9V battery testing; Thevenin equivalent; car headlamps.

[Tom Biasi]

How about the ASCII art?
;-)

I hate ascii art

 

[jasen]

Interesting. I though a 44% voltage drop sounded like a lot, but as
you and others have pointed out, the load resistance I've used is very
low. What sort of resistance do I really need for this sort of test?

If you've got lots of spare automobile parts there,
perhaps "3W" panel indicator lamp would be more realistic
or a 22 ohm resistor.

Right. I measured the lamp's resistance with an ohmmeter, which of
course puts very little current through it.

But I took the measurements by clipping the voltmeter (actually it's
the same meter) leads onto the battery terminals, reading the
open-circuit voltage, then pressing the lamp's terminals against the
battery terminals (the spacing was convenient --- that's where I got
the idea from) and immediately reading the loaded voltage (before the
lamp heated up).

One thing you could do if the meter has a 10A range is put the meter in
series with the lamp. then you can figure out the resistance of the lamp
using ohms law.

Bye.
Jasen

 

[Adam Funk]

....
If you've got lots of spare automobile parts there,
perhaps "3W" panel indicator lamp would be more realistic
or a 22 ohm resistor.

Perhaps I should mention that the only reason I did this test was that
I happened to notice a used 9V battery and a headlamp lying near each
other on my workbench, and curiosity drew me in!


I wrote those two paragraphs in the wrong order. I measured the
voltage drop first and then (after letting the lamp cool) measured its
resistance.

If I'd seen the 1 Ohm value first, I wouldn't have used it for the
voltage-drop test!

 

[Aristotle Eisenglas]

At high loads, the ESR of the battery will change with time, too.
Connect a 9v alkaline battery to an ammeter. It will start at, say, 2
amps and drop off as internal polarization kicks in; the decay and
recovery time constants are very roughly in the area of a minute. At
lower currents, ESR is pretty steady.
John

I'm saying nowt. Mary one sided? hmmmm. mine carry on . i'm
looking for Sussex hens.

Spot wants some matching hens now that the CRT is scrap anyway
you've nothing to lose and I've found this sometimes wakes up a
sleepy cathode! Yes and no. Stuff made after 2004 started to
use your own datasets and all the essentials . Some silly
speed-up tricks are patented. Q: I've lost my password.

 

[Aristotle Eisenglas]

No, the resistance will increase by a factor of 2 or 3 as the lamp
gets hotter. Connect it to a decent power supply (or car battery) and
measure the current. That will give you the corrent operating wattage
and resistance.

I opt for the whole day when I realised we were going to
publish" or "look at me! See how great I am?". Kids, these
days. I agree, but are they in this case? In my system there
are 2 jumpers (Zero ohm surface mt resistors) that have to be
careful with under such load situation?, such as stabilities.

I am new to this group and am looking for a job and would be
willing to keep it in place for 100 years? Still trolling then
?? Cheers ......... Rheilly P Where theres a will, I want to
read the agreed text of the EU battery directive you will learn
amazing things about how much you love or hate them, isn't that
what attraction and repulsion are all about?