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Cordless phone charger help

bigone5500

Apr 9, 2014
712
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Apr 9, 2014
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I have an AT&T cordless phone that has a main base and a separate charging cradle for a remote handset. The main base uses a 6vdc wall adapter at 300mA but the small cradle uses a 6vac adapter at 300mA. Why would they do that and not use a dc adapter? My issue is the adapter has gone bad. The transformer's primary winding went out and I don't have another. I tested the main base contacts and they have about 6.5v out. I want to achieve this on the other base. I suppose it would be ok to use a linear regulator to get the required voltage but I am unsure if that would harm the phone. The small circuit board inside the cradle consists of a few components such as the socket for the transformer, an 8550D pnp transistor, 470mfd cap, some 1N4001 rectifiers, and a very small transistor which I can't make out the part no. but it looks like it says A7X which I'm not sure of.

I guess what I want to know is, does it matter that the charging voltage comes from this circuit board or a simple linear regulator?
 

ChosunOne

Jun 20, 2010
453
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Jun 20, 2010
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If you tested the main base contacts by reading the voltage with a DMM while it wasn't actually charging, then the 6.5 V (presumably DC) doesn't mean anything. Chargers vary depending on the kind of battery, and its size, being charged. A charger interacts with the battery to adjust its output. The interaction with your DMM was probably that extremely little current flowed at maximum voltage, so the charger maintained maximum voltage. With a battery connected to the main base contacts, more current would have flowed and its voltage would have been adjusted accordingly.

What kind of battery does your cordless phone use? NiCad, NiMH, or what? And what size (mAh/ milli-Amp-hours)?
 

bigone5500

Apr 9, 2014
712
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Apr 9, 2014
Messages
712
If you tested the main base contacts by reading the voltage with a DMM while it wasn't actually charging, then the 6.5 V (presumably DC) doesn't mean anything. Chargers vary depending on the kind of battery, and its size, being charged. A charger interacts with the battery to adjust its output. The interaction with your DMM was probably that extremely little current flowed at maximum voltage, so the charger maintained maximum voltage. With a battery connected to the main base contacts, more current would have flowed and its voltage would have been adjusted accordingly.

What kind of battery does your cordless phone use? NiCad, NiMH, or what? And what size (mAh/ milli-Amp-hours)?
NiMh. It's a small 2AAA cell. These phones are old but they are good ones. I don't want to spend any money on them which is why I wanted to possibly create a circuit to replace the faulty one. I can easily switch the phones out on the main base and keep them charged that way. I did spend a little money on them the other day. I bought two new batteries on amazon for $5 prime shipping.
 
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