# OK to use generator to recharge power-tool batteries?



## Off-Grid2009 (Nov 5, 2010)

When it comes to electricity, I am pretty much your basic moron. :confused1:

At my off-grid property I have a couple of portable generators (800w & 4000w) which I use to run my more powerful tools (circular saw, planer, sander), but I use my cordless drills and impact driver a LOT. ...Seems like I read that I should NOT use a generator to charge the drills' batteries, but instead I should use standard AC current from a wall-socket. Based on that recollection, I've never used my generators to charge the 18v & 19.2v batteries, I've been driving them 10 miles to a friend's house to recharge them. ...But now I'm wondering why?

I realize that neither of my generators is putting out a perfectly groomed current, but I think the output of the little Honda is pretty flat and consistent. The inverter on the generator converts the 12V DC to 110 or 115V AC, and I think that should be 'clean' enough to feed the battery chargers. That would sure make my life easier.

Does anyone know of a good reason I *shouldn't* use the generator to recharge cordless batteries? :huh:


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## mpoulton (Jul 23, 2009)

Off-Grid2009 said:


> Does anyone know of a good reason I *shouldn't* use the generator to recharge cordless batteries? :huh:


Nope, that should work fine. Every contractor on earth does it. There's no technical reason not to.


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## Off-Grid2009 (Nov 5, 2010)

*Thank you!*



mpoulton said:


> Nope, that should work fine. Every contractor on earth does it. There's no technical reason not to.


To MPoulton -- I really appreciate the fast answer, and I am super happy that the answer is the one I wanted to hear. :thumbsup:

Thanks again!


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## frenchelectrican (Apr 12, 2006)

The issue with some of the generator they do make very dirty power source which it mean like sine wave like normal power company supply which they are very clean.

some of the generators make really dirty power it can affect the electriconic stuff like battery charger which they use electronic stuff to regluated the battery charger etc and it can affect some computer if the power supply can not take the dirty power input at all.

Most small to med size generators the voltage regualtion is not really tight at all when they run unloaded or light loaded the voltage will be on high side { useally at 125 to 130 volts } and the HZ will be a bit higher as well so that why some of the electronic will not take any power if out of the scope or torance.

The sine wave or a true sine inverter generator tyically little more expensive but very clean power source { a clean sine waves without any peaking or damaging surge voltage }

Hope that help you on that one.

Merci,
Marc


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## Off-Grid2009 (Nov 5, 2010)

*Thanks...I think (?)*

To FrenchElectrician,

Marc, your English is a lot better than my French [il faut que je pratique mon français...or should I say "Je dois pratiquer mon français" (?)...it's been a long time, and I was never terribly fluent]. I applaud your efforts to help folks using a second language.

But your answer leaves me wondering...can I use the small Honda generator to charge my tools' batteries or not?

MPoulton says contractors do it all the time. Your response seems to say it is a bad idea unless I have a quality inverter that puts out current with a clean sine wave.

Obviously, the little Honda 800 doesn't have a real oscilloscope to show the sine wave of the electrical signal, but there is a dumbed-down version of a "sort-of" oscilloscope, a guage that either shows a fairly stable vertical light signal in the center of the guage when the motor is idling or operating smoothly with a light load, or a wildly fluctuating signal when the generator is first started, or when there is a sudden load placed on it (e.g., pull the trigger on my circular saw).

I figure that as long as I plug in the battery chargers only when that signal is steady, I should get a reasonably "clean" output from the generator, which shouldn't harm the simple electronics in the chargers. At least, that's what I hope. Does that sound like a reasonable plan?

In any case, I thank you for your input...it reminds me very much of the warning I once read, the warning that has caused me to avoid using generators to charge these batteries.

Jim
"OffGrid2009"


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## frenchelectrican (Apr 12, 2006)

Bonjour Offgrid.,

Speaking of Honda generators as far I know genrally they are pretty clean units { on electrique side } so therefore I don't think you will have any major issue with them.

For other brand names it kinda a toss up depending on the design of the generator itself.

And of course the generator will surge a bit when you put a load on suddenaly like your circulaur saw or motour loads it will drop a bit then get back up to the speed that is pretty common for most small to mid size generators { Diesel genrally the best with load regulations but they cost more to buy it new but can justifed with fuel cost when you run half load majorty of the time }

I have two diesel generator in my shop in Wisconsin one at 5 KW and other one at 20 KW { Ouias I have larger one as well that is on trailer mounted that is 75 KW } both engine are very slow speed type so the load will not affect them at all. { both run at 600 RPM } 

Je ne peux parler en français sans aucun problème du tout { I can speak in French without any problem at all }

Merci,
Marc


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## Off-Grid2009 (Nov 5, 2010)

*What I needed to hear!*

OK, then. When I need to charge the drill batteries I'll use the small Honda generator, wait until the engine is running smooth, and charge one or two batteries without any other load on the generator, should be no problems. 90 minutes will give me a 75% charge. That little generator just sips gas, and I will save a ton of time NOT driving back and forth to my buddy's house to charge batteries.

Thanks, Marc, and thanks again to you, too, MPoulter.

Jim


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## joed (Mar 13, 2005)

The charger converts to DC there should be no issues using 'dirty power' on a battery charger.


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## frenchelectrican (Apr 12, 2006)

joed said:


> The charger converts to DC there should be no issues using 'dirty power' on a battery charger.


Joed.,

I am aware with charger that converted to DC supply however the standard automotive charger that do not bother much at all but as for cordless tools battery charger some of them are pretty picky on power supply to charge the battery up.

The last cordless battery charger I have did went up in the smoke due bad generator power supply { it was cranking near 280 volts.,, Keep in your mind we have normal 240 volt L-N supply } and fix the generator but ditch the battery charger that cost me over 60 Euros!

Merci,
Marc


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