K10 battery charger output voltage?


Lloydy

Link Posted 16/02/2010 - 17:30
I bought a new multimeter today and was sat here playing with it and I measured the voltage on the K10 battery charger terminals, and it's varying in approximately 1 second cycles from 2.49 to 4.33 to 6.68 volts.

I have checked the meter against other known voltages, AC and DC, and against my ancient AVO.6 ( I needed a new meter ! ) so I'm confident of the reading.

The detail on the base of the charger states "Output DC 8.4V"

Is this oscillating voltage because there's no battery in the charger?

I'm a mechanical engineer, not a sparky.

terje-l

Link Posted 16/02/2010 - 17:50
Any charger (or power supply for that matter) needs a decent load to show the correct output voltage. I suggest you repeat the measurement with the battery connected.

Also an engineer, but this time an electronics.
Best regards
Terry

K20D, Optio I10, DA 18-55 1:3.5-5.6 AL II, A 1:1.7/50, D FA 1:2.8/100 Macro, Sigma 70-300 1:4-5.6 APO DG Macro, Pentax AF 360FGZ

Lloydy

Link Posted 16/02/2010 - 18:17
That's what I thought might be the reason, thanks for confirming it.

BUT......

I just checked a few other chargers and they show constant voltage that equates with the stated output. So now I'm confused. ( This is the point a fitter hits something with a BFH )

bretti_kivi

Link Posted 16/02/2010 - 19:29
chargers for what? Li-Ion or NiMH?
my pics: link
my kit: K3, K5, K-01, DA 18-55, D-FA50 macro, Siggy 30/1.4, 100-300/f4, 70-200/2.8, Samsung 12-24/f4, Tamron 17-50, and lots of other bits.

Lloydy

Link Posted 16/02/2010 - 19:34
It's the standard K10 charger, and I've just checked it with a Li-Ion battery and it's dead on 8 volts.

Oggy

Link Posted 16/02/2010 - 19:50
It depends on the type of charger. If it's a delta peak detect (automatic shut-off) charger, then without the battery attached it may yo all kind of strange things. Basically it will be "looking" for a battery. An oscilloscope would tell you more accurately what it is up to.

If it is the old fashioned trickle charger, then the voltage without a battery attached will be quite a bit higher than the rated value.

Lloydy

Link Posted 16/02/2010 - 21:30
Quote:
If it's a delta peak detect (automatic shut-off) charger, then without the battery attached it may yo all kind of strange things. Basically it will be "looking" for a battery.

Which it apparently is.

If it's looking for a battery when there isn't one in it, is it allright to leave it plugged in?

I do, it's been plugged in for a couple of years at least with apparent side effects so far.

terje-l

Link Posted 16/02/2010 - 22:40
It's technically OK to leave the charger plugged in.

But for the sake of the enviroment, and possible fire hazards, it is considered good practice to disconnect any appliances from the mains when unattended.

That's why we never leave the washing machine, dishwasher, TV, etc. running when leaving the house.
Best regards
Terry

K20D, Optio I10, DA 18-55 1:3.5-5.6 AL II, A 1:1.7/50, D FA 1:2.8/100 Macro, Sigma 70-300 1:4-5.6 APO DG Macro, Pentax AF 360FGZ

Oggy

Link Posted 17/02/2010 - 13:18
Personally, I wouldn't.

K10D

Link Posted 17/02/2010 - 13:56
terje-l wrote:
Any charger (or power supply for that matter) needs a decent load to show the correct output voltage. I suggest you repeat the measurement with the battery connected.

Also an engineer, but this time an electronics.

Not quite true that a decent load is required, as a constant voltage output power supply will hold the required voltage whilst within its current output capacity. Constant current chargers will have a headroom voltage high enough to keep a constant current flowing through a load and regulator circuit. If that load is a battery who's voltage will rise, the differential voltage will decrease as the battery voltage rises. The headroom or source voltage will be selected at a value that maintains the constant current into a fully charged battery.

I agree that you are correct in terms of unregulated circuits.

In the case of the Pentax chargers, the battery does provide the load and capacitance to stabilise the circuit.

Regards
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