DIY Electric Car Forums banner

1 - 4 of 4 Posts

·
Registered
Joined
·
418 Posts
Discussion Starter #1
so not sure where to post this but this is the only electronics forum i know of, so here goes.
i want to run a water pump directly from solar panels (no batteries)
ill control it with arduino
plan is to have some big fat capacitors to help with the start up current.
have the panels shorted through a mosfet at night and the arduino measure the current through a shunt in the morning, when the panels are producing the desired amount of current, the mosfet opens the panels and turns on the pump.
panels dont like being shorted i know but this is the most effective way i know to measure if the panels are producing enough to get the pump started.


panels will be your standard 37voc 250w ones you see everywhere.
pump is a 24v 900w job.
panels never ever produce what they r rated for so will need to have about 1.5kw of panel to keep it going i would think. load also depends on how high and how far it is pumping the water but lets assume it is a constant load of 900w.


i was thinking to run the arduino through a buck converter off the panels to avoid using batteries there too, the buck converter needs 6.5v input to turn on so as the sun comes up, the arduino turns on and i dont think there will be too much hysteresis because its 1.5kw worth of panel and the arduino only draws a couple watts at most.


it can be set to switch to shunting the solar panels for a few ms every 10seconds or so to make sure there is still enough sun to keep it going, so it doesnt just burn up the pump, if it detects there isnt enough power it returns to phase 1 where it just keeps shunting until it detects there is enough.


anyway you guys are the smartest in electronics that i know so id really appreciate any input you have!
 

·
Registered
Joined
·
4,796 Posts
Would the short circuit current be any better as an indication of available power than open circuit voltage? As soon as you connect the load, you won't get either of them.

I don't know why it is important to avoid a battery, but it seems like a battery, plus a simple voltage-controlled switch, would be easier. This would shut off when the battery runs down (due to sunset or just too much cloud), and would start up in the morning when the panels were able to charge the battery enough. If there is not quite enough sun to run the pump, it will cycle on and off at an interval determined by the battery capacity and a duty cycle determined by available solar power compared to pump consumption. The battery would handle the starting surge.

Voltage-controlled (or voltage sensitive) relays are readily available in 24V, but it might be a challenge to find one with sufficient current capacity, so you might need to use a small voltage-controlled relay to run a larger relay (contactor) to actually switch the pump. This one can handle 100 amps: BAINTECH Voltage Control Relay - 12V & 24V 100A
 

·
Registered
Joined
·
1,773 Posts
You are going about this all wrong. They make pumps to run directly off solar panels. The pump motors have current boosters and speed varies with the amount sun light panels receive.
 

·
Registered
Joined
·
152 Posts
anyway you guys are the smartest in electronics that i know so id really appreciate any input you have!
It sounds like a fun project but as someone said, there are pumps ready to do this. Do you know about the Grundfos SQFlex series of pumps?

I, for example, have an off-grid well 315ft deep with a Grundfos 11SQF-2 dropped at 290' (standing water is about 270')... and it is wired directly to solar panels (1500 watts - 5x 300watt panels wired in series).

I do have a bypass switch diverting the power through a "pump up" float switch hanging in my water holding tank. This way the pump shuts off when the tank gets full. In fact I did this part a little fancy - the actual "pump up" float switch is only rated for 1hp so I'm using it to control a contactor which actually controls the panels. But that's my quirk. The point is, the pump runs directly from the panels.

So this setup pumps about 10 gpm @ 300ft deep. The Grundfos pumps are not cheap however - about $2300 maybe a little less if you find one on ebay. They do have a wide range of solar pumps in the SQFlex series which are designed to maximize output / depth / power.

The other awesome thing about these pumps is their voltage input range:
30 - 300v DC and
90 - 250v AC

Yes that's right if your panels aren't giving you the power you need, you can plug that pump directly into a 110 or 220v generatoer and pump all night.

They are super intelligent, with MPPT technology built into the pump itself.

Only draw back is there are virtually no repair parts. You have the pump body and the motor body which can be replaced separately but that's about it. And you get a two year warranty. Better treat it good!

They offer all kinds of additional "control boxes" but you don't actually need them to use the pump. Just plug it in and go.......

good luck!
 
1 - 4 of 4 Posts
Top