Figuring out the 2nd Number on the Victron

[AgroVenturesPeru]

Is that the number that @Will Prowse suggests in this lesson at the 12:20 minute mark?

When I calculate based on my projected 3,600W panel array and 48v battery bank I get 75A.

Buuuuuuut...I want to wire the panels in series parallel (2s4p). Based on the panels' specs that array would then give an output of 81.3V and 44.28A
So wouldn't that mean I only need a Victron MPPT where the second number is 45 minimum?

 

[gnubie]

If you want to provide full array power to the 48V battery you need to carry 75A at least out of the battery charger terminals. So the 2nd figure must be at least 75. The amp rating applies to the solar input, battery output, and if load output terminals are in your model (at this current they won't be) them too.

model = 100/75 (made up but you get the idea).

 

[RickP]

What he said. Personally I would go XXX/100 to have some add room. Also, this gives you flexibility in how you connect them.

 

[AgroVenturesPeru]

Okay so when we're considering series; parallel; series-parallel configurations for our panel array, the amperage output from this array (in my case 44.28A) is not relevant to the selection of which MPPT to purchase?

I don't yet completely understand the difference between the 75A figure and the 44.28A figure in my scenario.

 

[gnubie]

Only in that you have to live within what ever that rating is. If the controller is a 30A model you will find that the absolute maximum amps available on the PV input for Victron is 35A. If you go beyond that and something happens and your controller catches on fire you have no warranty cover. Strictly speaking if you do put more than 30A of solar current available on the controller's input nothing is going to go wrong as the controller will just current limit at 30A on the input but it's highly likely that the 30A limit on the battery charger output will be met first so in reality it is the side of the equation that is limiting.

The amp limit presents an opportunity for safe over-panelling or putting more watts on the controller's input that it can provide to the battery with the aim of improving over all production across the day or other non-peak conditions. Suppose you had a 100/30 controller connected to a 24V battery. That gives you a maximum power to the battery of about 720W. Suppose your solar array has a Vmp of 65V. 720W is about 11A. You have plenty more amp work space on the input of the controller so you put 1400W (made up, there are recommended sane limits to over panelling) of panels on the controller, still at 65V but now at a total of 20A about. You'd still only ever get 720W into the battery but now with the extra panels you can be providing 720W for more hours of the day, and even when production falls below 720W still providing more power than you could with only 720W of panels.

The system can be thought of in terms of watts with limitations, being voltage and current, overlaid. You have 81.3V at 44.2A on the input yielding 3600W. Your controller takes that 3600W and reduces it to 48V using a buck converter. The converter reduces the voltage but gains current in the process so that you get approx 3600W on the output but now it's transformed to 48V at 75A. If you can do 3600W with a differently arrange array, lower Vmp but higher amps, that's good too. There's a practical limit on the solar input voltage, it has to be above battery voltage but below the controller limit. If you had a 24V battery it would be feasible to have the array at 44V at 75A and get 3300W into the controller.

 

[AgroVenturesPeru]

If you want to provide full array power to the 48V battery you need to carry 75A at least out of the battery charger terminals. So the 2nd figure must be at least 75. The amp rating applies to the solar input, battery output, and if load output terminals are in your model (at this current they won't be) them too.

model = 100/75 (made up but you get the idea).

So would an MPPT with these specs be good enough?

 

[gnubie]

That'd certainly cover it and give you space to expand too.

 

[AgroVenturesPeru]

The system can be thought of in terms of watts with limitations, being voltage and current, overlaid. You have 81.3V at 44.2A on the input yielding 3600W. Your controller takes that 3600W and reduces it to 48V using a buck converter. The converter reduces the voltage but gains current in the process so that you get approx 3600W on the output but now it's transformed to 48V at 75A. If you can do 3600W with a differently arrange array, lower Vmp but higher amps, that's good too. There's a practical limit on the solar input voltage, it has to be above battery voltage but below the controller limit. If you had a 24V battery it would be feasible to have the array at 44V at 75A and get 3300W into the controller.

How would you go about sizing for a Victron 150/100? Looking at the spec sheet it seems there is a 70A input limit (if I'm interpreting "Max. PV short circuit current" correctly). This is limited further by only 30A per MC4 connector!
A bit further down the spec sheet I see that it says there are only 3 MC4 inputs...so is it possible to do something like a 2s7p array (say the panel's Isc is less than or equal to 10)? If it is possible, how would you do it? It sounds complicated.

 

[gnubie]

You'd do well keeping all of these questions in the same thread rather than spreading it all around. I've addressed your question here

Quick question about Jinko max. series fuse rating?

This is the first time I've noticed this on a solar panel spec sheet. Does this mean you're limited to only two panels per series?

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