Undersize MPPT?

[yeahnah]

I want to get 4x 150W Newpowa mono panels for my van (due to size constraints this is my best option). Theoretically I need a 50 amp MPPT. Considering the efficiency of panels and the fact its unlikely I'll ever get an ideal sun angle since they'll be fixed flat to the roof, if they're 70% efficient (i.e. put out 105W each) I'd only need a 35 amp MPPT.

In one of Will's videos he compares 4x 100 amp panels and he gets an output of 57-70 watts under quite ideal conditions (57-70% efficient).

Can I realistically buy a 40 amp MPPT to save myself a couple of hundred dollars and not break anything?

 

[Forbisher]

Is the difference between a 40 amp and a 50 amp SCC $200?
What brand and model SCC are you comparing?
You will not break anything as you could be over paneled by more than that.
Undersized or over paneled? its your choice.
A 40 amp SCC will produce less power in the morning and evening than a 50 amp.
It all depends on the size of your 12 volt battery, daily useage and days without sun, etc.

My AIO 40 amp SCC is recommended with 500 watts panels but can be over paneled to 800 watts.

 

[yeahnah]

I'm looking at the Renogy which only have 40 or 60 amp options (no 50), a $200 difference between those two.

The batteries are 3x 12V 190Ah DIY (570Ah total). Heavy usage since we have kids (appliances, laptops for work, electric water heater used sparingly etc). We'll be living in it full-time on the road, so sun will vary as we'll be moving a lot in the U.S.. North in summer, south in winter. We'll also have DC-DC since 600W is no where near enough for 570Ah with our planned usage.

 

[Fred S]

MBR, why do you say that a 50 amp controller will exceed a 40 amp in the morning and evening? The 50 amp is more efficient in indirect light?

 

[yeahnah]

Scratch that, I've decided to avoid Renogy....

 

[Forbisher]

I'm looking at the Renogy which only have 40 or 60 amp options (no 50), a $200 difference between those two.

I cant be bothered googling Renogy controllers but $200 more?
You wanna save money?

60AV118 MPPT SOLAR CHARGE CONTROLLER – MakeSkyBlueUSA

makeskyblueusa.com

60A MPPT SOLAR CHARGE CONTROLLER
$109.99

 

[Forbisher]

MBR, why do you say that a 50 amp controller will exceed a 40 amp in the morning and evening? The 50 amp is more efficient in indirect light?

40 amps x 12 volts = 480 watts panels.
60 amps x 12 volts = 720 watts panels
You have 600 watts panels but on a 40 amp controller you will never get more
than 480 watts in perfect conditions so thats why 50 amp will produce more in
less than perfect conditions like morning or evening, etc.
You say you only can fit 4 x 150 on your van and you need all the power you can get with all those loads.

 

[Fred S]

Thanks MBR. I only asked because the statement is a bit misleading. For all parts of the day, up to a 40 amp threshold, both the 50a and 40a controllers will provide the same charge rate. And above 44a (600w max/13.5v), there is no additional benefit from the 50a controller, because 600w is the bottleneck. The amount of time spent between 40a and 44a likely will be negligible, since several factors will nearly always keep the generation below 40a (90% of 44, the max the panels can provide via a controller). So, saving the money and getting a 40a may be a good choice.

yeahnah, having said all that, if you want to use the controller for a bigger system in the future, you can get a larger one now, or buy a 2nd one later. You'd put your additional panels on the 2nd one but you can connect it to the same battery bank as the 40a. Good luck, and fun travels!

 

[DASH]

My experience is, that You should never buy a controller where the panels will put out more voltage then what the controller is rated for. Some controllers, however, can take more watts then what they are rated to convert to the battery storage system. The excess watts would not be converted. For instance, The EPEVER Trancer4210AN can convert up to 520 watts of solar for a 12 volt battery system, but will operate up to 780 watts. The difference of 780 watts and 520 watts will not be transferred to the battery. Anything over 780 watts (12 volt battery system) or 100 volts to the controller may damage it. One of the advantages of getting a controller that can't process all the watts the solar panels can provide under ideal conditions, is limiting the amount of current that is used to charge the battery. With a 100 amp 12 volt Lithium Ion Phosphate battery, I know the maximum charge rate will be approx. .5c (under the above conditions) which some folks feel is the maximum rate, if You want long life for your lithium ion phosphate battery and/or the maximum rate the BMS will allow. AGM batteries are generally rated .3C or less.

 

[ScoTTyBEEE]

I have 660w hooked up to the 4215 Epever Triron. The most watts I have seen, considering it's only been in use for a week was around 550w. You'll never get full power and 550w is probably around maximum anyway, most of the day the controller sits around 35amps so I'm not missing out on much. Go for the 40A, I'd say it's the perfect match for 600w.