Solar fountain pump. [RE-wrenches]

[Windy Dankoff, Dankoff Solar]

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I have to agree with Allan. We have agonized over this for years. I 
have had the weird luck several times of testing cheap bilge pumps and 
getting 1.5 seasons before failure, then selling them, and getting 
3-week to 3-month life.

The essential problem is that you have a brush-type DC motor with air 
in it, and a mechanical seal around the motor shaft. If you get even a 
few drops of water in, then when the motor stops and cools, the 
moisture condenses over everything, including the brushes and 
commutator, and that causes rapid brush failure. That happens if the 
seal is slightly imperfect. Often, it's more than slightly imperfect, 
and the failure occurs in a few weeks.

We found that even when we got an especially high quality marine pump, 
that we got just enough success to make us overconfident. The factory 
made some physical improvements, but that only served to lead us on.

Conclusion:  Bilge pumps and similar cheapies are wonderful for 
demonstrations at short-term events, but (always bring a spare). If you 
have a customer who really wants one for full-time use, sell him the PV 
module and give him the source for the pumps so you are off the hook 
when luck is against it.

The only viable answer is BRUSHLESS. A brushless motor is really an AC 
motor driven by a small, simple 3-phase inverter built-in. DC hot water 
circulator pumps work this way. The Oase fountain pump also does. 
Mechanically, it is just like a simple aquarium pump. It has a magnetic 
rotor that runs in water. Unfortunately, it is very low in power, and 
rather expensive.

We recently found an industrial quality brushless sub that is stronger 
than the Oase (3/8" outlet but much higher lift). We are testing it for 
PV-direct application and it looks good. I assure you that if you ever 
see our company offer a fountain pump again, it will be brushless and 
well tested. There's a good chance you will, for next year. If you are 
interested sooner, contact me off-line.

Windy
Dankoff Solar Products


On Aug 9, 2004, at 11:23 AM, Allan Sindelar wrote:
>
> Be careful with the Rules; they don't last and aren't rebuildable. 
> They're
> bilge pumps, designed for intermittent duty, not the long hours in 
> fountain
> use. Also note that most of the small DC subs sold by Grainger are the
> Rules.
>
> Good to hear good feeback on the Oases. I had given up on selling or
> recommending any fountain pumps.
>
> Allan at PosE

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