Advice on upgrade

Discussion about the FM100, FM80, and FM60 Charge Controllers

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darman
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Advice on upgrade

Post by darman » Mon Mar 23, 2020 8:46 pm

New here but I have reading a lot of good info on here-alot is pretty much over my head.I'm hoping for some help with planned upgrades.My existing system has been in place since 2003 although batteries were changed out 3 years ago.I recently purchased 3-24v 3kwh Lifepo4 batteries w/BMS and some used Sanyo 190w panels that are 54.8v MPV.I am wanting to replace my existing panels with 4 of the Sanyo panels run in parallel to a new outback flex 80 controller to the new batteries and use my existing inverter.Am I at all on the right track?Your help and advice is much appreciated-Thanks Darman

darman
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Re: Advice on upgrade

Post by darman » Thu Mar 26, 2020 9:19 pm

Can someone give me a yes or no???

raysun
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Re: Advice on upgrade

Post by raysun » Fri Mar 27, 2020 1:31 am

Whether you are on the right track or not depends on several factors, and information not provided in your post.

Let's start with what you have now:
A battery bank 24V @ 860AH ~ 20kWH capacity
4kW inverter
320W PV Panel array
45A charge controller

There is considerable mismatch between battery capacity and (solar panel) charging capacity. The array, producing maximum power would develop about 13A net charging current into a 24V battery. The L-16 should be charged at roughly 10%-13% of its rated capacity or approximately 85A-110A. I'd expect this battery has been chronically undercharged.

FYI, the FM80 is rated at 80A maximum charging current, below the ideal minimum for this battery. The array that would support charging at the maximum charger output would be 80A x 24V =:1920W, roughly 2kW. Since PV arrays don't put out full output generally, the battery really would need almost the capacity of 2 FM80 controllers and 4kW total array power.

The 4kW inverter is capable of driving fairly large loads. It's not likely your demand is all that high, because if it was, the battery would be drained quickly (easily within a day or two) and the small charging source would never be able to make up the consumption. Under high load and low charging the battery would be dead in a month. Given they've lasted 3 years, I'd guess daily consumption to be 1.5 - 2.5kWH, very low.

All the above is based on the PV panels being the only charging source.

Do you have any other charging sources? A generator perhaps?

On to the new battery. Three 3kWH lithium battery blocks would be 9kWH / 24V ~ 375AH (Amp-Hour) capacity. Let's assume the battery is discharged 50% every day, or roughly 185AH. The PV array needed to recharge the battery would need to be roughly 1500W. This assumes about the equivalent of 4 hours of full array output. In practice the full 1920W that the FM80 could handle would be better.

What is your average daily power consumption?

The 4 190W panels would need to be wired as 2 parallel strings of 2panels in series. Wiring them a 4 in parallel would not provide high enough charging voltage.

As used panels, lets assume their output to be roughly 175W each. The 4 panel array would equal 700W max. output. Assuming the same equivalent 4 hours of full output would equal 2.8kWH total charge. If daily consumption Is under 2 - 2.5kWH, the array might keep up, otherwise the new battery may be chronically undercharged unless additional charging source is available.

Are you planning on keeping the existing array and charge controller in service to assist with charging?

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Re: Advice on upgrade

Post by sparksalot » Fri Mar 27, 2020 5:21 am

darman wrote:
Thu Mar 26, 2020 9:19 pm
Can someone give me a yes or no???
How about...It depends...

darman
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Re: Advice on upgrade

Post by darman » Fri Mar 27, 2020 6:24 am

Thanks for the reply-Our system is in a high mt. cabin that's mostly used 2 to 3 days at a time with a week or more in between with no usage.Inverter off,charge controller on.While we are there we are very conservative running only lights. as needed and ceiling fan.At the beginning of a stay battery voltage is usually up around 27.5v and by end of a stay battery voltage around 24v.If we are staying longer we end up running generator (Onan 3500w running propane at 12,000 ft.)I run the gen to try and equalize every so often,probably not as much as I should.Panels are on a pole mount,no tracking,but no shading either.The only way I could enlarge array beyond 4 panels would be with roof mount and panels would be covered with snow quite often.Thanks very very much for your help!!Darman

raysun
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Re: Advice on upgrade

Post by raysun » Fri Mar 27, 2020 8:52 am

OK, that makes sense.

Large lead acid batteries that are lightly used/lightly charged tend to have a shorter service life then ones that are discharged and charged more along their designed specs.

There's lots of advice out there about putting in an over large battery to provide "days of autonomy", it ignores this, and the result is poor battery performance, IME, if the ask was about replacing lead acid with lead acid, I'd have recommended putting in a much smaller battery matched to the charging capabilities of the larger panels.

What brand is the lithium battery?

Lithium may be a better choice in the type of service the system is delivering. There are a couple of things to consider.

At 12,000' it's likely there will be time the temperatures are below freezing. Be very careful about charging/discharging a lithium battery at or below freezing temperatures. Check with the manufacturer for their guidelines on this, including battery stored at below freezing temps. Lithium is far less tolerant than lead acid.

Lithium battery held at 100% state of charge can be subject to growth of "dendrites" - little spikes of lithium metal that can pierce the thin plastic membrane separator inside the battery, leading to premature cell failure. Some method to draw off the "excess" charge may help maintain expected service life. Traditional lead acid battery likes to be used between 100% and 50% state of charge. Lithium is more like 90% - 20% state of charge.

It will be an interesting exercise to integrate a new battery into the system. I know you were asking "what time it is" and we're telling you "how to build a clock", but in this case, you are "appointed" to do your own engineering, so working through all this headache-inducing stuff is in order. Keep asking questions. I, for one, want to know how it all turns out.

raysun
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Hyundai 355 watt panels (6 - 3 strings of 2 in series)
Honda EU7000is gas fuel generator

Re: Advice on upgrade

Post by raysun » Fri Mar 27, 2020 9:38 am

One more piece of unbidden advice. For a lead acid battery, voltage is not an ideal method to track state of charge. It only correlates when the battery is completely at rest (no load, no charging) and is only accurate when at rest for 24 hours.

The very flat discharge/charge curve of lithium makes voltage impossible to use to track state of charge - except at the end points where voltage rapidly falls off or rapidly climbs a very steep "cliff".

These voltage end points are very important, especially for proper charging. However, some sort of quality battery monitor that tracks current flowing into and out of the battery will be helpful for knowing the state of charge between the extremes.

darman
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Re: Advice on upgrade

Post by darman » Fri Mar 27, 2020 7:51 pm

Thanks again for the great input.I will try and answer some of the questions where I have left gaps.The batteries are used units purchased from battery hookup,but actually came from Bigbattery.com in Cali.I believe they assembled them there from units out of E-busses.They have BMS installed,circuit breaker,and digital voltage readout.The mech room where batteries are is downstairs and underground so temp tends to stay between 40 and 55 degrees F year around.Has very rarely gone down to freezing,but is my understanding that BMS would stop charge and protect batteries if that ever happened.I currently have a victron BMV 501 Battery Monitor, it may be needing to be upgraded to something newer.Also have a 24v heater in mech room for overload to divert to,there is a 2nd morningstar tristar 45 PMW controller for that.This was all put together in like 2003 by local solar guy-I'm not that smart.If I run the panels 2 in series my voc will be 67.5x2=135v is that still ok for the Flex80? Thanks Darman

raysun
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Suniva 330 watt panels (12 - 6 strings of 2 in series)
Hyundai 355 watt panels (6 - 3 strings of 2 in series)
Honda EU7000is gas fuel generator

Re: Advice on upgrade

Post by raysun » Fri Mar 27, 2020 8:08 pm

How is the 67 5V figure arrived at? Voc at the expected lowest temperature? It sounds like a high voltage for the panel power.

Whats the model number of the panel?

darman
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Re: Advice on upgrade

Post by darman » Sat Mar 28, 2020 7:13 am

Here is the page with rating label,I was trying to post it last night but being tech challenged,https://batteryhookup.com/products/sany ... 1867684996

fcwlp
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Re: Advice on upgrade

Post by fcwlp » Sat Mar 28, 2020 11:03 am

You are going to have issues with these panels at 12,000 feet with an FM80. I ran the numbers in the string sizing tool with typical values for the Voc and Vmp temperature coefficients. With two panels in series at temps below 32F you are exceeding 145VDC which is the most you want to design for. At -4F (-20C) your at 153VDC and at -40F(-40C) your at 162VDC. And of course with one panel per string you don't have enough volts to do anything.

You should instead look at the FM100 if you want to use these panels.

raysun
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My RE system: Flexpower One: FX3048T, (2) FM80, MATE3s, FlexNetDC
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Outback IBR3 battery enclosure
Suniva 330 watt panels (12 - 6 strings of 2 in series)
Hyundai 355 watt panels (6 - 3 strings of 2 in series)
Honda EU7000is gas fuel generator

Re: Advice on upgrade

Post by raysun » Sat Mar 28, 2020 11:48 am

fcwlp wrote:
Sat Mar 28, 2020 11:03 am
You are going to have issues with these panels at 12,000 feet with an FM80. I ran the numbers in the string sizing tool with typical values for the Voc and Vmp temperature coefficients. With two panels in series at temps below 32F you are exceeding 145VDC which is the most you want to design for. At -4F (-20C) your at 153VDC and at -40F(-40C) your at 162VDC. And of course with one panel per string you don't have enough volts to do anything.

You should instead look at the FM100 if you want to use these panels.
Or wire them in parallel as originally planned. Since its a 24V system, they will provide more than enough voltage headroom.

Its an unusual panel voltage. They must be purpose designed for early string inverter technology perhaps?

Its ironic, they would be unsuited to work with 48V battery charging for the reasons pointed out above, but should be OK for 24V. The low current output is suited to parallel wiring with 10AWG cabling.

darman
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Re: Advice on upgrade

Post by darman » Sat Mar 28, 2020 2:01 pm

The parallel hookup would work well for replacement of existing panels as I have #10 coming down pole to combiner box (15 ') then #6 from there 25' to charge controller and batteries.The panels came off a school in Cali and they said something about commercial panels.I tested several while I had good sun-showing 68.7 voc.Thanks so much again I feel pretty good to move ahead.Will post back with results although with this virus it may be 2 months or so.

raysun
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My RE system: Flexpower One: FX3048T, (2) FM80, MATE3s, FlexNetDC
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Suniva 330 watt panels (12 - 6 strings of 2 in series)
Hyundai 355 watt panels (6 - 3 strings of 2 in series)
Honda EU7000is gas fuel generator

Re: Advice on upgrade

Post by raysun » Sat Mar 28, 2020 2:25 pm

darman wrote:
Sat Mar 28, 2020 2:01 pm
The parallel hookup would work well for replacement of existing panels as I have #10 coming down pole to combiner box (15 ') then #6 from there 25' to charge controller and batteries.The panels came off a school in Cali and they said something about commercial panels.I tested several while I had good sun-showing 68.7 voc.Thanks so much again I feel pretty good to move ahead.Will post back with results although with this virus it may be 2 months or so.
FWIW

The "kosher" method would be parallel wiring from panels to a mount-attached combiner box, each cable terminating at a bus bar. For bonus points, a 30A circuit breaker could feed the "down" wiring. Nice to have a cutoff at the panels, should any need disconnecting under load conditions.

The super-kosher method would be to use one of these and 4 15A breakers: https://www.solar-electric.com/mnpv6.html

Avoid, if at all possible, using a nest of those parallel "Y" cables. Even though the total current is low, they are a fire waiting to happen in the right circumstances.

darman
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Re: Advice on upgrade

Post by darman » Sat Mar 28, 2020 3:07 pm

I understand what your saying ,I think what I have is close to what you are recommending.I will have to look at it-I know there is a breaker/disconnect on the pole mounted combiner box.Darman

raysun
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My RE system: Flexpower One: FX3048T, (2) FM80, MATE3s, FlexNetDC
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Suniva 330 watt panels (12 - 6 strings of 2 in series)
Hyundai 355 watt panels (6 - 3 strings of 2 in series)
Honda EU7000is gas fuel generator

Re: Advice on upgrade

Post by raysun » Sat Mar 28, 2020 3:56 pm

darman wrote:
Sat Mar 28, 2020 3:07 pm
I understand what your saying ,I think what I have is close to what you are recommending.I will have to look at it-I know there is a breaker/disconnect on the pole mounted combiner box.Darman
If there's a disconnect, then there's likely bus bars. A good solid mechanical connection point is the best way to assure trouble free performance. A couple hundred watts out of the panel array is not such a big deal. 500 watts or so and it's time to really pay attention.


48V is the low threshold of the lethal voltage classification.

darman
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Re: Advice on upgrade

Post by darman » Sat Mar 28, 2020 6:08 pm

I like the box you gave the link for.

raysun
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Suniva 330 watt panels (12 - 6 strings of 2 in series)
Hyundai 355 watt panels (6 - 3 strings of 2 in series)
Honda EU7000is gas fuel generator

Re: Advice on upgrade

Post by raysun » Sat Mar 28, 2020 6:57 pm

darman wrote:
Sat Mar 28, 2020 6:08 pm
I like the box you gave the link for.
I use 2 of 'em for 6kW, room for +2kW

The latest 78" x 39" 72 cell panels are tipping 400W.

4×400W=1.6kW

4 sun hours avg. 1.6kWx4H=6.6kWH/day

You need a frame heating system to keep the panels a few degrees above freezing. If putting in AGS, it might as well do something with the gas it burns. Auto clearing the array after a winter storm on a clear day is going to permit substantial PV production by and large.

fcwlp
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Re: Advice on upgrade

Post by fcwlp » Sat Mar 28, 2020 7:14 pm

raysun wrote:
Sat Mar 28, 2020 11:48 am
Or wire them in parallel as originally planned. Since its a 24V system, they will provide more than enough voltage headroom.
Raysun, thanks for catching that it is a 24V system, I missed that in my response.

raysun
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My RE system: Flexpower One: FX3048T, (2) FM80, MATE3s, FlexNetDC
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Suniva 330 watt panels (12 - 6 strings of 2 in series)
Hyundai 355 watt panels (6 - 3 strings of 2 in series)
Honda EU7000is gas fuel generator

Re: Advice on upgrade

Post by raysun » Sun Mar 29, 2020 10:43 am

fcwlp wrote:
Sat Mar 28, 2020 7:14 pm
raysun wrote:
Sat Mar 28, 2020 11:48 am
Or wire them in parallel as originally planned. Since its a 24V system, they will provide more than enough voltage headroom.
Raysun, thanks for catching that it is a 24V system, I missed that in my response.
I did too, at first. We're so conditioned to 48V systems it the first response, and why I was asking about pv panel config.

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