I really should have paid more attention at school but do not recall this being taught.
I have an adaptor with output stated as 13.5v Dc and 700Ma. It stopped working and as part of the search for a cause I used a multimeter across the output wires. At times, most times in fact, output was zero but at others and with a bit of wiggling of the output wires where they entered the adaptor casing, I got about 19.5v. Clearly a wiring issue but the voltage puzzled me as I have another 13.5v adaptor that gives me 13.6v across the output.
I took the casing apart to find a standard bridge rectifier of 4 IN4002 diodes and a 3300 microF 25v capacitor. There is no obvious damage anywhere. I rewired the unit to get a wiggle free system of 19.5v. I then connected it to the original equipment and tested the adaptor under load. Voltage dropped to 18v. I tried another load, this time a 12v car bulb, most likely 5w rating, and voltage dropped to 15.5v.
Now the original equipment has a voltage requirement of 12 - 18v DC according to the manual so the adaptor would appear to be OK for that use. But is it? Why am I getting a value of 19.5v DC without load with this adaptor but 13.5v (13.6v)DC with another adaptor when both state 13.5v DC on the adaptor casing, albeit a different make.
Could it be that one or more diodes are failing or failed? Could it be the capacitor?
Sorry to be asking what may seem such an elementary question but my theoretical knowledge of these matters is dismal
All advice gratefully received
Cheers, Phil
I have an adaptor with output stated as 13.5v Dc and 700Ma. It stopped working and as part of the search for a cause I used a multimeter across the output wires. At times, most times in fact, output was zero but at others and with a bit of wiggling of the output wires where they entered the adaptor casing, I got about 19.5v. Clearly a wiring issue but the voltage puzzled me as I have another 13.5v adaptor that gives me 13.6v across the output.
I took the casing apart to find a standard bridge rectifier of 4 IN4002 diodes and a 3300 microF 25v capacitor. There is no obvious damage anywhere. I rewired the unit to get a wiggle free system of 19.5v. I then connected it to the original equipment and tested the adaptor under load. Voltage dropped to 18v. I tried another load, this time a 12v car bulb, most likely 5w rating, and voltage dropped to 15.5v.
Now the original equipment has a voltage requirement of 12 - 18v DC according to the manual so the adaptor would appear to be OK for that use. But is it? Why am I getting a value of 19.5v DC without load with this adaptor but 13.5v (13.6v)DC with another adaptor when both state 13.5v DC on the adaptor casing, albeit a different make.
Could it be that one or more diodes are failing or failed? Could it be the capacitor?
Sorry to be asking what may seem such an elementary question but my theoretical knowledge of these matters is dismal
All advice gratefully received
Cheers, Phil