Is it bad for the charge controller when the battery is full and solar is still coming in strongly so it has to shut off?

[canadian0]

Before I had too little solar now I have so much that it fills the 100ah battery in only a couple of hours.

Of course that is not necessarily going to stay that way when the days get shorter and shorter, which is why I upped the panel output for the main reason.

Is it causing unnecessary stress on the charge controller to have to shut itself down in these days where there is large surplus? I wondered if it would be better to throw the DC isolator to switch them off when the battery gets topped.

I thought that maybe the SCC is doing effectively the same thing and breaking the circuit however I checked with the clamp meter and current was still coming into the SCC whereas with an isolator I think the whole circuit is cut? So this means the SCC is having to 'shed' that surplus power doesn't it in which case shutting down via the isolator would be better?

 

[shvm]

The SCC should just enter float/maintainence charging mode whenever batteries get full.

I assume the current you're seeing is how Solar Panels and consequently the MPPTs based on them work. Current at a low voltage drop.

 

[canadian0]

The SCC should just enter float/maintainence charging mode whenever batteries get full.

I assume the current you're seeing is how Solar Panels and consequently the MPPTs based on them work. Current at a low voltage drop.

Can you explain this some more please?

I thought you were the same user who commented on my other thread as a very similar discussion was made and you are both from similar parts of the world but different people.

They also discuss this but didn't really understand how it works.

I accept it as the answer but unsure how/why current would drop when voltage increases?

I am thinking this is different than the float now I think about it though because I know the SCC does have float and that still shows about 0.6 or so current but in this case I there is 0 current at all and the PV light goes out totally and also the current shows as -0.1. However it can't be a total circuit break because current is still shown as going into the SCC from the PV wires while I would expect nothing if the circuit was disconnected? So is the SCC just shedding this excess as heat? This is something I read happens before with charge controllers but don't know if it is relevant in this case.

 

[timselectric]

if there's no work to do, the SCC will just rest.
Similar to if you were filling up a bucket rocks. When the bucket is full, you just stop working. It doesn't put stress on you, if there's still lots of rocks that could be picked up. You are done, because your bucket is full.

 

[IdiotJeff]

if there's no work to do, the SCC will just rest.
Similar to if you were filling up a bucket rocks. When the bucket is full, you just stop working. It doesn't put stress on you, if there's still lots of rocks that could be picked up. You are done, because your bucket is full.

Great analogy!

 

[Mike.S]

Is it causing unnecessary stress on the charge controller to have to shut itself down in these days where there is large surplus?

Only if your SCC is undersized (PV voltage rating). When it stops putting out power, the input voltage will rise to Voc or more depending on temperature and irradiation.

 

[outboard1196]

I checked with the clamp meter and current was still coming into the SCC

How much current?
Is the meter able to measure DC current?
If so did you zero out the meter before testing?

 

[740GLE]

Is the concern about the abrupt switching of current?

Say it’s rocking at 50a into the battery and then hits float and stops current coming into the battery?

I’d say they’d have to design a fly back diode or some other trick to eliminate and concerns of switching current on and off.

 

[J.H.]

Is the concern about the abrupt switching of current?

Say it’s rocking at 50a into the battery and then hits float and stops current coming into the battery?

I’d say they’d have to design a fly back diode or some other trick to eliminate and concerns of switching current on and off.

Maybe I’m wrong but mine will fill up by noon each day…let’s just say…

pumpin those amp like crazy ..
As it gets near full it starts “tapering off “ in a sorta quick slide down to very low… or 0 ..

The SCC’s have been doing this since day one..

I’ve never seen a high amp to quickly 0 amp scenario ..or am I missing the question here..

I have watched this before and wondered is this thing Gona slow down or crash in the wall.

It always slows down …so far anyway..

J

 

[outboard1196]

Maybe I’m wrong but mine will fill up by noon each day…let’s just say…

pumpin those amp like crazy ..
As it gets near full it starts “tapering off “ in a sorta quick slide down to very low… or 0 ..

The SCC’s have been doing this since day one..

I’ve never seen a high amp to quickly 0 amp scenario ..or am I missing the question here..

I have watched this before and wondered is this thing Gona slow down or crash in the wall.

It always slows down …so far anyway..

J

Unless the battery goes into protection or some other fault it should taper off easy.
Or you have high loads that the charger is carrying in absorption then switches to float and drops to 0A till voltage falls.

 

[J.H.]

Unless the battery goes into protection or some other fault it should taper off easy.
Or you have high loads that the charger is carrying in absorption then switches to float and drops to 0A till voltage falls.

It does … that’s what I was saying…it knows what it doing…
Sorta like like watching a Falcon land …there’s a bit of anxiety at the end …

J.

 

[740GLE]

All depends on how it’s being controlled, some closed looped with the BMS controlling are pretty abrupt. My shunt is in control of the SCC based only on voltage.

Here’s my taper one absorbtion voltage is reached and held for 20min, it does stop current once it flops to float.

 

[RCinFLA]

I accept it as the answer but unsure how/why current would drop when voltage increases?

A PV cell is an illumination based current source, capped in voltage by a PV cell's inherent diode, with some parallel shunt leakage resistance.

Maximum power point is approximately where 5% of the illumination generated current is shunted (wasted) through the cell's inherent diode, with about 95% of the illumination current yielded to the external load (charge controller). This maximizes the product of illumination current to external load times PV inherent silicon diode forward conduction voltage to an external load.

When a charge controller does not need the PV power it lightens the load on the PV array which causes the PV array voltage to rise towards Voc, open circuit voltage, where more and more of the illumination current is shunted down the inherent silicon cells' diode causing a greater diode voltage. For the total shutdown case, this causes approximately a 20% increase in panel heating which is approximately the 20% PV efficiency. The extra panel heating of 20% is relatively small and does not damage PV cells.

 

[Brucey]

When a charge controller does not need the PV power it lightens the load on the PV array which causes the PV array voltage to rise towards Voc, open circuit voltage, where more and more of the illumination current is shunted down the inherent silicon cells' diode. For the total shutdown case, this causes approximately a 20% increase in panel heating which is approximately the 20% PV efficiency. The extra panel heating of 20% is relatively small and does not damage PV cells.

So in this scenario if the array is a pergola or on the roof of a dwelling, actually disconnecting them from the scc could result in a 20% reduction in heat being radiated versus letting the scc idle?

 

[timselectric]

As it gets near full it starts “tapering off “ in a sorta quick slide down to very low… or 0 ..

The SCC’s have been doing this since day one..

It's not the SCC, doing it.
It's the battery not pulling current, because it's reached the charger voltage.

 

[timselectric]

So in this scenario if the array is a pergola or on the roof of a dwelling, actually disconnecting them from the scc could result in a 20% reduction in heat being radiated versus letting the scc idle?

It doesn't matter if the SCC stops drawing power, or you disconnect it to stop the power draw, the outcome is the same.
The panels get hotter, because all of the sunlight is converted to heat, instead of part of it being converted to electricity.

 

[1ufvlsi6x]

Something tells me this question comes from the same old misconception, that devices draw unlimited power if power is available. Electronics draw as much as they need because they are not a typical dumb resistor.

 

[canadian0]

if there's no work to do, the SCC will just rest.
Similar to if you were filling up a bucket rocks. When the bucket is full, you just stop working. It doesn't put stress on you, if there's still lots of rocks that could be picked up. You are done, because your bucket is full.

Hmm ok but what I was thinking, to follow the analogy, was that, since there was still current being read, that it would be like having a bucket under a tap and once the bucket is full of water the excess will be gushing over the sides. In this case the excess 'gushing' into the SCC still, causing excess heat/wear which it would have to shed. This was my concern. That is may be causing excess wear having to 'work off' the excess.

A better analogy would be eating excess food. The person is full but they keep eating and must burn off those excess calories. I am not saying that is what is happening but that was my concern to find out if that is actually what is happening.

How much current?
Is the meter able to measure DC current?
If so did you zero out the meter before testing?

It was partially cloudy yesterday so the input currents were low at about 0.8 for the 300W string and 1.7 or so for the 890W string. Yes I did zeroing, the currents were the same when it was inputting current as when the SCC had switched off which is what spurred the question. Important to clarify current reading coming in from the PV panels as well as the SCC current reading going into the battery. So the readings are for the first one, the PV strings, while the second, the current going from SCC to battery was reading -0.1. So what is why I asked where is that current going, which is coming in from PV, because if I had flipped the DC disconnect then there would be no current coming in at all as the circuit is broken which leads me to question what is happening in the case of the SCC 'shutting down' since there clearly seems to be current still coming in.

Maybe I’m wrong but mine will fill up by noon each day…let’s just say…

pumpin those amp like crazy ..
As it gets near full it starts “tapering off “ in a sorta quick slide down to very low… or 0 ..

Ok, this is the behavior mine does too and nice to see yours fills up quickly and shuts down and is no problem. There is the large influx, reaching to maximum current of 40A SCC limit sometimes, then taper to 0.XA for a while then shutoff after that low level. My concern is not about the large change, but as I explained above of whether it would be putting excess strain on the SCC which could be avoided by cutting the circuit with the DC isolator instead, but from the other replies, particularly from @timselectric below, it seems this was a misconception.

A PV cell is an illumination based current source, capped in voltage by a PV cell's inherent diode, with some parallel shunt leakage resistance.

Maximum power point is approximately where 5% of the illumination generated current is shunted (wasted) through the cell's inherent diode, with about 95% of the illumination current yielded to the external load (charge controller). This maximizes the product of illumination current to external load times PV inherent silicon diode forward conduction voltage to an external load.

When a charge controller does not need the PV power it lightens the load on the PV array which causes the PV array voltage to rise towards Voc, open circuit voltage, where more and more of the illumination current is shunted down the inherent silicon cells' diode. For the total shutdown case, this causes approximately a 20% increase in panel heating which is approximately the 20% PV efficiency. The extra panel heating of 20% is relatively small and does not damage PV cells.

View attachment 337274

Thanks for the explanation but still went over my head mostly. I guess I have to read up more about open circuit voltage?

It doesn't matter if the SCC stops drawing power, or you disconnect it to stop the power draw, the outcome is the same.
The panels get hotter, because all of the sunlight is converted to heat, instead of part of it being converted to electricity.

Hmm, so I made that assumption above that it was happening at the SCC, being shed through the heatsink, whereas it is actually happening at the panels themselves then?

That is good to know that the effect will be the same either way so won't have to concern myself with wanting to disconnect them all the time. So as such it is just the same as if they weren't connected to anything at all then and just laying there unplugged, in the sun? That puts the mind at ease if so.

Very useful to have these discussions to understand things better and demystify things.

 

[Mattb4]

As a rough analogy think of your solar panel as if it was a battery. When you draw from it he produces current. Once you stop it sits there. it does not feed current to your load or inverter. The action that creates energy in a battery is chemical. In a panel it is photovoltaic.

 

[JWLV]

I'm not sure if I need more buckets or more rocks...

 

[canadian0]

As a rough analogy think of your solar panel as if it was a battery. When you draw from it he produces current. Once you stop it sits there. it does not feed current to your load or inverter. The action that creates energy in a battery is chemical. In a panel it is photovoltaic.

Actually this is still not making sense as I was thinking about it more. If it is like how you say, and others have noted that it stays at the panels, then when is there still current on the PV wires going in to the SCC?

It is sunnier than yesterday and I just checked and the current on the wires to PV seems the same as what it would be if it was going on full blast. However the MT50 shows 0V and 0A, which is rather confusing. So the current seems to go into the SCC then hide.

I am back to thinking that that current is just being shed via the heatsink on the SCC?

 

[Mike.S]

It is sunnier than yesterday and I just checked and the current on the wires to PV seems the same as what it would be if it was going on full blast. However the MT50 shows 0V and 0A, which is rather confusing. So the current seems to go into the SCC then hide.

I am back to thinking that that current is just being shed via the heatsink on the SCC?

How did you measure the current? What was it? More detail needed. You can't have current with no voltage.

If the panels were in full sun, and connected to the controller, the MT50 is simply wrong. With no/little PV current (charging off or float mode), the voltage would be close to Voc. And with no PV voltage (i.e. the controller is short circuiting the array), the current should be near Isc. Anywhere in between, there would be both voltage and current.

 

[RCinFLA]

Actually this is still not making sense as I was thinking about it more. If it is like how you say, and others have noted that it stays at the panels, then when is there still current on the PV wires going in to the SCC?

What current? When a SCC totally unloads a PV array it will be open circuit. If you want to get nit-picky, there is some minuet leakage current into the charge controller at its minimum loading setting. The charge controller may also be supplying its overhead power to run its electronics from PV sourcing causing some current consumption from PV array even when no output current for charging battery is needed.

There is a continuum of current reduction as the charge controller reduces loading on PV array. This forces more and more of the PV illumination generated current to be re-absorbed by PV array causing more current through their inherent diodes driving up the diode voltage forward conduction voltage drop. This causes the array output voltage to rise towards totally unloaded Voc voltage.

Basic rule, if power is being generated it must be consumed somewhere.

 

[Mattb4]

Actually this is still not making sense as I was thinking about it more. If it is like how you say, and others have noted that it stays at the panels, then when is there still current on the PV wires going in to the SCC?

It is sunnier than yesterday and I just checked and the current on the wires to PV seems the same as what it would be if it was going on full blast. However the MT50 shows 0V and 0A, which is rather confusing. So the current seems to go into the SCC then hide.

I am back to thinking that that current is just being shed via the heatsink on the SCC?

What value of amperage are you measuring and your method to obtain it?

 

[canadian0]

What value of amperage are you measuring and your method to obtain it?

DC clamp meter. I am clamping on the PV input wires for each string. The amps were ~3A for each string when I last check a few minutes ago yet no current showing on MT50.