Electronics question, aluminium as power rail?

Gundog48

Gundog48

Gundog48

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Long story short, I am building a dummy load for testing PSUs which will consist of a bank of 12x 100W bulbs set up in parallel with switches for each bulb. The design is OK, but it means that the power rail will have to handle up to 100A on full load which would require some thick wire and good homemade screw terminals.

Instead, I had the idea of using an Aluminium strip as the main voltage rail, which I can drill and bolt the switches and bulbs to. Is there any problem with using this method instead of normal wire?
 
Aluminium is quite a good electrical conductor, but not as good as copper.

Google 'copper bus bar', you're really gonna need something chunky if you're going to want something that's gonna take 100A. :eek:
 
I did think that, but the advantage is I can get thick aluminium strips for free! A big ol' aluminium strip has got to be better than 4mm wire surely? Anyway, what mostly concerns me is the fact that it is non-linear. Ie. when using wire, the current is forced along a direct path to each connection, whereas here it isn't forced directly to a connection. It's probably not a problem but I felt I should check!
 
Yeah, the bulbs are 100W car headlights. The advantage is that as they are car headlights they run on 12V just like the PSU, so 1 bulb = 100W load!
 
Yeah, I've got some 500W halogen floodlights and they are bright enough! It will be enclosed in a box but it's sure as he'll going to get hot! At least when I'm not testing PSUs it will double up as a lighting system for videos and photos and a 1200W room heater!
 
Gundog48 said:
Yeah, the bulbs are 100W car headlights. The advantage is that as they are car headlights they run on 12V just like the PSU, so 1 bulb = 100W load!
Click to expand...

Got it.

You'd better put one of these up:

Worn-Eye-Protection-Caution-Sign-S-1309.gif
 
Thanks for the quick responses anyway, had a brainwave in the middle of the night and had to post before I forgot!
 
But surely because they're going to get hot they will use more power? So it wouldn't be exactly 100W, it would be 100W worth of light energy and a hell of a lot of heat energy.

Also, enclosed box? What's the box made of? Something that will set on fire? If not, something that will conduct heat to something that will set on fire?
 
Gundog48 said:
I did think that, but the advantage is I can get thick aluminium strips for free! A big ol' aluminium strip has got to be better than 4mm wire surely? Anyway, what mostly concerns me is the fact that it is non-linear. Ie. when using wire, the current is forced along a direct path to each connection, whereas here it isn't forced directly to a connection. It's probably not a problem but I felt I should check!
Click to expand...
You should be fine, if it's thick. If it's not that thick, just use more than one layer. If you really want to go to be sure, you can calculate how much CSA you will need, using the I=NAVE formula. How thick are they roughly?

While most cable is made from copper, you sometimes see aluminium cable as it's more lightweight and it used when copper is too heavy to carry. It's thicker than it's copper counterpart however, so don't feel afraid to use more than you think you need.

Do not use steel, as it has far higher resistance than aluminium...
 
why not use the right value resistors, you can do simple calculation to work out what you need, as you know the Amps and Wattage you want to draw.
 
It's going to be set on an MDF base with the rest made out of aluminium sheet. 100W is the total energy, so 100W of light and heat combined. Fortunately I will mainly be testing 700-850W units so it shouldn't be a massive issue. Although I have decided to install the 120mm fan now!
 
stulid said:
why not use the right value resistors, you can do simple calculation to work out what you need, as you know the Amps and Wattage you want to draw.
Click to expand...

100W resistors are pretty expensive, and these also need to be heatsinked.

If you just want a dummy load for a 12v rail, then car bulbs are a cheap and cheerful way of doing it.
 
stulid said:
why not use the right value resistors, you can do simple calculation to work out what you need, as you know the Amps and Wattage you want to draw.
Click to expand...

That was the original plan, however big power resistors are expensive and need to be kept cool otherwise they break. Also with the lights, some of the heat is being removed as light rather than heat, and the bulbs don't need to be kept cool. I also considered using MOSFET transistors, however they have to be kept even cooler, which I didn't consider a problem until I realised I needed to remove 1200W of heat and my CPU only uses 140W in total! Plus the MOSFETS are more sensitive to heat than a CPU.
 
Aluminium is a good conductor, but is also highly reactive (compared to most metals) - so much so that it reacts instantly with oxygen to form a protective/insulating layer which then prevents further "rusting". Hence it is considered unreactive as it always has an inert coating. [This layer, along with a high melting point, is what makes welding aluminium so tricky.]
/lesson

As far as your system is concerned, this may not be too critical at 12V, as long as you are not using croc clips to connect to the aluminium bars. Ideally use something like a tapered brass screw, threaded into a pilot hole to give a good 'bite'. If using a nut/bolt through the bar, wirebrush/sandpaper the contact areas first to minimise the insulating layer.
 
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