An interesting experiment in battery charging…

…is not working out in a satisfactory manner. I have exceeded the ability of a Battery Minder to do something it never was designed to do in the first place.


I just went out to check on the fuel in the Honda, which today will run continuously for a major percentage of the total hours it has ever run. I may want to move up the next oil change. I plugged my old Battery Minder into the generator, and connected it across 4 225Ah 6-volt batteries wired for 12 volts. Given that the BM was really designed for single automotive batteries that hover around 100Ah, that’s asking a lot.

And the results are … better than nothing.


On sun power alone, at 11 am the battery voltage stood at less than 12.5v, when on a sunny day the system would already be floating at greater than 14.3v. After two hours on the Battery Minder, at 1 pm, the combination of all influences did this…


Which is no better than ‘better than nothing.’

I’m not really surprised. I am a little disappointed in myself for not moving more proactively on the issue. I’ve had the Honda for five years now, and it has revolutionized the way I perform several once-complicated chores. But I have spent no skull sweat at all on how I can use it to charge the batteries, and the way I assumed would work doesn’t work at all. Basically, I’m going to go shopping for a more capable battery charger.

About Joel

You shouldn't ask these questions of a paranoid recluse, you know.
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12 Responses to An interesting experiment in battery charging…

  1. randy says:

    Wild guess here, maybe the generator controls the DC voltage to a constant supply (13ish volts) instead of a higher charging voltage?

  2. Jim Price says:

    I suspect you know this, but you’ll get a whole lot more amps per gallon with a real charger than with a battery tender.

  3. Ben says:

    Do you have the manual for your inverter? I seem to recall that it has a charger built in.

  4. Anonymous says:

    Honda gens have an amp charger port.

  5. Anonymous says:

    Mr. Fusion. Need we say more?

  6. Abcdefghij Klmnopqrst says:

    Your EU2000 has two NEMA 15-5R receptacles (120 volt plugs); either will support a *REAL* battery charger (Schumacher models seem to be highly regarded as the best, if not the cheapest), a couple of the moderately-priced Schumacher models will deliver up to 15 amps.*

    This one is $65 – https://amazon.com/Schumacher-SC1280-Charger-Automotive-Batteries/dp/B07895QQBN/ref=sr_1_9?crid=2CLL46L915SSJ&keywords=schumacher%2Bbattery%2Bcharger&qid=1670247726&sprefix=schumacher%2Bbattery%2Bcharger%2Caps%2C175&sr=8-9&ufe=app_do%3Aamzn1.fos.fa474cd8-6dfc-4bad-a280-890f5a4e2f90&th=1).

    (Incidentally, read the comments on this one – there’s a long comment by a “Stephen Throop” with a lot of info on how chargers, and this particular one, operate.)

    * Schumachers, like all “newer” battery chargers have internal circuitry that will prevent charging if battery voltage is below a certain charger brand/model-specific threshold. Safety stuff to protect us idiots, doncha kno. Don’t know about others, but there is a procedure for the Schumachers (that’s NOT in the manual, you have to call them to get the info) to get around this. I doubt you will encounter this problem since the PV panels will do something to keep the charge up.

  7. Ben says:

    For occasional manual charging, it’s hard to beat an old-school manual charger with no electronics between you and what you are trying to accomplish. The trouble is, they are hard to find these days. If you stumble across one, treasure it, but remember what it is, and especially that it will happily change your batteries to death if you don’t supervise it.

  8. RCPete says:

    It looks like some of the smaller Honda generators have a (non-controlled) DC output, but the latest at greatest (EU2200i) doesn’t have one. The notes on the EU2000i say it could overcharge an automotive battery.

    As a reference point, my ancient 1800W Coleman generator has an 8A 12V output.

    I have a generator input to charge my pumphouse solar system, but haven’t used it. That system runs at 48V and the generator charge runs through the inverter. (The older 24V system has the capability, but I never did the wiring to use a generator. Would not be fun to hook it up now.)

  9. John says:

    More Amps!
    You have 450 Amp Hrs of 12V battery capacity. Without access to their specs I would think they will take up to 40-50 amps of bulk charging current. At a charging voltage of about 14.5v x 50 Amps = 725 Watts.

    You have a 2KW generator so easy peasy and power to spare!

    I have 2 x 100 AHr AGM batteries in my van – 45% of your capacity.
    When I get a few days of overcast defeating my 250 Watts of panels I use a 45 Amp version (comes in 35,45,75,100 amp versions) of this with my generator:

    Powermax 110 Volt AC to 12 Volt DC Power Supply Converter Charger
    https://www.amazon.com/gp/product/B00F8MC42C/ref=ppx_yo_dt_b_asin_title_o04_s00?ie=UTF8&th=1

    It is a regulated charger so no overcharge. I have been using it for six years and it has been great back up. I use it mostly to bulk charge when batteries are well down. As they reach charged state the current will fall off and at a point I’m then wasting gas. So bulk charge early, then top off with whatever panels can offer. Pretty efficient.

    I offer you might consider something similar, and best of luck Joel !

  10. Joel says:

    John: yes, thank you. That is useful information.

  11. s says:

    The manual for your Honda EU2000i generator is here.

    https://cdn.powerequipment.honda.com/pe/pdf/manuals/31Z07610.pdf

    Your generator has an 8-Amp, 12-Volt DC charger already built into it. The manual says:

    “The DC receptacle should ONLY be used for charging 12-volt
    automotive type batteries. The DC charging output is not regulated.”

    “Automotive type” means 12 V lead acid. You know how to connect your batteries for 12 volts. “Not regulated” means you have to run the gen without eco-throttle.

    The manual does not warn about overcharging. With your relatively large batteries it would take a very long time to get past float voltage.

    It won’t charge as fast as the 45-amps version John linked, but you already own this one.

    You can certainly rig the cable to connect to the generator charging port, but Amazon will sell you one for $12.

    https://www.amazon.com/Generators-Generator-Replacement-Connection-Practical/dp/B07YKFN61Y

    Even at your altitude the generator has plenty of power for 112 watts (8 amps x 14 volts) but you would burn less fuel if you replaced the standard 62 mm jet with the 60 mm jet as Honda recommends.

    http://cdn.powerequipment.honda.com/pe/pdf/pubs/pci54675.pdf

    Amazon sells that jet for $14.

    https://www.amazon.com/Honda-99101-ZG0-0600-Jet-Main-60/dp/B004DR3B5M

To the stake with the heretic!