Voltage selector

Y

yigiter

Guest
hello,
i am looking for a circuit. according my project, there are two different
input voltage 12V and 24V. and i want to switch my cicuit accordint to
input. i mean, if the input is 12V it will forward the input to A, if the
input is 24V it will forward the input to B. is there a way to achieve it,
out of using relay? if you can help, it would be very appreciated..
best regards,
 
hello tim,
soory for grammar mistake. i mean "without using relays".
 
On Wed, 03 Nov 2004 11:22:06 -0500, yigiter wrote:

hello tim,
soory for grammar mistake. i mean "without using relays".
Click to expand...
Do a search on "window comparator".

Good Luck!
Rich
 
i have posted a block diagram to make it more clear. also i want it to be
available for high currents(5Amp for 24VDC and 10Amp for 12VDC)
thanks again...
http://s02.imagehost.org/0625/BLOK.jpg
 
i have a dc-dc converter which is not available for 24V input. i don't want
to change it. so i must keep 24V off converter's input. the circuit must
be suitable to topology on the block diagram.
 
yigiter wrote:

i have a dc-dc converter which is not available for 24V input. i don't want
to change it. so i must keep 24V off converter's input. the circuit must
be suitable to topology on the block diagram.
Click to expand...
Study this webpage, and it will lead you to the answer you seek.

http://www.catb.org/~esr/faqs/smart-questions.html
 
"yigiter" <e.yigiter@denker.com.tr> wrote:

i have posted a block diagram to make it more clear. also i want it to be
available for high currents(5Amp for 24VDC and 10Amp for 12VDC)
thanks again...
http://s02.imagehost.org/0625/BLOK.jpg
Click to expand...
What's wrong with just connecting a permanent 24V supply to your
load?! That seems to satisfy the requirement specified in your block
diagram, that the load must *always* have a 24V supply.

Or, contrary to the statement in your original post ("there are two
different input voltage 12V and 24V..."), is there in fact a *third*
possible input voltage, Vin = 0?

If so, is the 24V rail available for the circuit?

--
Terry Pinnell
Hobbyist, West Sussex, UK
 
i want to use that circuit in car and the battery of car may be 12V or 24V.
so if the battery is 24V i have to forward it directly to the output but
if the battery is 12V i have to boost it to 24V so i have to forward it to
the converter. and i don't want my circuit to be manual selectable for
battery. when i connect it to battery it must be selected automatically.
 
On Fri, 05 Nov 2004 09:12:17 -0500, yigiter wrote:

i want to use that circuit in car and the battery of car may be 12V or 24V.
so if the battery is 24V i have to forward it directly to the output but
if the battery is 12V i have to boost it to 24V so i have to forward it to
the converter. and i don't want my circuit to be manual selectable for
battery. when i connect it to battery it must be selected automatically.
Click to expand...
Then just use a relay that pulls in at, say, 18 V. I've seen this done
to plug in a battery charger to 110/120 or 220/240, and the switchover
was simply a 220VAC relay.

Good Luck!
Rich
 
"yigiter" <e.yigiter@denker.com.tr> wrote in message
news:0ead3aba4374662cd49e789414f9ec94@localhost.talkaboutelectronicequipment.com...
thank you for your help. you are very kind.....
Click to expand...
Love it when such a simple statement says so much!
 
Rich Grise <rich@example.net> wrote in message news:<pan.2004.11.05.18.08.19.998103@example.net>...
On Fri, 05 Nov 2004 09:12:17 -0500, yigiter wrote:

i want to use that circuit in car and the battery of car may be 12V or 24V.
so if the battery is 24V i have to forward it directly to the output but
if the battery is 12V i have to boost it to 24V so i have to forward it to
the converter. and i don't want my circuit to be manual selectable for
battery. when i connect it to battery it must be selected automatically.

Then just use a relay that pulls in at, say, 18 V. I've seen this done
to plug in a battery charger to 110/120 or 220/240, and the switchover
was simply a 220VAC relay.
Click to expand...

Exactly. Relay current draw is a non issue for in car use. Will these
people ever learn to tell us what they want to start with? What a
waste of time.

A 24v relay should fail to pull in at 12v, a series zener of a few
volts would make sure it works as desired.
A second slower relay (RC on coil) will keep the 24v off the 12v input
while the main relay decides what to do. A zener/tr on the 12->24
convertor would be a cheaper option for that.

The only reason I can think of to avoid a relay is if youre doing mass
prouction. Did you tell us how many youre making?


NT
 
"N. Thornton" wrote:

Rich Grise <rich@example.net> wrote in message news:<pan.2004.11.05.18.08.19.998103@example.net>...
On Fri, 05 Nov 2004 09:12:17 -0500, yigiter wrote:

i want to use that circuit in car and the battery of car may be 12V or 24V.
so if the battery is 24V i have to forward it directly to the output but
if the battery is 12V i have to boost it to 24V so i have to forward it to
the converter. and i don't want my circuit to be manual selectable for
battery. when i connect it to battery it must be selected automatically.

Then just use a relay that pulls in at, say, 18 V. I've seen this done
to plug in a battery charger to 110/120 or 220/240, and the switchover
was simply a 220VAC relay.

Exactly. Relay current draw is a non issue for in car use. Will these
people ever learn to tell us what they want to start with? What a
waste of time.

A 24v relay should fail to pull in at 12v, a series zener of a few
volts would make sure it works as desired.
Click to expand...
How about a 12V zener in series with a 12V coil ?


Graham
 
Pooh Bear <rabbitsfriendsandrelations@hotmail.com> wrote in message news:<418CA8EB.55EB10FA@hotmail.com>...
"N. Thornton" wrote:
Rich Grise <rich@example.net> wrote in message news:<pan.2004.11.05.18.08.19.998103@example.net>...
On Fri, 05 Nov 2004 09:12:17 -0500, yigiter wrote:

i want to use that circuit in car and the battery of car may be 12V or 24V.
so if the battery is 24V i have to forward it directly to the output but
if the battery is 12V i have to boost it to 24V so i have to forward it to
the converter. and i don't want my circuit to be manual selectable for
battery. when i connect it to battery it must be selected automatically.

Then just use a relay that pulls in at, say, 18 V. I've seen this done
to plug in a battery charger to 110/120 or 220/240, and the switchover
was simply a 220VAC relay.

Exactly. Relay current draw is a non issue for in car use. Will these
people ever learn to tell us what they want to start with? What a
waste of time.

A 24v relay should fail to pull in at 12v, a series zener of a few
volts would make sure it works as desired.

How about a 12V zener in series with a 12V coil ?


Graham
Click to expand...
would probably work, but the relay coil would be liable to overheat.
Car system V for nominal 12v is upto around 15v at max. 30v-12=18v,
and on a 12v relay thats a bit steep.

A 24v relay and a 3v zener would have no problems.

NT
 
In article <418E0A8F.9DA289F8@hotmail.com>,
Pooh Bear <rabbitsfriendsandrelations@hotmail.com> wrote:
"N. Thornton" wrote:
[....]
I thought that a lead-acid battery on charge should be 13.8 V max.
Click to expand...
There can be a few volts between "should" and "is". It is not uncommon
for the charging system in a car to run up to 14 or even 15V for a while.
There are sometimes spikes much above this but they are too short for the
relay to be troubled by them.

Making 27.6 V for a 24 V system.
Click to expand...
When designing for a 28V system, I always allow for voltages up to about
35V.

Simply adding a resistor in series with the realy coil, is a good way to
adapt standard relays to non-standard voltages. It divides the pull in
and hold voltages down by the same amount. Using a zener leaves the same
difference between the two which is not as good.


--
--
kensmith@rahul.net forging knowledge
 
kensmith@green.rahul.net (Ken Smith) wrote in message news:<cmlm9a$1nu$4@blue.rahul.net>...

Simply adding a resistor in series with the realy coil, is a good way to
adapt standard relays to non-standard voltages. It divides the pull in
and hold voltages down by the same amount. Using a zener leaves the same
difference between the two which is not as good.
Click to expand...
The zener provides more V discrimination due to it giving more V
variation on the coil. As long as the relay is rated for the max V
this will be more reliable.

NT
 
Pooh Bear <rabbitsfriendsandrelations@hotmail.com> wrote in message news:<418E0A8F.9DA289F8@hotmail.com>...

I thought that a lead-acid battery on charge should be 13.8 V max.
Click to expand...
Over 14v is more typical on cars when alternator running. Some go as
high as 15v.


Making 27.6 V for a 24 V system.

I'm sure a 12 V relay would accept a 3.6 V overvoltage - but your point is well taken.
Click to expand...
v and i both increased by 15.6/12 --> 1.7 x the power diss. I wouldnt
assume that myself.


You'll need to pay attention to 'pull-in' and 'drop-out' voltages too.
Click to expand...
With a resistor you will, with a zener you wont, thats the point of
the zener, it eliminates any issues with relay spec variation.


NT
 
Fred Bloggs <nospam@nospam.com> wrote in message news:<418E5F0F.2060606@nospam.com>...
Ken Smith wrote:
In article <418E0A8F.9DA289F8@hotmail.com>,
Pooh Bear <rabbitsfriendsandrelations@hotmail.com> wrote:
"N. Thornton" wrote:

Simply adding a resistor in series with the realy coil, is a good way to
adapt standard relays to non-standard voltages. It divides the pull in
and hold voltages down by the same amount. Using a zener leaves the same
difference between the two which is not as good.



Then use a current source limiter in series with the relay.
Click to expand...
that would ensure the relay is energised at either 12v or 24v, which
would be no use. Unless Im misunderstanding your suggestion.


NT
 
Fred Bloggs <nospam@nospam.com> wrote in message news:<418F9967.9050907@nospam.com>...

I think you should scrap the relay idea and interpose a 15A step-down
DC-DC converter between the unknown VBatt and the existing 12->24VDC
converter. The National hysteretic converter LM3485 will do the job- no
turn-on surges or relay wear out. http://cache.national.com/ds/LM/LM3485.pdf
Click to expand...
I cant think of any way in which that would be advantageous.

NT
 
bigcat@meeow.co.uk (N. Thornton) wrote:

Fred Bloggs <nospam@nospam.com> wrote in message
news:<418F9967.9050907@nospam.com>...

I think you should scrap the relay idea and interpose a 15A step-down
DC-DC converter between the unknown VBatt and the existing 12->24VDC
converter. The National hysteretic converter LM3485 will do the job- no
turn-on surges or relay wear out.
http://cache.national.com/ds/LM/LM3485.pdf

I cant think of any way in which that would be advantageous.
Click to expand...
Advantageous perhaps not. But maybe Fred was having a laugh?

On the other hand, it does actually cure the problem and it's not particularly
complicated or expensive so perhaps he was quite serious?

Gibbo
 
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