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Going slightly over the max MPPT voltage

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Y2JB

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Hi,

I am looking at adding a victron 100/30 to manage one of my strings. The VOC from my string would be 100.68V. Would that extra 0.68V fry or substantially shorten the lifespan of the controller? The 150V version is almost twice the price!
 
Is that Voc at the lowest temperature your panel will experience? You can't just use the Voc for 25 C.

All the parts rated at 100 volts have some engineering margin in them, and the circuit designed may have added their own margins to everything, but how much is uncertain. Going over less than 1% is highly likely to be tolerated.

You can't really take into consideration the PV wire voltage drop since your max volts will occur at zero amps.

Mike C.
 
The general rule is, allow a 20% safety margin. This accounts for changes in voltage when temperature drops. Yes. You should go for a larger mppt.
 
Y2JB said:
On balance would you say I should pony up the extra money for the 150V version? Even given the 0.5% margin here?
Click to expand...
Yes, buy the 150. Since you haven’t answered, I’m going to go ahead and assume you didn’t do temperature compensation for you Voc, which means that at 0 Celsius, your 100.68V is going to be something like 109V, which is not a chance you should take on a 100V SCC.
You’ll save money in the long run since if you bought the 100, the first cold sunny day you’d smoke it and need to buy a 150 anyway.
 
You could put a solar diode in series with your string. Depending on the diode type, there is a 0.2v-0.6v voltage drop. But still you would be on the edge.
Personally, I would go for the 150v, since we all have the tendency to want more (expansion) in the future. Depending on the single panel voltage, you might be able to add another panel in the future, with the 150.
 
poof white smokey smoke

1.25 factor for temperature correction always needs to be taken into account, as well. in the winter my 2kw array regularly produces 10-15% over calculated VoC.
 
Y2JB said:
On balance would you say I should pony up the extra money for the 150V version? Even given the 0.5% margin here?
Click to expand...
Just think the 150v today is substantially cheaper than last year, what other gear can you say that about?
 
meetyg said:
You could put a solar diode in series with your string. Depending on the diode type, there is a 0.2v-0.6v voltage drop.
Click to expand...
Max Voc will happen at zero current and diodes at zero current are basically zero voltage drop.

So this trick won't work, the max Voc will still be as high as without the diode. All the diode will do is lower you efficiency and provide another failure point.

No device rated at 100 volts will blow up with a 0.68 % overage. All the prognostications about smoking it are wrong. Ratings simply can't be designed to be that tight.

Mike C.
 
mciholas said:
No device rated at 100 volts will blow up with a 0.68 % overage. All the prognostications about smoking it are wrong. Ratings simply can't be designed to be that tight.

Mike C.
Click to expand...
Put your money where your mouth is!!

Your statement is valid for some of Midnights gear, victron not so much.

But it’d be a great test if someone had the equipment and the desire to destroy something beautiful.
 
mciholas said:
No device rated at 100 volts will blow up with a 0.68 % overage. All the prognostications about smoking it are wrong. Ratings simply can't be designed to be that tight.
Click to expand...
There’s also whether temp compensation was added and how safe they were playing with it relative to their climate.

That information was not supplied so I feel some super conservative nagging is warranted
 
Y2JB said:
Hi,

I am looking at adding a victron 100/30 to manage one of my strings. The VOC from my string would be 100.68V. Would that extra 0.68V fry or substantially shorten the lifespan of the controller? The 150V version is almost twice the price!
Click to expand...

Yes.

Y2JB said:
On balance would you say I should pony up the extra money for the 150V version? Even given the 0.5% margin here?
Click to expand...

No. We're SCREAMING it.

Can you reduce the series panel count? Might be a lot cheaper.
 
Whenever one does stoopid stuff like this, if it works, it always fails at the most in-opportune time, causing the most damage possible, at which point you say: "What on earth was I thinking." But feel free to pay the "stupid tax". I make it a point to not test the limits a manufacturer stamps on their products, normal failures, and unintentional stupidity, are already enough for me without attempting to introduce any intentional ones.
 
740GLE said:
Your statement is valid for some of Midnights gear, victron not so much.
Click to expand...
If Victron's gear blows up under any circumstance at 0.68% over rating, it is extremely poorly designed with no safety factor provided. Ordinary component tolerances greatly exceed that figure.

I'd be very surprised if the components aren't chosen to be at least 20% over the input rating.

740GLE said:
But it’d be a great test if someone had the equipment and the desire to destroy something beautiful.
Click to expand...
You will need a lot more than 0.68% overage to destroy it.

Take it from someone who designs electronic circuits for a living, a properly designed 100 volt rated input that safely tolerates 100 volts isn't going to smoke at 100.68 volts.

Mike C.
 
Some equipment has headroom built in and some does not.
Just as an example, the EG4 18k inverter can handle an absolute maximum of 600 volts PV input but works fine up to 500 volts input. The capacitors are 315 volt * 2 in series with balancing resistors to give you a theoretical maximum voltage of 630 volts until they possibly might start smoking.
 
Our reaction to Voc limits:


tumblr_nk10g3LdNz1rp0vkjo1_500.gif
 
mciholas said:
If Victron's gear blows up under any circumstance at 0.68% over rating, it is extremely poorly designed with no safety factor provided. Ordinary component tolerances greatly exceed that figure.
Click to expand...

Good for you. Don't forget that almost all manufacturers publish this as a hard limit. The only exception that I can think of is Midnite with their HyperVoc protection.

mciholas said:
You will need a lot more than 0.68% overage to destroy it.
Click to expand...

Please cite your source for this claim. I'll use that when trying to get warranty from Victron if I ever over-volt my MPPT.
 
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