To extend or not to extend (float) that is the question...

Discussion about the FM100, FM80, and FM60 Charge Controllers

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emcvay
Forum Member
Posts: 5
Joined: Mon Oct 22, 2018 6:46 am
My RE system: System1 - 3 205w 12v panels in series (FE3's), Morningstar TriStar MPPT controller
System2 - 6 305w 24v panels in series/parallel (3 sets of 2 panels), Outback FlexMax 80 MPPT controller
Batteries -- 12 6v GCB's @ 220AH ea (24v config)
Aims 4000 watt pure sine inverter
Location: WA
Contact:

To extend or not to extend (float) that is the question...

Post by emcvay » Mon Oct 22, 2018 7:28 am

Hi All,

I've been running an off-grid system for 8 years now and recently upgraded my system with 6 new panels and a Flexmax 80 controller and am pondering some setting changes and a limitation (as I see it) on the FM80 controller....hoping you can help me out.

OK, here is the scenario: I was originally running 3 205w 12v panels (FE3's I believe they are) in series feeding a Morningstar Tri-Star 80 MPPT controller. I was getting a max of around 16.5amps of charging power at 29.6v going into my 12 6v GCB's in a 24vdc system. Overnight I typically used about 45AH and as a newby to off-grid systems didn't change much on the controller which had a 1.5h Absorb and a 1.5h Absorb extension if the battery bank dropped to 25vdc or less. Float was set to 1h and I believe there was a float extension allowed also but I never paid much attention.

The system was 'ok' most of the year as I live in Northern WA and in the summer I had plenty of solar charging when the system was in use (it's a cabin I don't live in). In the winter when there is less sun I have a Generac EcoGen 6kw running to an Aims 4000w inverter with 55amp charge triggered by a Magnum Research AGS switch. However, I knew I needed to do something to improve overall battery bank recovery under heavier use (I do spend a couple nights every couple weeks at the cabin due to work and can use 60+AH overnight in the winter) and purchased 6 CSUN305-72P-M156's and an Outback FlexMax 80 MPPT controller for them as I was unhappy with some issues I had with the MS controller (though overall I actually like the MS and they have since fixed the main issue I was having). My main reason, in all honestly and full disclosure here, switching to Outback was support. I'd heard it was second to none so here I am :D

Anyway, I've set up these new panels with 2 in series and the 3 sets running into a Midnight Solar combiner box and then feeding the OB controller. This is giving me a LOT more charging capacity and I'm finding that the system is charged back up to what the OB and my Tri-Metric meter tells me is 100% in a very short 90 minutes or so. (yes I have a hygrometer and can check SG readings but battery manufacturers tell me I have to leave the system off for at least 12 hrs to get a good reading and any reading under use is suspect so I don't take SG readings often without shutting the system down overnight).

OK, sorry, I digressed. So now that the system is charging up much faster I thought I would extend float on the OB to 3+ hrs like I have on the MS so the controllers will provide enough power to run the inverter etc throughout the day once the batteries are fully charged leaving the batteries topped up right until the sun goes down and I no longer can use the incoming solar to run things however, unlike the MS I can't seem to automatically extend float on the OB??? it seems I have to go in and extend float manually. Is there a way around this?

This brings me to my next 'to float or not to float' question: Assuming I am using 45-65AH overnight and have ~40amps of charging power coming in with the sun (10:30am to 2:30pm right now it's easy to get that) and assuming the math is as simple as AH out, AH in, why not allow the controller to float as long as there is sun once you've hit 100% SOC which under the above conditions should be about 90 minutes into charging? I figure once Bulk on both systems reaches 29.6vdc and absorb pushed the required 45-65AH back into the system there isn't any reason to continue to absorb but floating will provide a few amps to run the various items (like the inverter) throughout the day reducing the amount of time power is drawn off the batteries vs, only floating for one hour (so charging from about 10:30am to 1pm and then quitting thereby starting the draw on the bank at 1pm vs maybe as late as 5pm since there is still penty of sun to that point).

Thoughts?

And one more for you: Does anyone with a partially used system consider two separate charging profiles? Profile number one would be for the above, when the system is in use, but the rest of the time when the inverter is off and the genset is shut down/off the system only uses 1 or 2 AH overnight to run some small DC fans in a composter room. Under that scenerio it seems the system could absorb for a very short period just to top off the batts and then run float all day until the sun goes down if for no other reason that for freeze protection (fully charged batts don't freeze as easily and will last longer in my mind).

Thoughts?

So far I've just let the system absorb for the 90 minutes it does now (I've shut down absorb extension due to the much higher capacity I now have) and then the OB quits floating after 1 hr but the MS I have floating for 3 hrs. I'm just curious about all the above and hoping some pro's can help steer me in the right direction.

Thanks

emcvay
Forum Member
Posts: 5
Joined: Mon Oct 22, 2018 6:46 am
My RE system: System1 - 3 205w 12v panels in series (FE3's), Morningstar TriStar MPPT controller
System2 - 6 305w 24v panels in series/parallel (3 sets of 2 panels), Outback FlexMax 80 MPPT controller
Batteries -- 12 6v GCB's @ 220AH ea (24v config)
Aims 4000 watt pure sine inverter
Location: WA
Contact:

Re: To extend or not to extend (float) that is the question.

Post by emcvay » Thu Oct 25, 2018 3:44 pm

Hmmmm......no one has any answers? Outback did reply to my support request with: Our controllers don't allow float time adjustments....and then:
It is my understanding that engineering decided that the functionality of the float (or trickle charge) should go on through out the day as needed when solar is available and that when it goes below the float to the re-bulk that it will then initiate a new charge cycle.
Um, not apparently on the FM80

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IanMcCluskey
OutBack Product Management
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Joined: Tue Aug 28, 2018 1:16 pm

Re: To extend or not to extend (float) that is the question.

Post by IanMcCluskey » Thu Oct 25, 2018 4:10 pm

Hey there, excuse me for the slow response. Our Apps Engineering team that often monitors the forum is working on an exciting project, and somehow I did not see your post on Monday. Glad you checked in.

Regarding the float timing, I will check with our tech's on that. How are the MS and OB controller outputs combined into the battery bank?

On your last question, are you proposing to use the OB system for profile one and the MS system for profile two, or switching both systems between profile 1 and 2 on demand?
And one more for you: Does anyone with a partially used system consider two separate charging profiles? Profile number one would be for the above, when the system is in use, but the rest of the time when the inverter is off and the genset is shut down/off the system only uses 1 or 2 AH overnight to run some small DC fans in a composter room. Under that scenerio it seems the system could absorb for a very short period just to top off the batts and then run float all day until the sun goes down if for no other reason that for freeze protection (fully charged batts don't freeze as easily and will last longer in my mind).
Ian McCluskey
Product Manager


Alpha Technologies Inc. / OutBack Power Technologies
3767 Alpha Way Bellingham WA 98226 USA
http://www.alpha.com

emcvay
Forum Member
Posts: 5
Joined: Mon Oct 22, 2018 6:46 am
My RE system: System1 - 3 205w 12v panels in series (FE3's), Morningstar TriStar MPPT controller
System2 - 6 305w 24v panels in series/parallel (3 sets of 2 panels), Outback FlexMax 80 MPPT controller
Batteries -- 12 6v GCB's @ 220AH ea (24v config)
Aims 4000 watt pure sine inverter
Location: WA
Contact:

Re: To extend or not to extend (float) that is the question.

Post by emcvay » Thu Oct 25, 2018 5:49 pm

Thanks for the response!

The OB and MS systems are both fed into a Disconnect box with both connected to the same main breaker. I'll have to draw something up but in short each Controller feeds via breakers and the shunt (on the neg side) to the bank so both can charge the bank at the same time. I was advised by sales engineers that this is common and normal.

As for the profiles, in all honesty I hadn't thought that far really, though I considered just leaving it as is or changing both to 30m absorb since the OB will continue if the amps remain high (I believe) vs the MS which is timed.

SandyP
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My RE system: 8 x 190W 24V Suntech panels (4 strings of 2) July 2011
4 x 325W 24V Suntech panels (2 strings of 2) added Sept2018
Mate2
Outback FM60 MPPT (max output lowered to 55amps)
12 x 2V Hoppecke GEL 660 Ah C100 - 24V System
Outback VFX3024 Inverter/Charger
Victron BMV-602s
Honda 5.5kW Genset
Location: Victoria, Australia

Re: To extend or not to extend (float) that is the question.

Post by SandyP » Thu Oct 25, 2018 8:26 pm

emcvay wrote:....yes I have a hygrometer and can check SG readings but battery manufacturers tell me I have to leave the system off for at least 12 hrs to get a good reading and any reading under use is suspect so I don't take SG readings often without shutting the system down overnight)....
If you are trying to use the battery voltage as an indication of the battery charge then this does apply but as far as I know it is NOT applicable for SGs
..unlike the MS I can't seem to automatically extend float on the OB??? it seems I have to go in and extend float manually. Is there a way around this?..
The OB charge controllers will switch to float stage after absorb and stay in float for as long as it can maintain the set float voltage - ie. you cannot manually alter the length of the float stage.
..and assuming the math is as simple as AH out, AH in..
Unfortunately this is not the case more amps in is required to return a battery to the charge state it was before amp were "removed"
..I figure once Bulk on both systems reaches 29.6vdc and absorb pushed the required 45-65AH back into the system there isn't any reason to continue to absorb..
With FLA batteries you should ensure that your absorb stage lasts as long as is required to get the SGs to the fully charged level (ie SGs no longer increase).
..floating will provide a few amps to run the various items (like the inverter) throughout the day reducing the amount of time power is drawn off the batteries..
Floating will just maintain the battery charge state/set voltage, if any loads are present the charge controller will ensure enough power is produced to cover them as well.
..Does anyone with a partially used system consider two separate charging profiles?..
No need for this, with a properly set up system it will allow for different usage (away or cabin in use)

blackswan555
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Re: To extend or not to extend (float) that is the question.

Post by blackswan555 » Fri Oct 26, 2018 3:16 am

yes I have a hygrometer and can check SG readings but battery manufacturers tell me I have to leave the system off for at least 12 hrs to get a good reading and any reading under use is suspect so I don't take SG readings often without shutting the system down overnight
As mentioned by Sandy P, The above applies to battery voltage not SGs, They can be read "on the fly"

Tim
My comments are based on my experience and research, They are not endorsed or checked by Outback.I am an independent British electrician living in Spain, So please take this into account when reading /acting on my post`s.

emcvay
Forum Member
Posts: 5
Joined: Mon Oct 22, 2018 6:46 am
My RE system: System1 - 3 205w 12v panels in series (FE3's), Morningstar TriStar MPPT controller
System2 - 6 305w 24v panels in series/parallel (3 sets of 2 panels), Outback FlexMax 80 MPPT controller
Batteries -- 12 6v GCB's @ 220AH ea (24v config)
Aims 4000 watt pure sine inverter
Location: WA
Contact:

Re: To extend or not to extend (float) that is the question.

Post by emcvay » Mon Oct 29, 2018 6:06 am

Thanks for the replies.

So, even though the FM80 shows 1hr float time and does drop to 0amps after 1hr you are saying it should not?

It's possible, I suppose, that it's doing so because the MS controller is still providing a charge?

In light of your reply (thank you, thank you, thank you!) I will have to plan a trip and check SG readings in the AM and then throughout the charge cycle to see how things go.

Thanks

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Kurt Lundquist
Alpha Energy Engineering
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My RE system: VFX3524, Mate3, 200Ah 24V AGM Battery Bank
Location: Arlington, WA

Re: To extend or not to extend (float) that is the question.

Post by Kurt Lundquist » Mon Oct 29, 2018 9:11 am

emcvay wrote:So, even though the FM80 shows 1hr float time and does drop to 0amps after 1hr you are saying it should not?
What is the message in the lower right-hand corner on the FM80 screen?
emcvay wrote:It's possible, I suppose, that it's doing so because the MS controller is still providing a charge?
This would be my guess. The controller is there to protect the battery from overcharging. If the battery only needs a trickle of power to maintain float it is common to see just one controller providing the charge. To test this theory you can either turn off the PV feed to the other controller or turn on more loads in the cabin.

Thanks,

-Kurt
Kurt Lundquist
Renewable Energy Project Engineer
http://alphaenergy.us/

emcvay
Forum Member
Posts: 5
Joined: Mon Oct 22, 2018 6:46 am
My RE system: System1 - 3 205w 12v panels in series (FE3's), Morningstar TriStar MPPT controller
System2 - 6 305w 24v panels in series/parallel (3 sets of 2 panels), Outback FlexMax 80 MPPT controller
Batteries -- 12 6v GCB's @ 220AH ea (24v config)
Aims 4000 watt pure sine inverter
Location: WA
Contact:

Re: To extend or not to extend (float) that is the question.

Post by emcvay » Tue Oct 30, 2018 6:26 am

I was thinking that would be the next step, to turn off the smaller set of panels that go to the MS and see what happens.

Thanks -- and it makes sense since that controller is set to float for 3hrs

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