Dump load to charge pressure tank (well)

[nailed]

There was a question posted in another forum.  I want to re ask this question because I think it has some value to others.  

Pert info off grid house with large PV system.  House has a well with a normal pump, pressure tank, and pressure switch.  

They were asking about using the wasted energy after the batteries were charged to top the pressure tank back off.  There were bunches off messed up responses because no one understood the question or know about this type of power systems.

They did not give a lot of the info.

I responded with;

If the old pressure switch is set at 45/65 (not changing this) then install a second switch at 60/65.  This second switch could run off a relay coming off the dump load on the charge controller.  There would need to be a timer to keep the relay open for an amount of time for the pump to make a full cycle (was thinking like a minute or so).

Did I fall off my rocker?

Did I over look a simpler setup.  They wanted to be able to set and forget.  

[vawtman]

I wouldnt think thats a good idea.You would need a big inverter just to start the pump.Why not preheat?

[Nando]

The idea, in principle is OK, but One needs to examine what is proposed in relation to the dual pressure switch and the pressure tank or vessel.

Normally these types of tanks have a limited volume of water with a bladder to keep the pressure up when the pump stops.

Unless, One has a very large capacity pressure tank (that is quite expensive) it is not worthy to place the additional equipment for possible adding just a few gallons to the tank, the investment has a very low return.]

Nando

[nailed]

That was my thought Nado but he was thinking it was a good idea.  This is the only way I could see it to do any good with out over pressuring there tank.  

[thefinis]

Your idea will work to a degree but for a totally off grid house (well included) it does not seem to make much difference. If the well is grid tied then you would need more switching to make sure the dump load does not connect while the pump is running to avoid interconnection. To make this work better something like an automatic yard sprinkler system needs to kick on at the same time. Actually if the well is on the battery bank then just kicking in the sprinkler(or drip irrigation) system would pull the bank down and when the dump switch shuts off the sprinkler system the tank would pump up to cutoff pressure.

The big problem I see here is that the dump load will be varied on amount of power available but the pump is going to give a set load.

Finis

[nailed]

It's not my setup, but I thought I would ask...

I was thinking about using the 2 presser switches.  They would have a box to split the power off the panel to the main switch and then to relay (that controls the second switch).

Off the charge controller I would run a line to the relay.  It would need timer on this so it would keep the relay open for the pump to run a full cycle.  The timer would be needed to keep the power on.  IMO once the pump would start to the well you would draw down the batteries and the charge controller would switch the dump load to off.