Thoughts on Grundfos running off 12v with step-up converter

slgz · July 2015

I have a 130’ well and I’ll be pumping into a 40 psi pressure tank, so for simplicity sake I’ll call it 220’. Well yields 2-3 gpm.

I’d like to run a DC pump off my 12v battery system (four 125AH AGM 12v in parallel). looking at Grundfos 3SQF-2. Grundfos accepts 30-300VDC with best performance being at or above 120vdc. To boost my 12v I’m looking at a 12 to 48v 4amp converter like this:

http://www.ebay.com/itm/New-DC-Converter-12V-to-48V-4A-192W-Step-Up-Boost-Power-Supply-Module-Car-/221828979379?pt=LH_DefaultDomain_0&hash=item33a6099ab3

Is there something better out there to do this job? I’d like to try and get a flow rate of around 2.5 gpm, and I think this might do that but unfortunately I find the Grundfos info difficult to interpret.

Since I’ll be running off of batteries at a constant voltage/current I’m thinking I can get away with wiring the pump direct without a controller?

I’d appreciate any comments or suggestions from knowledgable folks on this before I put down $$ for it - Thanx!

inetdog · July 2015

The controller, AFAIK, contains the circuitry that converts the incoming voltage to the inverter output pulses that the motor needs. Without controller, it will not work at all.

vtmaps · July 2015

slgz wrote: »

Id like to run a DC pump off my 12v battery system (four 125AH AGM 12v in parallel).

Welcome to the forum.

I don't know much about your system or the design criteria that went into it, but four AGM batteries in parallel is a red flag that the design is not optimal. Before you compound your errors by spending more money, perhaps you should give some thought to raising your system voltage to 24 or 48 volts.

You are not the first to paint yourself into a 12 volt corner. Learn from others... sooner or later, that if you need more capacity than one 12 volt battery can provide, you should be at a higher voltage.

--vtMaps

Dave Angelini · July 2015

No way to do what you planned without the controller.Without the controller the SQ pump is 240VAC. Most people use SQF's near the max DC to get the most water in less than average solar conditions. As vtmaps said you really need to spell it out more. Like how is it running now?

slgz · July 2015

Thanx for the input guys, now that I know I need a controller if I go with the SQ Flex it makes it a bit less appealing (more $$). another option might be to go with one of the Grundfos SQ 120V pumps and run off the inverter (Trace 2012) which would be cheaper. I figured the Flex would be more efficient, but maybe not if it is also really just AC being converted to DC?

Right now I’m running a Baker Monitor, that was installed in 1975. My generator powers a DC motor, in between there is a converter to change the AC to DC. It pumps to a 2500 gallon redwood water tower. From there I have low flow into my dwelling (an old caboose) I use that water for showering and washing dishes but I carry fresh water in a jug from the well for drinking. So the plan is to install a pitiless adapter and a direct line into the caboose, and into a pressure tank so I don’t have to worry about freezing and can have fresh water and normal flow.

I inherited this property from my dad and it’s been a continuos education trying to keep everything going and trying to understand what he was doing and how. I have pretty low needs and up till now have seen no reason to change from 12v. I would like to add more solar panels though and I know higher voltages are more efficient, so it's something else to research for sure.

Dave Angelini · July 2015

The SQ Flex is more efficient in that you can control the desired outcome. An SQ is either on or off. The 110V SQ is a good pump also and they all are about as good as you could get for a long time. Only in the last 5 years have Goulds, Franklin and ? started to make product that competes. I still have my Trace on a shelf. A caboose is what I played in as a kid. How old?

slgz · July 2015

Thanx Dave for the tip on Goulds and Franklin, I'll have a look at those before I make a decision. The caboose is a 1951 all steel SP bay window built in Southern Pacific's L.A. shops.

Texas Wellman · August 2015

Not really true. The pump can be direct wired, all the electronics are in the motor itself. It doesn't care whether the volts are AC or DC, it will work as long as it has enough power 30-300 VDC or 90-220 VAC. Grundfos states that anything less than 90VDC there is a performance loss but you can run as low as 30 VDC. The box is simply an interface that will allow the pump to play nicely with whatever set-up you have (AC back-up, wind, pressure switch, etc).

Dave Angelini wrote: »

No way to do what you planned without the controller.Without the controller the SQ pump is 240VAC. Most people use SQF's near the max DC to get the most water in less than average solar conditions. As vtmaps said you really need to spell it out more. Like how is it running now?

Dave Angelini · August 2015

Texas Wellman wrote: »

Not really true. The pump can be direct wired, all the electronics are in the motor itself. It doesn't care whether the volts are AC or DC, it will work as long as it has enough power 30-300 VDC or 90-220 VAC. Grundfos states that anything less than 90VDC there is a performance loss but you can run as low as 30 VDC. The box is simply an interface that will allow the pump to play nicely with whatever set-up you have (AC back-up, wind, pressure switch, etc).

A 12 volt step-up is really not a good way to do this in my opinion. Even if there would be enough water pumped at 30 vdc, I have had clients tell me that all was well once they used around 100 VDC. Get it? all was well....

The interface box (CU) does a few more things also like vary the house pressure which is important with the advent of sprinklers in the home for fire code on new homes in my state and others to follow. The differences are below from Grundfos.

SQ, SQE pumps feature an innovative motor design
incorporating permanent-magnet technology. By
combining permanent-magnet motors and a Grundfos
micro-frequency converter, we are able to deliver
unmatched performance and the ability to control and
communicate with the pump in ways never before
possible. A few of the features that result from this
combined technology are Constant Pressure Control,
Soft-Start, and Integrated Dry-Run Protection, but
these are just a few of the features these pumps offer.
SQ pump models operate at a constant speed much
like today’s conventional pumps. The difference is that
SQ delivers the benefits of an electronically controlled
permanent-magnet motor that cannot be achieved with
a conventional induction motor.
SQ pumps are available for single-phase power; a
simple 2-wire design makes installation easy.
SQE pumps are equipped with a Grundfos "Smart
Motor." Like the SQ models, SQ pumps have a high
efficiency permanent-magnet motor — but we add the
ability to communicate.
The "Smart Motor" communicates via the CU301
status box through the power leads.
It is not necessary to run any additional wires down the
well. Communication with the pump provides Constant
Pressure Control and the highly useful ability to
change the pump performance while the pump is
installed in the well. Like the SQ motor, this is also a 2-
wire motor designed for single-phase operation.

HarryS · August 2020

we are totally off-grid, utilizing solar panels, battery storage and auto start generator. We have a Grundfos SQ flex pump and CU-200 controller. Current system is 6-160 Watt solar panels and we also have inverter power to the well. We are using a GoPower TS-30 switch to which the installer wired an electric eye to switch between solar and inverter power. The only problem is that on low sun days, there may not be enough solar generated to run the pump, so we have to cover the eye so it will tell the switch to use inverter power. However, it is not always convenient when the sun is not always constant, clouds come and go, so the pump fluctuates in output or not at all. What I was thinking was some kind of timer (or maybe just a manual switch) that we could set to have the solar on during daylight hours and then use the inverter power at night. Has anyone done this or have suggestions. I know we can never get away entirely from the sun fluctuating during the day and not pumping; but at least if it was like that, we could run the pump on inverter power on those days.

Dave Angelini · August 2020

Sure you could do this if your battery can handle a new load at night? Most would just add more solar if the pump is not getting close to full output, is it? Probably need to know the model in there? Measure the current or output water to see if you are near max already. A flow meter might help.

mike95490 · August 2020

If you want the SQ flex w/o controller box, you need to set up a 48V battery bank.

But before that happens, you need to get the pump curves for the voltage/head you are planning on.

Will the flex cycle on and off, on it's own, to maintain pressure or will it run continuously until the batteries go flat at 1AM ?

MichaelK · September 2020

Grid-tie panels have gotten so cheap now that the framing I use to mount them is more expensive than the panels themselves. You could very cheaply create a stand-alone array just for pumping water at an optimal voltage. Take a look at this array I built, holding four grid-tie panels. Wired in series, they are producing 120VDC, which is getting into the optimal range for the pumps you a discussing. Notice though that I mounted the panels vertically. If I had instead positioned them horizontally, I could have mounted six, wired in series for a total of 180VDC. These four panels cost me 220$, out the door. Let's assume I could have bought six for 330$.

You are really doing yourself a dis-service maintaining a legacy system still at 12V.

Thoughts on Grundfos running off 12v with step-up converter

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