AC adapter for cordless power tools?

[ahofle]

On occasion, I would like to be able to use some of my cordless power tools via wall power instead of a battery.  Has anyone heard of/found/built an AC adapter for power tools such as the Craftsman 19.2V C3 series, Bosch 18V, etc?  I can't find a single mention of it anywhere.  Seems dumb that tool makers don't offer something like that as an accessory.  I was thinking of hacking apart one of my dead NiCd batteries, removing the little C batteries inside it, buying a switchable AC adapter, and soldering the connections to where the battery pack connects to the tool.  Problem is, I'm not too sure how close I need to be on the voltage and current.  Most battery packs are measured in mAH while the wall warts are just mA (or wattage).  If my battery provides 2000mAH, would a 20V 2000mA wall wart, work?  Or here's a rather expensive switchable laptop charger which seems to go up to 4.5A:
http://www.newegg.com/Product/Product.aspx?Item=N82E16842207001

Any suggestions?

[HaRuMaN]

Buy corded tools.

[MaineEvent]

This reminds me of something I was thinking about the other day...
I am sick of walking to work...it takes me about an hour to get there, and if there is bad weather obviously longer. If there was some way I could get there faster it would really save me time and energy. Obviously teleportation is kind of ridiculous, an a horse is out of the question for my living space....but maybe some kind of vestibule that doesn't require human powered energy to operate. Something that could traverse all kinds of pathways, something that would keep me safe from the elements and if I could park it in a lot for $25 a day that would be swell too!

Sorry man...but seriously...REALLY?

[ahofle]

Is this really that difficult for you to grasp?  Here, maybe this analogy will help you understand:

- You own a laptop which runs off a battery.
- You plan on operating the laptop for more time than the battery will supply.
- There is a wall socket nearby.

Your ingenious solution is to buy a desktop instead of plugging the laptop into the wall using an AC adapter?  

[drventure]

I've wondered the same thing for a while now. I did some searching at one point but never turned up anything.

I'd prefer to just have cordless, but dang near every time I need a drill, etc, the battery's dead. For many, i could see this being as much a space issue as a cost issue.

Yeah, i could buy piles of batteries and chargers, but then they might sit for several months on occasion, and those batteries do not have a great shelf life.

Anyway, i'd love to see something like that too.

[gryhnd]

I wonder if you could follow this instructable using this power supply (assuming 18V).

[ahofle]

Thanks, that looks like a good start.  Although he is using a really crappy walwart and leaving the NiCd cells in the battery (I want to get rid of those completely and just have an AC adapter).  It sounds like I just need to determine the maximum current draw of the tools and get an adapter that supports at least as much. 

drventure: I'll update this post when I get it sorted out.

[Kevin Mullins]

Thanks, that looks like a good start.  Although he is using a really crappy walwart and leaving the NiCd cells in the battery (I want to get rid of those completely and just have an AC adapter). 

Yeah, that guy in the instructable was just "charging" his battery as he used it..... that's why gryhnd pointed out that other power supply to use instead and gut your batteries.

[gryhnd]

bingo.

BTW, I use a 12V version of what this looks like a twin of to power an automobile audio amp (60W x 4) which drive bass transducers in my home theater. They are pretty inexpensive. The eBay listings are direct from China...mine did come from a US vendor fwiw, for about the same price.

[ahofle]

Gotcha.  I actually need 19.2 volt but that one would work perfectly for my dad's dead 18V battery.  Looks like that site has an adjustable one that goes up over 20V: http://www.powerstream.com/AC-A0407.htm
That's still about half the price of a new 19.2V Lithium ion battery.  
It says it's rated at 4.5 amps at ~20 volts.  If the tools draw between 2 and 3 amps, that would be OK right (ie. it would only draw what it needs)?
I guess that's my main concern.  I don't want to overpower anything.

[gryhnd]

I don't want to overpower anything.

You can't "overpower". The tool (or any item for that matter) will only use what it needs. The bad thing is to under power it.

For example, your computer only uses a couple hundred to a few hundred watts. Yet your typical 15amp circuit can provide around 1700 watts

[drventure]

I wonder if the guts of that PS are small enough to fit inside a battery housing? That'd be the ideal solution. A battery housing with an AC cord coming out of it that, when you need to, you can just slap into whatever tool you need and go.

[Ed_McCarron]

Key thing here - cordless tools depend on 100's of amps being available for short bursts - which is why the NiCd and MiMH cells have dominated for so long.

The LiPo packs are -just- starting to be able to hold their own.

A drill may cruise at 500ma, but bear down on it and you're talking 30, 40, 50 amps easy.  Think about how hot your drill gets when working hard.

[ahofle]

Well just an update...I ended up getting this AC adapter: http://www.powerstream.com/AC-A0407.htm
Was a little disappointed in the quality of the adapter (came in one of those cheap Chinese packages and didn't look like the one on the website), but it seems to be fine. 
I opened up the old battery, chucked the dead sub-C cells out, and attached the AC adapter wires to the old battery terminals. Had a little issue with the battery terminals staying put once the Cs were out.  The cells were basically keeping the terminals in place, so I had to bend the two unused charging terminals to keep it in place.  Kinda hard to explain, I'll have to take a picture.
Anyway, once I finally got it in place, I cut a small hole in the battery housing to run the cord out and reassembled the battery pack.  Put it on the 19V setting, plugged it into a drill, and I'll be damned if it doesn't seem to run exactly like a fully charged Li-ion battery pack. I tried 6 different tools and they all functioned normally.  The only thing I noticed different is that the drills took a fraction of a second longer to spin up to full speed when the trigger was fully pressed.  I mean like a 1/4 second.  Maybe this is the short burst Ed is talking about?  I have yet to test with a high load (the saw for instance), but so far I'm happy.  I'll report back with any updates.

[Samstag]

A motor needs the most current at the lowest speed, so you're noticing a slower acceleration because the adapter can't produce the same surge current as the batteries.  Since you're using the same voltage you'll eventually get up to the same speed with no load but as soon as you try to do some real work with it you're going to probably notice you don't have the torque you used to. 

For jobs that let you keep the RPMs up it should work fine.

[HaRuMaN]

How about you guys just admit that ahofle proved all of you wrong already?

How so?

[Ed_McCarron]

How about you guys just admit that ahofle proved all of you wrong already?

Put a 1/2" bit in and drill through a piece of 1/4" steel.  Report back.

Then we'll decide who's been proven wrong.

[ahofle]

I will do some more tests and report back (don't know if I have any 1/4" steel scraps laying around to try though).  My only goal here was for the tools to operate with an AC adapter as they did with batteries, not to somehow become super-powered corded tools.  There seem to be a lot of assumptions that I wasn't happy with the performance of the tools in their cordless mode, which is not true at all.

[Ed_McCarron]

Nah, no assumptions intentionally made.  I've burnt up more than my share of premium cordless drills drilling to mount antennas on water tanks - its a pain to haul extension cords up there, so I know what kind of current they draw when pushed.  I can kill a Milwaukee 18v battery in about 3 minutes.

So, mathwise, if the pack is made of 2200mah cells, that means it can supply 2.2A for an hour.  Since I killed it in 1/20th of that, I'm pulling 2.2 * 20  --  44A.

I'm just thinking that when pushed hard, you may find the drill stalls.  I'd love to hear otherwise -- because then I'll be buying that same adapter.

[ahofle]

Well I was able to drill through a 1/8" piece of steel with a small bit with no problems.  I changed to a 1/2" bit and I was able to make it stall by pushing really hard.  I wasn't able to stall it or notice any difference in wood.  I also noticed some torque issues with the circular saw.  It definitely appears that certain tools draw more than 4.5 amps when pushed really hard as Ed mentioned.  I wonder if the 150 watt supply would have worked out better: http://www.powerstream.com/AC-A0407.htm (I got the 90 watt thinking that would be more than enough).   

Anyway, I would definitely say this mod is not for people doing heavy duty work like drilling 1/4" steel plates or framing houses.  It's also not a substitute for corded tools (but I already knew that).  But I am still happy with it for my limited hobby usage.

[ChadTower]

All that work to avoid buying a second battery to swap on the charger.