Rechargeable batteries emitting RF noise? - Page 1
Forum section: electronics / projects

author: peteb2
author_rank: Regular Contributor
timestamp: November 30, 2017, 01:52:43 am
content: Where I work we used to litterly pour through alkaline AA batteries because its a practice to always begin a job on a new set of cells, removing any chance of mic system going mute all because of discharged batteries.Then came the idea to use rechargeables however there was always that issue of using a freshly charged set. Enter another problem of the 1.2V per cell ability. There was now a shortened run time shown via the telemetry fed back from the transmitters with the design based on volts measurement and an expectation a Normal Fully Charged cell is 1.5V....Enter the iPowerUS AA1.5V 2600mWh Li-Polymer which we've used for over a year (including their 9V) and this have been .... well excellent.www.ipowerus.comThe AA has a built in DC-DC inverter (assumed) to maintain a terminal voltage of 1.5V until they 'crash out' once discharged to the point they need a recharge. Not a problem when you are always pulling them from the equipment in use in a process of of always starting a job on a fresh charged set no matter what...Here's my main question though. Has anyone else be using such devices and over time have you noticed a peak in the "hash" as in an increase to the noise floor for your gear? In this context we have seen a peak centred around 228MHz with enough RF hash multiples to gate open squelch on our wireless mic receivers (that usually run in various channels of the +600MHz HDTV band)...In the bench test mockup we can switch cut away from the AA cell to a lab powersupply feed leaving the iPowerUS AACell on no load and instantly the 228MHz noise peak goes away with the entire noise floor becoming much quieter... Here it would seem the DC-DC inverter in this AA cell must be producing the RF hash but what is a double fail is that the increased noise actually affects the system to the point there is a reduction to the range of the wireless mic system i.e. the distance between mic and receiver defined by the squelch gate point .... (a user setting)One final thought is the cells have been fantastic but are now aging and a couple would have been dropped by fumbling fingers so the thought is perhaps this damages the internal inverter to the point it radiates higher levels of RF noise than when new. In all this we've not made measurements yet, just an oh-look comparison. It'd be interesting to hear from others' experience...

author: David Hess
author_rank: Super Contributor
timestamp: November 30, 2017, 09:58:10 pm
content: I would have been surprised if they did *not* produce noticeable RF noise. You just happen to be using it in an application where this matters.You might get some improvement by adding a decoupling capacitor and some EMI suppression beads close to the battery terminals.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 30, 2017, 11:33:04 pm
content: Heh, that, and foil inside the battery compartment... and more, depending on just how dirty it is?I'm shocked that there is equipment that doesn't understand NiMH cells. They've only been around since forever. Must not be very good equipmentTim

author: james_s
author_rank: Super Contributor
timestamp: December 01, 2017, 01:57:22 am
content: That is surprising, especially since NiCd cells have been around even longer and have roughly the same voltage and discharge characteristics. Does a set of fully charged NiMH cells not work? Any sort of boost converter is going to produce some amount of RFI.

author: David Hess
author_rank: Super Contributor
timestamp: December 01, 2017, 02:18:08 am
content: Quote from: T3sl4co1l on November 30, 2017, 11:33:04 pmThat is a good point. A metal shielded battery compartment with a feedthrough capacitor for the isolated terminal would solve this easily. This is sometimes down in reverse with the sensitive circuit on the inside of the shielded enclosure.Aluminum foil or that metal film paper could make a big difference.