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Old 08-03-14, 11:18 AM   #1
stevehull
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Default PV powered pond aerator

I have a ~ 2 acre irrigation pond that needs aeration to prevent algae growth in summer.

On another pond, closer to the house, I use a 110 AC powered air compressor that leads via tubing to an air stone on the pond bottom. Works like a charm.

I have been looking on e-Bay and have seen 12 V DC diaphragm type air compressors that put out about 50 L/min (~13 gallons/min) and they use about 35 watts. Don't need a car tire type pump as I don't need that high pressure. Can't use the cheap ($10) air pumps to blow up air mattresses as they are too low in pressure. Need about 15-20 psi max and the $50 e-Bay pumps do this.

Don't need to run this air pump 24 hours a day and daylight hour operation would be fine. Here is the question . . .

Can I buy a 50 watt PV panel and connect it directly to the DC air pump? I could easily use a small charge controller connected to a battery, but that battery is another $80 expense and I don't need to run the air pump all the time.

Couple concerns. What if the PV panel is putting out 50 watts and the pump only requires 35. Is the PV panel a voltage source or a current source? Also what about start up when the PV panel is not putting out enough voltage - will the pump burn out (due to higher current?).

Thinking of putting on a small voltage regulator . . ., but do I need to go to this trouble.

Thoughts? As always, thanks in advance.

Steve

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Old 08-03-14, 12:42 PM   #2
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Steve, my understanding is that PV alone, i.e. without a battery and everything that goes with it, can't be used with anything that might require a surge current on turn on. Could be wrong... Maybe someone else has a definitive reference.

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Old 08-03-14, 01:26 PM   #3
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Use a MPPT controller. That will automatically boost the current for starting.
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Old 08-03-14, 05:22 PM   #4
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Mike,

Any particular suggestions for an MPPT controller? Most I looked up need a battery.


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Old 08-04-14, 07:52 AM   #5
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Kind of sounds like a good place to use an Ultra Capacitor.
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Old 08-04-14, 07:49 PM   #6
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What you need is more or less a buck converter that tries to regulate the input voltage. Set it to try to keep the input voltage at the MPPT voltage speced on the panel and it's good enough for small applications.
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Old 08-04-14, 10:12 PM   #7
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Mike,

I haven't heard that name (buck converter) for more decades that I would like to name. These were brute force voltage regulators if I recall that generally lowered output voltage from a varying DC source input.

Do I recall correctly?

Is this in a single element device - or do you need to wire up a circuit for it.


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Old 08-05-14, 12:55 AM   #8
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You use a PWM controller to switch a MOSFET. In your case, the motor acts as the inductor, so you just need to add a diode across the motor and a bypass cap on the input. Have the PWM controller try to hold the input voltage at the MPPT spec and it should work great. I suggest using a slow response (10Hz bandwidth or so) as that helps keep it stable. A good switching frequency to use is about 4kHz if audible noise is not an issue, 20kHz if it is.
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Old 08-08-14, 10:31 AM   #9
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Mike,

Xringer just suggested this.

150W DC DC 10 32V to 12 35V Converter Boost Charger Step Up Booster Power Supply | eBay

What do you think? They are $5-6 and might solve the problem . . .


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Old 08-08-14, 07:46 PM   #10
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That's a boost converter when you need a buck converter. It also needs to try to regulate the input voltage rather than the output like most converters.

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