Looking to identify the 4v battery used to backup settings on 1980 HP2621A CRT video display terminal. I can't find the battery type online. Seems all the manuals are truncated at chapter 5. It is discontinued and I just want the specs. seems 4.2v Hg or 3.8v Li.
Hg is bad for marketing. It was probably discontinued when everybody found out that mercury (Hg) was a dangerous poison.
Ok, say I need a rechargeable 4v battery. What Amps likely? Any added circuitry? On the terminal.
Here's a _general_ answer.
A setting holding backup battery does not need to supply a lot of current. I don't know what your device needs, but it is likely very low, perhaps not measureable with a dmm as it may draw current in pulses.
That said, there are plenty of lithium batteries you can choose from, and small voltage boost converters (look on ebay) you could use to boost to 4.2 volts.
You may not need exactly 4.2 volts - I have no idea what your device needs, other than what you posted, except that setting backup is almost always (always ?) very low current.
Ok, assuming 4.2 volts, here's where we are, so far: lithium===>boost circuit===>device
Now, you want to charge the battery. Ebay has lithium cell charger/protector circuits. Now your circuit looks like this: (view in fixed font) lithium=+=>boost circuit===>device | chg/pr==+
In case the view is "scrambled" you'll connect the charge/protect (chg/pr in the diagram) to the same battery terminals that the boost circuit connects to.
Ok, that's the general idea - using lithium, lithium charge/protection circuit and boost (or buck/boost) converter. You need to know what you're doing with lithium batteries, how to protect them etc, and how to properly connect to your 2621A.
Good luck. Ed
Thanks. I have found there are 3.7v batteries that look like the original out there and they even come with chargers.
I doubt you want those. The primary-cell lithium batteries (3.6V fresh, 3.0V at end-of-life) are what would have been in a 1980 device, not lithium ion rechargeable batteries. A few lithium vanadium pentoxide cells were available, but rare. If the
2621A doesn't charge the battery, you want a nonrechargeable Li battery. If it DOES charge it, you probably want a NiCd stack of button cells...
I have been following this thread for several weeks now. I found it interesting.
Just a quick thought, If the terminals fit to the length of the battery I speculate might work, provided the physical width of the battery chamber (which holds the battery in place can support), assuming the numeric values (for voltage, etc... indicated remain constant), one could use an "N" type battery in some situations. Nickle Cadmiums (Ni-Cad's) are very expensive these days- retail cost is over 5 bucks for one or two of the Ni-Cad's (in current 2023 prices, due to recent world events, high inflation, etc.. ). One 'N' type battery or similar type may very well work (as long as it is rated properly and fulfills all of the other previously indicated criteria) and may help you to get the task accomplished at a far less expensive financial outlay. With the rise in prices these days, I am surprised more people "seem like they have to take out a second mortgage", just to actually buy the stuff. Big thing is safety, meeting all of the ratings and requirements, but price is really important to. Just thought I would mention that.
Good Luck. Hope this helps out.
Charles Lucas Senior Electronics Technician Senior Technical Consultant
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