DC Pool Pump 1

[Cyrock]

I am looking for pumps suitable for pool filtering that can run on DC current.

I know about one company (Lorentz) that sells these pumps but the price seems abusive if compared to an AC pump of similar capacity.

What I need is a pump that can handle a volume of about 15m3/h at 1.5 bar(loses from the filter in the pool).

Do you know where I could get such a pump? Or should I mount a DC motor myself?

Thanks

 

[itsmoked]

Please explain why you are limited to inefficient maintenance needing DC for this application.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Cyrock]

Because the intention is to power the pump with solar panels.
I was thinking of a brushless DC motor, no maintenance.

 

[itsmoked]

Oh! OK, that fits morebetta.

Your alternative would be to run the solar array at a high voltage and feed the DC to the DC-Link of a VFD. It would then put out 3ph for a 3ph pump.

Um, wow, that looks to me to be about 2.5kW or 3.3HP. Ouch.
2.5kW / 200W/panel = 13 panels for the required power at local noon.

Looks like you will need something to PPT and run the pump at the available power. Note that centrifugal can get really inefficient at lower speeds. Could be a positive displacement pump would be in order here.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Cyrock]

Thanks for the reply.

As you say, there are multiple solutions, the problem is to find an adequate one.
To put the thing into perspective:
A 3/4 Hp centrifugal AC pump costs about 200€.
A 3/4 Hp centrifugal DC pump with its controller costs 1200€.
(From experience i know that 600W panels is enough for filtering a residential pool).

I am wondering what makes this product so expensive. The pump itself should not be much different, it is all about the DC motor.

Option 1:
Get a normal AC pump and replace the motor for a DC one (should work?).
Option 2:
Like you said, a VFD + AC. Would this work for lower powers? I have no experience with these, and I dont know if they work well with a non-constant input (solar panels).

The two brands that are on the market that sell DC pumps for pool are centrifugal, but I am not sure why. With these systems, the idea is to filter for many hours with a small flow. Maybe a different kind of pump would be more adequate.

 

[itsmoked]

Brushless DC motors are much more expensive to produce and are certainly specialty devices => premium prices.

Can you get more out-of-the-box on this? I would look at gravity filtering. Have the filter be tall. Have the filtration provided by the water gravity flowing back down to the pool. Then any water at any flow that makes it to the top of the filter container WILL be filtered on the way back down to the pool.

With that type of setup you could then use the most efficient pump you can find to reach supply only the head to the top of the filter. Then you could use something like a diaphragm pump that still pumps efficiently at whatever speed the system can deliver. Rather than a centrifugal that at low power is forced to spin slowly and ends up producing just about nothing.


Anyway, just a thought.

If you haven't messed with VFDs it would probably be too risky for you to go that route. I think you can program some of them to run only at the power rating that keeps their DC link at some minimum voltage but I have not personally tried that.

Just replacing an AC motor with a DC motor is not as straight forward as you might think. The two types of motors have different characteristics.

A brushless DC motor is really a fully synchronous AC motor and requires a sophisticated controller to run it. A standard DC motor has brushes and only about 70% efficiency which when coupled to a pump that is only 70% efficient really starts to suck as you are using expensive solar.

Got regular wind?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[ScottyUK]

I'm pretty sure Control Techniques allow their Unidrive to run on a low-ish voltage DC emergency source. I seem remember about 80V or so from an emergency battery for safety-critical stuff like lifts in the event of a mains power outage. I'm not sure if the drive will allow the DC bus to operate continuously from the nominal level all the way down, or if it is a completely separate mode.



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If we learn from our mistakes I'm getting a great education!

 

[BigInch]

what about a small inverter.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[BigInch]

http://store.solar-electric.com/shacdcwapu.html

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[Cyrock]

Gravity filtering might be interesting. The issue will probably that it cant filter enough water over the day. Normally a the filter should filter a volume equivalent to the pools capacity. So 50m3 of water -> 50m3 filtered/day.

VFC + AC pump could be the way to go. Really the VFC you mean is an inverter, since it is just DC-AC. Normally inverters have fixed frequency though, which is not what we want. Frequency should decrease with the voltage supplied by the PV-array.

Know of any of this kind of inverters?

@itsmoked, Wind is not an option. In the summer, when you want to swim, there is no wind(at least in Spain), but a hell of lot of sun
@scottyuk, Arent those thought for just for AC-AC? Unfortunately they dont seem to have just the DC-AC part.
@Biginch, yeah I looked into Shurflo before, but they wont cut it, they have low power.

Thanks for the replies

 

[BigInch]

Most solar pumps are of lower power.
High power DC is costly from all perspectives.

Where are you? I'm just outside of Malaga.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[Cyrock]

Well we need to filter a certain amount of m3 per day. So if this is to be done with solar we should have an efficient filter, because that is the biggest energy sucker. I'm finding it offensive that manufacturers don't even have a pressure-drop curve for their sand filters.

I'm in provincia Alicante

 

[BigInch]

Try the water treatment and distribution forum for that.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[cvg]

you may also want to check out the "Energy (wind, solar) conversion engineering" forum for more information on either utilizing DC current or transforming it to AC.

Also check out SunPower for inverters:

http://us.sunpowercorp.com/residential/products-services/products/inverters.php

 

[Cyrock]

Thanks cvg for the tip.
Normal inverters dont cut it, because the power delivered by the solar array is variable, but the output of the inverter should always be the same. The pump should be able to run fast when there is a lot of sun, and slow when there is little.

By the way BigInch, congrats for being in Spain...and still working

 

[BigInch]

Who's working?

You can't size the pump load for the maximum available power delivered from a variable source. You'll have to oversupply power from the panels such that the pump will start and run normally at design minimum panel output (say around 9 am) and then run faster than that as more power becomes available (at 1 pm.)

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[ScottyUK]

"@scottyuk, Arent those thought for just for AC-AC? Unfortunately they dont seem to have just the DC-AC part."

Yeah, they are primarily intended for AC-AC use, but the cheapest / dumbest ones do so little with the initial AC-DC conversion that feeding them raw DC doesn't really matter provided the voltage is somewhere near where it should be. A few of the intelligent ones can operate off a DC source, and some are designed for a common DC bus where one large rectifier unit provides power to a group of inverters.

There is definitely a battery power option for the Unidrive:

http://www.controltechniques.com/CTcom/solutions/lifts_and_elevators.aspx.

I have no idea about it's capabilities or limitations in this mode - you might want to do a bit more digging.


----------------------------------

If we learn from our mistakes I'm getting a great education!

 

[hydrae]

Pressure drop on a clean sand filter is about 1 psi, backwash when you have 10 psi. assumes a #20 grade media, 4 gpm/sqft, (Sorry about ft-lb units)
Most of the energy requirements for filtering a pool are from the minor losses; skimmer weir, drain strainer, fittings and elbows, backwash valve, and the return fittings are also a large minor loss, as they are a nozzle to aid in mixing the pool water in the pool. Standard losses from the pipe lenth depending on how far away the filter is from the pool will also play into this equation.
If you reduce the minor losses, you may need to filter more water per day to keep a clean pool, as the one turnover per day is based upon a good pool water collection and return mixing systems. Also, if you lower the mixing in the pool, the use of a solar cover will drastically degrade water quality.

So if you are looking to filter the pool with solar power, look at the whole system, reduce the losses which will reduce the pump size, in turn reduce the size of the panels. I assume this is new and not a retrofit. The cost of upsizing all the parts and downsizing the pump is minor compared to the cost of the panels

Keep in mind the affects on the water quality as you change the filter system design.

Hydrae

 

[itsmoked]

Thanks for the walk thru hydrae.

Keith Cress
kcress -

http://www.flaminsystems.com