question

https://www.victronenergy.com/blog/2014/03/28/matching-victron-energy-solar-modules-to-the-new-mppt-charge-regulators/

Hi RV. The 75/15 will simply limit itself to 15A into Vbat.

It's not just about looking at the V it's charging into either. If there's a load on the batts it will do it's best to charge batts and cover loads too. Up to 15A. All's well. Pretty good match too, that's what you'd do.

Guessing you're going 4x mppt's with 4x panels for shade issues? If not, you could do this also with a single 100/50. Say by wiring all panels in parallel (4P) or 2S2P depending on panel specs.

If you need help with that option, just give us your panel specs, say Voc, Vmp, Isc.

My biggest concern is to ensure that the customer can drop their LiPo 24V battery down to 19v and have the system still function. Apparently this was an issue in their last coach (23V low).

Then you/they have a *real* issue. That's flat-battery territory, no grunt left - blackout. Or a genny.

Boekel's link is probably as good as any. But you talk just *one* panel, so let's be clear - how many is there?

And yes , rest assured that the /15 mppt will reject any current over 15A, in total safety.

Sorry we're not quite there yet - how many panels?

I tried to use the link. But the Excel spread sheet didn't work for me. I cannot enter a voltage. It just says all the drop down choices are #INVALID. This could be because I could not indicate a module. All I saw was a list of victron modules. I tried one at the bottom, which seemed like it should be customizeable?

It is a LiPo battery and they want to get every penny out of it. Nominal is 24V, how low do you think they should go. I think telling them they can only go 23V because its a LiPo limit is one thing. But it would be a whole different thing to say it's cause of the solar setup.

Also, I see from spec that BlueSolar Max Current is 20A, max cut-off is 15A. But SmartSolar is 15A for both. Can BlueSolar be changed so it's max is 19A? Because even if I got them to 20V, they might be okay with. That's about the cut-off for the Victron Inverter (anyway).

20V is 16A.

Thank you!

Yes the 4 x75/15 would be ample and the extra amps when at 19v battery voltage would be discarded.

Also keep in mind that the Panels 69V VOC is getting VERY close to the Regulators Max voltage and on a cold day this may exceed the regulators limit

BUT 1 x 50 amp or 2 x30 amp units would be a better solution as the max voltage would be 100 and may even be cheaper. overall.

WARNING However dropping the LP down to 19 volt is not a good idea, as this would be close to a 100% discharge, the BMS should be cutting it off way before that anyway. sounds like his bank is to small for the loads he is drawing overnight.

anyway thats up to your customer but he is looking for battery trouble, if he keeps going down to 19v .

@rvsolartech

Please use a knowledgeable Victron installer, your numbers don't make any sense, and you don't seem to read the links and solutions provided.

My answer was too long to post as a comment, so here it is as a seperate answer:

I posted this link:
https://www.victronenergy.com/blog/2014/03/28/matching-victron-energy-solar-modules-to-the-new-mppt-charge-regulators/

If you'd have read it, you'd have read that the 75/15 MPPT is capable of handling 15A of solar current, your panels have a short circuit current of 6,05A, so it could even handle two panels in parallel

At 12 volt, say 14,5 volt charging, one 15A MPPT can deliver 220 W of power, so you wouldn't use the full output of the panels during the peak of solar.

At -10 degrees C, your panels are at the limit of the input voltage limit of the MPPT's, I don't know what temperatures your installation will see.

A 100/20 MPPT is only a little bit more expensive, but can safely handle voltages at sub-zero temperature, and can handle almost 300 W so the panels are used more efficiently

As I suspect the panels are mounted horizontal, you could also use 100/15 MPPT's as the full output power will never be seen except when the sun is directly aimed at the panels.

Please do over.

This is a 24v system not 12v.

Also, I responded to your original link the first time and explained that the program was giving me an error when trying to enter voltage. All drop downs are #INVALID.

On the 19V, surely they have had some advice that referred to lead acid batteries and they are trying to apply to LiPo.

My lipo has an absolute do not cross discharge line of 20V (i.e. if you go below that, you have damaged the battery). I wouldn't have thought its sensible to cross 22V as a maximum scheduled discharge.

Back to basics for an RV or boat with flat-mounted panels.

• The nn/ part of an MPPT product specifies the absolute maximum open circuit voltage. Always calculate the open circuit voltage at the expected minimum panel temperature.
• The /nn part of an MPPT product specifies the maximum current that is transferred to the battery independent of the battery being 12 or 24 volt. Any excess power will simply be ignored as the controller limits the current to the battery.
• Derate the nominal panel power for conversion loss, horizontal operation and temperature. In Australia we typically use .7 as the actual maximum power.

For this case using a 330-watt panel into a nominal 24-volt system, the available maximum power is 330 x .7 = 231-watts. On a 24-volt Lithium, with a battery voltage around 27-volts, the nominal MPPT output current will be 231 / 27 = 8.5 amps. At 28.4 volts it will be 8.13 amps. At 24 volts it will be 9.62 amps.

This shows that a 75/10 MPPT is a perfect match to the 330-watt panel in a 24-volt system. In a 12-volt system, one would need the 100/20. For multiple panels, each panel can have its own dedicated MPPT.