Single solar panel simultaneously connected to 2 separate MPPT controllers

[towe0609]

Hi - having trouble getting my brain around this one ... hope someone can help. I suspect its a silly question ... but I need to have my eyes opened.

Question 1

Situation: 80W panel permanenty mounted to roof of vehicle, and can be connected via Vitron 15A MPPT controller connected to starter battery.

Slide on canopy with CTEK250S and 170Ah AGM, solar panels permanently mounted to canopy doors.

I can manually switch the solar input of the Vehicle mounted panel between the Vitron to the CTEK but I'd rather it was set and forget.

I have a WAECO CDF-11 fridge as centre console which is powered from starter when slide on is off, and from 170Ah AGM in canopy when slide on is on.

The slide on MOSTLY stays on the vehicle, but I recently added the Vitron so when the slide on is off vehicle, the solar on the vehicle roof can charge the starter.

Once isolated the CTEK250S doesn't provide charge back to the starter battery.

What I'm wondering is how will the Vitron and CTEK250S behave if I connect the solar input to both controllers simultaneously?

The main purpose of the solar is to keep the 170Ah battery in the slide on happy as it is powering the fridges, but it would be a bonus if the solar could be 'shared' with the Vitron to ensure the starter is maintained.

I have had issues with the starter being drained if it sits for extended periods, so it always getting some solar charge would deal with (well mask it!) that as well.

Question 2

Will the Vitron blow a fuse if more than 15A of solar is supplied? The manual specifies "Max. PV short circuit current 15A" and "Nominal PV power, 12V (1a,b) 220W" with the note reading "1a) If more PV power is connected, the controller will limit input power." I'm not sure how to interpret all this.

I understand it will only provide 15A of charge/load.

[Tombie]

So....

Victron is attached to its own panel on the vehicle.
Ctek to its own panel on the camper.

Start battery connects to camper battery when mounted on the vehicle?

If so, just leave both controllers running their panels.
No it won’t share back to the front from the Ctek, but the main battery will charge from the Victron

[towe0609]

The Starter Battery is connected to the Camper Battery via the Alternator connection on the CTEK250S.

"Victron is attached to its own panel on the vehicle.
Ctek to its own panel on the camper."

'Own panel' ... there are are separate panels involved (3 permanently mounted and a folding portable), but I was hoping to connect them all in parallel and connect to both controllers.

Having the vehicle roof mounted panel only connected to the Vitron-Starter is OK so long as the 'excess' power available is directed back to the camper via the CTEK250S ... is that what you are saying will happen ... ie. assuming the starter is depleted a bit and hence isolated by the CTEK, the solar input via the Vitron will lift the voltage of the starter, the CTEK will connect the batteries in parallel, and the charge from both the Vitron and CTEK will be available to 'the bank'.

[Tombie]

Here’s where a trap occurs.

The Ctek can only provide power via 1 method at once.
It is a limitation of the unit.
Either Alternator input or solar.

What happens is when the vehicle is running the alternator passes through the ctek to the auxiliary. Once you stop the voltage drops and the solar cuts in.

I’ll post this bit, get back to the office and type on a keyboard

[roverrescue]

Towe
I’m not fully up to speed on the Ctek unit
But what you say at the end makes logical sense

Victron should keep starter above 13.5V with sun on it (you can manually adjust bulk absorption and float voltages if you want)
(Which is over the trigger voltage for Ctek) so charge then flows from starter to Ctek
Which will drop voltage of cranker and Victron will drop back to bulk or absorption states and pour in current.

Meanwhile the Ctek is taking charge from cranker and it’s own PV input to charge the house bank.

To be honest it is not the most efficient use of power but should work?


With regards to over supplying a Victron
I’ve seen it done! if you feed in 800W of panel the output is limited to 15A
BUT things melt - namely the wiring connection at the input to the Victron!

Not ideal


If it was me (and I know it’s not) I’d lose the Ctek
But a big Victron for the camper
Run heavy cabling via a marine switch from cranker to house
Then have two isolated PV systems

Of house is down and you want to bump it’s charge open switch

Steve

[Tombie]

At a keyboard now....

Depending on the model Ctek 250 there are 2 methods of function:

Ctek D250S (older silver unit) is mutually exclusive.
Ctek D250SA (Black unit) can run Solar & Alternator inputs concurrently.

If you have the Black unit:
The Victron will supply power to the primary battery and will open the connection to the Auxilliary battery assisting in charging. (Your set up will work perfectly).

If you have the silver unit:
This is where you'll struggle.
The unit will isolate on voltage and the Solar on your camper will commence charging the auxillary house battery.
*if* you then add the Victron to the main battery, its voltage will rise. The Ctek will connect and the Ctek connected solar will cut out.
This will effectively result in only the single panel on the vehicle providing any charge to all the batteries - reducing charging capability.


Which unit do you have?

[roverrescue]

Thanks Mike
Details I didn’t know

My idea is even more sound now
Lose the DCDC replace with solid wiring and a switch
Buy a bigger Victron for the camper

S

[towe0609]

At a keyboard now....

Depending on the model Ctek 250 there are 2 methods of function:

Ctek D250S (older silver unit) is mutually exclusive.
Ctek D250SA (Black unit) can run Solar & Alternator inputs concurrently.

If you have the Black unit:
The Victron will supply power to the primary battery and will open the connection to the Auxilliary battery assisting in charging. (Your set up will work perfectly).

If you have the silver unit:
This is where you'll struggle.
The unit will isolate on voltage and the Solar on your camper will commence charging the auxillary house battery.
*if* you then add the Victron to the main battery, its voltage will rise. The Ctek will connect and the Ctek connected solar will cut out.
This will effectively result in only the single panel on the vehicle providing any charge to all the batteries - reducing charging capability.


Which unit do you have?

D250S - the older one.

re "This will effectively result in only the single panel on the vehicle providing any charge to all the batteries - reducing charging capability." I'm struggling to communicate the situation clearly - but when the camper is on the vehicle I'm considering connecting all the solar together in parallel (acting as 1 big panel) and connect that to both the CTEK solar input and the Victron solar input simultaneously.

But I think what you are saying is that if the Victron lifts the starter voltage above 13.4V for 5 secs, the CTEK will connect the batteries together, and accept charge via the alt input, and shut off the solar input. With the CTEK solar input shut off, all the solar will be available to the Victron. The only real downside I can see is that the Victron is only 15A wheras the CTEK is 20A ... but should work?

Am I getting there?

Lose the DCDC replace with solid wiring and a switch
Buy a bigger Victron for the camper

Appreciate the advice, but I'm focussed on a suitable set of connections working with what I've got at hand - the CTEK will remain, flaws and all. I've read plenty of threads on the stupidity of these DC-DC units and the lack of efficiency of charging via alternator (and their poor MPPT performance), and I get it ... but unfortunately I bought one long ago before my education, and will stick with it in the interests of my wallet and laziness (ie. re-doing wiring).

[Tombie]

You can’t wire all the panels to both controllers.

It’s one or the other

[Blknight.aus]

Generally

you can but shouldnt run multiple controlers from a single panel bank.

you can join the output end of multiple controllers but shouldn't

the first issue will wind up with the controllers fighting to do their thing, old school diode blocked regulators will let you do it but they're not very efficient (massively reliable though)

the second issue can wind up with controllers getting confused as they try to monitor voltages, best case one will turn off completely and leave the other doing the work untill the battery is discharged to the point where both can run, a good way to get to say 80% completely but its guess work after that.