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PSU Load bank

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Dngrsone

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I am looking at building a load bank for testing and troubleshooting ATX computer power supplies.

I obviously will need a bank for each voltage rail (5vsb, 3.3, 5, 12v1, 12v2) and I want to make the banks switched to get different current load requirements ranging from min current (ex 12vdc @1a), to current limit for a particular power supply (a 250w PSU should have 8a on the 12vdc rail 1) ranging up to around 600w levels (for now).

So, rather than sit and waste hours on end calculating the values for each resistor to go in the stack for the next current level (it took me more than an hour to calculate the 12v1 bank alone), I opened up Excel and created a spreadsheet that would help me calculate the values of the precision power resistors I needed for each stage of each bank.

Attached image shows the results for one set of calculations.
Also attached is the Excel file. I would like a sanity check on my calculator before I start ordering components based off teh output of this calculator.

The rail voltage is entered in cell B1, the current requirement for each bank step is plugged in under Amperage.

The first R-value resistance matches the impedance required for teh minimum amperage level, and is used by the calculator to establish the actual impedance and actual R-value req'd, which I then round-up/down and plug into the next R-value slot to continue calculation.

The R-values will be the resistance I add for each current step, the actual amps and actual watts are my checker to make sure I don't misstep in setting my r-values.

At least, that's how it's supposed to work. Am I off?

Regards,
 

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  • psu_calculator.jpg
    psu_calculator.jpg
    52.5 KB · Views: 322
  • psu_load_calculator.xls
    16.5 KB · Views: 158
I don’t want to rain on your parade but I have to ask; is there really a market for this, I mean repairing these PSUs? If I get a suspect or faulty one I scavenge the goodies I can use and then put the rest in a dumpster. A new cost only from $15 to $30 US (400W). :?
 
ante said:
I don’t want to rain on your parade but I have to ask; is there really a market for this, I mean repairing these PSUs? If I get a suspect or faulty one I scavenge the goodies I can use and then put the rest in a dumpster. A new cost only from $15 to $30 US (400W). :?

Well, good power supplies cost quite a bit more than that, and it's also useful for evaluating new PSUs (I write the occasional article fo an online computer magazine).

I realize that I will have to factor in the impendance caused by my voltmeters and the cooling fans I use for the load, that isn't in the excel file yet, but it will once I have those items nailed down but before I order any resistors.
 
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