2.4V battery for settings retention - Page 1
Forum section: electronics / repair

author: JKKDev
author_rank: Regular Contributor
timestamp: March 30, 2020, 07:01:27 pm
content: Hey guys,quick question. My Gould 4074 scope uses a 2.4V battery to keep the settings, clock,... Finding one isn't easy (the same footprint is out of the question) but there are some. I just don't think paying 6€+ for a battery (even tho it'll last forever probably) is reasonable.Do you think it would be ok to use two rechargeable 1.2V batteries in series in a battery holder? They would probably have a higher self-discharge rate compared to the original button cell but going with two AA batteries they would also have something like 10x the capacity compared to the original (the original one was 2.4V 110mAh).Any thoughts are appreciatedHave a nice day/night

author: TheMG
author_rank: Frequent Contributor
timestamp: March 31, 2020, 06:34:08 pm
content: A couple of NiMH AAA in a holder should do just fine. They do exist nowadays in a version that has extremely low self discharge.

author: shakalnokturn
author_rank: Super Contributor
timestamp: April 01, 2020, 10:23:13 am
content: Depending on the (cheap) alternative you choose also consider moving your batteries off the PCB, cheaper often means more prone to electrolyte leakage.Taking into account the original price of the scope, it's value today, I wouldn't say spending 6€ on a quality battery that needs replacing every 15 years is a big investment.How much cheaper can you findqualityAA or AAA cells plus holder?

author: JKKDev
author_rank: Regular Contributor
timestamp: April 01, 2020, 02:22:51 pm
content: I'm definatelly going to move the battery off board. Tbh the only reason I don't feel like getting the 6€ battery (from Farnell in this case) is the shipping cost being half the price of the battery or more and I know I'd probably be better of just getting one of those but I already own some rechargable AAs and getting a hold of a holder for them shouldn't be too hard even with the current situation. And I can even recharge them when needed(if the slow discharge won't damage them).Now if you take what I paid for the scope into account, paying over 15% of the price just to keep some settings and system time feels too much to me. I know I'm a cheapskate sue me

author: Ian.M
author_rank: Super Contributor
timestamp: April 01, 2020, 02:31:17 pm
content: NiMH batteries don't stand up well under trickle charging currents that a NiCd battery of the same capacity will tolerate. In older pre-ROHS equipment, either replace like-for-like (i.e. same chemistry and a close match for capacity) or if you put in a battery holder and expect to use modern 'consumer' NiMH cells, expect to have to faff around modding the charging circuit to get the trickle charge current in the much narrower NiMH 'sweet spot' between death by over-charging, and failure to keep up with the self-discharge.If you do fit a replacement in-situ on the PCB, its worth protecting the PCB under the battery with Kapton tape, with minimum diameter holes for its pins, sealed with a dab of lacquer after soldering, to protect the PCB against electrolyte leakage. It wont help if it spews its guts, but if it develops a slightly leaky seal and the typical furry positive terminal, odds are the tape will prevent board damage.

author: JKKDev
author_rank: Regular Contributor
timestamp: April 01, 2020, 02:51:37 pm
content: Quote from: Ian.M on April 01, 2020, 02:31:17 pmWhy are we talking about trickle charging here? Are these on board button cells being charged? I was always under the impression that this were one time use however, the circuitry that they supply just pulls such a low current they take ages to discharge. Am I completely wrong in this thinking?Now if you were talking about super low discharge currents (trickle discharge I guess) I guess I can understand what you were talking about altho I'm still not too sure.

author: Ian.M
author_rank: Super Contributor
timestamp: April 01, 2020, 03:28:31 pm
content: You said 2.4V battery - that almost always implies a NiCd or NiMH rechargeable battery (1.2V per cell), especially in late '80s / early '90s equipment. The self-discharge characteristics aren't particularly good so they *MUST* have a charging circuit.Post a picture of the offending battery with any markings clearly visible, and I'm sure we can resolve any remaining confusion.