Off the shelf  "tube" needed for dummy load bank - Page 1
Forum section: electronics / projects

author: ocset
author_rank: Super Contributor
timestamp: February 29, 2020, 10:23:12 pm
content: Hello,The three pdfs attached depict the “chimney tube” resistive load bank, which here is for 48V,6.5A (312W)It is an el-cheapo load bank, easy and quick to make.We just need to find the tube itself……we’d like it to be metal, but will settle for plastic.Do you know of any off-the-shelf tubing like this? (we can cut the air intakes out ourselves).It can be round or square cross section..or “any-side-oganol” for that matter...approx at least 16 cm long….approx 6cm radius...or any length (we can cut it to size)

author: langwadt
author_rank: Super Contributor
timestamp: February 29, 2020, 11:27:19 pm
content: cut four strips of fr4 and solder the corners ...

author: Ian.M
author_rank: Super Contributor
timestamp: March 01, 2020, 12:02:07 am
content: A couple of food cans with both ends cut out then soldered end to end. It will be strongest if you get ones that have a slightly reduced diameter rim at the bottom so they stack. Beware of ones without a rim at the bottom as you cant cut the bottom out cleanly and safely with an ordinary can opener.The 68R resistor (Load Bank 1.pdf, bottom right) is pointless as it only reduces the total resistance by approx 1.2%, but the MCPRW025JW150B00 15R resistors are 5% tolerance, and if they are from the same batch, their errors may well be correlated. If you do need to trim the total resistance, you'll need to measure the actual resistance as built before calculating the shunt trim resistor value.

author: Nusa
author_rank: Super Contributor
timestamp: March 01, 2020, 03:34:30 am
content: I don't know UK sizes, but there are bound to be many choices in both metal and plastic among sewer/drain/plumbing/hvac/dryer/other piping that have the right diameter. Other possibilities are terracotta pots, tea or biscuit tins, big-gulp size mugs, or simply riveting some sheet metal in a circle.If you go with cans, instead of cutting the bottom, one could simply poke a lot of vent holes around the base and put the fan (if any) at the top.

author: duak
author_rank: Super Contributor
timestamp: March 02, 2020, 12:39:31 am
content: Here in Vancouver we have a number of stores that have Chinese and Korean cooking supplies. I recall seeing little stainless steel pots that might be about the size you're looking for. One colleague has a stacking set of small steaming pots that his wife picked up in Thailand. Google "stacking stainless steel steamers" (really) and you should get an idea.I've also had good luck at finding formed metal things like this at the local metal recyclers.Cheers,

author: Zero999
author_rank: Super Contributor
timestamp: March 02, 2020, 10:09:48 pm
content: I Googled 60mm pipe/tube and found quite a few sellers.http://www.everyexhaustpart.com/cart/tube/60mm-2-3-8-tubehttps://www.ebay.co.uk/itm/60mm-2-36-T304-Stainless-Steel-Tubes-Pipes-For-Exhaust-Tube-Repair-Any-Length/142068145224?var=441164200988&hash=item2113ebdc48:m:m2c2OzAToqhrlyoIupJsblghttps://turbozentrum.co.uk/1m-Aluminium-tube-with-60mm-diameter?curr=GBP&gclid=CjwKCAiA-vLyBRBWEiwAzOkGVJIYfKLEwtCvMK3t5EOPzENEBWlpgLNDDW54ijrqVEr1RibxGSio-hoCoQwQAvD_BwE

author: Nusa
author_rank: Super Contributor
timestamp: March 03, 2020, 06:13:14 am
content: Except he said radius. Most stuff is sold by diameter, so twice that.

author: floobydust
author_rank: Super Contributor
timestamp: March 03, 2020, 07:27:14 am
content: You would not make this of plastic or wood, running unattended unless you want to risk drama if the fan stops or it falls over. A thermal cutoff might be a good idea. Or you could let the place burn and confirm why Dyson moved it all to Singapore.In North America, steel ducting is commonplace at the local hardware stores, for home heating and gas vents, dryers etc. I'm not sure what the UK stores might have.The resistors have a 400ppm/C tempco, so you will see the load current sag as they heat up.They are rated for about 200C RISE at 17W under convection cooling, and let's say you achieve half that with forced air to 100C RISE to give 15.6 ohms I think and 6.15A 295W if that drop is OK. Otherwise, you would have to trim or add a rheostat, after temp stabilizes.In reality the top resistors will run hotter as the lowers heat the air, and there is turbulence, so I would stagger the parts and have them cross the center of the duct.You could look at using a mains-appliance like a room heater or toaster oven, stove/range element for the load.I use the power resistors that can be mounted to an aluminium heatsink but this is expensive.

author: Zero999
author_rank: Super Contributor
timestamp: March 03, 2020, 08:51:44 am
content: Quote from: Nusa on March 03, 2020, 06:13:14 amYes, I should have read more carefully.120mm diameter is tricky to find, but 125mm steel ducting seems to be fairly common and is probably near enough for the OP's application.https://www.ebay.co.uk/itm/5-125mm-O-D-T304-Stainless-Steel-Exhaust-Tube-Pipe-0-5m-Half-Meter-/320580672640https://www.dustspares.co.uk/ductwork-parts/galvanised-ducting/galvanised-steel-spiral-duct.html?gclid=EAIaIQobChMI4vvt_vT95wIVgrTtCh1xXQB_EAQYCCABEgI9N_D_BwEhttps://www.industrialproducts-uk.co.uk/size/galvanized-ducting-metal-pipes-heating-round-duct-125mm-180mm-3073/4721?gclid=EAIaIQobChMI4_vOl_X95wIVCbrtCh3kUwCFEAQYASABEgJoofD_BwE

author: nctnico
author_rank: Super Contributor
timestamp: March 03, 2020, 10:14:20 pm
content: Quote from: treez on February 29, 2020, 10:23:12 pmJust buy a friggin' wirewound resistor! Put two in parallel to get to the right value. Look for panel mount resistors in the Farnell and RS catalogues. Why mess around with making something your self which you can buy for a small amount? No need for a fan.

author: ocset
author_rank: Super Contributor
timestamp: March 04, 2020, 07:34:25 am
content: Thanks, but the right values arent in stock.....and we will need to tweak a bit anyway.....and well need to source an alu block from somewhere....and drill it out etc.

author: nali
author_rank: Frequent Contributor
timestamp: March 04, 2020, 09:45:37 am
content: If you have to go that approach then use a real "chimney tube" from a wood burner or boiler flue - they should be available in 6" or 150mm diameter.