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oldspark 
Gold - Posts: 4,913
Gold spacespace
Joined: November 03, 2008
Location: Australia
Posted: March 12, 2013 at 4:10 AM / IP Logged  
You shot Everclear? Hero!
I should have added that the power given off by the 7805 is the voltage across it times the current thru it.
Assume 15V in and (obviously) 5V out. (15V because most charging system are limited to ~14.4V maximum but can be higher at times, so we'll add a bit extra. Besides, 15 - 5 = 10, and 9 or 9.4 might require a calculator - though many of my friends & colleagues use a calculator to multiply by 10.)
So, 15V - 5V = 10V.
Current I = 900mA = 0.9A.
P = VI = 10V x .9A = 9 Watts.
I can't find the usual "simple" statement that the TO-220 will handle x-Watts at 25C etc. Instead I see the engineering formulae.
But the UA7805C is rated for 1.5A (intead of the norm of 1A), and they have internal thermal and current limiting.
Hence if they get too hot, they shouldn't self destruct - they'll drop their output current (and hence output voltage) instead.
I saw one example but that was only 500mA output (a bit over half your current) however it had a 21V input, hence about double your in/out voltage difference - ie, 8W - about the same as your power dissipation.
And that did not mention needing heatsink so I reckon you'll be okay. But cars may be hotter than that example's air temperature...
On te other hand, your 900mA may be a maximum input - eg, charging its battery, display lit, writing/recording etc.
But add your heatsink to be sure. It'll probably look cooler anyhow. (Ha ha, cooler...)
And a great thing with these regulators - the "tab" is connected to the common or 0V = GND terminal, hence it and its heatsink can touch grounded bodies & chassis etc. (Some inconsiderate regulators have their tabs or bodies connected to the input or output and hence it has to be electrically insulated from the heatsink etc or encased to prevent accidental shorts.)
BTW - if the output cap C2 is similar or bigger than the input's C1, add a diode that conducts from the output to the input. That will discharge C2 if its voltage ever exceeds the input voltage which can damage or destroy the volt reg.
It sounds like you'll do ok eh? Congrats!
myonus 
Copper - Posts: 54
Copper spaceThis member has made a donation to the12volt.com. Click here for more info.spacespace
Joined: February 24, 2013
Location: Arizona, United States
Posted: March 12, 2013 at 6:12 PM / IP Logged  

oldspark wrote:
You shot Everclear? Hero!

.......................................................

It sounds like you'll do ok eh? Congrats!

I wouldnt call it hero,  hero is a couple months back finally having the will power to function without it.  I had to take it easy for a while,  so now i find comfort in a couple premium lagers when im stressed or when i need to celebrate or reward myself.  Life is totally different.  To me thats a hero my friend.  But yea,  everclear is pretty rott gut,  but try Southern Georgia Moonshine,  sip on that all night and it will not only prevent anything viral in your body to die,  but it burns the cancer right out of your colon.  Trust me I've frikkin seen it. 

Now back to the regulators.  This is going to take some time to processs.  I get what your saying,  which means i see the logic.  My brain says the math right.  but Im going to have to get on the design board and put it all together befor I can invision the way the signal is converted and its travel and destination.  Im going to buy 6 VRs and some more heat sinks like this.  and put them all in a small box so I can have future use available,   maybe a couple of different voltages available.  The circuts are small enough shouldnt take much room. 

First step is to design the scematic.  and before that focus on all that hydrographics you just wrote up there,   and get out my scratch pad.  I have plenty of patience, and I wanna do it right,  and I want to learn somthing besides just soldering the ends together and crimping with my needle nose. 

Im taking the night off the project,   for now,  ,,,so I say,  but i'll probably be back to wiring up the amp rack tonite.  Seems i have plenty of that to do,  and i know wht im doing there.  Its starting to look functional,   have a few more parts coming.  but a long way off from done. 

So would  you say a 1A diode across the cap?  Im gonna ditch the VR that i have since i only have one.  so Tonite maybe i will have a parts list ready and I can shoot that to ya and see what you think?

to shield or not to shield - Page 2 - Last Post -- posted image.

Be not guided by morality, but rather, integrity.
oldspark 
Gold - Posts: 4,913
Gold spacespace
Joined: November 03, 2008
Location: Australia
Posted: March 12, 2013 at 7:21 PM / IP Logged  
Keep in mind that those "linear" VRs are inefficient. Whatever voltage they drop is given off as heat.
EG - assume your load is 5W (5V @ 1A; P=VI). With 10V in, the VR drops another 5W as heat - ie, the 10V down to 5V (=5V) @ 1A.
If 15V in, that's a 10V drop x 1A = 10W.
IOW you are wasting 50% to ~66% as heat.
Apart from generating heat, it's a waste of electricity.
Hence the modern dc-dc converter which uses switching techniques (SMPS). They are more like transformers - ie, 15V @ 1A in for 5V @
3A out (15W in, 15W out) although in practice they are usually only up to 95% efficient but typically better than ~85%. (Hence only 15% to 5% wasted as heat.)
You might thus want to consider converters, and they'd normally be purchased complete. Current-Logic have several that might suit, and they are cheap - look at the lower "non-solated converter" section at current-logic dcdc_converter_all (search for "5V").
Just make sure any 12V input means "automotive 12V" - ie, operates with input voltages up to at least 16V, and below 12V - preferably own to 8V.
5V 10A converters as below are under $20.
PS - some dc-dc converters can be electrically noisy. Metal casing/shielding should prevent radiated noise. Capacitors across the output - usually around 0.01uF to 0.1uF - usually stop any conducted noise.
to shield or not to shield - Page 2 - Last Post -- posted image.
myonus 
Copper - Posts: 54
Copper spaceThis member has made a donation to the12volt.com. Click here for more info.spacespace
Joined: February 24, 2013
Location: Arizona, United States
Posted: March 12, 2013 at 11:06 PM / IP Logged  

oldspark wrote:
Keep in mind that those "linear" VRs are inefficient. Whatever voltage they drop is given off as heat.
Just make sure any 12V input means "automotive 12V" - ie, operates with input voltages up to at least 16V, and below 12V - preferably own to 8V.
5V 10A converters as below are under $20.
PS - some dc-dc converters can be electrically noisy. Metal casing/shielding should prevent radiated noise. Capacitors across the output - usually around 0.01uF to 0.1uF - usually stop any conducted noise.

Hello, again,  now im feeling like a pest. and a little frustrated.  let me explain:

I went to ebay to start gathering some parts thinking this should be easy,  then as i was looking at parts saw other parts then it just snowballed.  Im pretty sure im over thinking this as I always do and sike myself out over nothing,  so I gotta get a ground here.  The primary goals of this voltage regulator:

DC auto 12 volt to DC 5volt 1A  -*keep a fixed 5 volt constant -*with a heat sink to prevent overheating -*caps across outputs to prevent noise

then ultimately duplicate this 6X

could you look at this option?  and i will look at your example now.  If i can just get this pre-made to the specs i need,  maybe spending a little extra isnt out of the question.  Especially if the integrity of the circut is depending on my skills to choose the right components.  (see this is me second guessing my ability)

http://www./itm/DC-DC-Converter-Step-Down-voltage-Regulator-Module-/250888508121?_trksid=p2045573.m2042&_trkparms=aid%3D111000%26algo%3DREC.CURRENT%26ao%3D1%26asc%3D27%26meid%3D6205306881770060294%26pid%3D100033%26prg%3D1011%26rk%3D2%26sd%3D221075949903%26

i saw some others too,  but thing is i get side tracked by all the other stuff that some of these products feature and really need to focus on what i need.  Like I said maybe im overthinking this a bit,  and getting gun shy.

Be not guided by morality, but rather, integrity.
myonus 
Copper - Posts: 54
Copper spaceThis member has made a donation to the12volt.com. Click here for more info.spacespace
Joined: February 24, 2013
Location: Arizona, United States
Posted: March 12, 2013 at 11:13 PM / IP Logged  

yea that link didnt work,  sorry

Be not guided by morality, but rather, integrity.
myonus 
Copper - Posts: 54
Copper spaceThis member has made a donation to the12volt.com. Click here for more info.spacespace
Joined: February 24, 2013
Location: Arizona, United States
Posted: March 12, 2013 at 11:15 PM / IP Logged  

try this one

http://www./itm/DC-DC-Converter-Step-Down-voltage-Regulator-Module-/250888508121

Be not guided by morality, but rather, integrity.
myonus 
Copper - Posts: 54
Copper spaceThis member has made a donation to the12volt.com. Click here for more info.spacespace
Joined: February 24, 2013
Location: Arizona, United States
Posted: March 13, 2013 at 12:00 AM / IP Logged  

Im guessing,  that this one would be ideal,  specifically says car audio etc

DC-DC Power Converter reducer 12V/24V Step down to 5V 3A 15W f Car Audio LED TV
ebay Item number :  360613180623
for some reason links to this item cannot be copied and pasted
this seems to meet my needs, simple and effective,  the price just sux. 
I will revist this tommorrow with a fresh head. a bit overwhelmed.  lol.  time for another fat tire! woohoo
to shield or not to shield - Page 2 - Last Post -- posted image.
Be not guided by morality, but rather, integrity.
oldspark 
Gold - Posts: 4,913
Gold spacespace
Joined: November 03, 2008
Location: Australia
Posted: March 13, 2013 at 4:33 AM / IP Logged  
Yeah - eBay and similar links don't work (you must have forgotten that line from The Rules when you joined this forum), but just quoting the item number (eg, 250888508121) is enough, and we simply paste that into the eBay search box.
I missed your 2 previous replies for some reason, but I think you may agree that getting a dc-dc converter is much easier (and probably cheaper) than making 6 "linear" circuits. Plus the efficiency bonus.
So, negating an notion of using linears...
There are lots of dc-dc conv products. As to how they perform, I don't know.
I like the looks of those Current-Logic alloy-cased units not only for their robustness, but more so because I reckon they should be well shielded (to prevent radiated noise). Price-wise I reckon they are cheap. I wouldn't hesitate to buy a spare (with any original order) even if it's never used (I'm a lover of redundancy - being able to replace or bypass faulty equipment anywhere and immediately).
Price is relative though. Prices for that sort of stuff is usually much cheaper stateside than it is here, so $20 for a 10A converter is nothing.
But those converters you found are cheaper still. I'd be concerned about plastic or no-cased converters, but common cig-plug converters for phone chargers, USB etc are plastic cased and they all use the same high-frequency switching (SMPS) and I don't know of any noisy ones - not that I use mobile digital radio nor TV etc. (GSM phone radiation is still the big problem lol.)
I do know the M2 & M4 PSUs are notoriously noisy, but they are for 12V PC applications (12V ATX supplies) and are irrelevant here.
So that uncased beast might be ideal for you. You can mount it in your hardware. And it might be cheap enough to buy a spare (assuming it works ok).
myonus 
Copper - Posts: 54
Copper spaceThis member has made a donation to the12volt.com. Click here for more info.spacespace
Joined: February 24, 2013
Location: Arizona, United States
Posted: March 13, 2013 at 6:35 PM / IP Logged  

hello, 

im going to move forward on these lil babys.  they seem to be a solution,  maybe not exactly,  but close enough for now,  I do like the ones above with the metal casings,  but couldnt find it under 20 bucks with shipping.  So,  I choose this one EUR 2.32 each free shipping anywhere in the world.  I got 3 for now,  if the work for me fine,  if not and i need to modify,   fine,  if that dont work I can attach it to a chain and hang it from my nipple ring; Im only out 6 - fity.

WTH? ..................... just kidding I would never hang anything from a nipple ring;  except my attention.

to shield or not to shield - Page 2 - Last Post -- posted image.

Heres the specs:

Input voltage: 4-40V

Output Voltage: 1.5-35V (adjustable)
Output current: rated current 2A, maximum 3A (need to add heat sink),
if the output power greater than 15W, the proposed combined heat sink
Conversion efficiency: Up to 92% (output voltage higher, the higher the efficiency)
Switching Frequency: 150KHz
Rectifier: Non-Synchronous Rectification
Module Properties: Non-isolated step-down module (buck)
Short circuit protection: current limiting, since the recovery
Operating temperature: Industrial grade (-40 ℃ to +85 ℃) (output power 10W or less)
Full load temperature rise: 40 ℃
Load regulation: ± 0.5%
Voltage regulation: ± 0.5%
Dynamic response speed: 5% 200uS
Size: 43 (L) * 20 (W) * 14 (H) mm (with potentiometer)
Output ripple:
Input 12V Output 5V 3A 60mV (MAX)
Input 24V Output 12V 3A 120mV (MAX)

Be not guided by morality, but rather, integrity.
oldspark 
Gold - Posts: 4,913
Gold spacespace
Joined: November 03, 2008
Location: Australia
Posted: March 13, 2013 at 7:03 PM / IP Logged  
Yeah, they certainly look impressive.
As long as people realise they are buck and don't lose their doe. (Puns, what puns?). IE, though the output is adjustable to 35V, they require the input voltage to exceed the output voltage.
That's irrelevant for you (ie, 12V in, 5V out is bucking fine), but as a caution to others (I think that Vin > Vout statement is on their page somewhere; it is not a buck-boost aka up or down converter.).
It's amazing how small packages can deliver relatively high currents (all thanks to high-frequency switching). Compare that module's size - or rather, that potted coil size - to a 50Hz or 60Hz 5V 2A transformer!
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