battery voltage dropping rapidly, troubleshooting help sought
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having just installed a small solar electric system at my off-grid house i am just getting my bearings. i'm experiencing an unusual-ish scenario and wanted to run it by y'all. in my system i have:
sanyo 205 watt pv
outback mx60 charge controller
outback fx 2012t inverter
sealed lead lifeline battery -- concorde ~235a/hr (not sure of exact specs on this)
outback temp compensated meter -- plugs into charge controller and attaches to battery
the usual fuses, disconnects, ground, etc.
i live in nw washington state approx 48.5 degrees n. latitude, days are pretty short right now. when we do get sun, i have about 3-4 hours of direct sun on my panel.
while you read this account, note that my battery disconnect is switched to the off position so there is no load on the battery at all.
i think the mx60 tells me the battery voltage in the upper right corner of the summary display. yesterday, for example, while charging in full sun the batt voltage read 12.6 volts. later in full shade the voltage read 12.3. last night we did not turn the inverter on at all.
today (a grey day) i pop outside to take a peek at the batt voltage reads 12.2
additionally, when the inverter is switched on and juice is flowing in the house i am using very minimal wattage. two (3watt) compact flourescent bulbs, some ipod speakers (~20watts). i learned from outback that the 2012t draws between 10 and 15watts.
in two or three hours my battery voltage will drop from say 12.8 to 12.2. the manufacturer recommends recharging the battery at 12.2.
any thoughts on this...? is there anything i should be thinking about to get more light out of my system?
thanks for your time and helping to initate a lill whippersnapper,
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Just a couple of thoughts that others may not agree with.
1) 3 hours direct sun on a good clear day, is not very much.
2) When only running a couple of low power CF lamps, I use a MSW low wattage inverter. The ones I use only consume a watt or two to operate, plus the load. CF's don't require a good sine wave to function well, unlike many other things. I use a 10 year old 150watt Statpower MSW and believe it or not, it's idle current is only about 20 ma. So, I leave it on all the time, just for the lights. All the newer low wattage MSW's I've tried, idle around 300 or more ma and the output voltage isn't controlled anywhere near as well as the old Statpower.
A lot better to use one of these when you have a limited power supply, than using 10 or 15 watts to power a pure sine inverter just to operate 6 watts of lights.
Keep in mind though, that many things will not operate properly and some will be ruined, if powered by MSW.
Now we'll see what others say.
it sounds like you aren't fully charging that battery for one thing. keep the inverter off as it is a definite load even when it idles. now that concorde is rated at 255ah and would require at least a 5% charge rate for about 11 to 13 hours if it was depleted to 50%. without looking up the pv i'm guessing it to be about 5.6amps at 24v. going through the mx60 and downconverting to 12v allows the doubling of the current so you are around 11.2amps and adding another 10% for the mppt action would give another 1.1amps for a total of 12.3amps. this is a tad under 5%, but it should be fine with no loads on and allowed the time to charge before putting any loads onto it. do note that concorde charge specs are between 14.2v and 14.4v for setting absorb and not 12.2v. the float should be about 13.2v. make sure all connections are good too and try recharging for a few days and see if it is at 12.8-12.9v after a several hour rest. if this doesn't seem like it's right to you get back to us again.
I would agree with Niel, it sounds like your battery is very low to start with and it is never getting charged. I would also recommend disconnecting the loads and shutting off the inverter and let the MX-60 do it's thing. Until you see the MX-60 in absorbing or float let it charge the battery.
If you have a small genset and charger I would recommend topping off the battery that way unless you can wait a couple of days topping off via solar, adding a second panel would help you out a LOT.
Yes, that's what I too was getting at, an undercharged battery, the result of not enough charge and too much load for the small charge you are getting. Save your battery, get it fully charged ASAP.
What you’re witnessing are some of the complexities of battery operation.
The correct charging voltage (the “absorb” setting) for your battery is ~14.3 V at 77 F (25 C). Your MX will indicate something like “MPPT” (the bulk stage) until the battery voltage reaches this point, and it will then switch to “absorbing” and hold the charging voltage steady. The value will be a bit higher when the battery is cold. The absorption cycle should last for ~3 hours or so, but that may be difficult to achieve in your location this time of year.
Once the battery is full and the charger is disconnected from the battery, the battery voltage will initially read ~14 V or so. This false high voltage value is the result of the high specific gravity electrolyte in direct contact with the battery plates, and it’s called “surface charge”. However, as the high SG electrolyte dissipates through the rest of the electrolyte – like tea steeping – the battery voltage will fall over a period of several hours to its target of ~12.8 V or so.
Similarly, the voltage of a battery will immediately drop when a load is connected, and then recover slightly. This negative surface charge is the “coup de fouet”, or crack of the whip. However, once the load is removed, the battery voltage will recover a bit from its indicated value, even with no charging source attached.
Based on the information you’ve provided, the wide voltage range (12.8 V under charge to 12.2 V under load) sounds normal. However, since you didn’t mention a target absorption voltage of ~14.3 V, I’d agree with comments from others that your battery is not being fully recharged. This “deficit recharging” is bad for your battery and it will lead to both poor capacity and a short useful life.
On a separate note, the FX 2012 inverter is overkill for your small loads. It’s idle load is closer to ~20 W, or 480 Wh/day if left on for 24 hours, which is probably ~90% of the net daily energy production from your system. Similarly, the MX is overkill for your 205 W PV module. I doubt that its efficiency is >85% in your configuration. However, if you plan to expand your system in the future with more PV modules (up to ~800 W for a 12 V battery system), a large battery bank and heavier loads, those two pieces of equipment should serve you well.
In the meantime, you might want to consider some 12 VDC compact fluorescent lamps (check on line or at an RV store), and perhaps a 12 V automobile power adapter for your iPod and its accessories. You could run all of these items directly from the battery and leave the inverter disconected and powered down.
Jim / crewzer
I agree with the above, too much load, and not enough PV to recharge.
as an interim fix, you may want to try lighting directly with LED's Either the white ones you can get at Radio Shack or the high power ones at http://www.lumileds.com/. You could string 2 or 3 together, with a series resistor, and run straight from 12V (set the current limit resistor for your full voltage - 14V otherwise you will shorten the LED lifetime) See charts at http://www.lumileds.com/pdfs/AB11.PDF for ways you could string 3 or 4 amber in series, make nite-lites for rooms and hallways, or group 3 white ones for a reading lamp. Less power consumed than CF bulbs and inverters.
But I think you really need more panels, or a mirror you can use in winter months to reflect more light onto your panel. With the cold temps, you may not cook the panel in winter.
|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
|| VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A
gen: http://tinyurl.com/LMR-Lister ,
My new SB2000 controller has a LC display so I can give you my battery voltages for comparison.
I have 300W of PV and a 222AH battery bank. I use a 400W MSW inverter to run my 13W CF's (seldom more than 0ne on at a time) and radio. The inverter is switched on the DC side and it's off unless I need light.
On a normally sunny day (Northern California) my batteries are charged by 0930 (14 VDC or a little more).
After the sun goes down the batts drop to 12.7 or 12.8 even with no load.
At night, while using lights and the radio, the voltage drops to 12.4 or sometimes as low as 12.3.
In the morning, before the sun comes up the batts are back up to 12.7V
I don't know how normal this is but that's what my batteries are doing.
first of all, thanks amigos. i appreciate your time in helping me understand this system.
from your messages i'm gathering:
*my battery is not being fully charged (bad over long term)
*wait for the absorb cycle to complete
*keep the inverter off when not in use, consider getting a smaller unit for lights only scenario
*consider adding another panel or tying in a generator during these dark months
*consider DC lighting
*i did set float/absorb values on the charge controller based on manufacturer recommendations. float 13.3, absorb 14.4. crewzer, your notes help to frame this new, confusing stuff for me.
*i put in this system so i can record a solar music project for kids this winter -- more info on harmonicapocket.com -- my decision to buy the burly true sine inverter was based in my need to run sensitive electronics (computers, hard drives, microphones, etc), but i did want to be able to scale this system up in the coming years as needed. maybe the future ain't so far away tho....
thanks again. may there be full sun on all your panels.
i thought mine were dipping too low , but with the constant load of 10-15w , plus laptop and cellphone charging, i guess its not so abnormal. you can see the effects of 3-4 days of rain (i forget) currently on my webcam if i get another day or 2 of rain ill probably get down to 12.1
i almost am looking forward to their death as i understand the agms require less power to keep charged.
I know my flooded L-16's seem to soak up tons of amps, huge amounts compaired to what is taken out of them.
I've had my four size 4D AGM batteries for about a year now. Their coulombic efficiency (Ah out / Ah in) is about 98% ~ 99%, as opposed to typically ~90% for flooded-cell batteries.
Jim / crewzer
That's well worth a very serious look.
I know the AGM's won't take abuse like the flooded cells, but is this a problem if there is proper charge control etc?? Do AGM's, in general, have a shorter life than Flooded?
During my "learning curve", my L-16's received a lot of abuse - and survived.
"Learning curve"! HA! I never stop learning. When I do, it'll be time to throw in the towel and move into "Sunset Mannor"!
well for twice the price.. yikes.. but i didnt know they were THAT good. i also suspect like wayne without the initiakl abuse (first winter went weeks w/.out top off) the t105s would be doing alot better. what is the rated lifespan on the agms? my dealer is new england solar electric (he literally wriote the book on batterys maint) and he says he has some clients with almost 10yr old t105's still. they dont treat em like i do (did rather) im sure.
:-o Twice the price?? WOW! Think I'll stick to L-16's if that's the case.
well, if they're almost 10% more efficient with less higher charging voltage, that makes for an overwall less amount of wattage/controller capacity so it still is worth looking at i guess. similarly sized banks:
surrete 546ah 6v's in 12v config for $1240.00
t105's 450AH in a 12v config for 420.00
464ah for $1088 Sun Xtender PVX-560T AGM sealed battery
hm... but need a temp compensated 14.8 to charge these things, mucho current. i think i read you only need 14.4 or something for the agms, right? and no EQ if im not mistaken as well. no maintenence... soo.... get charged faster with less light w/same sized system.. i still might do it , but looking at the numbers does hurt a bit :oops:
edit: oops forgot actually use agm for pricing, duh..
My Deka size 4D AGM 12 V batteries were $220 each, and they’re still available from my “local” source at that price. That’s 198 Ah x 12 V / $220 = 10.8 Wh/$ for comparison purposes.
Their efficiency makes a real difference in overall system economics. For example, if I stayed with flooded cell batteries, I’d have to increase my PV array’s size by at least 11% to match the improvement from the AGM batteries’ higher efficiency. Adding 80 W to my array would have cost ~$450 just for the PV module.
And the value of essentially “maintenance free” batteries? Priceless…
Here’s a link to MK batteries specs for the battery, including cycles. MK is a subsidiary of East Penn (Deka).
AGM batteries are sensitive to overcharging. However, I think that risk is adequately mitigated by using a quality charger with a remote BTS.
Our extended battery discussion “sticky” topic over on OutBack’s forum may be of additional interest: http://www.outbackpower.com/forum/viewtopic.php?t=848
Jim / crewzer
I couldn't agree more with Jim. I was the skeptical king on AGM's before I bought them, now I will never go back to flooded. I have 8 AGM 8A8D's, just about 2000 amps at 12v. My old T125 1000amp bank used about 80 amps a day to hit float, my new bank, about 9 months old, uses about 25 amps to hit float and it’s twice the size. Amazing! I am also in that 98-99% range.
For price I got them for $2200 from a local industrial battery supply place. So I paid about $9 a watt, but I bought more then Jim at one time. In pricing them out it was about 1.5 times what I could have got L-16 for, but still less then big Surette's. I know the Surettes are better quality and would likely last longer but...
I never had a problem with watering, cleaning and checking my old batteries. I didn't think it was a big deal. But let me tell you when you don't have to do anything it is really nice. The first month or two I kept looking them over, completely clean and dry, there was just nothing to do
And for my bank size in summer I have almost an extra kw to use for what ever. It was like adding some panels. I honestly thought I was going to have to add panels just to keep them topped off, and the opposite is true.
i'm curious why you cited the concorde pvx 560s in your example when you could've used 2 higher capacity batteries like the 2580l yielding 510ah for the naws pricing of $1016? even 2 of the 2120ls would be 424ah at a naws pricing of $816. the pricing crewzer lists for his batteries is a very good deal in my opinion, but in any case you've got a lot of life yet in your current batteries so it's too early to think of replacing them yet. the agms would be a good option for you at that time in the future when they are too old and getting ready to give out. by then battery improvements may even be realized. don't jump the gun just yet for an efficiency improvement of around 10%.
I love this form, it keeps opening my eyes and teaching me new things. Thanks guys for telling your experience with batteries etc.
You make it sound like AGM really is the way to go, so when my L-16's give up, I expect to take a real hard look at AGM's. And, if I understand right, there would be no need to have them vented outside? Unless they got badly overcharged anyway.
the only real complaint i have about them is that the warantee needs to be longer. my concorde is for 1 year and i have no idea why so short on the time. these batteries could match many other warantees. i guess it's difficult for them to go that extra step as they would last long when the voltage specs for charging are followed. they haven't any way to determine if this is the case or not. l16s can take some voltage abuse that agms can't.
Yes, I agree with the warranty issue, but most likely, it's because of a total lack of control the manufacturer has over what customers put the batteries through. Where I work, we sell among other things, automotive batteries and the abuse we see is shocking to say the least. Some people will even wait for the last month of warranty, then replace the acid in ONE cell, with tap water, just to get a "free" newer battery!
Thanks again for the info on your experience.
to answer your ? i just picked one, i am sure (and have been proven) there are betters deals and ecomnomy of scale.
ok guys im sold but the querstion: whats the life expectancy in a cycling situation like solar assuming not too discharged ever etc,.. the usual care.. also, when you say sensitive overcharging .. too high voltage of too often charged ? that is one issue i find tricky w/solar: in summer im floating every morning bright in early it seems so theyre going through the charge cycle probably way more than needed, and then in winter im spread out sometimes a week.
The MK spec sheet above says 3200 cycles at 10% discharge, and 1200 cycles at 25%. At ~15% average discharge cycle per day. those specs suggest the bank should last ~5.5 years. Concorde's chart for their Lifeline batteries suggests 4000 cycles (~11 years) at an average 15% discharge. GNB (Exide) claims their Absolyte IIP AGM batteries are good for 1200 cycles of 80% discharge. :-o 8-)
The voltage issue has to do with overcharging. Too much charging voltage can cause the vents to open and release hydrogen gas. Since there's no way to replace the lost electrolyte, the result is a permanent capacity reduction.
All lead acid batteries need to be ventilated to one degree or another. However, AGM batteries typically do not vent hydrogen gas, so there's a lot of flexibility in how and where they're stored. FWIW, mine are in a box (closed but not sealed) in my garage, but I'm not using any kind of forced ventilation. The AGM battery bank in my office's network operations center does not have any special ventilation system.
AGM batteries and long term float situations seem to get along just fine. GNB expects their Absolyte IIP AGM batteries to last for 20 years in float service.
Here's a link to a useful technical manual for VRLA (AGM and gel) batteries: http://www.eastpenn-deka.com/assets/base/0139.pdf
Jim / crewzer
We use AGM's (Concorde) and they're every bit as good as everyone says. I would never use flooded PBA's.
Back to Keeth's issue: Keeth, are you sure that when you disconnect the inverter via the battery disconnect that the MX60 output is still connected to the batteries? I know this is a simple, basic question but if the MX output is wired to the "wrong" side of the disconnect switch, one can inadvertently disconnect PV output to the batteries.