Ansmann 9V rechargeable Li-ion battery in Fluke 87 - high-pitched noise - Page 1
Forum section: electronics / testgear

author: 6SN7WGTB
author_rank: Regular Contributor
timestamp: November 14, 2024, 08:48:08 pm
content: Thought I'd try one of the above in my Fluke 87.Mystified by a very high-pitched noise emanating from the multimeter, even when switched off.Turns out it is the Lithium battery. Note that this type is 9V, not 8.4V. It's this one:https://shop.ansmann.de/en/li-ion-battery-9v-block-typ-400-min-340-mah-1pcs-cardboard-boxMy (quite old) Fluke 87 draws about 9µA when 'off'Anyone come across this?

author: tunk
author_rank: Super Contributor
timestamp: November 15, 2024, 01:42:57 pm
content: "Stable voltage of 9 V over 100% of the runtime."This suggests some kind of switching step-up circuit.

author: Atlan
author_rank: Frequent Contributor
timestamp: November 15, 2024, 09:59:48 pm
content: My alkaline 9V battery for unt204 ran out. I quickly put in a charging lipol with a changer. Switched to current measurement, and the device showed 287. So I couldn't measure anything. I disassembled the device to the contacts for the battery, installed 220uF, I also disassembled the battery with the inverter and put a 100uH choke there. Such an LC filter member seems to be sufficient. I didn't get to the tests. But the interference no longer manifests itself.

author: Fungus
author_rank: Super Contributor
timestamp: November 15, 2024, 10:50:50 pm
content: Quote from: 6SN7WGTB on November 14, 2024, 08:48:08 pmPut a 1M resistor across the battery terminals and see if it makes the noise.

author: thm_w
author_rank: Super Contributor
timestamp: November 16, 2024, 01:01:23 am
content: If you use nimh or li-ion without active circuitry, there will be no issues with noise or interference.The only downside with 9v li-ion is that they take a bit more effort to charge (soshine brand for examplehttps://lygte-info.dk/review/batteries9V/Common9Vcomparator.php).Quote from: Atlan on November 15, 2024, 09:59:48 pmStill sounds slightly risky. Who knows what measurements it might effect unless you do a full comparison.

author: daisizhou
author_rank: Super Contributor
timestamp: November 16, 2024, 02:56:07 am
content: You need to add a transistor. See the circuit below. You can try to copy it. This is an open source project.https://www.mydigit.cn/thread-163962-1-1.html

author: 6SN7WGTB
author_rank: Regular Contributor
timestamp: November 16, 2024, 08:14:38 pm
content: Quote from: Fungus on November 15, 2024, 10:50:50 pmYes, will do when I have finished doing a capacity measurement on the electronic load. It's silent at 25mA...Most likely it is the boost regulator, which does not 'like' low current draw. 'Like' being a non-technical explanation.

author: Hydron
author_rank: Super Contributor
timestamp: November 18, 2024, 03:18:06 pm
content: I'm using an Ansmann 8.4V NiMh LSD battery in my Fluke 87 V. Nothing in there other than 7 cells, no noise and very compatible with 9V (an alkaline will drop to a similar voltage after some use).You can also get a LiPo equivalent (2 cells in series, no DC-DC/charger) but they do go down quite low in voltage when near empty, so the gear needs to handle this (can just test with a PSU first), and you also want to get one with the right shape (mine came with very sharp corners on the case instead of the rounded normal 9V shape, and won't work in some items due to this).

author: AVGresponding
author_rank: Super Contributor
timestamp: November 18, 2024, 06:21:00 pm
content: Thought I'd posted a reply in here, but was a similar threadhttps://www.eevblog.com/forum/testgear/use-of-rechargeable-batteries-in-test-equipment/msg5718069/#msg5718069

author: sardonyx
author_rank: Newbie
timestamp: July 01, 2025, 02:16:02 am
content: This is my solution: 2 cell lithium polymer battery + charging/balancing board + type C socketNo noise, no need to disassemble, charge or change the battery. Just connect the cable, charge and continue workinghttps://youtube.com/shorts/UhsmOHw7m-c

author: Manuel Ferreira
author_rank: Newbie
timestamp: July 02, 2025, 02:03:41 pm
content: Como se sabe não Há baterias de Iões de litio de 9V.Estas baterias são apenas de 4,2V máximo quando carregadas.Há tempos resolvi comprar 2 destas baterias recarregáveis por cabo USBCchegaram descarregadas, recarregueis e coloquei uma num multímetro, algum tempo depois as leituras do multímetro começaram a ser eroneas pensei que o multímetro estivesse com a varia depois de alguma pesquisa verifiquei que a tensão desta bateria tinha caído para cerca de 2V.verifiquei ainda que a outra bateria que havia recarregado á poucas semanas mas que não estava em uso também se encontrava descarregada.Abri uma dessas baterias e verifiquei que tinha dentro uma pequena bateria de litiode 4,2V e um carregador para carregar a mesma a prtir dos 5v USB e um circuito electrónico elevador de tensão para elevar os 4,2V da bateria para os 9V que supostamente é esta bateria.Assim e como choper elevador de tensão funciona com uma frequência próximo dos 100Kz é possível que subarmónicos desta frequência se transformem em ruído auditivo.Para mim não quero mais este tipo de baterias.

author: Aldo22
author_rank: Super Contributor
timestamp: July 02, 2025, 02:37:03 pm
content: @Manuel Ferreira:Este é um fórum de língua inglesa.Pode utilizar um tradutor em linha.https://www.deepl.comhttps://translate.google.com/

author: BILLPOD
author_rank: Frequent Contributor
timestamp: July 02, 2025, 07:21:27 pm
content: Good Morning Manuel Ferreira, Me no comprendre

author: floobydust
author_rank: Super Contributor
timestamp: July 02, 2025, 07:59:33 pm
content: I useEBL9V Li-ion batteries from Amazon, they are 2S and have no boost-converter in them. BUT no USB port. Have not tried their Amazon Basics version.