Can a 3.6v memory battery be replaced with a capacitor for usage only when plug - Page 1
Forum section: electronics / repair

author: jorgemef
author_rank: Regular Contributor
timestamp: October 23, 2023, 05:34:32 pm
content: Hello,I have 5 of these equipments and all developed battery leakeage inside.https://de.hama.com/00223561/hama-energiekostenmessgeraet-mit-lcd-anzeige-digitaler-stromzaehler-fuer-steckdoseI rarely use them in recent times and would like to repair them but if possible to leave them without NIMH batteries to avoid the same damage if they stay put for long.Do they need a battery to operate, and so can I use a capacitor instead in case some charge is needed?What is the best way to clean the motherboard from this nimh leakeage stuff?Thanks and BR,Jorge

author: bdunham7
author_rank: Super Contributor
timestamp: October 23, 2023, 05:43:24 pm
content: You could use a capacitor or supercap, but you should shunt it with a 3.9V zener. It looks like this may be a very crude design that uses the battery as a voltage regulator. Or you could just get a higher quality NiMH battery. Cleanup of NiMH leakage usually isn't too bad and can be done with 70% isopropyl and a cotton swab, but your corrosion looks worse than typical. Hopefully there's no PCB trace damage.

author: TimFox
author_rank: Super Contributor
timestamp: October 23, 2023, 06:37:06 pm
content: When replacing Ni-Cd batteries in line-powered equipment, I have used TL431s with appropriate feedback as more exact zeners to give correct voltages while being "recharged".

author: jpanhalt
author_rank: Super Contributor
timestamp: October 23, 2023, 06:42:06 pm
content: I had a camera that used one because of its flat discharge curve. They were also used a long ago as voltage references in some lab equipment. Replacement is often a zinc-air battery, but it has nowhere near the capacity of the mercury. Otherwise, you are probably stuck with a voltage regulator-based substitute.

author: TimFox
author_rank: Super Contributor
timestamp: October 23, 2023, 06:48:50 pm
content: The zinc-air battery has a hard current limit: you first unseal it, which opens a small hole to admit oxygen, and the current is limited by the small flow rate of air through that hole.(Another thing I discovered the hard way.)

author: wasedadoc
author_rank: Super Contributor
timestamp: October 23, 2023, 06:59:42 pm
content: Quote from: jpanhalt on October 23, 2023, 06:42:06 pmThe battery in question is clearly marked NiMh, And the post title contains the word "memory", not "mercury".

author: fenugrec
author_rank: Frequent Contributor
timestamp: October 24, 2023, 02:43:13 pm
content: if the damage can be cleaned easily (and the thing still works), I would just replace it with another nimh battery but mount it away from the PCB if you have room. That way in 10 years when it leaks again it takes 30 seconds to clean up and not 30 minutes.

author: Miti
author_rank: Super Contributor
timestamp: October 24, 2023, 05:33:55 pm
content: I have one similar to yours, at least inside, and the battery was dead within couple of years. I replaced it with a small Li-po cell (300 mAh IIRC) with protection board, and is working fine for few years now. The battery never charged to more than 4V so it’s at an ideal voltage for long life. I think it can work without battery but you would lose some variable settings such as cost per kwh every time you unplug it.

author: Greybeard
author_rank: Frequent Contributor
timestamp: October 25, 2023, 07:49:02 am
content: Quote from: Miti on October 24, 2023, 05:33:55 pmExactly!

author: jorgemef
author_rank: Regular Contributor
timestamp: October 25, 2023, 01:22:36 pm
content: Yes, just confirmed it can work without battery.The charging circuit pumps 4.2V. I added a 470uF cap just for safe of mind.Unfortunately I baked two of the circuits by undoldering the CS5460A and one of the memory eproms 24C02. Eprom I have around, easy fix. The chips need to get some from Aliexpress.I was trying to remove them to clear underneath as there was some green stuff in the pins.Seems hot air station and memory chips and some this specific power measuring chip dont go along.I did the same mistake in two so the other are fine. Firts I thought something else was wrong and moved on to try to have a comparative system which I could measure to come back to the first but at second failure I imagined I was the issue and reviewed what I was doing wrong. I think I would have to unsolder by leading the pins first and hot hair undernead afterwards or maybe get some low melting point stuff.Anyway, always learning something.