Is it okay to use lightbulb for dummy load? - Page 1
Forum section: electronics / beginners

author: bshi02
author_rank: Regular Contributor
timestamp: July 04, 2024, 02:47:28 pm
content: I read through below article and I figured out which resistor should be desoldered in order to disconnect the supply just before the fly back B+ vcc pin.https://www.electronicsrepairmadeasy.com/2010/11/solving-power-supply-problems-smps.htmlSo I prepared a chinese lightbulb of below link and a bulb holderhttp://itempage3.auction.co.kr/DetailView.aspx?itemno=B339100342But It just have noticed that most of chinese lightbulb is dedicated to not DC voltage but AC,So I doubt that a lightbulb will be lit when I attach this lightbulb and switch on.Is it okay to use lightbulb for dummy load?

author: themadhippy
author_rank: Super Contributor
timestamp: July 04, 2024, 02:56:52 pm
content: Quoteyes,as long as its an ole skool incandescent filament type.

author: CaptDon
author_rank: Super Contributor
timestamp: July 04, 2024, 02:58:14 pm
content: Never use anything but an incandescent bulb!!! Trying to use an LED or CFL bulb is pointless!!

author: Stray Electron
author_rank: Super Contributor
timestamp: July 04, 2024, 03:11:50 pm
content: I've been around radios and electronics all of my life and I never saw a dummy load, other than an incandescent bulb, until I went into the USAF. The resistance in an incandescent bulb is non-linear but it will get you in the ball park. And it's easy enough to measure the voltage across one and the current through it and to calculate the exact resistance (i.e. Load) at any given point. Besides being cheap and readily available, the other advantage of bulbs is that they're available in many different voltage and wattage ranges. You can also add more in parallel to increase the load or string them in series to decrease the load. With a bit of ingenuity and a half a dozen bulbs you can make just about any size load that you can imagine by wiring them in series and/or parallel strings.

author: TimFox
author_rank: Super Contributor
timestamp: July 04, 2024, 04:14:52 pm
content: Unfortunately, they are no longer cheap and readily available in many voltage and wattage ranges (if they could be used for actual illumination).

author: jzx
author_rank: Regular Contributor
timestamp: July 04, 2024, 04:28:08 pm
content: Another advantage is that they lit if the current is enough.

author: langwadt
author_rank: Super Contributor
timestamp: July 04, 2024, 06:26:42 pm
content: Quote from: jzx on July 04, 2024, 04:28:08 pmwith the disadvantage that some types of bulbs have very low resistance when cold

author: Benta
author_rank: Super Contributor
timestamp: July 04, 2024, 07:09:08 pm
content: The problem is that incandescent bulbs' cold resistance may be 5...10 times lower than at nominal current.Could give your supply starting problems.I normally only use wire-wound power resistors.

author: bshi02
author_rank: Regular Contributor
timestamp: July 04, 2024, 09:35:23 pm
content: Thank very much for all of reply.Can I use Incandescent light bulb regardless of AC or DC voltage?And If I have to use Incandescent light bulb for dummy load,Then How can I tell positive and negative terminal of Incandescent light bulb in order to soldering its wire to PCB?

author: coppice
author_rank: Super Contributor
timestamp: July 04, 2024, 09:47:43 pm
content: Incandescent bulbs are a nice cheap option for a lot of test load applications. However, you need to beware of their enormous resistance change between cold and hot. If your system can't take that initial low impedance, a simple bulb load might not be right for you.

author: TimFox
author_rank: Super Contributor
timestamp: July 04, 2024, 09:53:09 pm
content: An incandescent bulb is a resistor (with strong temperature co-efficient and self heating).As such, its current is independent of the polarity of the applied voltage (as opposed to a diode) and can be used on AC or DC.RMS values for voltage and current should be used for either AC or DC, where the RMS value for DC equals the DC value.

author: Psi
author_rank: Super Contributor
timestamp: July 04, 2024, 10:26:20 pm
content: You can use a high wattage dummy load resistor if you want.The main reason people used light bulbs is they were plentiful and you get an immediately indication that something is wrong (The light bulb lights brighter) which you can see out of the corner of you eye and yank out the power.You can use a dummy load resistor and make your own light or sound indicator across the resistor to let you know if the current reaches a set level. hell, you could make a circuit that starts beeping after a set point and the rate/freq of the beeping is proportional to current. That would be coolIf you use a resistor maybe put a thermal cutout switch on it, just for safety.

author: Rick Law
author_rank: Super Contributor
timestamp: July 05, 2024, 01:33:30 am
content: I work mostly with 12V or below. I use automobile light bulbs for load testing and/or battery drain test.The plus of using incandescent light bulb over resistor is heat dissipation. The light bulb is made to be able to dissipate up to the light bulb's nominal wattage without external supplement such as heat sink. You do have to avoid touching the hot light bulb.The minus is, incandescent light bulb's resistance changes as it warms up to the stable brightness. Good to calibrate it before using it. Calibrate not to the exact 1% number but merely in the sense of knowing in approximation the cool resistance (at your desired voltage) and the stable resistance when running in room temperature.

author: BeBuLamar
author_rank: Super Contributor
timestamp: July 05, 2024, 02:18:12 am
content: Quote from: TimFox on July 04, 2024, 09:53:09 pmIt doesn't have a high coefficient just that the temperature change is too much from off to full on. From normal room temperature to about 4400F (2700K).

author: radiolistener
author_rank: Super Contributor
timestamp: July 05, 2024, 02:51:48 am
content: you can use incandescent lamp, but it's resistance is very dependent on lamp temperature and it's temperature highly dependent on a feeded power. So, if dummy load with variable resistance is ok, you can use it.Also note that incandescent lamp has inductance and is not good for using as RF dummy load, especially on SW, VHF and higher.LED lamps has semiconductors inside and will be very bad reactive load with non linear properties