A Strapping Good Dump Load

[OperaHouse]

I picked up some pipe strapping the other day and thought it might be a good dump load.  Cheap and easy to manipulate  with lots of surface area.  The holes not only make it easy to connect to but serve to increase the resistance.  The dimensions I measured were .700 wide and .019 inches thick.  A fifteen foot length measured .07242 ohms.   Fold back over in itself for a double thickness for several inches with large washers to reduce heating at connections.  Strapping could be mounted diagonally between wood sections with 2 1/2 inch screws so strap never touched the wood. 

[Larsmartinxt]

What kind of driver are you using to drive the dump load?
At that low of a resistance it would be a tremendous load on the fet/igbt/relay (around 2kw on 12v supply/8kw on a 24v supply)

Also if the strapping is galvanized (looks like it is from the picture) The gasses produced if they are heated would be poisonous.

[SparWeb]

I tried using threaded rods once, not just as dump load but also as a quick-and-dirty shunt, aiming for 0.1 ohm resistance between terminals.
I found that the steel just won't cooperate.  The terminal connections develop corrosion easily enough, especially where fasteners have scuffed it, and it takes just the SLIGHTEST bit of corrosion to make a big change in resistance through the screw.

If you want the easiest cheapest dump load, just go to the dump (sorry, recyclers)(better yet, behind every appliance store is a storage container), find an old dryer, and pry the heating element off of it. 
Minimum 2500 Watts of nichrome in there, if not much more.

[Frank S]

Sparweb I was thinking that probably one of the better dump-loads is like Chris O and others have done by using hot water heaters. the elements can be daisy chained or wired to primary input voltage when a dump load is not required and to provide heated water when needed

[OperaHouse]

None of the dryers and replacement elements I have seen were nichrome.  They were just mild steel.  Might just as well buy a spool of rebar wire.  I don't know why everyone wants things to glow red hot.  The large surface area of this strapping makes it an interesting choice.  Connections are a problem with any part of a system.  Keep them cool and dry, shouldn't be any problem.

I don't dump to a resistor.  I will never dump to a resistor. 

I offer this as an interesting choice and provide an accurate resistance measurment to those who don't have that capability.

[birdhouse]

None of the dryers and replacement elements I have seen were nichrome

are you sure?  usually the actual nichrome wire has a black covering over it that does resemble mild steel. 

I don't know why everyone wants things to glow red hot

i used nichrome wire for my dump load, and by varying the lengths and number of parallel runs, you can get virtually any amount of amps per given dump voltage, and also let the nichrome run as hot or cool as you like.  my dump gets far from red hot.  i did it that way because it made me feel more comfortable about the whole idea.  i also mounted a muffin fan on the enclosure just as added insurance. 

i used the nichrome out of an electric wall heater (cadet). 

adam

[Bruce S]

Far easier to get to would be the sliced bread/bagel toasters. I see them out on bulk pickup days.
They're built to glow red :-). IF I get to dumping extras that means ALL my batteries and cell phones are completely charged.
IF I see it dumping more and more, I check the batteries and add more if I think it's warranted.

Cheers;
Bruce S

[OperaHouse]

I know very well what nichrome looks like.  I've bought a few replacement coils for dryers FSP brand and they were cadnium plated.  That didn't make much sense except they wouldn't rust when stored.

[zvizdic]

Dryer element from old dryer.
Cheap 20$ space heater .
Welding wire
Some of my choices

[XeonPony]

NiChrom from toaster ovens is my faverit source, easy to come by good thick guage and easy to connect.

I've seen loads made with carbon guaging rods after the copper plating been stripped, SS ready rod, steel ready rod, SS welding wire steel chicken wire, all worked and didn't glow unless you wanted them to!

[gww]

Oprerahouse
Why never resistors?
Thanks
gww

[SparWeb]

I didn't mean to stir a debate, OperaHouse.  Cad-plated nichrome?  I don't get it either.  The nichrome that I've got is just dull grey.
The handy thing about using the clothes-dryer element, or even better, a water heater or space heater, is that you get insulated supports with it, too.
Much more convenient to get the heating element inside a heat-resistant box, rather than having to make/find/buy ceramic terminals and enclosure to match.

Opera House, you've given me much good advice and many good ideas over the years (on this forum and the other "tips"), so I must repay the favour a little.
I proved to myself already that it's pretty frustrating to use steel conductors for a fixed resistance.  Hope I can save you some trouble in the future.
Steel strapping will not be a reliable dump load.  Zinc plated or not, the resistance of the connection terminals is very unpredictable.  Dependent on humidity, weathering, corrosion, friction, amount of scuffing through the surface plating and oxides.... on and on.  You can prove me wrong if you work hard enough at it, there certainly are steel screws used in terminal blocks and grounding terminals fixed to all those NEMA steel cases.  But those were made for that purpose, with coatings to suit, and note that the conductor in all those cases is still copper, not steel.  Steel strapping is made to hang ducts in the ceiling.  I have rolls of it on my workbench shelf.  It gets a bit rusty just sitting there.