Decade box and dc electronic load - Page 1
Forum section: electronics / beginners

author: Unknown
author_rank: Unknown
timestamp: July 03, 2013, 04:04:03 pm
content: Hi,Dumb question, but i'm wondering what's the difference between a decade resistance box and an electronic load.

author: c4757p
author_rank: Super Contributor
timestamp: July 03, 2013, 04:07:40 pm
content: Resistance boxes are generally not made to dissipate much power (often 1W max), whereas loads will frequently do 25, 50, 100W. Also, loads can be set to a specified current as well as resistance, and will often provide some monitoring features.On the other hand, a load is a poor approximation of a resistor, so you wouldn't exactly want to use a DC load set to constant resistance mode to choose a feedback resistor for an op amp.

author: Unknown
author_rank: Unknown
timestamp: July 03, 2013, 04:11:02 pm
content: So, it's only an issue of power dissipation?

author: c4757p
author_rank: Super Contributor
timestamp: July 03, 2013, 04:11:57 pm
content: Quote from: c4757p on July 03, 2013, 04:07:40 pm

author: Unknown
author_rank: Unknown
timestamp: July 03, 2013, 04:15:10 pm
content: Quote from: Oracle on July 03, 2013, 04:04:03 pma decade resistance box is a series of resistors, in which you can select any resistor you want to apply to a circuit or a breadboard for testing or trying to find a replacement for an unknown resistor. you wouldn't want to use it as a "load"an electronic load is for testing a device for minimum or maximum current draw, to see when and where the load drops out or starts to work / regulate. this will be able to handle larger amounts of current.

author: Unknown
author_rank: Unknown
timestamp: July 03, 2013, 04:35:04 pm
content: To put it succinctly, an electronic load is a current sink. That's not what a decade resistance box is designed to do. It is possible to use each as a substitute for the other in limited circumstances, but that's not what they're designed for.

author: edavid
author_rank: Super Contributor
timestamp: July 03, 2013, 04:37:49 pm
content: There are power decade boxes... Clarostat 240-B, 240-C, and 250, and a few similar ones. They are still very popular, as you can see from eBay prices. Nice and simple compared to an electronic load, and of course they also work for AC (although they are made of wirewound resistors).

author: Unknown
author_rank: Unknown
timestamp: July 03, 2013, 04:42:41 pm
content: In fact: at school i had one of those... Anyway, a decade resistance box i assume is more accurate than a dc load and will cost much more

author: c4757p
author_rank: Super Contributor
timestamp: July 03, 2013, 04:43:13 pm
content: Quote from: edavid on July 03, 2013, 04:37:49 pmThat's definitely nice. I wonder how much inductance there is in those wirewound resistors.

author: Unknown
author_rank: Unknown
timestamp: July 03, 2013, 04:46:07 pm
content: Quote from: edavid on July 03, 2013, 04:37:49 pm? wirewond resistor?

author: c4757p
author_rank: Super Contributor
timestamp: July 03, 2013, 04:48:00 pm
content: Quote from: Oracle on July 03, 2013, 04:42:41 pmNot necessarily. Some are calibration-grade, some are crap-grade. That applies to both.QuoteFrequently.Quote from: Oracle on July 03, 2013, 04:46:07 pmA resistor made by winding resistance wire. Most power resistors tend to be wirewound. They're not the best for AC because the winding gives them inductance as well as resistance. (You can get low-inductance wirewounds, which are wound in such a way that the inductance cancels out.)

author: Unknown
author_rank: Unknown
timestamp: July 03, 2013, 04:49:36 pm
content: It's strange, never hear about wire wounded decade resistance box.

author: c4757p
author_rank: Super Contributor
timestamp: July 03, 2013, 04:52:25 pm
content: The precision one Dave recently tore down used wirewound resistors.

author: Unknown
author_rank: Unknown
timestamp: July 03, 2013, 04:54:55 pm
content: really? I'd missed it.

author: Unknown
author_rank: Unknown
timestamp: July 03, 2013, 09:20:48 pm
content: Quote from: Oracle on July 03, 2013, 04:54:55 pmwow, I have made it a "requirement" to watch every video he has made, or my employee no longer has a job.Right Steve???

author: ptricks
author_rank: Frequent Contributor
timestamp: July 03, 2013, 09:46:20 pm
content: And when in a pinch, incandescent bulbs are great for loading a supply.

author: c4757p
author_rank: Super Contributor
timestamp: July 03, 2013, 09:53:03 pm
content: Don't underestimate the utility of common, everyday resistance elements. I have a couple incandescent lamps of different sizes and a length of resistance wire I yanked from a toaster that make for excellent loads in a pinch. The toaster wire's even adjustable.

author: Unknown
author_rank: Unknown
timestamp: July 03, 2013, 10:25:48 pm
content: The guys at The Geek Group use a bunch of light bulbs as a current sink for their "thumper" capacitor bank.

author: Unknown
author_rank: Unknown
timestamp: July 04, 2013, 06:32:09 am
content: good tip making load whit bulbs!