Any way to set a minimum Absorb Time on a FM80

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Surfpath
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Any way to set a minimum Absorb Time on a FM80

Post by Surfpath » Mon Mar 18, 2013 3:50 pm

IÔÇÖm about to wrap up the 1st few weeks of charging my Trojan L16ÔÇÖs using PV. Everything is going generally fine. But a small finding is that I've experienced gradual battery SG drop-off over this time (my FM80 is inputting roughly the same number of amp hours IN (PV) as OUT (my usage) each day, so SG's gradually fall).

Despite that my Outback CC says I am at 100% SOC by the end of the day's charging, when SG's are checked I am actually reaching a slightly lower SG value, say each 2-4 days. I have tons of sun and my CC typically goes into float by 11am.

Despite that my absorb time limit is set at 2hrs in the advanced menu, my actual typical absorb time is 20-35 minutes. End amps are not set (yet).

I am not too concerned. These SG's drop gradually and I know that every 10-14 days I can perform an EQ if need be to get back to 100%/95% real SOC. It also seems like there are lots of folks out there who have this same battery experience, and just deal with a(n eventual) 80-50% DOD.

However, my gut tells me I should slightly increase the number of positive AMPs coming into my bank each day by increasing my absorb time slightly (say to 1hr). Perhaps the resultant SG drop would be just very slight and I would only have to perform EQ's once a month, as opposed to every 10-14 days. EQ's seem to be harder on my batteries.

Outback says I can only set a maximum absorb time on my FM80 in the CC advanced settings, but not a minimum absorb time. I have seen no screen that allows you to input a minimum absorb time. The older MX chargers may have had something along these lines.

Is this really the case? Also can anyone help me to understand why my CC is only inputting roughly the same AMP hrs as my batteries take out. Surely it should take into effect battery/system inefficiencies?

I have entered basic info into my FNDC (such as amp hours), and will read up on the "how to calibrate your FNDC" .pdf. However, please direct me if there is a better, easier way. Or that I should not bother tinkering with my system. :-k
Thanks!

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Re: Any way to set a minimum Absorb Time on a FM80

Post by Gordon-Loomberah » Mon Mar 18, 2013 5:15 pm

What do you have your absorb voltage set to? Do you have RTS connected for temperature cmpensation?
The FM80 will do a minimum time- it is the time you set in the advanced menu, so long as you leave end amps at zero. However, if you have anything else connected to the FM80 that overrides it...
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Re: Any way to set a minimum Absorb Time on a FM80

Post by BlackCherry04 » Mon Mar 18, 2013 5:55 pm

Page 55 for the explanation and Page 90 for the mate menu.

http://www.outbackpower.com/docman/0307 ... 00RevB.pdf

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Re: Any way to set a minimum Absorb Time on a FM80

Post by Surfpath » Tue Mar 19, 2013 10:55 am

Hi Gordon,
Good to hear about the minimum time capability. I have a flexpower panel, standard set up, nothing exotic connected to it. I use an RTS.
I am not home right now, but I have my Abs Voltage higher than the recommended 58.8V. I think it's set as 59.4. This was suggested to me when I was generator charging, before my PV was installed, in order to shorten some lengthy charge times. I've also gone back to this setting once I started experiencing slightly diminishing SG's while PV charging. I can't tell whether it has made a difference though. From my AMPs in and out logs it still seems that the outback CC will put in only what it takes out.

However, you got me thinking about end amps. I thought I set up an end amp number 3 weeks ago when I first set up my PV (the advice was 2% of battery bank amp hours: 7.4 in my case. I thought I even inputted a value of "7"). Anyhow, when I went to check (the Mate?) if I had inputted this value I saw "00," so I thought maybe I didn't.

But then again, I think you can program advanced settings in both the CC panel as well as in the mate. Perhaps I did input an end amps figure in the CC, and my system is following this - however the Mate isn't aware. I will look and see if this is the case.

BlackCherry: Thanks for the attachment. That manual is more extensive that the one that came with my system. The relevant text being: "An Absorbing charge stage normally ends when the battery voltage is maintained at the Absorbing set point for the time period set in the Absorb Time Limits screen." This sounds logical. Again, perhaps what I said above about end amps is what is actually terminating my absorb a little sooner.

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Re: Any way to set a minimum Absorb Time on a FM80

Post by Gordon-Loomberah » Tue Mar 19, 2013 2:59 pm

Surfpath wrote: I have a flexpower panel, standard set up, nothing exotic connected to it.
Other than the Mate, which will override it AFAIK!

I have my Abs Voltage higher than the recommended 58.8V. I think it's set as 59.4.
My Trojan user manual says it should be 59.2V @ 25C
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Re: Any way to set a minimum Absorb Time on a FM80

Post by Surfpath » Wed Mar 20, 2013 1:42 pm

So.

To confirm I did not enter an end amps value in the CC, nor in the advanced settings for the CC found in the Mate.

What I did was (in the Mate) enter a value of "7amps" in the "ADV/DC/CHARGE--------return amps" screen.

Per the FNDC manual: "Return amps: See the manuf. recommendations or set to 2% of the battery bank amp hour capacity."

So I put in 7amps.

It probably has no impact on my absorb times being shorter than what I set, but that is where I thought I inputted "end amps."

What is the difference between these 2 (end and return amps)?

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Re: Any way to set a minimum Absorb Time on a FM80

Post by BlackCherry04 » Wed Mar 20, 2013 2:51 pm

It's the same thing. You really need to add to the ending value the background load amps on your Inverter. That background could be a computer that is always on or other household items. My background amp draw is about 6 amps. The reason you have to add it is because the CC will being to try to replace it and stay in absorb and never go into float and float voltage. Once it goes to float it will replace the amp draw but at a lower voltage as long as there is input from the CC or charger.

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Re: Any way to set a minimum Absorb Time on a FM80

Post by gww » Wed Mar 20, 2013 3:25 pm

I read a paper on batteries that mentioned outback time for absorb. It basically said that the amp hours on the mate were ac amps meaning one amp was ten amps dc. It basically said to set the absorb for a really long time. Then watch the absorb cycle and when it got down to 1 ac amp for one hour, you should set your absorb for one half hour less then the time it took to do this. Even with loads (if constant) you would think that if it got to a certain point and just stayed there that it would be where you need to be. Maby even to set your end amps to that value. Make sure someone agrees with me before you take any of my advice, as I only know anything by reading, my stuff is not installed yet.
Hope I help more then I hurt
gww

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Re: Any way to set a minimum Absorb Time on a FM80

Post by Surfpath » Wed Mar 20, 2013 3:29 pm

Thanks for that addition. I basically only have 1 item in total that operates in the background while I am not at home (a 115w/220V fridge). So I can add those running amps.

I read the newish looking outback manual, and can't see anything different about truly establishing a minimum absorb time. My system is set to absorb for 2 hrs, however it has never recorded an absorb time longer than 44 minutes (typically it's about 30 minutes). I'm basically still trying to add some positive Amp hours into my batteries each day. Despite excellent sunshine the CC always only puts in about the same as it takes out, unless I perform an EQ & SG's keep on dropping when I don't think they need to. I am back to 1.250 at sunset, will double check this with my new hydrometer, just now.

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Re: Any way to set a minimum Absorb Time on a FM80

Post by BlackCherry04 » Wed Mar 20, 2013 4:00 pm

Surfpath wrote:Thanks for that addition. I basically only have 1 item in total that operates in the background while I am not at home (a 115w/220V fridge). So I can add those running amps.

I read the newish looking outback manual, and can't see anything different about truly establishing a minimum absorb time. My system is set to absorb for 2 hrs, however it has never recorded an absorb time longer than 44 minutes (typically it's about 30 minutes). I'm basically still trying to add some positive Amp hours into my batteries each day. Despite excellent sunshine the CC always only puts in about the same as it takes out, unless I perform an EQ & SG's keep on dropping when I don't think they need to. I am back to 1.250 at sunset, will double check this with my new hydrometer, just now.
You have to realize that you are now into Battery Management and no system is perfect, they all require some intervention and adjustment. Your DOD & SOC and the SG's of your Bank will dictate the settings you choose. Your available Sun Hours figure into the seasonal changes you make. By making the SG's your constant you always have a point to return to. Having a small EQ in the plan is a good thing. I usually use the Absorb voltage to make slight changes over time, I will bump up or down of the voltage and see where it takes you.

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Re: Any way to set a minimum Absorb Time on a FM80

Post by gww » Wed Mar 20, 2013 4:49 pm

This is where I took my advice from.

http://www.greenhousepc.com/free/PUB-BATT-001.pdf

Thirty mins for absorb can't be right.

Good luck.
gww

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Re: Any way to set a minimum Absorb Time on a FM80

Post by blackswan555 » Wed Mar 20, 2013 4:51 pm

Sounds like your FNDC is terminating charge too early, Go through the programming and disable it ( set SOC start & stop to "0")
I read a paper on batteries that mentioned outback time for absorb. It basically said that the amp hours on the mate were ac amps meaning one amp was ten amps dc.
This is when charging from gen/grid, It also depends on battery and mains voltage, eg 230vac > 24vdc is about 10, 230vac > 48vdc is about 5,

It basically said to set the absorb for a really long time. Then watch the absorb cycle and when it got down to 1 ac amp for one hour, you should set your absorb for one half hour less then the time it took to do this. Even with loads (if constant) you would think that if it got to a certain point and just stayed there that it would be where you need to be
Don`t read to much from the "number" itself it is more what is doing, ( DC is a better measure) As you Say another way to find end of charge time is to set long absorb then watch amp`s until they flat-line,

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.

gww
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6. 1 mx 60 charge controller, 1 fm 80 and 1 morningstar ts60 pmw
7. outback mount, panel and sub panel
8. mate
9. 4 place hub
10. couple more cc, doc wattson
11. 800 ah, 48 volt fork truck battery

Re: Any way to set a minimum Absorb Time on a FM80

Post by gww » Wed Mar 20, 2013 5:05 pm

Tim
I love when you guys add info to the small amount I think I know. I learn every time and if I could remember any of it I would be great.
Thanks
gww

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Re: Any way to set a minimum Absorb Time on a FM80

Post by Gordon-Loomberah » Wed Mar 20, 2013 5:11 pm

Here is my oft used graph to demonstate that point :)
The red line is Net charging- and after about 2 hours it has stopped decreasing, and that is when the batteries are at 100% SOC.
There is then some EQ time and later it is Float until the end of the day.
20111217-netcharge.gif
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Re: Any way to set a minimum Absorb Time on a FM80

Post by BlackCherry04 » Wed Mar 20, 2013 6:39 pm

Gordon-Loomberah wrote:Here is my oft used graph to demonstate that point :)
The red line is Net charging- and after about 2 hours it has stopped decreasing, and that is when the batteries are at 100% SOC.
There is then some EQ time and later it is Float until the end of the day.
20111217-netcharge.gif
Great Graph, a picture is worth a 1,000 words, it helps to visualize it. Thanks for sharing.
Last edited by BlackCherry04 on Thu Mar 21, 2013 5:12 am, edited 1 time in total.

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Re: Any way to set a minimum Absorb Time on a FM80

Post by blackswan555 » Thu Mar 21, 2013 1:38 am

Gordon, Is that using Inverter to charge ? The "Spikes" seem strange
Tim
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Re: Any way to set a minimum Absorb Time on a FM80

Post by Gordon-Loomberah » Thu Mar 21, 2013 2:09 am

No Tim, only charging with an FM80 and a BlueSky SB50- the SB50 actually gives a much smoother output when looked at in detail (mV level, 1sec or faster sampling), but that's not important right now ;) The spikes are mostly due to a large elecrical load with a thermostat- a 1300W bench-top oven and a bit of cloud every now and then.
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Re: Any way to set a minimum Absorb Time on a FM80

Post by blackswan555 » Thu Mar 21, 2013 2:23 am

Ahh makes sense, I was looking at your graph and thinking about mentioning the amount of "spare" you have, I was guessing you could run something around 1 KW for most of the rest of the day " After dinner"

Tim
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30 evacuated tube 250litre hot water (no elect or gas boost), Hydronic heating- 78 evacuated tube 250litre(+1000l tank which I'll plumb in one of thee days) Heat exchanger to transfer heat from hydronics circuit to hot water when required. Davis VP2 +Solar & UV Wx Station.
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Re: Any way to set a minimum Absorb Time on a FM80

Post by Gordon-Loomberah » Thu Mar 21, 2013 4:22 am

It's even better now I have LiFePO4s, they are significantly more efficient, and for a few days running in January I used 20 to over 24kWh per day- ie more than the full capacity of the batteries, and had no trouble getting back to 100% SOC each day, often by mid-morning, with a bit under 4kW of PV.
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Re: Any way to set a minimum Absorb Time on a FM80

Post by blackswan555 » Thu Mar 21, 2013 9:07 am

I was a little puzzled there :smile: You profile lists LiPo`s but the plots were apparently FLA`s, I have a load of plots on an old machine somewhere using watplot & a SG sensor from http://www.jsaphotonics.com/ that show what is happening internally to SG`s v Amp`s & V, Would be well interested to see the LiPo graphs
Tim
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Re: Any way to set a minimum Absorb Time on a FM80

Post by Surfpath » Thu Mar 21, 2013 10:54 am

Gordon-Loomberah wrote:The red line is Net charging- and after about 2 hours it has stopped decreasing, and that is when the batteries are at 100% SOC.
There is then some EQ time and later it is Float until the end of the day.
Hi Gordon,
Novice PV battery charger here. Is this graph representative of your daily charge cycle? Or just a cycle with your (occasional) EQ? It looks like 2pm is when the EQ kicks in for 1-1.5 hours. On an average day of charging do you input more amps into your batteries than you take out and, if so, what is that ratio in rough terms?

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Re: Any way to set a minimum Absorb Time on a FM80

Post by Surfpath » Thu Mar 21, 2013 11:13 am

Tim,
regarding my 30 minute absorb times, you said that it "sounds like your FNDC is terminating charge too early, Go through the programming and disable it ( set SOC start & stop to "0")." I guess this is a diagnostic step? I'll try it out.

Last night I took SG measurements using the new hydrometer, and it confirms the readings of the previous one (ie. slightly declining SG's).

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30 evacuated tube 250litre hot water (no elect or gas boost), Hydronic heating- 78 evacuated tube 250litre(+1000l tank which I'll plumb in one of thee days) Heat exchanger to transfer heat from hydronics circuit to hot water when required. Davis VP2 +Solar & UV Wx Station.
Living off-grid since 1991
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Re: Any way to set a minimum Absorb Time on a FM80

Post by Gordon-Loomberah » Thu Mar 21, 2013 4:26 pm

Surfpath wrote: Hi Gordon,
Novice PV battery charger here. Is this graph representative of your daily charge cycle? Or just a cycle with your (occasional) EQ? It looks like 2pm is when the EQ kicks in for 1-1.5 hours. On an average day of charging do you input more amps into your batteries than you take out and, if so, what is that ratio in rough terms?
That graph is from a couple of years ago when I had Trojan FLA batteries. These days I have LiFePO4s, and the graph looks completely different. On the day of that particular graph I chose to do an EQ so that I'd have a good representation of all the stages of battery charging in one place, so I could demonstrate various things to others. The EQ was done manually, and the oven thermostat was responsible for the spiky parts of the graph.
I don't actually take any notice of AH in and out, other than what is in the FM80 log, as it isn't a useful guide to state of charge.
These days my daily plots include Voltage Net Amps (not AH), various Net and Gross kW and kWh, and Net SOC

Here's a net SOC/charging/voltage graph- absorb/balance is done in 24 mins. My gross cumulative kWh is multiplied by 0.94, which carries through to the SOC curve here- that's the efficiency of charging and discharging with lots of Float time for the LiFePO4s, it's about 95% when there isn't any Float time- way better than the ~85% for Lead-acid batteries!
20130209Net.gif
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Re: Any way to set a minimum Absorb Time on a FM80

Post by blackswan555 » Fri Mar 22, 2013 1:47 am

regarding my 30 minute absorb times, you said that it "sounds like your FNDC is terminating charge too early, Go through the programming and disable it ( set SOC start & stop to "0")." I guess this is a diagnostic step? I'll try it out
Yes, Sorry, bit more info :smile: I think it may be your FNDC ending charging too early, To save running all through it`s setting`s to see if/where it is, Disabling it`s charge control and letting the FM`s internal timer take control will prove either way, To be honest I do not use FNDC for solar charge termination :smile:

Tim
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Re: Any way to set a minimum Absorb Time on a FM80

Post by Surfpath » Mon Apr 01, 2013 3:19 pm

A quick update on this newby's experience with setting the right battery charge parameters for his battery bank:

It's been a little frustrating (partly because I am often not at home during prime sunlight charging times). However, over the past weekend I was home more frequently and able to make some headway. BTW: I decided to try to experiment with and master my FNDC (rather than turn it off).

First, some observations (please set me straight if any of these appear to be off):

1. There seem to be 2 places to enter a "END AMPS" value on my flexpower system. a) On the FM80 (using the Mate: select advanced, then charger, then end amps, and b) on the FNDC, under "RETURN AMPS" (using the mate: select advanced, then DC, then Charge). I experimented with these 2 "locations" for END AMPS and it seems like the CC follows the higher end amp value, wherever it is set. Ie. When I had both locations set as 1.5A the FM80 terminated absorb at 1.5A, however after I inputted 1A into the CC "END AMPS" and then 1.8A into the FNDC "RETURN AMPS," my CC terminated Absorb after charging amps went below 1.8A for a short while.

2. END amps can be increased/decreased by a value of "1" (ie. 7,6,5,4,...). While RETURN AMPS feature is more fine tuned and can be adjusted by tenths (ie. 7.0, 6.9, 6.8...). If I can tame my FNDC I intend to use return amps as my "end amps" value location.

3. On the FNDC Return Amps there is no zero or "00" value, like there is on the CC END AMPS screen (in fact below "1" it annoyingly goes to 999, and you cannot go "up" to return to 1. Yes, I had to hold down the "down" button for something like 10 minutes to return to single digits again. Thus it seems that one cannot turn off the "END AMPS" feature (like I was advised in another forum) by simply entering '00' in the END AMP field, because a FNDC "Return Amp" value will still exist & take precedence over a "00" END AMP value set in the FM80.
-SP

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