Batteries insufficient?
I’m having what I think are battery issues with my first solar system setup that I did last Fall. It’s a small 12V system to power a TV (AC) and a portable Dish satellite receiver at our off-grid ranch in Northern Arizona. I tried to keep my costs down since this is only for entertainment and we’re not there full time so the batteries sit unattended in a hot building while we’re away. The system consists of a Morningstar TriStar controller (TS-MPPT-30), one Canadian Solar 305 watt panel and two Costco Interstate GC2 6V golf cart batteries. The TV and satellite gear only draw about 70W (based on Kill-A-Watt meter reading) so I started with a Samlex 150W inverter (PST-150-12) so I could get more hours from my batteries – wanted to draw the minimum I needed. All went well through this winter – could watch TV for hours. But now that it’s hotter, the inverter needed to run its fan more and the Samlex started setting off its alarm. Continuous alarm – presumably overload since it would stop if I shut off the TV screen while the satellite still ran. So I bought a Cotek 200W inverter (SE200-112) to just up the power a bit. Just started using it this week and quickly hit issues. With the Cotek, it starts throwing a low voltage alarm within about an hour of use. So I pulled out my little Ideal voltmeter to see what’s going on. Here’s the scenario:
Battery voltage prior to starting inverter (we're running the TV at night after a full day of charging): 13.1V
Battery voltage as inverter starts running: 11.6V
Inverter alerts start when battery voltage shows 11.1V; frequency of alerts increases as voltage drops
Battery voltage after about an hour of TV but once inverter has been shut off: 12.8V
So now I’m wondering if my decision to go on the cheap with the Costco batteries is my problem. I really don’t want to invest in expensive batteries that will be brutalized by our hot building when we’re away. I could switch to an RV DC TV, like a Jensen, since the TV portion of the system takes about 55W – but they’re expensive for the bigger screens – so I’d want to be sure this is the best path before doing that. We're here less than half time so I'd really like to stick with lower costs. Any insights into what’s likely going on here would be much appreciated. Thanks!
Comments
Perhaps the batteries suffered extended periods with low voltage (below 12.0 volts) somewhere in the past few months. Sulfation also kills batteries.
Take the batteries back while you can. Keep the next pair as cool as possible. Preferably under 75F - somehow.
Everybody kills their first set of batteries. Much of the reason for the expense of solar batteries.
The Costco batteries were never the issue.
So have you been checking the electrolyte?
Has it always been topped off?
Never had plates exposed?
What size wire goes to your inverter? and how far is the inverter from the batteries? with a 70 watt load plus another 15-20 watts running the inverter You are drawing over 7 amps from the batteries, If you have a long distance to the inverter, you will have some voltage drop over small wires. If you are using 14 gauge house wire over 50 feet the voltage drop for a 7 amp load goes from 12 volts to 10.23 volts.
Once the load is removed the voltage would go back up, even measured at the inverter as the load would be reduced. This could also reflect the voltage drop and return. The results would be as you checked them, the alarm sounds when the TV was on, but when turned off (load removed) the alarm quit. With a 2-3 amp load (Sat and inverter) the drop is only 1/2 - 3/4 of a volt.
Also how is the inverter connected to the battery? jumper cable like pinchers are a pretty poor connections, all connections should be bolted down and checked. A loose connection can play havoc with tracking down problems. Be sure to check the connections as heating and cooling will loosen aluminum and copper connection.
You never say for how long you consume 70W from the system . 70w is only half load for a 150w inverter, heat should not be a issue.
70w for 6 hours is 420wh, plus overhead, so say 600wh consumed. Any lights you you will add to that , A larger inverter will have larger overhead losses.
300w panel is actually only 240w when in the field, x 5 hours is 1,200watt hours. Could be enough if you get solid 240w all day but the sun moves out of alignment, so call it half. now you are at 600wh. Just barely making it..
Any daytime loads, rob your batteries of recharge. Recharge takes 1.2x what you took out because of losses, so you really need 720wh to fully recharge.
( with 5,000w of panels, I can harvest about 12kwh in long days of summer - not as great as it would appear, batteries only take what can can absorb in a 6 hour charge cycle.)
|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
|| VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A
solar: http://tinyurl.com/LMR-Solar
gen: http://tinyurl.com/LMR-Lister ,
Re Photowhit’s questions:
*So have you been checking the electrolyte? Yes, once a month
*Has it always been topped off? Yes, most of my checks have also included topping off
*Never had plates exposed? No
*What size wire goes to your inverter? and how far is the inverter from the batteries? Also how is the inverter connected to the battery.
I used the alligator clip style wires from the Samlex with the Cotek since I disconnect the inverter when we leave (since nothing is using power while we’re gone) - that style has been easier to deal with. These have 16 gauge wire and with 200W at 12V, a chart I found on The Inverter Store indicated that that wire size should be sufficient. They are about 3 feet long. But from what you’ve indicated, sounds like I need to switch over to regular ring-type connectors and I’ll also increase the gauge just to help.
Re Mike95490’s points:
*how long you consume 70W from the system; Typically a few hours each night for the one or two weeks that we are there
An additional thought since the Costco batteries aren’t being flagged as insufficient – I’ve never run an equalization cycle on them because I haven’t setup the custom voltages for the charge stages that the Costco/Interstate batteries would require. The standard voltage setting that I selected on the Tristar controller via dipswitch was:
Absorp Float Equal
14.7V 13.5V 15.4V
Interstate told me the Costco batteries need:
Absorp Float Equal
14.8V 13.2V 15.6V
So maybe I need to do the custom settings that the Tristar supposedly supports and then do an equalization? The settings might require a laptop connection with the management software – can I just equalize using the standard setting that I’ve selected, even though the voltage is lower than Interstate says I should use. Would that be more beneficial to equalize with the existing settings versus waiting until I get the custom voltages all set up?
Thanks again for your help!!
|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
|| VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A
solar: http://tinyurl.com/LMR-Solar
gen: http://tinyurl.com/LMR-Lister ,
General guidelines would be an array able to provide 10-13% of the battery capacity for daily use or 20-28 amps charging say 14 volts. So with a 75% derating 225 watts/14 = @16amps + a sunnier environment.
I take it you also have utility AC? or are you surviving without air conditioning?
Re the question on AC - I wish! This is really just a recreational camp for us - had it for 25 years but never took it to the full level of a "city" house - just a bunkhouse to stay and recreate in the wilderness basically. An electrician friend put in our first solar that runs RV lights only in 2015 - uses the same kind of Costco batteries and has lasted this long with no equalization because it's just on a low-end controller that won't do one. But it doesn't have an inverter so the usage is no doubt so small that the batteries continue to do fine. The system for the TV was my first attempt at doing my own solar system, after much reading. Having never run an inverter this is my first time seeing the difference that makes with a system.
Sounds like I should get the custom settings going to correct the chronic undercharging. I'll get to work on that after the equalization.
Thanks again for all the input!
https://www.solar-electric.com/midnite-solar-battery-hydrometer.html
https://www.youtube.com/watch?v=BkUBffSv2O0
1, Do you shut down the inverter when not needed?
2, With the light gauge wire from inverter to battery, is there any corrosion visible on the wire?
2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 700 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.
Dig a pit in the shade, line the pit so it will hold water, put the batteries in the lined pit, add water to close to the top of the batteries, loosely cover. The cover needs to be above the batteries enough to allow evaporation. The batteries never get above 85 F using this water bath. You’ll need to add water occasionally.
Batteries are lasting much longer.
Best of luck...
14 CS 370 watt modules. HZLA horizontal tracker. Schneider: XW6048, Mini PDP, MPPT 80-600, SCP. 1 Discover AES 48 volt LiFePO4 battery 130 ah
Most automotive batteries in the tropics have a life expectancy of ~3 years where high.ambient temperatures only add to the under hood gains generated from the engine itself. Lead acid's enemy is temperature, the deep cycle ones I've used begin to decline at 2 years rapidly declining thereafter, it's one thing having high temperatures for a few weeks or months, but having temperatures average >30°C all year is very different.
Second system 1890W 3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.
5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
https://www.electronics-cooling.com/2017/08/10c-increase-temperature-really-reduce-life-electronics-half/
For me, in one of my Calculus classes, we derived the +10C -> 1/2 life as one of the examples of Calculus in "real life" usage.
There are other failure modes too... HALT (Highly Accelirated Life Testing) is used in engineering to qualify designs:
https://en.wikipedia.org/wiki/Highly_accelerated_life_test
From my own past life--I did disk drive testing/qualification for our company (back in the day when 5 1/4" disk drives (and various new tech tape drives) were a new thing and heald 10-100 MBytes or so)... I set up a chamber to cycle between 5C and 40 C, twice a day with an ~1 hour ramp of temperature change... Everything was within the printed operating specifications of the drive. At the same time, ran drive tests (seek/read/write) test to both stress the drives and show they still worked.
More or less, after 2 weeks of testing, a majority of the drives would fail (could be anything, drives would write cold, could not read hot, surface mount components with pop of the boards, flex cables to read/write heads would fail, etc.). If a drive passed 2 weeks of testing, I rarely had any fail after even another 2 weeks of tests.
In engineering labs, they would do HALT (and similar testing) to distruction to figure out what would fail and need redesign for improved product life.
Remember--For batteries--There are different values for what a failure is... Concorde AGM batteries (as I recall) used 20% loss of capacity as value for warranty failure.
In your car, the batteries are assumed to be only cycled for 15% discharge (shallow discharge)--So you could have 50% loss of capacity and the battery still is "fit" your your needs in Florida...Take that battery to a deep cold climate in Canada/Northern USA in winter), and you will probably find the battery could not reliably crank start a cold soaked motor (chemical reactions being dramatically reduced in -40C/F weather--Also temperature cycling causing cracks/failure of materials--And as batteries sulfate, the specific gravity falls (electrolyte becomes more "water like" leading to possible battery freezing in cold snap where a fully charged newer battery with high SG would not)
And we had folks in Canada that could get 12+ years from their battery banks that cold soak unused in winter (stored fully charged, perhaps with a small "floating solar array") where we would expect 5-7 year life in the lower 48 states.
-Bill