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After failing to find an answer online I hope someone here would know how to solve n issue I have. I use a 12v, ~10w solar panel to activate a couple dc fans. The problem is that when activated, the voltage drops from ~13.5v to around 3v which prevents the fans from working completely. I have different fans of Delta brand, model PFB0912EHE and they have a built in electronics that actually makes them work at any sun exposure and that is exactly what I need... the problem is - they are pricey and I need a lot.. does anyone know how do they work? Can I buy any component that would do the same without using too much energy? Thanks in advance guys!

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    \$\begingroup\$ Each of your fans requires 8W. How many of them did you expect to be able to run from a 10W panel? \$\endgroup\$
    – Dave Tweed
    Jul 1, 2017 at 13:41
  • \$\begingroup\$ I use 2 of them and they run pretty good solely on solar panel... Sometimes I add additional power source \$\endgroup\$ Jul 2, 2017 at 16:52
  • \$\begingroup\$ Wait, in your question you said that it doesn't work! Which is it? Sorry, but we do real engineering here. If all you want something that may or may not work, you're already on the right track -- just try it and see. \$\endgroup\$
    – Dave Tweed
    Jul 2, 2017 at 17:06
  • \$\begingroup\$ I said that "normal" dc fans doesn't work, but model pfb0912ehe works great even though it uses 16 watts. If anyone knew what is the reason they work so good it would have solved the problem... I need something that would work good on any condition since it'll be a part of a product... Sorry if it sounded not serious but I really struggle with this one \$\endgroup\$ Jul 3, 2017 at 19:26

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You may have the following issue: In startup your motor eats much higher current than if the motor were running. No starting happens and the current draw stays high. If you have large enough capacitor that stores enough energy to kick the motor running and the output power of your panels is enough for steady state running, you probably get your fan working. Unfortunately I do not know, how high capacitor is needed in your case. Maybe not a Farad, but plenty of millifarads. A rechargeable battery also does the job.

In both cases you need a properly designed auxiliary circuitry. For batteries proper designs are surely available, but the buffer capacitor needs something different.

Do a test. Start your fan with a DC power supply or battery. Then fastly (less than 1 second) disconnect the starting supply from the fan and put a panel instead. If the fan still runs, you have a possiblity to succeed.

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  • \$\begingroup\$ Thank you. Adding a battery would solve the issue but it'll need heat resistance and it would cost much more... The ideal solution is to add a circuit that would prevent the voltage drop (hopefully) \$\endgroup\$ Jul 2, 2017 at 16:55
  • \$\begingroup\$ @GuySahariya That circuit must create the needed power to kick your moto running. It cannot take that power from elsewhere than a storage and the panel. A capacitor can be one form of storage. In theory an active matching network (=switch mode power converter) without any massive storage could solve your problem if the available power from the panel were enough for startup. We need load current-output voltage diagrams of your panel and voltage-current-rpm charcteristics of your fans (a lot of curves) to be able to make any quantitative suggestions. NOTE: One battery is enough for several fans \$\endgroup\$
    – user136077
    Jul 2, 2017 at 22:21
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  • revised with corrected fan specs of 8W * 2 rather than 24W * 2

12V cheap PV's are often 21Voc and 18Vmp. Yours appears to be 10W (at some undefined load) which would require two 5W 18V fans instead of two 24W 8W 12V fans. ___You must determine the optimum

At Max power transfer MPT on the PV panel, R=V²/P= 18²V/10W= 32.5Ω or 0.55A maximum. or you can briefly short circuit the panel and expect 80% of Isc at MPT of 80% of Voc.

The Each PFB0912EHE draws 24 watts 8.16W (12.56W max) at 12V or 2A and 28.2W

Also consider than fan RPM increases with Voltage but power may be linear at low speeds but more quadratic and cubic order at high speed. Thus test your fan power vs supply voltage and RPM pressure loading effects. Never assume it is linear.

If two Zfans(12V)are 8W * 2=16W @12V then from \$R=V^2/W= 12^2/18W = 9 Ω and Zfan(13.2V)=13.2V/2.35A= 5.6Ω Thus two fans together are 3 Ω at 12V

Better learn to do Engineering power calculations next time then confirm your estimates with measurements and consider that reduced solar input may cause the fans to stall from the load line solar current source intersection.

you indicated > they have built in electronics that actually makes them work at any sun exposure

You have been misinformed if someone advised you that these two fans will work on this panel. All fans are somewhat constant current sinks which can match constant sun PV panels only if the power ratings are matched at the same max power voltage. and FWIW EBAY specs are terrible.

Experience

Airflow is proportional to rpm but power is a cube function or \$Pd= k*rpm^3\$. RPM is no longer linear with voltage at full speed due to loading effects.

  • But for most muffin fan designs, Power reduces 50% when rated voltage drops to 66% of Vrated
  • Whereas a PV source at MPT ideally, at 50% max sun , the power drops 50% while voltage drops to 45% of Vmpt or 36% of Voc and current can rise 8% .

So they are not matched for maximum power transfer. Normally you load max. open circuit Voltage 80% Voc +/-5% depending on PV profile for V vs I.

The key to remember in matching any load to any unregulated power source for max power transfer is to match impedances even with a non-ideal current source of the PV array.

  • Although using a regulated voltage source you want the biggest load to be 99x bigger than the source ESR impedance so full load only drops the voltage 1% or \$\frac{99}{99+1}\$, a PV is not a voltage source.

At max power below at 120W the slope of ΔV/ΔI=ESR ~ 9Ω with estimation error while Vmpt/I=31V/3.75=8.3Ω is matched linear load resistance. But it is an important concept to realize the PV cell at fixed solar power changes from a voltage source with low impedance to a current source with higher resistance. Then after which, current reduces with sun power ( as well as dust, tilt and aging) enter image description here

Reference https://www.physicsforums.com/threads/fan-rpm-vs-power-consumption.788965/

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    \$\begingroup\$ Your link text says "PFB0912EHE" (the 8-watt fan), but the document you linked to is actually for the PFB0912UHE, a 24-watt fan. Also, modelling a solar panel as a resistive source is completely bogus -- it's much better to treat it as a current source. \$\endgroup\$
    – Dave Tweed
    Jul 1, 2017 at 15:44
  • \$\begingroup\$ Sorry Dave I dont see where you see 8W . THe spec link states 24W. But contrary to your opinion , impedance analysis anywhere on the load curve is the best way to understand that the power Q point is when impedances are matched since it is neither a constant current source or constant voltage source but a dynamic power source that demands impedance matching for efficiency. At full solarity with MP at about 80~82% Voc. Bogus applies to your advice as current source into a *mismatched current sink or dynamic load impedance. \$\endgroup\$ Jul 1, 2017 at 16:14
  • \$\begingroup\$ See the link​ that I inserted into the question. \$\endgroup\$
    – Dave Tweed
    Jul 1, 2017 at 18:45
  • \$\begingroup\$ I use two pfb0912ehe fans, each one consume 8 watts and they work great with a panel of 10w... Any other fan falls to start even using less watts.. I wish I could find out what are the electronics that makes them work so good... \$\endgroup\$ Jul 2, 2017 at 16:59
  • \$\begingroup\$ Thanks @DaveTweed for the correct fan spec. @ GuyS your last comment contradicts your question, which suggests you had a problem( perhaps you forgot to mention which fans fail). If you read my revised answer until you understand it. The fan has NO SPECIAL ELECTRONICS. The answer is due to having closer to matched impedances of load to source yet albeit imperfectly matched so you cannot possibly get 100% of 10W unless impedances are matched. Pls Ask a better question if you dont understand. \$\endgroup\$ Jul 6, 2017 at 1:05

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