Electronics Help (Fan control Related)

[BrianW]

This post is here to clean up the thread, and to provide one post where I can ask a few questions.

Project:

Construct an adjustable power supply that will control both of my 24vdc-1amp Comair Rotron Major DC fans with one control interface.

Parts:

Adj. Power Supply- Input 24vdc, output 3-24vdc @ 2.5 amp
Order Code: CPS1007

Transformer: (Above kit recomends 24vdc 3 amp transformer)- I would like to get a desk transformer if at all possible, if not I will build one with a case mount transformer. I am thinking I may go with a slightly lower voltage transformer due to their higher availibility. Besides I do believe 20 vdc will give me plenty of airflow. What do you guys think on this one? Any ideas?

Additional mods for the power suply:

Since the fan does not start up until 6 vdc, is it possible to set a minimum voltage for the adj. power supply. Instead of 3-24vdc, make it 6-24 vdc? Please help. I do not want to worry about the setting being too low, and have no fans.

I would like to wire in a voltmeter into the powersupply, that will mount in the front of the case. I am looking for a small 0-24vdc voltmeter. Any ideas?

I plan on using a relay to turn on the fan power supply. Since I plan on using an external transformer, do they make 12vdc - 24vdc relay switches? In other words when the relay is supplied 12vdc it opens a 24 vdc switch. It would need to handle 3-4 amps? Any ideas/suggestions/sources?

Well I guess that sums it up. Sorry for posting so much on this thread, but it helps me work it out.

BrianW

[bigben2k]

You could add a resistor in parallel (or series?!?) with the pot, to set a minimum resistance, which ought to give you your minimum voltage. It would be easier to use a pot instead, that way you don't have to guess what the resistor ought to be, and you can change the minimum setting at your will.

Does the voltage increase with the resistance, or is it the other way around?

[airspirit]

Voltage drops with resistance.

[BrianW]

So what would you recomend Airspirit? What I invision is setting the main pot to lowest level, then adjusting another pot to set the min. Then the main pot will work fullrange from min. setting to max supplied voltage? How would I do this?

BrianW

[TerraMex]

> desk transformer

As in light an cellular phones? Too low output current. The best i've see was 500mA.

You could try an old HP printer power supply. If i remember correctly, the old 500 series printer had a big PS.

>Since the fan does not start up until 6 vdc, is it possible to set a
>minimum voltage for the adj. power supply. Instead of 3-24vdc,
>make it 6-24 vdc? Please help. I do not want to worry about the
>setting being too low, and have no fans.

Yes, but.

Without knowing the actual shematic of the PS, it's kinda hard.

If it was a simple LM type regulator, you'd just have to connect a proper pot, for the range that you want. Or two, and the second one would regulate the minimum voltage. The first would give the full range (maximum to minium set by user).

You can try to do the same with the PS, but you need to know the reference for that pot. Ohm value and watt rating. But that circuit will always go to 3v if you dont "mod" it.

>I would like to wire in a voltmeter into the powersupply, that will
>mount in the front of the case. I am looking for a small 0-24vdc
>voltmeter. Any ideas?

Any electronic stores have them. Just ask for a analog voltage meter display (or similar). You'd probably have to make a small adjusting circuit thou.

>do they make 12vdc - 24vdc relay switches? In other words
>when the relay is supplied 12vdc it opens a 24 vdc switch

Yes. Again, any electronic store. Just have to ask for it.

[bigben2k]

Originally posted by BrianW
So what would you recomend Airspirit? What I invision is setting the main pot to lowest level, then adjusting another pot to set the min. Then the main pot will work fullrange from min. setting to max supplied voltage? How would I do this?

BrianW

Exactly.

Wire up two pots in series: that'll do it (again, depends on circuit, but it looks OK).

[airspirit]

Or you could do this. Say you have a 5V line and you want it to range from, say, 2V to 4V, right? Put a resistor in the line to lower it to 4V. Then calculate the amount of resistance to lower it further to 2V. Find a pot close to that resistance, and then you'll be able to go from no resistance (4V) to full resistance (2V). Does that make sense?

[BrianW]

I want to be able to go from 6v to 24v.

BrianW

[airspirit]

What amperage or W are we talking about here? What is the starting voltage?

[BrianW]

It is all in the first post. I will be powering 2 - 24voltdc 1 amp fans.

BrianW

[airspirit]

If you are running JUST ONE fan per circuit (meaning one fan->one pot you will need a pot or rheostat of at least 18 ohm and 18W. You'll probably only find a rheostat in that spec. If you run the two after one pot, you will need a 9 ohm 36W rheostat at least. Do not skimp on either the resistance (you won't get down to 6V) or the wattage (you'll overheat and fail) or you'll be an unhappy camper.

Here is a 15 Ohm 15W:
http://www.allelectronics.com/cgi-bi...-15&type=store
This may work, getting you to around 7-8V without an overheating problem.

Meh, that was the only quick candidate. Mebbe you'll have to order two of them?

[BrianW]

I am running both fans off of one adj. power supply. I linked to it up above. I will link it again. Scroll down till you see this order code: CPS1007 . At stock it adjusts between 3-30 volts. I just want to change it so it adjusts from 6-30 instead. Hope that clears it up.

BrianW

[BrianW]

Originally posted by TerraMex
> desk transformer

As in light an cellular phones? Too low output current. The best i've see was 500mA.

You could try an old HP printer power supply. If i remember correctly, the old 500 series printer had a big PS.

When I say desk transformer, it is similar to a wall transformer except that it does not hang off the wall. It has two cords, one for the wall, and one for whatever needs the power. Laptop transformers are very close to what I need. Many times they support the amperage I need, but come up a bit short on the voltage, only supplying 16-20 vdc. I have found a place that sells exactly what I need, but I have to buy 10 of them....


BrianW

[airspirit]

Your solution, then, is to get two of the above rheostats and make two parallel circuits coming from the power supply.

[BrianW]

Ok that is what I will do. Thanks for all the help guys. Still looking for a small (2" diam.) analog voltmeter with a range of 6-24 voltdc.

BrianW

[murray13]

How about THIS ONE, will it do?

The price is right.

The size is about right.

It has the right range.

Hope you like it.

[BrianW]

Thanks for the link. Looks like it would fit the bill, although I was looking for one with a more car guage look. Again thanks for looking. A little more googling produced this page. I am interested in 0-30 vdc-(MTR)2437C or 0-40 vdc-(MTR)301-84. What do you think. Very industrial looking, me likes.

[murray13]

Personally I like the 2437C better but both are nice. You would be able to see 6V on the 2437C better I think since it only goes up to 30V instead of 40V for the other.

[BrianW]

I just bought the one you linked, better resolution, smaller, and cheaper. 30Vdc Multi PM-2 Analog Panel Meter! What does yje Multi PM-2 mean?

BrianW

[BrianW]

Well I do not know if I was reading wrong, or they changed it, but the CPS1007 Power Supply I previously linked does not use the LM350, but the LM723. In addition it does not have 24vdc input, but rather 24vac input. I am almost certain they changed it. Oh well, if it still is rated @ 2.5a we should be cool right? As far as a transformer, I am thinking of using this: 24V CT 3A POWER TRANSFORMER. Does that output AC or DC? I am planning on putting it in a project box, to be placed on the ground next to my power strip.

BrianW

[TerraMex]

> but the LM723. In addition it does not have 24vdc input, but
> rather 24vac input

They usually do . The circuit you buy is to rectify, regulate and filter de AC signal to a DC signal.

The transformer alone output at leads always an AC signal (in that case 24v AC) . Part of the transformer job is to reduce the amplitude of the 110v / 220v signal.

http://www.national.com/pf/LM/LM723.html

It's the datasheet. It reads 150mA output current. But the datasheet , however, says it can support more, by regulating a power transistor, instead of direct output.

There's a Darlington type transistor attached to the heatsink (if I'm not mistaken) , if you check the picture of the circuit (that, as far as I can see, hasnt changed), so it checks out. It'll still do what you want .

> this: 24V CT 3A POWER TRANSFORMER.

Like i said above, AC. It looks good anyway, and not very big.
I've got one that looks like king kong, and weights a ton.

[BrianW]

Thanks TerraMax, i will order both, and keep everyone updated.

BrianW

[BrianW]

Well I got the Power Supply (CPS1007), and dry fitted all the pieces. I have a couple questions:

1) The Voltage regulator uses two transistors to off load the linear regulation heat. Both have 3 connections. The larger one (2N3055 NPN Power Tramsistor) goes to a heatsink, and the smaller one (BD135 NPN Power transistor) is on the board. The one on the board has no indication which way to put it. The middle pin goes to a pin on the voltage regulator. One of the outer pins goes directly to the +24VDC , and the other one goes to a pin on the large transistor. I did some searching on the small transistor, and found out that the middle pin is the Collector, and one of the outer pins is an Emitter, and the other is Base. Any Help???

2) The plans call for two ceramic capacitors (100 pF & 100uF), yet in the kit the only ceramic capacitors are labeled 101 & 104M. I am at a loss as to which one is which. {EDIT} I did a little searching and all I could find info on is the one labeled 104M. I read a few spec sheets, and it always lists a uF voltage. So I imagine that the 104M is the 100uF, and the 101 is the 100pF. What do you think?

BTW, the heatsink is large (4.75"X2.5"X1.5"), but I think i will have a spot for it.

Any help on the above questions is appreciated, but I am also emailing the supplier.

BrianW

[TerraMex]

1) Althou i sound unhelpfull , but the PDF is pretty straight forward to me. The casing , the flat frontal part and the indicator of the pins, should have given enought information to you to solder it.

Doesnt the PCI has any labels ? C (collector), E(emitter) or B(base)? If not, doesnt it come with a paper with the circuit schematic?

http://www.tpub.com/neets/book7/25b.htm

PNP and NPN transitors. If you've got an schematic, it gives you which is Base, Collector and Emitter . Just follow the arrow, literally . Each transistor pin can be identified by the arrow.


> and the other one goes to a pin on the large transistor

Usually, it gives current to the base of the large one, and regulate the flow of current though the transistor .

2) What do they look like? (reference).

If (2) then the 104 is the 100nF. Usually is Z and not M. Must be a voltage reference or similar. 101 it's an 1nF . Both ceramic.

You should have a (3) type one for the 100uF. Ceramic type capacitors usually dont go over 1 uF. The larger ones in the picute are 220nF and go up to 250v.

[BrianW]

The larger transistor has labels for ECB, but the smaller one does not. Where the smaller transistor is on the board it is simply labeled TR2, and in the directions there is no detailed cirquit drawing. I suppose I will have to await an email response.

As far as the resistors, er capacitors(thanks terra) they both look very similar, and both are disk shaped. Like # 2. both are brown.

BrianW