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Jan 30, 2013, 12:14 PM
RC beginner
Quote:
Originally Posted by phil_g
Ok, arrogant and pretentious. And rude. Further, you seem to take a strange pride in that attitude. Maybe its a culture thing.
culture? i got sh!tloads 'a culture!

Quote:
Originally Posted by phil_g
Did it occur to you that some of us teach the stuff you've been learning?
"Those who can do, do; those who can't, teach".

sorry that WAS rude. as part time ta (that dont stand for what some of you are thinking) i should show more respect. imagine having me as a student though. count your blessings.
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Jan 30, 2013, 12:20 PM
RC beginner
Quote:
Originally Posted by jakestew


So what is the logical dispute against Dave's theory that the load bearing reg heats faster causing the resistance to increase and thus decrease it's current load?
.
hi jake,

but thats not my theory. i never said anything like that and makes no sense. sound like something a guy who recommends homemeade copper tips for soldering and thinks resistive dividers make good regulators for high current. fortunately theres nobody around here like that.

want any milk duds with that popcorn?
Jan 30, 2013, 03:04 PM
Registered User
Quote:
Originally Posted by dave1993
i should bring up another point that maybe hasnt been discussed much here. did you know that most escs actually have a row or two of linear regulators on the back? and they are ALL wired in parallel. rarely with any "equalizing" resistors. i kid you not.
Yep. Did you know that many modern voltage reg ICs now have what you call "equalizing" resistors built in ? Even some of those marketed as 78XX replacements ?

It's almost as though the manufacturers had noticed that people weren't bright enough to follow instructions and decided to save them from the results of their own foolishness .

Steve
Jan 30, 2013, 03:25 PM
RC beginner
or maybe they are parametric rejects due to process failure and they decided to re-market with "built-in equalizing resistor". in my own experience any added resistance at all did little more than reduce current capability. and little benefit in reliability either.

one thing cheapo chinese controllers might have that help level things off at lower drain is the parts are from same batch and bandgap probably varies little.
Jan 30, 2013, 05:47 PM
Registered User
Sounds to me like nobody here really knows the answer and would rather continue the argument endlessly rather than risk a pair of regulators to find out and settle the issue once and for all.

Makes for some good drama at least.
Jan 31, 2013, 01:37 AM
Stuart
srnet's Avatar
Quote:
Originally Posted by jakestew
Sounds to me like nobody here really knows the answer and would rather continue the argument endlessly rather than risk a pair of regulators to find out and settle the issue once and for all.
Probably because it would not prove a lot.

So one pair of regulators from a particular batch from a particular manufacturer do work in parallel. Can you then say the same applies to all regulators ?

Prudent design means following manufactures advice, if they advise against paralleling of regulators ...............

Linear changed the architecture\design of some of thier regulators specifically to allow paralleling, was that not necessary maybe ?
Jan 31, 2013, 04:54 AM
Oxford Panic
AndyOne's Avatar
Here's one that Linear says you can parallel providing you insert 15mOhm current sharing resistors in the outputs but it has a specification that goes up to 7.5A which means you probably wouldn't want to.

http://www.linear.com/docs/3741

I haven't read the entire datasheet so there may some "gotchas" in there, but isn't that what we've been discussing here.

A.
Jan 31, 2013, 05:06 AM
Registered User
Quote:
Originally Posted by AndyOne
Here's one that Linear says you can parallel providing you insert 15mOhm current sharing resistors in the outputs but it has a specification that goes up to 7.5A which means you probably wouldn't want to.

http://www.linear.com/docs/3741

I haven't read the entire datasheet so there may some "gotchas" in there, but isn't that what we've been discussing here.

A.
I used ic linear AMS1084, It is very vey hot
Jan 31, 2013, 11:26 AM
Oxford Panic
AndyOne's Avatar
There's no getting away from heat dissipation with a linear regulator (or any number in parallel), that's why it's best to use a switching regulator for high current.

A.
Jan 31, 2013, 12:16 PM
RC beginner
there are some applications where a linear can be far more efficient than switching. also switchers are noisy and usually cost more so i only consider them as a last resort..

please note my tests were done with venerable 7805/lm340 5v. however i suspect the same principles apply to other types and its safe to parallel any of them. imo mfg spec sheets, even if they did recommend against (which, apparently, they dont), might only be a consideration in mission critical or life support apps where liability is an issue. not the case here anyway.
Jan 31, 2013, 01:45 PM
Stuart
srnet's Avatar
Quote:
Originally Posted by dave1993
might only be a consideration in mission critical or life support apps where liability is an issue
If its perfectly safe it obviously would not be a concern in mission critical or life support apps or where liability is an issue.

Its safe and or recommended or its not, which is it ?
Jan 31, 2013, 02:56 PM
RC beginner
Quote:
Originally Posted by srnet
Its safe and or recommended or its not, which is it ?
yes. its safe and or recommended or its not.
Feb 03, 2013, 04:46 AM
Registered User
Little different question:
I'm about to build kind of Zagi mainboard (connections between rx, vid tx, servos, camera, 2 dividers for frsky & bec for servos).

As I don't want regular radiator on the vreg I came to conclusion to use LM2940 together pass transistor (tip42C).
Additionally 200ohm transistor with jumper in paraller to switch between 5/6v.
Up to 0.6A power wasted is about 2W per IC - should be fine without radiator, and little aluminium plate should make 1A safe.

Can you find anything wrong with this solution? (except caps - as I need to adjust them..)
Feb 03, 2013, 05:40 AM
Stuart
srnet's Avatar
[QUOTE=xader;24018421Can you find anything wrong with this solution?[/QUOTE]

The circuit diagram does not relate to your description, different pass transistor, different regulator.
Feb 03, 2013, 07:35 AM
Registered User
Quote:
Originally Posted by srnet
The circuit diagram does not relate to your description, different pass transistor, different regulator.
Yes - I cannot find LTSPICE models for LM2940 or TIP42C, thus I've used somehow similiar models - I'll try it next week on breadboard if i'll get ic's. But preffer get opinions earlier especially that I'm just starting having fun with electronics.

Attached schema without correct caps yet. (need to find ones with appropriate esr and adjust position)


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