8 Feb
2009
8 Feb
'09
11:15 p.m.
Ethan Dicks wrote:
On Sat, Feb 7, 2009 at 5:38 PM, Allison <ajp166 at bellatlantic.net> wrote:
That all sounds consistent with observed behavior.
I can't speak to the NLS scope specifically, but it may be worth noting: in
some equipment with rechargeable batteries the battery is an integral part of
the power supply, providing both filtering and voltage limiting. Charging
circuits don't need filter caps when the battery is fulfilling that
function, so filter caps get left out of the design. An absent or open battery
and the equipment gets pulsating DC.
Chargers also may run at a much higher voltage than the battery. The battery
electrochemistry together with series R losses in the charger pulls V down to target.
HP calculators from the 70's are an example of this. The display goes
squirrelly when run from the charger with the dual-AA NiCd battery pack
removed. (I wonder how many good HP calculators were discarded because people
mistakenly thought the electronics had failed.) I don't like keeping equipment
stocked with batteries so I replaced the battery pack in my HP-21 with an
(approximately) equivalent-circuit of a filter cap in parallel with a shunt
regulator (actually just some diodes).
The nice thing about this solution is because everything is in parallel no mods
to the equipment were necessary.
> On
Thu, 5 Feb 2009, Allison wrote:
> > The only reason batteries are needed to run the NLS is the charger is way
> > too small run run it directly.
For the NLS 'scopes the battery is between the charge source and the
scope power supply so if it's open (badly sulfated as the battery is
lead acid gell type) the PS has to carry the load. It's only a charger.
if you substitute a larger charger then you find the charge circuit
does not have the capacity to start the unit (initial surge current). In this case (nls miniscopes) a 6V PS can
substitute for the battery at
less tha 1A (must be connected to the ground and +6V termianls of the
battery connection point internally). Only if the battery is removed first.
Note that is the battery has failed (usually sulfated from not being kept
charged) they tend to build corrosion around the terminal, they are best
removed and recycled as any gelled lead acid battery should be.
OK. I may try that. I can probably use a bench-top supply, and now
that I know the batteries are not made from unobtanium, I'll probably
just remove them and drop them off at a Batteries Plus or wherever one
disposes of non-alkaline batteries these days.
Since I use my miniscopes intermittently I've
long since removed the
battery and disconnected the internal charge circuit (pull the fuse).
The battery area has a small board inserted to allow it to accept any
voltage from 9 to 30V and run from that. Since I have a number of small
12V gell cells that fit nicely in the probe pocket of the carry case
this proves more useful and maintainable. The change is completely
reverseable and the ability to use a larger and longer lasting 12V
battery as source is very handy.
Interesting. I have the schematics somewhere (I found them on the
'net after not too much searching), so I may give that a try
The NLS is somewhat unique as it uses a lead acid
type rather than NiCd,
Nimh, lithium or even common dry cells. In an emergency I have run it
off 4 'D" sized alkaline cells in an external holder for many hours.
Also an interesting suggestion.
I will probably try some temporary method of powering this up first -
it came to me in an inert state, so I can't be sure the device doesn't
require repair first.