12v cordless to corded drill thread

[flipper]

After being inspired by the thread on here the other day, I decide to convert an old 12v Ryobi cordless drill with dead batteries to a corded one I could use on the boat via a cigar lighter socket. Went into Maplins to buy the bits when a young assistant asks me what the amperage is as plug will need to be fused. Well I don't know the amperage draw but if my knowledge of Ohms law is correct - amps = voltage/load, so absolute max is 12 amps.

He wouldn't have it so in the end I put the stuff back and walked out.

Is that correct? Don't know what the draw is but current models seem to be about 6amp

 

[prv]

Well I don't know the amperage draw but if my knowledge of Ohms law is correct - amps = voltage/load, so absolute max is 12 amps.

I think you mean resistance where you have load (what property is "load" supposed to represent?) and I can't see where you got a maximum of 12 amps from.

Being pragmatic, I wouldn't worry massively about fusing in this situation - if it does start overheating you're right there to notice it. Not like a wire starting to smoulder behind panelling while you're on deck, which you don't notice until the flames appear. Just make sure the wiring (including on whatever circuit you plug it into) is enough for the current you'll be pulling.

Pete

 

[nigelmercier]

Your calculations have two unknowns: the current and the resistance, so don't mean anything I'm afraid.

For this sort of thing a fuse in the cigarette lighter plug is a pain, when the drill starts up, or is put under load, the fuse will blow.

Your socket will probably be fused at between 10A and 15A, so just rely on that. Either bypass the plug fuse, or get a plug without one.

[Later] I see Pete has said much the same thing. I must be slower at typing, although I did go to the Maplin (spit) site to check what fuses they had in their plugs.

 

[Sailfree]

After being inspired by the thread on here the other day, I decide to convert an old 12v Ryobi cordless drill with dead batteries to a corded one

In case you reconsider I had 3 dud NiCad batteries for a set of Ryobi tools.

I bought a replacement Makita but then read someones report that replaced his batteries with Ryobi LiIon batteries and new charger (necessary i'm afraid).

They reported that it completely transformed the tools performance. I did the same and they are great. Got my batteries & charger from Screwfix but can probably get chearer on e bay.

Now my hammer drill/rt angle drill/jigsaw/circular saw/recipricating saw/hoover all work great!

Just wasted my money on top of range Makita!!

 

[flipper]

Thanks all.

 

[nigelmercier]

Just wasted my money on top of range Makita!!

A man can never have too many drills.

I just spent £200 on a new drill, then fixed the faulty switch in the old one. If I had done it the other way round there would have been a whining noise coming from the kitchen.

 

[rogerthebodger]

I have done the same with my 12V Ryobi cordless drill and some old 9 V B&D cordless tools.

Can't remember the fuse size I had to start but it ran OK on no load but blew when I put a load. I increased it to I think 20 Amp and they run OK now.

BTW Ohms law does not work for motors as they are inductive. That's why my first lower fuse ran the drill but loaded the drill takes more current,

 

[elton]

For this sort of thing a fuse in the cigarette lighter plug is a pain, when the drill starts up, or is put under load, the fuse will blow.

Needs a properly rated slow-blow fuse, that's all.

 

[Avocet]

Or run it un-fused with crocodile clips direct on to the battery terminals and a longer lead. I don't know for certain, but with a fully charged batter and running nearly stalled, I'd have thought they could pull 30 Amps for short periods.

 

[fergie_mac66]

put an amp meter on my hitachi 12v now 12v corded uses about 4 amps

 

[oldsaltoz]

Probably 20 years + when I dug out the contents of the old battery drill and soldered some domestic figure 8 wire, made ot long enough to run from the cabin cigarette lighter to the top of my mast and about 3 feet extra, back then the boat I had only had a 25 foot mast.

No idea what brand or make the is but she works just fine and has never needed any repairs. I do recall it was cheap to buy when new, probably why the both batteries failed after just 18 months.

It now lives on the Cat and has an extra 30m extension lead and standard 240 volt plugs fitted to join them.

Last used to drill out some sad looking rivets on the boom about a month ago.

Good luck and fair winds.

 

[William_H]

put an amp meter on my hitachi 12v now 12v corded uses about 4 amps

I will bet you simply operated the drill and measured amps. OK but not useful. This kind of motor will also act as a generator if powered. What actually happens is that as the motor drives itself it also generates a voltage which is in opposition to the supply. This opposing voltage called back EMF reduces the current drawn. So the faster the motor runs with no load the less current drawn. This is fortunate as it then levels out at the max speed of the motor. (Without back EMF it would keep accelerating to destruction.)
This means on start up at 0 speed it draws a lot of current which then diminishes as it attains high speed. If you then load the motor with drilling the current rises again. Explaining why a battery drill when the battery gets flat slows down and quickly flattens the battery.
Mean while back to the original question. 4 amps as fergie-mac states is probably quite reasonable for no load but it will be a lot more on start up and when you load it. The high current in practice will be limited by the long wires you attach. (figure 8 flex is fine) It may get warm with hard work and especially if not spread out for cooling. My guess is that with 6 metres of figure 8 flex you won't blow a 10 amp fuse.
If however you used very short heavy wires and stalled the drill you could pop a 20 amp fuse.
The original NiMH batteries are good at providing a lot of current for short periods. So 20 amps might be seen at peaks. good luck olewill
good luck

 

[nigelmercier]

So 20 amps might be seen at peaks.

Exactly. This is why I don't use a fuse in my drill plug; if I stall the drill for too long, it just pops the 16A breaker.

 

[savageseadog]

Forget using lighter plugs and sockets they won't carry the load and will drop a higher than necessary voltage. Everything resistive will lose you voltage to the drill and hence torque and because torque is less it's more likely to stall and will draw even more current and trip breakers etc. Use a larger connector or clip on with big croc clips.