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graham avatar image
graham asked

Maximum Panel wattage for Smart Solars 150/100 and 250/100

Hello, I need some info urgently and wondered if there might be help here.


The Smart Solars 150/100 and 250/100 both have a nominal PV for 12V systems of 1450W – notes on the spec sheet says


1a) If more PV power is connected, the controller will limit input power to the stated maximum.


Now what I need to know is what is the maximum panel power that the units can handle and limit assuming the unit is at maximum output of 100A.


I have a situation where I would like to have more watts of panels than the nominal 1450W to increase the output during the dark days of the year.


The panels will be mounted flat on the top of the cabin.


There is the going to be the occasion when the sun is in exactly the right position that the panels will likely develop maximum power.


So I need to know what is the maximum wattage the MPPT can limit?


Many thanks


Graham

MPPT Controllersoversizing mppt charge controller
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4 Answers
markus avatar image
markus answered ·

Hi Graham,

the good thing with mppt charge controllers is, that virtually the only limit you have to keep in mind is the max PV voltage.

The controller only converts the power needed. You could theoretically connect as much panels in parallel as you want, as long as you don't exceed the max PV Voltage stated in the specifications of the controller, it should work.


There is a 35 Amp limit, for Panel short circuit current on those chargers, for reverse polarity protection.

There are more safety mechanisms. Not only the the reverse polarity protection. An example of another is one that prevents overcharging the battery in case there is an internal short between battery output and PV input. This one will short the PV array to prevent overcharging the battery.


Connecting a PV array with a max Isc above the rated maximum as stated in the manual will make those other safety mechanisms fail; leading to unpredictable results.


In short: our rule is to stay below the rated Isc. Don't go over it; the rule is there for a reason. If you do; you are on your own. Both when it comes to charge controller warranty; but also in the worst case condition: batteries that have been charged directly from the PV array; leading to 100V or higher on to the battery bank.


Regards,

Markus

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mvader (Victron Energy) avatar image mvader (Victron Energy) ♦♦ commented ·

Hi @Markus could you please remove the 'better have connected etc'? See below :-). thanks.

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markus avatar image markus ♦♦ mvader (Victron Energy) ♦♦ commented ·
@mvader (Victron Energy Staff) done. And learned something. Thanks.
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markus avatar image markus ♦♦ mvader (Victron Energy) ♦♦ commented ·

*Joke Alert* @mvader (Victron Energy Staff) is it ok, to rectify the AC output of my wallplug to DC and use a MPPT 250/60 as a AC to DC charger as my wallplug is fused with 16A and therefore safe below the 35A input limit of the charger?

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mvader (Victron Energy) avatar image mvader (Victron Energy) ♦♦ markus ♦♦ commented ·

Yes sure. It’s no problem to compare AC amps with DC amps. Also, 250 volts is a very safe voltage and fine to work with; also when you don’t know what you are doing.

;-)



(For any onlookers: this is also a joke and all not true)

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markus avatar image markus ♦♦ mvader (Victron Energy) ♦♦ commented ·

Assuming, that we talk about theoretical things which should never happen in real life, the reason for me, why this wont work, is the DC Voltage after rectification is too high for the MPPT rather than the difference between AC Amps and DC Amps.

230*SQRT(2)=325V

If you have a e.g. 110V US grid available, there is a good chance that the MPPT will work, theoretically.

I would say 230V DC Voltage coming from a PV array is at least as unsafe to play with as 230V AC Voltage. Because muscles in a DC circuit tend to cramp.


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mvader (Victron Energy) avatar image mvader (Victron Energy) ♦♦ markus ♦♦ commented ·

indeed; 230V DC is very dangerous. Its the reason why I often advise against making long strings of panels on boats & RVs.

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markus avatar image markus ♦♦ mvader (Victron Energy) ♦♦ commented ·

The reason why I am interested in this debate is, that I am using Victron MPPTs as a AC to DC charger for my Hydro Power installations. Maybe you remember me, I am the Firehose Hydro Power Guy. :o)

This works great without any problems. I am wondering why Victron does not support Hydro or Wind applications for the MPPTs, because there is for sure a market for this and competition is rare.

This would require minor changes in the MPPT characteristics (slower), Hydro Generators have other characteristics than solar panels. And a storm brake for wind use, maybe done via Reverse Polarity Circuit;)

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markus avatar image markus ♦♦ mvader (Victron Energy) ♦♦ commented ·

@mvader (Victron Energy Staff) The ultimate MPPT extension regarding generator use, would be a generator excitation output, having the MPPT managing the generators output voltage. This would also make it possible to use MPPTs with automotive alternators. Or having a independent device for that.

(Also requested in another post here)

Called "Victron Alternator Control" and is programmable and to monitor via VE.Direct.

XMAS is soon!

The best chance for wishes to come true, is to ask for them :o)))

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mvader (Victron Energy) avatar image
mvader (Victron Energy) answered ·

Hi all, @Markus wrote:,


There is a 35 Amp limit, for Panel short circuit current on those chargers, for reverse polarity protection. If you exceed this limit, you better have connected your PV Panels the correct way. :o)


Please be aware that there is more to it: there are more safety mechanisms. Not only the the reverse polarity protection. An example of another is one that prevents overcharging the battery in case there is an internal short between battery output and PV input. This one will short the PV array to prevent overcharging the battery.


Connecting a PV array with a max Isc above the rated maximum as stated in the manual will make those other safety mechanisms fail; leading to unpredictable results.


In short: our rule is to stay below the rated Isc. Don't go over it; the rule is there for a reason. If you do; you are on your own. Both when it comes to charge controller warranty; but also in the worst case condition: batteries that have been charged directly from the PV array; leading to 100V or higher on to the battery bank.


Its a worst case, and unlikely, but not impossible.


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mvader (Victron Energy) avatar image
mvader (Victron Energy) answered ·
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porcini avatar image
porcini answered ·

The official limit is 70A on the PV-Side (30A each Cconnector). Markus already mentioned the reason for this. A few years ago there hasn't been a limit in the datasheet at all.

But in nearly all cases 70A input should be more than enough, especially with a 12V system on the battery side.

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graham avatar image graham commented ·

@Porcini On liveaboard boats it is becoming common to have systems where the total Isc is pushing 70A. This is a 12V system, part of a Lithium upgrade and the ideal would be with the Isc total of about 100A. That would give the client nearly 8 months a year full solar. Which is less than their aim. I suspect that cashflow and physical space is likely to hold things down below an Isc total of 70A.



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porcini avatar image porcini graham commented ·

Okay. With "70A is enough" I meant that you can put >10kWp on a single 250/100 by connecting panels in longer strings while it only charges with 1400W. If even more is needed why not adding a second charger?

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graham avatar image graham porcini commented ·

Thanks Porcini. We tend to wire the panels in parallel rather than in string to reduce the problems with shading that we get on canal boats.


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porcini avatar image porcini graham commented ·

I unterstand. In that case you could think about (more) 100/50 charge controllers. They are less expensive and can handle up to 60A at the input officially. That's a max. of 120A allowed with two units by lower costs than one 150 oder even 250/100. Additionally you have two units if one fails. But unofficially an 150/100 also should work if you avoid reverse polarity. I would better take two 100/50 to keep warrenty.

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