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Author: Subject: Setting up and testing a boost power converter
tegwin

posted on 9/1/17 at 10:45 PM Reply With Quote
Setting up and testing a boost power converter

I am currently putting together a power supply to change some drone batteries for work.

The PSU needs to supply 26.3v at a maximum of 9A

I basically need to simulate a load on the PSU for testing. Any thoughts on what I could wire to the voltage output to enable me to simulate a 26.3V, 9A load?

I bought a set of these DC-DC boost converters. Rated at 600W 10-60v in and 12-80v out. Current and voltage can be controlled via multi turn potentiometers
Boost DC-DC Converter Step-up Module Power Supply 600W 10V-60V to 12V-80V 10A

I have wired them up to a 12V 2000w power supply and have managed to set the unloaded voltage to the desired 26.3V.

I am struggling to set the maximum current. The device I wanted to plug in only seems to sit at around 3A current draw but can pull up to 9A in specific conditions. I need to test this maximum to make sure the supply will not give more than the 9A limit.




These are pretty big power units connecting to exceedingly expensive batteries so I don't want to get this wrong.

Appreciate your thoughts

[Edited on 9/1/17 by tegwin]

[Edited on 9/1/17 by tegwin]





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rf900rush

posted on 9/1/17 at 11:02 PM Reply With Quote
A 3ohm load will give a 8.76A load at 26.3v

Aluminum power resistors can be bough cheap (ish)

6 of these in series will give 3 ohms at 300w max.

https://www.rapidonline.com/arcol-hs50-0r5-j-50w-aluminium-clad- resistor-62-8137

I find the 50w ones are generally the cheapest option per watt.

You can use more combinations of these resistors to get different loads.

Just mount them on a big heat sink .

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paulc

posted on 9/1/17 at 11:13 PM Reply With Quote
If i was at work I'd build a couple of test loads using some suitably rated power resistors.

Quick calculation suggests:

3 ohms would draw 8.77A at 26.3 Volts
(This would test your load regulation close to the current limit)

2.7 ohms would draw 9.74A at 26.3 Volts
(this will test your current limiting. You should see the voltage drop to 24.3 Volts, or if you have a suitable Ammeter you could measure the current directly)

Youll need resistors rated at least 250W, 300W would be better.
(Or you could use several lower rated resistors in parallel)

They'll probably need to be bolted to a decent sized heat sink.


Hmmm, a quick google suggest 3 x 10R 100W in parallel would be a lot cheaper than a single 250W

3 x 10R in parallel would give 3.33 ohms (7.89 Amp load)

4 x 10R in parallel would give 2.5 ohms (10.52 Amp load)


[Edited on 9/1/17 by paulc]

[Edited on 9/1/17 by paulc]

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nick205

posted on 10/1/17 at 09:17 AM Reply With Quote
I believe our engineers at work use a rheostat to simulate a load on a battery system they're working on.

Not sure how you spec them or indeed what the cost is, but it may provide you a solution.






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tegwin

posted on 10/1/17 at 09:23 AM Reply With Quote
Thanks for the input gents.

I have ordered a box of power resistors so will have a play with them.



Would I be wrong in setting the voltage without a load?


My theory is that if I set the voltage unloaded. Add the load and then adjust the current until it is what I need. Sound sensible?





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dinosaurjuice

posted on 10/1/17 at 09:45 AM Reply With Quote
a mix of lorry headlight bulbs and tail lights should work too and dissipate the heat nicely
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02GF74

posted on 10/1/17 at 09:57 PM Reply With Quote
If companys paying and has deep pockets, then power resistors, you can always fit to heatsink.

If you are oaying and want to do it locost, then ye olde filamemt household bulbs or car bulbs, whatevet makes up the load.

Actually. 12V or 24 v bulbs are better if you are unable to measure high currents, due to resistanvce of bulbs decreasing with temperature and most likely you will measure restance of them when cold.






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02GF74

posted on 10/1/17 at 10:15 PM Reply With Quote
quote:
Originally posted by tegwin[/i

Would I be wrong in setting the voltage without a load?


My theory is that if I set the voltage unloaded. Add the load and then adjust the current until it is what I need. Sound sensible?



Hard to say without knowing details of the power supply circuit, but it sounds readonable.. Then start connecting headlamp bulbs in parallel to uncrease load , at each stage measure voltage and current, the voltage will show how welll regulated the power supply is.

If you are worried the batteries can draw more than 9A, fit a 10A fuse.






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