FM80 goes straight from absorb to snooze

benthere

My wife went back to school the other day and now with nobody home, our FM80 is only charging about 1.5KWH per day.

Today I was near the FM80 when it finished absorbing (never seen it in bulk, I think my array can always meet absorb). It went straight from absorb to snoozing. After panicking and hitting a few buttons, I was able to see a status of "charged" and I think the voltage was 53.6. There were no loads on the system as I had the inverter turned off (at the Mate).

So, I dusted off the manual and set about trying to understand what the FM was doing. It looks like it was snoozing because the voltage was over the float setting (52.8 in my case). I guess this might be normal that a surface charge has to bleed off after absorbing before the CC goes to float.

Anyway, now I'm wondering if I shouldn't lower my absorb setting or time. I need to get my butt in gear and measure the water usage, but haven't yet. It seems like it would be hard to get an accurate reading unless the water was refilled to exactly the same level, which means that eyeballing is not going to cut it. I'm really starting to think that I want some sort of automatic watering system...

From Surrette.com:

We recommend a three step charging procedure. Recommended voltage settings are as follows:

Equalization 61.9-64.1
Absorption/Bulk 56.9-58.8
Float 52.8-53.5

Caution: The ideal float voltage is the lowest voltage setting that will maintain the battery at full charge. The higher the voltage the more water the cell will consume. The minimum equalization voltage is highly recommended unless it is suspected a sulfation problem exists and a corrective equalization is required.

Absorption times are dependent on the battery series (4000 or 5000). The recommended times are general guidelines and the optimum time is dependent on absorption (bulk) voltage settings, charging current and should be adjusted such the batteries are brought back to full charge and use a small amount of water (approximately 5 ml (1/8OZ) of water per 100 AH of battery capacity per cycle assuming a 10% overcharge).

I've been absorbing at 57.6 (middle of window) for two hours, and floating at the minimum 52.8 since that seems to hold me at 100%.

So, given the complete and total lack of water usage information in this thread... Would you change anything besides measuring how much water is used?

Any ideas on a good way to get that measurement? I guess I need to make a water filler that fills to the exact right level every time.

Solar Guppy

Re: FM80 goes straight from absorb to snooze

For Offgrid living, I would suggest you should absorb all day ( not just 2 hours ), there is no point of going to float or off as you want to keep the battery's topped at 100%. Now if your at a unattended or low average use site, have it float or a shorter absorb time as you don't want to cook the battery's ( flooded not AGM ), the key is to harvest the most energy with battery damage.

boB

Re: FM80 goes straight from absorb to snooze

I'm not totally up on the FM80 changes from the older MX60 that it was cloned from, but I would think that the display should show "Battery Full" or whatever they call it now. Maybe Batt Full still ? Not Snoozing. Snoozing means something else.

I wouldn't Absorb all day, every day. That's sort, kinda, like EQing every day.

Ideally, the charger should stop Absorbing when the amps into the battery fall below some small percentage of the Amp-Hour rating of the battery bank. For instance, if you had a 1000 Amp-Hour bank and the Ending-Amps were,say, 2%... You would want it to stop Absorbing when the battery charge current fell below 20.0 Amps.

Since the MF80 doesn't know exactly what is going into the battery, it has to time it with the minimum Absorb time. IF you don't have any extra DC loads on when you are Absorbing, then you can use the MF80's Ending Amps feature to do exactly this. I think it's still in there ?? Just set it to whatever current is around 2% of the Amp-Hour capacity of the bank and set the minumum Absorb time for 3 or 4 hours to make sure that the Ending-Amps stops the charge cycle before the timer does.

OR, get an OutBack FNDC and all the trimmings necessary to make that work. Again, I'm not fully versed in that system anymore. Crewzer may show up with some more good info.

boB

benthere

Re: FM80 goes straight from absorb to snooze

Solar Guppy,

I've seen you around this and other boards, and respect your opinion but; wow, that is pretty far off of my understanding and what I believe the battery manufacturer's recommendation to be. Would you care to elaborate on your reasoning and indicate the arguments for not absorbing all day? I guess one of those arguments will be water consumption? Do battery manufacturers tell us to do what is easier and more maintenance free, or what is best for battery performance and longevity, or something in the middle?

Bob,

There is a setting for Absorb End Amps. Could you point me to some documentation of the proper use of that feature? My battery manufacturer says to absorb for two hours but doesn't say anything about amps.

Thanks to both of you for your input!

crewzer

Re: FM80 goes straight from absorb to snooze

I guess this might be normal that a surface charge has to bleed off after absorbing before the CC goes to float.

Correct. The charger will snooze if the battery voltage doesn't fall below the float target within 30 seconds of ending absorb. think it's supposed to wake back up and go into float mode after the battery voltage has fallen far enough.

I agree that "all day" absorbs are not a good thing. Surrette used to have some guidance on low target voltage and long absorb (~4 hrs?) for the summer (longer days), and a higher target voltage for a shorter period in the winter (not including temp comp offsets).

HTH,
Jim / crewzer

boB

Re: FM80 goes straight from absorb to snooze

benthere wrote: »

My battery manufacturer says to absorb for two hours but doesn't say anything about amps.

The battery manufacturer most likely knows that 2 hours at that absorb voltage is about what it takes for the current to drop to whatever that ending Amps is. Timed is fine but ending Amps, if you can use that, should be even better. Battery condition and aging etc can change that amount of time. Even then, if the time is not done correctly, it may not actually be the proper amount of time. Say, if the loads come on and off and the sun and weather doesn't allow the battery to get that full absorb time that it needs to get its full charge, then it's not 100% charged. By this, I mean that the charge controller's algorithm has to work correctly. Usually, people just don't absorb long enough and their batteries wear out sooner.

It sounds like you are one of those that actually can get it fully charged often. Solar Guppys' all day scenario sounds a bit off, but for a lot of folks, it may not matter cuz a lot of them will do more harm to the batteries from undercharging than overcharging anyway. So, stopping the Absorb cycle on ending Amps is just the better way to go, but costs more money to do cuz the system is a bit more complicated. I'd just stick with the timed method for now if it's working good.

And Crewzer, I did not know that OB changed the wording to the MF80's status screen.

boB

Solar Guppy

Re: FM80 goes straight from absorb to snooze

If one is offgrid and living off the system, one wants to be refilling the battery's at all opportunity's.

Leaving the unit in Absorb ( no float or snooze ) with only the current exit is best because if you load the unit during the day your using energy but maybe not enough to restart the charge cycle ( re bulk value ).

So for example, you use 10% of the capacity but the battery is above a typical re bulk of 12.5V, your battery won't go back into bulk/absorb cycle and your not harvesting energy to replace that energy ... very wasteful

Battery's won't be harmed, if they are AGM's it makes NO difference, if you have flooded, you will use a bit more water. The only "cost" is using the energy you would not harvest, wasteful if you charging from a non-RE source but good to use the PV instead of letting it be wasted ( not put into the battery's )

boB

Re: FM80 goes straight from absorb to snooze

Solar Guppy wrote: »

If one is offgrid and living off the system, one wants to be refilling the battery's at all opportunity's.

Leaving the unit in Absorb ( no float or snooze ) with only the current exit is best because if you load the unit during the day your using energy but maybe not enough to restart the charge cycle ( re bulk value ).

So for example, you use 10% of the capacity but the battery is above a typical re bulk of 12.5V, your battery won't go back into bulk/absorb cycle and your not harvesting energy to replace that energy ... very wasteful

Battery's won't be harmed, if they are AGM's it makes NO difference, if you have flooded, you will use a bit more water. The only "cost" is using the energy you would not harvest, wasteful if you charging from a non-RE source but good to use the PV instead of letting it be wasted ( not put into the battery's )

True, except that for off grid, AGMs aren't used very much. Flooded lead acid is usually the battery of choice for that market.

boB

mike95490

Re: FM80 goes straight from absorb to snooze

boB wrote: »

True, except that for off grid, AGMs aren't used very much. Flooded lead acid is usually the battery of choice for that market.
boB

Now you are complicating my plans ! I had just about decided to jump to AGM instead
of golf cart batteries, because I do not want to be cleaning terminals and watering them.
I figured the 15% extra recharge efficiency and nil maintainiance (relying on the charge
controller to not BBQ them) would be worth the price penalty.

Cariboocoot

Re: FM80 goes straight from absorb to snooze

There's no reason why you can't or shouldn't use AGM's off-grid.
It's just that most of us horrible "off-gridders" are also cheapskates and the flooded cells offer more Amp/hrs per $ spent.

Solar Guppy

Re: FM80 goes straight from absorb to snooze

boB wrote: »

True, except that for off grid, AGMs aren't used very much. Flooded lead acid is usually the battery of choice for that market.

boB

My reading suggests AGM's are not used as much due to cost, not performance. Flooded need to be watched regardless of the charging cycles chosen.

boB

Re: FM80 goes straight from absorb to snooze

Solar Guppy wrote: »

My reading suggests AGM's are not used as much due to cost, not performance. Flooded need to be watched regardless of the charging cycles chosen.

I did't say "performance". Of course some brands, either technology, are built better than others, quality wise. I suppose that could be called a performance thing.

And, either technology can "screw up", such as, one battery becoming unbalanced with the others in a string. Be very careful of that, flooded or VRLA.

No..... go for it ! Those serious, hard core off gridders seem to watch their batteries fairly closely either way. Time = money... Which one do you have more of ?

boB

nigtomdaw

Re: FM80 goes straight from absorb to snooze

Well, I,m 3 yrs in full time off grid still on my training batteries (probably 10/12yrs old) see signature, and the maintainance issue on FLA is really a non starter. Once a month a electrolyte check and top up and a clean down takes me less than 30 minutes on 36 2v cells, not a biggy issue really. My better half spends more time doing the laundry each and every day.

The cost of a quality AGM its life span (cycles) compared to a quality FLA cost and life span means that I will stick with Flooded Lead Acid when my training batteries finally die. The only factor going for AGMs for full time off gridders is the better charge efficiency 90% vs FLA 80% but that can be offset by adding more PV panels on the money saved by buying FLA.

I can see why Dealers would prefer AGMs because of there low self discharge rate and this would also appeal to part time off griders and when leaving PVs on display would be a security issue.

Kamala

Re: FM80 goes straight from absorb to snooze

boB wrote: »

Time = money... Which one do you have more of ?
boB

Precious little of either!

I use AGMs off grid because they are under my bed in my camper. Next to the propane water heater. I believe, actually bet my life upon the claim, that under proper charging constraints the AGM will not outgas.

Craig

nigtomdaw

Re: FM80 goes straight from absorb to snooze

Craig you make a good point for AGMs and that is another plus point for them over FLA !

Thats why they are popular and in certain situations the only safe option. I think boB was referring to people who live off grid full time. Plus FLA can made safe if you have the space to build a proper battery box with gas extraction

RCinFLA

Re: FM80 goes straight from absorb to snooze

AGM will vent if held at absorb voltage for long periods. This will shorten their life.

I can watch the ends of the plastic case bulge slightly on mine when in bulk. After a several hours on bulk, a very low audio level whistle can be heard.

niel

Re: FM80 goes straight from absorb to snooze

that would sound like they may be venting. they do this in the bulk stage?

boB

Re: FM80 goes straight from absorb to snooze

niel wrote: »

that would sound like they may be venting. they do this in the bulk stage?

They only vent (normally) if they get over voltaged for too long.

They plump when you cook 'em... Kind of like the hot dogs do.

boB

westbranch

Re: FM80 goes straight from absorb to snooze

Hi guys, Just back from the cabin looking at the ''plumping on my AGM batteries".. as I had lowered the FLOAT Voltage last visit, now I am thinking that I should lower the ABSORB level as well.

I recently was in discussion with one of the tech types at www.batteryresearch.com

and he sent me this, in our back and forth emails about potentially using "CatVents",

>POSTIVE PLATE GROWTH:
>The positive plate growth is indicated when the cover starts to swell or
>bulge. Cover will show signs around the post that starts to turn white
>from plastic being stretched. Most manufacturer's claim that 5% growth
>is the expected maximum limit during the life of the battery. It's
>indication that the plates have reached the maximum growth and should be
>monitored to ensure the plates are not continuing to grow at
accelerated
>rate. Positive plates can grow to the point where they have generated so
>much pressure that the jars have cracked.

I did not ask for his definition of PPG as assumed it was due to sulphation...

Eric

ps added... The absorb time is 2 hours, factory setting on the MX

benthere

Re: FM80 goes straight from absorb to snooze

An update:

I found in a document from Surrette called Rolls_Solar_Instructions.pdf a calculation for setting the absorb time based on battery bank capacity. The formula is: t = 0.42 * C/I

Where:
t= Absorbtion Charge Time
C = 20 hour capacity of the battery bank
I = Charging Current
.042 = (20%/50%)+5%.

In my case 6.2 = 0.42 * 450/30.75

6.2 hours is much closer to Solar Guppy's recommendation than to the "rule of thumb" I had picked up at http://surrette.com/content/renewable-energy-bulletins-solar-wind?q=node/47&phpMyAdmin=2eda4dec0bd69647b9e3cf0f71e01d23&phpMyAdmin=9dec4a269d70t7a63be7c

The calculation assumes that a battery bank transitions from bulk to absorb at 80% SOC, and I don't think we get that low in one night, but lately we bulk for a while before absorbing.

I've adjusted my absorb time to 6.2 hours but I don't think we've seen it yet. This time of year we are lucky to get 5 or so, which I don't really worry about as I believe we only cycle down to about 90% SOC each night.

Dave Angelini

Re: FM80 goes straight from absorb to snooze

Why don't you measure the specific gravity? Sounds like you would be using alot of water with long absorb times like you stated? Forgive me but it is Monday and this thread has lost me.....................

jeffkruse

Re: FM80 goes straight from absorb to snooze

Absorb times of 6+ hours!??? (I set mine to 8 hours) With times like these how on earth can these batteries be used for off grid solar :roll:

I originally used the default (2 hours) setting on my XW. No wonder my first set of batteries wouldn’t get the SG up to full.

Funny thing is that the battery manufacturer wouldn’t point this out, instead they sent me a new set of batteries at no charge. It they just would have told me to change the settings I might not have had a problem. :grr: I can’t complain much because I got a free set of batteries and the 3 month old ones are now sitting with an SG of 1.27.

I still don’t like putting 8KWH in to get 4KWH out

benthere

Re: FM80 goes straight from absorb to snooze

I measured the SG when I got home last night and had 1.267 after absorbing a couple hours yesterday and a few the day before. This morning it was 1.263.

I'll keep checking it for a few days and report back.

Dave Angelini

Re: FM80 goes straight from absorb to snooze

There is a bug in the XWCC charge algorithm that you can compensate for or update your firmware. I can give you an unreleased copy if I get a snail mail address and an e-mail to send the file. X wants the snail! It has one other nice thing in the fix. You do need the dongle!

To compensate without the firmware you need at least 1/2 hour or more absorb time than your battery manufacturer recommends. What is happening is the absorb timer is starting at the float set-point on the way up to the absorb set point in bulk.

AntronX

Re: FM80 goes straight from absorb to snooze

Question to guys with AGMs that puff up during absorb. At what C rate do you charge them and your bulk voltage? I charge mine at C/30 rate to 14.4V and keep it there until Amps fall below C/100 rate, which almost never happens unless I am away for 3 days. I only notice tiny whistling and bubling inside the battery if during absorbtion if I set voltage to 14.6 - 14.8V and if I hold my ear within 2 feet of the battery. Even then I don't see noticeable bulging of battery case.

niel

Re: FM80 goes straight from absorb to snooze

boB wrote: »

They only vent (normally) if they get over voltaged for too long.

They plump when you cook 'em... Kind of like the hot dogs do.

boB

sorry for any misunderstanding boB as i know about agms being a sunxtender owner, but i was asking of what his were doing.