RE: [CAD_CAM_EDM_DRO] Re: Batteries in Power Supply

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@...>
> [mailto:mariss92705@...]
> 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
>
>
> Addresses:
> FAQ: http://www.ktmarketing.com/faq.html
> FILES: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/
> Post Messages: CAD_CAM_EDM_DRO@yahoogroups.com
>
> Subscribe: CAD_CAM_EDM_DRO-subscribe@yahoogroups.com
> Unsubscribe: CAD_CAM_EDM_DRO-unsubscribe@yahoogroups.com
> List owner: CAD_CAM_EDM_DRO-owner@yahoogroups.com,
> wanliker@..., timg@...
> Moderator: pentam@... indigo_red@... [Moderators]
> URL to this group: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO
>
> 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/
>
>
>