Electronics > Beginners
Standard electric kettle as a DC dummy load ?
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Doctorandus_P:
Sorry about double posting Mike's video, I didn't realize it was already linked to.
A kettle made for 120V (ac or DC, does not matter) is going to see 1/10th of the voltage at 12V, which will be 1/144th of the power.

Over time I've come to dislike the gold colored aluminimum resistors such as in Mikes YT vid. These are very heat sensitive, break easily, and are more expensive than ceramic resistors.

Ceramic resistors are pretty cheap, and you can easily mount 2 of them to a chunk of aluminimum. Just tap a single hole in the Aluminimum between them and use a big washer with a screw. More neatly also more effective would be to use a short piece of Aluminimum U-profile with a hole in the middle. The flanges of the U-profile provide extra cooling.
5W ceramic resitors cost about 15ct from Ali / Ebay / China, and I would not be surprised if these can safely & reliably handle a 10 fold overload, if bolted to a chunk of aluminimum.
If you want to go fancy, bolt them to a piece of square aluminimum tubing, and pump water through the tube.

These ceramic resistors can get bloody hot without failing.
A very simple & effective overload cutout would be to solder the wires  close to the resistors, and ad a spring. If the thing gets so hot that the solder melts, the spring will pull the wire away and break contact.

Edit:
I just had a peek at a datasheet for a 5W Ohmite resistor, Series TWM/TWW:
https://octopart.com/tww5jr39e-ohmite-1147827
http://datasheet.octopart.com/TWW5JR39E-Ohmite-datasheet-8450738.pdf

These resistors are rated for a temperature of 275 Celcius, and have to be derated lineairly from the ambient temperature. So they can be safely used to temperatures above the melting point of solder, and they have 2 nice flat surfaces to bolt some aluminimum on.
Brumby:

--- Quote from: Doctorandus_P on July 14, 2018, 08:15:43 pm ---A kettle made for 120V (ac or DC, does not matter) is going to see 1/10th of the voltage at 12V, which will be 1/144th of the power.

--- End quote ---
(Ahem...  Check your math.)
Nusa:

--- Quote from: mtdoc on July 13, 2018, 03:55:50 pm ---Cheap water heater elements can be used for a dummy load but even they have a high enough resistance (the one I have is 8 ohms) that many in parallel would be needed to fully test a 1200W 12V supply.

--- End quote ---

Fairly cheap water heater elements can also be had for 12V, 24V, or 48V systems.
Shock:

--- Quote from: Nusa on July 15, 2018, 03:03:10 am ---Fairly cheap water heater elements can also be had for 12V, 24V, or 48V systems.

--- End quote ---

12V travel hair dryer with different heat settings might work as well. They go for as little as $20 have built in cooling. Plus you can do your hair.
max_torque:
If you need to pull really high currents at low voltages, get yourself a roll of 1/4" (or 6mm for people who live in proper countries..... ;-) ) diameter thin wall copper tube, typically used for automotive brake lines.  Unroll it  into a spiral onto a wooden 'former' and by sliding the contacts up and down the spiral you can change the load.  And, using something like an aquarium or car windscreen washer pump, (or just a hose off a kitchen tap) you can pump cold water up the middle of the tube to cool it.

When i was developing a high current / low voltage DC/DC project this is what i used!
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