what size solar controller for 2019 tab 400

Tundra57

I have a 2019 tab 400 with factory solar. Earlier units have 200W and a PWM controller mine has 190W solar with an mppt controller. I was told this by tech support at Nucamp.

So I am adding a renogy suitcase 200W to add to this seperately external. I decided I would buy an MPPT controller for them. The tech guy at Renogy reccomended a 20Amp unit. Also if you look at the solar kits, the 200W version has a 20A controller.

So I bought a Vicron 20Amp 100volt MPPT controller. When I started to install it I noticed the factory Vicron is a 10

Amp 75Volt unit.

Now I understand it is difficult to get full output from Solar panels, but it seems that the factory solar controller could be limiting the ouput of the factory cells. 190W let's say battery charge voltage is 14.4v fast charge, that could be 190/14.4 =   13.2 Amps. I see the 10 Amp controller can do a little more, but 10Amps is it's continuous rating.

Any one with more knowledge know what I am missing?

Sharon_is_SAM

Maximum wattage the controller can manage 10 amps x 12 volts = 120 watts

Panel amperage output under ideal conditions 190 watts/12 volts = 15.8 amps

Although it appears the charge controller may be under sized, remember, these results are generous and probably typically not achieved.  For sure you could not add any more panels to the installed charger.  

How are other owners with 10 amp controllers managing with their solar?

DenisP

I have 200 watts of factory solar on my 2018 400 with a Victron 75/15 solar controller.  I have a 100 watt Renogy suitcase with its' own MPPT controller which is wired directly to the battery bank (independent of the factory solar).  I have yet to see full solar gain (200 watts) regardless of amount of sunshine so I believe the the 15 amp solar controller may be right sized rather than under sized with my configuration. I just checked my controller and it is a 15 amp not 10 amp and have edited the post accordingly. 

Cbusguy

@DenisP sounds like and experiment to me.     Someone with a 400 and factory installed solar should borrow or install a 100/20 or better victron to see if the limiting factor is the 75/10 charge controller.

DenisP

@Cbusguy I checked my controller and it is a 75/15 as noted in my edited post. 

Cbusguy

@DenisP I am fairly certain in my 320 I have a 75/10 which makes sense as the best I have seen out of the stock solar is about 6 amps.    the 400 with more and larger panels would need a bigger controller

Denny16

We have a TaB 400 with the factory single 194 watt solar panel and a Victron 75/15 which seems to keep up with the battery just fine, judging by the history reports during actual normal use.  Place a heavy load on the battery, and any solar controller is going to have a hard time catching up, as you are only getting 30+/- VDC at 190+ watts max in bright sun, which is less that 10 amps of,charging power, so a 100/20 is not going to pass on more charging amps than the panels generate.  Seems to me the 75/15 is correctly sized for the 200 watt solar setup.
cheers

Tundra57

@Denny16 my point is that since I have a 75/10 with my 190w factory solar it seems Nucamp is relying on the panels not being 190W so fitting an underpowered controller. However they do advertise it as 190w. If ever the panels did give full output, the controller would limit it. So it really is not 190W ever.

So either fit a 15Amp controller or don't advertise it as 190W. Am I wrong? The cost difference is a bit over $100 between the 10Amp and 15 Amp. So it is a significant saving for Nucamp.

I'll text their tech line to see what shakes out.

Denny16

I follow you now yes, a 75/15 seems like a better fit.  However say your panels could output 30VDC at 10 amps, you would have 300 watts, so 190W at 20-30 VDC output at 190 watts is less than 10 amps, so I do not think your 75/10 is limiting your solar charge capacity.   Have you used the Victron phone application to check your charging history, showing the VDC and watts of charging you are getting?
Cheers

Tundra57

I see your logic but the purpose of the mppt is to correctly convert the watts in to watts out. So if the output is less voltage than the input, surely I'll get more current out to maintain Watts. Else what is the point of the expensive controller?

I have not logged on to the Vicron for a while. I can look maybe tonight.

Denny16

I think it depends on the solar panels and what they can actually output.  Components in a solar system are usually matched in a system.  The new one piece 194 watt solar panel now used outputs more useable power than the older 2-panel 190 watt setup.  The new panel was matched to the 75/15, and seems to work well based on my history readings.

You might get a slight increase in charging with the 75/15 over your 75/10, but the 100/20 would be overkill unless you plan to add more solar panels to the setup.  Not all,solar panels are built equal, and often watt ratings are in the high side.  You need to determine the actual watt output at 12vdc or 24vdc to determine the correct size controller.  

A MPPT, “checks output of PV module, compares it to battery voltage then fixes what is the best power that PV module can produce to charge the battery and converts it to the best voltage to get maximum current into battery. It can also supply power to a DC load, which is connected directly to the battery.”

If you determine your PV panels are outputting more than 140 watts at 12 VDC, than going to a 75/15 might be an advantage.  The charge controller changes the charge voltage going to the battery determined by the current battery charge state and temp.  It does not change the charge amperage going to the battery, the PV determines the watt/amperage level at a given voltage.  So if your panels only generate 140 watts of power, you are only going to get 10 amps out max to the battery, upgrading to a 15/15 or 100/20 is only an advantage for using larger output PV panels.  The 75/10 is rated for 140 watts per PV panel and the 75/15 for 220 watts per PV, both are rated for a 15 amp load output.  How are the two panels connected, series or parallel?  

For details see the PDF downloads at the bottom of the main page here:  https://www.victronenergy.com/solar-charge-controllers/mppt7510

That said, the only way to find out if upgrading will add more change to your setup is to get a 75/15 and try it out.  Your PV panel setup is too small for a 100/20, so no advantage for getting one, as it will not increase your available charging rate from what a 75/15 would do with a sub 200 wattt PV setup.
cheers

Tundra57

I ordered a new 75/15 from Vicron to deal with the factory solar.

I am keeping the Renogy 100/20 Vicron for the new 200W external panels.

PS I know the controller varies output voltage, but that is how it controls charge current. Mr Ohm was a clever guy. BTW when I was am electrical apprentice, one of my teachers was called Billy Ohms. No relation - I asked lol.

Denny16

The MPPT 75/15 should work just fine.  This is what I have on the 2018 TaB400 factory 194 single PV solar system.  I just added the Victron 712 Smart Battery Monitor also, which will work with the Solar controller to optimize charge levels.

Yes I was also an apprentice to a house electrician for a summer whilst in school.
I also studied electronic engineering in college for a short while, and switched to photo journalism.  Mr Ohm was very clever indeed.  

PV panel output varies the voltage, but the max current available at full output is the max.  From what I understand, the MPPT varies the charge voltage, which would control the current to match what the battery needs, depending on the charge rate, which is variable.
cheers

Tundra57

Yep correct. So I chatted with an engineer from the USA main dealer, he agrees with you that most likely the 10Amp controller would be fine, however it it possible that it's output could be exceeded then I would lost some of that energy. He tells me it's not uncommon for RV manufacturers to rely on this to save a few bucks. When you multiply up by production numbers it's a significant saving for Nucamp.

I'm not sure if that's why they did it.

However I still have gone ahead and purchased the 75/15 which some Nucamp trailers have. I guess the later 194 Watt were even more efficient and they would have lost what they gained with a 10Amp Vicron.

So I guess I've said everything I wanted to say in this post and usual learnt a lot. I'm excited to find out how good

Tundra57

Interesting. I have upgraded my solar controller to a 75/15. I just got word through my dealer that Nucamp would send me one for free. Pity I have installed mine. Nice to know they all care. :-)

Denny16

Yes, you only need to ask.  NuCamp is very good at customer service and correcting ant issues.  They are replacing the front window and are redoing the floor in our TaB400, two years after is was built.  We purchased the new 2021 larger aluminum tub, which will get added with the floor replacement.

Our late 2018 (built in the last 2018 run) has the 194 watt single solar panel and came with the Victron 75/15.  Not sure why your 2019 came with the smaller controller?  I also added the Victron battery monitor, which provides the 75/15 controller with battery temperature info, to further fine tune the charge rate.
cheers

Tundra57

Maybe they realized it was a mistake. Either way onward we go lol.