# Best inverter for charging tool batteries



## Lone Crapshooter

What is the best inverter for charging Tool batteries? I want to put in the bed of the Super Duty under the Diamondback. I have been told by a truck upfitter to run the circuit through a contactor and wire the coil of the contactor to ignition power.(They will make the connections to the truck wiring) I am thinking of using 12/3or 4 tray cable.
Thanks for your help.
LC


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## HackWork

For charging batteries you want a pure sine wave inverter. It doesn't have to be very big (they are very expensive in bigger sizes).

I wouldn't use a contactor because you want to be able to use the inverter even when the truck is off. Sure, it will kill the battery if you do it for too long. But you want to be able to run into a store quickly without disturbing the charging.

Some people install a second battery with an isolator so that the inverter will never discharge the battery used for starting the engine, but I personally don't have the need for that.

I use a 600watt pure sine wave inverter to charge all my tool batteries. I have done 4 M12 and 3 18v Dewalt batteries at once with it. I now do 4 M12 and 1 M18 batteries.

I keep all my batteries and the chargers in the passenger compartment of my van for 2 reasons. First, I can warm the batteries up in the Winter with the floor heater. Second, I can rotate them in and out of the chargers while driving. I always have plenty of charged batteries this way.


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## trentonmakes

I just put a 750 watt in the van and wired right too battery. Was going to tap ign source but now you got me second guessing that.






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## splatz

If you want to have your cake and eat it too, you could put an HOA switch on it!


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## HackWork

trentonmakes said:


> I just put a 750 watt in the van and wired right too battery. Was going to tap ign source but now you got me second guessing that.
> 
> 
> 
> 
> 
> 
> Seen As A Tiny Blip From Space


Powering a 750w inverter from the battery is the only way you could do it. If you want it switched by the ignition you need to use a contactor/relay because you aren't going to find any switched source that has 60a+ of free capacity.


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## splatz

Lone Crapshooter said:


> I am thinking of using 12/3or 4 tray cable.


Isn't #12 going to be way too small?


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## Lone Crapshooter

I was thinking of using a 400 watt or smaller. Inverters use to draw 10 times the load current on the input side because of the turns ratio of the transformer used in them.I don't know if that is still the case.


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## HackWork

Lone Crapshooter said:


> I was thinking of using a 400 watt or smaller. Inverters use to draw 10 times the load current on the input side because of the turns ratio of the transformer used in them.I don't know if that is still the case.


There is some inefficiency in an inverter. So if your load is 500 watts, it may use 550 watts of power. At 12v that is 46 amps. At 14.4v when the engine is running, it would be slightly less current.


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## RePhase277

Lone Crapshooter said:


> I was thinking of using a 400 watt or smaller. Inverters use to draw 10 times the load current on the input side because of the turns ratio of the transformer used in them.I don't know if that is still the case.


It isn't even about the turns ratio, it's a matter of thermodynamics. A watt is a watt, no matter what the voltage is, therefore the current must be the changing variable. 1 amp at 120 volts must be at least 10 amps at 12 volts. No way around it.


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## frenchelectrican

If you going to use hardwird sine wave inverter use #6 felixable cable useally a starter cable is most common one you will find them in auto parts store but that is sized for 600 watt inverter but larger one you will have to increase the size of cable to compreised with voltage drop.

Keep in your mind the 12 volts circuits is very senstive with voltage drop so pay attetion to sizeing the conductors.

Normally I useally connected at either battery or starter connection but once a while at the alternator port only if the alternator cable is large but most factory cable useally are little undersized so try to advoid it unless you got one of the big arse 200 amp alternator then tap it there.,,


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## V-Dough

Anything that is pure sine wave should do. As a rule of thumb buy inverter thats twice the size of your expected load. Id recommend samlex or xantrex - these are pretty solid brands or dimensions if you want something very heavy duty. I wouldn't use any wire smaller than #6...


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## HackWork

V-Dough said:


> Anything that is pure sine wave should do. *As a rule of thumb buy inverter thats twice the size of your expected load*. Id recommend samlex or xantrex - these are pretty solid brands or dimensions if you want something very heavy duty. I wouldn't use any wire smaller than #6...


That rule of thumb can get expensive when dealing with PSW inverters. 

I have found that my 600w inverter is easily able to power tool battery chargers with rated current draw adding up to significantly more than 600 watts. 

I'm not saying it's bad to buy bigger if necessary, I just don't want to see someone spend $400-500 more because they think they need it, if they actually don't.


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## telsa

Don't Super Duty's come with double batteries, anyway?

Cummins Ram trucks, do.


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## frenchelectrican

telsa said:


> Don't Super Duty's come with double batteries, anyway?
> 
> Cummins Ram trucks, do.


Not on gas powered super duty trucks but they do have optional for second battery but on diesel verison it always two batteries in there.

Note : If gas unit do come with ambualance package then yes it will come with dual battery as standard feature plus two alternators ( that what I heard )


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## HackWork

2 batteries doesn't automatically mean that one is isolated from the other.


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## frenchelectrican

HackWork said:


> 2 batteries doesn't automatically mean that one is isolated from the other.


Majorty of the time .,, no they dont isolated from each other at all unless you put in the isolater in there but the weak point is the isolater size that you have to sized by the alternator size so if you have 130 amp alternator then you should have isolater rated at least 140 amp or larger. but never smaller but ya can go larger.


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## trentonmakes

Ok
Currently my inverter is connected with #12 thwn wire.
No issues charging batteries or light loads. I tried useing a circular saw and it did run for about 2 seconds, will bigger wire let it run and cut a 2x4?

Should I bump up the wire for safety?
I figured I am only tapping 12, 14 volts max the inverter does the rest.

Its a 750 watt inverter, mainly installed to keep batteries charged while driving but would be nice for other things when there is no power present.















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## splatz

trentonmakes said:


> Ok
> Currently my inverter is connected with #12 thwn wire.
> No issues charging batteries or light loads. I tried useing a circular saw and it did run for about 2 seconds, will bigger wire let it run and cut a 2x4?
> 
> Should I bump up the wire for safety?
> I figured I am only tapping 12, 14 volts max the inverter does the rest.
> 
> Its a 750 watt inverter, mainly installed to keep batteries charged while driving but would be nice for other things when there is no power present.


I'd definitely use bigger wires for safety and less voltage drop. 

I imagine the circular saw will spin but not cut anything unless you go real, real, real slow on 750w - I think they are mostly 10A or more at 120v, in the 1200-1800w range. 

If you calculate the voltage drop on ten feet, you'll want #4 to keep it under 3%.


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## HackWork

Trenton, the voltage doesn't matter when it comes to wire size, the current does. The lower voltage simply means that it's much higher current. Number 12 wire is way too small.


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## trentonmakes

Thats exactly what it did. Lol

We putting up parking lot lights and POCO hadn't hooked up to our panel yet.
I knew it wouldnt work, but what the hell....

I have some scrap 6 wire, I'll switch over to that






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## trentonmakes

HackWork said:


> Trenton, the voltage doesn't matter when it comes to wire size, the current does. The lower voltage simply means that it's much higher current. Number 12 wire is way too small.


Thats what im getting confused about!

Its 12v DC, I didnt think it would draw that much.

Then again I have gotten the chit shocked out of me on a cracked distributor coil before! Lol






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## splatz

trentonmakes said:


> Thats what im getting confused about!
> 
> Its 12v DC, I didnt think it would draw that much.
> 
> Then again I have gotten the chit shocked out of me on a cracked distributor coil before! Lol


The coil and plug wires are at a much higher voltage (there's a coil / winding involved...) 

The same little power takes much more amps and therefore a much bigger wire with DC! It's that whole Tesla / Edison thing.


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## HackWork

Splatz, I thought it was more of an ohms law thing?


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## emtnut

trentonmakes said:


> Ok
> Currently my inverter is connected with #12 thwn wire.
> No issues charging batteries or light loads. I tried useing a circular saw and it did run for about 2 seconds, will bigger wire let it run and cut a 2x4?
> 
> Should I bump up the wire for safety?
> I figured I am only tapping 12, 14 volts max the inverter does the rest.
> 
> Its a 750 watt inverter, mainly installed to keep batteries charged while driving but would be nice for other things when there is no power present.
> 
> 
> 
> Seen As A Tiny Blip From Space


I=P/V
750W @12V is 62Amps and around 50Amps if your vehicle is running (~14.5V)


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## RePhase277

HackWork said:


> Splatz, I thought it was more of an ohms law thing?


Because Edison didn't give a damn about Ohm's Law and was prepared to construct as many smokey DC central stations as it took.


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## HackWork

RePhase277 said:


> Because Edison didn't give a damn about Ohm's Law and was prepared to construct as many smokey DC central stations as it took.


Lol :thumbup:

But what I meant was that I thought the issue with wire size and voltage drop was from the lower voltage, not the fact that it was DC?


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## RePhase277

At the time the best way of making high voltage and stepping up and down was a transformer using AC. But now, there are these DC-DC converters that run at 95% efficiency. High voltage DC is coming. In the not-too-distant future, there will be DC receptacles on the walls of houses.


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## frenchelectrican

trentonmakes said:


> Ok
> Currently my inverter is connected with #12 thwn wire.
> No issues charging batteries or light loads. I tried useing a circular saw and it did run for about 2 seconds, will bigger wire let it run and cut a 2x4?
> 
> Should I bump up the wire for safety?
> I figured I am only tapping 12, 14 volts max the inverter does the rest.
> 
> Its a 750 watt inverter, mainly installed to keep batteries charged while driving but would be nice for other things when there is no power present.


That the excat unit I just have one not too long ago and now you know why you cant run #12 at all ., it ok for super light loads but when you put a saw or drill that will kick it hard .,, 

the 12 - 120 v 750 watts you need #6 is barebone minuim size but being see that distance you are at if you are running near full load often .,, bump up to #4 conductor size 

mine verison is on 24 volt input so I used #8 conductor. and it handle it pretty good.


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## splatz

HackWork said:


> Splatz, I thought it was more of an ohms law thing?


Actually you're right, it's not the AC versus DC it's just the voltage, the ampacity of the wire is more or less the same for AC and DC. It just happens that the AC is the higher voltage in this case. 

Thanks!


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## Jhellwig

trentonmakes said:


> Thats what im getting confused about!
> 
> Its 12v DC, I didnt think it would draw that much.
> 
> Then again I have gotten the chit shocked out of me on a cracked distributor coil before! Lol
> 
> 
> 
> 
> 
> 
> Seen As A Tiny Blip From Space


Are you an electrician?


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## trentonmakes

Jhellwig said:


> Are you an electrician?


Back off jacka$$!

I didnt think it through....shoot me

Im here to learn and grow

I had this inverter for years collecting dust and just wired it up as I had it back then






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## Going_Commando

Jhellwig said:


> trentonmakes said:
> 
> 
> 
> Thats what im getting confused about!
> 
> Its 12v DC, I didnt think it would draw that much.
> 
> Then again I have gotten the chit shocked out of me on a cracked distributor coil before! Lol
> 
> 
> 
> 
> 
> 
> Seen As A Tiny Blip From Space
> 
> 
> 
> Are you an electrician?
Click to expand...

Best electriciantalk reply ever. I miss seeing that all the time. :laughing:

It's an honest mistake, but one that definitely deserves a little ribbing. 

I've been pondering setting up a charging station in the van too. A customer mentioned just putting an inlet in the van and plugging it in at night to charge the batteries, but I can get kind of spacey and feel like i would drive away with it plugged in. I would probably have to do the 2nd battery with an isolator so there isn't a way to kill the start battery.


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## HackWork

Going_Commando said:


> Best electriciantalk reply ever. I miss seeing that all the time. :laughing:
> 
> It's an honest mistake, but one that definitely deserves a little ribbing.
> 
> I've been pondering setting up a charging station in the van too. A customer mentioned just putting an inlet in the van and plugging it in at night to charge the batteries, but I can get kind of spacey and feel like i would drive away with it plugged in. I would probably have to do the 2nd battery with an isolator so there isn't a way to kill the start battery.


They have inlets with an auto eject function. You wire it to a key,switched circuit so it pops out the cord when you start the vehicle. Ambulances and other service vehicles use this inlet. Or you could just wrap the cord around the driver's mirror the old fashioned way.

I was in your same position, thinking about installing "shore power" wiring or second batteries. But in the end all I needed was the inverter and a bunch of chargers. I charge the batteries on the commute to and from jobs as needed. 

As I mentioned, keeping the chargers and batteries in the passenger compartment makes it easy to rotate them in and out of the chargers.


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## Jhellwig

trentonmakes said:


> Back off jacka$$!
> 
> I didnt think it through....shoot me
> 
> Im here to learn and grow
> 
> I had this inverter for years collecting dust and just wired it up as I had it back then
> 
> 
> 
> 
> 
> 
> Seen As A Tiny Blip From Space


There are no dumb questions, just dumb people.


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## trentonmakes

frenchelectrican said:


> That the excat unit I just have one not too long ago and now you know why you cant run #12 at all ., it ok for super light loads but when you put a saw or drill that will kick it hard .,,
> 
> the 12 - 120 v 750 watts you need #6 is barebone minuim size but being see that distance you are at if you are running near full load often .,, bump up to #4 conductor size
> 
> mine verison is on 24 volt input so I used #8 conductor. and it handle it pretty good.


Its just too charge batteries on the ride too and from jobsites. The 20amp inline fuse never blew and will protect the wire from overheating.

Thats just how I've had it years ago in another vehicle. Never had an issue with it.

I'll be switching it out to #6 or 4 too handle heavier loads soon, but I'd be surprised even then if it will handle a saw.






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## drspec

If its just for charging batteries, why not just buy the charger that plugs into a 12v outlet?


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## HackWork

drspec said:


> If its just for charging batteries, why not just buy the charger that plugs into a 12v outlet?


I believe the answer is that most of us already have many 120V chargers since they come with many of the tool packages.

But if you are going to be buying chargers, the 12V ones are more efficient (ie. less total drain on the battery) than using an inverter and a 120V charger.


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## oliquir

the ampacity of wiring into a car is not the same as raceway, a 12awg can easily support 40amp, here some chart i found
https://www.tessco.com/yts/industry/products/itm/automotive/get_wired.html

most of the time the free air rating apply


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## drspec

My point is if you're just going to be using it for charging batteries while driving then it's cheaper and easier to get the 12v charger for your batteries.

Now if you plan on using power tools, lights, etc then an inverter would be the way to go.


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## HackWork

oliquir said:


> the ampacity of wiring into a car is not the same as raceway, a 12awg can easily support 40amp, here some chart i found
> https://www.tessco.com/yts/industry/products/itm/automotive/get_wired.html
> 
> most of the time the free air rating apply


I don't know if you want to go by the free-air rating when that wire is sandwiched into tight places with plastic and carpet, etc. Nevermind the temperature of the vehicle in the Summer.

Plus, you haven't taken into account the voltage drop, which becomes a big issue on #12 wire at 40A.

For car wiring, using the basic NEC ampacities is a good baseline.


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## HackWork

drspec said:


> My point is if you're just going to be using it for charging batteries while driving then it's cheaper and easier to get the 12v charger for your batteries.
> 
> Now if you plan on using power tools, lights, etc then an inverter would be the way to go.


I understand your point, and gave the reasoning why I personally don't do it and I think others as well: Because we already have many 120V chargers.

I can use an inverter and use all 8 of my 120V chargers at once. How much would it cost to buy 8 12V chargers?


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## telsa

HackWork said:


> I understand your point, and gave the reasoning why I personally don't do it and I think others as well: Because we already have many 120V chargers.
> 
> I can use an inverter and use all 8 of my 120V chargers at once. How much would it cost to buy 8 12V chargers?


Makita, Milwaukee, DeWalt,... et. al. have CUSTOM chargers for custom power packs.

They are ALL set up for 120 VAC.


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## frenchelectrican

HackWork said:


> I understand your point, and gave the reasoning why I personally don't do it and I think others as well: Because we already have many 120V chargers.
> 
> I can use an inverter and use all 8 of my 120V chargers at once. How much would it cost to buy 8 12V chargers?


Hackwork did make a very good point there about the 120 volt charger .,, 


It more encomal to use all those 120 volt charger what we get them in the tools so it make sense with it.,

Plus with 120 volt charger I do noted that it charge alot faster with 120 volt charger than standard 12 volt charger plus it cost more money to buy 12 volt charger and throw it in the mix..

I have mixed bag of 120 volt , 240 volt chargers plus couple 12/24 volts charger ( I dont use those lv charger often at all )


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## drspec

HackWork said:


> I understand your point, and gave the reasoning why I personally don't do it and I think others as well: Because we already have many 120V chargers.
> 
> I can use an inverter and use all 8 of my 120V chargers at once. How much would it cost to buy 8 12V chargers?


personally I have the 6 pack charger for Milwaukee and toss several batteries on it when I get to the job

Havent had the need to charge batteries on the go in a long while


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## Jhellwig

You would think with as mobile as everyone is and as popular are battery tools are there would be better chargers to use in vehicles but there isn't. The ones they do make are slow since they make them plug in through a cigaret lighter outlet. That really limits the charge rate.


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## Lone Crapshooter

Just looked at a friend's 2017 F250 Super Duty it is better tricked out than my Amish pickup it does have a 400 watt inverter built in.
I bought a 200 watt Wagon Pure Sine Wave inverter. Going to feed it a 80 amp automotive contactor with the coil powered from a ignition powered and the circuit will be 10/3 XHHW tray
cable . The inverter has a 25 amp built in fuse.


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## HackWork

drspec said:


> personally I have the 6 pack charger for Milwaukee and toss several batteries on it when I get to the job
> 
> Havent had the need to charge batteries on the go in a long while


I hear you.

That's cool if you are going to be on the job for a while, or you park the truck near the house and have an outdoor outlet.

But I often found myself having to make a special trip during a smaller job from the truck to the house to carry the batteries and chargers in, then back out. My goal is to make things as easy as possible with the least amount of trips, so charging in the truck works out well. I can have all of my batteries 100% charged when I need them, without having to spend time dealing with them.


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## HackWork

Jhellwig said:


> You would think with as mobile as everyone is and as popular are battery tools are there would be better chargers to use in vehicles but there isn't. The ones they do make are slow since they make them plug in through a cigaret lighter outlet. That really limits the charge rate.


I did not know that, glad you mentioned it. That's even more of a reason to use 120V chargers with an inverter.


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## elecwired

Originally Posted by trentonmakes View Post
Ok
Currently my inverter is connected with #12 thwn wire.
No issues charging batteries or light loads. I tried useing a circular saw and it did run for about 2 seconds, will bigger wire let it run and cut a 2x4?

trentonmakes 

I ran across this post and am concerned deeply that you are not getting what you are attempting to do with your inverter. First off a 12 volt 750 watt modified inverter will never run a circular saw. The proof comes with wattage/voltage=amperage 750/120=6.25. Meaning that your inverter will only pull 6.25 AC amps at full load before something trips as you described. Most circular saws draw more amperage than that to operate. And also any motor will always take more voltage at startup. On the DC side 750/12=62.5 required to run at full load. This is where the 2nd battery comes into play but the 2nd battery should be a AH (amp hour) not a auto CCA (cold cranking amp) the reason is the AH battery has larger plates inside versus the CCA. Personally I would ditch the toy inverter that you have now and go with a Pure Sine Wave inverter that is capable of running your circular saw or any other large wattage load that you may want to throw at it. A larger inverter will allow you to install an AC circurit breaker panel inside the auto to control AC loads like dedicated 120 volt AC outlets, lights,ect. Square D QO supplies will tackle that issue safely, efficient and reliable. As for charging the 2nd battery it can be done with solar panel power, small gas generator or leaving the auto running.


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## trentonmakes

Modified, toy inverter?

The main reason for useing this was to charge batteries while driving. I never had any issues accomplishing this with my toy inverter.

I tried useing the saw, more out of curiosity knowing it likely would not work as we did not have our generator on site.

Thanks for your concern, but ill keep my jerry rigged toy of an inverter and have my batteries gully charged.

Texting and Driving


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## HackWork

elecwired said:


> Personally I would ditch the toy inverter that you have now and go with a Pure Sine Wave inverter that is capable of running your circular saw or any other large wattage load that you may want to throw at it.


I disagree with this. A large pure sine wave inverter is extremely expensive and unnecessary. 

It's much more cost effective to buy a small, good quality PSW inverter for the things you need it for, such as battery charging. As I mentioned earlier, 600w is plenty for me to charge all my batteries.

Then buy a larger 2,000w+ MSW inverter for things like power tools. 

There is a huge cost difference.


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## MechanicalDVR

HackWork said:


> I disagree with this. A large pure sine wave inverter is extremely expensive and unnecessary.
> 
> It's much more cost effective to buy a small, good quality PSW inverter for the things you need it for, such as battery charging. As I mentioned earlier, 600w is plenty for me to charge all my batteries.
> 
> Then buy a larger 2,000w+ MSW inverter for things like power tools.
> 
> There is a huge cost difference.


I have a toy inverter from Bed Bath an Beyond that charges my batteries just fine, not bad for $14.


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## HackWork

MechanicalDVR said:


> I have a toy inverter from Bed Bath an Beyond that charges my batteries just fine, not bad for $14.


 Some modified sine wave inverters will work with tool battery chargers. But I have read that they have ruined many people's batteries. So if you're going to do it a lot, I would look for a low-wattage pure sine wave inverter to use, which could be found for a really good price.


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## MechanicalDVR

HackWork said:


> Some modified sine wave inverters will work with tool battery chargers. But I have read that they have ruined many people's batteries. So if you're going to do it a lot, I would look for a low-wattage pure sine wave inverter to use, which could be found for a really good price.


I've been using it to charge M12 batteries for a long while now without any bad results I wouldn't use it for M18s but I appreciate the advice.


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