## Welcome to Electrical Engineering Stack Exchange

Electrical Engineering Stack Exchange is a question and answer site for electronics and electrical engineering professionals, students, and enthusiasts. It's built and run by you as part of the Stack Exchange network of Q&A sites. With your help, we're working together to build a library of detailed answers to every question about electronics design.

We're a little bit different from other sites. Here's how:

This site is all about getting answers. It's not a discussion forum. There's no chit-chat.

Just questions...

up vote

Good answers are voted up and rise to the top.

The best answers show up first so that they are always easy to find.

accept

Accepting doesn't mean it's the best answer, it just means that it worked for the person who asked.

# Do I need a 50/60Hz notch filter for battery powered devices?

Given that battery powered devices are not plugged in the mains power, can I assume that there will be no 50/60 Hz frequency noise?

This question came up while thinking about what the circuit for a portable ECG monitor would look like and it seemed obvious that the 50 Hz notch filter could be eliminated. But is it so?

Thank you

If you are talking about power inputs. There will be no ripples in a battery powered system to be filtered. You don't need to use a filter.

But a parallel capacitor can be useful for reducing instant voltage change during power off/on.

Batteries are DC, the − and + poles do not alternate, therefore there is no frequency in batteries. Unlike AC, where − and + do alternate between poles. Depending on where you live, the mains will be 50 Hz or 60 Hz. The UK is 50 Hz and the USA is 60 Hz for example. So, you don't need a 50 Hz filter.

## Get answers to practical, detailed questions

Focus on questions about an actual problem you have faced. Include details about what you have tried and exactly what you are trying to do.

• a specific electronics design problem
• the theory and simulation of electromagnetic forces
• a communication scheme
• the writing of firmware for bare-metal or RTOS applications

Not all questions work well in our format. Avoid questions that are primarily opinion-based, or that are likely to generate discussion rather than answers.

Questions that need improvement may be closed until someone fixes them.

• Consumer electronics such as media players, cell phones or smart phones, except when designing these products or modifying their electronics for other uses
• Programming software for a PC
• Anything else not directly related to electronics design
• Questions that are primarily opinion-based
• Questions with too many possible answers or that would require an extremely long answer

## Tags make it easy to find interesting questions

All questions are tagged with their subject areas. Each can have up to 5 tags, since a question might be related to several subjects.

Click any tag to see a list of questions with that tag, or go to the tag list to browse for topics that interest you.

# Do I need a 50/60Hz notch filter for battery powered devices?

Given that battery powered devices are not plugged in the mains power, can I assume that there will be no 50/60 Hz frequency noise?

This question came up while thinking about what the circuit for a portable ECG monitor would look like and it seemed obvious that the 50 Hz notch filter could be eliminated. But is it so?

Thank you

## You earn reputation when people vote on your posts

+5 question voted up
+2 edit approved

As you earn reputation, you'll unlock new privileges like the ability to vote, comment, and even edit other people's posts.

Reputation Privilege
15 Vote up
125 Vote down (costs 1 rep on answers)

At the highest levels, you'll have access to special moderation tools. You'll be able to work alongside our community moderators to keep the site focused and helpful.

2000 Edit other people's posts Vote to close, reopen, or migrate questions Access to moderation tools
see all privileges

## Improve posts by editing or commenting

Our goal is to have the best answers to every question, so if you see questions or answers that can be improved, you can edit them.

Use edits to fix mistakes, improve formatting, or clarify the meaning of a post.

You can always comment on your own questions and answers. Once you earn 50 reputation, you can comment on anybody's post.

Remember: we're all here to learn, so be friendly and helpful!

If you are talking about power inputs. There will be no ripples in a battery powered system to be filtered. You don't need to use a filter.

But a parallel capacitor can be useful for reducing instant voltage change during power off/on.

Due to things like a battery's internal resistance, doesn't that only hold true if the size of the battery is large enough that fluctuations in load current only produce insignificant fluctuations in voltage? Putting a filter between battery and load should help smooth out these load induced fluctuations. - BeowulfNode42 Jul 17 at 7:15

## Unlock badges for special achievements

Badges are special achievements you earn for participating on the site. They come in three levels: bronze, silver, and gold.

 Informed Read the entire tour page
 Student First question with score of 1 or more Editor First edit Good Answer Answer score of 25 or more Civic Duty Vote 300 or more times Famous Question Question with 10,000 views