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I've built a small desktop fume extractor for soldering.

It uses a 120mm 1000RPM, 12V, 0.08A case fan. Not huge, but it does the job.

The fan is only drawing roughly 0.04A and I have been fault finding and theory checking all afternoon and I can't figure it out and I feel like such a fool now, I should know this.

The fan is powered by a 12V DC 1.5A supply.

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  • \$\begingroup\$ You can only increase current draw by increasing the voltage and I wouldn't do that. \$\endgroup\$
    – po.pe
    Commented Jan 13, 2021 at 9:07
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    \$\begingroup\$ In what way do you think there's a fault? Is it not running at around the correct speed? \$\endgroup\$
    – Andy aka
    Commented Jan 13, 2021 at 9:15
  • \$\begingroup\$ Thanks po.pe, that was my only thought out of it so far and as you said, wouldn't be ideal. \$\endgroup\$
    – Brendan
    Commented Jan 13, 2021 at 9:17
  • \$\begingroup\$ Andy it seems as though its running slower than it should, and given that its drawing half the rated Amps I thought there must be something wrong. \$\endgroup\$
    – Brendan
    Commented Jan 13, 2021 at 9:18
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    \$\begingroup\$ Internally the fan is a BLDC motor with a three-phase switching circuit and position sensing. It's not a brushed DC motor. Note that if you are addressing someone in a comment you should ping them by using @username (with no spaces). Then your response will show up in their inbox. \$\endgroup\$
    – Transistor
    Commented Jan 13, 2021 at 10:29

2 Answers 2

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The .08A is most likely just a guide to power consumption, not a spec. The fan is designed to work on 12VDC, and that's what you should give it. The current draw will depend on the load on the fan which usually won't change much. You could try upping the voltage a bit but it's really pot luck how far and at some point you will damage it if you go too far.

(Of course if you have a comprehensive data sheet for the fan you might be able to learn the max voltage, but mostly this info doesn't exist on cheaper models.)

If you don't have enough air movement, the solution is a bigger and stronger fan, or multiple fans.

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    \$\begingroup\$ Absolutely, thanks @danmcb I understand what you're putting across there. 12VDC indeed was exactly what I gave it. All seems to make good sense now. \$\endgroup\$
    – Brendan
    Commented Jan 13, 2021 at 10:35
  • \$\begingroup\$ thank you, pls mark as answer if this does what you need. \$\endgroup\$
    – danmcb
    Commented Jan 13, 2021 at 10:36
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0.08A is probably the MAX power consumption while the fan is spinning at its rated rpm, Not normal power consumption. Fans are used in casings which decrease the airflow and make fans struggle hence they draw more amps, try covering both sides of fan with something like a cardboard or your hands and you will notice increase in Amp draw.

Regarding the rpm, you are probably guessing rpm by the sound fan is making, fans makes louder noise when attached to something because of vibrations and decreased airflow mimicking the effect of higher rpm, Ambient temperature also is a huge factor

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  • \$\begingroup\$ Fabulous, thanks @asim I appreciate it. My understanding was that applying "drag" to the fan would increase consumption, and so it did. Youre spot on with the sound, and air restriction of cases too. Great point. Need to brush up on my HVAC engineering too! Mostly my curiosity was just by eyeballs the fan and noticing it seemed a little slow, but I don't have much to reference 1000rpm to. Will likely invest in something more powerful. Thanks! \$\endgroup\$
    – Brendan
    Commented Jan 13, 2021 at 10:38

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