Furthering Rybren's Education - Battery charging from generator

RybrenRybren Solar Expert Posts: 348
As I continue to gather more knowledge and information, I find that I keep coming up with more and more questions that I can't seem to find an answer to.

Today's scenario and question: I have a small Homelight generator that is rated for 1700W max and 1450W continuous. In addition to the 2 x 120V outlets, it has an 8A, 12V cigarette lighter type port that the manual calls a "Battery Charger".

I do have a small solar array (60W PV and 75Ah hybrid starting/deep cycle battery) that came with my off-grid cottage. The system supports a total of 60W of 12V LED and CFL lighting. So far, we've only been using a maximum of about 60WH per day (and only on the weekends). As the summer draws to a close and the nights grow longer, I can forsee a much heavier demand for lighting and more frequently (I'll be at the camp for 4 or 5 days at a time during the month of September) Obviously, the demand on the battery will increase and with the shorter days, the PV may not be able to fully charge the battery.

My question is: If need be, can I connect the "Battery Charger" output of the genny directly to the battery to suppliment the PV? If so, what precautions and/or issues should I be aware of? Can the CC remain connected to the battery while the genny is also connected?

As always, thank you for your advice and continued support. You guys make this so much easier; you are truly appreciated.

Comments

  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Furthering Rybren's Education - Battery charging from generator
    Rybren wrote: »
    My question is: If need be, can I connect the "Battery Charger" output of the genny directly to the battery to suppliment the PV? If so, what precautions and/or issues should I be aware of? Can the CC remain connected to the battery while the genny is also connected?

    Answer: It depends....

    If the output of the genny charger is regulated, it is probably configured like a car alternator to produce a compromise voltage between charging and float. Which may or may not work together with a solar charger. If you run the genny's charger only when the panels are not producing, the chances of interference are minimized and you could make up for any insufficient charging from PV that way.
    SMA SB 3000, old BP panels.
  • RybrenRybren Solar Expert Posts: 348
    Re: Furthering Rybren's Education - Battery charging from generator

    Thanks. I'll read through the (very thin) manual again when I get home to see what it says about the DC output.

    So, if I understand correctly, if I disconnect the PV/Charger from the battery or wait until dark, it should work.
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Furthering Rybren's Education - Battery charging from generator
    Rybren wrote: »
    Thanks. I'll read through the (very thin) manual again when I get home to see what it says about the DC output.

    So, if I understand correctly, if I disconnect the PV/Charger from the battery or wait until dark, it should work.
    Yup, and it may also work just fine with both connected. But you may have to watch the battery voltage carefully and shut the generator off when it is charged, depending on the output voltage and the battery type. So keep measuring and watching the first time you try it!
    SMA SB 3000, old BP panels.
  • BB.BB. Super Moderators, Administrators Posts: 29,482 admin
    Re: Furthering Rybren's Education - Battery charging from generator

    In general, you are more fuel efficient and faster charging if you use an AC charger foot the battery.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Furthering Rybren's Education - Battery charging from generator

    bill is right that the ac portion is far better to use. now i don't know if the full 1450w cont output can be used in one outlet or if the power is split between the outlets. even split that is 725w at 120vac or about 6a ac. this would roughly convert to 60a at 12v and accounting for inefficiencies and such could drop that to 30a-40a through a good 3 stage charger. this is about 4x better and maybe even 5x better than that 8a outlet on the genny.
  • RybrenRybren Solar Expert Posts: 348
    Re: Furthering Rybren's Education - Battery charging from generator

    Thanks guys.

    I misspoke slightly on the generator specs: It is 1750W Surge and 1400W continuous. The manual doesn't specify whether the AC is split between the two outlets, but on the other hand, it doesn't tell you not to put the full load on one. For DC, it only says that the outlet is designed to charge flooded vented batteries.

    I don't know much about chargers (or much else related to this endeavour). I suspect that the charger capacity is linked to the size of the battery bank. If so, then I'd be reluctant to pick one up just for the rest of this season, as I do plan on putting together a new system next year.
  • icarusicarus Solar Expert Posts: 5,223 ✭✭✭✭
    Re: Furthering Rybren's Education - Battery charging from generator

    I would look to invest in a good 3 or 4 stage charger, like the IOTA or Xantrex TC series. A 20 amp charger will run fine on your gennie. In the future you will need a good charge going forward anyway.

    You are beginning to learn the basic rules of PV/off grid living. The loads always grow with time. As you move forward, design any changes with a realistic load estimate, and then build a system with proper components to service these loads,,(battery bank, PV, charge controller, PV capacity, inverter etc.)

    Good luck,

    Tony
  • BB.BB. Super Moderators, Administrators Posts: 29,482 admin
    Re: Furthering Rybren's Education - Battery charging from generator

    Some light reading (really goes into detail--not everyone's cup of tea):

    Selecting a charger for the Honda eu2000i (1,600 watt genest)

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RybrenRybren Solar Expert Posts: 348
    Re: Furthering Rybren's Education - Battery charging from generator

    Thanks Tony.

    Would one of those 20A chargers still be useful on a 220Ah or larger bank?

    I keep the forum's "Ready, Aim, Fire" mantra in mind with every bright (and not so bright) idea that I get. My winter project will be to design and then start to purchase the items that I'll need to make the camp everything that my wife would like it to be. (like running water and indoor plumbing and a toilet instead of an outhouse)

    I'm on the verge of retirement and we do plan to spend a lot more time at the camp once that happens.
  • RybrenRybren Solar Expert Posts: 348
    Re: Furthering Rybren's Education - Battery charging from generator

    Thanks Bill,

    Reading now.
  • icarusicarus Solar Expert Posts: 5,223 ✭✭✭✭
    Re: Furthering Rybren's Education - Battery charging from generator

    FLA batteries like 5-13% charge current, ergo , a 200 ah battery would like 10- 26 amps.

    I personally use a 20 amp Xantrex on a 450 ah bank,, a bit too small, but I don't use it very often, and it runs on the EU 1000. Before you "ready, fire, aim," try to look ahead as best you can. In the short term a cheap charger, even a automotive charger (properly monitored!) Might get you through until you rebuild your system.

    Tony
  • RybrenRybren Solar Expert Posts: 348
    Re: Furthering Rybren's Education - Battery charging from generator

    Tony,

    Thanks again. I will be picking your collective brains as my plan for the new system evolves.

    Bill. I think that I'll wait for the english version of that thread :) My head hurts!
  • BB.BB. Super Moderators, Administrators Posts: 29,482 admin
    Re: Furthering Rybren's Education - Battery charging from generator

    The short answer...

    First, trying to keep the generator around or over 50% of rated load--That is the most fuel efficient... If you run at much less than 50% load, the fuel economy goes down (i.e., the fuel flow stays at around 50% of full load when the load is between 50% and 0% load).

    Second--The AC powered battery chargers vary widely in their "efficiency" or use of power/current/VA from gensets... A typical AC battery charger may only use around 52% of the power from the genset (80% efficiency and 0.66 Power Factor). So, your generator may put 1,000 Watts (really VA) into the power supply, but the real power "Watts'" into the battery bank is only ~520 watts.

    You can get "very good" AC battery chargers (many times Inverter/charger combination units) that run closer to 90% efficiency (90% efficiency and 1.0 PF)--That means when you load the genset to 1,000 Watts (or VA), you get upwards of 900 Watts into the battery bank.

    These number don't matter too much for people living "on the grid"--But for folks living off grid--The fuel savings can be very significant (a badly matched genset to AC battery charger can use 2-3x as much fuel--At $4.00 per gallon at the "cheap stations" here in California--that can be a bit of change).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RybrenRybren Solar Expert Posts: 348
    Re: Furthering Rybren's Education - Battery charging from generator

    Thanks Bill

    If it makes you feel any better, the cheap gas stations here in Ottawa charge ~$4.80 a gallon ($1.28/Litre) for regular and up at my camp, it jumps to ~ $5.50/Gal

    As a side note, I checked my battery yesterday morning just as the sun was rising and before any light cleared the trees and hit the panels.

    The voltage was 12.62 and the SG in each cell was ~1.26. We had used the lights for a few hours the night before, so ~90% SOC seems about right. I was surprised that the battery wasn't in worse shape. I don't think that the previous owner had ever added water to the battery and it is about 3 years old. It didn't appear to need any water yesterday.
    Luckily, I guess, the draw on the system has always been fairly low.
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