Bill McCarthy wrote:The battery you linked is 4ah. If the pump draws 1amp it will run for approx 4 hours. 2amps and it will be 2 hours. Find out what the pump draws and do the maths.
But for longevity you don't really want to run it down much past 50%.
The solar cell is rated at 1.5W so at 6V that would be 0.25A that the solar panel can supply. This may limit the pump speed, and you may find that supplying 6V from a battery has a higher current draw and runs faster. Who knows until you try it?
(unless you have a regulated power supply where you can adjust the current supplied)
Rob P wrote:My thought was that with no form of control / throttle on the motor, applying 12v would make it run at (approx) twice the speed it runs at now on 6v. We like the gentle cascade, we don't want a geyser. Or is this simplistic thinking?
This is possible, for a short period of time before the motor starts smoking and burns out.
The easiest way of charging the battery is, as I said, to use the solar panel.
Would suggest putting a Schottky diode between the panel and the battery to stop the battery back-feeding the solar panel.https://www.ebay.co.uk/itm/10x-SR5100-SB5100-SB5B0-SR5010-SR510-100V-5A-Schottky-Rectifier-Diode-TV-Solar/281884407018
This even says, "These diodes are also perfect for standard DIY solar panel protection. (To block DC current from re-entering your solar panels and damaging the solar cells...ie blocking or bypass diodes).
If you buy 10 of them, you can keep a couple and give the rest away. Maybe to me.
Have a look at the Pro Elec range of batteries in CPC. I don't know if they're any good but they're quite cheap.https://cpc.farnell.com/search?st=6v%20lead%20acid
On the plus side, if you order from CPC, you can also get the diode from them.https://cpc.farnell.com/c/electronic-electrical-components/semiconductors-discretes/diodes/schottky-rectifier-diodes?searchref=searchlookahead