Battery Charging: Which is faster? Onboard built in charger, or separate battery charger?

Hi, I was wondering which method would be the fastest for charging the [email protected] battery while using a generator.  Since generator usage time is limited to just a few hours a day at some campgrounds, I wanted to be able to charge the battery the fastest way possible.  Should I just use the onboard pre-wired battery charging system, or should I unhook the battery from the [email protected] wiring and use a separate battery charger that is just plugged into an outlet?  Thanks.

Comments

  • ScottGScottG Posts: 1,994Moderator
    I think it depends on the charger. A high capacity plug-in charger would probably be your best bet. Plug-in "smart chargers" are often just fancy trickle chargers that may take up to 24 hours to top off you battery. My understanding (perhaps wrong) is that the [email protected]'s built-in charger is more of a trickle charger (as are those built into some generators).

    Look for the amperage rating on the charger. In general, charging at lower amperage is slower but better for the battery. Higher amperage can be employed if time is a factor. In any case, be sure not to exceed the maximum recommended charging amps for your battery. You probably don't need to unhook your battery while using an external charger.

    Hopefully someone with experience doing what you describe can chime in with more specific information.
  • RatkityRatkity Posts: 3,398Member
    You can only charge a battery at a fixed rate (meaning, the way a stand alone charger does). There's no way to charge a battery "faster" without making the thing explode.

    A generator is a very inefficient way to charge a battery and the 2-hour generator time can add some extra juice, but won't fully charge it. If you have electricity, the converter will maintain a charge on the battery. If you mean to have the camper plugged into the generator to charge the battery, you have to take into account the parasitic loads inside decreases how much juice you can put into the battery. Flipping the cut-off switch and running a separate charger (some gennies come with built in chargers) for 2 hours would be better than using the converter.

    The places I've been that have generator times, usually have 2 sets of 2 hour times. If you use all 4 hours, you can get a battery to 85-90% charge. It's takes an overnight charge to get that other 10-15% into the battery - it's just chemistry, not a charger issue. 

    2017 820R Retro Toy Hauler from 2015 Tabitha [email protected] from 2009 Reverse LG Teardrop (but a [email protected] at heart)
  • ScottGScottG Posts: 1,994Moderator
     
    Ratkity said:
    You can only charge a battery at a fixed rate (meaning, the way a stand alone charger does). There's no way to charge a battery "faster" without making the thing explode.
    ...
    My statement was inferred from things I've seen printed on some motorcycle batteries regarding charge times, for example:

    Standard: 1.4A for 5-10hrs
    Fast: 6.0A for 1hr

    These were sealed AGM batteries. Admittedly, I'm not sure of the chemistry involved, or how this translates to larger deep-cycle wet-cell batteries. I do know that chargers come with different amperage ratings for different applications, and that lower amperage is typically indicated for smaller batteries.
  • RatkityRatkity Posts: 3,398Member
    edited August 2017
    Sealed AGM motorcycle batteries are not deep cycle (thinner plates), have CCA (cold cranking amps) of 225 avg, and 20 amp hrs total. I ride a Harley and sorta want to see if I can't get one with higher capacity! Some Group 24 deep cycle lead acids have amp hours of 60-80. My Group 27 has 110 amp hours.

    AGM motorcycle batteries still don't get a full charge unless charged overnight. I keep my Harley on a smart battery tender full time (it lets the battery drop a bit and then charges it). I still need to do an overnight periodically. If you charge an AGM battery too fast, it'll start to bulge because of the hydrogen gas being made. It's still chemistry.

    Think of the electricity going into a battery like a down sleeping bag being shoved into the tiny duffle bag it arrived in... You can put a lot of sleeping bag in at first.. maybe most of it if you take your time getting air out of the sleeping bag. Then you have to slow down a LOT to get the last part in or you'll split the bag. That's what happens with a battery. The electricity has to go in very slow in the last 10-15% or the chemistry (hydrogen gas) can build up and become dangerous (splitting the battery casing). 

    I hope that helps!! :)
    2017 820R Retro Toy Hauler from 2015 Tabitha [email protected] from 2009 Reverse LG Teardrop (but a [email protected] at heart)
  • ScottGScottG Posts: 1,994Moderator
    edited August 2017
    I like the sleeping bag analogy. It sounds like the key to a full charge is getting that last bit in at a lower current. Smart charges should do this automatically, but it explains why charge times for dumb (i.e., non-variable amperage) chargers are carefully prescribed.

    Getting back to robyn769's question (and boo's observation), does regularly charging a battery to only 85-90% have a significant detrimental effect on the health of the battery? I.e., if you can stuff most of the power back in with a relatively powerful charger in two hours, is that good enough for all practical purposes?

    Given the conditions I usually camp in, I'm pretty sure my solar set-up often provides nothing better than a partial charge.

    Aren't you glad you asked, @robyn769?  :-)  
  • RatkityRatkity Posts: 3,398Member
    @ScottG, yes, eventually it'll decrease the life of the battery. Some people say you'll replace the battery in a year, but I had one last 5+ years doing that. That said, if you have 2x 6V batteries, that would be an expensive replacement schedule if your batteries stopped holding a charge even after 2 years.

    The theory is, if you replace one 6V of two batteries with a new one, the remaining weaker battery is the one drops your overall amp availability. Normally, a person replaces both batteries at the same time. That said, I'm not sure real-life experience supports that unless you have a 4x 6V battery bank in a huge RV.

    If you just have a group 27 and that's all you need for power while boondocking full-time, I wouldn't worry too much about not getting it up to full charge. You'll replace it sooner, but it's not as big of investment as those 68 lb 6Vs. If you boondock for a week (for example), have a great time (picts properly posted here)... you go home... just flip the disconnect on the battery (or pull fuse) and hook it up to a regular charger overnight. Deep cycle batteries are designed to boondock for extended times! Just don't go below 50% (12.1-12.2V) often. That sort of scenario won't decrease the life of the battery. That's exactly what the batteries are designed for! So go camping and show us pictures! :)


    2017 820R Retro Toy Hauler from 2015 Tabitha [email protected] from 2009 Reverse LG Teardrop (but a [email protected] at heart)
  • ScottGScottG Posts: 1,994Moderator
    That's pretty much been my approach. We typically spend 4-8 days without hookups and with variable solar gain. With judicious power use, I don't think my bargain-basement 105ah group 27 battery has ever gone below 12.3V. I'm in my second season with it, and--anecdotally--it does seem to drain a bit faster than last year. However, at $90 a brand new replacement even every three years is a drop in the bucket of camping-related expenses.

    I do spend a lot of time thinking (but not worrying) about battery science, but I'm not real quick with the camera. (And while I have three smart chargers, I do not have a smart phone!)
  • robyn769robyn769 Posts: 103Member
    Thanks everybody for thr detailed responses.  I think my brain needs a recharge now though, haha.  Im getting ready to upgrade to 2 6 volt batteries so Im thinking Im not going to drain the batteries down all that much and perhaps the 2-4 hours of generator time might be plenty.  I know my generator does have a battery charging feature so Im guessing I would be better off using that.  ScottG says its ok to leave the camper charging feature engaged while also using a secondary charging device. 
  • ScottGScottG Posts: 1,994Moderator
    @robyn769, in retrospect, I'm not sure I'd leave the battery hooked up if I also had the generator connected to the [email protected] and therefore running the onboard converter/charger. 

    In doing so, you are in effect connecting two chargers to your battery at the same time. It's conceivable that the chargers might "confuse" each other or even damage the battery. In such a situation I would probably disconnect the battery while the generator is providing power to the camper.

    Admittedly, I'm just guessing here, as I've never tried this particular configuration. If someone knows better than I, please chime in!
  • cfsaccfsac Posts: 5Member
    Hi, I started a new post, but thought maybe someone here could answer my question.

    Hi, Can someone recommend a quality battery charger/maintainer? I have 2 6 volt wet cell flooded batteries @210 amps each connected in series and I bought a noco genius charger someone recommended, but it says only for batteries up to 120 amp and I am not able to maintain a full charge. Am I correct that I would need a battery charger that could charge 420 amps? I sure can't find a charger/maintainer that can do that.  How are all of you maintaining your 6 volt battery bank setups? 

  • robyn769robyn769 Posts: 103Member
    Hi, I will need to see what charger I'm using when I get home, but when I first get back from camping, I hook my 2-6 volt batteries (also 210 amp hours each), wired in series, so that they charge as one 12 volt battery up to my main charger.  The charger is essentially seeing one 12 volt battery with 210 amp hours.  I may be mistaken, but I don't think the battery charger cares about the amp hours of the battery.  I thought the chargers measure in volts, 6 or 12? When the two 6 volt batteries are wired and charging in series you still would only have 210 amp hours, and 12 volts.  I do know its matters how fast the charger can charge.  The trickle chargers or maintainers are not meant to recharge the battery to its fullest capacity, although it may if you have it connected long enough.  What I do is hook the two batteries up, wired in series, to my main charger, and then once they are fully charged I hook up the trickle charger.  I will have to see what mine is when I get home and I will re-post the details.
  • RonRon Posts: 90Member
    Does anyone know what the maximum output of the onboard charger is?  If your batteries are discharged enough "easily achieved", a higher output portable charger could shorten run time.
    2016 [email protected] MaxS, 2012 Jeep Rubicon 2dr, Rural Scottsdale, Az.
  • LSkrabutLSkrabut Posts: 100Member
    @Ron,

    What charger/distribution center do you have. This would be the best way to answer your question.

    On a new 2018 [email protected] 400, NuCamp installed a WFCO WF-8900 (8955) model. Per the specs in "Bulk" mode this model can charge up to 55 amps in a single 4 hour period as detected or needed @ 14.4 Vdc. Then switch to Absorption mode to 13.6Vdc supplying the required DC to RV and slow charge the battery.

    So whose onboard charge is installed on your 2016 Max S? I had to remove my cover and take photos to find all of the required information to search the web for the make and model I have.

    Now in my case, I feel the WF-8955 is plenty to charge my battery or maintain it if plugged in to the correct power source.

    Utah Driven

    2018 [email protected] 400

    MB GLK 250 Diesel

  • RonRon Posts: 90Member
    Thanks I got it.  The second pair of numbers gives the amp output of the charger.  WF-8735P has a maximum output of 35 amps.
    For my setup carrying a portable 50 amp charger isn't worth it.  The charge level drops to less than 35 amps fairly quickly.  My portable Schumacher charge is not a smart charger like the one in the tab either.
    2016 [email protected] MaxS, 2012 Jeep Rubicon 2dr, Rural Scottsdale, Az.
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