Battery charger questions...

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offgridder
offgridder Registered Users Posts: 25 ✭✭
Hello all! Great site, just joined after browsing for a couple months! We are currently off grid in NM, since Sept last year. We have learned a lot by trial & error, along with a non-typical winter here in the mountains - so not quite newbies but still much to learn.

I am looking for a 30amp battery charger to run off of our generator when needed. Most chargers I find are automotive & they are only at 30amps for quick starts... Where can I find something that can be plugged into our generator that will produce 30 amps for extended time periods to give our bank a good strong charge without breaking the bank$$? Thanks for any input on this! Jonathan

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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
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    Re: Battery charger questions...

    it really depends on what you consider to be breaking the bank, but quality multistage chargers with any appreciable amperage will cost you. i should note that the chargers in the link do need the plug-in 4 stage controller and do not offer temperature compensation.
    http://store.solar-electric.com/bach1.html
  • offgridder
    offgridder Registered Users Posts: 25 ✭✭
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    Re: Battery charger questions...

    Hey thanks for the link! I tried to find battery chargers thru a search on W&S & kept getting an error with no results. The: Iota DLS-30M 12 Volt 30 Amp Regulated Battery Charger looks to in our ballpark as far as price & I am guessing that I can hook up a grounded plug to plug into our generator? Would I need anything else with this unit or can it stand alone?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,479 admin
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    Re: Battery charger questions...

    By the way, if you are running the charger only off of a generator (no grid power)--you can save the cost of the IQ float module for the IOTA charger. You will never be running the generator and floating the battery bank for days on end (in my humble opinion).

    By the way, what is the Amp*Hour and bank voltage of your battery bank. And what is the rating (brand/model/fuel type) of genset.'

    In general, if you can run the battery charger at ~50% (or a bit more) of the generator rated capacity (for fuel efficiency) and charge the battery at 5-13% of the 20 Hour Rate of the Battery bank--you are in the happy medium zone of the genset & battery bank.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RandomJoe
    RandomJoe Solar Expert Posts: 472 ✭✭✭
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    Re: Battery charger questions...

    The Iota chargers (or, at least, mine) come with a short pigtail with standard 3-prong plug on the end. So you can just run an extension cord to it or whatever. Nothing else is required.

    Do note they (again, *mine* does anyway) use a square-head screw for the wire terminals. That was a bit off-putting, I had to dig a while to find a tool for those...

    I have a 55A one, and it will happily (if noisily, once the cooling fan starts) crank out the full amperage for as long as the battery bank needs it!
  • Ralph Day
    Ralph Day Solar Expert Posts: 1,019 ✭✭✭✭
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    Re: Battery charger questions...

    Square headed screw...Robertson! Another great Canadian invention, like penicillin. They're great screws when you need to hold onto the ladder with one hand and the screw can be stuck on the end of the driver and won't fall off (usually).

    Ralph
  • offgridder
    offgridder Registered Users Posts: 25 ✭✭
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    Re: Battery charger questions...
    BB. wrote: »
    By the way, if you are running the charger only off of a generator (no grid power)--you can save the cost of the IQ float module for the IOTA charger. You will never be running the generator and floating the battery bank for days on end (in my humble opinion).

    By the way, what is the Amp*Hour and bank voltage of your battery bank. And what is the rating (brand/model/fuel type) of genset.'

    In general, if you can run the battery charger at ~50% (or a bit more) of the generator rated capacity (for fuel efficiency) and charge the battery at 5-13% of the 20 Hour Rate of the Battery bank--you are in the happy medium zone of the genset & battery bank.

    -Bill
    We have a 12volt setup, 800ah (8 100ah AGM Werker Batts). We are PV underpowered at only 270 watts, our next purchase upgrade after the tax return shows...
    Our Genset is a Briggs & Stratton, gasoline, 5500 watts optimal 8500 maximum. Can you adjust the IOTA charger to the power of the generator? Trying to understand what you mentioned: "In general, if you can run the battery charger at ~50% (or a bit more) of the generator rated capacity (for fuel efficiency) and charge the battery at 5-13% of the 20 Hour Rate of the Battery bank--you are in the happy medium zone of the genset & battery bank."

    Jonathan
  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
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    Re: Battery charger questions...

    Re the generator, it has (should have) a self regulating carb and will draw as much gas as needed to meet the demand. If the load is ~ 50% of the gen rating you should be in the 'sweet spot' for economy ad efficiency.

    hth
    Eric
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • offgridder
    offgridder Registered Users Posts: 25 ✭✭
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    Re: Battery charger questions...
    Ralph Day wrote: »
    Square headed screw...Robertson! Another great Canadian invention, like penicillin. They're great screws when you need to hold onto the ladder with one hand and the screw can be stuck on the end of the driver and won't fall off (usually).

    Ralph

    Hey Ralph... are these just random facts from Canada? :)
  • Ralph Day
    Ralph Day Solar Expert Posts: 1,019 ✭✭✭✭
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    Re: Battery charger questions...

    Not entirely random...more to make us look good.

    Don't forget insulin!

    The DeHavilland Beaver, Otter, Twin Otter.

    The Olympics 1976, 1988, 2010. We were after the big tv audience ratings by letting your mens hockey team make it to the final game ;)

    Ralph

    Ps Vulcan battery chargers. (to keep thread related) I have one for my system

    http://www.vulcanenergy.ca/
  • BB.
    BB. Super Moderators, Administrators Posts: 33,479 admin
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    Re: Battery charger questions...

    Most of the battery chargers are set for rated power/current... I would suggest that you purchase the charger and genset as a "matching set"...

    There are some "solar RE" chargers that can be programmed for input current/output current/charge profile--but many of those seem to be in the inverter/charger category.

    I have seen programmable fork lift charge controllers--but I cannot recall seeing a "off the shelf" AC to DC charger around here that is programmable to that degree. It would be nice to find one.

    For example, your 800 AH 12 volt battery bank. Recommended rule of thumb charging range is ~5%-13%. Assume charger is 80% efficient. For various reasons, aiming at 50% generator capacity is another good rule of thumb.
    • 800AH * 0.05 = 40 amps minimum recommended charge
    • 800AH * 0.13 = 104 amps maximum charge rate rule of thumb
    • 40 amps * 14.4 volts charging * 1/0.80 charge eff * 1/0.50 gen loading = 1,440 watts minimum generator (with minimum charge)
    • 104 amps * 14.4 volts charging * 1/0.80 charge eff * 1/0.50 gen loading = 3,744 watts maximum generator (with maximum charge)
    At this point, purchasing one or two more Iota Chargers (mix and match current ratings?) to run in parallel to charge your battery bank would be one way to get the loading higher on your genset (obviously, not cheap).

    Another is to purchase a smaller genset (believe it or not, I do not get one cent from this recommendation, no matter how many times I say it--a Honda eu2000i 1,600 watt generator--if you can use pull start and it fits your needs otherwise)...

    To compare running the two gensets charging your battery bank from 50% to 85% capacity. Assume ~5.5 kWhrs per 1 gallon of fuel for gensets. The Briggs will pull 50% fuel flow from 0-50% load (roughly) and the Honda will pull 25% fuel flow for 0-25% load--when set to ECO throttle). Assume battery bank and chargers are both 80% efficient. Also assume that charge controller outputs nearly rated current to 80-85% state of charge--past that point, you should either use solar array to finish the charge, or assume that you will run the generator for another 2-4 hours to get near 100% battery state of charge (pick 3 hours for exercise below):
    • 800 AH * 12 volts * (0.85-0.50) = 3,360 WH = 3.36 kWHrs
    • 40 amps charger * 14.4 volts * 1/0.80 eff = 720 watts from genset
    Note that 720 watts is > 25% rated power (1,600 watt * 25% = 400 watts) of Honda eu2000i. But this is way under 50% of 5,500 watt Briggs (2,750 watts).

    For charging the first stage (bulk):
    • 3.36 kWHrs battery / 5.5 kWhrs per gallon = 0.6 gallons for Honda
    • 3,360 Watt*Hours / (14.4 volts * 40 amps) = 5.8 hours run time
    For the Briggs--assume 50% fuel flow if load is below 50% rated power.
    • 5.5 kW * 1/5.5 kWH per gallon * 0.50 fuel flow * 5.8 Hours run time = 2.75 gallons
    If you want to charge the final 15% of the battery capacity, then 3 more hours of run time--assume below 25% load on Honda, below 50% load on Briggs:
    • 0.4 kWatts * 3 hours * 1/5.5 kWhrs per gallon = 0.22 gallons for Honda
    • 2.75 kWatts * 3 hours * 1/5.5 kWhrs per gallon = 1.5 gallons for Briggs
    The above is a series of SWAGs (scientific wild a$$ guesses)--but gives you a good idea of what the difference can be if you better match the battery charger and generator capacity...

    So, for charging the same 800AH 12 volt bank with a 40 amp charger from 50% to 100% capacity is less than 1 gallon for a 1,600 watt genset and possibly over 7 gallons for a 5,500 watt genset...

    My suggestion is to measure battery state of charge and how much fuel (and time) you are taking to recharge your battery bank with the current setup. You can even use a Kill-a-Watt meter to measure the output loads (watts and kWhrs) on your genset and compare against fuel flow. It will pretty quickly give you a good handle on the kWhr per gallon efficiency of your setup.

    I would be interested to hear the results of your measurements...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset