jack hodges: The reason for using a filament light bulb and not a normal resistor is
that the light bulb is a variable resistor.
If the current being drawn by the circuit is low then the filament will
have a very low resistance so the circuit can operate normally. Only when
the current drawn is high does the filament heat up and become a high
resistors dont do this so well.
Raul Schay: Hi Jerry...
I have a pure sine power inverter that I used to run an air conditioner
that used 450 watts without problems until the other day that will not turn
on the ac compressor , the inverter is rated up to 1500 watts, I tested
with a watt meter, and I load a toaster that used 1300 watts and it work
with no problems , but will no turn the compresor ac no more.
Do you have any idea what could be the problem?
Thank you Jerry in advance !
CHIBA280CRV: Got to love it ! And laugh about it. I am glad you made the mistake and the
outcome was a learning experience lol. The light bulb trick is awesome to
know for a beginner like myself. Thank you bro , keep the videos coming...
John Rose: i have the same problem as you have i did not think about the cabes being
have soon as i turn it on dead short think you for your tips and money john
Victor Silva: If you don't have a light bulb you can use a bench supply that has CC mode.
Chuck Holder: Interesting lesson.but very slow
vance byers: i am so grateful you shared this in spite of the mix up . i have been
looking for the lightbulb tick in action for a while and now i have learned
a lot about it even some from the comments section thank you
Paul Brace: Man your a pickle any expearenced engineer would have checked the polarity, a
lot of circuits have a reverse polarity dioad in them to blow the fuse
"hopefully" before any dammage is done, but a good video anyway. i also use
a bulb on things i am repairing here in the uk we have 240v and a 100w
Bob Bozanic: Hi ther Jerry
This might be late to add, but at the beginning of the video you were on
the right track and you almost got it. One thing you should have realised,
when your lamp lit up,because of the” short “ you have used all of voltage
available (reconnect and measure the voltage drop across lamp. I bet you
will be reading 12V or 13.7V) If so, what was left for the inverter to fire
up?Maybe 0.6-0.7V. It is like this. Sum of ALL voltages (drops) in a closed
circuit must be equal to the supply voltage. So if your lamp "took” 12V
what was to power your inverter?
LearningZone: LOL. This is known as dig a whole mountain and get a mouse only! The
polarity was creating a big trouble. Great work. I am sure you know the
problem from the beginning of the video.
villigasruel: hahaha......LOL it's so funny
MrBugsier5: If you want to draw 400 watts it wil draw 33 amps at 12 volt, so what the
7,5 fus does inthere i do not know!
NiHaoMike: For large AC loads, a hair dryer or space heater would be more compact than
a bunch of light bulbs.
12voltvids: Ha ha. Good for a laugh. I was thinking reversed power supply as soon as
you got the .6 volt drop. The light bulb load was one of the first things I
learned some 30 years ago when I first got into the repair business, and
the second thing I learned was to keep one hand in my pocket when working
on a live circuit. Only been bit twice, one time by an operating microwave
power supply, some 2500 volts, and the second time by 30,000 volts from a
second anode lead that was not attached properly to a picture tube by a
junior tech that changed the CRT. I was performing a convergence job, and
the lead popped off and dropped on my hand. It felt like I hit my thumb
with a hammer. Fortunately I was wearing insulated shoes, and had my other
hand in my pocket, so it just charged me up. I got almost as big a shock
when I discharged the energy in my body! Talk about a major spark from my
finger. (body charged up like a capacitor, just like static electricity
only a bigger jolt!)
Saved my life, that's for sure. Sure glad to be out of the electronics
Ryan96se: don't feel bad dude. I've done stuff like this before. still interesting
how you were able to check things out. You know if they were smart when
they built the circuit they would have put a diode right on the power inlet
terminals to prevent a short through the FET's but being made in China I'm
guessing it would have added a few cents to the cost of manufacturing to
add a reverse polarity protection circuit with a red light
585585MC: Are you under sedation?
John Ratko: I see by your magnifying-glass-alligator-clips device sitting on your bench
that you must have been to the Harbor Freight store. Well, that's where I
rpcomms1: whoops a daisy classic,Ive done some like that before now I always check
12V battery leads on DVM before plugging moral of story!
tim b: i have a rally 600 watt 24 volt inverter i need to fix do you repair other
Giuliano Damiano: In Few simple words, Thank you. This is a cool and helpful trick!!
H2GenerationX: I honestly love this. I don't know how many times I've made simple
mistakes like this. But hey, that's how we learn! I'm glad I learned the
LIGHT BULB trick! GENIUS!! I honestly never heard of that! Thanks. :)
inventhead: by the way the lamp trick works with mosfets to i used it with tv sets
mostly p n channel out of circut
inventhead: to me thats a toy not a useful inverter i like big power transformers and
heavy duty transistors cause seeing the tiny transformers in therse units
thers no way it will out hundreds or thousands of steady watts. hi watts is
thick wire . what thay try to do is pulse that lil toy and on a scope looks
good until you add a load then the output drops and current rises . i have
a few inverters best built is a apc 24 vdc in but has a heavy transformer
iron core good 25 lbs. also keep in mind with anay inverter make sure the
feed cable is thick enough for max draw .even thicker is better than
thinner ,that will limit amps/volts and output will be poor.
inventhead: isent dc fun lol good you found the problem no transistors dont switch in
inventhead: you can use a rheostat with amp meter to, most inverters need 0ver 12
volts if the lamp cuts it down it wont start properly i did tv shop repair
over 30 yrs might i sugest look for shorted caps and mosfets fets need
to be outa circut due to resistors diodes
WECB640: Inverter takes a 15A reverse connection draw and nothing blew? Sounds like
it was built properly and not your normal run of the mill cheap junk. I say
go get a few more and use them for emergencies. Better to have a few
smaller ones than all the eggs in one basket with a large one. Good job.
RedDragonUKTech: I'd expect to see a much larger fuse for a 400W inverter.
whiskeyify: I used to work in a tv repair shop and we used the light blub trick, if the
set had a shorted output transistor we would put a light blub in it's place
and power on the set to check the switch mode power supply. The blub might
blink, come on bright, or just glow. This is a good way to troubleshoot.
Jerry Pommer: Thanks! Sure, I can do that.
TheCrazyStudent: Cool trick, thanks for sharing. Although, I don't really see the point in
using a big lightbulb that takes up quite a lot of space on your workbench
when you can just use a power resistor with a suitable wattage rating
instead. Checking the voltage drop across that resistor will then tell
whether the circuit under test is shorted or not. Advantages: Takes less
space on your workbench and you can use almost any value of resistor you
Jerry Pommer: Thanks! It's such a useful thing when you only have one fuse left in your
tan hock jun: thanks,I have learn the light bulb trick from your video and it is a nice
video to watch :)
Donal Leader: Great video. Loved the real time thought process. Ha heard of the light
bulb trick from hams here in Ireland.
TheCrazyStudent: Very true. I was mostly referring to this situation in particular, where
you had a rather big 12V light bulb on your workbench. Finding a 12 ohms
17W wirewound resistor in ceramic case shouldn't be much of a problem, and
it will probably be much cheaper than buying a big 12V light bulb. But
regardless the method, using a current limited supply to troubleshoot a
shorted circuit is indeed a very good idea, which you demonstrated very
well here. Thanks for posting, will check your other vids too :)
Ken F: Great technique, I kept blowing a 2 amp internal fuse on my power board
from my oscilloscope even after replacing a shorted transistor. After
replacing a shorted toroidal coil I lost the ground. The light bulb
technique saved me some fuses in the process. Thanks for the informative
video and sharing your knowledge.
Jerry Pommer: Thanks! Life wasn't meant to have the rough patches edited out. Even the
dumb mistakes that others might learn something from.
Jerry Pommer: It's probably that part of the power cable that belongs to some other
device. Because you're right, to get the rated 400w out of it, you'd need
around 40 amps in!
Jerry Pommer: Thanks!
Jerry Pommer: Well, if the circuit under test is powered by 100 volts and normally draws
100 mA, but has a short somewhere that now makes it pull 1 amp, 100v * 1A =
100 watts. How big, expensive and difficult to source is that resistor?
Light bulb starts to look pretty good then. Thanks for watching!
JonathanAnon: So today's lesson is: Dont invert the power to your inverter? :-) I saw
that lightbulb trick in Jestine Yong's book. very useful.
Jerry Pommer: That's great Ken! Glad it helped.
formtapez: 7.5 Amp fuse for 12 Volts (90 Watts) - Writing 800 Watt on the case - Thats
crzren: interesting.. great video!
Jerry Pommer: Yep, working in TV repair is where I learned it too.
TakeTheNarrowPath GloryIsHisName: Great video I also didn't know about the light-bulb trick A+ on that. Can
you make a more detail video on the light bulb trick thank you.
Jerry Pommer: Nice setup!