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Low power low flow rate high temp. pump

tomandsophie

By tomandsophie
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tomandsophie Rising Star

tomandsophie

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This is getting really frustrating now. I've installed our solar panel for the hot water but the little Jabsco pump pushes the water round at 13l/m - far too fast for it to heat the water in the calorifier. This is definite - I have spoken to many professionals in the solar water heating world and they all say it needs to be more like 1 or 2 litres/min. So now I need to find a pump which will do that. The only one I've found that comes close is a Jabsco one with 5 flow settings, but it only handles up to 80 degrees. I need one that does a low flow rate, takes very little power, and handles up to or over 100 degrees. Help?!

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smileypete Veteran II

smileypete

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This is getting really frustrating now. I've installed our solar panel for the hot water but the little Jabsco pump pushes the water round at 13l/m - far too fast for it to heat the water in the calorifier. This is definite - I have spoken to many professionals in the solar water heating world and they all say it needs to be more like 1 or 2 litres/min. So now I need to find a pump which will do that. The only one I've found that comes close is a Jabsco one with 5 flow settings, but it only handles up to 80 degrees. I need one that does a low flow rate, takes very little power, and handles up to or over 100 degrees. Help?!

 

Hi,

 

Have you followed up the suggestion of running it on a reduced voltage?

 

cheers,

Pete.

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tomandsophie Rising Star

tomandsophie

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Hi Pete,

No I haven't been able to do that as I haven't got any way of connecting the transformer I've got to the pump. Also, I really want ideally to get a pump that will take much less power, as this little bugger swallows up 1.3a - too much basically.

I have found a little Bolin pump here that Kuranda use on their backboiler systems. It looks like it might be just right. My only slight worry is that it might not be able to circulate the water up the system while only using 0.1a. However, the friendly guy I spoke to at Kuranda said that they use these pumps on all their backboiler systems on narrowboats of 60ft and more, so it should do the job.

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tomandsophie Rising Star

tomandsophie

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Thanks Gary, but I have been in touch with them already this morning and they don't have anything that will suit my needs. Ah well. I think I'm going to install a flowsetter in the system and try reducing the flow rate using that before I go buying any other pumps and so on.

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smileypete Veteran II

smileypete

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I have spoken to many professionals in the solar water heating world and they all say it needs to be more like 1 or 2 litres/min.

 

Hi,

 

Did you also mention that only 3/4 of the calorifier is insulated, and explain how much insulation is on the pipes and calorifier?

 

Also is the angle of the panel 30° or more, and if not did you mention that too?

 

cheers,

Pete.

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tomandsophie Rising Star

tomandsophie

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The panel is at an angle of roughly 35 degrees. Didn't mention about the calorifier only being 3/4 insulated, but have since found out a few more things...

We definitely need a lower flowrate pump.

We need a differential controller.

Will update once I have looked into installing both of these...

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smileypete Veteran II

smileypete

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The panel is at an angle of roughly 35 degrees. Didn't mention about the calorifier only being 3/4 insulated, but have since found out a few more things...

We definitely need a lower flowrate pump.

We need a differential controller.

Will update once I have looked into installing both of these...

 

Hi,

 

If you would like to slow the pump down you could try putting a 10W or 20W 12v bulb in series with the pump.

 

I get the feeling that on an overcast cloudy day heat losses from the calorifier will overwhelm any output from the panel.

 

cheers,

Pete.

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chris w Veteran II

chris w

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Hi,

 

If you would like to slow the pump down you could try putting a 10W or 20W 12v bulb in series with the pump.

cheers,

Pete.

 

 

Two problems with this possibly:

 

1. The motor may not start as it would only have about 3v across it, and...

 

2. The motor will only be consuming 6% of the power it previously did and therefore (even if it started) it would only just about be moving.

 

 

I have assumed a 20W bulb and a "normal" water pump (ie: 12v 8A)

 

Chris

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smileypete Veteran II

smileypete

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Two problems with this possibly:

 

1. The motor may not start as it would only have about 3v across it, and...

 

2. The motor will only be consuming 6% of the power it previously did and therefore (even if it started) it would only just about be moving.

 

FFS Chris!!! B)

 

Why do you follow me around questioning everything I write?

 

I have assumed a 20W bulb and a "normal" water pump (ie: 12v 8A)

 

Well, maybe your assumptions are wrong, again!

 

P'raps tomandsophie can remind us what pump it is and maybe even the running current...

 

Anyway, how would you solve tomandsophie's problem of low than expected water heating on an overcast day?

 

Do you think a slower pump would help or not?

 

cheers,

Pete.

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chris w Veteran II

chris w

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FFS Chris!!! B)

 

Why do you follow me around questioning everything I write? Everything? I don't think you mean that literally do you?

Because, being an electronics guy, I believe I have a valid opinion regarding your statement which just might be helpful. None of us has a monopoly in being correct so we all get a chance to comment I hope!! There is also rarely one correct answer but a range of "correctness".

Simply putting a resistor in series with a pump is very inefficient and usually causes pump starting problems if the pump is slowed as much as Tom needs (by about 75%).

 

 

Well, maybe your assumptions are wrong, again! Maybe they are, then you can chase me.

P'raps tomandsophie can remind us what pump it is and maybe even the running current...

 

Anyway, how would you solve tomandsophie's problem of low than expected water heating on an overcast day?

 

Do you think a slower pump would help or not? Yes I do, as I stated very early on with some theory as to why.

 

I also proposed at the same time, what I believe to be, the perfect solution to controlling the pump speed. A PWM circuit, which I use on my boat to control 12v light brightness and fan speeds.

 

The pump can be run as slow as you like and will start everytime and the circuit is over 90% efficient. Tom and I exchanged some PMs about it but unfortunately Tom has no electronics background so my circuit diagram would be meaningless to him.

 

Chris

cheers,

Pete.

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tomandsophie Rising Star

tomandsophie

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The most frustrating thing about this whole search for a low flowrate 12v pump is the fact that a 240v one that would do the job perfectly can be bought easily for around £35. How annoying. Does anyone know firstly how much current drain would a standard 240v pump take if run through a small inverter, and secondly is it possible to get them rewound to effectively make a 12v pump? I'm talking about this kind of pump.

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chris w Veteran II

chris w

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Does anyone know firstly how much current drain would a standard 240v pump take if run through a small inverter, and secondly is it possible to get them rewound to effectively make a 12v pump? I'm talking about this kind of pump.

 

 

The pump shown will typically consume around 50W-100W depending on which speed setting you select. This will still be the same power (+maybe 10%) if you run it from an inverter. The current draw from your batteries would thus be about 5-10A depending on speed.They cannot be converted to run off 12v due to their design as they use the changing mains waveform to produce rotation.

 

If you have a modified sinewave inverter you may get an issue with this type of induction motor. I cannot be absolutely sure as I have never tried it but the rotation is due to the changing mains phase so I would guess there may be an issue with a non pure sinewave.

 

Chris

Edited by chris w
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tomandsophie Rising Star

tomandsophie

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Thanks Chris. What you were meant to say however is that "yes of course it'll be easy to alter, no problem. Nice and cheap and easy." B) Ah well, looks like I'm back to having buy a horribly expensive 12v pump.

Do you think it would damage this pump if I installed it and restricted the flow rate down to 3l/m with a flowsetter?

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chris w Veteran II

chris w

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Do you think it would damage this pump if I installed it and restricted the flow rate down to 3l/m with a flowsetter?

 

I honestly can't say regarding this specific pump. Why not copy the domestic C/H jockeys and simply connect a bypass pipe between the flow and return. That way the pump's total flow will not be restricted but the amount of water that actually goes through the pipework rather than the bypass can be controlled very precisely.

 

Chris

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tomandsophie Rising Star

tomandsophie

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Sorry to be a muppet Chris, but I'm not quite sure what you mean. How would this bypass be put in and where? It sounds like it might be the answer, but I need a little more detail before doing it. Sorry to be a pain!

In fact, if this works, perhaps I could easily restrict the flowrate of my current pump down to the required 2 or 3 l/m without putting ridiculous strain on it. That would save me an awful lot of money too!

Edited by tomandsophie
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Alan Saunders Rising Star

Alan Saunders

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Sorry to be a muppet Chris, but I'm not quite sure what you mean. How would this bypass be put in and where? It sounds like it might be the answer, but I need a little more detail before doing it. Sorry to be a pain!

In fact, if this works, perhaps I could easily restrict the flowrate of my current pump down to the required 2 or 3 l/m without putting ridiculous strain on it. That would save me an awful lot of money too!

Pump Bypass<-(click link if you cannot see this image)

With the valve closed the flow will be the same as without the bypass. As the valve is opened some water will flow through the bypass and therefore less through the main circuit. If you restrict the flow the load on the pump will increase and so will the current; with a bypass the load and the current will decrease.

 

If you have measured the current at 1.3A you should see a considerable reduction, maybe 50%. If 1.3A is the pump rating you will most likely find that it is already drawing half of that.

 

Alan

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pagan witch Community Regular

pagan witch

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I honestly can't say regarding this specific pump. Why not copy the domestic C/H jockeys and simply connect a bypass pipe between the flow and return. That way the pump's total flow will not be restricted but the amount of water that actually goes through the pipework rather than the bypass can be controlled very precisely.

 

Chris

Neat idea - a variable parallel resistor for water !

 

Like you say, because it is in parallel the pump can do it's thing.

 

Simple and cheap just like Tom & Sophie's request B))

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dcruk Engager

dcruk

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Hi there,dont know if you are still looking but maplins sell a couple of PWM motor speed controllers for £15. Designed for 12v nominal input , 3A output. May give you further options to reduce speed and power consumption, hth, Dave

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