20A load tester

Thread Starter

SimpleJoe

Joined Mar 22, 2016
38
I'm looking for ideas on a quick and dirty way to make a cheap load tester for a 18V 20A boost converter, ideally with household parts that I can salvage. My first thoughts are electric kettle elements in a bucket of water but I believe they are around 10 ohm so I'd need around 10 to get the amperage i'm looking for. Also possibly electric radiator fans, a little outside of their usual operating voltage but I think they should be fine. Has anyone made something like this/any recommendations for testing circuits with high amperage? All of my projects so far have been max 5A so any input is welcome


A little bit of background info behind the project:

I'm looking to add a 21700 Li-ion battery pack to my car to run a centre console fridge almost indefinitely and charge it from the alternator and possibly a small solar setup. The pack will be 4S (16.8v) and around 30AH. I haven't actually purchased the cells yet, however I've found uncycled tesla 21700 cells around the same price as used ex laptop batteries, but the customisable size/shape as well as the cost and life is the rationale behind going with them, 4S as 3S's voltage is too low for the fridge and I'd prefer to do the voltage conversion on the charge side to get the most out of the pack. To charge this correctly I'll need an input of 16.8-18.1V which means I need a boost converter to up the alternators voltage, I would also like it to charge at around 20A (post voltage boost so around 25A on the input) or as close to as possible. I've linked a boost converter I'm looking at below, but I'd like to do some testing on it before I hook it up to my battery pack as I've found most of these converters are electrically noisy and I'd prefer to still be able to listen to the radio in my car.

Boost converter I'm looking at: https://au.banggood.com/1500W-30A-D...yCh1jFA9XEAQYAyABEgKob_D_BwE&cur_warehouse=CN

TIA SimpleJoe
 

Thread Starter

SimpleJoe

Joined Mar 22, 2016
38
Have you thought about using halogen lamps?
Funnily enough, I thought common light bulbs but then dismissed them due to the low voltage and then I thought 100W LED cobs with their own voltage boosters to bring the 18v up to their forward voltage but decided that just going to be noise on noise and painful to cool properly. Halogen never crossed my mind to be honest I'll give it a look, thanks for the input
 

Danko

Joined Nov 22, 2017
1,039
Last edited:

Thread Starter

SimpleJoe

Joined Mar 22, 2016
38
Simple make spiral from nichrome wire and put it in your bucket of water.
For example: 85 cm of 18 gauge (1mm dia) nichrome wire has resistance 1Ω.

https://www.basictables.com/electronics/resistor/wire-resistance.
You are right, that is simple.
I've never really spec'd a wire to intentionally heat up, surely there is some maximum amperage that can be put through a wire like this, is it safe to assume it follows the rough scale of regular wire? So I'm looking at ~14AWG to safely handle 20A or is that irrelevant in cases like this?
 

drc_567

Joined Dec 29, 2008
1,062
The best load test part is a pure graphite or carbon rod out of a toaster oven. ...
In the event that you don't have a spare toaster oven to take apart, industrial supply stores should stock them.
 

AlbertHall

Joined Jun 4, 2014
10,903
You are right, that is simple.
I've never really spec'd a wire to intentionally heat up, surely there is some maximum amperage that can be put through a wire like this, is it safe to assume it follows the rough scale of regular wire? So I'm looking at ~14AWG to safely handle 20A or is that irrelevant in cases like this?
It is irrelevant if all the nichrome is under water. The current limit is to prevent the wire overheating but the water will conduct/convect the heat away very quickly.
 

Marley

Joined Apr 4, 2016
403
Have you got any iron fencing wire? Or even a fence with wire on it! On wooden posts. No matter if it's galvanised. The zinc coating is too thin to make much difference.
Use this calculator https://www.owenduffy.net/calc/WireDcResistance.htm
to work out the length of wire required.
For example: 30m of 2mm diameter iron wire has a resistance of 0.954930 ohms.
CAREFUL - The wire might get hot!
You did say you wanted a real cheap and dirty resistive load!
Beware that the resistivity of iron (like most metals) increases as it warms.
 
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