How Do I Reduce The DC Output Of A Step-Down Transformer From 14V To 12V?

1. 82

   quicksandposted 11 years ago

   How Do I Reduce The DC Output Of A Step-Down Transformer From 14V To 12V?
   
   I have a handheld drilling machine purchased in the UK, which operated on a re-chargable battery. After many years of usage, I find this battery cannot be charged any more, and these batteries are no longer available. However, the step down transformer that was used to charge the battery has an output of 14V DC. The driller needs a supply of 12V DC to operate. I intend utilizing the transformer's output to supply power to this gadget. Do you know any simple method to reduce the voltage from 14V to 12V. If I need to use resistors, please mention the color code. Much obliged for your attention.

   replyreport
2. 0

   JThomp42posted 11 years ago

   The chances are the device will work from 12V so a 14V supply is not required...
   But if you still want to do this, go to National's website and run their WebBench software. You can design and simulate your circuit before building it. It will assist with all the parts values.

   replyreport
   1. 82

      quicksandposted 11 years agoin reply to this

      It will, but I guess not for long. I fear that a voltage overdose might cause the motor to burn up. So I don't wanna take a risk. Thanks anyway!

      replyreport
3. 68

   wandererhposted 11 years ago

   Try using rectifier diodes.  You didn't mention the power but I think 1N5400, with a rating of 3A should be enough.  Each 1N5400 will drop about 0.7V, so 3 in series should drop 14V to about 12V.  Diodes have a polarity, so you should be mindful of that when you connect them up.  Let me know if you need help with the connection.

   replyreport
   1. 82

      quicksandposted 11 years agoin reply to this

      Thanks Wanderer, the output is DC as it has already been rectified by an inbuilt circuit. Otherwise it won't be able to charge the battery. I intend buying a Black & Decker to simplify things. Would be useful on the long run. Thanks anyway.

      replyreport
   2. 68

      wandererhposted 11 years agoin reply to this

      I wasn't talking about the internal bridge rectifier but external diodes that you can connect up to drop the dc.  But since you intend to buy a Black & Decker to simplify things, problem solved. 

      replyreport