Is there an easy way to multiply / step up DC voltage?? - Page 2

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Re: Is there an easy way to multiply / step up DC voltage??



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Hello Dave,
you are clued up on switchmode power supplies.
Your last comment
"You can also build your own with discrete components if you want."
interests me.

 A mate of mine has a large 12V car battery in his caravan
which he charges via a large isolating diode. The caravan
battery is parraled with the car battery but has the diode in
series with it.  So current can flow from the car to the caravan
battery but not the other way.  
Problem is the caravan battery doesn't get a good charge
this way due to the isolating diode.

A DC to DC converter made with discrete components, or
common ICs that could charge the caravan battery with
10s of amps and then backs off to a trickle current in the same
way the car battery charges up would be a nice thing to have.

Sorry for sucking your brains here Dave, but I just had to ask
for your ideas and suggestions.  My mate doesn't want to use
fancy switchmode power supply chips that are expensive.
hard to find, here  today but unobtainable in several years
time type of thing.  

Thanks for those links,

Regards,
John Crighton
Sydney


Re: Is there an easy way to multiply / step up DC voltage??



"John Crighton"

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  **  Lick , lick,  lick


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  **  The motive.



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**  Utter bullshit.



...........  Phil



Re: Is there an easy way to multiply / step up DC voltage??


On Sun, 9 Oct 2005 12:40:14 +1000, "Phil Allison"

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Hello Phil,
I live at 18 Talwong Street
Hornsby Heights
NSW

I don't get involved in slanging matches,
or making personal insulting remarks,
life is too short.
If you are interested in sorting something out
face to face with me, techo or otherwise,
come on up.  

I am quite happy to discuss techo stuff with
you or anyone but if involves personal insults
then forget it.

I don't very much care for your lick lick remark, take
that back and we can continue this discussion.
Over to you Phil.

Regards,
John Crighton

Re: Is there an easy way to multiply / step up DC voltage??



"John Crighton
 "Phil Allison"
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 **  What damn bad luck.


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**   The Jock jerk is a raving psycho.


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**  Boo,  hoo  -   poor baby.


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**  It was a blatant example of public arse licking.

Revolting stuff to see on a NG.

This quote from the same post conform you motive:

"  Sorry for sucking your brains here Dave, but I just had to ask
for your ideas and suggestions.  "


TIP:

Don't post site like this again if you do not want to draw justified
criticism.




........  Phil




Re: Is there an easy way to multiply / step up DC voltage??


On Sun, 09 Oct 2005 02:26:40 GMT, john snipped-for-privacy@tpg.com.au (John Crighton)
wrote:

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If the diode is causing that much of a problem when charging the
battery, then why not put a (large) relay across the diode, and have
it activate only when the alternator is actually running, (charging)so
as to bypass the diode.   I believe also that SC described a device to
replace this diode, and instead used a FET to minimise the losses.

Alternately, connect directly to the AC windings of the alternator
(before the alternators internal diode pack) bring the wires out and
install a second diode pack on them, take this supply direct to the
caravan.  A suitable diode pack should be obtainable from an auto
electrician

If you are getting bad losses like this at the caravan battery, you
should also look at the diameter of the wire running from the car
engine bay to the caravan, and the connectors used  A diode should
lose less than 1.0v under load,  I would bet that you would lose
substantially more than this (under load) in this wire run to the
caravan, unless you used some pretty hefty cable, and good solid
connectors.  Remember, you could be looking at a cable run of easily
around 10 metres or so, and with a load of "10's of amps" at 12v, the
cable is going to have to be bloody big cross section area to minimise
losses !

Dont forget to have a really good earth too, between the car and van
chassis.


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Re: Is there an easy way to multiply / step up DC voltage??





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Hello jj<k>,
thanks for those suggestions, I will pass them on to my mate.

The reason I was asking Dave about the smps approach
was also to directly charge a 24V battery bank used in the
caravan without the hassle of switching two small 12 V car
batteries from parrallel to series.   I haven't come across
a smps charger project in the magazines or the web that
would do this.

Regards,
John Crighton
Hornsby


Re: Is there an easy way to multiply / step up DC voltage??



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Another method before adding a boost charger (which would be a good idea) is
to make up a circuit (just a darlington transistor etc) that turns on a
relay or FET to connect the auxiliary battery only when the motor is
running. This removes the need for a diode. I have this scheme on my
vehicle, the "high" or "low" found on the oil pressure lamp controls the
relay.

--
Regards ......... Rheilly Phoull



Re: Is there an easy way to multiply / step up DC voltage??


On Sun, 9 Oct 2005 13:11:32 +0800, "Rheilly Phoull"

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Hello Rheilly,
a bit more icing on the cake!  
Thanks for that.
Regards,
John Crighton
Hornsby


Re: Is there an easy way to multiply / step up DC voltage??


On Sun, 09 Oct 2005 05:28:58 GMT, john snipped-for-privacy@tpg.com.au (John Crighton)
wrote:

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There are commercial devices available that do this for you. Go to
your local 4wd accessory shop and ask them.

Re: Is there an easy way to multiply / step up DC voltage??


On Sun, 09 Oct 2005 17:54:46 +1000, The Real Andy




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Hello Andy,
Yes, I will, thanks for that.
Regards,
John Crighton
Hornsby

Re: Is there an easy way to multiply / step up DC voltage??


On Sun, 09 Oct 2005 21:42:01 GMT, john snipped-for-privacy@tpg.com.au (John Crighton)
wrote:

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The bonus with the commercial units is that they will only charge the
house battery when the starting battery is fully charged. I think EA
or SC did one of these as a kit many moons ago too.

Re: Is there an easy way to multiply / step up DC voltage??



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Hi John

What you want is an Arrid Twincharge,
http://www.allabout12volt.net.au/cat04/info.html

These will take 8 to 15 volt and regulate to correct voltage to charge the
auxilary battery. No need to worry too much about voltage drops.

David





Re: Is there an easy way to multiply / step up DC voltage??





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Hello David,
yes that is the sort of device my friend is looking for. Certainly
sounds good in the write up.  Ideally he would like to make his
own.  Thanks for that.
Regards,
John Crighton
Hornsby
 


Re: Is there an easy way to multiply / step up DC voltage??



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Hi John

They do work well. I have one installed to charge the battery in my
campertrailer. It works well, providing the correct voltage, and ensures
the battery is charged fully. It it well built, having done 1000's of
kilometers on bumpy roads.

David

Re: Is there an easy way to multiply / step up DC voltage??



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An isolating switch and a separate charger should fix that problem,
John. Your mate may be able to pick one up from a car parts retailer.
My brother has one in his Formula Ford, so they shouldn't be too
expensive. Connect up a mains based lead acid charger and he
can trickle charge it on-site, if there's AC available of course.  8-)


Re: Is there an easy way to multiply / step up DC voltage??


On Sun, 09 Oct 2005 13:11:31 +1000, dmm

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Yes, my friend does that.  

 jj<k>'s suggestion with the FET or relay sounds like
the easiest improvement to make.

Regards,
John Crighton
Hornsby

Re: Is there an easy way to multiply / step up DC voltage??


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Hi John,
As others have mentioned, there are likely to be solutions already
available for this.
This is one applicaiton where there is most likely a very simple
solution available (FET or relay etc), so a DC-DC converter and
subsequent charging circuitry would be overkill I would have though.

Look inside many DC-DC converter apllication notes and datasheets and
you'll see that often there isn't much to it, so you could duplicate
the functionality with garden variety parts if you wanted. Some people
still do too, for the reason you mention, they want to be able to get
the parts in 20 years time.
The basic devices don't have any real "magic" in them, they all operate
on basic DC-DC converter topologies which were traditionally done with
discrete components.

Dave :)


Re: Is there an easy way to multiply / step up DC voltage??


For those interested in DC power supply design, the Hewlett Packard DC
Power Supply Handbook circa 1978 is a good read:
http://www.slack.com/pdf/HP-AN90B.pdf

Dave :)


Re: Is there an easy way to multiply / step up DC voltage??



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Hello Dave,
the link that David (just up thread) provided to an Arrid Twin Charge
is the sort of device my friend is looking for.
http://www.allabout12volt.net.au/cat04/info.html

One of these devices to charge his big 12Volt caravan battery
and a second device to charge his small 24 Volt battery bank
from the car as well.

It is always fun to build something DIY but if the price
is right he'll buy it.

The power supply handbook mentioned
in your other post. Thanks for that.

Regards,
John Crighton
Hornsby



Re: Is there an easy way to multiply / step up DC voltage??



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Maxim are good for one offs / samples

Maxim can be dam hard and more expensive to get bits
than National , ST or others if you need quantity
and even for small quantities.


DC-DC converter chips - Boost , Buck and switching regulators

http://www.national.com/appinfo/power/   has a nice calculator

ST
http://www.st.com/stonline/prodpres/standard/vregs/dcdc/dcconv.htm

Linear
http://www.linear.com/pc/viewCategory.do?navId=H0,C1,C1003

ST662ACN    is good for 5v to 12/20 volts  30mA
http://www.st.com/stonline/products/literature/ds/5068/st662ab.htm
good for making a usb pic programmer




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