Charger doesn't like ammeter in circuit?

[Mr Happy]

I thought I would try to see what kind of top-off or trickle charge my Duracell Power Gauge charger uses after the finished light comes on, so I put an ammeter in series with one of the cells.

While charging, I sure enough see a pulsed 400 mA charge current, which is in line with the charger specs. But when the cell is (or should be) fully charged, that channel starts showing the blinking red faulty cell light rather then the green charge complete light. I've tried it twice now with different cells, same result each time.

Does anyone have any thoughts about what the charger might find upsetting about having an ammeter in the circuit that would make it do this? The meter doesn't have any significant resistance, and it passes current equally well in both directions. If I return the same cell to the charger without the ammeter in circuit, the channel shows the green charge complete light without fuss. It's mystifying.

 

[VidPro]

sucks dont it
its hard to do, there are tight tolerances, and any variation in the resitance during, or to much resistance and the computer knows your trying to find out its secrets

De-oxit. have all your parts and pieces clean metal, like sand things with 600grit alum oxide.
use copper shims, and short copper leads with lots of connection points, so as it pulses the little molecular connections made dont burp.
clip your clip leads over sand paper, or a nail file and drag them closed through it, to clean the exact clip lead contact points.

you do have the meter on the big amps shunt (10amps).

:nana: good luck really persistance will pay off, dont let the computers win, remember John Conner its up to you.

 

[Mr Happy]

Hmmm...I wonder where I could get some copper foil? :thinking: I know, I could peel some off a piece of copper clad board.

I'm using heavy gauge aluminium (Brit alert!) foil, and alligator clips to make the connections. I could make up shorter test leads I suppose. I am indeed using the 10 A range on the meter.

I've got to assume that something about the increased inductance or capacitance of the circuit is upsetting things, but that does surprise me.

 

[PhotonWrangler]

I'm guessing that the charger is sensing a change in impedance of the cells that it doesn't understand. Your ammeter has inductive and capacitive reactance elements inside, and those charging pulses are undoubtedly producing weird echoes back to the charger's sense circuit.

 

[VidPro]

Hmmm...I wonder where I could get some copper foil? :thinking: I know, I could peel some off a piece of copper clad board.

.

when you cant find flat copper Punt, get a wire and beat it flat on a flat metal surface with a hammer. then clean it up.
corrected to say any copper wire can be made flat. (i do it for battery packs)

remake meter leads:
meter leads are desinged more for to keep human safe, with high voltages, and not great amps
make Low voltage ones, unsafe for high voltages.
if you get some banana plugs and Copper speaker wire, like 22Guage or down, and clip leads, assemble and solder them they have 1/4 the resitance, when shorter than the long leads.

banana plugs shouldnt have the loose flange
like this style http://www.radioshack.com/product/index.jsp?parentPage=search&summary=summary&cp=&productId=2103796
the loose flange works but it sucks compared to connected flanges, or split ends
more like this style http://www.radioshack.com/product/index.jsp?productId=2103582

then there is a little known clip lead, that is copper clad, and does a flat wide connect, instead of toothy one
http://www.radioshack.com/product/index.jsp?productId=2062233
its a miserably small one, liteweight , but connects flat
or the brass one http://www.radioshack.com/product/index.jsp?productId=2062267

so if you have to remake leads, that is some items (purchaces locally) to attempt to improve them.

 

[evan9162]

Hmmm...I wonder where I could get some copper foil?

Craft store. Ask for copper tooling foil.