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Exceeding voltage or amps on SCC

moonlitsouls

moonlitsouls

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Hey guys I’m a little confused about some thing, a few weeks ago I attached five panels and series and exceeded my max voltage on my charge controller, I got an error on the device, and was not able to use it.

Someone mentioned to me that it’s recommended to be slightly “over paneled”

But What happens when I exceed the amps rating for the SCC? The max amps of my array will be approx 53a and it’s a 50a SCC

I realize the conditions would need to be perfect for the charge controller to pull that many amps, but that didn’t stop the device from giving me an error message when I exceeded my voltage
 
moonlitsouls said:
I realize the conditions would need to be perfect for the charge controller to pull that many amps, but that didn’t stop the device from giving me an error message when I exceeded my voltage
Click to expand...
Over voltage can destroy a CCs electronics instantaneously. If you are lucky the components will cease to work until the the V drops back to a safer V.
Over current may take a little longer depending on the amount. Feel the back of the CC to get some understanding of how the heat sinks are coping and hope the assembly line worker was having a good day and aligned the mosfets just right to the heat sink.
 
Assuming the 50A is the rated max output current to the battery then if there is enough wattage coming in that would exceed that output current then the output current is simply limited to the max, 50A in this case.

Let's say you have a 12V battery and it is at 13.6V. The 50A output would be reached at 680W input. If you were able to get 800W, the SCC would just "ignore" the extra power and you would just get the 50A output. No damage would be done.

But as you've seen, exceeding the input voltage can be bad. Exceeding the output current is a non-issue. Overpaneling is fine as long as it can't ever result in exceeding the input voltage.
 
rmaddy said:
Assuming the 50A is the rated max output current to the battery then if there is enough wattage coming in that would exceed that output current then the output current is simply limited to the max, 50A in this case.

Let's say you have a 12V battery and it is at 13.6V. The 50A output would be reached at 680W input. If you were able to get 800W, the SCC would just "ignore" the extra power and you would just get the 50A output. No damage would be done.

But as you've seen, exceeding the input voltage can be bad. Exceeding the output current is a non-issue. Overpaneling is fine as long as it can't ever result in exceeding the input voltage.
Click to expand...
Alright thanks a lot
 
moonlitsouls said:
The max amps of my array will be approx 53a and it’s a 50a SCC

I realize the conditions would need to be perfect for the charge controller to pull that many amps, but that didn’t stop the device from giving me an error message when I exceeded my voltage
Click to expand...

Just be careful of over paneling until you are sure of your CC's capabilities.
 
Just remember that the Load PULLS the current from the power source, so if your load can only draw 50A from the source, that is all it will draw from the source even though the Source can provide more.
BTW, the 50A is the rating of the charger can provide to the batteries (Load). The Input Amp into the SCC is not the same as the output Amp rating since SCC is the smart Buck converter that converts high Voltage to Lower Voltage to charge the battery. The input current number is not the same as the charger output current number.
For simple example: Your AC outlet in your house can supply power up to 1800W (120Vac 15A), so if you plug in 100W lamp into the sock, will you be pulling 1800W of power? Of course not.
What to watch out for not to destroy your SCC is the Voltage feeding the SCC PV input, you should also factor in about 15% more if you live in cold weather since the VOC of the panel will go up in cold weather.
 
MPPT can/will control the current. Over voltage jumps over the component ratings and the magic smoke is released.
Five panels is a bit awkward. All in parallel or 2 parallel, 2 series is good. A 6th panel gives more options.

Leave at least 20% headroom on the series Voc rating or you need to take a deep dive with specifications to calculate the exact amount.
 
Overpaneling generally means higher wattage, not higher voltage, which is deadly to charge controllers

Better controllers have output limiting and thermal foldback to keep the controller healthy when overpaneled.
 
Bud Martin said:
For simple example: Your AC outlet in your house can supply power up to 1800W (120Vac 15A), so if you plug in 100W lamp into the sock, will you be pulling 1800W of power? Of course not.
What to watch out for not to destroy your SCC is the Voltage feeding the SCC PV input, you should also factor in about 15% more if you live in cold weather since the VOC of the panel will go up in cold weather.
Click to expand...
I have a Sun2000 10KTL GTI. It has 3 PV inputs, rated for 360v@15amps for each input. I understood this to mean the inverter will draw 15amps, if available, with a planned DC voltage of 360v from the Array. If I plan my array to meet that 360v, that the amps on the line can be anything I want. I can have 500amps available on the line and the inverter should only draw 15amps max, as long as the voltage remains in range, correct?

I know, folks will say why have ALL those extra panels and amps if the Inverter can't use it. I agree, my question is more understanding Inverters and the PV input lines. Loads pull amps, batteries don't push AMPs into a device. As long as the volts are within range, how much amperage on the line is a don't care in terms of Inverter going POOF?
 
It would be good if you could provide a bit more detail on your panel specifications and also your charge controller ratings. It would help to be able to provide valuable advice.
 
WindWizard said:
It would be good if you could provide a bit more detail on your panel specifications and also your charge controller ratings. It would help to be able to provide valuable advice.
Click to expand...
I have no charge controller, I don't have battery backups and never needed it. My PV arrays are 2 arrays of 15 panels (QPLUS_L_G4_2_335-345_2017-01_Rev01) feeding the SUN2000 GTI. The GTI has 3 inputs, I'm currently only using 2.

The question is more aligned with understanding AMPS/Volts. If the PV Input says 15amp max, that means, it can only pull (load) 15amps max, and then based on the Voltage input gives you your total DC->AC conversion. So, my Inverter wants (planned) 360v @ 15 amps = ~5100 watts per PV input line. So two inputs, if operating peak, is close to the 10Kw max. If I size one of my PV arrays for 360v @ 100 amps = 36,000 watts, the Inverter should still only pull 15amps, correct? Sure, I'm wasting a ton of energy, but, AMPs are load driven, not "pushed" into the inverter?
 
NO........If your GTI is rated at 15 amps and you are trying to stuff 100 amps, then that is BAD very BAD. If your unit is rated at 360 Volts @ 15 amps then you need to adhere to the specs. Series your panels to get the voltage up to 300 volts.

I would not exceed the 15 amp max if that is the specification. That is not the load but the maximum input current that the unit can support. If you exceed that then you can possibly damage your equipment. Most Charge Controllers are concerned with the maximum voltage and state that in the Specs such as due not exceed such and such voltage. Where the current rating of the charge controllers is just the maximum current that the charge controller can push into the loads and battery. Solar panels are interesting because they do not produce any usable power when the panels are not connected to a load of some sort. The voltage on solar panels just rises up to the VOC which is basically an open on the connector and it doesn't heat up or produce any power. The job of the Charge Controller is to find a voltage where the panel produces a maximum amount of power.

Back to the question. strange and bad things happen when the manufactures recommendations are ignored or disregarded.
 
The specifications of many MPPTs are not sufficiently detailed IMO.

There are going to be two current limits:
i. the MPPT's operating limit
ii. the MPPT's Isc limit

The first defines how much current the MPPT can maximally draw from a PV array. e.g. if you have two strings in parallel, and each string is capable of supplying 10 A while the MPPT has an operating current limit of 16 A, then the MPPT will, at most, draw 16 A from the PV array.

Ordinarily this arrangement would not present any threat to the MPPT, as it self limits by design. Indeed it is often good design to over panel a little, but there are limits.

Which is where the Isc limit comes into play. One needs to consider what happens if something goes wrong, such as a short circuit.

It's perfectly fine to design a PV array to exceed the MPPT's operating current limit, however do not exceed the MPPT's Isc limit.

See here for examples:

Inverter Isc DC Input Ratings - SolarAPP+ Knowledge Base

Inverter short circuit current (Isc) rating is required to verify that the PV module string short circuit current under high irradiance does not exceed the maxi
help.solar-app.org help.solar-app.org
 
WindWizard said:
NO........If your GTI is rated at 15 amps and you are trying to stuff 100 amps,
Click to expand...
I'm not trying to stuff anything. I'm saying additional AMPs are available on the line, amps can't "push" themselves into a load that didn't ask for it. Granted, you can have a short circuit or similar fault, but, that's not the point on this.

Granted, I'm no Inverter expert and I'm learning, it just seems to be "stuffing" loads into a circuit is opposite of what I understood circuits to do.
 
You still need to guard against a fault current that equipment is not able to handle. This is addressed in many non-PV parts of electrical code.

EG putting an appliance with 5-15P on 30A circuit. NEC says in most cases you can only go up to 150% of the nameplate unless maximum overcurrent protection is explicitly stated.
 
I will have a 20amp DC breaker in the circuit, so, if a short does occur and a run-away condition exists, the DC breaker will trip. I do appreciate the guidance/feedback. Learning is listening, but also questioning....
 
I suppose that stuffing is not the correct term. I look at it like when you have a tire and you just keep pushing more air into it then eventually it will blow. I think that wattmaters post sums it up more clearly than I attempted to do. Especially the post ISC DC input ratings. The job of the Charge Controller is to produce as much power as possible without burning itself up. If your panels are making 100 amps and your Charge Controller ISC limit is 15 Amps then I do not recommend doing it. The way around it is to put your panels in series which boosts the voltage and also keeps the current low. Wattage is a simple Volts times Current. So if you have 350 volts and 15 amps for the panels then you have 5250 watts. Now if you are using a 48 Volt battery then the Charge Controller takes that 5250 watts and Converts it to say 50 Volts at 105 amps. If your charge controller is only a 80 amp Charge Controller then the maximum current that it will produce is 80 amps. So you would only be able to use 4000 watts of the 5250 watts.
 
Is there a downside to overpaneling at the maximum safe series voltage for the SCC, and then fusing the input to the SCC at either Isc or 1.25* max current?
 
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