Modding an 18v worklight?

[Yoda4561]

I'm getting kinda tired of replacing the bulbs in my 18v Bosch worklight, and I was thinking that maybe it would be a good subject for my first mod. I'd really like to keep it simple though, and was wondering if maybe it would be possible to just stick a resistor inline with one of the leads, and use something like the maglight drop-in conversions. I can't remember exactly what size bulb the worklight took but iirc it was pretty similar in dimensions to the mag bulb, not to mention the internals of the bosch are pretty sparse, a couple springs for contact and the bulb is held in by the aluminum reflector. Doable? Should I forget the mag-drop in and just start from scratch?

 

[ken2400]

How about a pic of the worklight? If you have the room try using 4 strips of 5 5mm LEDS in parallel. That gives 20 total. If done this way I don't think you will need any resistors. Use a meter to keep track of the current drain each strip is using. It should be around 100 ma. So 4 would give you 400 ma all together.

I have seen LED work lights for around $20 for the basic ones.

I'm getting kinda tired of replacing the bulbs in my 18v Bosch worklight, and I was thinking that maybe it would be a good subject for my first mod. I'd really like to keep it simple though, and was wondering if maybe it would be possible to just stick a resistor inline with one of the leads, and use something like the maglight drop-in conversions. I can't remember exactly what size bulb the worklight took but iirc it was pretty similar in dimensions to the mag bulb, not to mention the internals of the bosch are pretty sparse, a couple springs for contact and the bulb is held in by the aluminum reflector. Doable? Should I forget the mag-drop in and just start from scratch?

 

[Yoda4561]

I'll try to post some pics after work today.

 

[emitter]

if it takes the so called bayonet push and twist bulb, try a terralux v-star. it's only a lux 1w but it will accept 9 to 24 v. It costs about $25 from brightguy.com. Seems like yours might take PR base bulbs though since you're mentioning the mag drop in. I think the mag drop ins are too fat for normal pr sockets. Maybe you could cram the V-star in there by drilling. The terralux 0.5 w pr based TL-20 kit would fit, but seems kinda dim for a work light.
The dropping series resistor to get from 18v to something like 6v would have to be pretty big. Say i(max) is .2 amps, 12v drop, so that's 60 ohms at 2.4 w dissapation. That's assuming a 4 cell mag drop in and a wag on the current. Doable though. 6 half watt 10 ohm in series? That should do it.

/\/

 

[Yoda4561]

I would have posted pictures... but I forgot my photobucket login and managed to trigger the timeout function guessing it.

There's a small spring which functions as the base contact, and a larger spring which fits around the lamp. These are both mounted to a black plastic plate with a small pcb, the bulb is held in place when you screw the bezel/reflector assembly on. Here's the spec page on bosch's website for their lightbulb, http://www.boschtools.com/tools/tools-detail?H=175983&G=57955&I=57956&T=1

I just grabbed a spare 3d mag bulb and checked, they're the exact same size and design, right down to the cutout in the bulb's flange. It also vaporizes the filament the instant you turn it on, so there's no voltage stepdown in the light from the factory. (or there is... after turning the light on with that 3d mag bulb it will no longer turn on, and I'm not getting a voltage reading at the "socket", I took off the little black plate and behind it there is what I'm assuming is a resistor, about 3/8in square, yellow in color, marked "LP30" and under it "135", I do believe I've burnt it out, it's reading zero ohms on my multimeter

*edit: which makes no sense because it should read 18v at the socket, I'ma take the whole light apart to see if there's anything in the switch that might have been damaged too
*edit: I have no idea, it's working fine now, gonna assume a finicky switch since it has done that to me before, will take it apart later and clean everything off inside.


I used to burn out or damage the 18v bulb every week before I stopped using the light because of that. I'm not really sure why, but these bulbs really drain a tool battery quickly, maybe 6-8 hours on a fresh battery by my estimation, and the thing is that I tend to just leave it on sometimes when I'm working in a ceiling, forget about it when I go to lunch, and come back to a nice black coated lamp and a dead battery. I'm hoping for a decent 16+ hour runtime on the led without too much loss in functional brightness. Heat is also an issue with the factory bulb, that abs/nylon body gets really hot to the touch when left on for a while, so a cool running light is also a + (sorta leaves out those 5 watt luxeons and stuff)

 

[emitter]

I miked the mag drop in I have, it is .45 inches in diameter, and same length as a regular bulb. Too fat for a regular socket. The kind of bulb you have is called a PR base. What you could do is something like this:
http://www.nifty-stuff.com/pr-led.php even 50 of those little 5 mm leds would still not be too bright.
Notice bosch does not spec the voltage of the replacement bulb. I'll bet it's 18v.

The yellow square thing is a LP30 series PTC thermistor from RTI, with I(hold) of 1.35 amps. That means positive temperature coefficient thermal resistor. Temp rises, resistance rises. That accounts for the bulb conducting better as it heats up. You don't need it anymore. Chuck it.

The best bet for you I think is to go for a mag drop in. Measure the volts at the wires coming from the battery to the bulb (with the switch on of course). It should be 18v unless they did something wierd. If it is, then figure out if you can cram in the drop inside of the large spring you mentioned. Maybe you could bend it open a bit. If it looks doable, pick up a mag drop in. You said you have a 3 cell Mag. Get yourself a 3 cell mag drop in, not a 4 cell like I said cause then you can use it in your existing light if the mod doesn't work.
3 cells, that's 4.5 v. 18-4.5=13.5v. (13.5v/0.2a)=67.5 ohms. Get 11 6 ohm half watt, connect them in series for 66 ohms. If you can't solder, use telephone crimp splices, they should be good for that current. Make sure there's no chance of the resistor leads shorting. Make a little package with electrical tape or heat shrink. Put that pack in series with either wire. The downside of using a mag drop in is normally the mag body would heat sink it a little. They do have thermal protection I think.

good luck. /\/

 

[Yoda4561]

Would the series resistors waste power(and possibly overheat?) I can do up a basic voltage divider, would that have the same sort of problem or am I just worrying about nothing?

Edit, Pics!

 

[emitter]

checking back in....
the spring looks promising for a mag dropin. You'd have to uncoil it with small pliers while inserting the drop in. Looks like a pain, but like I said at least you'd be able to use the module with your mag.
The resistors do waste power, but since the luxeon is so efficient your light will still last much longer than on the old bulb, which basically was a resistor itself. The power used by the resistors will be V squared over R, (or I squared R), so 13.5^2 / 66 = 2.76 watts. That plus whatever the drop in uses still isnt a lot considering the battery pack has at least 30 watt-hours in it I'm sure. The resistors must be half watt rated to handle the current going through them, though since they'll be close to the limit maybe 1 watt rated ones should be used., Yes they do waste the energy as heat, but it won't be near the luxeon module so no big worry. I wouldn't stack the resistors on top of each other, maybe leave some space. Ideally they would be potted in some kind of silicone heat sink stuff. See how it goes.
This is the extent of my knowledge. Something I've been considering as I write though: Initially the voltage buck regulator inside the lux module will see 18v because the resistors will not be dropping any voltage until the current goes up. We're talking milliseconds but I'm afraid of blowing the module. I'm not an electrical engineer so my thinking might be all wrong on this.

There is plenty of room for the terralux V-star and it is made for 9-24 v input, but it's got a fat base and you'd have to grind down the reflector some, but electrically there's zero risk and zero resistors to add.

good luck