Power supplies

[evdama]

Sorry this is a little domesticated .
I have a set of cordless phones which charge from a wall adapters .One adapter has died or was killed.
I 'found' a replacement at work with the correct jack diameters and polarity.
The original adapters are rated 5v 200ma ,this one is 5v 330ma.
Im guessing that would be near enough and good enough- the phones each have a pair of 750mah AAA nimh inside.

Playing safe, I put a multimeter on the end before I let it loose on a phone -the reading was 7.64v.
I know chargers have higher voltage than their subject ,ie car battery chargers run at 14v, but this is more double the voltage of a pair of AAA's.

Now, with a furrowed brow on my tiny,bony little head, I tested one of the original chargers - 6.54v.

So,after all that, my question is ; would the honourable forum members risk using the 'aquired' charger?

[Simon (Webmaster)]

Hi,

It depends if the adapter is actually a charger or just a power supply. From the voltage (5V) I suspect it would more likely be the latter. In this case, the charging circuit / voltage regulation will be in the handset or the base. The difference you are measuring in the actual output will be due to poor regulation - when the phone base / cradle is connected the voltage will drop.

Is the adapter for the main base phone (the one that also plugs into the phone line) or one of the extensions, and if it is an extension one, is it identical in specification to the base one?

[evdama]

Thanks for the quick reply Simon.
The broken unit is on one of the peripheral phones-the main base unit has a different power supply quoted 15v 1200ma.
The reading I get from this is 18.71v

[Simon (Webmaster)]

The old adapter is almost certainly just a power supply, not a charger, so the replacement should be fine. That said, for safety's sake and since the thing is left on and unattended continuously it might be better to get a proper replacement.

If you do use the replacement adapter that you have, check that the output is DC not AC (I guess you already know this since you have measured it), and check that the batteries aren't getting excessively warm. If there is a problem, the batteries are the most likely things to suffer.

[evdama]

Thanks Simon
In the interim I located an exact match by the part number on an infamous online tat-bazzaar.
It arrived yesterday and like the others is giving off an excess at 6.53v.
So I'm sorted now-many thanks for the advice
It just puzzles me how these outputs can be allowed such a huge percentage above the stated values.

Best wishes
Martin