help understanding battery chargers

bgarrettbgarrett Solar Expert Posts: 48
I am using a deep cycle battery on my travel trailer.
I bought a new automotive battery charger and I have a 7700 watt portable generator.

So I'm good, right?
Well, no. The generator has to run for hours before the battery seems to be charged.
Thats nuts, and uses a lot of gas.

First is there a tool, (meter?) so I can tell when its fully charged?
Second is there a quicker way to charge the battery?

I use the battery for a light to read with when it gets dark and some nights I cant sleep so its many hours of discharge.
Also is there any good LED to read with?
I have bought many but they are turn to junk soon.

Comments

  • BB.BB. Super Moderators, Administrators Posts: 29,724 admin
    Re: help understanding battery chargers

    What size (Amp*Hour / Voltage) and type (flooded cell, AGM, brand/model) of battery do you have?

    Have you accurately measured the voltage at the battery terminal? Do you know the current flow into the battery bank over time and how much current (amp*Hours) you use?

    And what gauge wire/size of battery charger do you have now.

    Normally, you can force C/8 (battery 20 Hour rating / 8) continuous charge into a Flooded Cell type battery bank--and even more with some AGMs.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • bgarrettbgarrett Solar Expert Posts: 48
    Re: help understanding battery chargers
    BB. wrote: »
    What size (Amp*Hour / Voltage)Dont Know/12V and type (flooded cell, AGM, brand/model) of battery do you have? wet cell

    Have you accurately measured the voltage at the battery terminal? NO, How do I do that?
    '
    Do you know the current flow into the battery bank over time and how much current (amp*Hours) you use? NO I think this is my question but I'm not sure

    And what gauge wire/size of battery charger do you have now.No idea, Whatever came on the travel trailer from the factory/10/8/2 amp charger

    Normally, you can force C/8 (battery 20 Hour rating / 8 ) continuous charge into a Flooded Cell type battery bank I DONT HAVE ANY IDEA WHAT ANY PART OF THIS SENTENCE MEANS


    I see I totally failed the test.
  • BB.BB. Super Moderators, Administrators Posts: 29,724 admin
    Re: help understanding battery chargers

    Do you know the "group number" or "BCA" or some other battery sizing standard?

    I will give some generic advise--but without knowing the details, it is going to be difficult to give better answers.
    What size (Amp*Hour / Voltage)Dont Know/12V and type (flooded cell, AGM, brand/model) of battery do you have? wet cell
    Lets assume this is a 100 Amp*Hour 12 volt battery (basically the size of a large automotive or Pickup battery).

    The "high side" charging rate should be C/8:
    • 100 AH * 1/8 charge rate = 12.5 amps
    It will take ~4-6 hours to fully charge the battery that is 50% full

    However, you can probably get it to ~85% charged by pumping current in at a high charging voltage (~14.5 volts) at the battery in a reasonable amount of time (2-4 hours). Leave the last 10+% for recharging when you get back home or a trailer park where you can plug in.
    Have you accurately measured the voltage at the battery terminal? NO, How do I do that?
    Get a Digital Multi-Meter that can read to at least 12.34 volts (3 1/2 digit meter). A more accurate meter would be nice.

    Set the meter to 20 volt scale and measure the battery charging voltage...

    Automotive battery chargers can be all over the place (some have different charging modes too)--so measuring the battery charging voltage will tell you if your automotive charger is doing well or not.

    Note, when the battery is below 80-90% state of charge, the battery bank will be less than the charger output voltage. As the battery fills up, the voltage will rise to the charger's "set point" and will (should) hold steady until the battery is nearly 100% charged...

    So, you may see 13.2 to 13.6 to 13.8... 14.4 to 14.5 volts, then hold at 14.5 volts for the next 2-4 hours or so... At that point the battery should be fully charged.

    Here is a quick link on how to use a DMM (volts/amps/resistance)

    As always, be careful with DMM's... Make sure they are set for voltage when measuring the battery voltage... If set for current when measuring voltage, you may be purchasing a new fuse/meter and underwear.;)
    Do you know the current flow into the battery bank over time and how much current (amp*Hours) you use? NO I think this is my question but I'm not sure
    There are several ways of approaching this problem... The "best way" is to use a Battery Monitor. The Trimetric meter is would be a good starting point.

    You place a current shunt (precision resistor) in the battery negative lead and connect the Battery monitor to measure battery voltage and current (voltage drop across shunt).

    The meter gives both "instant readings" (i.e., 12.7 volts and -3.0 amp current flow) and cumulative current flow (i.e., The battery is now at 95 AH capacity out of 100 AH)... Think if a fuel tank meter that estimates the gallons in the fuel tank by monitoring the fuel flow in and out of the fuel line. Fairly accurate--but they do need to be reset to 100% full once in a while (basically, battery is fully charged for a couple hours).

    You will use the meter to monitor both how much power you pull from the battery bank (discharging to some where between 50% to 20% state of charge--never below 20%, and below 50% does reduce battery life over time).
    And what gauge wire/size of battery charger do you have now.No idea, Whatever came on the travel trailer from the factory/10/8/2 amp charger
    12 volt battery systems need a fair amount of current compared to 120 VAC systems... For example, a 12 watt filament reading light will draw:
    • P=I*V
    • I=Power/Volts= 12 watts / 120 VAC = 0.1 amps AC
    • I=Power/Volts= 12 watts / 12 VDC = 1.0 amps DC
    So, depending on your loads, wire gauge, and length--too much current creates a lot of voltage drop on the wiring... 1 volt drop is about as much as a typical 12 volt circuit can tolerate. Where as 1 volt drop on a 120 VAC circuit is virtually nothing (nominal maximum voltage drop on a 120 VAC circuit ~3.6 volts maximum).

    And, this affects the battery charger/battery converter in the RV too... If you have a 0.5 volt from the charger to the battery bank--that really "hot" 14.5 volts for quick charging the battery bank becomes a very gentle 14.0 volts (at max current)--As the current falls, the voltage at the battery bank does slowly rise--so eventually the battery does become full--but this can add many hours to the charging time (fine if you are in an RV park, a killer using a gasoline genset).

    Again, a great place to use your new DMM... With the battery discharged to less than 80% state of charge--Turn on the charger and measure the voltage at the battery and the charger--and see how much voltage drop you will have.

    You may end up wanting to replace that 5' of 14 AWG wire (or whatever they used) with 8 or 6 AWG to reduce voltage drop at the battery when charging.
    Normally, you can force C/8 (battery 20 Hour rating /
    8 ) continuous charge into a Flooded Cell type battery bank I DONT HAVE ANY IDEA WHAT ANY PART OF THIS SENTENCE MEANS
    We really need to know the approximate capacity of your battery bank and charge controller... If this is a small RV with a single 12 volt battery--you may have as small as a 100 AH or less battery in there (it could be 200 AH or more--I just don't know).

    Remembering our rules of thumb that we aim for between 5% and 13% rate of charge ( C/20 to ~C/8 )--This is usually the most cost effective charging current...

    Below 5%, it takes forever for batteries to charge, and the batteries may not last as long (various reasons).

    Above 13%, the batteries can overheat and if done with solar panels--that is a huge amount of expensive solar array and charge controllers... For an AC battery charger you can probably go to C/4 (25% of Capacity)--But some of that may be wasted--Normally check recommended battery specifications... For generator charging with an adjustable charger, you could probably charge at 15.0-15.5 volts--but you need to turn off/crank down the voltage (to float) to prevent battery damage (when charging current drops).

    Note that 14.2-14.5 volt charging is compatible with most all "12 VDC" appliances/electronics... At 15.0+ volts, it has been reported that some 12 volt devices may die (12 volt car adapters for computers, etc.).

    If you have access to the battery cells--you probably want to get a hydrometer to measure your battery's specific gravity to check for state of charge/cell balance.

    Read about batteries here:

    Battery FAQ

    www.batteryfaq.org

    Now--how to put all of that together... Say that you don't currently have solar (or not very much) and need to use the genset for much of your charging--Noise, cost, and amount of fuel storage is a big issue... So, here is how I would proceed. Note I am making lots of assumptions that are probably wrong--so you will need to use your real information:

    Assume 100 AH battery bank, and ~C/4 approximate max charging ( over C/8 ) to quickly charge your battery bank:
    • 100 AH * 1/4 = 25 Amps maximum
    • 100 AH * 1/8 = 12.5 Amps minimum
    So, we are looking at:
    The Xantrex TC2 is a very nice 14.4 volt charger. Has a remote battery temperature sensor (option: good for fast charging your battery and reduce chance of thermal run-away), is Power Factor Corrected (uses less genset current).

    The Iota is much less expensive and is just a solid 14.2 volt charger (with manual float switch or IQ4 automatic 2 stage charge control--not really needed for a generator based charger--more for Grid Powered).

    The 15/20 amp chargers will run on either a Honda eu1000i (900 watt) or eu2000i (1,600 watt).The 30 amp will probably need a eu2000i sized genset.

    If your current chargers output appropriate voltage and current--probably no need to change them out right now.

    Next, generator size... If you have a small battery / battery bank -- a 7,700 watt genset is absolutely going to bankrupt with fuel costs...

    For most gasoline gensets, at 50% or below rated power, they will consume on the order of 50% fuel flow...

    Assume that your genset uses ~1 gph at 100% load and ~0.5 gph at 1/2 load or less... That would mean that you are using ~0.5 gph for 4-6 hours or so to recharge your battery bank or 2-3 gallons of fuel (big SWAG).

    A 20 amp charger on a small Honda eu1000i:
    • 20 amps * 14.5 volts * 1/0.77 charging efficiency = 377 Watts
    The eu1000i uses a minimum of 0.6 gallons of fuse at 1/4 load (900 watt rated) or 225 watt load for 8.3 hours (econo throttle on--reduce engine speed at low loads) and 3.8 hours per 0.6 gallons at 900 watts:
    • 8.3 hours * 225 watts * 1/0.6 gallons = 3.1 kWH per gallon 225 watt or less load
    • 3.8 hours * 900 watts * 1/0.6 gallons =5.7 kWH per gallon 900 watt load
    So, somewhere better than 3.1 kWH per gallon. So 4-6 hours at ~377 watts:
    • 377 Watts * 6 hours * 1/3.1 kWH per gallons = 0.73 gallons
    With this setup--I would expect that you would use about 1/4 the amount of fuel using the small Honda eu2000i genset vs your 7.7 kW (unless you are running tools on a job site or something where you need to run the large genset anyway).

    Now the above may be way overkill for your application--or may be well worth your time and effort (sort of the difference between camping 6 weekends a year vs living on a job site).

    Problem is without knowing your power usage and battery bank size--I really can't do more. Perhaps a larger battery bank would be helpful (run the genset every 2nd to 3rd day). Or perhaps installing a 135 watt solar panel + charge controller could keep up with your power needs 9 months of the year (reading light, radio)...

    You will be the best judge of what works well for your needs/lifestyle.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarusicarus Solar Expert Posts: 5,355 ✭✭✭✭
    Re: help understanding battery chargers

    A side note to Bill's extensive answer(s)

    If you are using the 12vdc side of 7700 watt generator, you will probably never get a bigger battery fully charged. The 12 vdc side of the genny is really only designed to keep a small starting battery (like one that might be used to start said genny) charged.

    As Bill suggest, after getting a handle on the battery size, the loads etc, then you will have to consider a proper 3 or 4 stage charger like the Xantrex Truecharge series or the Iotas.

    Tony

    PS Instead of using such a huge genny on a small battery (comparatively small) you might consider a Honda Eu 1000 type genny. It will run a 20 amp charger at idle, use very little fuel, and is very, very quiet. They can be had used for ~$600.

    Good luck and keep in touch,

    T
  • bgarrettbgarrett Solar Expert Posts: 48
    Re: help understanding battery chargers

    Bill
    I thank you for the information and specially thank you for being patient.
    This is very stressful for me and I feel stupid that I dont understand what to do.
    In contrast to your rocket scientist knowledge I am like a barefoot country boy who has never been to town.
    It is a struggle to comprehend what you say and I google the words to find their definitions and try to understand you.

    I looked at my 12V batteries.
    One has 'deep cycle' 31-950 850CCA 207RC
    there are no other words or numbers on this battery
    it is longer than a battery in a 1/2 ton chevy pickup

    the other battery is a mack bulldog maintenance free with--- 180 min, repl pin bd31650A BCI group 31
    thats all the words and numbers on that battery
    it is longer than a pickup battery
    One is for lites at nite. one is for the shurflo pump for water out of the creek to bathe
    I plan to repeat this living arrangement the next time the weather warms up.




    You say 4-6 hours to charge, that sounds like what I have been doing and it seems unreasonable to run the generator that long
    my charger has a 10 amp charge rate that they say is for starting a car. In my ignorance I have not used that setting, Think I should?
    I spent 5 months last summer in the travel trailer in the woods. There was no "home' or trailer park to use to charge my battery so I spent $1000 for the 7700 watt gasoline generator hoping it would charge my batteries and operate my crackerbox welder


    You say DMM
    The first thing that google shows me is a Fluke FLU 115 and a FLU 87-5 at $133 and $300


    Trimeter $140
    This seems like a wise purchase that can be used when I advance to solar panels.
    NAWS says this must have a shunt. the 100 amp is $24
    I priced this one because my electrical demand is small
    Is the 500 amp a wiser purchase?

    *And, this affects the battery charger/battery converter in the RV too You may end up wanting to replace that 5' of 14 AWG wire (or whatever they used) with 8 or 6 AWG to reduce voltage drop at the battery when charging.*
    .I dont follow your thought here. I bought an automotive type battery charger and run it straight off a portable generator to charge my battery. The travel trailer wires are not relevant (unless I am missing something)

    *We really need to know the approximate capacity of your battery bank and charge controller... If this is a small RV with a single 12 volt battery--you may have as small as a 100 AH or less battery in there*
    You dont know because I dont know. What charge controller are you asking about? Yes. a single 12V battery for the small travel trailer
    My creek/pump/bath is 200 feet away, totally separate system but that battery has to be charged too.
    I have been through several batteries in the last 3 years. Yes I ruin them . Anyway, one had a 125 AH rating, but these now have no info like that

    *Normally check recommended battery specifications... For generator charging with an adjustable charger, you could probably charge at 15.0-15.5 volts--but you need to turn off/crank down the voltage (to float) to prevent battery damage (when charging current drops).*
    There you go again, speaking a foreign language that I am totally unable to understand . :)
    There aint no battery specifications, is my charger adjustable?? is that the 2, 6 and 10 amp setting? 15 Volts?? Maybe this is where I use the DMM?

    Next up, you say
    Xantrex Truecharge2 12=volt, 20 amp battery charger $264

    So far we are up to about $500 plus shipping
    Then you mention Honda eu1000i (900 watt) or eu2000i (1,600 watt) at $1000 or $2000
    I just bought a $1000 generator last summer, dont see why I need another

    I could buy one heck of a lot of batteries for $1500 to $2500 and just run'em as far as they could go.

    I know, I know. Thats just plain wrong. At this point I am having a difficult time making it thru the month on my income since I have two properties 300 miles apart and I am making many trips between the two moving my possessions and paying for both properties.
    If I can get to the point that I sell the old property the pressure will be off and I can put up a building and afford a solar system
    I appreciate your thoughts on this mess I am in.
    Bruce
  • bmetbmet Solar Expert Posts: 630 ✭✭
    Re: help understanding battery chargers

    I am a solar newbie, but I was an electronic technician for 10 years in the military.

    A DMM can be as cheap or expensive as you want. You can buy one from Harbor Freight Tools for $2.99, or one from Fluke for $2,999. Regardless of price, some functions will be the same, and do not need extreme precision. If all you are measuring is battery's voltage, then a $3 meter will show you that voltage. If you need to measure current (reliably) down to the milliamp, then you can spend less than a $100 for the DMM for that accuracy. A few retailers sell Digital Multi-meters, sometimes called DVMs for Digital Volt Meter. Radio Shack, Sears, Harbor Freight, most auto parts stores, just to name a few. Even Walmart sells them under the Eclipse brand, $50, that would do measure most of what you need.

    Fluke is just a brand, but it is used extensively with industrial technology, so they cost more.
  • BB.BB. Super Moderators, Administrators Posts: 29,724 admin
    Re: help understanding battery chargers

    Bruce,
    bgarrett wrote: »
    I looked at my 12V batteries.
    One has 'deep cycle' 31-950 850CCA 207RC. There are no other words or numbers on this battery. It is longer than a battery in a 1/2 ton chevy pickup

    The other battery is a mack bulldog maintenance free with--- 180 min, repl pin bd31650A BCI group 31. Thats all the words and numbers on that battery it is longer than a pickup battery.

    Those are probably Group 31 Batteries. The first one 850 Cold Cranking Amps and 207 Minute Reserve Capacity... Basically, these are automotive/truck starting batteries and most likely not deep cycle storage batteries.

    Roughly, the storage capacity of a "typical" Group 31 battery is 95-125 Amp hours... So lets go with 100 AH.

    The "problem" with using automotive batteries vs deep cycle (from Wind-Sun Battery FAQ):
    • Starting (sometimes called SLI, for starting, lighting, ignition) batteries are commonly used to start and run engines. Engine starters need a very large starting current for a very short time. Starting batteries have a large number of thin plates for maximum surface area. The plates are composed of a Lead "sponge", similar in appearance to a very fine foam sponge. This gives a very large surface area, but if deep cycled, this sponge will quickly be consumed and fall to the bottom of the cells. Automotive batteries will generally fail after 30-150 deep cycles if deep cycled, while they may last for thousands of cycles in normal starting use (2-5% discharge).
    • Deep cycle batteries are designed to be discharged down as much as 80% time after time, and have much thicker plates. The major difference between a true deep cycle battery and others is that the plates are SOLID Lead plates - not sponge. This gives less surface area, thus less "instant" power like starting batteries need. Although these an be cycled down to 20% charge, the best lifespan vs cost method is to keep the average cycle at about 50% discharge. Unfortunately, it is often impossible to tell what you are really buying in some of the discount stores or places that specialize in automotive batteries. The golf car battery is quite popular for small systems and RV's. The problem is that "golf car" refers to a size of battery (commonly called GC-2, or T-105), not the type or construction - so the quality and construction of a golf car battery can vary considerably - ranging from the cheap off brand with thin plates up the true deep cycle brands, such as Crown, Deka, Trojan, etc. In general, you get what you pay for.
    These batteries are not going to last very long if you cycle them by more than 10-20% (90% to 80% state of charge).

    For now, just use them until they do not meet your needs (next time, lookf for Deep Cycle, and don't get a Marine type battery either).
    One is for lites at nite. one is for the shurflo pump for water out of the creek to bathe
    I plan to repeat this living arrangement the next time the weather warms up.
    Just use these two batteries to experiment and setup your system with... You can wait until they fail, or by a new set for spring.

    Using separate batteries and charging them together is a bit tough... It would possibly be better if they where used in pairs (shared capacity meaning less battery management and/or deep cycling of one vs the other)--But for your current needs, it is not mandatory (normally, we try really hard to match sets of batteries so they "wear out" together).

    For power use, as an example--say you use the ShurFlow pump for 20 minutes a day at 5 amps (that sounds like a long/cold shower):
    • 5 amps * 20min/60min per hour = 1.66 Amp*Hours per day
    A typical 100 AH battery you could take your time and cycle it to 80% of capacity--20% of a 100 AH battery would be 20 AH of usage before recharging (very "soft" usage):
    • 20 AH / 1.66 AH per day = 12 days of use
    The reason I am suggesting not to go below ~80% of capacity is storage batteries tend to sulfate if keep for days/weeks/months below 75% state of charge--If you recharge before you hit 75% state of charge, the battery should have a very long life (assuming otherwise well taken care of and good quality).

    How much for the night lighting? Just a simple 12 watt filament bulb (dome light, brake light, etc.) draws ~1 amp from a 12 volt battery bank:
    • Power = Voltage * Current
    • Power / Voltage = Current = 12 watts / 12 volts = 1 amp
    If you can replace the filament bulb with a 1-4 watt LED lamp--you would save quite a bit of power (just a small example).
    You say 4-6 hours to charge, that sounds like what I have been doing and it seems unreasonable to run the generator that long
    my charger has a 10 amp charge rate that they say is for starting a car. In my ignorance I have not used that setting, Think I should?
    I spent 5 months last summer in the travel trailer in the woods. There was no "home' or trailer park to use to charge my battery so I spent $1000 for the 7700 watt gasoline generator hoping it would charge my batteries and operate my crackerbox welder
    Hmm... This is where planning comes into play. To "quickly" charge the batteries you have... 200 AH at 12 volts... That would be a 20 to 40 amp battery charger (you need a large charger to pump current quickly into the battery bank).

    Many small battery chargers for charging a car may have a 2 amp charging mode and a 10 amp jump start mode... The problem with using the 10 amp jump mode is many battery chargers will overheat if left running for hours.

    Also, you need to check the charging voltage from the charger... You are looking for something that outputs around 14.2-14.8 volts or so. I have no idea what your charger is set for (or even if it has a "set point").

    If you had Utility Power--if you had to leave the batteries plugged in for 24 hours to recharge the batteries, it would not be a big issue. In your case, because you want to limit the generator run-time--you really need as large as battery charger as can be supported by your battery bank (20-50 Amps).

    When charging your battery bank, if you draw out, for example 50 AH, then to recharge that amount of current will take (50 AH / 200 AH = 1/4 of 200 AH bank capacity):
    • 50 AH / 20 amp charger = 2.5 hours
    But, the batteries as the go over 80-90% state of charge, they start accepting less current (absorb phase of charging--basically the constant voltage set point of ~14.5 volts) it takes around 1-6 hours (call it 2+ hours, lots of factors affect this final time) to finish charging to 100%...

    So the total time to 100% charge for 50 AH recharge with a 20 amp charger:
    • 2.5 hours + ~2 hours = 4.5 hours
    You can monitor the current / voltage at the final stage of charging and cut it back to 1 hour when you are out camping using the genset--You have the battery mostly charged--so you are doing OK.

    It is not worth the cost of fuel and even battery wear and tear to recharge to 100% capacity every day.

    Break--continued on next post
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.BB. Super Moderators, Administrators Posts: 29,724 admin
    Re: help understanding battery chargers

    Second half of post:
    You say DMM
    The first thing that google shows me is a Fluke FLU 115 and a FLU 87-5 at $133 and $300
    As Bmet says--just a digital "multi-meter" (typically volts, current, and resistance)... You do not need to spend a lot of money for one. Very handy for use around home/work/camp.
    Trimeter $140
    This seems like a wise purchase that can be used when I advance to solar panels.
    NAWS says this must have a shunt. the 100 amp is $24
    I priced this one because my electrical demand is small
    Is the 500 amp a wiser purchase?
    The 100 amp shunt is good for smaller systems (more accurate current readings for smaller current)... That would support loads up to 100 amps or:
    • power = volts * current = 12 volts * 100 amps = 1,200 watts
    Certainly enough for your current sized system.

    For systems that use more power, you would need the larger shunt.
    *And, this affects the battery charger/battery converter in the RV too You may end up wanting to replace that 5' of 14 AWG wire (or whatever they used) with 8 or 6 AWG to reduce voltage drop at the battery when charging.*
    .I dont follow your thought here. I bought an automotive type battery charger and run it straight off a portable generator to charge my battery. The travel trailer wires are not relevant (unless I am missing something)
    "Good Quality" Battery chargers are actually pretty accurate when controlling their output voltage (should be to 1/10th or 1/100th of a volt 14.X or 14.XX volts).

    Many times, in expensive car chargers use small cordage (like 16 gauge lamp cord) for your 10 amp charger... For 5' of cord and 10 amps with 16 AWG cord, the voltage drop is around 0.5 volts--Depending on how your charger functions, that can cause a significant reduction in current flow (battery looks to be 0.5 volts higher than it really is). For an automotive charger, it may not matter--but for a good quality charger--that is a huge deal (especially if you are interested in quick charging).
    *We really need to know the approximate capacity of your battery bank and charge controller... If this is a small RV with a single 12 volt battery--you may have as small as a 100 AH or less battery in there*
    You dont know because I dont know.
    At this point, we can guess that you have two x 100 AH 12 volt batteries--so my previous calculations are close enough for government work.
    What charge controller are you asking about? Yes. a single 12V battery for the small travel trailer
    Many RV's include their own battery charger / converter to run the trailer on AC power when available--I don't know if your RV has one or not...

    And even if it has one, it may be too small to quick charge to 100 AH batteries anyway.
    My creek/pump/bath is 200 feet away, totally separate system but that battery has to be charged too.
    I have been through several batteries in the last 3 years. Yes I ruin them . Anyway, one had a 125 AH rating, but these now have no info like that
    Ideally, we would like to know how much power you are using--then we can plan on recharging the batteries every X days...

    However, if you have a hydrometer or an accurate volt meter, you can instead measure your state of charge every morning and decide if you need to recharge that day... For example if you have a meter, measure the resting voltage (no charging/discharging for a couple hours). From the Battery Faq above, the resting voltage is:
    • 100% SoC = 12.7 volts (~77F)
    • 80% SoC = 12.42 volts
    • 70% SoC = 12.32 volts
    • 50% SoC = 12.06 volts
    • 20% SoC = 11.58 volts
    Note the above is at standard temperature of 77F--If the batteries are very cold, the measured voltage will increase. Hot batteries, the measured voltage will decrease...

    So, you can monitor your battery resting voltage and decide when to run the charger--The idea is that you don't want the batteries to set below ~75% state of charge for days/weeks, you don't want to cycle the battery below 50% very often, and never below 20% State of Charge.
    *Normally check recommended battery specifications... For generator charging with an adjustable charger, you could probably charge at 15.0-15.5 volts--but you need to turn off/crank down the voltage (to float) to prevent battery damage (when charging current drops).*
    There you go again, speaking a foreign language that I am totally unable to understand . :)
    There aint no battery specifications, is my charger adjustable?? is that the 2, 6 and 10 amp setting? 15 Volts?? Maybe this is where I use the DMM?
    Since you are at home right now, you can run some experiments... And see how well the current charger works for you.

    You can try the 10 amp setting and see how quickly it brings the battery to ~14.5 volts. And then let it sit charging on the AC charger for a few hours and see what the voltage eventually stabilizes at.

    In the end, you have some fairly large batteries and a fairly small battery charger. And a huge AC genset.

    If, for the most part, you are using the genset for charging the battery bank... You really need a much smaller genset.

    A typical 20 amp 12 volt battery charger will run on a Honda eu1000i generator.

    3/4 gallons of fuel and 4-6 hours of run time every every time you need to recharge with the small Honda should do it for you with the right batteries (deep cycle) and good battery charger (assuming you are not using the batteries too heavily--say you recharge once per week).
    Next up, you say
    Xantrex Truecharge2 12=volt, 20 amp battery charger $264

    So far we are up to about $500 plus shipping
    Then you mention Honda eu1000i (900 watt) or eu2000i (1,600 watt) at $1000 or $2000
    I just bought a $1000 generator last summer, dont see why I need another

    I could buy one heck of a lot of batteries for $1500 to $2500 and just run'em as far as they could go.
    The Iota chargers are certainly less costly and would work fine too.

    For Honda Generators, you can try Mayberry's or Wise Sales (both have good reputations last I heard--been quite a few years since I purchased mine). I have no idea what the current pricing is (you need to call for prices).
    If you cannot justify the Honda--Find as small as possible 4 cycle AC generator (down to 900 watts for a 20 amp charger). It will use a lot less fuel than the 7.7 kW.

    I know, I know. Thats just plain wrong. At this point I am having a difficult time making it thru the month on my income since I have two properties 300 miles apart and I am making many trips between the two moving my possessions and paying for both properties.
    If I can get to the point that I sell the old property the pressure will be off and I can put up a building and afford a solar system
    I appreciate your thoughts on this mess I am in.
    If your power usage is so low and you have good sun where you are at--Somewhere around 190 Watts of solar panels will give you a minimum of 5% rate of charge for the battery bank... Perhaps that + an inexpensive charge controller would be a better deal for you than the genset...

    Also, looking at your power usage, perhaps a smaller set of deep cycle batteries (match battery needs to your loads--and reduce your loads through conservation, LED lighting, small pump, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • bgarrettbgarrett Solar Expert Posts: 48
    Re: help understanding battery chargers

    ................Thanks, Guys
  • ShadowcatcherShadowcatcher Solar Expert Posts: 228 ✭✭✭
    Re: help understanding battery chargers

    Yes good LED lights will work well and you can get them in a color temperature closely matching an incandescent bulb and they save a lot of watts. I have fixtures that take a G4 (usually a halogen bulb) and yes we use them for reading.
    What model is the Trailer, it may well already have a converter used when hooked up to shore power that will do a better job than your 10A automotive charger at recharging the battery.
    A 45A Progressive Dynamics converter charger will run about $150 and charge your battery correctly and a lot more quickly and with gas topping $3.00...
    You have my sympathy, the guys on this forum absolutely know their stuff but some times the explanations lack shall we say, simplicity.
  • bgarrettbgarrett Solar Expert Posts: 48
    Re: help understanding battery chargers

    Hey shadow, thanks for chiming in. I appreciate Bills answers but its difficult to comprehend what he says.
    A lot of advice on the internet starts out, First add up your usage.....
    IMPOSSIBLE for me.
    I am starting at close to zero.
    I will have heavier electrical demands as I begin to live there full time.
    My only use is a light bulb, but I want to make wise purchases that will be used as my system grows.
    A lot of advice on the internet is "Conserve!" Thats also kinda impossible. Its only one light bulb and I only turn it on when I need it.
    Its frustrating.
    I'd like to buy components as I can afford them and build a nice system but if I understand correctly, ya gotta buy one complete system at a time. (batteries age has to match, charger has to match battery bank which has to match the solar panels) My travel trailer is NOT an RV, it a 1983 model trailer , so it has way out of date electronics with no battery charger.
    I'm ok with the trailer for now. It is temporary til I get a building up and expensive solar systems expenditures must wait til the building is erected

    I tried to explain that in the opening post of this thread.
    The suggestion for a Trimeter sounds like an answer to one of my initial questions.
    Your charger may answer another of my questions.
    Now if I can find some decent LEDS
  • SevenSeven Solar Expert Posts: 292 ✭✭
    Re: help understanding battery chargers

    BG, I am right there with you man. I thought I had a general understanding until I came here. I was wrong! Lol. You just need to figure out the formulas they use. To many of them it is as simple as English, and they use it as such. To guys like you and me, it is like looking at a menu in a Chinese restaurant without the translations, and no pictures. I have some new production books coming to me so I can get my head wrapped around it better.

    I didn't know that batteries needed a huge initial charge, followed by one or two lower charges to work properly. The monitoring surprised me too. You can get a cheapy volt meter from auto zone to do what you need, mostly. You have a huge generator, but what does it do for you? Are you running a 12v output from it, or do you have a battery charger hooked to it? One that would plug into the wall? Deep cycle batteries and regular automotive batteries take a completely different charging style. If your batts are not deep cycle, you can just put them in your truck and drive around and they will charge. I run a group 31 in my diesel and I used to run one in my 4x4 to handle the winch and all the rock lights. They were not deep cycle. Deep cycles will burn up with a regular alternator.

    Hope this helps some. From one noob to another.
  • bgarrettbgarrett Solar Expert Posts: 48
    Re: help understanding battery chargers

    This is pretty bad, guys. The more I learn, the more confusion.
    Bill suggested a 20 amp charger, or 15 amp and 30

    * Xantrex Truecharge2 12-Volt, 20-Amp Battery Charger
    * Iota DLS-15: 12 Volt 15 Amp Battery Charger
    * Iota DLS-30-M 12 volt 30 amp regulated battery charger

    showcatcher suggests a 45 amp

    How can all of those different sizes be OK?

    and shadow, the 45A Progressive Dynamics converter charger
    is available as PD9245C and PD9145A

    One has a Total Charge Management System and the other has a Converter Status Remote Pendant
    The total Charge Management System has the Charge Wizard which can select one of three charging voltages and one of four operating modes depending on the condition and use of the battery.
    Does it do this automatically??
    .
    The Converter Status Remote Pendant patented Charge Wizard built-in to provide you with the most advanced RV battery charging system on the market today.
    Its the Most Advanced! Shouldnt this be the Best? And if it is, why are they selling the other one?

    Guys, I apologize for being so dumb, but how can anyone make sense of this?
  • icarusicarus Solar Expert Posts: 5,355 ✭✭✭✭
    Re: help understanding battery chargers

    Never apologize for asking a what seems to be a simple question. A: we all started somewhere, B: we are all here to help and C: there are no dumb questions, only dumb answers.

    To answer your question, there is never only one "right" answer for every situation. There are often many ways to get to the final destination.

    I suggest that to better understand battery CHARGERS it might help you by better understanding BATTERIES . For that I suggest you spend some considerable time reading and understanding the following links:

    http://www.batteryfaq.org/

    http://www.windsun.com/Batteries/Battery_FAQ.htm#Lifespan%20of%20Batteries

    By learning and understanding the information in these very good links, you will begin to understand why charging voltage and current should change with temperature, or why equalizing is important, or what a float charge is. Once you know these things, you can then tailor a solution to your own circumstance.

    Don't get discouraged. Folks here are more than willing to walk/talk you through situations as long as you are willing to do your part and study and understand. If terms seem jibberish, then ask for clarification. Some here with great knowledge roll engineering terms off like water off a ducks back while others have a great grasp of the practical (Not mutually exclusive mind you!) but occasionally the really technical guys need to be reminded that not everyone coming in knows what a watt is for example. No shame in either, but it takes effort on everyones part to communicate well.

    Good luck and keep in touch,

    Tony
  • ShadowcatcherShadowcatcher Solar Expert Posts: 228 ✭✭✭
    Re: help understanding battery chargers

    As Tony said folks are willing to answer questions, but some times you got to haul them down a bit to be understandable.

    You can start out modestly, but you do need to do your homework or you will spend money on things that do not work or do not work well.

    Yes switch do an LED reading light.
    Get a charger/converter that will use the output of your generator, not waste gas and not damage the battery.
    When you have the money get a solar panel and charge controller for that panel.
    You can monitor your battery state of charge with a digital volt meter from Harbor Freight.

    I am going to suggest that you check out and joint the Teardrop & Tiny Travel Trailer forum http://www.mikenchell.com/forums lots of how to restore fix build stuff and lots of adaptive reuse hears what works. One of the folks there sent me here for additional information.
  • bgarrettbgarrett Solar Expert Posts: 48
    Re: help understanding battery chargers

    Bill suggested a 20 amp charger, or 15 amp and 30

    * Xantrex Truecharge2 12-Volt, 20-Amp Battery Charger
    * Iota DLS-15: 12 Volt 15 Amp Battery Charger
    * Iota DLS-30-M 12 volt 30 amp regulated battery charger

    showcatcher suggests a 45 amp

    How can all of those different sizes be OK?
  • icarusicarus Solar Expert Posts: 5,355 ✭✭✭✭
    Re: help understanding battery chargers

    Battery charger size (and charging) is related to battery size, so indeed there is no one right answer. Larger chargers=shorter charging times. That said too much charger can charge a battery too quickly and damage it. To small and you have longer charging times and may not charge with enough current to stir up the electrolite. Re post the size of your battery, I can't remember how big it is. The Iota and the Xantrex TC series are good chargers.

    Tony
  • BB.BB. Super Moderators, Administrators Posts: 29,724 admin
    Re: help understanding battery chargers

    Basically, the charging rate for a battery bank ranges for ~5% to 13% for solar PV systems... Lower, it is hard to quickly recharge the battery bank with pure solar. Higher, will charge, but it is a lot of solar array that will not be used that often (battery spend much of their time at less than full charging current).

    You can put upwards of 30% of charger on a battery bank--but for sustained charging bove ~13% (C/8), that can over heat your battery bank (flooded cell battery typical charging current limit).

    The last 10-20% of charging a battery bank, the battery voltage has rose to the charger set point, and over the next 2-4 hours or so, the charging current will taper down to ~2% of maximum charging current. At that point, the battery is 100% charged.

    With generators, they operate at good fuel efficiency at 50% or greater load--Below that point, generators tend to not reduce fuel flow as electrical loads drop below 50% of rated load.

    Also, for diesel gensets, they tend to coke/carbon up and glaze cylinder walls if operated below 50% (some I have seen 65%) rated motor load...

    So matching the generator output with battery charger output with battery capacity balanced against your loads becomes a big balancing act.

    I don't know what to tell you about sizing a system... Solar PV systems just don't scale well. Going about 2-4x larger, and you are looking at a bunch of new batteries and hardware... You can probably reuse the solar panels and some of the larger MPPT type charge controllers can support 12/24/48 volt battery banks--so you do not need to buy new charge controllers as you up the battery bank voltage.

    Here is some good information and even a couple videos about installing a smaller PV system into an RV.
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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