Foldout Solar panels wiring questions ...

[Hodge]

Still sort of cloudy-ish, but the volts out of panels are now 19-21V, and the Redarc is now happily keeping the whole thing "floating". So far it works... Going to be very sunny next 3-4 days when I'm going away so, it'll be great having that keeping the charge up while car is sitting there.

Not too savvy on electrics.
Question: Does the ignition need to be left "on" for the panels to charge in the above set up?

No. Which is the whole purpose of the switchover relay coupled with the redarc bcdc. If ignition is on, and car is running and the primary battery / alternator volts are above 13 or something, the unit is charging from that...
If ignition is off, the relay switches over to solar input and charges from there if the panels are plugged in and the voltage conditions are right. It is a set and forget system ... Especially for people with permanent mounted panels, like on the roof or something.

If so, why not just use the panels + solar controller and connect directly to battery via a Anderson plug?

[the evil twin]

All wired up ready for the sun.
Excuse the following solar amateur question...
Is it normal for a solar regulator/charger not to charge below 17V or so under no load? Or is it mainly the bcdc chargers that do that ? Or maybe even only redarc?
It's 20% sunny now and I'm getting 15-16V at the connectors.... And the redarc isn't kicking in, so I dug this table up and it sort of made sense then.

Not the table below... Under no load, shuts off below 17.2V. This is my Redarc BCDC1240 unit rules. Am I understanding this right?
I assumed even at 15-16V the unit may keep "float" charging the battery....

Hiya Cobber,

For most MPPT Regs, yes that is normal becauuse if the O.C. voltage is below 17.5 then it isn't seeing the Sun

To get the system to 'initially' turn on it needs to see 17.5 Volts but may take up to a minute and a half to do so.
If there is no load and the Panel voltage drops below 17.2 the Reg turns off until it sees 17.5 volts again
If there is a load being drawn (IE something is connected and not just an Anderson swing in the breeze) the Reg will ignore the 17.2 Volt threshold and drag as much as it can from the Panels unless the voltage drops to 8 Volts (IE the sun goes away)

Hope that helps

[Hodge]

Thanks ET ! That is exactly what's been happening, I've been monitoring it and playing with different scenarios and all those rules check out.

It's funny the "raw" open circuit volts of the Panels sometime shoot above 20V ! It's sitting on just below 20 as I type this as it's in full sunshine.

[the evil twin]

Thanks ET ! That is exactly what's been happening, I've been monitoring it and playing with different scenarios and all those rules check out.

It's funny the "raw" open circuit volts of the Panels sometime shoot above 20V ! It's sitting on just below 20 as I type this as it's in full sunshine.

Yep, that 20 to 21 Volts is normal... you should have a sticker on teh Panel that has "VOC" or "Open Cct Voltage" or somesuch and then a voltage value.

The 17.5 Volts (give or take) that the Reg is looking for is the peak of the Power Curve knee.
IE that is where the panels produce the most useable power IF you have a true MPPT reg.

While we are chatting, you will also have a "Short Circuit Current" rating with an Amps value.
To test a Panel, with nothing connected and preferably at the terminals on the back of the panel in full sun and at 90 degrees plane
Check the VOC value and note the actual versus stated.
Check the Short Circuit Current (make sure you select the correct current range then just short it straight acrosss the Meter)
Work out the difference in percentage and that is how much the Panel has deteriorated
EG say the VOC was 18 and the sticker was 20 then 18 is 90% of 20 or if the Current was 3.6 amps instead of 4.0 Amps then same thing.

Depending on quality... Panels will deteriorate approx 1 to 2 % per year as normal.
Better than that, good for you, worse than that, bummer dude...