I have a vehicle that uses a 24 volt system. I would like to run 12
accessories and have looked at various dc to dc converters. I assume
these are simple BUCK converters using duty cycle to drop the voltage.
I however cannot find a straight forward schematic for such. There
are a lot of info devoted to theory of operation and some plans but
the useable amp output is too low. The output should be 12-14 volts
and have an amp output of at least 10 amps more is better. The plans
should be as straight forward as possible and the components should be
available. (ie I am not interested in the plans where one has to
dissect a home appliance, rewind coils, kill a chicken and pray that
it wont burn up your accessories)
Thanks Jason |
Request for Question Clarification by
maniac-ga
on
24 Apr 2006 19:41 PDT
Hello Hobiecat,
Would purchase of a fully assembled unit (about $50) be acceptable
instead of a design for such a unit?
If you need a design, are there limits on the cost of parts?
--Maniac
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Clarification of Question by
hobiecat-ga
on
24 Apr 2006 23:02 PDT
Hello Maniac
I have looked at the units available from http://www.powerstream.com
and yes for around 50 dollars they fit the requirements of my original
request. Possibly my original requirements were too low? 20-30 amps
continuous, is more in line with what is needed. As well I would hope
that a design or schematic would maintain some level of user
customization regarding voltage and amp output.
In short I am intrigued by the circuit as well as my inability to find
it myself on the www so I am holding out for the plans.
Thanks Jason
|
Request for Question Clarification by
maniac-ga
on
25 Apr 2006 11:59 PDT
Hello Hobiecat,
Requiring 20 to 30 amps on output limits the options (and increases
the price!) but there are commercial options for this as well such as:
http://store.wmjmarine.com/-c14868.html
which at $429 allows a wide range of input voltages (20 - 45 V) and
supports the required current on the output side. Nominal voltage for
this unit is 32; I can't tell right off what the efficiency will be
with 24 V input (your case). There is a lower cost unit in the same
family at $279 as well, but it is limited to about 15 amps.
I will take some time to look for schematics / other control options as well.
Again, if you have a hard price limit, let me know what that is as well.
--Maniac
|
Clarification of Question by
hobiecat-ga
on
25 Apr 2006 22:38 PDT
Commercial options do meet the requirements but honestly there is NO
way to justify $429.00 for a converter that I imagine to have less
than 100 dollars in components in it. From
http://www.powerdesigners.com/InfoWeb/design_center/articles/DC-DC/converter.shtm
the basic design idea is very straight forward and in fact it would
seem reasonable that one could just keep adding more BJT?s or FETS in
parallel to get the required current output. With regard to
controlling the duty cycle I was thinking of making use of a very low
current draw voltage divider to set up a reference voltage then simply
compare the output voltage to the ref. voltage. If not the same, the
duty cycle to the transistor could be modified to get more or less
voltage out. Certainly someone has done this and knows the process.
Short of buying a unit already made and reverse engineering it I
cannot find plans for such, hence the ?Google answers? post.
As well this sort of converter is based on the BUCK converter. I
figure it is reasonable to assume there are other ways to make this
conversion. The BUCK converter seems very straight forward. It looks
that there may be an issue with noise though. Possibly with heavy
filter caps this would not be a problem?
Looking forward to plans, schematics, or comments letting me know I am
pissing in the wind.
Regards
|
Request for Question Clarification by
maniac-ga
on
26 Apr 2006 19:50 PDT
Hello Hobiecat,
After some more searching, it appears there are commercial models more
in line with your expectations:
- Powerstream PST-D24/12-400 $137 for 20 amps continuous, 30 amps for 3 hours
- Powerstream PST-D24/12-600 $173 for 30 amps continuous, 40 amps for 3 hours
both of the above require some "protection" since they use a fan for cooling.
- TRC Electronics SD-250B-12 $147 for 27.5 amps (350 watts)
also appears to use a fan for cooling.
On designs w/ parts lists, most are optimized for 5 volt (or less)
voltage for computer supplies. For example:
http://www.linear.com/pc/downloadDocument.do?navId=H0,C1,C1003,C1042,C1033,P1005,D4236
using power IC's. As you mentioned, higher voltage / power designs
don't seem to be available.
There are some more general references such as
http://www.smpstech.com/tutorial/t03top.htm
which goes into the design issues. This latter site has a number of
good articles, blog entries, links to on line references, and lessons
learned on power supplies.
Let me know if this is the kind of information you need & I can
package it up into a complete answer.
--Maniac
|
Clarification of Question by
hobiecat-ga
on
28 Apr 2006 18:08 PDT
Dear Maniac
I am aware of the Powerstream units available as it was in my posting
where I listed their web site.
The 5 volt unit information is all over the web and in fact a small
voltage DC to DC converter can be purchased as a single unit. However
these are far too small in volatage and current requirements.
Your last entry made reference to
http://www.smpstech.com/tutorial/t03top.htm This is like most of the
information on the WWW only theory. I did not see one practical
schematic.
It might be helpful to look back at our previous post. I am looking
for plans and schematics. These should be straightforward and have
parts list as well the parts should be available. The output voltage
needs to be 12-14 VDC and an absolute min of 10 amps more like 20-30
amps. I am well aware they can be bought as I am the one who posted
the site with the cheapest prices. If I were interested in buying a
unit I would have done so and never posted this question to Google. I
am not looking for pre-made units. I am not looking for generic
theoretical information regarding such units. Finally I am not
looking for plans for a unit that does not meet the stated
requirements.
Regards
Jason
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