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Charging power tool batteries direct from solar 12v system.

 
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I have a cabin powered by a 12v solar system.

In order to change my power tool batteries I need to convert the power to 120v ac to plug in the charger.

The power supply for the charger is 120v ac in and 18 v dc out.

I would like to convert my 12v dc to 18v dc to power the charger without the need to convert to ac.

Any recommendations for the right component to perform the power conversion from 12v to 18v dc.

Trying to keep as simple as possible and don't want to do anything that would harm the batteries.

 
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You'll need a DC Step up converter to make that swap, and you'll have to intercept the line of your charger post inverter. If you have a box looking object at the plug end(inverter), then you can intercept the wires coming out of it, but most chargers now days have the inverter inside the body of the charging block, and you'll need to take it apart to access the wires downstream of the inverter. Be sure to check rated amperages and wire inline the appropriate fuses to protect your charger/batteries. You can get the step up converters on amazon for a reasonable price, or you can go back to 1990 and walk into any radio shack in the country. Best of luck and keep us updated on how things turn out.
 
Rusty Ford
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Also, it's important to not bypass the electrical board inside your charger. It reads the batteries and stops applying voltage at the appropriate time. I'm sure you know this, but I couldn't just leave it out here without saying it.
 
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Christopher Shepherd built a system like that a few years ago

I made one to charge dewalt and ryobi batteries 20v and 18v lithiums. .  I have found 100w is not enough in Ohio.  The 12volt chargers I am using pull 6 solid amps at 13 volts.  I used 2 x 100 watt panels, a 5 farad capacitor "battery" and a 30 amp mppt controller.  It works great.  I wired the panels in series so this gives it about 40 volts open circuit.  This seems to work well on the half cloudy days.  Your old battery will be fine as long as you have enough solar coming in to maintain 6 amps at 13v.  Good luck and happy experimenting.



He made a Youtube video of his system in action.
 
pollinator
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The quickest method is certainly to buy a 12V car charger for your particular brand of power tools, if available. Some brands have one that handles 12-24V nominal input, others only 12v.. and some brands may have nothing to offer.

As others have noted you don't want a 12V to 18V power converter, you want a charger that is correctly set up for your batteries...
 
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D Nikolls wrote:The quickest method is certainly to buy a 12V car charger for your particular brand of power tools, if available.


I agree 100%. Battery packs are expensive and vulnerable to damage. In a couple of minutes I was able to track down name-brand DC-powered chargers for Makita, Dewalt, Milwaukee and Ryobi. These would be more efficient (less conversion loss) than a 120V wall charger plugged into a pure sine wave inverter (which would work fine otherwise).
 
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D Nikolls wrote:The quickest method is certainly to buy a 12V car charger for your particular brand of power tools, if available. Some brands have one that handles 12-24V nominal input, others only 12v.. and some brands may have nothing to offer.



This is how I charge all my laptops, phones, hotspots and lights - dedicated car charges that can accept 24V - the voltage of my panels.
By talking about it (here, in reviews, everywhere) and supporting only the brands that have an option to use 12/24V eventually the other brands will catch up. I think it should be a standard - option for direct 12/24 VDC charging for all devices that use batteries.
 
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Douglas Alpenstock wrote:

D Nikolls wrote:The quickest method is certainly to buy a 12V car charger for your particular brand of power tools, if available.


I agree 100%. Battery packs are expensive and vulnerable to damage. In a couple of minutes I was able to track down name-brand DC-powered chargers for Makita, Dewalt, Milwaukee and Ryobi. These would be more efficient (less conversion loss) than a 120V wall charger plugged into a pure sine wave inverter (which would work fine otherwise).



If you can find one for Makitas cxt range, I will be eternally grateful.

It's probably quite difficult build a 12v charger for batteries with a nominal voltage of 10.8v and a full charge of about 12.6v. You'll need to switch from buck to boost part way through the cycle and I don't know if that's in the constant current or constant voltage phase.
 
Tom Brookens
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Thanks for all the responses.

I have mostly ridgid tools, so is for a rdgid charger.

The interested.

20250131_135112.jpg
[Thumbnail for 20250131_135112.jpg]
 
Tom Brookens
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So the photo in last post is the plug side box indicates to me the power conversion from ac to 18 v dc is complete before the charger and internal electronics.

So I just need to source a step up dc to dc charger.

Knowledge gained from responses also led me to the following:

https://youtu.be/idpWmOmBtRY?si=k90RT-pP4hgVCamY

Looks like  parts available for around $20

Thanks


 
Douglas Alpenstock
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You may be able to buy prebuilt circuits on Amazon.

Checking the no-load voltage of the wall wart would also be useful (probably higher than 18V).

It's hard to know if the charger/battery electronics will work properly in an undervolt situation. To avoid that, I suggest overbuilding the DC-DC converter by a good margin, rated for a continuous output of 4-5 A and 20 VDC.
 
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not to set anyone on a dangerous path of spontaneous combustion, but a solar panel that is nominally 12V may well have a substantially higher <Voc> (open circuit voltage) - perhaps as high as 30V. It is designed to work with 12V batteries, but solar panels are pretty much constant current devices - that is, as long as they are in full sun they will deliver a pretty much constant current over a broad range of voltage. The current will drop as you approach Voc, but it does not keep rising as the voltage drops, which is why the panel can be connected to a 12V battery but also have such a high <Voc>. It is not constant wattage.

a 12V solar panel may well be able to directly charge an 18V tool battery by a direct connection. Check it out with a multi-meter.
 
Tom Brookens
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Douglas Alpenstock wrote:You may be able to buy prebuilt circuits on Amazon.

Checking the no-load voltage of the wall wart would also be useful (probably higher than 18V).

It's hard to know if the charger/battery electronics will work properly in an undervolt situation. To avoid that, I suggest overbuilding the DC-DC converter by a good margin, rated for a continuous output of 4-5 A and 20 VDC.



Thanks for this, I will definitely test the wall wart and make sure the components I purchase are overbuilt.
 
Douglas Alpenstock
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Cade Johnson wrote:a 12V solar panel may well be able to directly charge an 18V tool battery by a direct connection.


I hear what you're saying, but unfortunately it's not that straightforward. Lithium batt packs require highly controlled charging that varies through the charging profile. I don't think this can be improvised easily; and battery packs are not cheap.

OTOH simple 18650 cells (or ganged, paired cells) can definitely be charged directly off a 12V 15W panel. I've been doing that for ages, and it's perfect for portable LED lights. I pull the cells from old laptop batteries; most of them are good! But monitor closely -- if you don't pull them off at 4.20V they will pop and then they're dead forever. Old Samsung cells are tough; Japanese cells are delicate; who knows what the current crop looks like.
 
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Hi Tom.  I have an idea that may be worth considering.

Like you, I also have Ridgid tools, and I get frustrated that they lack some basic components like a car 12/24 volt charger.  If you want to try charging with a solar panel and some type of home made charging system (which I totally support for all the reasons you have already mentioned!), perhaps you might want to test it on batteries other than the expensive Ridgid brand batteries.

A couple of summers ago I bought a pair of 3rd party Ridgid compatible 6 AH 18v batteries for about $50 on Amazon.  Typically, a single 4 AH battery was running $100, so getting a total of 12 AH for half the price was pretty amazing.  I use these batteries every single day and they work great.  Maybe these would be the better test items as they work fine but are a fraction of the cost.

And for the record, I now mostly buy spare battery packs from 3rd party vendors and save a bundle!

Just a thought,

Eric
 
Eric Hanson
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Tom,

Ok, you got my mind stuck on this project and I can’t easily get out—therefore I looked a little further and found something that you might find interesting.

Turns out that Ridgid DOES make a car charger for their 18v lithium batteries, but it is not a part of their regular lineup.  And the charger will set you back $175 for a single, no-frills, ordinary charger aside from being able to charge directly from a car/truck.

This still might be ideal and even a bargain as you won’t have to build your own, dedicated lithium battery charger with all of lithium’s quirks.  If this were my project (and it might be a future project as I have something similar in w), I might go this route for simplicity’s sake.  The only downside would be that I wouldn’t be building my own contraption from scratch, which I like to do, but it does get very complex and time consuming.

Either way, I thought that this might be useful.  If you need a link, just ask.

Eric
 
Tom Brookens
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A link to the car charger option would be useful, I have not found a model for ridgid tools in my search.

Thanks in advance
 
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Douglas Alpenstock wrote:......In a couple of minutes I was able to track down name-brand DC-powered chargers for Makita, Dewalt, Milwaukee and Ryobi. These would be more efficient (less conversion loss) than a 120V wall charger plugged into a pure sine wave inverter (which would work fine otherwise).



A quickie along the lines of Tom's last entry..... I could find knock-offs for 12VDC->20VDC chargers for Dewalt, but is there a Dewalt-branded charger with this capability?  If you come across it, could you please send a link?  Again, just for the 20V-size battery.  Much thanks in advance!......
 
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Dewalt used to make one for the 18v batteries, but most current generation chargers pull more than 120 watts, the limit for a cig plug.

The newest Milwaukee and hilti chargers will pull 1500 watts.
 
Eric Hanson
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Hi Tom,

I should have posted the links long ago, but I was on my phone and not in an easy position to get the link in the post.  Of course, after I got a chance to include the link from an actual computer, my mind had long since wandered on to some other topic.  At any rate, here is a link to the charger that I found on Amazon:

https://www.amazon.com/RIDGID-64383-18V-Advanced-Lithium-Battery/dp/B0B1BWN84T?source=ps-sl-shoppingads-lpcontext&ref_=fplfs&psc=1&smid=ATVPDKIKX0DER&gQT=1

I will be up front and honest, I have no idea why this particular charger is almost $200.  This seems like a small fortune compared to other chargers.  Nonetheless, in the right circumstances, maybe it is worth the price?  This will have to be a judgement call that each one makes on their own.  That said, if we are talking about trying to connect direct to a solar system without having to step up the voltage just to step it right down again, I know that I would spend much, much more if I was trying to build a similar component from scratch based on components purchased through Amazon.  I did look into this at one point and I was shocked at how complex the build became and how quickly the bill tallied up.  

Maybe some possibilities,

Eric
 
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I have been down this path with my dewalt battery systems.
I found that I did not have the time to build a custom battery charging station.
Time saver, not money saver- buy a dedicated solar generator (basically a big battery with solar panels for recharge, plus the ability to recharge with a plug or gas generator) and charge the tool batteries from that.
I am building a gasifier this year to run a generator off the gaseous product of destructive distillation of green woody shrubs, primarily for off grid charging of my battery packs.

Please keep us informed and best of luck.


 
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