MPPT spec clarification needed

Solarfun4jim · Jan 13, 2020

Looking at the spec on an 'All in one' unit, it states that maximum string voltage as 145V
It also states that MPPT in operating range 30-115v
If the open circuit voltage of my array string is 130v, what happens with the MPPT?
Does it simply ignore the voltage from 115v up to 130v or does it shut down the MPPT as an overvoltage parameter?
see unit here....

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ghostwriter66 · Jan 13, 2020

You need to be asking Voltacon that question .. here is their customer service email ...
info@voltacon.com

ghostwriter66 · Jan 13, 2020

BUT typically a MPPT SCC will shut down and go into overprotect when it hits the maximum rated ... in your case 115V ....

jasonhc73 · Jan 13, 2020

This is an exact copy of MPP-Solar 5048. The actual manufacturer is Axpert. (https://solaradvice.co.za/product/mecer-5kw-48v-off-grid-inverter-ii/)

Setup your solar in 2S and then P the panels at 2S voltage. Don't exceed 80 amps in the P, ie 4 kW per mppt. Each has 2 mppt, so you can do 8 kW of SOL input.

Solarfun4jim · Jan 13, 2020

ghostwriter66 said:
BUT typically a MPPT SCC will shut down and go into overprotect when it hits the maximum rated ... in your case 115V ....

Thanks. Most of the 'All in one' units are similar in this respect, so not unique to this supplier. Just seemed a bit pointless, if it shuts down. If it ignores the 'extra' voltage above the 115V limit, might this give a degree of over panelling for cloudy weather conditions???

Solarfun4jim · Jan 13, 2020

jasonhc73 said:
This is an exact copy of MPP-Solar 5048. The actual manufacturer is Axpert.

Setup your solar in 2S and then P the panels at 2S voltage. Don't exceed 80 amps in the P, ie 4 kW per mppt. Each has 2 mppt, so you can do 8 kW of SOL input.

Thanks jason, 2S would be just over 80Voc. Might not have room on top of RV for 2S2P, but 3S would be doable. That would be under the 145V threshold, but above the 115 MPPT limit. Just trying to make sense of the spec on these units.

jasonhc73 · Jan 13, 2020

Solarfun4jim said:
Thanks jason, 2S would be just over 80Voc. Might not have room on top of RV for 2S2P, but 3S would be doable. That would be under the 145V threshold, but above the 115 MPPT limit. Just trying to make sense of the spec on these units.

I think 1 panel won't be enough voltage to make it work.

I am in the same situation. I just ordered 12 panels for my house to add to my 5048, but didn't understand the voltage info stuff. I think you have to have at least 34V to make it work.

From the Book:
PV Module Selection:
When selecting proper PV modules, please be sure to consider the parameters below:

Open circuit Voltage (Voc) of PV modules can’t exceed the maximum voltage of the PV array open circuit of
the inverter.
Open circuit Voltage (Voc) of PV modules should be higher than the minimum voltage of the battery.

Solar Charging Mode
Solar Charger Type	MPPT
Number of MPPT	2
Max. PV Array Open Circuit Voltage	145Vdc
PV Array MPPT Voltage Range	60~115Vdc
Min. battery voltage for PV charge	34Vdc

ghostwriter66 · Jan 13, 2020

jasonhc73 said:
I think 1 panel won't be enough voltage to make it work.

I think you have to have at least 34V to make it work.

From their website it says 30V's so I guess just one panel could at least function ... but i would go with the higher number 34 to be safe

jasonhc73 · Jan 13, 2020

I just realized you are looking at a UK model, mine is a US model, so mine quite is a bit different on SOME specs. With your's being only 30V~115Vdc MPPT Range, that makes a big difference. What does your PV spec say it is? Vmp-36.0V for mine, therefore inadequate as a single panel

Solarfun4jim · Jan 13, 2020

jasonhc73 said:
I think 1 panel won't be enough voltage to make it work.

I am in the same situation. I just ordered 12 panels for my house to add to my 5048, but didn't understand the voltage info stuff. I think you have to have at least 34V to make it work.

From the Book:
PV Module Selection:
When selecting proper PV modules, please be sure to consider the parameters below:

Open circuit Voltage (Voc) of PV modules can’t exceed the maximum voltage of the PV array open circuit of
the inverter.

Open circuit Voltage (Voc) of PV modules should be higher than the minimum voltage of the battery.

Solar Charging Mode
Solar Charger Type MPPT
Number of MPPT 2
Max. PV Array Open Circuit Voltage 145Vdc
PV Array MPPT Voltage Range 60~115Vdc
Min. battery voltage for PV charge 34Vdc

Thanks jason, so at 2 in series, thats 2 x 40v = 80v open circuit. My battery bank would be at 48V. However, if i could get away with 3 in series, that would be approx 120v open circuit, but only 98v max operating voltage, which effectively takes me up closer to the 115v ideal. Its just trying to understand the difference in the spec figures.

Solarfun4jim · Jan 13, 2020

I'm kinda thinking, the unit can handle 145v OCV, but the MPPT is calculated on the max operating voltage, which is always much less. Hence, you could use 2 panels in series up to 57.5v max operating voltage each, or 3 panels in series up to 38.33 max op voltage each or, 4 panels in series up to 29v max op voltage each. Does this make sense?

Solarfun4jim · Jan 13, 2020

Just had clarification from voltacon themselves....

"Hello James it will work fine at 120V, it will not stop charging, the inverter will auto-adjust the volts/amps to track the maximum power point of the solar panels.
If the voltage is over 145V , the inverter will disconnect the panel until the voltage range falls in the MPPT window.

It is very common to have 3 panels in series and multiple strings of 3 panels in parallel, this is the best configuration"

jasonhc73 · Jan 13, 2020

Solarfun4jim said:
Just had clarification from voltacon themselves....

"Hello James it will work fine at 120V, it will not stop charging, the inverter will auto-adjust the volts/amps to track the maximum power point of the solar panels.
If the voltage is over 145V , the inverter will disconnect the panel until the voltage range falls in the MPPT window.

It is very common to have 3 panels in series and multiple strings of 3 panels in parallel, this is the best configuration"

Thanks for the info!
I get it now, too!

So this is what is called "Clipping".

I get clipping on my grid-connected panels, so far after 4 months online, it has clipped 3 times, for about 2 hours total.

Voltage is directly related to how much sun is hitting directly at the time. So to clip, the string has to have the best solar situation. Which is a pretty low probability. My grid-connected strings are setup 125% of the inverters max.

Give it a shot, 3-panel string, the probability of maxing out the V is pretty low, but it lets the panels kick in sooner.

Solarfun4jim · Jan 13, 2020

jasonhc73 said:
Thanks for the info!
I get it now, too!

So this is what is called "Clipping".

I get clipping on my grid-connected panels, so far after 4 months online, it has clipped 3 times, for about 2 hours total.

Voltage is directly related to how much sun is hitting directly at the time. So to clip, the string has to have the best solar situation. Which is a pretty low probability. My grid-connected strings are setup 125% of the inverters max.

Give it a shot, 3-panel string, the probability of maxing out the V is pretty low, but it lets the panels kick in sooner.

@jasonhc73
Post edited.....error in calculation.

MisterSandals · Jan 13, 2020

Solarfun4jim said:
Obviously 3 panels in series would produce 3x 9.49A =28.5A

Not true. The amperage would be 9.49 in series. The volts are added (multiplied by 3).

Solarfun4jim · Jan 13, 2020

MisterSandals said:
Not true. The amperage would be 9.49 in series. The volts are added (multiplied by 3).

Of course.....senior moment....lol
Have edited the post due to my stupidity. Ta

ghostwriter66 · Jan 13, 2020

wondering if you could run 2 panels in series to keep the volts up and then one of the same two in parallel to keep voltage below MAX ... so basically the middle panel being in series with one .. and parallel with the other ... ??????

JeepHammer · Jan 14, 2020

ghostwriter66 said:
wondering if you could run 2 panels in series to keep the volts up and then one of the same two in parallel to keep voltage below MAX ... so basically the middle panel being in series with one .. and parallel with the other ... ??????

Good question...
Amps would double with a parallel panel in the string.

I might consider a blocking diode in the parallel panel.
You wouldn't have Voc anymore with a half voltage in one panel, the series would always be heating the half voltage panel in an open circuit situation.

With an isolation diode in the parallel panel line, as far as I know it can contribute but is isolated from double voltage of series panels. You would loose a volt from the parallel panel but I don't think it would be a resistance heater in the circuit anymore.

I do series/parallel all the time, but always balanced, I never thought to try 1 panel parallel on a series string...

jasonhc73 · Jan 14, 2020

Easy test, get 3 AA batteries and see what kind of circuit it makes.

I would think 1.5 more amps and 1/3 less volts.

So like if 50v10amp panel for easy math.

2series, 100v10amp.
Add another but parallel.
66v, 15 amp maybe?

JeepHammer · Jan 14, 2020

jasonhc73 said:
Easy test, get 3 AA batteries and see what kind of circuit it makes.

I would think 1.5 more amps and 1/3 less volts.

So like if 50v10amp panel for easy math.

2series, 100v10amp.
Add another but parallel.
66v, 15 amp maybe?

During production usage by inverter (Load), very true.

What happens when the inverter opens (Voc) but panels are still interconnected?

What happens to the single series battery when you try to recharge the AA's?
Parallel do fine, but while they are demanding twice the charge the single cooks.

What happens when you try to charge equalize a 12 volt battery with a 24 volt battery?

Or put a smaller battery in a parallel string with larger batteries?
If you ever did that you know the smaller battery become 'Load' and cooks...

When charge controller opens (charged batteries or shut down) the half voltage panel becomes Load and will shed the extra voltage as heat.

Probably isn't an issue since it's rated for Voc voltage, just running the hypothetical in my head...
No doubt it's going to heat, but by how much?
I've just never done it knowing lesser voltage panels can get cooked by higher voltage panels in parallel, I made that mistake.

I simply isolate the matched series panel strings so the parallel connection doesn't cook the lesser/older panels.
Same way I isolate lesser or different batteries from each other so stronger doesn't cook weaker,
Mismatched battery STRINGS in parallel will most certainly cook each other,
And weaker battery strings will demand more charge and over volt the newer, stronger STRINGS in parallel.
Parallel charge controller for every battery type, charge & string isolation solves those issues.
Run any battery In Bank with any other size, type or age battery (as long as they are the same voltage) that way.

I'm running LFP in parallel with lead/acid, even Edison batteries with reversion isolation.

I can't say the parallel panel will ever see the charge controller disconnect entirely, but I run those 'What If' things through my head when I picture the circuit.

ghostwriter66 · Jan 14, 2020

JeepHammer said:
During production usage by inverter (Load), very true.

What happens when the inverter opens (Voc) but panels are still interconnected?

What happens to the single series battery when you try to recharge the AA's?
Parallel do fine, but while they are demanding twice the charge the single cooks.

What happens when you try to charge equalize a 12 volt battery with a 24 volt battery?

Or put a smaller battery in a parallel string with larger batteries?
If you ever did that you know the smaller battery become 'Load' and cooks...

When charge controller opens (charged batteries or shut down) the half voltage panel becomes Load and will shed the extra voltage as heat.

Probably isn't an issue since it's rated for Voc voltage, just running the hypothetical in my head...
No doubt it's going to heat, but by how much?
I've just never done it knowing lesser voltage panels can get cooked by higher voltage panels in parallel, I made that mistake.

I simply isolate the matched series panel strings so the parallel connection doesn't cook the lesser/older panels.
Same way I isolate lesser or different batteries from each other so stronger doesn't cook weaker,
Mismatched battery STRINGS in parallel will most certainly cook each other,
And weaker battery strings will demand more charge and over volt the newer, stronger STRINGS in parallel.
Parallel charge controller for every battery type, charge & string isolation solves those issues.
Run any battery In Bank with any other size, type or age battery (as long as they are the same voltage) that way.

I'm running LFP in parallel with lead/acid, even Edison batteries with reversion isolation.

I can't say the parallel panel will ever see the charge controller disconnect entirely, but I run those 'What If' things through my head when I picture the circuit.

So from a "book" perspective the parallel/series thing should work ... BUT i have never tried real world ... IF you do try it .. and it works (no fires - LOL) please let me know .. I have learned pretty quickly that allot of stuff they taught us in class does not actually work in the real-world (YEP thats why we all carry fire extinguishers)

Mik · Mar 25, 2021

I have bought a similar system to this

10KVA Solar Inverter 60A MPPT 8000W Off Grid Inverter 48V 220V Pure Sine Wave | eBay

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only one off at moment though

Need some help with the array config

Mik · Mar 25, 2021

I have 15 panels as below to run a single one of this item
I have a bank of 4 190ah batteries which will make 48V

Panels
Open circuit voltage Voc: 36 V
Nominal power Pmax: 235 W.
Nominal voltage Vmp: 29.6 V
Nominal current Imp: 7.78 A

MPPT inverter
Model ISolar SML 5K
BATTERY&AC CHARGER
Battery voltage 48VDC
Floating Charge Voltage 54VDC
Overcharge Protection 60VDC
Maximum Charge Current 20A or 30A
Maximum PV Array Power 3000W
MPPT Range@Operating Voltage 60VDC~115VDC
Maximum PV Array Open Circut Voltage 145VDC
Maximum Charging Current 80A
Maximum Efficiency 98%
Standby Power Consumption 2W

I am thinking of creating array, but not sure what would be best configuration.
I realise reading this thread that its a tad more interesting than I thought
I connected 2 panels in series in bright sunlight and got 60volts and 1.1 amps, I want to make sure I am not going to blow something up!!
This is Open Circuit measurement, I realise this is wrong but I am not looking to blow things up, and I would like to learn at a not very expensive rate lol
I didnt load the panels, so the 1.1 amps was me just turning my meter to amps???
think this is wrong as need to test under load

4 in series would be around 120V and 2.2 amps if I did in series
4 arrays in parallel 30v and 8.8amps????

over to you guys, complete newbie so be nice...

Forbisher · Mar 25, 2021

4 panels in Series is 36Voc x 4 =144V which is too much for the 145V max.

3 in Series will work well.
3 series 5 parallel for your array.

Mik · Mar 25, 2021

Forbisher said:
4 panels in Series is 36Voc x 4 =144V which is too much for the 145V max.

3 in Series will work well.
3 series 5 parallel for your array.

Thanks for that, I am intending to add another 15 and another mppt in parallel to the mix also, looking to get more out of the system

Would you know what rated power solar charging means, the 5k model shows 4000W rated power and pv charge current at 80A

so 36Voc is the array without load, currently the Voc is sat at 30v or 60 with 2 panels connected, I have to presume that 36Voc is attainable and would clip as required if I did 4 in series. I get the same out with 3 in series. This is the reason behind my question as you can see

MPPT spec clarification needed

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