CAD CAM EDM DRO - Yahoo Group Archive

Re: Batteries in Power Supply

on 2003-01-21 13:41:32 UTC
Ive worked on telephone switch battery supplies. when replacing lead
acid batteries they must all be from the same mfg and lot# period in
order to charge and prevent problems between the 24 cells.

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Carl Mikkelsen, Oasis"
<Carl.Mikkelsen@o...> wrote:
> Just some thoughts ...
>
> It was suggested that the capacitors could be eliminated if a
battery was
> floated across the power supply output. This started me thinking
about the
> battery problem.
>
> I would be concerned about the high ripple current through the
battery, and
> constant switching between charge and discharge cycles (120 times
per second).
>
> I would not build my own system to work this way, and would put
significant
> filter capacitance on the output.
>
> I would also used lead-acid batteries, because they are rated for
> "floating" on the mains.
> I would use a regulated output supply, set to the proper float
voltage for
> the batteries I was using.
> I would make the power supply be able to gracefully and safely
handle the
> over current condition, and allow power to come from the batteries
(current
> fold back regulation).
>
> I would oversize the batteries, making the batteries peak discharge
current
> be five times the expected peak servo load. [This may be too
conservative,
> and I could change my mind after seeing the battery prices. :) ]
>
> My father would have built this by taking a 12.6 V filament
transformer,
> running it through a selenium bridge rectifier, across some caps,
through a
> light bulb, across the battery, and off to the load.
>
> Since we like to use higher voltages as CNC supplies, I'd be
concerned
> about cell-to-cell variance when placing a large number of cells
(lead-acid
> or otherwise) in series. Each lead-acid cell has a voltage of
about 2
> volts, so you must stack 30 cells to reach 60 volts. That allows a
lot of
> cells for temperature variances, chemistry changes, and other nasty
things
> to build up and cause problems.
>
> Some one of you who is a battery engineer will probably point out
the
> fallacies in what I've said. Even if some of my concerns are
valid, there
> may be rational ways to engineer around them.
>
> It is an area where a little engineering up-front (temp sensors,
current
> monitoring, maybe a little closed-loop charging control) could save
a lot
> of grief later.
>
> I'm sure it is possible to make it work. The phone company had 48V
> lead-acid batteries floating across the line supply for decades,
and maybe
> still does. It's been quite a few years since I've been inside a
phone
> exchange building.
>
> -- Carl
>
>
> At 03:27 PM 1/21/2003 -0500, you wrote:
> >So would this mean that you could eliminate the filter capacitor
from the
> >power supply leaving only the transformer and rectifier?
> >
> >John Guenther
> >'Ye Olde Pen Maker'
> >Sterling, Virginia
> >
> > > -----Original Message-----
> > > From: Mariss Freimanis <mariss92705@y...>
> > > [mailto:mariss92705@y...]
> > > Sent: Tuesday, January 21, 2003 14:14 PM
> > > To: CAD_CAM_EDM_DRO@yahoogroups.com
> > > Subject: [CAD_CAM_EDM_DRO] Re: Batteries in Power Supply
> > >
> > >
> > > Bernard,
> > >
> > > I posted on this topic about a year or so ago. The main
advantage
> > > mentioned was servomotors usually have a large ratio between
their
> > > stall current and continuous rated current (5:1 or more).
> > >
> > > This means the power supply has to be 5 or more times bigger
than
> > > needed just to supply very short duty cycle accel/decel current
> > > pulses to the motor.
> > >
> > > The idea was to use low AH batteries to supply this current;
they
> > > would recharge between accel/decel cycles. The battery would
connect
> > > to the power supply "+" terminal via a rectifier and it's
voltage
> > > would be a little less than the power supply's voltage. Under
load,
> > > the supply voltage would sag, forward biasing the rctifier from
the
> > > battery, which would now supply the pulse current.
> > >
> > > A motor stall current 5 times the max rated current implies a
4% duty
> > > cycle. Theoretically a 1AH battery could supply 20A for 3
minutes,
> > > way longer than you would need for accel/decel (1 or 2 seconds).
> > >
> > > Now the supply could be sized for the continous current only
plus
> > > what would be needed to restore the battery charge (5 * 4% =
20% or
> > > 1.2 times the max rated motor current).
> > >
> > > Mariss
> > >
> > > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Bernard R
> > > <bwjarandall@c...>" <bwjarandall@c...> wrote:
> > > > In view of the recent interest in power supplies has anyone
thought
> > > > about using batteries in place of capacitors in some of the
larger
> > > > power supplies?
> > > >
> > > > If you used 5 12Volt batteries and 1 6Volt that would give a
> > > nominal
> > > > 66 volt, with a fully charged cell rising to 2.4 volt that
would
> > > give
> > > > an additional 13.2Volt (33 cells @ .2V) for a total of 79.2
volt.
> > > >
> > > > In a recent post Les Watts reports routinely seeing 60 amp
peaks on
> > > > rapid starts, stops and sharp curves, I would think batteries
could
> > > > cope with these conditions better than conventional caps.
> > > >
> > > > I'm not sure if there would be any significant price
difference
> > > > between caps and batteries, a 100Volt 15,000uF cap is almost
$30
> > > and
> > > > for a reasonably stiff supply you probably need at least 3 in
> > > > parallel. Without doing the math, I suspect you need more
than 3
> > > caps
> > > > to cope with 60 Amp peaks. 12V 4.5 A/Hour batteries are about
$17
> > > and
> > > > 6V 4.2 A/H $9 for a total of $94. (12V 12 AH cost $$35)
> > > >
> > > > I'm not sure how effectively batteries kill spikes, I would
have
> > > > thought much better than caps, they should absorb overvoltage
from
> > > > motors quite effectively.
> > > >
> > > > I can see difficulties in disconnecting the batteries from the
> > > drives
> > > > at power off, but this should be offset by being able to use
> > > smaller
> > > > transformers.
> > > >
> > > > Just a thought.
> > > >
> > > > Bernard
> > >
> > >
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> >
> >OFF Topic POSTS: General Machining
> >If you wish to post on unlimited OT subjects
> >goto: aol://5863:126/rec.crafts.metalworking or go thru
Google.com to
> >reach it if you have trouble.
> >http://www.metalworking.com/news_servers.html
> >
> >http://groups.yahoo.com/group/jobshophomeshop I consider this to
be a
> >sister site to the CCED group, as many of the same members are
there, for
> >OT subjects, that are not allowed on the CCED list.
> >
> >NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY POSTING
> >THEM. DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO
EXCEPTIONS........
> >bill
> >List Mom
> >List Owner
> >
> >
> >
> >Your use of Yahoo! Groups is subject to
http://docs.yahoo.com/info/terms/
>
>
> Carl Mikkelsen
> Oasis Semiconductor, Inc.
> 201 Jones Road
> Waltham, MA 02451
> (781) 647 8775

Discussion Thread

Bernard R <bwjarandall@c... 2003-01-21 10:34:58 UTC Batteries in Power Supply Mariss Freimanis <mariss92705@y... 2003-01-21 11:13:46 UTC Re: Batteries in Power Supply Bernard R <bwjarandall@c... 2003-01-21 11:35:58 UTC Re: Batteries in Power Supply Kevin P. Martin 2003-01-21 11:58:09 UTC RE: [CAD_CAM_EDM_DRO] Batteries in Power Supply Bernard R <bwjarandall@c... 2003-01-21 12:17:20 UTC Re: Batteries in Power Supply j.guenther 2003-01-21 12:27:53 UTC RE: [CAD_CAM_EDM_DRO] Re: Batteries in Power Supply Kevin P. Martin 2003-01-21 12:48:07 UTC RE: [CAD_CAM_EDM_DRO] Re: Batteries in Power Supply Carl Mikkelsen, Oasis 2003-01-21 13:30:57 UTC RE: [CAD_CAM_EDM_DRO] Re: Batteries in Power Supply Mariss Freimanis <mariss92705@y... 2003-01-21 13:36:44 UTC Re: Batteries in Power Supply Alan Marconett KM6VV 2003-01-21 13:41:18 UTC Re: Batteries in Power Supply sparkness2001 <mark@c... 2003-01-21 13:41:32 UTC Re: Batteries in Power Supply Bill Higdon 2003-01-21 14:54:56 UTC Re: [CAD_CAM_EDM_DRO] Re: Batteries in Power Supply turbulatordude <davemucha@j... 2003-01-21 16:00:43 UTC Re: Batteries in Power Supply 0good in theory