Made a new test light

[2ndGearRubber]

Most incandesant test lights I've used draw 1/4 amp (250ma) when connected across a battery. This is usually not enough to load a circuit. The common work around is a 3057 tail light bulb as a load. This method pulls about 2 amps across a battery.



But what if you need to really load a circuit? I made this today, 5.2 amp load when connected across the battery.

10amp in line fuse, with stackable banana jacks so I can voltage drop test if the test fails. (amazon is bringing me another red one)

 

[MattT]

Threw this together today. 3 scrap test leads and a 55w H3 light so it should pull about 4.5 amps.

 

[oilslick]

Lol, I have an old sealed beam with dedicated leads with backprobe pins attached. It leaves no doubt about a circuit's ability to carry a load for me.

 

[johninct]

I made one too last year. I hooked it up to a free HF multimeter so I can check voltage all in one.

 

[theoldwizard1]

You guys all have the right idea, but I would like something a little more portable/user friendly ! Anyone have any other ideas beside a huge head lamp ?

 

[2ndGearRubber]

A normal headlamp bulb would work fine. Wattage=Amps x Volts. Pick your bulb and you can ballpark the amp reading. IMO it's still preferable to make a measurement with an amp-clamp and mark the actual draw off of a daily-driven car battery. Obviously fuse it.

The reason sealed beams are preferred is ruggedness. At 9006 isn't going to respond well to getting touched/dirty as well as a sealed beam.

 

[3 Gun Shooter]

Most incandesant test lights I've used draw 1/4 amp (250ma) when connected across a battery. This is usually not enough to load a circuit. The common work around is a 3057 tail light bulb as a load. This method pulls about 2 amps across a battery.



But what if you need to really load a circuit? I made this today, 5.2 amp load when connected across the battery.

10amp in line fuse, with stackable banana jacks so I can voltage drop test if the test fails. (amazon is bringing me another red one)

GM taught us that back in the early 90's in SET class. You can have a wire just about cut in two with 3-4 strands left. Will pass testing with a DVOM, and even a normal test light. Load it with a headlight and you will barely get the bulb to light. I use a halogen headlamp bulb and have long wires on the connector to the bulb and spades on the other end to put different ends it.

 

[MattT]

Obviously fuse it.

The lamp is going to limit current so I didn't bother fusing mine.

At 9006 isn't going to respond well to getting touched/dirty as well as a sealed beam.

It will also get hot enough to melt plastics and burn your fingers.

 

[bonneyman]

Interesting

 

[2ndGearRubber]

The lamp is going to limit current so I didn't bother fusing mine.



It will also get hot enough to melt plastics and burn your fingers.

I fuse mine in case of a 1 in a million failure. Bulb somehow burns out and forms a magical dead short between the terminals. I've lit test/jump leads on fire before, so I like fuses.

 

[wood02]

True story. When I was a kid back in the early fifties...I hooked and extension cord to a six volt headlight from an old junk car. I cut the female connector and wired the cord to the prongs on the light. I can not remember the make of the car or bulb. I used this to light up an area to play basketball at night...my first thought was I think this might be a bomb. Well it did not blow up and we played basketball. I made a stand to mount the bulb out of wood. I do not know if I hooked it to the high beam or the low beam of the light or if they even had high/low beam back then. The thing was really bright.

 

[Professional Tool User]

It's always good to have a test unit. It doesn't have to be anything fancy.

 

[theoldwizard1]

The lamp is going to limit current so I didn't bother fusing mine.

This a variation of Ohm's Law that few people know/understand.

If you are probing actuators/motors with +12VDC to see if they operate, you should limit the current. On variation of Ohm's Law is I = V / R. So your actuator has an unknown resistance, but you don't want to feed it more than 1A in case the actuator has a dead short, ZERO ohms. If you have a 10W-15W light bulb (W=I²R so 1x1x12, a bulb with approximately 12 ohms of resistance). If the 12VDC feed goes through the bulb (i.e. the bulb is in series withe the load) irregardless of the resistance of the load the maximum current it can draw is 1A !

 

[Copymutt]

Here’s a bit o nostalgia for you.
As Boy Scouts, late 50’s, we used to raise money by soldering six ft. leads to head lights, put batt. clips at the end of the leads. Glue the bulb into a toilet plunger and tape the lead to the handle, instant spot, trouble light. Genius!

 

[torqueman2002]

South Main Auto - YouTube channel
How To Make Your Own Test Lights
<a href="<iframe width=" 560"="" height="315" src="https://www.youtube.com/embed/-L_fw7xn19k" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen="">"><a href="<iframe width=" 560"="" height="315" src="https://www.youtube.com/embed/-L_fw7xn19k" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen=""><iframe src="https://www.youtube.com/embed/-L_fw7xn19k" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen="" width="560" height="315" frameborder="0"></iframe>

 

[Bobioz1]

This a variation of Ohm's Law that few people know/understand.

If you are probing actuators/motors with +12VDC to see if they operate, you should limit the current. On variation of Ohm's Law is I = V / R. So your actuator has an unknown resistance, but you don't want to feed it more than 1A in case the actuator has a dead short, ZERO ohms. If you have a 10W-15W light bulb (W=I²R so 1x1x12, a bulb with approximately 12 ohms of resistance). If the 12VDC feed goes through the bulb (i.e. the bulb is in series withe the load) irregardless of the resistance of the load the maximum current it can draw is 1A !

If the 12VDC goes through the bulb then it won’t be 12VDC at the actuator/ motor. Better to fuse your lead if your worried about it.

 

[FigureItOut]

I've had this idea for an adjustable load "test light" percolating in my head for a while. Basically, I'd take a big rheostat like this OHMITE RLS50RE RHEOSTAT, WIREWOUND, 50 OHM, 150W, and put it in an electronics project box with a knob. I'd put a pair of banana jacks across one side and the wiper, then I'd have either a built in volt meter like the dash-mount type, or an extra pair of banana jacks to plug in a DVOM. I'd probably go ahead and put in a switch that throws another pair of banana jacks in series to measure current. At $200 in parts and an hour or so to build it, it'd be a heck of a useful tool.

 

[2ndGearRubber]

This a variation of Ohm's Law that few people know/understand.

If you are probing actuators/motors with +12VDC to see if they operate, you should limit the current. On variation of Ohm's Law is I = V / R. So your actuator has an unknown resistance, but you don't want to feed it more than 1A in case the actuator has a dead short, ZERO ohms. If you have a 10W-15W light bulb (W=I²R so 1x1x12, a bulb with approximately 12 ohms of resistance). If the 12VDC feed goes through the bulb (i.e. the bulb is in series withe the load) irregardless of the resistance of the load the maximum current it can draw is 1A !

Basic V=IR, same deal as one strand of copper in a battery cable to a starter. 12volts all day X 0.0001 amps = no start. Same deal as a resistance check a component by checking the amp draw and voltage at an identical time frame on the scope. I=V/R is a nice ballpark for setting amperage scales. You gotta have a clue as to resistance value though.

That's the HUGE importance of knowing max current draw of any test light. I fear little poking my 250ma light basically anywhere. Obviously the big 'ol 5amp monster might require a bit more thought. Although a dead short is the most dangerous condition to the wiring/system. I still fuse everything out of habit. A damaged wire between my light bulb and the power source could still send wires up in smoke; dead short.

 

[2ndGearRubber]

I've had this idea for an adjustable load "test light" percolating in my head for a while. Basically, I'd take a big rheostat like this OHMITE RLS50RE RHEOSTAT, WIREWOUND, 50 OHM, 150W, and put it in an electronics project box with a knob. I'd put a pair of banana jacks across one side and the wiper, then I'd have either a built in volt meter like the dash-mount type, or an extra pair of banana jacks to plug in a DVOM. I'd probably go ahead and put in a switch that throws another pair of banana jacks in series to measure current. At $200 in parts and an hour or so to build it, it'd be a heck of a useful tool.

Wouldn't a carbon pile accomplish the same thing? A variety of light bulbs with banana jacks has been my work around to building such a device. I'm a mechanic, so my 1/4, 2, 5 amp setup is usually more than enough for my requirements.

 

[FigureItOut]

Wouldn't a carbon pile accomplish the same thing? A variety of light bulbs with banana jacks has been my work around to building such a device. I'm a mechanic, so my 1/4, 2, 5 amp setup is usually more than enough for my requirements.

I guess, but in a much higher range than I would find useful, and not a very convenient form factor. My idea gives you up to about 10 amps, with an actual measurement rather than judging bulb brightness. Granted, it'd only be marginally better than a setup like what you describe, hence why I haven't done it yet. Still though, I think it's a cool idea and I'll do it one of these days. It's always nice to have a variable resistor around also, and this way I'd always have one handy with easy connections. Heck, it could even test small batteries like 9V and AAA effectively.

 

[tutti57]

You can always just start with the voltage drop test. Test lead extension to battery neg, activate circuit, backprobe source side and ground side at component. Near battery voltage on source side, near 0v on ground side. Bam.

Nissan Technician

 

[MattT]

I've had this idea for an adjustable load "test light" percolating in my head for a while. Basically, I'd take a big rheostat like this OHMITE RLS50RE RHEOSTAT, WIREWOUND, 50 OHM, 150W, and put it in an electronics project box with a knob. I'd put a pair of banana jacks across one side and the wiper, then I'd have either a built in volt meter like the dash-mount type, or an extra pair of banana jacks to plug in a DVOM. I'd probably go ahead and put in a switch that throws another pair of banana jacks in series to measure current. At $200 in parts and an hour or so to build it, it'd be a heck of a useful tool.

That rheostat is kinda spendy This one is probably good enough for a heck of a lot less.

https://www.amazon.com/dp/B012SKMY76/?tag=atomicindus08-20