AC to DC Pump Step Down Details

[shaniac]

Greetings everyone, on my off grid home, I am always looking for ways to reduce my energy usage. My next plan is to replace the large AC jet glass pump that creates our water pressure with that of a more efficient DC Dankoff booster pump. My current pump hose is located about 220 feet from my power house, so I need to do one of three things.

A. Bring the water closer to my batteries so I can use the DC pump more efficiently as it will be closer to the DC.
B. Run 220 feet of some enormous expensive cable from the batts to the pump house to minimize loss.
C. Step down the AC that is already running to the pump house and turn it to DC at the pump.

The first two options above require trenching, expense and the long term problems of buried lines or water. Stepping the AC down seems to be the simplest way to go, even though I understand I will loose some energy in the process.  I just replaced the Bridge Rectifier http://en.wikipedia.org/wiki/Diode_bridge on a different Dankoff AC slow pump, so I have recently learned it is not that hard to drop the AC to DC via such device.

My question to the group is… In the context of the information above, what is the best and most affordable way to drop the AC to DC at the pump so I can replace my 8 Amp 110 pump with a more efficient DC pump?

Thanks in advance everyone.

[Madscientist267]

By far, your easiest, most effective, and cheapest method is #3.

There are a handful of ways to go about it, but depending on the current your pump will need, a switching type power supply should be able to handle it most efficiently.

Steve

[shaniac]

So according to Dankoff, (now conergy) the booster pump pulls anywhere from 6.5 to 11Amps DC at 24V, depending on the PSI it needs to build.  http://www.altestore.com/mmsolar/others/FLOWLIGHT-TD.pdf

My water pressure switch stops at 50psi so I should not be using anymore than about 8 amps, so a 10A power supply unit like this one would do the trick, correct?
http://www.wago.com/wagoweb_china/public/787/eng_dat/d590400e.pdf

I can install this AFTER the pressure switch, presumably so I will not have a constant phantom load.

Any thoughts? Is that all there is to it or am I missing some newbie knowledge? Do I need to worry about start up surges?
thanks again!!!!!

[Madscientist267]

Looks good, other than like you said, the startup surge.

I didn't see any Ipeak rating on it, just a nominal of 10A continuous.

At pressure, the startup current could be a couple times that, maybe more.

I think I would go with a higher capacity supply (but stay in the switching arena)...

If this isn't practical (or otherwise possible), you might consider a relief/check valve system with a small bladder tank, so that the pump can start under zero pressure and then will just naturally make water flow when the bladder tank goes above the pressure in the outlet line leaving the pump house. This would minimize your startup surge and would probably keep it within limits of the power supply, or at least a very short spike, which a lot of switchers can usually handle fairly well.

As so (forgive the crude ASCII art LOL):

[Water to be pumped]
    | |
    | |
    | |
[Pump] ---(DC)--- [Pwr Sup] ------------ [Pressure Switch] ------ < AC In
    | |                                         |
    | |                                      (AC)
    | |                                         |
    |  =========== [Relief Valve] ====> Relief Discharge
    | |
    |  === [Bladder Tank]
    | |  
[Check Valve]
    | |
    | |
    \ /
Discharge to wherever water is needed

The relief valve could be a 24V solenoid (or 120V if you stay on the AC side with it, may be a bit more efficient).

It would be closed when energized (pump on), and open when not (pump off), allowing the pressure to bleed off.

The discharge from the relief valve would need to be run outside or somewhere where a gallon or so of water showing up every time the pump shuts off wouldn't be a problem. For that matter, depending on your circumstances, you may be able to get away with running the relief discharge back to the intake side of the pump.

Make sense?

Steve