12 Responses to Efficiency in Battery Charging (Bill Rogers)

  1. Bill Knighton says:

    I’ve wanted to know if this would work well, using an mx60.
    I took the easy way, but at more expense. I am running a second vfx3624 with its only function as a battery charger. I’ve looked far and never seen a charger offered with the same function. It works fine with an eu2000i. Especially appreciated is being able to set the load on generator by “inc/dec” menu buttons on the Mate. I leave that screen open and even after turning off the inverter when not being used as a charger, that screen on the mate and its “inc/dec” buttons will still be active once the the charging inverter is repowered. It’s doesn’t need a repoll or the annoying outback password and menu navigation. That assumed no other devices on the outback net have been energized when the charger was down.

  2. russ says:

    That was a fascinating mountain of info.

    It showed me how very little I know! I’ll have to read it a few more times to get some of it to sink in!

  3. BP101 says:

    Like to post PDF of Ecoult’s 48v 25KW storage rack for Bill R. to check out. Well in lue of being able to do that a link to the manufacture of the LAC Ultra Flex battery.

  4. Joeelectro says:

    So THAT is what all that “extra stuff” does in a quality battery charger!
    Key point is that if you only use a bridge rectifier, zero current flows except at the top and bottom of the waveform when the voltage output from the rectifier exceeds the battery voltage. I think I will need to read the post a couple more times to wrap my brain around it, but this is a GREAT source of info, and a great help in understanding power factor and power factor correction. Thanks!

  5. David Baillie says:

    Love this article. It will take at least a few more reads to get even the basics down. I have an mx60 and want to turn a pmg to feed it. To be honest I don’t think I have the chops for something this beautiful… It is highly aspirational. I want to decouple my battery charging from the generator bypass that forces me to run a larger more stable genny then I would prefer. I also run charcoal gasifiers to run the gennies so power can fluctuate….
    Best regards, David Baillie
    Best regards, David baillie

  6. Tim Bartlett says:

    I just found this post and found this quite interesting about generators versus pure sine inverter power.
    I have a 24v Xantrex XW4024 inverter that has a gen assist feature which allows me to operate everything except the electric dryer using my 3.7kw Yanmar diesel generator. This feature allows the generator to operate the house and will assist the generator when consumption exceeds the capacity of the generator and it also manages excess capacity to recharge the battery bank.
    I have the inverter set to assist when the load approaches 3000 watts.
    I also have the option to directly charge the batteries with a 24 volt DC generator that is belt driven by a 10hp Yanmar L100 diesel.
    Some have said that directly charging the batteries and using the inverter to power the electronics is the way to go because of the quality of the power.
    The question I have here is about using the generator assist feature.
    Does anyone know if the inverter conditions the generator input to improve the quality of the generator output while operating in the generator assist mode?
    Thank you

  7. Russ F says:

    Gday George – your posts are sorely missed, as I’m sure you know.
    I looked back in to utterpower, and took the time to re-read Bill Roger’s article (and buy his kindle book). I think the battery efficiency piece is just starting to sink in to my thick skull a little now.

    I had a thought – My little truck has a 24v alternator, and those seem to be more efficient (perhaps – I’ve not seen/done a test) than the more compromised 12v ones for cars. Can you use two of them to charge a 48v battery bank – either simply in series (which “feels wrong” somehow), or (isolated) charging a pair of 24v battery banks, themselves in series for 48v?

    • George B. says:

      Gday back you you Russ!

      I am going to post more often, so don’t give up on me. It’s timely you bring up Bill Rogers, as he just made a decision on Shop lights that some might take note of. With the recent inexpensive LED screw in bulbs, I’ve been buying cheap bathroom fixtures (4 bulbs each) and converting my fluorescent fixtures. I did this because they make plenty of light, and I was tired of dealing with tube on a ladder 10 feet up in my shop ceiling. The bulbs make 60 watts worth of light, and show 9 watts.

      Bill Rogers waited and noted the LED tubes are an easy conversion, but he also noted the power factor of my bulbs are poor, somewhere around a .60? The LED tubes he has are well engineered with an excellent power factor! This is the kind of stuff an off gridder shouldn’t miss! My bulbs are on grid, but they’d use more of a generator’s capacity off grid.

      you question about two 12V generators used to charge a 24 volt string, you should be able to do that…


  8. Joshua says:

    I’ve had a real problem coming up with a solution for engine power to battery charging in the most efficient manner. The biggest issue is cost. You can throw money at it and solve it pretty quick but I don’t want to and nor can i afford it. I have a large 12 volt battery bank. 1064 AH at the 20 hour rate. I want to do a full 14.8 bulk/absorb and the option of a 16 volt equalize. Problem I have is with a PMG you run the risk of frying the charge controller if it over speeds. I have an extra midnite classic 150 but the guys at midnite don’t recommend because they say its a “stiff” source. I did find a cheapish PMG that has a very stable voltage curve, which doesn’t go over 100 volts until 10k rpm but the amps spike at low rpm. Not sure if that would damage it.
    Alternators have horrible efficiencies and slow regulators not designed for battery charging. Also a majority will fry before they even get close to the rated capacity.
    Best case scenario maybe 500 bucks with a cheap harbor freight engine, a zm4 regulator and cheap alternator. Its a real stump of an issue.

    • George B. says:

      “Alternators have Horrible efficiencies”

      I hope others weigh in, but I think all dynamos start out as alternators, in the early ones, we use the commutator to rectify to DC, and we later see the rectifier deployed which followed the slip rings when DC was needed. One of the first to make use of the three phase alternator in autos was Crysler, at least that’s the way I remember it here in the states, and they used six diodes to rectify the three phases, and I believe the goal was to get good charging current and slower shaft speeds. The unit was a compromise as most things are, here it was a balance of performance VS cost, and the bobbin wound rotor save a lot of money at the cost of efficiency. Redesign the rotor, and you’d have better efficiency.

      If you don’t like alternators, what are you going to use to make DC from a prime mover?

      Batteries can have several sources of charging power, maybe there’s no need to put it all through the charge controller? Telcos had huge investment in their batteries, and they charged them with a big DC generator. What was nice about it, was they set the current for the bulk charge rate, and as the battery voltage came up, it would auto taper for the finish charge… come back the next morning and turn the generator off…

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