24vac to 24vdc

A

Thread Starter

Aaron

I need to power a 24vdc fan that draws 80ma and 2W. I have a 24vac supply. What is the best way to rectify it?
 
L

Larry Decker

Use a bridge rectifier. They are cheap and available at any electronics store, even Radio Shack.
 
S

Steven Shepard

You need to solarize the power system for this DC device and take it off the electric grid completely. Solar would be a more economical and reliable means of powering any DC electrical load.

For your application all you need are:
2 each 12VDC, 500mA solar modules (to acheive 24VDC operation $94.95 each.
1 each 6 Amp/hour battery $30.00
1 each 24VDC charge controller $183.00

Add some wire and misc. hardware and your done.
The solar modules will last about twenty years or more. So will the electronics. The battery will have to be replaced every three to five years. It really is too simple not to do.

You install this power system and you can almost forget about it. Most certainly it is a one time electric bill to power your DC device instead of
paying to power it every month for the rest of your life.

SBT Designs
25840 IH-10 West #1
Boerne, Texas 78006
210-698-7109
FAX: 210-698-7147
www.sbtdesigns.com

Please note we are moving our email address to [email protected].
Please update our information in your records.
 
R

Ramer-1, Carl

I, too, am a solar enthusiast, but this particular application (at least with so little information provided) hardly sounds like a candidate for solarization. The initial dollar budget doesn't include proper brackets for the modules and a reasonable cost for the labor involved. Assuming the omitted items to be worth about $100, the initial cost would be about $500.
Depending on whether you use the 2 watt or the 80 milliamp figure, the load for the fan would be 2 watts x 24 hours=48 watt-hours per day running
continuously. That's less than 1.5 kilowatt hours per month. Even if grid power was 25 cents per kilowatt hour, the break even point for the initial cost would be somewhere near 2000 months. It's safe to assume that during the first 166 years of operation the system would need repairs so the payback period would be extended.

A simple full wave rectifier, bought or made with a few dollars worth of diodes from Radio Shack will convert the 24 VAC to clean enough and close enough DC for the fan. Even assuming a very inefficient conversion process, the return is short order.

Don't forget the K.I.S.S. principle.

Carl Ramer
Controls & Protective Systems Design
Space Gateway Support, Inc.
Kennedy Space Center
 
K
Hello...

Please tell me you are joking here...

Aaron stated, in his message, that he wanted to run a 24 Vdc 2 watt fan. That sure sounds like a small PC case fan to me. You suggested a solar
option to save money... lets look at the dollars involved here.

SS> For your application all you need are:
SS> 2 each 12VDC, 500mA solar modules (to acheive 24VDC operation
$94.95 each.
SS> 1 each 6 Amp/hour battery $30.00
SS> 1 each 24VDC charge controller $183.00

Your proposed solution has a cost of (94.95 x 2) = 189.90 + 30.00 + 183.00 = $ 402.90.

The fan in question pulls a whopping 2 watts from the power supply. Lets assume that it is the worst power supply in the world and it actually pulls 2.5 watts from the wall due to losses. So... at 2.5 watts it would take us 400 hours of run time to consume 1 KWh.

Where I live... we pay, on average, 8 cents per each KWh consumed. So... we can pay for (402.90 / .08 = 5036) 5036 KWh with our money.

As we saw before... it takes us 400 hours to consume 1 KWh so we can pay for 2014400 (400 x 5036) run time hours. 2014400 hours is (2014400 / 24) 83933 days or (83933 / 365) 229 years. I bet the fan in question won't last any longer then 5 years.

Someone please check my math... So does the solar solution make sense... not to me.

Best Regards...

Rick Kelly

Chief Electrical Technician
Natural Cuts, Cheese Operations
Kraft Canada Inc.

[email protected]
(613) 537-8069 (V)
(613) 537-8044 (F)
 
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johan bengtsson

Well, 4 diodes and a capacitor. Since you need much less than 1A you can take almost any diode you find since most of them is 1A or bigger (I usually use 1N4002, but it doesn't really
matter) The capacitor could be any with enough capacitance and voltage, I would suggest at least some 220uF (80mA discharges this approx 3V in 1/2
period at 50Hz, very much rounded value) bigger capacitor is ok, more than 2200uF would never be needed in this application.

This gives you a voltage somewhat higher than you might want to. I think the fan will accept this quite happily (it will go a little bit faster than
expected). If you really want to give it more exacly 24V put in a 7824 or similar circuit. If you select this way you should have the capacitor to be around 1000uF - 2200uF otherwise the IC might not work good enough. Preferably a capacitor at approx 1uF at the output from the IC too.


/Johan Bengtsson

----------------------------------------
P&L, Innovation in training
Box 252, S-281 23 H{ssleholm SWEDEN
Tel: +46 451 49 460, Fax: +46 451 89 833
E-mail: [email protected]
Internet: http://www.pol.se/
----------------------------------------
 
S

Steven Shepard

No, it is not a joke.

You guys are not even considering the savings that a power system like this would provide your companies. The application discussed is a place to start solarizing the operation of any facility. And I am referring to long term
operation that is truly more reliable than what you are receiving from the utility at this time.

I am referring to 99.9% reliable power. You have no power system at this time with that kind of capability. Your utility cannot make that claim.
Utility power goes out all the time for maintenance and repairs due to storms. I am referring to long term operation. In order of twenty years or more of capability and performance. I am referring to energy independence that no utility would bother to offer you. With solar you become your own
power producer. I am referring to clean power that does not pollute, does not make noise, does not endanger your working environment at all.

So justify converting utility AC power to DC power and then paying for that power over and over and over again every month, every year. Your not buying power, you are just borrowing it. Justify all the hardware required to make
that conversion. Justify the wasted power in the effort. Justify the dirty AC power received. Then justify subsidizing a energy source and utility energy provider whose only purpose in life is to take your money. Your claim makes no sense.

The simple justification for solar is, after you pay for your hardware the power source is free today, free tomorrow, free next year and you can
absolutely bank that the Sun is going to rise. It is clean. It is the right thing to do once you start thinking long term and cease being a short sighted consumer.

SBT Designs
25840 IH-10 West #1
Boerne, Texas 78006
210-698-7109
FAX: 210-698-7147
www.sbtdesigns.com
 
M

Michael Griffin

You can get full bridge rectifiers in a single 4 pin package which will mount to a panel quite nicely. This is much easier to mount than 4
individual diodes would be. We've used them to supply DC to large contactor coils (this is sometimes referred to as an "economy DC circuit"). I don't have a part number handy, but you should be able to find what you need in
whatever your local equivalent of an Electrosonic catalogue is.

I might also be inclined to dispense with the capacitor suggested by Mr. Bengtsson. Filtering is always nice, but I doubt that the motor will mind the ripple. The core losses would be slightly higher, but this is probably not significant compared to the existing losses in a such a small motor. Of course if Mr. Bengtsson had a particular reason to suggest the capacitor, you would be better off listening to him, rather than me on this matter.


**********************
Michael Griffin
London, Ont. Canada
[email protected]
**********************
 
D
Hi Steven,

I think we all appreciate that your heart is in the right place, but for most industrial users I think solar power on a small, local scale, is impractical.

Sure, you can use solar to cleanly and perpetually power all the 24VDC fans on your desktop computers, but at my plant it is not the desktop computers that are critical to plant operation. We have thousands of horsepower worth of AC motors operating at 600VAC. How am I going to run all these on solar power, especially in Vancouver, BC where it is overcast 8 months of the year? Who cares if all my computers work in a power outage when the plant is down and we aren't producing our product?

I think solar power has great potential in residential or office type environments, but Rick Kelly's argument was right on - from a pure cost
perspective there is absolutely no payback. You would have to justify the expense based on environmental considerations and the uninterruptible nature of the power source (especially valid for a computer data centre for example).

Cheers,

Dean Reimer
BPB Westroc Inc.
 
Steven...

This is shaping up to be an interesting discussion. However as it is not directly tied to the interests of the list, I will respond to your last message via e-mail instead of through the list.

Ohh... if anyone else wants to partake in this thread... send me a message and I will CC you on my response to Steven.

Best Regards...

Rick Kelly

Chief Electrical Technician
Natural Cuts, Cheese Operations
Kraft Canada Inc.

[email protected]
(613) 537-8069 (V)
(613) 537-8044 (F)
 
A

Alberto Maldonado

Hi Aaron:
Firstable I think the power for your surge of 24 Vac is appropiate. (You don't ask about it).
Then your Surge is not appropriated for 24 Vdc under a light calculation, it is for 33 Vdc when You use a full wave rectifier with capacitor. For 24 Vdc, better 25 Vdc (over the nominal requirement in this case), we need a source of 17,7 Vac with the following calculation: Vef=0,707 Vmax for a senoidal wave rectifier where in our Case the measured V is Vef.(17,7 Vac)
and Vmax is 25 V. For this reason You must down your source Voltage of 24 Vac to 17,7 Vac with accoupling a trafo or use at the output of the DC (after a 4 diodes Bridge and a Capacitor, under suggest of Mr .Bengtsson and Mr. Carl Ramer ) a, Voltage Regulator chip to 24-25 Vdc.

I hope it helps You.

Ing. Alberto Maldonado
E-Mail:[email protected]supernet.com.bo
 
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Johan Bengtsson

Well, whatever...


/Johan Bengtsson

----------------------------------------
P&L, Innovation in training
Box 252, S-281 23 H{ssleholm SWEDEN
Tel: +46 451 49 460, Fax: +46 451 89 833
E-mail: [email protected]
Internet: http://www.pol.se/
----------------------------------------
 
S

Steven Shepard

Troll this.

With a thanks and a nod to Steve Spence, this is contributing material from the book I am working on. Hope for publication by the end of this year.

Top twenty reason for using solar:

Reason #1 - Solar is the "IDEAL" source of energy simple because it is delivered free to your home, business, plant, work place, etc. each and every day. It comes in many varieties that seem to suit your particular local in the form of wind, sun, water, bio gas, wood, etc. and of course you can mix and match systems to again suit your particular energy needs.

Reason # 2 : There are NO costs associated with "delivery " of solar energy to your site, unlike fossil fuels which require transmission lines, open mining, blasting, digging, strip mining, laying power lines, transport, and
finally conversion all of which cause BILLIONS of tons of pollution worldwide in doing all this busy work. Solar energy is delivered RIGHT to
your "front door" and causes NO pollution in the delivery of the energy course.

Reason # 3: Solar energy is generated from the most awesome nuclear power plant in the universe - our star called the SUN. Fortunately the Sun
requires NO maintenance at this time and is not schedule for any blackouts for the next few billion years.. Sorry engineers, we cannot touch it or tweak it!

Reason # 4: Once installed PROPERLY and CORRECTLY, solar energy collectors virtually require NO upkeep and VERY LITTLE maintenance compared to a system that uses fossil fuels to generate electricity or produce hot water. I can
understand installation ignorance being a challenge for some users of this group.

Reason # 5: Solar requires ABSOLUTELY NO FUEL TO BUY FROM ANYONE to produce the energy (electricity or thermal energy) on site once a suitable collector is installed on site.

Reason #6: Once the collector is purchased and up and operating the collectors product ABSOLUTELY NO EMISSIONS as do ALL fossil fuel sources and
nuclear reactors, breeders or otherwise.

Reason #7: Solar energy gives you piece of mind NO fossil fuel source can ever give you. That is an intangible , but none the less - VERY valuable. It is controlled by NO one. It is mostly free of politics and cartels at this point in time. Even better, management and marketing cannot get their hands on the source and artificially limit and control the supply.

Reason #8: IT requires NO military presence and thus we could be using the money spent on "protecting or vital interests" for other more important things on this planet. Like making the automation industry much more substantial in this country.

Reason #9: Once the solar energy device is turned on it GIVES YOU BACK YOUR INVESTMENT day in and day out over its lifetime. That can NEVER be said for ANY fossil fuel generating system. The cost to decommission a nuclear power plant alone is in the BILLIONS of dollars. Guess what? The cost to
remove a solar hot water heater is minimal and all the glass, copper and aluminum can be recycled very easy.

Reason #10: Solar energy once paid for is virtually FREE!

Reason #11: As the price of fossil fuels increase the "payback" of a solar energy system decreases.

Reason #12: The saving you get from a solar energy system by displacement of fossil fuel energy are TAX free.

Reason #13: You can bank the energy savings (caused by NOT buying fossil fuel energy) and let it compound and at the end of its useful life one can more than purchase another system or take a well deserved vacation! One CANNOT do this with a fossil fuel generating system as it COST you money to :feed" it day in and day out!

Reason #14: Solar energy systems can be deployed in the field RAPIDLY, unlike fossil fuel plans or nuclear plants which take YEARS from start to
finish simply because of their complexity.

Reason #15: Solar energy is ideal because the technology is not overly complicated and can be installed and deployed by most people with minimal
education. (Excluding skeptical engineers and technicians.)

Reason #16: Solar energy DISPLACES a fossil fuel energy source, so when and if a blackout comes to your area guess what? YOU will have hot water or
electricity when your neighbors may not!

Reason #17: Solar thermal energy is a great match for DHW and radiant floor heating and cooling. With fossil fuel energy sources such as baseboard heat, steam heat, or electric resistance heat one uses WAY more energy than needed when a lower grade of heat will do the same thing!

Reason #18: In combination with energy efficient building practices the cost of a solar electric or solar thermal system one can drastically reduce the initial cost of a system, so that it is simply more affordable.

Reason #19: It is "decentralized power" and collectively it has the power to transform our world quicker than we may realize.

AND, the top twenty reason for using solar: Promoting the purchase, installation and use of solar technology upsets and disturbs a lot of stupid people.

The whole idea is to use solar energy devices FIRST and fossil fuel as an energy BACK UP. If anyone wants to add to this list of reason why solar energy is the ideal energy source, please do so!

SBT Designs
25840 IH-10 West #1
Boerne, Texas 78006
210-698-7109
FAX: 210-698-7147
www.sbtdesigns.com

Please note we are moving our email address to [email protected].
Please update our information in your records.
 
Steven

Your tone is both insulting and inappropriate there are no IGNORANT or STUPID readers of this list. If you do not wish to discuss this in an
professional manner then there is nothing further to discuss. I have neither the time or the patience for a discussion that offers no intelligent discourse. I consider this thread closed.

Best Regards...

Rick Kelly

Chief Electrical Technician
Natural Cuts, Cheese Operations
Kraft Canada Inc.

[email protected]
(613) 537-8069 (V)
(613) 537-8044 (F)
 
J

Jacek Dobrowolski

Steven Shepard wrote:
No, it is not a joke.
.......


I am referring to 99.9% reliable power.......

Try to achieve that somewhere near the North or South Pole - something like lasting for half a year, long night :) - sorry I couldn't
resist saying that.

I'm working in rather small machinery company and we need about 50 kVA of power, so tell me how much would cost us a solar system of that capacity - overkill.

Regards,


Jacek Dobrowolski
Software Eng.

Automation Department
Secondary Division
ITM Poland Ltd.
26-600 Radom
ul. Warsztatowa 19a
POLAND
direct line: +48(48)3686341
fax: +48(48)3686101
 
M

Mark Genovese

As this is a small DC motor the 'Quality' of the DC should not be an issue. Therefore consider a Half-wave rectifier.

This is simply a single diode placed between the AC supplay and the DC motor. A diode acts as a one way valve allowing the flow of electric current in only one direction.

The diode wired in series with the fan will block half of the AC. It should be sized large enough to handle the current draw of the motor. You may place more than one diode in paralle to acheive the necessary current rating. Beware that diode are polarized the negative end is marked with a band. So if you gang several together make sure the bands are all on the same connection side.
 
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