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Power-User

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Small Wattage DC Motors

03/31/2017 9:17 AM

How come the solar developers harp on mega solar parks supplying electricity at 440 VAC to grids.? Even small timers want solar power produced in DC mode to be inverted to 220 VAC and supplied to the grid.

The ideal would be: produce solar power to be used in same DC mode and voltage it is produced. Thereby there will be saving. Since DC power cannot be transmitted to long distances, it should be consumed within short distances as is done in trillions of automobiles. For storage, since the popular work horse, Lead-acid battery is the most economic, use it.

There is one better alternative. Use a small wattage low volt DC motor to pump water with a jet pump, throughout day when sun shines, and use the water 24 x 7. If sun fails, this small wattage motor could be run off the grid, with a small suitable transformer.

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Guru

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#1

Re: Small Wattage DC Motors

03/31/2017 11:15 AM

Probably because the world wide power systems are now based around alternating current distribution systems that are designed for high power transfer and distribution over long distances large areas.

Same with common household electrical power. The vast majority of those of us who live in modernized civilized locations use enough electrical power that simple on site low voltage DC power generation and battery based storage is totally impractical due to both the cost and overall work required to keep such a system functioning properly.

I typically use around 650 - 900 kilowatt hours of energy per month and pay less than $100 a month for it with near zero effort on my part to have and use it.

Do the math on what a system of your proposal would cost to purchase, build and maintain and you will easily see why the industry prefers that any locally generated electrical power of any quantity be compatible with the existing systems. It's just he most practical efficient and cheap way to work with it on the scale the typical homeowner in a modernized location needs.

Also there are not 'Trillions' of vehicles in the world either. Maybe a few billion at best.

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#2
In reply to #1

Re: Small Wattage DC Motors

03/31/2017 11:52 AM

Include two wheelers too in list of automobiles. Secondly, I do not propose replacement of all appliances; I am interested only in water pumps to work without a storage element.

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#3
In reply to #2

Re: Small Wattage DC Motors

03/31/2017 12:03 PM

Okay?

Trillions ( 1,000,000,000,000) would imply more than one, so assuming a Two Trillion minimum would equate to every one of us ~7.3 Billion people on the planet have to own no less than ~250 wheeled and powered automobiles/two wheelers/three wheelers/ etc that have electrical systems of some sort each.

Not buying it.

The rest of your question and overall logic sort of falls apart form there.

But, yes, a solar panel can directly drive a DC pump if they are properly matched but it's a very limited range of applications where that would be practical.

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#5
In reply to #3

Re: Small Wattage DC Motors

03/31/2017 12:20 PM

Good enlightenment. Sorry for my over enthusiasm and thanks for your correction.

I still feel that use of small wattage Solar powered DC motor for water service (for that matter, a group of small motors individually driven) without storage element would be ideal, however uneconomical it is compered to large AC installations, at least ro reduce carbon dioxide emissions.

Thanks once again for your clarification.

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#9
In reply to #5

Re: Small Wattage DC Motors

03/31/2017 3:52 PM

Is this for irrigation? Maybe a good idea. Have you considered using a stabilized tornado (vortex) that is solar driven but has high velocity wind harvesting at the intake?

That works really well when the sun shines, and is somewhat low technology.

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Guru

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#4

Re: Small Wattage DC Motors

03/31/2017 12:18 PM

When the sun is shining, solar panels may produce more power than is needed locally, and less than is needed when it is not shining. Interfacing to the grid removes the problem (and expense) of storing this energy with batteries or other means.

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Power-User

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#6
In reply to #4

Re: Small Wattage DC Motors

03/31/2017 12:29 PM

Grid power is generally fossil fuel based. The system has some cushions in shape of higher spare boiler power that could be brought on line at very short time gap, and also in voltage and frequency that ate not palpable for ordinary user of power. But in case of solar there is a maximum, but no minimum. Thus the load dispatcher will have very tough time if solar power forms a higher percentage.

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#7
In reply to #6

Re: Small Wattage DC Motors

03/31/2017 3:02 PM

Thus the load dispatcher will have very tough time if solar power forms a higher percentage.

True. Another problem, if solar (and wind) provide a higher percentage, is that inverters, unlike generators, do not provide rotational inertia and stability to the power system.

https://arxiv.org/pdf/1312.6435.pdf

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Guru

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#8
In reply to #7

Re: Small Wattage DC Motors

03/31/2017 3:50 PM

That is why there is a developing need for systems like this:

Ramgen shock wave engine

That thing has an amazing startup time, but even better is the idle to full load ramp time.

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Guru

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#23
In reply to #6

Re: Small Wattage DC Motors

04/05/2017 7:46 AM

Not in France; most of it here is nuclear.

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Guru

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#10

Re: Small Wattage DC Motors

04/01/2017 12:33 AM

"Since DC power cannot be transmitted to long distances"

I can't agree with that statement and a couple of your other ones, some reasons below.

DC can be transmitted greater distances than can AC.

Higher voltages (roughly 2X) can be used for DC than for AC, although protective devices are considerably more expensive for DC.

Longer distance underground or undersea transmission is possible with DC than with AC due to lower capacitive effects.

Transmission line losses are lower with DC than with AC.

Smaller diameter and fewer transmission cables are required to transmit DC than for AC of the same current, but DC cables can also be much thicker as skin effect is non-existent.

It's much easier to integrate different un-synchronised grid systems with DC than it is with AC.

Lead Acid batteries may be cheap, but they are not the most economic in terms of dollars per cycle life.

Better to use an inverter to feed a standard AC pump from the DC source, and then simply switch to AC when required

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Power-User

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#11
In reply to #10

Re: Small Wattage DC Motors

04/01/2017 1:05 AM

You are referring to HVDC, where high voltages are envisaged. My point is with low voltage, as low as 12, when the resistance offered even for short distances would be sizeable. My point is to have very short lengths of conductor, not to use AC anywhere, nor storage.

If it is not possible to have a low wattage low voltage DC motor, to be driven directly off a suitable wattage solar PV. Panel, please tell me so and also why.

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#12
In reply to #11

Re: Small Wattage DC Motors

04/01/2017 1:45 AM

Whether HVDC or LVDC, losses are still less than for AC, so your statement re. distance transmission is still incorrect.

You can certainly run a low wattage, low voltage DC motor off a suitably sized solar panel, and this is done on a regular basis - generally with the aid of an MPPT controller which, by way of impedance matching, can regulate the motor's input voltage with respect to the output of the solar panel, and allow greater current at the output than what is being produced by the panel.

If you don't want to use any form of storage, then an MPPT controller is almost mandatory otherwise the motor will likely pull the panel voltage too low. I suggest that you study PV cell knee curves to understand this.

If, as you now say, you "don't want to use AC anywhere" what happened to the mains and small transformer option in your earlier post? With no storage either, all will cease to proceed when insolation is insufficient to run the motor- a 12v (nominal) solar panel under low insolation conditions may show an OCV of 20 volts or more, but still have insufficient current production to run your motor.

Conductor length is a secondary consideration as a simple increase in cable size will negate any losses due to length, eg. an AWG12 cable of 4 metres carrying 10 amps will drop about 0.065v, increase the cable to AWG8 (an increase in diameter of only about 60%) and then double the length to 8 metres and voltage drop is now down to 0.052v.

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Power-User

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#13
In reply to #12

Re: Small Wattage DC Motors

04/01/2017 2:00 AM

We are definitely coming nearer my requirements. If you mean that a MPPT is a must, be it so. Please specify the appliance for a 12 V 100watt motor, so that I could scout around for it. I may also require the indulgence of our fellow members for locating a 12 V BLDC 2800 RPM VERTICAL flanged motor and hope that this motor is not too costly versus a similar wattage AC motor.

When I said I do not want AC, it pertains to the cable after it is transformed to DC from AC, which would lead to the well. This has to be at ground level and likely to be crossed by pets and children. I hope you have caught the point.

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#14
In reply to #13

Re: Small Wattage DC Motors

04/01/2017 2:44 AM

You may be better off with a 24v motor as they are likely more readily available, plus your line losses would be lower on both sides of the MPPT controller. You would obviously then need 24v solar input.

A 24v 100w BLDC pump motor will likely require about 25 amps to run and will probably be considerably more expensive than a comparable AC version.

There are plenty of cheap 30+ amp MPPT controllers out there, check out Ebay for the MPPT, and someone like Gems motor for the motor.

In terms of economics - factoring in the cost of panels, pump and controller, plus installation of them, you would be way ahead just using a mains powered AC pump.

If you want to be ultra cautious, then a transformer and ELV AC pump would still be much cheaper even with the running costs over a number of years, and you don't lose out on cloudy days.

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#15
In reply to #14

Re: Small Wattage DC Motors

04/01/2017 3:50 AM

From what little I know of electricity, for a 24 V connected motor of 100 watts, amps in circuit would be 100÷24=4.2. you were giving a figure of 25. I am unable to understand. Starting torque could be double the running load. Please educate me.

Now for the cost. May be a DC. Motor armature is wound round permanent magnets and that would make it costlier. But how much ?

Any way, unless the total cost of a solar set up is cheaper or at least slightly more than Grid based AC system, no fool, unless a SOLATIC (like Lunatic) would opt for it. My sole purpose is to find out such a system. I seek your help. May be smaller bore pipes and smaller pump could offset the cost.

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#16
In reply to #15

Re: Small Wattage DC Motors

04/01/2017 5:12 AM

You need to do a lot more study.

Here is a link to a range of BLDC motors, check out the peak current requirements for 24v motors around 100w rated power.

Starting torque (stall torque on that link) and starting current (which is what I assume you really meant) are not the same thing

The armatures of standard DC motors rotate inside the permanent magnets, they are not wound around them - although BLDC motors do have the permanent magnets on the rotor, the coils are not wound around them. As for cost, an AC motor is generally cheaper than a comparable DC one, but a universal motor can be used on either AC or DC and would obviously be the same cost.

Brushless DC motors are far more complex as they require electronics to track armature position and to create the rotating magnetic field - in the case of those on the link - 8 poles and 3 phase - - very different to a basic DC brushed motor with an armature, a few pole pieces and brushes.

Unless there is some compelling reason to not go with mains power for this, you will spend considerably more than is warranted for the solar/DC option.

I am unable to give you sufficient education if you do not understand the basics of this stuff - a lot more study of those basics will help you, there's plenty of information that you can access on the web - here's one on how BLDC motors work.

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#19
In reply to #13

Re: Small Wattage DC Motors

04/01/2017 9:34 AM

What does pets and children crossing it have to do with anything? Do they have razor blades and needle sharp spikes on their feet?

Is the wiring of such cheap low grade quality it's below that of common extension cords that safely handle line level AC voltages in such applications without issue?

To me your whole thread gives me every impression you are an extremely cheap person to the point of using irrational justifications for it.

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#20
In reply to #19

Re: Small Wattage DC Motors

04/01/2017 9:43 AM

You seem to equate small and economical to cheap. Well every one has his/her perceptions. Nothing wrong. We are all individuals with specific quirks. Live with them in society.

My intention is to provide a viable alternative to fossil fuelled energy at economic prices, acceptable in third world countries. If you want to call me cheap, you are welcome, but that is me.

Your earlier posts were really helpful to correct myself, but the latest is ....

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Guru

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#21
In reply to #20

Re: Small Wattage DC Motors

04/01/2017 12:37 PM

The problem many of us in the more developed world see with these sort of 'third world' ventures is that they are typically driven by idealistic not realistic views of things largely driven by gullible people who fall for the 'poverty porn' feel good by helping the poor scams that do far more harm to those being targeted by gullible do gooders as needing help than good.

Then to add insult cover excuses like 'Clean Energy, Alternative/Renewable Energy, Going Green, Reduces fossil fuel dependency, safe for children and pets, if only one life is saved' and so forth gets tagged onto it as if it's going to justify whatever it is to now be some sort of above and beyond what is already available and in use technology that is well thought out and developed plus above all already in place and used by millions in such locations now.

Now as for helping the poorer less fortunate I have no problems with it provided they are those who are capable of and actually will do something with the help given to them which most do not and will not because they either have no need of the tech or it's actually far less workable than what methods they already have in place for doing such work.

In fact for far too many of the idealistically driven technologically based help concepts 'for helping the poor', they are about as realistically useful as giving cell phones to dogs.

As I see your batteryless solar powered pump system what advantage does it have over a simple cast iron hand powered pump? It costs more and is less long term reliable, it's easily damaged and not repairable by common people, it only works when the sun is shining, and it's a good target for vandalism and theft.

Where as a simple all mechanically easily fixed pump system that is guaranteed to pump the water the user needs all the time every time day night, sun, rain or whatever plus is of such low technological value no one will try and steal it to make some fast money either?

If you want to help people move water then find out who actually needs that help and work directly with designing a system to fit their particular needs and realistically workable resources.

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#22
In reply to #21

Re: Small Wattage DC Motors

04/03/2017 1:31 AM

I have come to the inevitable conclusion that people from developed nations view efforts at technology development by developing nations, puerile and not worthwhile from their context. This forum is generally used by them to decide, even insult at times, and generally unhelpful. In this circumstances, I would like to withdraw from the discussion, I started.

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#17

Re: Small Wattage DC Motors

04/01/2017 8:56 AM

A lot of nice chit chat, but when were you going to put this thing together and present an image of it ?

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#18
In reply to #17

Re: Small Wattage DC Motors

04/01/2017 9:08 AM

When I get a system that is not too uneconomical when compared to regular grid connected AC pump. With all the 'Chit chat with members, I seem to inch -sorry millimetre my way, towards my goal. Hope you also will contribute.

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