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BFL13's avatar
BFL13
Explorer II
Jan 26, 2017

Camping in the Cold--Some AH Figures

So camping off grid for four days--arrive Monday go home Friday temps : Night 0C/32F , Day 7C/44F-ish (Annual Rathtrevor provincial park late January episode to start the year off) Park gen hours 9-11am, 6-8pm (dark at 5--phooey on that second gen time)

Got six, 6 yr old batts down about 90% by age and a bunch more down by near freezing temps, somewhere around 600 AH. Charging with two PowerMax Adjustables, one 100amp and one 55 amp, Honda 3000i to run them.

OK so by Wednesday morning, down 292 AH by Trimetric, "morning voltage" is 12.1 so if that is half, full must be 584. Yipes , kind of low, but you do take a hit in the cold.

So 9am, kick off the recharge. Temp is 3C/35F, the 100 is doing 100a so turn on the 55, get 123 amps total. Play with the adjustment knobs to try and get them equal, get 156 amps, turn it up and the Honda pops its breaker. Rats. More fiddling settle on 150 amps total as good enough, Honda to Eco. All is well. Amps slowly rise.

0915- 153a, 14.6v Tri, 15.1v set (on both)
0922- 149a--tweaked voltage 15.3, amps to 150 again
0930- 145a, 14.7 tweaked set v up again 15.4 150 amps
0932- 148a, 14.7 Tri, 15.4 set
0950- 132a, 14.9 Tri, 15.4 set
1004- 118a, 15.0 Tri, 15.4set
1030- 90.5a, 15.0 Tri, 15.4
1100- 65a, 15.1 Tri, 15.4 set, 214 AH restored by Trimetric in two hours.

So if full was 584, am now at 87%. Shut down gen according to park rules. At which time park staff start cutting fallen wood with chain saws for a couple hours, and those chain saws are not Hondas! :(
Oh well.

So idea was to do another two days till Friday and recharge when home. BUT since that was about 150AH a day so far, there is no way to stay near 50% by Friday morning. I will have to do a small recharge again tomorrow. Rats! Last year at this time I was able to last till getting home and only do the one recharge "50-90" but it was a bit warmer then, more like 40F vs 35F

So temperature is everything! Once you get down near Freezing the whole thing falls off a cliff and it is not linear from 40F to below that anymore. Whole new ball game once you get near freezing.

Bottom line is the set-up still works--good for another year :)
  • MrWizard's avatar
    MrWizard
    Moderator
    Jan 26, 2017
    Run the Honda in the morning
    Get what you can
    Then idle the engine for another hr Or two

    I learned..it's fuel versus comfort and happy batteries
    I chose comfort and happy batteries
  • landyacht318's avatar
    landyacht318
    Explorer
    Jan 26, 2017
    My chrysler 50/120 alternator does 68 amps cold idle(800 rpm), but at hot idle (550rpm) with a 14.7v absorption dialed in, the alternator falls to a max of 42 amps, and its temperature will quickly climb to and then hover in the 220F range. If I start moving amps of course go back up, but stator temperature rapidly declines, especially over 25MpH. At 65MPH maxed out at near 120 amps, It is hard to get stator temperature above 130f, but it also kind of hard for me to present 120 amps worth of load for long as I do not have lots of battery capacity.

    At least in my vehicle, the airflow at Idle and the reduced alternator fan speed at idle, makes it so I never Idle just to recharge as it gets so hot so fast when maxed out.
    Also the temp sensor on my voltage regulator heatsink, revealed it too was getting hot (135F max) sending 8+ amps of field current to alternator when idling with a depleted battery, and more rpms lowers the field current and its temperature. That was before I added a 60Mm computer fan to it's additional heatsink for the overkill factor. Now it is rare to see VR go above 104f.

    But Ignorance was bliss. The temp sensor on alteranator stator casing did not show me what I wanted to see.
    Measurement tools are so enlightening though.

    BUt I always hated idling anyway, so no biggie.
  • pnichols's avatar
    pnichols
    Explorer II
    Jan 26, 2017
    Hmmm ... I guess you need a couple of alternators on your truck. One of them being a 250+ amp model for battery charging so as to get ~150 amps idling ... or maybe using two 150's under hood in parallel might get you ~150 amps idling?

    FWIW, I can easily get 70 amps idling from our Ford's 130 amp alternator.
  • BFL13's avatar
    BFL13
    Explorer II
    Jan 26, 2017
    pnichols wrote:
    BF - the last time I checked those Honda 3000is were expensive (but quiet).

    I shouldn't bring up this taboo subject but here goes ... couldn't you have just idled your truck engine to good-enough charge your batteries? Unless it's a diesel, it probably idles as quiet as the big Honda, anyway.


    We got this gen in early 2003, so 14 years still going strong makes it come out better in $/yr :)

    No, the noise is ok, and no issues with long time idle for the gasser, but the amps are not ok. I have tested for that using fat jumpers and also with inverter on truck battery with inverter running chargers. Best I got was about 50 amps. As seen above, I need more like 150 amps to do a 50-90 in two hours in this situation.

    You might get away with running the truck outside of park gen hours though.
  • pnichols's avatar
    pnichols
    Explorer II
    Jan 26, 2017
    BF - the last time I checked those Honda 3000is were expensive (but quiet).

    I shouldn't bring up this taboo subject but here goes ... couldn't you have just idled your truck engine to good-enough charge your batteries? Unless it's a diesel, it probably idles as quiet as the big Honda, anyway.
  • BFL13's avatar
    BFL13
    Explorer II
    Jan 26, 2017
    brulaz wrote:
    BFL13 wrote:

    ...
    OK so by Wednesday morning, down 292 AH by Trimetric, "morning voltage" is 12.1 so if that is half, full must be 584. Yipes , kind of low, but you do take a hit in the cold.
    ...


    Think that 12.1V ~= 50% SOC is at ~25C.

    And there's different SOC vs V charts depending upon your mood.
    But think they all indicate that at lower temps 50% SOC is at a lower V? If so, at 0C, 12.1V might actually indicate you are closer to 60% SOC.

    Then back calculating from that 50-60% SOC (and your Trimetric) makes for a really poor estimate of your bank's capacity.

    And are you really using 292 Ah per day? Or was that from Monday to Wednesday?


    LY, no. The AGM is in the truck camper and has only floated so far.

    Got that because the flooded one in there was gassing a bit and setting off the LP alarm. The battery box (under the step up to the bed ) is inside, not really vented. The AGM has cured that problem. The TC usually has 15a shore power where it goes, so not expecting to give the AGM much of a work-out.

    It would be interesting to have some more of those AGMs in the 5er to test them out. One thing is I could keep them inside where it is warm and effectively gain a bunch of AH in winter just from that!

    -- Actual capacity is always an estimate, but I did IMO accurate load tests last year and then you play with the temperature/capacity charts which are not all the same. I also go with the recharging patterns for consistency over the years doing the same thing and it all comes together fairly well looking at all the evidence.

    ---Follow up on OP, this morning just before top-up recharge, "resting" was 12.3, down 227AH, so 227-78 = 149 used. No attempt being made to save battery. Idea is to have enough set-up so no change in "lifestyle." "Lifestyle" takes about 60AH and the rest is furnace. No solar here in the woods to help. No problem--that's what the Honda is for. :)

    --I don't know about volts vs SOC being different in the cold. I did read that batts need higher voltage to recharge them when it is cold.
    Note the 15+ voltages in the OP I set as temperature compensation. 14.8 is 15.2 in these temps. Gottaluv adjustable voltage chargers! :)
  • brulaz's avatar
    brulaz
    Explorer
    Jan 26, 2017
    BFL13 wrote:

    ...
    OK so by Wednesday morning, down 292 AH by Trimetric, "morning voltage" is 12.1 so if that is half, full must be 584. Yipes , kind of low, but you do take a hit in the cold.
    ...


    Think that 12.1V ~= 50% SOC is at ~25C.

    And there's different SOC vs V charts depending upon your mood.
    But think they all indicate that at lower temps 50% SOC is at a lower V? If so, at 0C, 12.1V might actually indicate you are closer to 60% SOC.

    Then back calculating from that 50-60% SOC (and your Trimetric) makes for a really poor estimate of your bank's capacity.

    And are you really using 292 Ah per day? Or was that from Monday to Wednesday?
  • landyacht318's avatar
    landyacht318
    Explorer
    Jan 26, 2017
    I am not seeing the significantly faster loss of voltage with my middle aged TPPL AGM at lower temperatures.

    This morning, my AGM battery got down to 46F by sunrise, At sunrise my monitor indicated I took 48AH of its 'new' 90Ah capacity from it and was still 12.2x volts under a 0.3 amp load before sunrise.

    I am used to seeing similar morning voltages for Ah removed in 60 +F over night temperatures, and I do notice my battery is aging, but what makes me notice it is NOt overnight voltage held under load for Ah removed, but Amps required to attain near instant absorption voltage when depleted are half of what it required when new.
    Also, amps take longer to taper to 0.4 or less at absorption voltage, meaning on solar I better get to Vabs earlier in the day and that requires alternator or 'other' charging sources, or less overnight usage, which I rarely ration.


    You had a chance to collect any Data on your group 27 UPG AGM yet BFL13?
  • MrWizard's avatar
    MrWizard
    Moderator
    Jan 26, 2017
    37*f last two nights

    130+ amphrs per night, some lights, PC but fridge and electric blanket are the bulk of the use

    and this is just a 12>13 hr period, does not include daytime use
  • SteveAE's avatar
    SteveAE
    Explorer
    Jan 26, 2017
    Before I switched to LED lights and before I got an Olympian Wave heater, I used around 90 AHr per day (24 hours) with lows in the 20's and highs of 35 to 45. This daily usage was without running the microwave.
    The usage was divided fairly equally among:
    - furnace at ~30 AHr/day
    - lighting at ~30 Ahr/day
    - trailer overhead (alarms, radio, fridge, water pump, fan) at ~ 30 AHr/day
    After switching to LED's and the Wave heater, I am using ~ 45 AHr/day under similar conditions.
    I suspect the reason it isn't less is because I still use the furnace for quick warm ups and I now run a couple fans to force warm air into enclosed areas that otherwise wouldn't get much heat. Probably use the lights more now too since it really doesn't matter much if I leave a few extra on.
    Unless I am parked in the shade or it is overcast/snowing, my 300 watts of flat mounted solar easily recharge the four GC batteries each day (~45 degrees latitude in the winter).....unless my wife uses the microwave a lot :)

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