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Re: MX60 self-protection?

Posted: Fri Jul 02, 2021 12:28 pm
by drstrip
Raysun - thanks for your patience in all my questions. After all this back-and-forth, I've concluded my real question is why a controller rated to deliver 80A continuously into the battery can in reality only do so in ideal conditions? Panels virtually never operate at STC output power. For most people the actual performance is below, or even well below that value. But it can exceed as well, though it seems to be much rarer. The design guidelines call for input such that the STC power matches the output rating which insures the controller is almost always operating below the level rated for continuous operation. Is this input/output balance inherent in the nature of electronics, or is it a design choice that perhaps reduces the cost?

And note that I realize that if the actual power input is 4000W, then anything short of 4000W going into the batteries has to be converted to heat. But we're not talking about actual power input, we're talking about spec-sheet power (and at STC, no less). The MPPT algorithm can pick a point on the curve that matches the desired output. No, it can't respond instantaneously, and maybe that's one of those inherent properties of electronics that limits the system to matching peak theoretical input to output limits.

Re: MX60 self-protection?

Posted: Fri Jul 02, 2021 1:10 pm
by raysun
There's an old engineering maxim (that I just made up): Design for the worst case in order to avoid the worst consequences.

I have no doubt, and personal experience, that the FM80 can exceed 80A output without, so far, suffering harm. I choose not to find the limit of that excursion, however.

I liken it to the race car classes that use stock motors. A Honda Civic with the stock engine used as a family car will have a service life of 100,000 miles. That same engine on the racetrack may last no more than 1000 miles. In both cases, the vehicle owner has chosen a performance profile to fit specific needs, and have accepted the consequence to engine life.

I'd expect no less from a FlexMax charge controller. If the myriad variables that affect performance are kept within specified limits, a long service life is a reasonable expectation. Exceeding the specified limits is certainly achievable (depending on the spec, for a very short period, or somewhat longer period), however, doing so will be more likely to contribute to a shorter service life.

Solar panels are cheap. Long gone are the $5/watt panels. Charge controllers aren't exactly cheap, but they aren't 2nd Mortgage material either. One controller driven hard and lasting 5 years is nowhere near as good an investment as two controllers driven modestly and lasting 20.

At least to my way of thinking.

If you choose to keep the 2 MX60s, you can conservatively design around a 70A output current. 70A x 48V = 3360W giving a total of 6720W for the pair. If you want to "round up" to 7kW, its likely a small enough risk.

The reason I say the latter is due to the panels not reaching full output first thing in the morning when battery voltage is lowest. As charging commences, 50 - 52V will be the norm and the power handling will rise slightly 52V x 70A = 3640W. Of course a wild card will be concurrent loads. If a large load demands current enough to drag the battery voltage down during charging, then the charger is put under considerable stress.

Re: MX60 self-protection?

Posted: Fri Jul 02, 2021 3:06 pm
by drstrip
raysun wrote: Fri Jul 02, 2021 1:10 pm There's an old engineering maxim (that I just made up): Design for the worst case in order to avoid the worst consequences.
That matches experience. It's just that in my book, a "continuous" rating would apply to a value you can sustain day in, day out with no adverse impact on lifetime.
I suppose I need to start my own charge controller company so the ratings mean what I want them to mean :grin:

If you choose to keep the 2 MX60s,
except that Outback says they are not compatible with Lithium batteries (apparently of any kind from a follow-up email). If the risk is to the controller, I might be willing to try. If the risk is to the batteries, that's a non-starter.

Re: MX60 self-protection?

Posted: Fri Jul 02, 2021 3:47 pm
by raysun
drstrip wrote: Fri Jul 02, 2021 3:06 pm
raysun wrote: Fri Jul 02, 2021 1:10 pm There's an old engineering maxim (that I just made up): Design for the worst case in order to avoid the worst consequences.
That matches experience. It's just that in my book, a "continuous" rating would apply to a value you can sustain day in, day out with no adverse impact on lifetime.
I suppose I need to start my own charge controller company so the ratings mean what I want them to mean :grin:

If you choose to keep the 2 MX60s,
except that Outback says they are not compatible with Lithium batteries (apparently of any kind from a follow-up email). If the risk is to the controller, I might be willing to try. If the risk is to the batteries, that's a non-starter.
I'd upgrade. The FM series works without a hitch. (My guess there's something in the charging profile settings that don't line up with all flavors of lithium.)

If those big LiFePo4 batteries are on the radar, you will find they charge amazingly easily. Compared to lead-acid the difference is night and day. Lithium charges far more efficiently, so more of what's collected goes toward useful charge. The chemistry is far simpler, lithium batteries are charged by shuffling lithium ions between cathode and anode. No acid chemistry to reverse, no impermeable salt degradation precipitates. The most marked contrast however, is lead-acid batteries degrade so precipitously at partial state of charge, that we all develop this lead-induced full charge mania. It causes all manner of behavioral issues in battery owners. Lithium on the other hand loves partial state of charge. They are actually far happier than when fully charged. Suddenly calling every last photon to account has far less import. In fact, my favorite days are ones my battery gets to about 80% SoC. An unintended consequence is lithium batteries are good for one's mental health.

Not that its an especially practical goal, but do you want a battery that would last 100 years? Buy a lithium battery much too large for your needs, and charge it to no more than 75% SoC, then discharge it to 30% SoC on each cycle. The longer a lithium battery lingers in the broad neighborhood of 50% SoC, the longer it will live.
I suppose I need to start my own charge controller company so the ratings mean what I want them to mean
Way back in the day, I made my living building systems using Ashton-Tate's dBII PC database application system. It was a pretty innovative tool, especially prior to A-T buying out the originator. After a much ballyhoo'd major release was repeatedly delayed by a succession of design flaws and bad code, A-T was increasingly excoriated by a howling user community, yours truly supplying no small portion of salt scrub to keep the wounds raw and painful. Finally A-T had a stable (enough) release to show their faces to the mob, and a spokesman showed up at our professionals user group to demonstrate the product and catch spears from the restive crowd. After a demo that went off well (enough) he bravely opened the floor to Q&A. Most is not worth recounting, but one of our more reserved members piped up and asked:
"Do you think the system is perfect now?"
Our presenter deftly disarmed the crowd:
"Perfect? Not even close. If it was perfect it would have exactly two commands -
•Set Bugs Off
and
•Do What I'm Thinking"

The crowd loved it. I loved it. Until I thought about it, and the consequences those commands would have for most of the developers I knew.

Set Bugs Off - would eliminate as much as 80% of their emitted code base.

Do What I'm Thinking - oh gawd, the envisioned outcomes give me nightmares even nearly a half century later.

Be careful what you're thinking. 😁

Re: MX60 self-protection?

Posted: Fri Jul 02, 2021 4:47 pm
by drstrip
raysun wrote: Fri Jul 02, 2021 3:47 pm I'd upgrade. The FM series works without a hitch. (My guess there's something in the charging profile settings that don't line up with all flavors of lithium.)
That's my plan, though I'm looking at Midnite Solar as well, as I've been told, thought haven't confirmed, that they are more tolerant of excess input.
If those big LiFePo4 batteries are on the radar,
Absolutely. They are one of the driving factors in my plans to upgrade.
In fact, my favorite days are ones my battery gets to about 80% SoC. An unintended consequence is lithium batteries are good for one's mental health.

Not that its an especially practical goal, but do you want a battery that would last 100 years? Buy a lithium battery much too large for your needs, and charge it to no more than 75% SoC, then discharge it to 30% SoC on each cycle. The longer a lithium battery lingers in the broad neighborhood of 50% SoC, the longer it will live.
Can the FM80 be programmed to stop at 75% or 80% SoC?

Re: MX60 self-protection?

Posted: Fri Jul 02, 2021 5:40 pm
by raysun
Can the FM80 be programmed to stop at 75% or 80% SoC?
Not really, though there are (somewhat fiddly) tricks to make it happen. I don't recommend them however.

Charging a lithium battery fully is not a bad thing, it just isn't a necessary thing. I don't celebrate a great accomplishment when they hit 100% SoC, and don't fret when they don't. For the battery I use, if it stays above 20% SoC, its all good.

TBH, my main method for moderating charge is to not have overly large solar arrays. I've lived with my location and off grid living to have a pretty good handle on power needs. I don't try to have a massive array that will provide full charge on deeply cloudy days, and don't worry about what to do with excess on profoundly sunny ones. On the average day, the battery sees 80 - 100% charge.

Every five or six weeks, I run my generator on a low sun day for enough hours that it gets some exercise and the battery gets to 80%.

If that lithium battery is a near-term objective, then I'd pump the breaks on driving the charge controllers over the cliff, Thelma and Louise style. My money is on it just not being necessary. Certainly not necessary like reacting to an aging lead-acid boat anchor that's growing ever more stubborn in its old age (unlike us, who grow more facile.)

Get a couple FM80s. Put a 3 - 4kW array on each one. Plug it into a big LiFePo4 battery and after a few months in off grid re-education camp, you'll wonder what all the drama was about. Seriously.

If there's some local condition that points to being able to "cheat" a larger array into place, it can always be done later. The only practical reason I'm aware of is roof architecture that doesn't permit all day solar exposure (east and west facing roof planes for example.) There may be others.

In our location? At 19°N latitude the 1kW / M² is a joke. The sun is high in the sky all year. On the intense days, if you're out in it, you can literally feel it cooking your brain through your skull. I've never measured the radiant field, but the number of times the panels have been delivering power above STC, even though they are too hot to touch, leads me to believe it's fairly high. When cloud effects are thrown in, short-term responses can just be off the charts. I'm happy with a conservatively rated array, because I don't need any more than that. I'm happy for clear mornings and partial cloud cover in the afternoons, because things don't get driven so hard. I used to love hard driving, now everything is mo' chill, mo' bettah.

When I got the new panels (20 @ 440W) I was going to keep my old 20 @ 330W arrays as well. When I set up the first new array, I ended up removing two panels (leaving 8), selling 4 of the 440W, and all 20 of the 330W. 16 440 panels are more than enough for the 450AH lithium battery and all the juice we can drink.

Re: MX60 self-protection?

Posted: Fri Jul 02, 2021 8:10 pm
by SandyP
drstrip wrote: Fri Jul 02, 2021 11:19 am ../..Is it possible that setting the output limit to 80A means "output everything you can", while setting it to 79A (or anything else) enables clipping to the limit?
^^^ That is my understanding, leaving it at the default results in no maximum being set.
raysun wrote: Fri Jul 02, 2021 11:49 am The controllers will limit output to their current limit settings - eventually - but will overshoot them if the input is overdriven. If one watches closely, it can be seen, even under "normal" circumstances. Response to an increase in input power is not instantaneous.
Yep, I have seen this and have found that you need to set the current limit to at least 10% below the FM's max to ensure you minimise/prevent any over current "excursions".

Re: MX60 self-protection?

Posted: Sun Sep 05, 2021 5:10 am
by BruceS
I've been reading this thread with some interest but kept my mouth closed till now. (I don't have an Outback solar controller)
I'd just like to put up a small section from the Scneider Conext 150-60 controller manual. (150V-60A)
array.jpg
I'm interested as I have 1500w @ 37V on the front of the houseboat & am in the process of installing the same on the rear.
In between is the top deck with bimini meaning shade on one or the other .
Seems I can put all of it on the one controller or buy another controller or my first thought, a changover switch for morning/afternoon.
Thoughts?

Re: MX60 self-protection?

Posted: Sun Sep 05, 2021 6:15 am
by Mike Curran
Hi Bruce - If the two arrays each get a significantly different sun exposure, but both get some sun most of the day, then your best option for maximum power would be a separate controller for each. OTOH, if one gets sun part of the day while the other doesn't, a single controller with a selector switch might be better. Finally, if both arrays get close to identical sun exposure, one controller for both would work as long as it can handle the combined power output of the 2 arrays, including factoring in the voltage limit of your controller.

Sounds like the Conext info is telling you to use a single controller, assuming your 2 arrays will never exceed 3500W because their sun exposure times don't overlap. But I think the array without sun may seriously degrade your output if it is paralleled with the one getting sun - depending on how different their exposures are.

Probably not telling you anything you don't already know, but hope this helps. - Mike

Re: MX60 self-protection?

Posted: Sun Sep 05, 2021 8:56 am
by raysun
BruceS wrote: Sun Sep 05, 2021 5:10 am I've been reading this thread with some interest but kept my mouth closed till now. (I don't have an Outback solar controller)
I'd just like to put up a small section from the Scneider Conext 150-60 controller manual. (150V-60A)
array.jpg
I'm interested as I have 1500w @ 37V on the front of the houseboat & am in the process of installing the same on the rear.
In between is the top deck with bimini meaning shade on one or the other .
Seems I can put all of it on the one controller or buy another controller or my first thought, a changover switch for morning/afternoon.
Thoughts?
Schneider is playing an interesting game with the array specification. 48A max input current is understandable. 140V(oc) max open circuit voltage is likewise understandable. 140V(oc) x 48A is nonsense. At open circuit, the array by definition is producing 0A, therefore 0W.

TBH, I have no idea what they are trying to specify. Certainly, it's not that 20 335W panels can be wired into a 60A controller and used to charge a 12V battery. (I'd love someone to prove this assertion incorrect, however I will not contribute anything to defray the cost of a fried controller.)

Re: MX60 self-protection?

Posted: Sun Sep 05, 2021 9:18 am
by Mike Curran
140V(oc) x 48A is nonsense. At open circuit, the array by definition is producing 0A, therefore 0W.
140Voc × 48A is still a reasonable estimate of what such an array could produce under the right conditions.

Re: MX60 self-protection?

Posted: Sun Sep 05, 2021 10:06 am
by drstrip
Mike Curran wrote: Sun Sep 05, 2021 9:18 am
140V(oc) x 48A is nonsense. At open circuit, the array by definition is producing 0A, therefore 0W.
140Voc × 48A is still a reasonable estimate of what such an array could produce under the right conditions.
It may also reflect the design criteria they used in sizing the components. ie, it will withstand 140V, which would occur at Voc, and 48A at the max power pt. Thus, the input can withstand 48A x 140V simultaneously. Admittedly, the wording is strange.

Re: MX60 self-protection?

Posted: Sun Sep 05, 2021 10:49 am
by raysun
drstrip wrote: Sun Sep 05, 2021 10:06 am
Mike Curran wrote: Sun Sep 05, 2021 9:18 am
140V(oc) x 48A is nonsense. At open circuit, the array by definition is producing 0A, therefore 0W.
140Voc × 48A is still a reasonable estimate of what such an array could produce under the right conditions.
It may also reflect the design criteria they used in sizing the components. ie, it will withstand 140V, which would occur at Voc, and 48A at the max power pt. Thus, the input can withstand 48A x 140V simultaneously. Admittedly, the wording is strange.
Strange indeed.

Re: MX60 self-protection?

Posted: Sun Sep 05, 2021 2:10 pm
by BruceS
Thanks all for the input. I just thought my post might throw a little input to this particular discussion as I can see more & more people adding cheap panels to their systems.
The six I am installing were $10au ea. I bought the 20 he had & passed the other 14 on to others.
I think I'm going to go with a second controller.
Going back to some of your earlier comments regarding heat generated ...... These Schneider units have no fan in them so I think the input must get snipped. Imagine when fully charged in bright sunshine? There would only be a couple of A going in from my 1500w array. Some houseboats here are sitting empty for weeks on end with all system turned on.

Re: MX60 self-protection?

Posted: Sun Sep 05, 2021 2:32 pm
by raysun
I think I'm going to go with a second controller.
Esoterica about power control aside, a second controller provides one simple, and extremely important attribute, redundancy.

Re: MX60 self-protection?

Posted: Sun Sep 05, 2021 3:24 pm
by JRHill
Mike Curran wrote: Sun Apr 11, 2021 5:17 pm
What else can I try to resurrect it?/quote]How did it die?
Maybe I missed it in the messages that followed. It is a really good question.