12V Cordless Tool Recharging

[rpmhart333]

Giving the choice between searching one of those out (which would require, like, excess Thought...not my strong point) and buying a charger, here's my debit card, Mr. Nearby Toolman. Don't wrap it up. I'll eat it here.
Many thanks.

 

[rruff]

Just wondering...does anyone know if there's a way to charge 12V cordless tools (circ saw & drill) directly from the 12V RV system, or does it have to go through an inverter to the charger and be converted back again?

All right...many thanks to you all...but let's go a little further here if I may. As someone whose knowledge of electricity is basically "ow. that hurt. I'm going to lay here on the floor for a bit until that tingling feeling goes away and I don't feel like barfing anymore," my question was based on simplicity of moving electrons. I figured (okay, you're right, Guessed) that going straight to the battery to do the charging was less drain on it than going through an inverter to do the same thing. Michael Faraday I ain't, obviously. Does the inverter cause any drain in the equation?

I'm frankly surprised at how many people are recommending dc-ac-dc conversion*. It's completely useless and probably wastes 20+% of the energy... maybe a lot more since they will be inefficient at low power levels. If the ac adapter for the device says "12v" output or near that, then charging it directly from your 12v main battery bank should be absolutely fine. Buy a plug with the same specs and wire it up.

EDIT: Maybe that's because most chargers have ac input, not dc... I was referring to models where the conversion from ac-dc happens before it gets to the charger... separate "brick" like a laptop.

 

[Freelander]

The problem I see is not everybody is comfortable with doing wiring. And how many of these chargers are you going to have to build?

I use my 300 watt inverter to run my printer and charge at least 4 cordless items, some of these have special plugs, and some of these use brick power adapters. The amount of time that the inverter is running is very small. I charge my cordless drill maybe once every 2 months, and I run my printer maybe once a month for a few minutes, and both electric razors I charge very rarely. To me it's a waste of time to spend money on modifying a bunch of chargers just to save a fews watts of power. If your power needs are that critical, then you probably need to by more panels or another battery.

And sometimes these chargers have the circuit built in so that you don't overcharge the batteries and risk blowing them up. For me if you can find a 12v charger go for it, but don't built or modify one with out knowing all the details first.

 

[maki2]

I travel with a couple of 18V makita tools and the charger for them. As I stated I power the charger with a small inverter plugged into a 15amp rated 12v socket. The AC charger input at 120v is 65 watts. its output 7.2v- 18v at 2.6 amps.

A 100 watt inverter will do just fine, the kind that go into a 12v accessory socket, is a sufficient size to pair with the Makita charger.

 

[AmargosaWayne]

The Ryobi and Makita tool batteries are 18V. A homemade 12V charger won't work to charge a 18V battery.

 

[abnorm]

I have 7 Dewalt 20V batteries that I cycle thru a single 120V REcharger powered by a PSW inverter/leadacid/solar

 

[Calaverasgrande]

There is a going to be an efficiency loss going through an inverter. You are converting DC into some form of AC (sinusoidal, square wave or modified sine which is really better called modified square) then converting back to DC.
At each conversion step there is energy lost as heat due to inefficiencies of voltage conversion.
This has improved over the years with switching power supplies and LSI power converters.
But you still lose energy as heat and magnetic fields. A good inverter is at best 85% efficient. Likewise, most of our tool chargers are only 70-80% efficient at best. Cheaper brands like Ryobi and Craftsman are probably going to cheap out on the charger's parts as well. So less efficient.

I'm currently working on making regulated power adapters for my portable music gear that runs off DC. I've a lot of devices that are 9V and 12V DC.
So basically I just need to make little boards with a couple capacitors and a voltage regulator.
Our 12v batteries actually output 13.4-14.6 volts, so it is no big deal to VR down to 12V. But just to be safe I'm using low loss voltage regulators. Normal ones will drop 1.5 volts or so. Low loss parts only lose about half a volt.
So yes it is certainly possible to directly use the 12V from AGM or LiFePo4 battery banks.
It seems the tough part is getting a battery dock for your particular family of cordless tools.
I keep hoping I will trip over one at a yard sale. Otherwise I'm paying $50 for a plain battery dock. Cutting it open and gutting it just to be able to save 20 lost watts or so.

 

[rpmhart333]

Wow. This thread has gotten amazing, and I'm not being sarcastic in any way. Can't believe what I seem to havestarted with a simple (first ever) question.
Am almost afraid to ask any other. But I thank all of you. As my father would have said...You're the aces.

 

[maki2]

The current, commercial, battery chargers for the lithium powered tools don't just do an on and off simple routine. They are "smart" with engineering and circuitry beyond the on and off function.

 

[Tom_M]

I'm currently working on making regulated power adapters for my portable music gear that runs off DC. I've a lot of devices that are 9V and 12V DC.
So basically I just need to make little boards with a couple capacitors and a voltage regulator.

The typical voltage regulator is a linear device and the most inefficient approach. For instance, if you need 9 volts at 5 amps you would be consuming 60 watts from the 12 volt source to generate 45 watts for the 9 volt device. The excess 15 watts is dissipated in heat.

You would be much better off using a DC-to-DC converter which converts DC to high frequency AC then rectifies and filters that back to DC. Here's an example of the type available on Amazon:

https://www.amazon.com/HiLetgo-Lith...efix=dc-to-dc+converter+5+amp,aps,421&sr=8-42

 

[Calaverasgrande]

The typical voltage regulator is a linear device and the most inefficient approach. For instance, if you need 9 volts at 5 amps you would be consuming 60 watts from the 12 volt source to generate 45 watts for the 9 volt device. The excess 15 watts is dissipated in heat.

You would be much better off using a DC-to-DC converter which converts DC to high frequency AC then rectifies and filters that back to DC. Here's an example of the type available on Amazon:

https://www.amazon.com/HiLetgo-Lithium-Battery-Charging-Converter/dp/B01EQT63SS/ref=sr_1_42?crid=SGDQU7HE5LWB&keywords=dc-to-dc+converter+5+amp&qid=1648034736&sprefix=dc-to-dc+converter+5+amp,aps,421&sr=8-42

I looked into those, but on the audio electronics message board I frequent all the old guys warned me off.
I'm powering guitar pedals and drum machines that draw less than an amp. So the inefficiency isn't significant.
Certainly not enough to get me into switchmode power devices and the whole debate over whether the HF carrier is sufficiently filtered.
Also there are low loss linear regulators, and they are much cheaper than DC DC converters.

 

[Tom_M]

I looked into those, but on the audio electronics message board I frequent all the old guys warned me off.
I'm powering guitar pedals and drum machines that draw less than an amp. So the inefficiency isn't significant.
Certainly not enough to get me into switchmode power devices and the whole debate over whether the HF carrier is sufficiently filtered.
Also there are low loss linear regulators, and they are much cheaper than DC DC converters.

Your use is a good example where a linear regulator is best, but when higher current is required or when the output voltage needs to be higher than the input voltage the only option is a DC-to-DC converter. Here's a link to an article that explains the differences:
https://www.renesas.com/us/en/products/power-power-management/linear-vs-switching-regulators

 

[jpat1773]

Dewalt has a 12V charger.