Re: Batteries in Power Supply

Mariss,

That makes it even more attractive, our local Altex sells, 12V 1.2AH
batteries for $11.19 and the 6V 1.2AH is $6.50. The physical size is
only 2x3.4x1.6".

Anyone want to buy 3 off 15,000uF 100VDC caps?

Thanks

Bernard

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Mariss Freimanis
<mariss92705@y...>" <mariss92705@y...> wrote:

> 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