Starting Small - Battery Chargers

TronTron Registered Users Posts: 20
I'm looking at building a relatively small, portable solar powered UPS.
In the short-run, I'm looking at building a custom UPS that I could later add solar panels to.
Hypothetically let's say I have an automotive/marine 12v battery charger/starter already. I want to use it to charge/maintain a 12v 80ah AGM battery. Would it work to temporarily put a Charge Controller such as a Trace C-35 to regulate the battery charger? Seems I read somewhere that using an automotive type charger 24/7 is not a good idea for these kind of batteries.
I know it seems overkill to use a Trace C-35. But I'm looking at this as something to build onto as I obtain the rest of the pieces I need to complete the system.

Comments

  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Starting Small - Battery Chargers

    if i read this correctly that would depend on the charger as some can drive a pwm controller successfully and some not.
  • TronTron Registered Users Posts: 20
    Re: Starting Small - Battery Chargers

    Ok, the charger is a Schumacher model #SE-50-MA-2.
    10/2 Amp, Fully Automatic / Manual Battery Charger.
    There are 2 slide switches on the front.
    One slide switch has 3 settings: Manual/Conventional Low-Maintenance/Maintenance Free Deep Cycle.
    The other slide switch has 2 Charge Rate Settings: 2 Amp / 10 Amp.

    So, I guess my basic question is, would I be able to use this to charge/maintain a 12v 80ah AGM style battery? If not, could it be regulated using an MPPT type charge controller? Bear in mind, I would be using the charge controller later when I add solar panels to the project.
  • mike95490mike95490 Solar Expert Posts: 8,463 ✭✭✭✭✭
    Re: Starting Small - Battery Chargers

    NO

    AGM needs a special setting, and that charger appears to be for automotive use only, it does not state AGM setting. "Maintenance Free", I suspect means automotive use, "deep cycle" means nothing in this context
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || 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 ,

  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Starting Small - Battery Chargers

    i think mike is confused a bit as to what you are proposing. anyhow, my 6/2 schumacher does not work into my sb50 which is mppt. it did function through a morningstar sunsaver pwm cc. maybe if somebody out there has morningstar's new mppt cc and a similar auto battery charger that they may try driving the cc with it and see if it works.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Starting Small - Battery Chargers

    The problem with many automotive-type battery chargers is they don't produce fully rectified DC. It's usually one side of the transformer straight to (-) and the other side(s) through rectifiers & control circuit to (+).

    I say side(s) because the internal wiring of these things is often screwy compared to what logical thought may dictate. :p Often the voltage/amperage changes are accomplished by switching the input AC to different primary taps, rather than altering the secondary side. This is so they can achieve the same result while switching less current. Secondary side is often center-tapped, with that going to (-) and the two 'ends' going to the rectifiers/regulators.

    Please note; this is not the way all of them are, just some. Those that are won't supply an MPPT controller properly.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Starting Small - Battery Chargers

    i suppose i could retry mine with some filtering. i'll get back to you guys on that as it is currently night and if i forget to try it then give me a reminder.
  • TronTron Registered Users Posts: 20
    Re: Starting Small - Battery Chargers

    The owners manual for the Schumacher 12v, 10/2 Amp battery charger doesn't provide any data as far as Peak Voltage or Float Voltage at the different settings, so I'll need to do some measurements to get that data. I don't have access to an oscilloscope, so I can't tell you what the "DC" output waveform looks like.

    I was reading a FAQ about battery chargers. One point I found interesting is that on some chargers, the charger leads won't supply voltage until they "see" a minimum voltage at the battery (4vdc minimum was the example). I assume this is a safety feature on newer chargers.
    I took some measurements on the Schumacher I have, and found the only time I measured voltage was in "manual" mode.
    So it appears my choices are, use "automatic" mode if the peak and float voltages are acceptable for an AGM type battery, or if I must use an MPPT Controller, I'd have to set the charger to "manual" mode? (Or, buy a special charger made for AGM batteries...)
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Starting Small - Battery Chargers

    do not use the automotive charger alone on an agm battery. agms are too sensitive to overcharging when the bulk voltage is exceeded and it could vent. if it does this you can't replace what is lost. all you basically need for a cc is a dc voltage about 2-3v above the max the battery should go. ripple if bad enough can confuse or even damage some components in the cc. think power supply and what is missing that a cc would need for it to function from a utility source. basically it would need transformed ac, rectified ac to dc, and the last part of filtering to feed the regulator circuits in the cc. some small auto chargers have smaller voltages which may not function well with a cc.
  • TronTron Registered Users Posts: 20
    Re: Starting Small - Battery Chargers

    Yeah, I guess the only thing worse than ruining your $150 AGM battery would be also ruining your $200 Charge Controller...
    So I guess the best bet would be to spend a little extra and get a decent AGM battery charger.
    Any recommendations for a 12v AGM battery charger in the 10 Amp range?
  • BB.BB. Super Moderators, Administrators Posts: 29,697 admin
    Re: Starting Small - Battery Chargers

    Certainly the Iota charger line (via our host NAWS) is not a bad place to look first. The only thing missing is a remote battery temperature sensor (if the charger and the battery are in the same "room"--it should work OK).

    My question is that you said you are trying to create a UPS? Are you expecting the charger to operate the loads of the "UPS"--Or to only charge after power has been restored...

    AGM's can take pretty high charge/discharge rates (check the specs. for your particular batteries). An oversized charger (to power the "UPS function" even when the power is up--is not the end of the world.

    This will affect the size of the charger you should pick.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • TronTron Registered Users Posts: 20
    Re: Starting Small - Battery Chargers

    Initially, I'm looking at a basic UPS consisting of a battery, charger, and inverter. Ideally, I'd like to run the inverter off the battery, kicking in the charger only after the battery discharges to around 75-80%. After the battery is fully charged, the charger would shut off. Kind of a reverse UPS, using grid as backup.
    Later, when I add solar panels, I would ideally run the inverter from the solar/battery combo, with the charger kicking in sometime late in the night if ever...
    Any suggestions how I could achieve this goal? I don't have any specific numbers to give for load, but let's assume a small 12v system operating 500w a/c load peak during the day, and possibly up to 200w overnight.
  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Starting Small - Battery Chargers

    I mentioned this on another thread, but according to this:

    http://www.samlexamerica.com/products/productdescription.asp?ProductsID=80021


    "By means of a DIP switch setting, conversion to a two-stage algorithm is possible to charge batteries connected to a DC load (DC UPS)."


    Which looks like it means that it functions as both a DC power supply *and* a charger at the same time (UPS). From what I understand, that is also the default operating mode (two-stage) of the Iota if you don't use the IQ/4 module.

    As for kicking in the charger when the battery gets down a bit...why? If you have grid power why not use it and only drain the battery when absolutely required?

    Then, you'd probably want a converter/charger large enough to power your loads and have some left over to top off the battery.

    At least...that's *my* plan. YMMV. :D
  • BB.BB. Super Moderators, Administrators Posts: 29,697 admin
    Re: Starting Small - Battery Chargers

    Your system would be better if the charger supplies the inverter load--and keeps the battery above ~12.7+/25.4+ vdc (remember inverters typically draw a 120 Hz current wave--so you could be "micro discharging/charging" the battery if the the current peaks are below 12.7 volts.

    Cycling the battery (lead acid) just wears it out. And, when you discharge/charge--there is an efficiency issue too (charging is ~80-90% efficient).

    If you can keep the battery "on float" the entire time (except power outages)--you probably would be better off...

    Remembering just running an 80% efficient charger and an 85% efficient inverter is only 68% efficient overall. Only put the appliances that actually need pure UPS power on the inverter.

    Othewise, use the standard transfer-switch/fail-over type inverter for devices that you want to back up (such as a refrigerator, printer, etc.). There you are near 100% efficient while the power is up.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • TronTron Registered Users Posts: 20
    Re: Starting Small - Battery Chargers

    You're missing the whole point of this project. The ultimate goal is to minimize grid usage.
    Initially, without the solar panel input, we must use grid power for the battery charger. But after the addition of solar charging, the solar/battery system would be the main power, only relying on grid in the event of insufficient charge on the batteries (such as several rainy days).
    A typical UPS uses the grid as the main energy source, then relying on the battery for backup. I want to reverse that role.
    I guess what I'm talking about here is a barebones system that can be gradually added onto demonstrating what it takes to become grid free.
    If the system is good enough, there should be very little reliance on the grid at all.
    Theoretically, the only time the battery would cycle would be overnight when there is no solar energy coming in, then either the morning would come, or the charger would kick in...
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Starting Small - Battery Chargers

    If the ultimate goal is to reduce grid usage then putting in an inverter set up that is charged by the grid is counter-productive. The efficiency losses in charging the batteries means your grid usage will actually go up.

    Start saving your money for panels and put any energy investment $ you've got to spend now into conservation.
  • TronTron Registered Users Posts: 20
    Re: Starting Small - Battery Chargers

    There are of course the side benefits of the clean Pure Sine Wave of the Inverter, as well as the Battery Backup in the event of grid power failure (brownouts, and surges too).
    To me, in the short run, would be worth the price until the solar panels could be added.
  • BB.BB. Super Moderators, Administrators Posts: 29,697 admin
    Re: Starting Small - Battery Chargers

    Tron,

    Actually, what I suggested (large enough charge controller to run the "UPS" without cycling the batteries) is the most efficient use of energy and money.

    A year or so ago, I did a post here where I guestimated the costs of making a "UPS like system" that used $0.09 per kWhr power at night to charge a battery bank and ran the home during the day when power is $0.30 per kWhr.

    Turned out, just using simple $/kWhr spread over twenty years--that the system itself cost $0.45 per kWhr offset (very rough numbers).

    So, that $0.09 per kWhr offset to summer peak time became $0.54 per kWhr -- or more expensive than my peak power costs. Much of the cost (1/2 or a bit more, was just the cost of battery replacement as the system cycled).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • TronTron Registered Users Posts: 20
    Re: Starting Small - Battery Chargers

    Somehow I think grid power is going to be costing us more than $0.54 per kWhr in less than 10 years. One could argue that future batteries will be cheaper and more efficient as well. I like the progress with Supercapacitors.

    I didn't post here to argue about the costs and efficiencies of this system, I simply came here to get some questions answered about feasability.

    Is cycling the battery bank once per day from 80% really that bad of a thing? Even the typical automobile battery sits overnight without being "on float".

    I have read on another post that a Battery Monitor can turn on a backup charging system at a pre-set battery charge level (80%?). I wonder if it would shut the charger off again once the batteries are at full charge?
  • BB.BB. Super Moderators, Administrators Posts: 29,697 admin
    Re: Starting Small - Battery Chargers

    Well, in the last 14 years, my grid power price had actually dropped a tiny bit (Northern California).

    1996: 0.11589 per kWhr
    2009: 0.11531 per kWhr

    But--that is only true because we have a "tiered" rate plan. If you keep your usage low (around 300 kWhrs per month--which we do through conservation--using less power than 10 years ago), the base tier has been pretty flat--Hence, why we keep talking about conservation here being a good investment for most people. The high tiers (such as if you have A/C) have certainly gone up quite a bit.

    If you want to make a mathematical model of discharge level verses cycle life... Look for graphs like this from your battery vendor (This is a Concord LifeLine AGM battery:

    cyclelife2.gif

    20% discharge will give you about 2,800 cycles (excluding aging effects). 10% discharge will give you about 5,000 cycles. And 50% discharge will give you about 1,000 cycles.

    So, if you have XXX Watt*Hours to discharge... If you take a bank down to 50%--it will last about 1,000 cycles--and if you get 2.5x more battery capacity and discharge it to 20% (same XXX Watt*Hour discharge, but more batteries) will last about 2.8x longer.

    So--here is the problem... You spend 2.5x on your battery bank (make it larger), you get ~2.8x the life. Either bank design will cost you almost the same to operate (in terms of battery replacement). One you spread the costs over a decade (small bank) or put a bunch of money upfront once in a decade.

    The Xantrex family of battery monitors include a programmable output. You can set it to "turn on" at 80% state of charge and "turn off" at 99% state of charge. Other mfg/models may also have similar functions (I have not looked).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • tallgirltallgirl Solar Expert Posts: 413 ✭✭
    Re: Starting Small - Battery Chargers
    BB. wrote: »
    The Xantrex family of battery monitors include a programmable output. You can set it to "turn on" at 80% state of charge and "turn off" at 99% state of charge. Other mfg/models may also have similar functions (I have not looked).

    -Bill

    The FN-DC from Outback has programmable AUX control based on state of charge.
  • TronTron Registered Users Posts: 20
    Re: Starting Small - Battery Chargers

    Thanks everyone. I really appreciate all your input on this project.

    Looks like the 12v Automotive Charger idea is out. Didn't expect the Battery Monitor would wind up being a key part of the functionality of this system.

    I'll stick with installing quality components throughout the system, and will likely change things around over the years as new technology provides. I'm especially excited about emerging advancements of Super Capacitors and High-Efficiency Thin Films.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Starting Small - Battery Chargers

    tron,
    i have the answer you were looking for. electrolytic capacitors are needed and should be at least 25v and with anybody using higher amperages they should use even higher voltage values as well as higher uf. measure the oc voltage on the charger to see what the next higher commercial value should be. i used a large cap with 31,000uf for this, but i'm sure you could probably get away with around 10,000uf and maybe less with more being better filtering of course. anyway, the 2a setting will output too low of a voltage and did not work (about 15v) so the higher current setting will be used. mine has 6a on high so yours will be more than enough on high i would think and it did work with the caps in place. remember my cc is an sb50 and it is mppt. pulling the cap out of line caused it to fail to work.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Starting Small - Battery Chargers

    Niel;

    You get yet another gold star. :D

    Did you try running the charger's output through a full bridge rectifier first? I actually stripped out the electronics from a couple of old "auto chargers' and fed the transformers' outputs into 35A bridge rectifiers so I'd have an emergency back-up 24VDC charger for my system. Haven't had to use it yet, though, and wasn't planning on feeding it through the MPPT. Because I'm chicken, that's why. :p
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Starting Small - Battery Chargers

    i'm not too sure what way they rectified the ac inside of the charger as it may already be full wave for all i know.:confused: going full wave would improve things if the charger is half wave to begin with, but the capacitors will still be needed even though the uf value may be able to be lowered going from half to full. most people can handle a capacitor being paralleled on the charger output/ cc input, but only some would be willing to delve into the guts of the charger.

    btw, thanks for the gold star. can i spend it anywhere?:roll::p
  • GreenerPowerGreenerPower Solar Expert Posts: 264 ✭✭✭✭✭✭
    Re: Starting Small - Battery Chargers

    A few years ago, I actually disected my old auto charger. Not sure other old-style auto chargers are the same but mine has transformer -> full bridge rectifier -> triac (control 2A/10A charging by slide switch) -> battery cable . Needless to say the output is full-bridge chopped by the triac.
    GP
  • TronTron Registered Users Posts: 20
    Re: Starting Small - Battery Chargers

    Now you guys got me curious to snoop around inside my old 10/2 amp charger.

    I like the idea of using a capacitor filter on the output of the charger. Seems like it could easily be soldered inside somewhere.

    The main reason I couldn't use my charger to drive an MPPT charge controller, was because in "automatic" mode it seems to have a safety feature preventing it to charge unless there was a minimum "battery" charge at the output. Not sure if there's a way to disable this feature until I look inside I guess. The "manual" mode didn't seem to have this feature.

    Another thought came to mind. Could install a 10w diode to drop the voltage output slightly in order to charge AGM batteries directly?
  • BB.BB. Super Moderators, Administrators Posts: 29,697 admin
    Re: Starting Small - Battery Chargers

    The problem is that you need a high enough voltage to quickly charge the battery bank. And then drop the voltage so you don't overcharge and boil the batteries (or cause them to vent in the case of AGM).

    So, at least, you need a two stage charger.

    Then you run into the issue of temperature compensation...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Starting Small - Battery Chargers

    take it out of automatic? the cc will throttle back if need be and can take into account the battery type and even temperature compensation. i should add that in my doing this years ago with a sunsaver 10 that the charger itself failed on me and sent 120vac down the line to the cc and blew it out. i do believe it was a 10/2 schumacher that i had that failed although it wasn't fancy with automatic or needing a minimum charge current to operate. imho, they are risky to use regardless if putting a cc in line or not.
  • TronTron Registered Users Posts: 20
    Re: Starting Small - Battery Chargers

    You're right, wouldn't need "automatic" mode driving a Charge Controller.

    Probably only need an inexpensive PWM Charge Controller with the 10/2 Schumacher since the output from the charger would be consistant (unless if fails like yours, lol). Seen 10A Charge Controllers for like $30. Using the Charge Controller would be a safer bet than using the Schumacher "automatic" mode directly to the battery. Especially since I would use AGM batteries.
    I think adding a fuse between the Charger and Controller would be a good idea.

    Could do all that, or just buy an Iota 15amp charger for $122 and peace of mind, lol.
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