Does this exist: 12V Variable Load Test Light?

[bwringer]

Like many tool-using primates who monkey with vehicles, I have a small collection of headlight and turn signal bulbs and sockets with wires hooked up to them.

The reason for this, of course, is that many, many vehicle electrical issues arise from insufficient current flow. If you test voltage, you might get a false good reading, but the second you place a load on the circuit, it fails. Usually corrosion, bad ground, or an almost-broken wire.

Is there a nice clean solution out there, or should I just stick to my semi-janky homemade versions with fragile exposed bulbs that burn my fingers?

If this is a real thing that exists, what the hell is it called?

I envision a wee box or test light sort of thing with two wires coming out of it. The black wire is longer and has a clamp for ground. The other wire is red and gets clamped or poked into the positive of the circuit you're testing. On the box is a switch or dial allowing one to select from assorted resistances or loads (0.5A up to 10A or higher?); maybe it switches between incandescent bulbs you can see (often bulb brightness or intermittence is crucial info, so physical light bulbs might be preferable), or there's some sort of resistor and heat sink arrangement with bulb and maybe a beeper.

If it's bulbs, the bulbs are protected so the bulbs don't break and you can't burn your fingers, but they're also replaceable.

I don't need a voltage readout, although that might be handy. I want to apply a chosen load, not measure resistance.

 

[2ndGearRubber]

I've stuck with my numerous homemade lights. I have seen people looking for what you're describing, but never heard of a company offering it. All my lights use stackable banana Jack's, and have the amp draw written on them.

Usually a 250mv, a 2 amp, and a 5 amp are all you really need. Basic 194 test light, tail light 3057, and a 5 amp sealed beam headlight.

 

[unslow1]

Basically a Load pro with variable load. I'm sure it would be a good seller if word got out.

 

[TuxThePenguin]

IMO if you're going to DIY one, you should consider using a LED for an indicator along with parallel resistor(s) for the current draw test. You could grab 2 power resistors, a low power series resistor for the LED itself, and a 3-position switch. Your positions on the switch could be "LED only (voltage-only test), low current draw test, high current draw test." Of course you could add more positions than that if you want. They sell 4-position slide switches or you could get into rotary switches.

There's no reason a bulb needs to actually be your load, or get hot. A bulb is just an indicator.

You could also use something other than a LED if you want it to be non-polarized, but you can still use a relatively low power lamp and still use resistors for (most of) your actual load.

You can get 25 watt power resistors on Ebay for like a dollar shipped, though those are from China and will take a long time to arrive especially because COVID-19 has affected shipments. They'll cost several times as much at an electronics distributor (Mouser, Digikey, Newark etc) but you'd only need a couple anyway.

(Could also use a potentiometer and some kind of transistor buffer but that's getting to the point where you're sacrificing ease-of-use and it probably won't increase the usefulness of the tool that much)

I suppose that's pretty much the same thing you thought of already. I haven't seen this on the shelf.

Edit to note: Reason I mentioned 25w resistors is because you won't need to heatsink or cool them in any way if you're running a couple of watts through them (unless maybe you intend to leave the device connected for long periods of time)

 

[bwringer]

Basically a Load pro with variable load. I'm sure it would be a good seller if word got out.

Nice! I didn't know this existed. And I really like the idea of using it in place of test leads with your multimeter.

But $53+? Yikes. Then again, I guess that's within shouting distance of the ballpark of reasonable for a high-quality pro tool.
https://www.amazon.com/dp/B004IKPUL2/?tag=atomicindus08-20

It's intended for low-draw circuits, so it only places a very small load on the circuit. You're back to the ol' box o' bulbs for a lot of stuff.

 

[bwringer]

....There's no reason a bulb needs to actually be your load, or get hot. A bulb is just an indicator.....


....I suppose that's pretty much the same thing you thought of already. I haven't seen this on the shelf.

I was thinking incandescent bulbs because quite often the brightness or "intermittence" of the bulb can tell you a lot. For example, hook it up and start wiggling wires and if the thing goes slightly dim and then bright as you wiggle, you might be getting close to the problem area, or that "almost broken" wire hanging on by a strand or two.

A little squeaker speaker could give you similar "analog" quality feedback without needing to look at it.




And yeah, I know there are a couple of tool makers hereabouts... Astro, Tekton, etc... are you listening? Do y'all ever monkey with stuff with wires? Opportunity is knocking...

 

[TuxThePenguin]

I'd rather have a voltmeter + ammeter than go by the brightness of the bulb, though I suppose you do have a point, and the incandescent bulb would take up less room than a meter or two for sure

 

[seber]

Pretty easy to build. All you need is a variac and a voltage meter. Mark some numbers around the variac dial to indicate the load. Shoud be able to buy both components and a box for less than $20.

 

[TuxThePenguin]

Pretty easy to build. All you need is a variac and a voltage meter. Mark some numbers around the variac dial to indicate the load. Shoud be able to buy both components and a box for less than $20.

I assume you mean potentiometer? A variac is (essentially) a variable transformer.

You could use a potentiometer but keep in mind most of them are rated 250mW or less. At 13.5v, that'd be about 18.5mA. You can probably run them a little bit higher for a short period of time, but overall that's pretty low.

Not like you'd want to make a tester like this that does a full amp or anything but you'd probably want more than 18.5mA.

(You could buy a "power potentiometer" but I don't think those tend to be all that cheap/available)

 

[travisn1]

What about a blower motor resistor? They have 4 different settings, pull decent current. They are meant to be cooled by the blower fan but for intermediate use it's probably fine without. Could mount one in a project box with some banana jacks.

 

[TuxThePenguin]

What about a blower motor resistor? They have 4 different settings, pull decent current. They are meant to be cooled by the blower fan but for intermediate use it's probably fine without. Could mount one in a project box with some banana jacks.

if you're going to get a box with jacks on it, you could use a decade box. Not too hard to find them built with 1W resistors anyway. Not that 1 watt is amazing for the task, but how much current do you really want to pull? (1W is gonna be WAY more useful than .25W)

Otherwise, maybe that's a good idea if the built in resistors are of appropriate values. Especially if you can get a used-but-working one for super cheap or free.

 

[spchsr]

I would love to get one of these for this purpose! https://www.amazon.com/dp/B00NPY02EW/?tag=atomicindus08-20

 

[TuxThePenguin]

I've seen people use those on Youtube. Looks like a nice product. Can you adjust the load that it creates?

 

[unslow1]

I think the point is to be able to substitute a load to check the circuit. That might require as much as 10 amps on some GM fuel pumps. It would be really nice to have one that you could set from 3-10amps. That would cover a lot of stuff.

 

[Astro_Pneumatic_Tools]

We worked on one a couple years ago, but it never really got off the ground for some reason. Maybe i'll dig it up

 

[seber]

I assume you mean potentiometer? A variac is (essentially) a variable transformer.

You could use a potentiometer but keep in mind most of them are rated 250mW or less. At 13.5v, that'd be about 18.5mA. You can probably run them a little bit higher for a short period of time, but overall that's pretty low.

Not like you'd want to make a tester like this that does a full amp or anything but you'd probably want more than 18.5mA.

(You could buy a "power potentiometer" but I don't think those tend to be all that cheap/available)

Yes, pot. Big ones are available surplus at lots of sites.

 

[2ndGearRubber]

I'd rather have a voltmeter + ammeter than go by the brightness of the bulb, though I suppose you do have a point, and the incandescent bulb would take up less room than a meter or two for sure

Volt meter without a load is worthless. One strand of corroded copper can show B+ on a starter wire. To use an amp meter in line while checking the drop adds further complications with hook up, and itself still doesn't truly load the circuit, unless the component you're testing is functioning properly and can be used as the load itself.

The ultimate test is the load of a test light with the meter hooked up to check the drop across the wire. But most in most applications a 2amp test light works plenty fine, use the 5 amp monster for bigger loads, and the standard test light for more delicate circuits or to simply control sensor inputs.

 

[TuxThePenguin]

Volt meter without a load is worthless. One strand of corroded copper can show B+ on a starter wire. To use an amp meter in line while checking the drop adds further complications with hook up, and itself still doesn't truly load the circuit, unless the component you're testing is functioning properly and can be used as the load itself.

The ultimate test is the load of a test light with the meter hooked up to check the drop across the wire. But most in most applications a 2amp test light works plenty fine, use the 5 amp monster for bigger loads, and the standard test light for more delicate circuits or to simply control sensor inputs.

I am talking in conjunction with load resistors and a light, not JUST meters. See post #4. In which I was thinking of testing relatively low currents anyway, though the concept applies if you want to do a higher current one and test your fuel pump or something as somebody had mentioned.

Of course, it's just one way to do it. Not "the correct" way or anything. I don't like using lights as loads (which is just my opinion, not "the correct" opinion).

 

[Wrench97]

Easier and cheaper to just test the circuit with the load applied.
If you testing a fuel pump circuit, test it by back probing the plug and turn it on.
Or do a voltage drop test with the circuit loaded of course.
I bought a loadpro a couple of years ago hardly ever use it, all I use is a good old fashion incandescent test lamp and some back probes.

 

[RPH]

Get a decade resistor box. Start out on the high impedance and adjust to the lower values. Used a calibration tool for board tuning to determine which resistor has to be installed. A good one will go from very low impedance to extremely high impedance. They are not that expensive unless you want it traceable to a standard.

 

[FigureItOut]

I've been planning to make this exact tool for quite some time. I haven't gotten around to it because there are other ways to accomplish the same end, test lights, load pro leads etc.

Anyway, when I do it, I'll use a 150W, 50Ω potentiometer like this, or a cheaper version, and panel mount volt meter similar to this.. It'll all go in a project box with a couple banana jacks. I may even throw in a SPDT switch and a couple more banana jacks so I can throw my DMM' ammeter in series into the mix.

It really doesn't do anything a selection of bulbs won't do, but I'd really like to have it in a nice little convenient package like you're talking about.

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[2ndGearRubber]

I am talking in conjunction with load resistors and a light, not JUST meters. See post #4. In which I was thinking of testing relatively low currents anyway, though the concept applies if you want to do a higher current one and test your fuel pump or something as somebody had mentioned.

Of course, it's just one way to do it. Not "the correct" way or anything. I don't like using lights as loads (which is just my opinion, not "the correct" opinion).

Okay, fair enough. I thought you were talking about just measurement devices for the test. Low current you can usually just step up to the next amp load in your arsenal. I have the load pro, found test lamps to just be simpler.


Why dont you like test lights as loads?

 

[mfewtrail]

Like many tool-using primates who monkey with vehicles, I have a small collection of headlight and turn signal bulbs and sockets with wires hooked up to them.

You could always buy up cheap auxillary/fog/driving lights and/or compact sealed beam headlights to make test lights out of. Check out rockauto clearances, closeout stores, etc. to find them dirt cheap.

 

[bwringer]

Easier and cheaper to just test the circuit with the load applied.
If you testing a fuel pump circuit, test it by back probing the plug and turn it on.
Or do a voltage drop test with the circuit loaded of course.
I bought a loadpro a couple of years ago hardly ever use it, all I use is a good old fashion incandescent test lamp and some back probes.

Using the component for the load isn't always helpful. Part of the whole reason for testing like this is to quickly figure out whether the component or the wiring is bad. It's also a way to chase down an intermittent or partial wiring fault. Another function of a test load is to place it where you can see it. For example, if you're chasing intermittent tail lights, you might need a test load up near the fuse box or under the dash, etc.

You could always buy up cheap auxillary/fog/driving lights and/or compact sealed beam headlights to make test lights out of. Check out rockauto clearances, closeout stores, etc. to find them dirt cheap.

That's exactly what I have and want to replace; a collection of cobbled-together bulbs in salvaged connectors and wires. The bulbs are fragile, bulky, and get hot if they're used for more than a few seconds.

I (and it seems many others) want a cleaner, faster solution.



I'm familiar with the Power Probe, and it's a very handy but expensive widget, but it does not have a load or resistance function. Some models read resistance, but AFAIK they do not apply a significant load.

 

[redwrench60]

I took a standard 12V incandescent test light that takes those little flashlight style bulbs and installed a really bright dome light bulb in it. I forget How many amps it pulls but it’s up there. It will stress test all but the biggest circuit with the convenience of a test light. Don’t leave it connected more than a minute or two, it will melt the plastic body though!

 

[tool_scrounge]

I would make one similar to what is shown below. You may want a fixed resistor to limit the max current. Otherwise you can set the pot to 0 ohms resistance (dead short) and blow a fuse at minimum.

So if you use a fixed resistor that is about 50 ohm 5 watt and a wire wound pot that is 500 ohms and 5 watts, you will get around 0.24A to 0.022A of load + whatever the current is from the bulb. Or use and LED with a series resistor instead of the light bulb on your tester.

You can get both resistors from Digikey for about $9 delivered if you mail check as payment (free shipping, no minimum order if you mail in a check or money order).

https://www.digikey.com/product-detail/en/cts-electrocomponents/026TB32R501B1A1/CT2156-ND/203777

https://www.digikey.com/product-detail/en/vishay-huntington-electric-inc/FVTS05R2E50R00JE/FVTS5-50-ND/257665

https://www.digikey.com/US2011/order.pdf

 

[dnschmidt]

Actually, I accomplished something like this using only standard Harbor Freight test lights and various current consuming bulbs that I bought off the Internet that have the same base as the bulb in the standard Harbor Freight test light but have higher current draws. I searched on the base type and the website provided me with a list of bulbs of that type and their current draw. One of these is halogen and draws a couple of amps. So I have three test lights labeled .2Amp 1Amp and 3Amp. Let me tell you the 3Amp model you don't let lit for long as it will melt the plastic of the housing. My view is that if the circuit can do that it hasn't got a problem.

 

[FigureItOut]

I'm familiar with the Power Probe, and it's a very handy but expensive widget, but it does not have a load or resistance function. Some models read resistance, but AFAIK they do not apply a significant load.

The IV has a test they call the Hot Shot. It's a pass/fail test, with no indication anywhere I've found as to what load is applied nor what voltage drop constitutes a fail. They almost did something cool there.



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[richfinn]

I think your overcomplicating it

150mA test light for computer activated circuits

Min/Max Voltmeter for volt drop testing

LoadPro is a useful tool in my experience, I use it on fuel pump/lighting/relay wiring and most 12v supplies to modules/coils and fuses, my only criticism is its a bit bulky to get at some locations, so I had some adaptors made so I can use 4mm extensions and accessories

 

[johninct]

I made one with a free HF voltage meter, 4 A bulb, an old small extension cord and some old alligator clips.

 

[MikeF2316]

I'm not a pro, so I don't need to do this too often, especially as my cars and bike are currently (get it?) both less than 2 years old. I have a toolbox drawer that has my 4 watt test light, and H7 (5 amps) and 1156 (2 amps) bulbs for load testing.