DC voltage regulation.

[GrimR]

Hello,

I am a 4th year railway sparky designing a private project (not related t
my job).

I need to supply my load with +5V DC and up to approx 1.2A.

My initial thought was to simply get one of those AC-DC wall supplies (lik
what a laptop uses except 5V DC out), which I am hoping to still do, but
also want to make it possible to use batteries to operate the device whe
the wall supply is not plugged in.

At first I figured I would have the load and battery combination (to suppl
4.8V, 4x 1.2V NiMh probably a couple sets paralleled to give more aH) i
parallel to the wall supply, thinking it will power the load and charge th
batteries at the same time, but when not plugged in operate the load fro
the batteries, does this sound right?

A problem brought up by another user of this device, is ensuring as clos
as practicle that 5V DC is delivered to the device, which may or may not b
an issue from one of those AC-DC wall supplies? But could definitely be a
issue with AA NiMh batteries.

So with some research I have come to this component
http://au.element14.com/stmicroelectronics/l7805cd2t-tr/ic-v-reg-5-0v-smd-d2pak-3-7805/dp/1366576

It has a minimum input of 7V (so I suppose use a 12V instead of 5V D
supply or another that can take lower).

I figure outright this should do the job in series from battery to load
But there is apparently an issue of heat, or potentially other component
that may be necessary. What else might I be looking at with this scenario?



---------------------------------------
Posted through http://www.Electronics-Related.com

 

[Baron]

GrimR Inscribed thus:

Hello,

I am a 4th year railway sparky designing a private project (not
related to my job).

I need to supply my load with +5V DC and up to approx 1.2A.

My initial thought was to simply get one of those AC-DC wall supplies
(like what a laptop uses except 5V DC out), which I am hoping to still
do, but I also want to make it possible to use batteries to operate
the device when the wall supply is not plugged in.

At first I figured I would have the load and battery combination (to
supply 4.8V, 4x 1.2V NiMh probably a couple sets paralleled to give
more aH) in parallel to the wall supply, thinking it will power the
load and charge the batteries at the same time, but when not plugged
in operate the load from the batteries, does this sound right?

A problem brought up by another user of this device, is ensuring as
close as practicle that 5V DC is delivered to the device, which may or
may not be an issue from one of those AC-DC wall supplies? But could
definitely be an issue with AA NiMh batteries.

So with some research I have come to this component:

http://au.element14.com/stmicroelectronics/l7805cd2t-tr/ic-v-reg-5-0v-smd-d2pak-3-7805/dp/1366576

It has a minimum input of 7V (so I suppose use a 12V instead of 5V DC
supply or another that can take lower).

Note that the above device has a maximum input voltage spec of 10V. So
if you are going to use 12V input the TO220 device is a better match.

In any case if you are going to charge the batteries at the same time as
well as supply the load, you will need to find some way of limiting the
voltage to the load from both the battery and 12V supply.

I figure outright this should do the job in series from battery to
load? But there is apparently an issue of heat, or potentially other
components that may be necessary. What else might I be looking at with
this scenario?



---------------------------------------
Posted through http://www.Electronics-Related.com

--
Best Regards:
Baron.

 

[John G]

It happens that Baron formulated :

GrimR Inscribed thus:

Hello,

I am a 4th year railway sparky designing a private project (not
related to my job).

I need to supply my load with +5V DC and up to approx 1.2A.

My initial thought was to simply get one of those AC-DC wall supplies
(like what a laptop uses except 5V DC out), which I am hoping to still
do, but I also want to make it possible to use batteries to operate
the device when the wall supply is not plugged in.

At first I figured I would have the load and battery combination (to
supply 4.8V, 4x 1.2V NiMh probably a couple sets paralleled to give
more aH) in parallel to the wall supply, thinking it will power the
load and charge the batteries at the same time, but when not plugged
in operate the load from the batteries, does this sound right?

A problem brought up by another user of this device, is ensuring as
close as practicle that 5V DC is delivered to the device, which may or
may not be an issue from one of those AC-DC wall supplies? But could
definitely be an issue with AA NiMh batteries.

So with some research I have come to this component:
http://au.element14.com/stmicroelectronics/l7805cd2t-tr/ic-v-reg-5-0v-smd-d2pak-3-7805/dp/1366576

It has a minimum input of 7V (so I suppose use a 12V instead of 5V DC
supply or another that can take lower).

Note that the above device has a maximum input voltage spec of 10V. So
if you are going to use 12V input the TO220 device is a better match.

25 volts max the info says.

In any case if you are going to charge the batteries at the same time as
well as supply the load, you will need to find some way of limiting the
voltage to the load from both the battery and 12V supply.

I figure outright this should do the job in series from battery to
load? But there is apparently an issue of heat, or potentially other
components that may be necessary. What else might I be looking at with
this scenario?



---------------------------------------
Posted through http://www.Electronics-Related.com

--
John G

 

[Baron]

John G Inscribed thus:

It happens that Baron formulated :
GrimR Inscribed thus:

Hello,

I am a 4th year railway sparky designing a private project (not
related to my job).

I need to supply my load with +5V DC and up to approx 1.2A.

My initial thought was to simply get one of those AC-DC wall
supplies (like what a laptop uses except 5V DC out), which I am
hoping to still do, but I also want to make it possible to use
batteries to operate the device when the wall supply is not plugged
in.

At first I figured I would have the load and battery combination (to
supply 4.8V, 4x 1.2V NiMh probably a couple sets paralleled to give
more aH) in parallel to the wall supply, thinking it will power the
load and charge the batteries at the same time, but when not plugged
in operate the load from the batteries, does this sound right?

A problem brought up by another user of this device, is ensuring as
close as practicle that 5V DC is delivered to the device, which may
or may not be an issue from one of those AC-DC wall supplies? But
could definitely be an issue with AA NiMh batteries.

So with some research I have come to this component:

http://au.element14.com/stmicroelectronics/l7805cd2t-tr/ic-v-reg-5-0v-smd-d2pak-3-7805/dp/1366576

It has a minimum input of 7V (so I suppose use a 12V instead of 5V
DC supply or another that can take lower).

Note that the above device has a maximum input voltage spec of 10V.
So if you are going to use 12V input the TO220 device is a better
match.

25 volts max the info says.

Sorry I should have read further down the specs. :-(

In any case if you are going to charge the batteries at the same time
as well as supply the load, you will need to find some way of
limiting the voltage to the load from both the battery and 12V
supply.

I figure outright this should do the job in series from battery to
load? But there is apparently an issue of heat, or potentially other
components that may be necessary. What else might I be looking at
with this scenario?



---------------------------------------
Posted through http://www.Electronics-Related.com

--
Best Regards:
Baron.

 

[Tim Wescott]

On Sat, 10 Mar 2012 11:14:51 -0600, GrimR wrote:

Hello,

I am a 4th year railway sparky designing a private project (not related
to my job).

What the hell is a 4th year railway sparky?

I need to supply my load with +5V DC and up to approx 1.2A.

My initial thought was to simply get one of those AC-DC wall supplies
(like what a laptop uses except 5V DC out), which I am hoping to still
do, but I also want to make it possible to use batteries to operate the
device when the wall supply is not plugged in.

At first I figured I would have the load and battery combination (to
supply 4.8V, 4x 1.2V NiMh probably a couple sets paralleled to give more
aH) in parallel to the wall supply, thinking it will power the load and
charge the batteries at the same time, but when not plugged in operate
the load from the batteries, does this sound right?

It sounds like a recipe for short battery life. See http://
batteryuniversity.com/ and look for information on NiMH cells. You can
get big cells, by the way.

If you decide to go lead-acid, look on there for their care and feeding
-- it's markedly different from the care & feeding of NiMH cells
(although potentially easier & cheaper).

A problem brought up by another user of this device, is ensuring as
close as practicle that 5V DC is delivered to the device, which may or
may not be an issue from one of those AC-DC wall supplies? But could
definitely be an issue with AA NiMh batteries.

Older wall-warts have terrible regulation, newer ones have pretty good
regulation, but its up to you to verify that the supply regulation is
good enough for the device you're going to use.

To clean up a battery supply you want a DC-DC converter, and you probably
don't want to build one from scratch:

http://search.digikey.com/us/en/cat/power-supplies-board-mount/dc-dc-
converters/4325599

So with some research I have come to this component:
http://au.element14.com/stmicroelectronics/l7805cd2t-tr/ic-v-reg-5-0v-
smd-d2pak-3-7805/dp/1366576

It has a minimum input of 7V (so I suppose use a 12V instead of 5V DC
supply or another that can take lower).

I figure outright this should do the job in series from battery to load?
But there is apparently an issue of heat, or potentially other
components that may be necessary. What else might I be looking at with
this scenario?

That's what's known as a "linear regulator", which works by burning up
power on-chip -- so at 1.2A, 12V in, 5V out, you'll be delivering 6W to
your load and dissipating 8.4W in the chip. It can be done, it's the
easiest way to get your 5V -- but it's exceedingly wasteful of power.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com

 

[GrimR]

Hi Everyone,

I have since found more information which has made things clearer (
haven't much dealt with power supplies or batteries and charging etc).

As far as my job goes, I do all the same courses and examinations to becom
a qualified domestic electrician, but also do specialized training fo
signalling electrical/mechanical with is a beast in it's own right and i
the main focus of the 4 years.

I did manage to find what appears to be a good quality +5V DC regulate
wall supply that can supply up to 3A, which should supply the load on it'
own perfectly.

I really do want to make it possible to use batteries as well, eithe
active with supply or isolated but from further research there is a lo
more involved than I first realized.

---------------------------------------
Posted through http://www.Electronics-Related.com

 

[ehsjr]

GrimR wrote:

Hello,

I am a 4th year railway sparky designing a private project (not related to
my job).

I need to supply my load with +5V DC and up to approx 1.2A.

My initial thought was to simply get one of those AC-DC wall supplies (like
what a laptop uses except 5V DC out), which I am hoping to still do, but I
also want to make it possible to use batteries to operate the device when
the wall supply is not plugged in.

At first I figured I would have the load and battery combination (to supply
4.8V, 4x 1.2V NiMh probably a couple sets paralleled to give more aH) in
parallel to the wall supply, thinking it will power the load and charge the
batteries at the same time, but when not plugged in operate the load from
the batteries, does this sound right?

A problem brought up by another user of this device, is ensuring as close
as practicle that 5V DC is delivered to the device, which may or may not be
an issue from one of those AC-DC wall supplies? But could definitely be an
issue with AA NiMh batteries.

So with some research I have come to this component:
http://au.element14.com/stmicroelectronics/l7805cd2t-tr/ic-v-reg-5-0v-smd-d2pak-3-7805/dp/1366576

It has a minimum input of 7V (so I suppose use a 12V instead of 5V DC
supply or another that can take lower).

I figure outright this should do the job in series from battery to load?
But there is apparently an issue of heat, or potentially other components
that may be necessary. What else might I be looking at with this scenario?



---------------------------------------
Posted through http://www.Electronics-Related.com

Use a regulated 5V wall wart like item number 18520 PS from:
http://www.mpja.com/5VDC-4A-Regulated-Plug-Supply-Openpeak/productinfo/18520+PS/

Ed

 

[fungus]

On Saturday, March 10, 2012 6:14:51 PM UTC+1, GrimR wrote:

Hello,

I am a 4th year railway sparky designing a private project (not related to
my job).

I need to supply my load with +5V DC and up to approx 1.2A.

My initial thought was to simply get one of those AC-DC wall supplies (like
what a laptop uses except 5V DC out), which I am hoping to still do, but I
also want to make it possible to use batteries to operate the device when
the wall supply is not plugged in.

Go on eBay and search for "5V dc boost".
Get one of the 3A ones.

With that you can power it from batteries
or a 4.5V transformer (which are quite
common).

I've been using those little boards to
power battery operated projects lately.
It makes life an awful lot easier to have
a fixed 5V supply instead of trying to
design the circuit to handle the voltage
variation as a battery discharges.

They can get quite hot if you draw
the maximum current. I wouldn't
recommend drawing more than about 50%.

PS: 1.2A is quite a lot of current,
make sure your batteries can handle
it...

 

[GrimR]

I should add that 1.2A is the average spiked draw (not sustained).

Seen as this is for a personal project I might simplify it by
using as said regulated +5V DC (choice of 1.7/3A locally) and
batteries, but use blocking diodes on supply and battery actives
and have a switch on the negative. (The batteries would still
use a voltage regulator).

I'm pretty sure this would work and effectively isolates the
wall supply from battery and vice versa, but obviously I can
only have one at the same time and I presume switching while
the device is operating would be a bad idea.

I do like the integrated rechargeable battery idea, but the
circuitry involved could blow out the overall physical size
and cost and complexity, probably explore that avenue later.

---------------------------------------
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