Charging 12V batteries with a generator

Charging 12V batteries with a generator
4 | 22 votes

You’ve bought a camping inverter generator with built-in 12-volt outlets. But how do you go about charging 12v batteries from your generator? Here’s a quick rundown of what you need to know.

The Yamaha EF2000iS inverter generator control panel with DC outlets at the bottom

The Yamaha EF2000iS inverter generator control panel with DC outlets at the bottom

Let’s get straight to point: camping generators may have a 12-volt output on them, but when it comes to the crunch, they are not designed to fully charge your batteries directly. There are two main reasons why:

First, the chances are your generator’s DC outlet is limited to a current of about 8 amps maximum. So any battery will take a while to fully charge.

Secondly, the voltage of the DC output isn’t regulated – it varies according to the generator’s RPM. This is fine if the generator is running a low load, but not if it’s running a medium to high load. Also, the generator won’t cut back the charge when the battery is nearly full, so you can’t risk leaving it charging for too long.

The bottom line: Your DC output on your generator is best for emergency or short term charging, i.e. providing your car battery a trickle charge. Anything more is a potential risk to your batteries.

The DC outlets on an inverter generator are good for small trickle charge to re-start a car battery

The DC outlets on an inverter generator are good for small trickle charge to re-start a car battery

So what’s the solution?

The best way to charge your battery is to run a proper 240-volt or 120-volt battery charger off the generator’s AC output. This will recharge the battery much faster and accurately. Also, most chargers regulate themselves down, so as charge builds in the battery, the charger won’t be pushing the same amount of amps.

So as an backup or alternative to your solar set up to charge your camping/caravan/motorhome battery packs, portable inverter generators are a great option, especially as you can also run your appliances on 240v straight from the generator also. But just remember, when charging your battery packs off a generator, use a quality battery charger plugged into your 240v outlets instead of the generator’s DC outlets.

For a range of quality battery chargers, check out our site HERE which includes options from leading brands such as Dometic and Enerdrive. For camping inverter generators, check out the expert selections or explore the full range at My Generator. The most popular model for charging your camping battery packs (via a battery charger) is the Yamaha EF1000is:

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Sean Connolly

Sean Connolly

Managing Director at My Generator
Sean is the co-founder and Managing Director of My Generator (mygenerator.com.au)
Sean Connolly

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Comments

  • Steven April 6, 2015, 10:23 pm

    Hi Sean I’d like a generator to run a small coffee machine in my Chrysler 300c stretch limo. Coffee machine is Nespresso pod.
    Wait for your response, Steven.

    • My Generator Admin April 7, 2015, 3:41 am

      Hi Steven,

      Thanks for your inquiry. We have helped many customers with selecting the right generator to run their coffee machines. The first and most important thing you need to do is to find out the starting and running wattage requirements of your machine (the starting wattage for some coffee machines can be quite high). This wattage information can be found in the product manual, on the product data plate, or you can contact the manufacturer to ask them. Make sure you get the starting wattage (this is the most important) as sometimes the specs will only list the running (or rated) wattage.

      Once you have that starting and running wattage info, you can then choose a generator which will be able to power your nespresso machine. You can check out our range of inverter generators (which would be the most suitable type for your purpose) and sort by Power Output to find the right sized generator model for you.

      You may like to talk to an expert if you have any more queries, in which case please call us on 1300 400 122. Many thanks!

  • Avinash September 8, 2015, 5:29 am

    What type and specs of dc generator is required for charging a car battery???

    • My Generator Admin September 8, 2015, 6:07 am

      Hi Avinash, we are not aware of a portable generator on the market that just produces DC power. However most inverter generators available today have DC outlets as a secondary power source to the AC outlets. With DC cables you can provide a trickle charge to car batteries to get you going. However it is not recommended that you fully charge your battery from the DC outlet, as the power is not regulated. Its only advised that you provide a small trickle enough to kick the car over. To fully charge your batteries using a generator, it is recommended you use the AC outlets and connect a battery charger between the generator and the batteries – this will properly regulate the power. Thanks

  • Steve October 1, 2015, 12:10 pm

    Interesting you talk about using a 240 VAC charger as most people would have a 120 VAC charger, but either works and all generators have 120 VAC. Just and observation, but your comments are right on about charging. charger vs. 12 VAC.

    However, in the event I have to charge from a generators 12 VDC system, (Honda 1000) what wires do I need? How heavy (gage) would I need to get max current to the battery? I am looking at this as an emergence charge / boost to get something started. Suggestions?

    • My Generator Admin October 1, 2015, 11:58 pm

      Hi Steve – great point, we will amend the post. It should read ‘240 Volt and 120 Volt chargers’.
      In terms of wires for your Honda 1000, we would advise you opt for a Honda 12Volt DC Charging Lead – for Honda Generators, these need to be purchased separately.
      Hope that helps, cheers.

  • Joseph PHILIP October 27, 2015, 1:15 am

    I would like to buy one, can I get your contact information please?

    • My Generator Admin October 27, 2015, 2:10 am

      Hi Joseph, you can call us on 1300 400 122 and we’d be happy to help you out. Many thanks, Steve.

  • Sean November 12, 2015, 11:44 am

    Hi Sean
    I play my music in my camper van for several hours and often run my battery down. Would it be ok to power my 6 amp trickle charger from my honda EX650 generator onto my vans 12 volt battery while I am playing music with the ignition off?
    Thanks

    • My Generator Admin November 16, 2015, 3:35 am

      Hi Sean, in my experience I am able to charge my battery (via a battery charger) and use the battery power to run my fridge etc. at the same time. Hope that helps, cheers – Steve.

  • galagali November 21, 2015, 11:05 am

    THANKS FOR SHARING, THE POST IS REALLY INTERESTING AND QUITE INFORMATIVE TOO.
    BRAVO FOR A REALLY IMPRESSIVE SITE

  • Mark December 11, 2015, 3:12 am

    I recently bought a Gentrax 3.2KVA generator for the purpose of doing odd jobs on my block of land.

    I was wondering, is it possible to connect a 12v Deep Cycle Battery to some part of the Inverter side during the evening when no one wants to hear my generator chugging away to produce 240VAC?

    Alternatively, I would need a separate Inverter.

    Any Ideas??

    • My Generator Admin December 13, 2015, 11:20 pm

      Hi Mark, from my understanding of what you are saying, you would need a separate inverter for this. The inverter within the generator could not act as the channel between your battery and your AC appliances. Thanks, Steve.

  • Viki December 14, 2015, 10:23 am

    I have a 3.6KVA inverter connected to four 150AH batteries with a charging current set at 12A. This inverter is connected to normal load.

    At the depletion of inverter power and in the absence of normal power, if I want to run the normal load off the generator, and any remaining current off the generator to charge the batteries connected to the inverter, is it possible?

    In other words, if I connect a 4KVA generator to charge the inverter batteries while 2KW is being used by the normal load, would the generator shutdown because of overload or would the inverter slow down its charging to run the normal load? The other way to ask the same question is, would a 4KVA generator suffice or would I need a higher rated generator?

    • My Generator Admin December 14, 2015, 11:35 pm

      Hi Viki, it would all depend on your battery charger, your batteries and how much power they would draw. Typically for standard camping battery packs / normal vehicle auxiliary batteries, charging them through a regulated battery charger will not draw much power at all.
      You need to know the running (continuous) watts of your generator, and if you are drawing roughly 2000 watts from other AC appliances then the difference between those two is the capacity you have to charge your batteries without overloading your generator. Hope that helps – cheers, Steve.

  • Bill Cochrane January 17, 2016, 10:32 am

    Hi can I run a 12 volt pump that draws 8 amps max of the 12 volt side of a 2kva Yamaha generator?

    • My Generator Admin January 17, 2016, 9:50 pm

      Hi Bill, to run 12volt appliances it’s advised that you use the AC output of the generator and then an inverter. The DC output of a generator provides unregulated power and is really designed for small trickle charge (say a flat car battery) purposes if required. Hope that helps – thanks, Steve

  • Alan Pickering March 13, 2016, 9:39 am

    Hi Steve,
    We’re about to embark on a trip through the Simpson desert and up to the Gulf Country, if it becomes dry enough by mid to late April.

    We’ve got a slide-on camper with an old 80 Litre Everkool fridge, which we will want to use as half freezer, half fridge. Other electrical use is minimal, apart from a CPAP machine, which draws 2 Amps, when being used.

    I anticipate wanting to spend up to 4 or 5 days in one spot, without shifting camp, meaning that the 115 Ah auxiliary battery won’t last, without charging. In fact, at the moment, I’ve two auxiliary batteries in series (100 Ah & 115 Ah), but I’m seriously thinking of substituting the smaller battery, by buying a Yamaha 1000 iS generator as a back up. This will save about 10 kgs in weight and provide me with the power security I want.

    The camper is rigged with two CTek chargers, namely one 240V Multi XS 15 Amp charger, for powered sites, and a Dual 250S DC-DC charger for recharging via the car’s alternator. I note your earlier comments about the DC supply being unregulated, but won’t this be overcome by the DC-DC charger regulating the charge?

    My main questin is, what mode would be quicker/more efficient to recharge the battery, a) using the 240V power lead into the external socket on the Camper, or b) running the DC lead into the input side of the DC-DC charger?

    If using the 240V 20 metre long orange extension lead to recharge the battery from the generator, will it pay to suspend the lead 30 cm above the ground, to minimise loss due to induction?

    Regards, Alan.

    • My Generator Admin March 14, 2016, 4:04 am

      Hi Alan, great questions. The Yamaha EF1000iS is very popular for your type of application. In our experience, using a good quality 240V charger is a very safe, quick and effective way to charge your batteries. I’m not as familiar with DC to DC charger unfortunately, as I don’t have one – all I know is that the DC outlet on inverter generators do not provide a regulated charge. However, if you are confident that your DC to DC charger correctly regulates the charge (which it should), then it would most likely be fine.
      In terms of extensions leads, any generator’s capacity can be diminished by the length and quality of the extension chord – our tests suggests that anything over 3-4 metres in length can start to slightly de-rate the generator’s power delivery. The power loss is not significant, but the longer the chord, the more it can de-rate.
      Hope that helps, cheers – Steve

    • Alan Pickering January 17, 2017, 5:19 am

      Hi Steve,
      I’m back again, after completing my trip across the Simpson and up to Lawn Hill.
      I was surprised how long it took to recharge the two 100 AH lead acid batteries, using the Yamaha EF 1000iS generator.
      The extension cord was a typical 20 metre long 15 Amp orange cord, which I’m thinking has fairly thick insulation. With the generator producing 800 Watts, or 66 Amps at 12 Volts, I’m presuming there is ample current to overcome any induction loss?
      The battery charger was a CTek 15000 (15 Amp), converting the 240V output from the generator. I’m guessing that I could expect 60 Amps to be replaced in the batteries in four hours, if there is 100% efficiency and that 45 Amps in four hours could be more realistic.
      I’m seeking your advice on using a CTek 25000 model to speed up the charging, instead of the CTek 15000.
      If I do this, will it be too rapid a charging rate, if I use this 25 Amp charger on a single 120 Amp Hour AGM battery, which is what I use in the other light weight 4WD car we have?
      I have heard it is better to stop recharging, when the battery is 80% recharged, because the last 20% takes almost as long again; a bit like pumping up a bicycle tyre by hand.
      So I’m not looking for a full recharge, just enough to bring a healthy amount back into the auxiliary batteries, for the next day’s draw.
      Cheers,
      Alan Pickering

  • dan bigham July 17, 2016, 3:02 pm

    why cant the dc output be used to power a dc light that can use dc power from 12v to 32 volt dc amp draw is very small as it is led bulbs

  • John Hudson October 23, 2016, 11:48 am

    Sean; I purchased a Champion 3100 Inverter Generator. It works well and I’m happy with it. I’m aware of using a digital battery charger plugged into one of the AC outlets to charge batteries…but. I would like to take advantage of the 12V / 8a outlet (waste not, want not!). Seems to me I could route that 12v output to a good MPPT Charge Controller attached to my travel trailer’s battery system to charge the batteries. Your thoughts on this would be appreciated before I purchase a pricey MPPT unit. John

    • L Adams October 24, 2016, 1:44 am

      Hi John,
      As you have rightly indicated, we recommended using the AC outlet via a quality battery charger to recharge your batteries. In terms of the DC outlet, we only recommend this for emergency battery charging, i.e car breakdown.
      My understanding of an MPPT controller is that it is used for Solar power set ups to convert the excess voltage from your solar panels into amperage to top up your batteries. You will need to contact the manufacturer of your generator and battery to check if this application of an MPPT controller is suitable.
      Regards, Steve

  • Ron Hughes October 31, 2016, 6:37 am

    Hi, in terms of battery charging; provided I am using an AC outlet with a quality battery charger, do I need to disconnect my main car Battery before charging it with an inverter generator like the Yamaha 2400?

    • L Adams October 31, 2016, 7:49 am

      Hi there, Thanks for the question. You do not need to disconnect your main car battery in order to recharge. The Yamaha 2400 will be more than adequate to perform this operation. Good work on choosing a quality charger, just be sure to “always” read the battery charger’s instruction manual prior to use.

  • Ben Bright December 13, 2016, 11:14 am

    Hi, I have 2 x 100ah batteries in the Complete Campsite camper trailer that currently supply a Waeco CFX50 fridge, some 12v LED strip lighting and the occasional use of a 12v pump for water from tank to kitchen. (Some 12v phone/tablet charging may also be on the cards during the stay) We are planning a 10 day camping trip earl next year at an unpowered site, with the use of an 80w Sunpower solar panel to keep us going. Question is, I’m thinking of taking a GMC generator that the father in law gave me for additional power backup. Will this put out safe power to supply the 240v battery charger for the batteries or do I need to do/add something else to allow us to utilise the generator to charge the batteries whilst camping?

    • L Adams December 13, 2016, 10:43 pm

      Hi Ben, I would recommend you check you battery charger requirements in terms of the type of power supply required. Typically for camping applications, inverter generators (with pure sine wave power) are used. However, we supply conventional generators for all manner of battery charging (including solar systems) without issue. Again, you are best to check your charger to see if there are any specific power supply requirements. Thanks.

  • Max b February 10, 2017, 3:15 am

    My Application has a 72V 100AH Battery Bank. I am interested in Just charging the Battery Bank While I am at Rest stops. Possibly at Night when I am Sleeping. Therefore I would like to know if This Generator Can Charge my whole battery bank with On Fill Up? My application has a Onboard charger to Regulate The Power being sent to the Battery Bank. I am interested in Saving Weight and Efficiency. If A 1000watt Gen can do the job in 8hrs or so I am satisfied with that.

  • waqar February 17, 2017, 8:55 pm

    What type and specs of dc generator is required for charging a car battery? Car weighing about 170kg .. I need to give power to a dc motor to run the wheels? Generating electricity through mechanical system and also using a diode circuit to control the dischrging system of the battery? can you help?

    • L Adams February 20, 2017, 12:02 am

      Hi Waqar, most of the DC power sources on inverter generators are designed for a brief trickle charge as a backup, not for continuous running power as it is not regulated. Thanks

  • Mike March 4, 2017, 1:17 am

    I have a 72v 100Ah battery pack with a 30amp charger. Can I charge the battery pack at 400 watt = 1/4 load and be able to charge the whole battery with one Gallon on a 2000w Gen?

  • rajkumar March 30, 2017, 12:49 pm

    I want to charge 12v, 48v batteries from bldc generator inbuilt in electric bike.
    Other than using transformer, which is the suitable method for charging the batteries?

  • Mark CH May 7, 2017, 7:41 am

    Hi,
    I would like to run a 200W 12v motor on an olive picking machine and wonder if there it can be run off the 12v outlet on a genrator rather than having to us a battery?
    If not, what size battery should I be looking for?
    Cheerio,
    Mark

    • Paul Campbell May 8, 2017, 2:19 am

      Thanks very much for the question Mark.

      Your olive picking machine will draw approximately 17Amps /’ Hr.

      The 12 Volt Outlet on the generator will not be powerful enough to provide this much amperage. The 12V outlet on the generator is designed for battery trickle charging only.

      You will need a 12V power supply that produces greater than 200W and can be plugged into the AC outlet of a small inverter generator like a Yamaha 1000W inverter generator

      These products draw about 600W AC, are readily available and range from $150 – $300.

      Feel free to call 1300 400 122 to speak to one of our product experts about this application.

      regards

      Paul

  • Mark CH May 31, 2017, 1:43 am

    Thanks Paul,
    I rang and spoke to someone but he said you don’t carry any transformers with enough grunt for the motor with the ones you have for fridges only going up to 150W. I have seen transformers in Bunnings that are rated up to 400W for outdoor lighting. Would you foresee any issues using one of these? I would imagine it doesn’t matter what the power is used for, just that there is enough? Same as plugging in a lamp into a power point as opposed to a large plasma screen TV?
    Cheerio,
    Mark

    • L Adams June 7, 2017, 7:45 am

      Hi Mark,

      Yes, this will be suitable for your application. As long as the transformer produces enough wattage to power your appliance you will be fine.

      regards,

      Paul

  • Kurt August 3, 2017, 5:53 am

    Hello Folks,
    I wish to run a 1kva inverter generator, not any larger or noisier than that, to power a 12v or 24v proper battery charger. How can I determine the highest wattage charger I should attempt to power?
    Your Enerdrive 60a 12v (720w) unit can be ‘dialled back’ to suit a 1kva generator – this implies a limit between 480w and 720w.
    Important consideration!
    Thanks, Kurt

    • Paul Campbell August 4, 2017, 12:33 am

      Hi Kurt,

      Your exactly right.

      The [Enerdrive ePOWER 12V 60A Battery Charger](http://mygenerator.com.au/media/Enerdrive_ePOWER_Battery_Charger_Manual.pdf) can be dialed down to run from a 1 kva generator.

      When the charger is on full load it will draw 1050W

      regards

      Paul

      • Kurt August 10, 2017, 6:09 pm

        Hi Paul,
        Can that maximum draw of a battery charger be roughly predicted, like this?
        ChargerWattage / (Efficiency x PowerFactor): say… 720 / (.79 x .87) ~= 1050
        Or more likely:
        (ChargerAmps x ChargingVolts) / (Efficiency x PowerFactor): say… (60 x 14.4) / (.92 x .90) ~= 1050
        If so, matching a charger to a generator becomes less risky.
        The dial-down feature of that Enerdrive charger is an asset, especially if mains power is sometimes available.
        Cheers, Kurt

  • Norman October 6, 2017, 5:02 am

    Hi,what size generator would i need to charge a 100ah deep cycle battery ?I have 180w solar panels which do the job but in the advent of bad weather i would like to use a generator with 240v battery charger .Thank you

    • L Adams October 9, 2017, 4:27 am

      Hi Norman, it is important to match the battery charger to the generator. Most battery chargers will draw less than 900W, therefore we would recommend a Yamaha EF1000iS inverer generator, which is the most popular model for purely charging camping/RV batteries – it is very light at 13 kilograms and super quiet. If you need a bit more power, then you would consider the slightly larger Yamaha EF2000iS generator model, which is also a very popular recreational generator. Many thanks.

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