can a deep battery of say 400ah at 12v be charged by a car?

edd_h
edd_h Registered Users Posts: 8
Hi
I have a 40 minutes round trip every day, and I was thinking of connecting my large battery to my car (4x4) alternator and charging it on a commute every day, and in the evening using the elecricity stored up in the battery for my RV, is this possible?
thanks
Edward
«1

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,422 admin
    Re: can a deep battery of say 400ah at 12v be charged by a car?

    Edward,

    The answer is probably "not a good idea" for several reasons.
    • Car Alternators are not designed for high current output--they will fall back and/or not last long with heavy loads. You would have to look at a truck or marine alternator designed for charging large battery banks and retrofit to your car.
    • With deep cycle batteries, you can charge them at a higher voltage than a typical car alternator will output (14.4-14.7, car is around 13.6-14.2). Deep Cycle batteries will charge much quicker with the higer voltage charging.
    • Car Alternators are not very efficient... Believe it or not, you probably would use less fuel by efficiently matching a genset+charger to your battery bank. The genset would ideally run around 50% of rated capacity to drive the appropriate output charging current. If the battery bank is relatively small, a Honda eu2000i or eu1000i might be a good fit (quiet, fuel efficient, and can power other 120 VAC loads when needed).
    • Not really a safe thing to do... Heavy battery will cut down on MPG. Disconnecting and reconnecting battery banks would require a plug---may cause issues with loads/chargers at home. Unplugging under load can damage plugs. Sparks can cause hydrogen gas to explode in battery cells. Battery needs cover to prevent rings/tools/etc. from shorting.
    • 40 minute round trip is really not much time for charging a battery. An hour or so at "full" charging current and a few hours of declining current is usually needed for a "good charge".
    Can it be done? Yes.
    Can you modify the car to make it better? Yes
    Can you setup your mobile battery bank to be safe? Yes
    Is it worth it to you? Don't know.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: can a deep battery of say 400ah at 12v be charged by a car?

    Yes, but then again no. There are several factors here.
    For instance, what is the alternator's capacity?
    And what is the vehicle's battery capacity?
    And will you be hooking it up through some type of 'dual battery' set-up?
    And how discharged is the deep cycle battery?

    Rough example: 400 Amp/hr discharged 25% = 100 Amp/hrs. To recharge that you'd basically (but not exactly) need to supply 50 Amps for 2 hours (plus losses - it takes about 20% more to 'put back' the Amp/hrs used).

    A typical truck alternator is usually 100 Amp. There are after-market units available up to 300 Amps (possibly more). In short, this is not a good option for trying to recharge a battery that's had significant drain on it. Might work to keep on 'topped up'.

    You'd be better off leaving the battery home and connected to a good 3-stage charger while you're at work.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: can a deep battery of say 400ah at 12v be charged by a car?

    NOTE: Bill is always faster than me, and more accurate with his replies. :D
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: can a deep battery of say 400ah at 12v be charged by a car?

    Remember however, that nothing is free. Charging the large battery from the truck alternator will come at some additional fuel consumption. It may not be enough to quantify if your truck is big enough. For example, my Xantrex TC 20 needs ~300-500 watts to run on my Honda Eu 1000, so 20 amps comes at about 1/16 gallon of gas per hour. So if you are trying to charge a 200 ah battery in 40 minutes it is going to take a big alternator.

    Tony
  • mshen11
    mshen11 Solar Expert Posts: 185 ✭✭✭✭✭
    Re: can a deep battery of say 400ah at 12v be charged by a car?

    let say you had a long daily commute anyways - would it be worthwhile to have such a charging setup (assuming your goal is not to fully charge the battery each day, rather little by little)

    im curious how would one create such a setup? let say its on a truck... you would have the batteries on the truck bed/car trunk and how would you hook it up to the alternator?
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: can a deep battery of say 400ah at 12v be charged by a car?

    Charging bit by bit is probably not a very good way of charging. Additionally, leaving a battery less than fully charged for more than a few days is a recipe to kill it quickly.

    I suggest you read the following:http://www.windsun.com/Batteries/Battery_FAQ.htm#Lifespan%20of%20Batteries
    http://www.batteryfaq.org/

    This will give you a bit more detail on the proper "care and feeding" of batteries.

    Aside from all of that, I think the idea of trucking heavy lead acid batteries around in the back of a vehicle only to charge them is kind of crazy. Between the extra fuel burned to charge them, (not to mention the wiring required to do so) and the extra fuel required to drag them around, (not to mention the manual labour required to heft them in and out, to reconnect on each edge) it doesn't sound like a terribly efficient way to charge. In addition certain battery chemistries don't like automobil charging voltages especially for absorb. (see links above) and there is a considerable risk of either chronically over or undercharging this battery. Also the added wear on the trucks alternator should be factored in as well.

    IF you were to do this, you could wire a suitably sized wire, fused, from the battery to an Anderson type connector mounted in the box of the truck. http://store.solar-electric.com/anhicupoco.html
    The beauty of these connectors is that it would be hard to mis-wire the battery

    Tony
  • BB.
    BB. Super Moderators, Administrators Posts: 33,422 admin
    Re: can a deep battery of say 400ah at 12v be charged by a car?

    Probably a good place to start would be with a Balmar Alternator.

    Balmar FAQ:
    Typically, when an alternator is working at full output, it will require approximately one horsepower for every 25 amps it produces. As such, a 100-amp high-output alternator will re up to four horsepower to operate.
    Assuming 12 volt battery--FAQ did not say (15 volts charging):

    746 Watts per HP
    ~0.5 lb per horse power hour of fuel (old rule of thumb for gasoline engine)

    25 amps * 15 volts = 375 watts

    375 watts / 746 watts = 0.50 = 50% efficient (typical number for alternator efficiency).

    So, for every 25 amp*hour you put in the battery bank, very roughly you will use a 1/2 lb of gasoline per hour...

    From Tony's experience:

    20 amps (at 12 volts) * 1/2 lb gasoline / 25 amps = 0.4 lbs of fuel per hour

    Gasoline weighs around 6 lb per gallon:

    0.4 lbs per hour / 6 lb per gallon = 0.067 gallons per hour = 1/15 gallon per hour for eu1000i+charger

    0.5 lbs per hour / 6 lb per gallon = 0.067 gallons per hour = 1/15 gallon per hour for eu1000i+charger = 0.083 gph = 1/12 gph for "truck"+alternator

    So, assuming Tony did not sneak Imperial Gallons in on me (:confused:)--it would appear that, in very round numbers, using a small genset is about the same or slightly more efficient vs using your gasoline truck/car to charge the bank.

    I guess the vehicle may come out ahead as it is already running to do the commute/trip... Vs the wear added to running the genset.

    Say you used 1kWH of power and need to recharge... You will need 2kWHrs of power:

    2kWHrs * 0.5 lb per HP Hour * 1/0.746 Watts per HP * 1/6 lb per gallon = 0.23 gallons of fuel to recharge (truck or small genset).

    Note, I am sure the numbers are not very accurate--but they do serve to gives a rough comparison of the costs. For example, I did leave out the 10-20% losses of charging the battery...

    Of course, you have additional losses with the alternator when it is not connected to the battery. Also check to see if the alternator can run without a load and not be damaged (batteries limit the maximum voltage of an alternator to ~15 volts--an unloaded alternator can exceed that by a whole bunch and may damage the regulator and/or diodes--Possibly).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: can a deep battery of say 400ah at 12v be charged by a car?

    In simplest terms, the "charging profiles" of automotive batteries and deep cycle batteries are so different that any system designed to properly recharge one type is not suitable for the other.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: can a deep battery of say 400ah at 12v be charged by a car?

    Bill,

    I am fluent in Imperial gals, as well as US gal and Litres. I just wish the US would adopt the metric! I haven't dealt with Imp. gals in so long I almost forget that unit ever existed!

    Tony

    Ps, I still think charging the battery with the truck is a solution in search of a problem though.
  • Ralph Day
    Ralph Day Solar Expert Posts: 1,019 ✭✭✭✭
    Re: can a deep battery of say 400ah at 12v be charged by a car?

    No-one has mentioned the obvious (to me anyway) joys of moving that big of a battery into and out of the truck every day! Not for me, you only get one back in life...look after it.

    Ralph
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: can a deep battery of say 400ah at 12v be charged by a car?

    Ralph,

    Not to polish my halo, but look at paragraph 3 of post number 7.

    Tony
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: can a deep battery of say 400ah at 12v be charged by a car?

    imo it will slowly charge it to a point if the alternator does not breakdown and will not reach a full charge due to alternators being limited in their charging abilities by not having multistage charging. simply put would be to say i wouldn't rely on it or do it unless the battery is in grave need due to deep discharge and something is put back in before a proper charge(r) is available for it.
  • Ralph Day
    Ralph Day Solar Expert Posts: 1,019 ✭✭✭✭
    Re: can a deep battery of say 400ah at 12v be charged by a car?

    Ah , yes Tony, must have been skim reading at that time.

    I'm in the midst of setting up a microFIT system. Site is prepped, concrete pad is in (just before freezup so to speak). If we have a warm winter more work can be done, or wait until spring. No worry of half loads trucking rock or concrete now...yippee! Sometimes 2.5 months of half loads in the spring to save the roads from certain destruction (only the secondary and smaller roads like mine).

    My target date for connection is May 1st, and should easily get there if only the OPA would move a little faster. It's 30 days past the 30 days from application and still waiting for a letter of offer for a contract. They've been very busy, lots of applications.

    Sorry, off topic. Batteries are heavy, every time you move one you also take the chance of dropping/spilling it too.

    Ralph
  • Brock
    Brock Solar Expert Posts: 639 ✭✭✭✭
    Re: can a deep battery of say 400ah at 12v be charged by a car?

    If you have no other way to charge the battery and did what others have mentioned then maybe. I did an experiment a couple of years ago with our diesel VW TDI. I had been getting 55 mpg pretty consistently with my daily commute. So I disconnected the alternator (belt still on, but electrically disconnected) and used an 8D battery, inverter and big charger to keep the cars battery charged while in use (it draws 55 amps until the engine is at 110F or about 5 minutes to power the coolant glow plugs). I saw the mileage go from 55 mpg to 60 mpg consistently over three tanks or 2400 miles.

    So your better off using the grid or as Bill suggested an efficient Honda 2000i or 1000i inverter genset and a good charger to charge the battery. A typical automotive alternator is about 50% efficient, with the gasoline engine being 25%, not good compared to the grid or solar panels or an inverter genset with a good charger.
    3kw solar PV, 4 LiFePO4 100a, xw 6048, Honda eu2000i, iota DLS-54-13, Tesla 3, Leaf, Volt, 4 ton horizontal geothermal, grid tied - Green Bay, WI
  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: can a deep battery of say 400ah at 12v be charged by a car?
    I just wish the US would adopt the metric!
    Good luck with that any time soon. As I understand it , Congress has changed requirements of the Metric Conversion Act of 1975 (Ford was president) and made them "voluntary".

    :grr

    Regards,
    Jim / crewzer
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: can a deep battery of say 400ah at 12v be charged by a car?

    I'm still voting for metric time, 10 second minutes, ten minute hours, ten hour days, ten day weeks, ten month years etc!

    Tony
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: can a deep battery of say 400ah at 12v be charged by a car?
    icarus wrote: »
    I'm still voting for metric time, 10 second minutes, ten minute hours, ten hour days, ten day weeks, ten month years etc!

    Tony

    so that you can get paid 10% of your wages?:blush::p
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Re: can a deep battery of say 400ah at 12v be charged by a car?
    icarus wrote: »
    I'm still voting for metric time, 10 second minutes, ten minute hours, ten hour days, ten day weeks, ten month years etc!

    Tony

    Don't forget 5 day weekends! (OK so it misses the '10' theme but I can dream!)
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Re: can a deep battery of say 400ah at 12v be charged by a car?
    edd_h wrote: »
    I have a 40 minutes round trip every day, and I was thinking of connecting my large battery to my car (4x4) alternator and charging it on a commute every day, and in the evening using the elecricity stored up in the battery for my RV, is this possible?

    Living and working around RV's for the past 7 years, it's not only possible but, it's done every day!

    80 minutes of charging should be pretty close to what you need to recharge 80 Amps at a C6 charge rate. I'd check your Alt you might well already have a 100 Amp alt.

    As to efficiencies you are already running the alternator, so I'd bet the difference in the efficiencies running at 10% capacity and 80-100% is not nearly as bad as just running at 10%. (the reason hybrids have batteries, so they can charge at the best efficiencies.)

    If I was to do this, I'd just put the inverter in the truck and plug the 'house' in when home. I might also have a second battery in the truck, just in case...

    I'd suggest a solar forum might not be the best place to ask these questions. Might try an RV site.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • hillbilly
    hillbilly Solar Expert Posts: 334 ✭✭
    Re: can a deep battery of say 400ah at 12v be charged by a car?

    I think that was 40 minutes round trip, not one way. Thus 40 minutes total time not 80.
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Re: can a deep battery of say 400ah at 12v be charged by a car?

    My bad...

    He'd be pushing it.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • jauguston
    jauguston Registered Users Posts: 20
    Re: can a deep battery of say 400ah at 12v be charged by a car?

    One issue that would have to be delt with to make it work is that the vehicle battery will be near full charge and will give the alternator the false message that it doesn't have to put out many amps. To get the alternator to go to high output the vehicle battery would need to be isolated from the charging system while charging the RV battery. I have some experience in this area.

    Jim
  • Brock
    Brock Solar Expert Posts: 639 ✭✭✭✭
    Re: can a deep battery of say 400ah at 12v be charged by a car?

    I don't think we are saying you can't do this, just some of the issues you might run in to doing this.

    If you do try it make sure you have a heavy gauge wire between the alternator or existing battery and the added battery. If the wire is 10 feet of #10, the alternator won't put out full power because of the voltage drop in the wire; in this case .2v can make a big difference in power in to the extra battery. And as always fuse the power running to the extra battery.
    3kw solar PV, 4 LiFePO4 100a, xw 6048, Honda eu2000i, iota DLS-54-13, Tesla 3, Leaf, Volt, 4 ton horizontal geothermal, grid tied - Green Bay, WI
  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    Re: can a deep battery of say 400ah at 12v be charged by a car?

    http://forum.solar-electric.com/newreply.php?do=newreply&noquote=1&p=44165


    "Now an alternator charging at 13.8 volts will do this. It will also charge a deep cycle battery that is used to run lighting, TVs, Hi Fi etc. But it will do it awfully slowly. To reach full charge state at 13.8 volts is possible, but it takes a ridiculously long time. The manufacturers of the external alternator controllers often state that a standard alternator will not get the batteries much higher than about 65% charge state. This isn't entirely true. 13.8 volts will reach 100% charge state. But it will take about 72 hours. "
  • 55carlos55
    55carlos55 Registered Users Posts: 1
    Re: can a deep battery of say 400ah at 12v be charged by a car?
    edd_h wrote: »
    Hi
    I have a 40 minutes round trip every day, and I was thinking of connecting my large battery to my car (4x4) alternator and charging it on a commute every day, and in the evening using the elecricity stored up in the battery for my RV, is this possible?
    thanks
    Edward

    hi,just thought id share 2 things with you (as i have a 390a/h AGM battery bank setup in my van being charged by the alternator) as the van came with a 55a alternator (and unfortunately cant fit a bigger one or extra alt)it does charge the batteries up to 12.7 volts (no problem there)but it takes 7 hours to fully charge after being 60% drained
    and second even though it has a dual battery isolator switch the second the main battery and rear batteries are connected,the rear batteries being so big suck all the power out of the small main battery (as electricity tries to equalize ) and you end up with a flat battery and cant start you car (aka car starts to go to work but when you try to go back home, boom flat battery) and it takes 7 hours to fully charge the rear (and the main battery) again,:cry: your best bet is to get solar panels at home and charge the 400a/h while your at work (love the sun) ,hope this helped.
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: can a deep battery of say 400ah at 12v be charged by a car?
    55carlos55 wrote: »
    hi,just thought id share 2 things with you (as i have a 390a/h AGM battery bank setup in my van being charged by the alternator) as the van came with a 55a alternator (and unfortunately cant fit a bigger one or extra alt)it does charge the batteries up to 12.7 volts (no problem there)but it takes 7 hours to fully charge after being 60% drained
    and second even though it has a dual battery isolator switch the second the main battery and rear batteries are connected,the rear batteries being so big suck all the power out of the small main battery (as electricity tries to equalize ) and you end up with a flat battery and cant start you car (aka car starts to go to work but when you try to go back home, boom flat battery) and it takes 7 hours to fully charge the rear (and the main battery) again,:cry: your best bet is to get solar panels at home and charge the 400a/h while your at work (love the sun) ,hope this helped.

    A dual battery switch (off-1-2-both) will not be of any use in this situation, while a diode isolator will. That will allow the alternator to charge both batteries without one being able to drain the other.
    The house battery will not be usable for starting and the starting battery will not be available for house.
    But putting in the diode will change the charging voltage applied to the batteries (lowering it by the forward voltage drop of .3 volts up to as much as 1.0 volts) and make that part of things worse unless you can increase the voltage regulator setting on the alternator to match.
    SMA SB 3000, old BP panels.
  • PeterBHT
    PeterBHT Registered Users Posts: 3
    edited August 2019 #28
    Hi, total newbie to solar etc and this will be my first post so hopefully my first post will contribute something.
    I watched a video of a guy who builds high end campers, well he had built 6 at the point the video was shot. Anyways he was running 600ah of lithium batteries in his van. He had under floor heating, infrared cook top, electric oven etc etc.

    He was saying, due to the restricted space for solar panels on a lwb van, to fully charge them would take 23 days of solar with good sunny days.
    So instead he had a second alternator fitted to his van with a charge profile specific to the deep cycle batteries, he could charge them fully in a 2.5 hour drive and that one charge would run his van for 5 days with no extra input.
    So as an ex motor mechanic, it's well within my skills to fit a second alternator on my ford transit camper I'm fitting out at the moment. I went looking for YT vids on how to do the wiring side and finding the "charge profiles" and found it hard to get any info except for this one video here, what he is saying is well over my head but sounds like he knows what he's talking about.

    He did mention at least one solution I understood and was related to something I read in this thread. About dumping the charge from the alternator to a separate lead acid battery with a load connected to it once the deep cycle batteries were fully charged thus protecting the alternator.
    https://www.youtube.com/watch?v=ZyIJRjJtCR0
    It's no good to me at the moment till I get a whole lot more learning under my belt in regards to what he was saying but it seemed unique so thought i'd share it here.
  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    Using an alternator designed for charging large house banks, (and appropriate regulator/controller) on a permanently connected house bank, there should be no need for a "dump" load IMHO.  Sounds like a hack around using the wrong stuff.

    Balmar gear is often used in RV/marine applications.  A bit spendy, but they are fit for purpose.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,422 admin
    One of the key differences is the use of Li Ion battery bank. Li Ion does charge much faster than FLA battery banks. More or less, you can feed C/8 to even C/5 into an FLA bank until you reach something like 80% State of Charge, after than the battery bank will require being held at (for example) 14.75 volts for 2-6 hours (longer time for deeper discharge). Li Ion batteries do not need that "absorb" cycle but can take full charging current upto the charging setpoint, then stop.

    Another issue why the Li Ion + alternator charging system MAY need a dump load... FLA batteries are fairly forgiving if held at charging setpoint after full... As long as the "high float" current is less than 2% rate of charge (I would suggest much less--But that is a different post), the FLA batteries will percolate OK--Possibly just run a little on the warm side and need more distilled water over time (not great, but FLA batteries will survive and--Albeit with a somewhat shorter lifetime).

    Li Ion batteries have almost zero self discharge and will be severely damaged/ruined if overcharged.

    And, if I recall correctly, even though alternators do have a rotating field winding, there is a residual magnetic field in the alternator field pieces, and this could supply enough current that even with the "alternator field turned off", the alternator would still generate sufficient voltage and current to damage a Li Ion battery bank that is at 100% SoC already.

    Again--This is a concern of mine--Not a prediction. There are, I am sure, enough different alternator systems out there that may have different behaviours when no charging current is required (in the olden days, generators and alternators used the residual magnetism of the field to "wake up" when the engine was started and power the regulator (no battery power required, so vampire loads).

    This would be my guess as to the reason for a "dump load" in the above RV system design. with a Li Ion battery bank.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    That sounds reasonable, but Balmar has had a LiFePo specific program on some of their regulators for a couple of years now.  You'd think if they were damaging expensive house banks, there would be a lot of unhappy campers (and vocal about it).

    Maybe other lithium chemistries are more prone to this, or maybe Balmar addressed it?
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter