ray]

Originally Posted by grjfield

I am learning this myself. Why are you wanting to series the panels to 48 volts when you have 24 v batteries? If you series/parallel them to provide 24 v wont you amps double up? (a good thing?)

If both of you read up about MPPT controllers you will see that they need a voltage higher than the maximum charge voltage of the batteries in order to do their job, Most 24v MPPT controllers will be happy accepting the solar input up to 150volts so just string the 4 panels in series which will probably give you something in the order of 65 volts. The better controllers will automatically set the charge voltage based on what battery you connect to them (12/24/48) some you have to configure what battery type (Flooded,Sealed/AGM/LiPo) etc. But all do the voltage conversion (high solar to low battery) and do the charge cycle (Bulk/Absorption/Float) that a mains charger does.

The advantage of the higher voltage from the Panels to the MPPT is lower losses (i.e higher efficiency) because the higher the voltage the lower the current for the same Power ( DC watts) because P (DC watts) = V (volts) x I (Amps).

Apart from these losses the current going into the battery will be the same for a 48v string as a 24v string) so long as the Input (solar voltage) is higher than the output(battery) voltage

Still confused? ask away

Regards

Mark

[grjfield]

Yup still confused...
I was told that some MPPT controllers can take a solar panel putting out 12 volts and boost it up to 48 volts if that is what the battery configuration is set up for. Is that not correct?
Thanks
Gerard

[Electric Ray]

Originally Posted by grjfield

Yup still confused...
I was told that some MPPT controllers can take a solar panel putting out 12 volts and boost it up to 48 volts if that is what the battery configuration is set up for. Is that not correct?
Thanks
Gerard

That's a magic box I haven't come across an MPPT that does that.

MPPT stands for Maximum Power Point Tracking. In order to do that effectively, the input voltage needs to be about 7 volts higher than the battery. It then works out the optimum input voltage that gives it the most power, it does this continuously. It cannot boost the voltage above the highest voltage that the panels can provide.

It is easy to provide the MPPT with 7 volts more than the battery as most big panels are at least 37volts so two in series gives you 74v = plenty

Keep asking, you will find out how easy it all is, its pretty much plug and play...

[tuberider]

the four 12v flex panels don't produce enough output volts when in series - parallel to work. Even though Blue Sky said 48v was to high I've had it set up in series since I first posted this question. So far no problem.

[Electric Ray]

Originally Posted by tuberider

I have 4- 12v 100w flex panels and want to put them in series for 48v. I have a blue sky 3024 controller and contacted Blue Sky but they said it will only support 24v and I don't want to series parallel them. I tried it anyway and the controller worked great for a few months but quit. Is there a solar controller out there that will take 48v and convert it to my 24v batteries.

Aha!

Going back to your original question

these are the specs of your controller, terrible cut and paste so you can read the whole thing here

http://www.blueskyenergyinc.com/uplo..._datasheet.pdf

Output Current Rating
Nominal Battery Voltage 12 / 24VDC
PV Input Voltage 57VDC maximum (Recommend Maximum VOC @STC <=45.6VDC
Power Consumption
0.35W Typical standby1.0W Typical charge on
Charge Algorithm 3-stage Bulk/Acceptance/Float Plus Equalize
Acceptance Voltage 14.4VDC (range 14.0 – 14.8VDC
, 10.0 – 40.0VDC
)
Float Voltage 13.2VDC (range 13.2 – 13.8VDC
, 10.0 – 40.0VDC
)
Equalization Voltage
15.2VDC (range 10.0 – 40.0VDC
)
•
automatic or manual operation
Single output field configurable as either: 20 Amp load controller –or– 2 Amp auxiliary battery charge

Bottom line is your controller can handle an open circuit voltage of 57volts but it is recommended that this not exceed 45.6 volts. It is quite possible that you exceeded these voltages on a sunny day as 4 x about 17 volts (typical of a 100w panel) would be about 64vDC, you will know what sort of voltages you exposed the controller to by reading the Open circuit voltage on the back of one of the panels and multiplying this by 4. Next time buy a controller that has a max voltage higher than this voltage (like a victron etc). If this Blue sky unit was still operational it should work with two series strings of two panels,connected in parallel. which would only expose it to about 34VDC, comfortably inside its max.

Keep asking, you are getting there

Mark

[finnarne]

Originally Posted by grjfield

Yup still confused...
I was told that some MPPT controllers can take a solar panel putting out 12 volts and boost it up to 48 volts

Originally Posted by Electric Ray

That's a magic box I haven't come across an MPPT that does that

Genasun boost controller will do that.
But I'm not sure OP asks about that

[Electric Ray]

Originally Posted by finnarne

Genasun boost controller will do that.
But I'm not sure OP asks about that

Yep you a right, up to about 350 watts and cheap. I guess if you wanted to just put a very small panel onto a 48v battery to keep it charged/ overcome self discharge that would work. For any serious PV charging I dont think this is very practical when compared with the efficiency of a step down MPPT because the current from the Panel to the MPPT (the greater distance) will be much higher than the current from the MPPT to the battery (the smaller distance). Putting that aside just because it is possible, it is probably not the best way of charging a 48v battery from a number of panels.