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7350Re: NSLU2 using 7805s and a 12V battery

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  • efilvasers
    May 4, 2008
      oabroad: a schematic and parts list would be great.
      I've been fiddling with other ways; if I don't have the parts to make
      a switching regulator, I'll probably use a 2N3055 with a 7805.

      --- In nslu2-general@yahoogroups.com, "oabroad" <oliverb@...> wrote:
      >
      > One option worth considering is a switching regulator. These have the
      > huge advantage that they are efficient so don't create all that waste
      > heat and could halve the current drain from the battery.
      >
      > If you can get hold of one you could do worse than get the Texas
      > instruments TPS5430EVM-173 evaluation module, I've seen it priced at
      > £7.99 and is supplied configured as a 5v 3A regulator. Failing that
      > I've got a design for a 5V 1A switch reg that can be built on
      > stripboard for a BOM cost of about £2.50 last time I costed it.
      >
      >
      > --- In nslu2-general@yahoogroups.com, "efilvasers" <efilvasers@>
      > wrote:
      > >
      > > Thanks for all your responses.
      > >
      > > I'm using a 12V battery because it's what I happened to have on
      > hand.
      > > The NSLU2, three Arduinos, and a few various ICs and LEDs need the 5
      > > volts, while the wifi router needs 12, and all the motors use 9 (the
      > > actual robot itself is made with LEGO).
      > >
      > > As for solving this problem, I googled around a bit and found a
      > > solution for connecting 78xx's in parallel; it involves diodes on
      > the
      > > outputs to isolate them, and one between their ground pins and the
      > > real ground to cancel out the voltage drop.
      > >
      > > The other solution I am considering is from the datasheet that
      > > bullfrog528 linked me to; on page 23, adding a PNP power transistor
      > > and 3 ohm resistor.
      > >
      > > I'll try both of these later tonight once I get myself to
      > RadioShack.
      > > I neglected to mention before that this project is already about one
      > > day late and I don't have the time to wait for orders to ship.
      > >
      > > --- In nslu2-general@yahoogroups.com, "bullfrog528" <yahoo@> wrote:
      > > >
      > > > Is there any particular reason your trying to run this off a
      > 12Volt
      > > > battery?
      > > >
      > > > If you need 12V to run the rest of the project.You could have two
      > > > 6Volt batteries in series use the the 12V to run whatever it is
      > and
      > > > tap 6V out from the link between the two and regulate that down
      > to
      > > > 5Volts. The lower battery will discharge quicker mind.
      > > >
      > > >
      > > > |------ 12v ---> to rest of project
      > > > []6volt batt
      > > > |------6V ----> to 5volt reg and onto nslu2
      > > > []6volt batt
      > > > |______ov
      > > >
      > > >
      > > > As they say there is always more than one way to string a cat.
      > > >
      > > > Bullfrog
      > > >
      > > > --- In nslu2-general@yahoogroups.com, "bullfrog528" <yahoo@>
      > > > wrote:
      > > > >
      > > > > Hi
      > > > >
      > > > > Must admit I'm somewhat rusty on my electronics theory.
      > Regulators
      > > > > are rated with suitable heatsinks fitted.They are very derated
      > > > > without heatsinks. Various problems here - the regulator has to
      > > > > disapate a 7V drop as well as the actual current drawn. There
      > is a
      > > > > way to use a 78xx regulator with an external transistor to
      > boost
      > > > > current.
      > > > >
      > > > > See page 22 of the datasheet below for a 7805 which shows a
      > > > typical
      > > > > cct.
      > > > >
      > > > > http://www.datasheetcatalog.org/datasheets/228/390068_DS.pdf
      > > > >
      > > > > A large Watt rated resistor between the 12V and the input to
      > the
      > > > > regulator may also help, but regulation might become an issue
      > as
      > > > the
      > > > > volt drop across the resistor would increase as current
      > increased.
      > > > >
      > > > > Jeremy (Bullfrog528)
      > > > >
      > > > >
      > > > >
      > > > >
      > > > > --- In nslu2-general@yahoogroups.com, efil vasers <efilvasers@>
      > > > > wrote:
      > > > > >
      > > > > >
      > > > > > I'm trying to run my NSLU2 (with a 1GB flash drive, connected
      > to
      > > > > an old wifi
      > > > > > router) from a 12 volt SLA rechargeable battery (5Ah) using
      > 7805
      > > > > voltage
      > > > > > regulators.
      > > > > > So far, I've tried a few different regulators (rated 1 or 1.5
      > > > > amps), and
      > > > > > when I turn the NSLU2 on, after about 30 seconds, the
      > regulators
      > > > > are too hot
      > > > > > to touch and soon shut themselves down.
      > > > > > I'm not sure what the problem is.
      > > > > > Just to try, I connected it with a single 7805 (1 amp), which
      > > > > immediately
      > > > > > shut itself off.
      > > > > >
      > > > > > I connected the regulators in parallel with each other to
      > > > provide
      > > > > up to 3
      > > > > > amps (more than the NSLU2 power supply), so I figured that I
      > > > > wouldn't need
      > > > > > heatsinks for them. Am I wrong, or is my NSLU2 just behaving
      > > > > strangely?
      > > > > > How many people out there have tried this?
      > > > > >
      > > > > > (For those wondering, this is for a robotics project for
      > school,
      > > > > and the
      > > > > > NSLU2 is running Debian)
      > > > > > --
      > > > > > View this message in context: http://www.nabble.com/NSLU2-
      > using-
      > > > > 7805s-and-a-12V-battery-tp17030363p17030363.html
      > > > > > Sent from the Nslu2 - General mailing list archive at
      > Nabble.com.
      > > > > >
      > > > >
      > > >
      > >
      >
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