Is my SCC dead or something else?

Rednecktek

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So I was out having a smoke at ungodsly hours this morning (because jet lag) and I noticed my driveway lights were really dim. I figured it was just the fact that it's fall in Western WA and we haven't seen the sun in weeks that the poor system just hasn't been fed enough. So I headed down with my meter (it's a long walk) and popped the case that houses all the guts and the two things that caught my attention were that the batteries were down to 8v each, and the SCC looked funny.

According to the SCC the batteries were "Charging" and "Fully Charged" even though the meter on the panel said 0v, 0a, and 0.00w incoming.

Is my SCC dead or does that just happen when the batteries get too low?

The Guts:
Rich Solar 100w Poly panel
2x 15Ah 12v AGM batteries
Solar day/night switch
Wirthco 10a PWM SCC

Thanks gang!

Also, can anyone recommend a cheap SCC for a lithium battery on Amazon I can get? I'm in a position to get a couple of Life's that will fit in the box but the current SCC doesn't do Lith.
 
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sunshine_eggo

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"SCC... Fully charged" - Most SCC base this purely on the voltage of the battery and are horrifically unreliable. I would expect a 10A PWM to fall into this category. They can indicated "fully charged" even with then battery is far from fully charged, especially when a charge current is being applied raising the voltage from resting.

Until you've determined that your consumption does not exceed what your 100W panel can recover in a 24 hour period, replacing batteries will just put you right back here.

Solar determines how much you can consume on a daily basis
Battery determines how much you can consume between full charges.

Lastly, 30Ah batteries should likely not be charged at more than 3-6 amps depending on ratings.
 

Rednecktek

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The setup feeds 2x 3w lights when it's dark, and it's been running great from last spring to last night. When I did the latest revamp back in March I went from 25w Amorphous panels on each light to a single 100w poly panel. That did the trick since Western WA isn't exactly renown for it's bright sunny days. :)

My big question was if I need to replace my SCC or not. At the time I looked at it yesterday it was too dark to have the panel doing anything so there was no current coming in (according to the power meter wired into it) and the voltage on each battery was down to 8v. The lights on the charger were both lying and I was wondering if that was the sign of a dead SCC or just the way the little PWM's work when the batteries are dead.
 

sunshine_eggo

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The setup feeds 2x 3w lights when it's dark, and it's been running great from last spring to last night. When I did the latest revamp back in March I went from 25w Amorphous panels on each light to a single 100w poly panel. That did the trick since Western WA isn't exactly renown for it's bright sunny days. :)

Possible that you were cycling these batteries below 50%, and you've caused their capacity to decrease well below 15Ah each.

My big question was if I need to replace my SCC or not. At the time I looked at it yesterday it was too dark to have the panel doing anything so there was no current coming in (according to the power meter wired into it) and the voltage on each battery was down to 8v. The lights on the charger were both lying and I was wondering if that was the sign of a dead SCC or just the way the little PWM's work when the batteries are dead.

Hard to say from the conditions you describe, but even a "bright" cloudy day (enough clouds to obscure the location of the sun, but still lots of ambient light) should still produce power to the panels. If you can't verify current is flowing from the panels and to the battery in those conditions, I would conclude it's bad.

Any PWM SCC that can be programmed to charge at 14.4V or less, disable equalization and float at 13.6V or less is fine for LFP.
 

rickst29

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Long and complicated, but maybe worth reading.

The SCC maybe disconnected the batteries due to low Voltage, although its panel saying "fully charged" is weird. An MPPT SCC would definitely do that, because the batteries are too low to run its internal electronics. But I don't know whether a PWM SCC needs to do that. You will need to check things under daylight in order to reach any conclusions: With the SCC disconnected from the panel leads, check both the V(open circuit) and the Current (short circuit) coming from the panel. If the readings show it capable of delivering at least some power, then I would look at replacing both the SCC and the batteries. (At only 8 volts, the AGM batteries are probably ruined, although you could try to recover them with a different charger first.)

If I assume midtown Seattle WA and an optimal South-facing roof location, a 100 watt panel averages only about 300 watts per day. In addition, the proportion of panel power created at Voltage above about 14.2 volts is wasted by the SCC - it leaves that power in the panel, unused, by switching on and off thousands of times per second (in order to create an average voltage of about 14.2V for the batteries. So, if your panel generates maximum power (100 watts) at an optimal Voltage of 18.5 Volts (that's typical), you can get only about 14.2/18.5 * 100 watts = 77 watts, and your "daily average" for the year is only about 230 watts. But, if the panel is not facing directly South, or has any shading at all, or sits on a less-than 5/12 slope, it will average less. November production is much worse than "average", and December will be worse than November.

Your 2x 3 watts = "6 watt" lights possibly run for up to 11 hours in wintertime, roughly 66 watt-hours. 30 Ah of AGM batteries should not be discharged past about 50% SOC, so you can "spend" maybe 15 Ah per night. 6 watts from 12v is only 1/2 amp, plus some power wasted in wiring losses. Maybe .7 amps total consumed while running? That's only half of your AGM battery capability. Your battery configuration seems OK, but your specific Solar configuration might not be enough to keep the batteries up through the whole night - or your PWM could have failed, or its internal microcode for deciding when to drop an AGM battery into "float charging" might be stupid.
- - -
I would NOT switch to an LFP batteries, unless the battery could be located indoors. They can't be charged in temperatures below freezing. If everything is installed outdoors, stay with AGM.
 

Rednecktek

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I wish my solar was that good. Due to topography I'm running a western facing panel at 45deg and the forecast says no sun until middle of next week. :(

Yeah, I doubled the battery because of the 50% DoD limit hoping I could get some power every couple of days. It only gets below freezing out here a few days a year and I was thinking Lifepo4's for the extra capacity, but at over $125 not sure if it was going to be worth it.

What I wish I had was a panel that ran a higher voltage and lower amperage, like a 30v/3a type panel so it would at least produce Something on overcast days but the only things I've seen that are wired up that way are the semi-flexibles and those are at least $2/w so I can go with Either a 50w semi-flexible that would produce power at lower light levels OR Life batteries and controller for about the same cash.

Once the sun comes out I'll go pop the box and see what it has to say. Fortunately I have another PWM controller I can replace it with if needed.
 

sunshine_eggo

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I wish my solar was that good. Due to topography I'm running a western facing panel at 45deg and the forecast says no sun until middle of next week. :(

Yeah, I doubled the battery because of the 50% DoD limit hoping I could get some power every couple of days. It only gets below freezing out here a few days a year and I was thinking Lifepo4's for the extra capacity, but at over $125 not sure if it was going to be worth it.

What I wish I had was a panel that ran a higher voltage and lower amperage, like a 30v/3a type panel so it would at least produce Something on overcast days but the only things I've seen that are wired up that way are the semi-flexibles and those are at least $2/w so I can go with Either a 50w semi-flexible that would produce power at lower light levels OR Life batteries and controller for about the same cash.

Even if you had a panel like this, you'd need a MMPT. PWM works by shorting the panel to the battery, which pulls the panel down to just a hair over battery voltage negating any benefit. Additionally, that 30V/3A panel (90W) would be limited to 14.8V *3A = 44.4W PEAK output.
 

Rednecktek

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So assuming a $100-ish budget, MPPT controller, Life batteries, or different panels?
 

sunshine_eggo

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So assuming a $100-ish budget, MPPT controller, Life batteries, or different panels?

I would explore the "is my current PWM working? If not, replace with $0 on-hand PWM and see if it's fixed" option first.

Consider also that higher/voltage & lower current panels and/or MPPT producing better results in poor solar conditions are very small improvements. If I had to put a number on it, we're talking < 5%. They add up over time, but on a daily basis, they're just another optimization.
 

Rednecktek

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So noodle test: Assuming it's not the SCC and that it's just a matter of the fact that we have no sun, what about getting 4 of the 25w panels or the 30w panels, connecting them up in series (about 80v-ish) and dump them into a simple 10a MPPT controller? That should start producing power under MUCH lower light levels, right?
 

sunshine_eggo

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So noodle test: Assuming it's not the SCC and that it's just a matter of the fact that we have no sun, what about getting 4 of the 25w panels or the 30w panels, connecting them up in series (about 80v-ish) and dump them into a simple 10a MPPT controller? That should start producing very small amounts of power still insufficient to harvest the needed energy under MUCH lower light levels, right?

Fixed.

MPPT isn't magical. It does not allow you to get energy from nothing. It has a ~20% boost over PWM in peak solar conditions, and it tends to start charging a little earlier in the morning and continue charging a little later in the evening, but per my previous post, probably < 5% better in those conditions.

MPPT will allow you to harvest more than PWM. To put it into perspective, if a PWM will get you 100Wh of energy in a given set of conditions, MPPT will get you about 110-120Wh that same day.

If I were Rednecktek, AND I determined that my PWM SCC didn't just crap out on me, and my replacement didn't fix the problem, I'd get a 10A MPPT and ANOTHER 100W panel in series with my 100W panel (prefer same brand or model - any is fine as long as Imp values are very very close). This over-paneled MPPT will harvest more than the prior setup and will better harvest energy from lower light conditions in a non-magical modest manner compared to PWM.

I'd also probably test the 15Ah batteries to see if they're still reasonably healthy. If not, replace.
 
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Rednecktek

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OK, well it was a thought to get power producing under low light conditions. I was thinking that if I could start producing some power before I had to have enough light to get a single panel to hit that magical 14v mark. I'll look at my wood pile and see if I have the stuff for another panel mount. I just hate to think that 6w of lighting needs 200w of panel, ya know? That's why I threw it up here before I went shopping. :)

The batteries charged up and still held voltage a few hours after I unplugged them and have been running all night without a hitch so I think I saved them. Those things were $50 a piece to buy locally so if I have to replace them I was considering just going to Life's and a new SCC for about the same money. The weather report says I might get some good sun so I'll check out the meter and SCC in the box later this morning when the panel is actually doing something.
 

Rednecktek

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Correct my logic please (still a n00b) on my thought experiment:

If I had enough light to get a panel to about 50% of its output (low light rough numbers)
100w panel would be 12v @ 2.5a
4x 25w panels in series would be 48v @ 0.5a

Now, because the PWM controller doesn't do anything until that magical 13.5v mark, 12v @ 2.5a = 0 watts to the batteries.
With the MPPT controller the 25w panels would be 48v @ 0.5a = 25w to the batteries.

So if someone needed to deal with lots of cloud cover the multiple smaller panels and MPPT would be more effective over time than a larger panel with a PWM by a significant margin over time, right? The single larger panel would produce more amperage when it got the light to work with, but only under near perfect conditions?
 

sunshine_eggo

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Correct my logic please (still a n00b) on my thought experiment:

If I had enough light to get a panel to about 50% of its output (low light rough numbers)

This is more than you might think, but we can use it. Actually, given the current you've chosen, we're getting 42.5% rated power.

100w panel would be 12v @ 2.5a

No. It would be ~17V @ 2.5A = 42.5W (using Vmp)

4x 25w panels in series would be 48v @ 0.5a

If they are 12V panels, then they'd be closer to 78V @ 0.54A = 42.5W (using Vmp)

Now, because the PWM controller doesn't do anything until that magical 13.5v mark, 12v @ 2.5a = 0 watts to the batteries.

No. That is not the case with any SCC I've ever seen. The PWM will charge at below 13.5V. The PWM will "see" battery voltage on one side, and it will "see" panel Voc (~20V+) on the PV side. It will then short the panel to the battery allowing the 2.5A to flow at battery voltage, 2.5A * 12V+ = 30W+ (depends on battery voltage). Once the battery approaches full at say 14.4V, the power is 14.4* 2.5 = 36W.

With the MPPT controller the 25w panels would be 48v @ 0.5a = 25w to the batteries.

No. You'd get the 42.5W calculated above minus inefficiencies.

However, you'd also get the 42.5W from the single 100W panel as well as it can work at its Vmp of 17V on the MPPT instead of being forced down to battery voltage by the PWM.

It's the PWM's forcing of the attached solar panels to battery voltage that reduces the power collected where the MPPT allows the panels to operate at or near their Vmp value.

So if someone needed to deal with lots of cloud cover the multiple smaller panels and MPPT would be more effective over time than a larger panel with a PWM by a significant margin over time, right? The single larger panel would produce more amperage when it got the light to work with, but only under near perfect conditions?

No. Your two configurations would produce almost exactly the same amount of power on an MPPT. In fact, the 4X 25W in series would likely be slightly less due to inefficiencies associated with converting the 78V down to ~12V for charging vs. converting 17V down to ~12V. This kind of jump from high voltage is typically 1-2% less efficient than a jump from about 1.5X battery voltage (18V).

Please refer to my prior post... if a PWM would get you 100Wh for a given day, an MPPT would get you 110-120Wh on that same day - 10-20% more. You've tried to create a scenario that changes that relationship dramatically.

100W w/PWM will produce 30-36W depending on battery voltage
100W w/MPPT will produce 42.5W
4S 25W w/MPPT will produce 42.5W
4S 25W w/PWM will probably damage it due to over-volt, but if you could, it would only produce 12-14.4V * 0.5A = 6-7.2W

MISSING CONCEPT: The presence of light induces Voc. It doesn't take much to get full panel Voc.

This is 14 minutes BEFORE SUNRISE @ 6:37am this morning:

1637082304604.png

My panels hit 104V before the MPPT started pulling current - no sun on them. That first bump in current you see is 0.1A, and that pulled the voltage down to the 80s.

The point is to demonstrate and ANY panel in low light conditions is going to rapidly yield > 12V. It's the INTENSITY of the light that determines how much current will flow.

The BIG question here is...

Did the other SCC fix the problem?
 

Rednecktek

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Aaahhhh, I always thought that voltage and amprage were corrolated more closely, I.E. more voltage = more amperage and that the PWM wouldn't do anything until the panel was getting close to max production, 14+ volts out of 22v max, or 75% or more to start doing anything.

As to the SCC, the batteries were at 12.8v this morning when I replaced the controller and the sun is just now starting to come out, so I'll see later today.
 

sunshine_eggo

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Aaahhhh, I always thought that voltage and amprage were corrolated more closely, I.E. more voltage = more amperage and that the PWM wouldn't do anything until the panel was getting close to max production, 14+ volts out of 22v max, or 75% or more to start doing anything.

As to the SCC, the batteries were at 12.8v this morning when I replaced the controller and the sun is just now starting to come out, so I'll see later today.

Nope.

Ignoring efficiency for the sake of argument...

Voltage is determined by the number of cells. They put out about 0.5Vmp. "12V" panels have 36 cells with a Vmp around 18V. You need 18V to be able to charge a 12V battery to 14-16.2V depending on the phase of charging (some equalization of FLA actually does occur at 16.2V).

The size of the cells determines their current, i.e., a 25W 12V panel has 36 cells that are 1/4 the size of a 100W 12V panel.

As light begins to shine on a cell, its voltage rises very quickly. With the voltage established, additional light energy produces current at that voltage.

Hoping all this was academic, and you're fixed with your backup SCC. :)
 

rickst29

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Your best solution for the 3-head problem of "only a single 100w panel, with many cloudy days and shorter days in winter" is probably another panel (in parallel) with more battery storage as well, so that you can last more than 3 nights of use under heavy clouds when the days have been completely overcast.

MPPT versus PWM is only about 20% "better" with a single panel running at around 18 volts. That difference doesn't become significant until you have a bigger solar array, with a lot more watts to start from. (Or when "bigger" Solar Panels have more cells and higher VOLTAGE than yours.) And more power from the Solar Controller is only useful if the battery bank can take it- so you might need another battery, to fully take advantage of a second 100w Panel.
 

Rednecktek

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Well here's the update now that the sun is behind the hills and I'm not going to get anything else out of it today.
Starting: 12.8v
End: 13.1v
Meter reads 1.26Ah produced

Looks like the SCC didn't even last 6 months. :(
 

Rednecktek

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Thank you guys, I learned a LOT with this, like how the voltage and amperage aren't linear and a better idea of how the MPPT system works. My brain hurts in a good way now. :)
 

rickst29

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Thank you guys, I learned a LOT with this, like how the voltage and amperage aren't linear and a better idea of how the MPPT system works. My brain hurts in a good way now. :)
When the sun is shining at all, the Voltage from a Panel is at its highest V(oc) when zero current is flowing into the controller. But, when you pull power (by pulling current in amps) the voltage drops. An MPPT controller tries to find the "maximum power point" of lowered voltage with higher current. Typically, this Voltage V(mp) is only about 2 volts lower than V(oc) in typical 100 watt panels: V(oc) in the range of 19-20.5 volts, V(mp) around 17-18.2 volts.

Please advise what you get with the "spare" SCC, if it turns out to be a sunny day.
 
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