12v air pump without battery

[p3ter]

My first post and first 'toe in the water' solar project... I want to run an air pump with air stone to aerate a a well at our summer place, to try to freshen the water a little and hopefully also remove some iron deposits int he water. We don't use the place all year round, and it's not critical, so the pump can run sporadically (when the sun is shining) I am buying an air pump usually used in Koi Ponds, a Resun MPQ-902 38L/MIN 0.06MPA 18W 12V from China, and I have assumed that a simple DC motor could be connected directly to a solar panel, on the assumption that the pump will run when it is sunny enough, and will not run when it gets too dark.

So my question relates to what size panel I should buy to drive a 12v 18w pump. Is there a risk of frying the motor if I go a lot bigger than the 18w the pump needs, or will a motor simply draw as much power as it needs? My gut feel is that I would go for a 30WP 12v panel, which from those I have looked at peak at 30w and about 17v in perfect conditions. I'm at 60 degrees north (Sweden) so I would prefer to over-dimension a bit as long as I don't risk damaging the motor.

I appreciate your input!

[Wy_White_Wolf]

First thing you need to look at is the voltage range of the motor? Can it handle the 17 volts? can it handle the VOC of the panel. That is the first thing that will burn up the motor.

Next can the motor handle under amperage conditions such as light clouds when the panel can not produce full power? A LCB (Linear Current Booster) can help with this but on some motors does not prevent damage.

Usually I size the panels IMP to between 1.5 to 2 times the amperage draw of the motor. This will help extend the time it can power the motor.

WWW

[p3ter]

Thanks, I was not aware of LCB's and they look interesting, looks like you also have the option of going to a higher voltage solar panel to give you more amps & regulated 12 volts in marginal conditions... Good food for thought. I guess without experience I am trying to second guess what happens in high & low output conditions.

In a low light condition, I assume a motor might stall (e.g. when a cloud covers the sun) and after the cloud passes, on a hazy day for example maybe the motor stays stalled, since although the panel is supplying marginally enough amps to run the motor, it is not supplying the initial kick of higher amps needed to start the motor spinning. I can see that the LCB would help with that.

In peak direct sunlight, as you said its the volts I need to worry about. I don't think I will be able to easily find out the voltage range of the motor, but e.g. 17v doesn't sound too dramatic for a 12v motor... Since there is no hurry with this, I guess I could try at home without an LCB first and get a feel for the ranges.

Thanks again!

[p3ter]

Found this warning in the instructions for one Linear Current Booster:
"It is highly recommended an external fuse or over temperature device is incorporated. This unit is quite capable of putting a continuous 15 amps into a stalled motor even from only 1 amps worth of solar panels, resulting in motor burnout."
...so it looks like an LCB actually could cause a new problem... Due to the well location and sporadic visits, I might prefer a motor running at over voltage intermittently and potentially shortening motor life than having to keep an eye on a fuse...

[inetdog]

Found this warning in the instructions for one Linear Current Booster:
"It is highly recommended an external fuse or over temperature device is incorporated. This unit is quite capable of putting a continuous 15 amps into a stalled motor even from only 1 amps worth of solar panels, resulting in motor burnout."
...so it looks like an LCB actually could cause a new problem... Due to the well location and sporadic visits, I might prefer a motor running at over voltage intermittently and potentially shortening motor life than having to keep an eye on a fuse...

If the pump is jammed and that causes the stall that draws the overcurrent, would you rather blow a fuse or burn out the motor. In either case (LCB or not) the pump would not be running and doing its job.
Consider a self-resetting circuit breaker instead of a fuse.

[Logan5]

I have done this with both water and air pumps. It can work, but much attention must be paid to the the selection of panel size and pump designed to work on solar or with tolerances within the voltages your array will be producing. I found it better to run 3 smaller panels arranged in an ARC facing SSE, S, and SSW, This will give you a full day run and help balance your system. I found the pumps rated 12 to 24 volts very useful in this application. although I have run 12 volt pumps at or above 17 volts, they do not last very long. I have since reverted back to the 120 volt outlet as much more reliable. Not to mention CHEAPER!

[p3ter]

Thank you all for the input! It starts to sound like the charge controller and battery make life a lot simpler even if it adds some cost