Reducing amps from Iota charger

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Steve961
Steve961 Solar Expert Posts: 93 ✭✭✭✭
I am in the process of putting together a minimal solar system, mainly for lights, in a small hunting cabin. The final pieces are on their way from NAWS, but I do have a question about using an existing charger on my new battery. I am starting off small with just a single 104 AH Concorde AGM battery, but may add another one if I really need to.

I already had an older 30 amp Iota charger, and I am a bit concerned that it might be too many amps for just a 104 AH AGM battery. I would like to stick with this one, not just to save money, but also since I might have a 208 AH battery bank someday. I do have the Iota IQ4 Smart Controller, but am not sure if that is a factor here.

My questions are:

1. The NAWS website states that a battery charger can be 15%-30% of the battery capacity. Is this correct for my AGM battery?

2. If the amps from the charger are too high, can I just add a load to my inverter to reduce the amps going into the battery. Would a 100 watt light bulb, for example, running on my Morningstar SureSine reduce the number of amps to around 20 or so?

Thanks.

Steve

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  • BB.
    BB. Super Moderators, Administrators Posts: 33,471 admin
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    Re: Reducing amps from Iota charger

    You certainly can add a load... However, it may not be needed. Some AGM's can take pretty high charge rates (from the Battery FAQ):
    Most flooded batteries should be charged at no more than the "C/8" rate for any sustained period. "C/8" is the battery capacity at the 20-hour rate divided by 8. For a 220 AH battery, this would equal 26 Amps. Gelled cells should be charged at no more than the C/20 rate, or 5% of their amp-hour capacity. The Concorde AGM batteries are a special case - the can be charged at up the the Cx4 rate, or 400% of the capacity for the bulk charge cycle. However, since very few battery cables can take that much current, we don't recommend you try this at home. To avoid cable overheating, you should stick to C/4 or less.

    Check the specs. for your battery...

    Also, you might be able to crank the charger voltage down a bit to the low 14.x's... Perhaps that will also help reduce the current flow too.

    Also, I would guess that the charging current will be somewhat based on the state of charge... Measuring the charging current may show that you are OK...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
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    Re: Reducing amps from Iota charger

    that battery can take every amp that charger has to give and in fact are rated for at least an amp for an amp hour. what you need to watch is that the voltages are not exceeded as set by concorde for no agm likes their voltage rating exceeded. doing so can cause outgassing that can't be replaced like fla types can.
  • Steve961
    Steve961 Solar Expert Posts: 93 ✭✭✭✭
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    Re: Reducing amps from Iota charger

    This is good news, I had no idea you could charge these batteries at such a high rate. Considering the cost of AGMs, it's good to find another benefit in using them.

    The specs for the Iota IQ4 smart controller are:
    Bulk = 14.8 volts
    Absorption = 14.2
    Float = 13.6

    The Concorde battery manual lists an absorption range of 14.2-14.4, and a float range of 13.2-13.4. It does not list a bulk voltage, but does list a value of 15.5 volts for "conditioning". The manual only mentions out-gassing when performing a "deep discharge recovery" where voltage can range from 15.6 to 18 volts.

    I hope all of this means I am good to go.

    Thanks for your help.

    Steve
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
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    Re: Reducing amps from Iota charger

    NO. The float is the critical one, 13.6 will overcharge and gass your 13.4 battery. Put it on a timer, let it charge for 1 hour or 2, and then shut down ? Big charger, small battery, not much time needed. Your mileage may vary.

    Will you power the Iota from a generator ? Bulk the battery for an hour in the AM, and let solar top it off
    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 ,

  • Steve961
    Steve961 Solar Expert Posts: 93 ✭✭✭✭
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    Re: Reducing amps from Iota charger

    I just checked with Advance Power Products (they provide the tech support for Concorde), and they did state that 13.6 volts is too high a float for the battery and would reduce its lifespan. But, he then asked how long it would be on float. When I told him that it would be infrequently charged from a generator for only a few hours when needed, he told me not to worry. With a small amount of charging (including float) time, I shouldn't notice any reduction in performance/lifespan - I would only have to worry if it was on the float charge continuously.

    Steve
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
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    Re: Reducing amps from Iota charger

    steve,
    he told you that because you won't normally keep the generator running just to float the batteries, but be on the safe side and reduce that to about 13.2v or 13.3v. set the bulk as you would the absorb as they do say not to exceed 14.4v period, hmm, i think i'm mistaken on that 14.4v as i'm thinking of my sunxtender, but you can see it in the manual and i'm assuming yours is a lifeline battery.
    unless it is upped due to temperature compensation or receiving an eq charge. i would be cautious on giving an agm an eq charge very often or very high in voltage as there's no rule the eq charge has to be at that high of a voltage. remember, an eq charge is an overcharge and agms are very sensitive to damage during an overcharge. reducing the interbattery connection resistances and keeping resistances from such equal to one another does help in averting the need of an eq or at least as often. sometimes rearranging the batteries can also help where you place low batteries where the high ones are and this requires a somewhat good dmm or dvm to see the small differences.
    also of note they list the max current at 5x the ah rating and this is the quote in the manual,
    "(500A for a 100Ah battery)"
    so do not worry of the current aspect of charging your battery.

    i'm probably driving you crazy as i'm adding to this while you read.
  • Steve961
    Steve961 Solar Expert Posts: 93 ✭✭✭✭
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    Re: Reducing amps from Iota charger

    Niel:

    I do appreciate your help, and this is definitely getting more complicated than I had expected. The battery I purchased is a SunExtender PVX-1040T, and the technical manual only lists a 14.4 volt limit for the absorption charging phase. See page 19 in the linked document.

    http://www.sunxtender.com/pdfs/Sun_Xtender_Battery_Technical_Manual.pdf

    In regards to the too high float level, is there any way to drop it from 13.6 to 13.3? I looked at the Iota manual, and they do not show a way to do this. Is there something I can do externally to drop it, or will I need to look for a different charger.

    Thanks.

    Steve
  • BB.
    BB. Super Moderators, Administrators Posts: 33,471 admin
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    Re: Reducing amps from Iota charger

    If you are on a genset--you will run out of fuel and money before you damage the battery bank on float (float is really for days-weeks+ of zero power usage standby charging).

    The only possible way, that I could see, that you could damage the battery would be if you put it on solar panels and left it for a season with no loads and had a charge controller with no float setting (or you could not crank back to 13.x volts, or you had the panels directly connected to the battery bank and no charge controller).

    At least while you are there were there--you will be cycling the battery and float will not matter.

    If you are looking for use at home (take the battery home for a season)--What I do is use a lamp timer and set it for 1 hour (+/-) per day of charging (I am using a 1 amp battery trickle charger). No boiling dry, no dead battery because I forgot to charge it in the last year.

    You could use the Iota too with the lamp timer--but I would be just as happy with a little trickle/maintenance charger on the timer).

    For a typical AGM, you could probably go 6 months between charging if you wanted (very low standby losses). You could check with an accurate DVM and charge when it goes done a few tenths of a volt when stored.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Steve961
    Steve961 Solar Expert Posts: 93 ✭✭✭✭
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    Re: Reducing amps from Iota charger

    Bill:

    The battery(s) will probably be in place at the cabin for 7-8 months out of the year. During this time it will be maintained with a Morningstar SS-10L solar charge controller. I figure I will use the cabin maybe 30 days total during that time. It is during those 30 days that I will bring my generator (Honda eu2000i) with me to make up for any solar shortages I may have. When I close up the cabin for the winter, I will probably bring the battery home with me and maintain it using a small trickle charger.

    Steve
  • BB.
    BB. Super Moderators, Administrators Posts: 33,471 admin
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    Re: Reducing amps from Iota charger

    From my experience, if you use a small generic trickle charger--I would definantely put it on a 1:24 lamp timer... In our families, we have a couple cars that don't get driven much and even a 1 amp trickle charger and a 180 mAmp draw (gps, old On-Star, lojack, car standby stuff)--it would boil a battery dry in a couple months.

    -Bilklk
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
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    Re: Reducing amps from Iota charger

    Another alternative would be a converter/charger from an older RV - quite a few I've seen are 13.2v - though I've also seen really old ones (early 70's) that are 12.8v.

    Still, the Iota should be fine for occasional use, and from the sound of the OP, it will really mostly be used to bulk up the battery and not to float it, which would be a non-issue.