jawrobo13 avatar image
jawrobo13 asked

Getting the Right Victron MPTT and Cable Sizing (SmartSolar 150/60?)

Hi Alll,

I am wanting to set up a small-ish solar system on my property to eventually be off-grid one day. This is my initial foray into solar and will likely want to do something a lot larger in the next 3-5 years. The charge controller is the brain the system (imo) so I wanted what I read to be the best brand. That is why I came to this forum for help.

I have "settled on" the following based upon my perceived (and future unperceived) needs as to power consumption/storage. I will keep the following "generic" as to brand seeing that this is a Victron-sponsored forum.

1) 4 x 200W (12V) panels that will be wired in series

2) 2 x 200 A-hr (12V) LiFePO4 batteries

3) 3000W-4000W (12V) inverter

4) Right-sized Victron Charge Controller

Here are my observations/questions:

A) I now need to know if I am picking the correct MPTT charge controller. I used the "calculator" that Victron provides and it lead me to the SmartSolar 150/60 (MC4). I do believe that this is correct. Am I? ;-) I will have ~800W of power and the 150/60 handles up to 880. The 60A output confuses me because I believe that my panels will generate a max of 11.7A being in series in optimal conditions.

B) I am also concerned about using the correct MC4 cables to connect the solar array to the Victron. I believe that they standardly come in 12/10/8 AWG. Looking at the spec sheet for the 150/60, it looks like the MC4 connections (footnoted) are limited to 30A that I believe would put me in a 10AWG cable? Am I correct?

C) My next question would be what gauge of wire would I want to connect the charge controller to the battery with? Once again - I believe the spec sheet states AWG2 wire. Looking at the charge controller pictures (alone without any other reference to size), and the real estate available for the wiring, it does not look like a beefy AWG2 wire would fit, that is why I am asking. Is AWG2 the correct wire size?

I have been all over the web looking to learn solar energy system design and integration ;-) I have a fair understanding of electrical (Ohm's Law and the basics), however, I do not do this for a living or am I specialized in it. I do not want to buy a "kit" or have to work with a dedicated dealer. I am just trying to build this on my own, getting it right the first time, without the markup of buying from one source.

Any help would be greatly appreciated! Thanks in advance!


charge controller compatibility
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jawrobo13 avatar image jawrobo13 commented ·
I appreciate the comments so far, however, let me further explain my use case.

1) Property is likely to be used late spring to late fall on weekends mostly

2) I have a wall tent that I will have set up and want to power simple things (box fans for cooling, maybe a mini-fridge, well-pump, some LED lights, maybe a TV for football season...). As temperatures get cooler, I would expect load to be less.

3) I mostly want the proposed system to meet basic needs - no extravagancy or full time living

4) Regarding the inverter (3-4 kW), I will not likely ever use the full capacity. I think the highest that I would likely ever use is 500W. I wanted to oversize the inverter in the event I ever needed a large power draw.

Does this change the answers in any way to what was posted above?

Thanks again!

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2 Answers
seb71 avatar image
seb71 answered ·

Get the "Tr" version (with screw down terminals) of SmartSolar.

Better get larger PV panels (60-cell). About 300W-350W each.

Current in (from PV) and current out (to the battery) are not the same for MPPTs. The voltages are different. Power out is about the same as power in (minus some losses) in case of MPPTs.

If you want a 3000-4000W inverter, 12V is a bad choice. Go for a 48V system (48V battery and inverter).

Also the 800W PV array is too small for that, if you plan to use it at (or close to) full power for long periods. You will draw most of the power from the battery and also not enough energy to recharge the battery.

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kevgermany avatar image kevgermany ♦♦ commented ·

Adding to @Seb71 excellent comments, adding panels later is easy, just needs an extra MPPT. Adding battery capacity may be trickier due to wear/aging of the existing batteries.

Victron's wire sizes are correct. There's no harm in using heavier guage wired than needed, unless they don't fit the terminal blocks. But it does I crease costs.

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Sarah avatar image
Sarah answered ·

Hi @jawrobo13 given you reduced power requirements you proposed configuration is more appropriate. I would still go for the larger panels if possible but understand that physical size/weight may be an issue. If you are assembling the system frequently the MC4 connectors might be beneficial as they are quick and protect against reversed polarity otherwise stick with the wire terminals (either way remember to put an isolator between the panels and the solar controller also solar panels operate a higher voltages so current may not be as much of a concern).

As @Seb71 suggests a 3-5 KW system is a vastly different (and more expensive) proposal to say a 2 KW system. It is generally not possible to just oversize one part of the system without taking into effect the impact on the system as a whole. I would also consider an inverter/charger in case you want to add a small generator at a later stage to top up the batteries or you could take advantage of the power assist option (generator+ batteries) for the rare occurance of using higher power demands. Consider either the multiplus 12/1600 or 12/2000. Either way you will want a charger so that you can fully charge the batteries before the initial install.

As far as 12 volt systems are concerned they can be convenient in smaller installs as they can be used with most camping/caravan equimement without the need for extra DC-DC converters.

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