Modifying cordless tools

[Ferrica]

Hi all, my first post here so sorry for jumping straight in with a long question...........

I have a number of DeWalt cordless power tools, both 12v and 18v. They are excellent for the jobs I use them for (shed/patio building, minor house repair/maintenance etc) But the only drawback is the cost of replacement batteries, genuine DeWalt batteries are very expensive so I am looking into alternative options.

I want to modify a battery casing and hardwire connect that up directly to a power source. It is quite a simple affair to adapt the battery but as an electronic noob I'm unsure of the power source to use. I would ideally like to connect to a mains adaptor so for bigger jobs I can use this without the hassle of re-charging and changing batteries every whip-stitch.

Tonight I saw this adaptor on Amazon and would like advice if this would be suitable for the purpose outlined above? Please can anyone give me some good advice?

I don't know if I can post links yet (as a noob here) but a google search for the below brings it straight up. Sorry for the long post BTW

DC 12V 29A 350W Single Output LED Strip Power Supply Switching

LINK

 

[ericmark]

Dewalt do say the 12 volt drill is 250W and 18 volt drill 300W so it would seem that power supply is large enough. However clearly only for the 12 volt drill. Using the larger battery drills with multi-batteries and chargers I have found one can over heat the drill. With a single battery the battery becomes flat before the drill over heats.

At £32 for the supply and it would need boxing as well I would say getting a mains drill was a better option. Looking at the Screwfix site as an example you can get a mains SDS for £40 which will drill through walls a site quicker than any standard battery drill. Even the £20 model has 710W compared with the Dewalt 250W so there seems little point making a mains power supply.

However I have considered the idea of using cheaper VRLA (Valve regulated lead acid) batteries my hedge trimmer had a belt and lead to connect battery to the hedge trimmer but 20A is a fair load so would need rather a large battery plus a much longer recharge time. I looked at this http://uk.farnell.com/panasonic-electronic-components/lc-xc1228p/battery-12v-vrla-28ah/dp/1769786 and once I saw the price when off the idea.

 

[bernardgreen]

When a motor starts the current it takes is several times higher than the current it takes when it is running at normal speed.

A battery can supply that short duration of high starting current where as a switch mode power supply is likely to see that starting current as an over load and either limit the current to the PSU's maximum or shut down until the load ( motor ) is removed. If it limits currrent then the motor will take longer to reach speed and this can increase wear and tear on the motor.

It is possible to "re-cell" bespoke batteries but does require that the correct type of cells are used.

 

[davelx]

I have successfully used replacement "non-branded" batteries from http://www.batterytrader.com/ for years. Cheaper than the tool manufacturers'.

 

[DaveHerns]

I got 2 18v drill batteries from B&Q in the bargain bucket for about £5 each and broke them down into cells to rebuild the batteries of 2 drills. There must be someone who supplies the cells for a reasonable price though

 

[JohnW2]

If it limits currrent then the motor will take longer to reach speed and this can increase wear and tear on the motor.

Can you elucidate - that sounds rather counter-intuitive?

Kind Regards, John

 

[bernardgreen]

While the motor is running below its nominal speed it is taking more current than its nominal current, Hence the contact between brush and the commutator sections is making and breaking a higher than normal current. If the supply can not supply the full start up current but can supply say 1/2 of it then the brush to commutator is handling more than nominal current for longer than in a normal start up. The over all wear ( duration X current ) on each startup on supply limited current will depend on many factors and in some designs of motor could be less than the wear from a rapid start up with "un-limited" current from the power supply. The main factor is if the motor is designed for frequent stops and starts ( high current brush gear ) or is designed to run continuously ( low current brush gear that wears quickly with start up currents

 

[Ferrica]

Hey thanks for all the replies (some were a little too tech for me but very interesting all the same) ........

Looks like I will plunge in and buy that power supply (and box it nicely up as suggested) and also refurbish at least one of my many duff battery packs with new sub-c cells. I have a cordless Dewalt circular saw and jig-saw that are very good but eat up the batteries like there is no tomorrow, this was my main motivation for finding a solution when last year building decking and a Pergola. I love the portability of the tools but found the need for constant power essential when cracking on with a job when the weather was good (not that often in Swansea :=])

Thanks again guys this forum is excellent and I will be hanging about for a long time to come.