Voltage regulators in parralel?

E

Evil Genius jr.

Member
if I put 10 (example) 1A regulators in parallel I should have a 10A max output. correct? Are there any downfalls to this approach besides space and cost?
Do you guys know of any high Amp 5V regulators?

Thanks.
 
E

Evil Genius jr.

Member
OK, just making sure. I have a battery that can supply up to 200A and a 5A servo that needs to be powered off of that pack but with 5V not 7.4V.
So does anyone know of a simple high Amp 5V regulator?
 
S

srnet

Senior Member
Well if you try to connect regulators in // like that, I would recommend you wear a pair of safety goggles whilst testingt.

There are plenty of regulators available for powering high current servo setups, this is a common requirement in the RC (Radio Control) world.

Do an eBay search on 'UBEC'.

Do you know if the servo load is actually as high as 5A, or is that just whats been 'recommended' ?
 
G

Goeytex

Senior Member
Some regulators will work in parallel , but most will not.

Do a parametric search at Linear Tech and at National Semiconductor to find some that will.

Linear Tech has a 7.5 amp linear regulator. Check out the LT1083 .... Open up the checkbook.
 
E

Evil Genius jr.

Member
Well, I dont have a specific servo in mind, What I am trying to do is design a DIY BEC for RC, so buying one wont exactly work.
I found a 10A at digikey but I cant seem to find again.
 
S

srnet

Senior Member
Using diodes to drop the voltage is not rerally appropriate for this purpose, sounds like you are aiming to provide a 5V supply from a 2S LIPO pack, this can vary from 8.4V (fully charged) to 6.6V (close to flat), add in some change in voltage drop across the diodes between a few 10s of ma and 5A and the the 'output ' voltage variance could be in excess of 2V, not good.

This is really a job for a switching regulator, at 8.4V in 5V out at 5A a linear regulator is going to be dissapating 17watts, that a lot of heat to be getting rid of. Plus the regulator would need to be a low dropout type, a lot of the high current linears may require Vin to be at least 2V above Vout, so when the battery is flat (6.6v) its not going to regulate.

I have built 1.5A BECs using LDO regulators for RC stuff, they work just fine, simple and cheap.

I have not seen a 5A Linear regulator used for a BEC, they are all switching types for the obvious reasons. And since they cost around £5 delivered on eBay most people would not be bothered to try an make a 'cheaper' one.

A better place to ask may be here;

http://www.rcgroups.com/diy-electronics-199/

The DIY Electronics forum for RC guys.

Whats the PICAXE angle ?
 
S

srnet

Senior Member
Using diodes to drop the voltage is not really appropriate for this purpose, sounds like you are aiming to provide a 5V supply from a 2S LIPO pack, this can vary from 8.4V (fully charged) to 6.6V (close to flat), add in some change in voltage drop across the diodes between a few 10s of ma and 5A and the the 'output ' voltage variance could be in excess of 2V, not good.

This is really a job for a switching regulator, at 8.4V in 5V out at 5A a linear regulator is going to be dissapating 17watts, that a lot of heat to be getting rid of. Plus the regulator would need to be a low dropout type, a lot of the high current linears may require Vin to be at least 2V above Vout, so when the battery is flat (6.6v) its not going to regulate.

I have built 1.5A BECs using LDO regulators for RC stuff, they work just fine, simple and cheap.

I have not seen a 5A Linear regulator used for a BEC, they are all switching types for the obvious reasons. And since they cost around £5 delivered on eBay most people would not be bothered to try an make a 'cheaper' one.

A better place to ask may be here;

http://www.rcgroups.com/diy-electronics-199/

The DIY Electronics forum for RC guys.

Whats the PICAXE angle ?
 
S

srnet

Senior Member
The 576-1143-ND looks good, quite a low dropout for a 5V regulator, not that expensive.

Bear in mind that at 5A output you will have a nice 17W handwarmer, getting rid of the heat in a typical RC plane (for instance) aint going to be easy, which is why switching regulators are pretty much universal in this application.
 
E

Evil Genius jr.

Member
Ok, well it would be in a car if that matters. Anyway I could seem to find any switching regulators that were simple. Do they all use inductors?
 
D

Dippy

Moderator
Anything above wimpy-amps (i.e. what would be classed as 'switched-mode') will use an inductor.
It's the charactersitic of the inductor that makes them popular and efficient.
When you start getting to healthy-amps then this is the territory for switrchers.

Are you worried about inductors?

People often overlook heatsinking. I was going to ask if you'd done any calcs but srnet has done it for you :)
 
S

srnet

Senior Member
Well in a car there might be a handy metal plate to use as a heatsink.

Switching supplies do use inductors, plenty of ICs out there designed just for the purpose. However DIY of this sort of supply is not trivial, carefull selection of components is required.
 
G

Goeytex

Senior Member
The Micrel regulator seems to give the best performance for the $$. LT has always been over priced for small quantities.
The National regulator has a much higher dropout voltage and will likely need a bigger heat sink.
 
S

srnet

Senior Member
Dippy said:
People often overlook heatsinking
Click to expand...
Indeed, not so bad in a car, but in a plane you could loose it.

An inadequate heatsink may cause the regulator to go into SOA mode, cutting the output volts to protect itself, and the radio stops working.
 
D

Dippy

Moderator
What is the minimum Input voltage required to give 5V out?

(How crucial is the 5V side for accuarcy by the way?)
 
D

Dippy

Moderator
OK, what is the minimum input for that regulator you quoted to give 5V output?
This is why people got excited about LDO on linears.

These things are important if your batteries aren't giving you much headroom.
Srnet suggested a battery voltage range of 6.6V to 8.4V.
If your reg requires 7V min to output 5V then that ain't brilliant.

Just have a read and a search.... yes, it can take ages.
 
hippy

hippy

Ex-Staff (retired)
Evil Genius jr. said:
This is an example of one the the best on the market. http://www.castlecreations.com/products/ccbec.html#
Click to expand...
I think there's a clue there in how to proceed with that being a switching regulator and their note that "most ESCs with linear BECs are not designed for these applications".

That recommendation of switching rather than linear regulator would reflect what's also been said here. It may be possible to produce a cheaper or even better BEC than that listed at $25 ( $45 for the Pro ) but the question would be is it worth the effort in time and development costs. You could possibly use a linear regulator and additional bypass hardware to raise the current but I believe a properly designed switching regulator would be the best approach to take.

How to proceed probably depends on your intentions and goals, whether a one off challenge 'because you can', or for some other reason.
 
E

Evil Genius jr.

Member
Well its mostly to see if I can do it, but after asking on an RC forum the thing people want most is for the wiring to be easier. So if I got it working I might see what I can do abut that and if that works maybe sell low quantities (10).
 
D

Dippy

Moderator
I would suggest taking the worst case, therefore Min input 5.6V at 5Amps.
Good for a device like that.
Big heatsinks are heavy.

Nothing better in switchers? Your >15W of heat might come down 2W. Result = cooler AND batteries last longer. It's the better way.

I'll leave you to it. I've got to go and work, so Good luck with your searching.
 
hippy

hippy

Ex-Staff (retired)
Evil Genius jr. said:
after asking on an RC forum the thing people want most is for the wiring to be easier.
Click to expand...
Maybe I'm missing something but existing BEC's seem to be like any other regulator; a common 0V pass-through, Battery voltage in one side and a lower, regulated, voltage out the other. I wouldn't have thought it could get much simpler than that.

There are wiring harness issues which make it look more complicated but I'd have guessed that's so a BEC can be retrofitted to an existing harness so you'd have that complexity if it were drop-in in the same way.
 
S

srnet

Senior Member
The 5V supply to a RC device is not normally critical, most RC radios will work down to the 4V region, some even lower.

However, in a Car or fast plane, fast and strong servo response might be important and the lower the volts the slower and less powerful servos become.

Its not uncommon for high torque servos to be run at 6V
 
E

Evil Genius jr.

Member
hippy said:
Maybe I'm missing something but existing BEC's seem to be like any other regulator; a common 0V pass-through, Battery voltage in one side and a lower, regulated, voltage out the other. I wouldn't have thought it could get much simpler than that.

There are wiring harness issues which make it look more complicated but I'd have guessed that's so a BEC can be retrofitted to an existing harness so you'd have that complexity if it were drop-in in the same way.
Click to expand...
Sorry missed this. anyway, what I am thinking is have a connector for the batttery, ESC battery plug, and ESC servo plug all soldered on the board. then just a servo plug going to receiver. for normal BECs you have to tap into the battery power and cut the ESC's internal BEC wire for it to work.
 
You must log in or register to reply here.
Top