Redarc BCDC 1240D - potential conflict?

[ntz1111]

I have the 1240D with built in mppt controller (solar functionality is unused) and a Victron MPPT 100/20 connected to a 180w fixed solar panel. The redarc and victron circuits operate independently.

Question : if I want to add a portable solar array ( I heard good things about the Bluetti PV200) can I simply utilise the Redarc solar input together, and without conflicting with, the Victron and the fixed 180w solar?

Ideally I'd want to suck up all the sunshine I can get rather than having to sacrifice (switch off) the less dominant array but I don't know if that's possible.

Question 2- I want to upgrade the existing solar panel and the x2 75AH leisure batteries as overnight, or overcast days, in hot climates, the 2 fridges/fans seem to be taking capacity down to 50%. What s the ideal battery Amp hour: solar Watts ratio?

Thanks for any advice

 

[e9999]

Not familiar with that Redarc unit specifically, but in general, AFAIK there is no problem having several different charging systems connected to the same battery. They will work along each other and of course charge the battery faster than if there was only one. So, barring some weird Redarc peculiarities, I don't see why you could not have the Redarc (on both starter battery and panel if it can do that) and the Victron working at the same time. One oddity that I'm aware of with several systems working at the same time is issues of excess equalization, but that is a minor consideration and can be taken care of with settings.

As far as how big a system to get I don't think there is a magical ratio. It depends on your circumstances. I would say figure out your load draw, figure out how much electricity your panel can generate on average per day, figure out how far down you want to discharge your batteries (LFPs are more forgiving than FLA), figure out how long you can afford to be without sun (UK, right?), and that will tell you. Basically, if your panel provides more on average over a typical day than your load draws that day, you are good overall. The battery is then there just to take care of the nights and lower than average radiation. But since you already have a DC-DC charger from the starter battery, you can always use that to replenish your house batteries anyways, so there is probably no need to go overboard on those, unless you are parked for days at a time. Myself, I would size the panels to be a big bigger than the load, and the battery to last for a couple of days without much sun. I think that would cover most of my needs.

 

[LandLocked93]

Question : if I want to add a portable solar array ( I heard good things about the Bluetti PV200) can I simply utilise the Redarc solar input together, and without conflicting with, the Victron and the fixed 180w solar?

Your solar controller redundancy is great!
I recommend adding the portable array to the existing fixed panel - all going thru the Victron primarily - in a way that allows a single connection to move both panels between controllers.
Keep the RedArc controller as the unused, redundant backup that can be switched to in the event the Victron goes toes up in clay county.

Question 2- I want to upgrade the existing solar panel and the x2 75AH leisure batteries as overnight, or overcast days, in hot climates, the 2 fridges/fans seem to be taking capacity down to 50%. What s the ideal battery Amp hour: solar Watts ratio?

Solar regen is a fairly weak source and unlikely to ever overrun the capacity of either the Victron or the RedArc. But also, it is unlikely that you will have enough solar cells to meet demand over days of no sunlight as well.
So...view the solar source as a trickle charge during sunny times. But view alternator regen as your primary source to top off the batt bank.

This eliminates potential conflict no matter which controller is in play at any given time.

 

[ntz1111]

Thanks chaps. I just realised it does amount to a redundancy ( always welcome!). On tour (beyond UK incessant rain) I tend to plot for up to 5/6 days but parked in the sun facing south each time to maximise solar uptake is sweaty business. The 180w panel can actually replenish depleted batteries during the day so I know it can be done with my power demand. But we were cooking and the discharge /charge graph was cycling a cross both upper and lower limits (not great for battery longevity).

I've been told that for any set of panels, the dominant array will always take priority but will be brought down by the shaded one. That, I'm guessing is for a single circuit which is why I'll probably not feed the Victron with 2 inputs.

From what I gather here if the Victron is putting in a lesser charge than the the solar of the redarc, it should be fine, right?.

 

[e9999]

Lots of info out there on what is happening with shading when in parallel vs series mode. Very different.

If you have two sources to the same battery, they don't have to have the same power delivery, they will each do what they can given what battery voltage they see and their settings. (You do want to have the settings match, ideally.)

 

[spressomon]

Charging your battery/batteries won't care if you're using more than one charge source. If you're using mismatched PV panels then you should utilize a separate solar charge controller for each panel/panel array. Although this involves more equipment (charge controller, fuses/circuit breakers if applicable, wiring, etc.,) it, depending on the specific application, could make your system more versatile and possibly less effected by shading.

Also note, at least with all the Victron controllers I've used/am using, be aware the solar panel(s) must "see" a minimum 5v differential (12v systems) between the Vmp of the panel(s) and the resting battery voltage otherwise current flow/charging will not be initiated (until such time the resting voltage of the battery lowers enough to be at least 5v differential between the panel and the battery. This is one potential advantage of connecting PV panels in series. Also, again depending on your panels and length of wire runs, this is another important reason to calculate voltage drop due to increased resistance and size the wire accordingly.

 

[e9999]

^ Of course, with a panel in series you get higher voltages, and there are certainly benefits to that, but TBF in real life, the 5V differential thing is really not much of an issue. A single typical "12V" panel will normally produce over well 20V open circuit even with very little sun. It's the current that is a strong function of radiation, not the open circuit voltage.

And, yes, of course having a controller/charger for each disparate panel is best, but that can be expensive, and with a bit of looking at MPP voltages and currents, one can figure out whether it's best to combine disparate panels in parallel or series or combo with just the one controller. You'll usually (not always) get more than just one panel, but usually just not the sum of both nominal powers as one might perhaps expect.

 

[ntz1111]

Thank you all