How To Verify Charging Current of Charger?

[lexina]

Prob a very basic question but how do I go about checking the actual charging current of my (LiIon) charger? I have a multi-meter. Do I just set it to measure current, switch on the charger and then touch the leads to the respective charging tabs/springs on the charger? Didn't want to try it yet in case I blow the MM! Thanks.

 

[rizky_p]

No you should use it in series with the charger and battery, i am not sure whether the load that the DMM has will effect its reading.

 

[lexina]

No you should use it in series with the charger and battery, i am not sure whether the load that the DMM has will effect its reading.

If the cell is in a cradle (for eg. the DSD charger), does that mean I will need to remove the cell, connect a wire from say, the negative tab to the negative end of the cell and then use the DMM leads to complete the circuit? I just tried it but had problem getting a reading.

 

[VidPro]

it indeed is not easy.
you either pull out the cell, and wire the whole thing externally, then assume that you also now have wire resistance.
that way you can put the Battery IN the curcuit, and the meter too.

or you can try and make a wafer connection and attempt to stuff it in between.
|||
metal, plastic insulator, metal. then you connect to the 2 metal strips.

the quick one shot method i use, is connect the meter to the top connection, then use the 2nd lead to PUSH the battery away from the connection. if you have enough spring that works and is quick. but it would be impossible to leave it there.

a cheap ammeter can only read sooo much , if the thing uses high rate PWM for charging it might be averaged it might be way off, so one other trick is to switch to AC current, and see if anything shows up there TOO. if current shows up on the AC setting, then chances are the DC meter cant even read it all or correctally, and you need a scope thing.

at any rate everything is in series to check for the current.
+ charger to +ammeter -ammeter to + battery - battery to -charger
or of course the ammeter can go anywhere
+ charger to + battery - battery to +ammeter -ammeter to -charger
is the same thing

 

[lexina]

Thanks, Vidpro for the very detailed instructions. I did try a variation of the method you suggested (i.e. pushing the battery against the spring) by inserting an RCR123 into the 18650-length slot so that only the -ve of the cell was touching the -ve charger contact and using the leads to complete the circuit but I had prob getting a reading. Guess my DMM is not up to scratch. Thanks, anyway.

Edit: Ok, I gave it one more try and this time I got a reading. It was surprisingly low - only 0.24A even though I am using a Nokia 800mA charger! Apparently, using a higher amperage charger on the DSD board doesn't seem to increase the charging current. I guess there's prob another board built into the charging cradle that is restricting the current flowing into the cells.

 

[VidPro]

the "rate" on various chargers can change depending on the voltage of the battery. a dum ni-?? charger will taper off a bit when the battery is full.
lots of li-ion chargers will taper off when the battery is full.
only the "smart" chargers will attempt to use the same current throughout its charge sequence, and even they taper on li-ion charging.

sooo, it will all depend on the charger type, and battery voltage.
a 500-800ma li-ion thing might read max that 500-800 ever during the first of the charge when the battery is very low.
and might read only 50ma when its almost done.

then meter leads and meter shunts add major resistance which changes your actual total that is passing through WHEN the meter is in seires with the curcuit
Clip leads too, they can add lots of resistance. Current controlled devices Might be able to overcome the added resistance, but usually even they will show a bit lower.
fat copper leads, and using your large shunts (like 10amp) on the meters can reduce that.
we have to remake clip leads with copper speaker wire, and of short lenght to use clip leads to do stuff like this.

 

[lexina]

Thanks again. I sure learnt a lot!:thumbsup:

 

[MrAl]

Hi there,

A good way to measure current without bothering the circuit too
much is to use a 0.1 ohm resistor in series with the load and measure
the drop across the resistor. To get the current, take the voltage
and divide by the resistance:
I=V/R
where V would be the measured voltage and R the resistance of your
series resistor.
Sometimes even 0.1 ohms is too much however, as the charger might think
the internal resistance of the cell is too high to charge safely, like with
the Energizer 15 minute charger. I cant even connect two short leads
and get that to work and that's with no resistor.
You may have to go down to 0.010 ohms, which means less voltage
drop, so you also need either a very good meter or a home built amplifier
to amplify the voltage by say 10 times. With the amp, a reading of 0.1v
would indicate 1 amp flowing. 0.010 ohms will not disturb most circuits.

You also need to make good contact with the cell and with the holder.
Perhaps some sort of home made adapter with a good cell holder to hold
the cells.

 

[rizky_p]

i have 800ma universal cas adaptor that outputs a 12v but measured at only 250ma with dmmm all thing considered it should not be that far of right?

 

[MrAl]

Hi again,

rizky: what do you have it connected to? The current depends partly on
what the load resistance is so if it only draws 250ma then that is ok, but
if it is supposed to draw more then 250ma is not ok.

 

[wptski]

Hi there,

A good way to measure current without bothering the circuit too
much is to use a 0.1 ohm resistor in series with the load and measure
the drop across the resistor. To get the current, take the voltage
and divide by the resistance:
I=V/R
where V would be the measured voltage and R the resistance of your
series resistor.
Sometimes even 0.1 ohms is too much however, as the charger might think
the internal resistance of the cell is too high to charge safely, like with
the Energizer 15 minute charger. I cant even connect two short leads
and get that to work and that's with no resistor.
You may have to go down to 0.010 ohms, which means less voltage
drop, so you also need either a very good meter or a home built amplifier
to amplify the voltage by say 10 times. With the amp, a reading of 0.1v
would indicate 1 amp flowing. 0.010 ohms will not disturb most circuits.

You also need to make good contact with the cell and with the holder.
Perhaps some sort of home made adapter with a good cell holder to hold
the cells.

Picture this: a 1"x1/4" magnet,insulator and a piece of 1"x1/4" rod the proper lenght between the contacts, 10A Radio Shack clips, #12AWG, Power Poles to a modified wood clamp holding the cell. I've used this on the D15 and E15 chargers. I do use a current clamp probe with this setup. That the way I did all my posted graphs on the C9000, BC900, E15, D15, etc.

 

[rizky_p]

I connect it to charge my 9.6v 900mah nicad pack.

Hi again,

rizky: what do you have it connected to? The current depends partly on
what the load resistance is so if it only draws 250ma then that is ok, but
if it is supposed to draw more then 250ma is not ok.