Thread: Semi-flexible solar panels - parallel v series

hey Weeds, does that read 4A at float?
how many batts?

Originally Posted by Pedro_The_Swift

hey Weeds, does that read 4A at float?
how many batts?

Umm...it must have switched to float while I was taking the pic....I pulled the system apart straight after the pic and silly me didn't check the pic when posting.

Yes in float and I'm assuming the fridge was cycling on hence the 4amps....as in float with no load I'm guessing it would be pulling 4amps

Just one battery at the moment.......

Weeds, when you say ........................ Sadly the panels don't put out the volts stated....yeah took the punt on price...best I get is high 16's are you referring to when the system is all connected up ? If so then you probably don't have a problem.

The panel specs show that they have a Voc of 21.6 volts and a 'rated voltage', probably meaning Vmp of 17.8 volts which is about right for a 12 volt solar panel. This means when the panel is placed in strong sunlight with no load connected it will read 21.6 volts and when connected to the solar reg under the same conditions with the reg working flat out the panel voltage will be manipulated by the reg to be 17.8 volts to give maximum power to the load. At any other time the panel voltage can be different.

A solar panel is not a constant voltage source, as the load on it varies the output voltage varies as does its output current. An MPPT solar reg manipulates these factors to produce the maximum output power when required.

In the case of a reasonably well charged battery the solar reg will reduce its output to match the load requirements/inbuilt charge programing so that it will not be operating at full power.

To test your panels place them in full sunlight with no load and measure the output voltage. It should read the full 21.6 volts or Voc. Switch your meter to current and 10 Amp scale and connect straight across the panel. It should read 5.97 amps or thereabouts which is full Isc. Do NOT connect the meter across any other voltage source (such as a battery) to measure current in this manner as it could produce a big spark and melt your meter or at the very least blow its internal fuse.

Your Victron 75/15 is good for a maximum of 75 volts of Voc so there is no problem in connecting your panels in series. They will actually work more efficiently this way with less power loss in the cabling to the reg which should be mounted near the battery not on the rear of the panels for optimum efficiency. Also connect the battery to the solar reg before the panels as the solar reg needs to 'know' the system voltage and be operational before the panels are connected.

Deano

Thanks Deano.....very informative

The readings are without the solar connect, just across the removals of the Anderson plug

I also have a scorpion 120w panel and it goes straight to 21v

I will have another play today over the middle of the day and post findings

No worries Weeds, sorry if I seem to be a bit 'pedantic' but this is bread and butter to me, and re reading my response I can come across a bit unforgiving at times. Not intentional, let me know how you go.

Deano