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Perhaps of interest...
https://www.edn.com/electronics-blogs/be...ck-to-life

(04-27-2018 04:25 PM)mdunn Wrote: [ -> ]Perhaps of interest...
https://www.edn.com/electronics-blogs/be...ck-to-life

Thanks for sharing this Michael. I like honest articles like this that reflect the real world of hobbyist electronics. Too many of these type articles are really showing the 2nd (or 3rd or higher) revision that are neat, tidy and everything fits just right and comes out looking perfect.

And continuing to use a classic device more than 45 years after introduction is it's own reward that feels good every time you use it! Thanks.

(04-27-2018 04:25 PM)mdunn Wrote: [ -> ]Perhaps of interest...
https://www.edn.com/electronics-blogs/be...ck-to-life

The author of that article seems to be concerned about the voltage of the LiPo battery that is used instead of the original NiCd pack. But... why? A fully charged NiCd cell has 1,4 V or even more, so the max. 4,2 V of the LiPo cell does not exceed what three fully charged NiCds would deliver. At least that's what I think. ;-)

Could the electronics experts please shed some light on this?

Dieter

(04-27-2018 08:40 PM)Dieter Wrote: [ -> ]

(04-27-2018 04:25 PM)mdunn Wrote: [ -> ]Perhaps of interest...
https://www.edn.com/electronics-blogs/be...ck-to-life

The author of that article seems to be concerned about the voltage of the LiPo battery that is used instead of the original NiCd pack. But... why? A fully charged NiCd cell has 1,4 V or even more, so the max. 4,2 V of the LiPo cell does not exceed what three fully charged NiCds would deliver. At least that's what I think. ;-)

Could the electronics experts please shed some light on this?

Dieter

Not only that when a classic is plugged into its charger, it is running off the regulated 5VDC supplied by the charger.

Paul.

Actually, I personally liked the fact that the HP-35 wasn't a pristine unit, It showed it had been used. I'm still trying to get my head around the hacked-up copper-tape dead-bugged SMD circuitry, I'm struggling to see how that can't short-circuit or something.

Did anyone else wonder about all the "emphasised" words in the article?

(Post 208)

Sure enough...I didn't properly research NiCd characteristics, and assumed 1.25V was pretty much the maximum. Looks like a raw LiPo is fine after all. Oh well...it was a fun build.

BTW, I haven't dug too deeply into LiPo either, but am told that charging to 4.1V instead of 4.2V will GREATLY extend its lifetime.


>A fully charged NiCd cell has 1,4 V or even more, so the max. 4,2 V of the LiPo cell does not exceed what three fully charged NiCds would deliver. At least that's what I think. ;-)

(04-27-2018 04:25 PM)mdunn Wrote: [ -> ]Perhaps of interest...
https://www.edn.com/electronics-blogs/be...ck-to-life

The low battery warning built into the HP-35 might not work any more under this arrangement, but probably of no concern.

A schottky diode in series with the battery would have reduced the voltage slightly at the regulator input and helped protect against reverse voltage which may occur with a home made setup.

cheers

Tony

(04-27-2018 11:33 PM)mdunn Wrote: [ -> ]Sure enough...I didn't properly research NiCd characteristics, and assumed 1.25V was pretty much the maximum. Looks like a raw LiPo is fine after all.

Oh, I hadn't realized it was you who wrote that article. But yes, that's what I wanted to say: IMHO the LiPo cell alone would have done it.

But then...

(04-27-2018 11:33 PM)mdunn Wrote: [ -> ]Oh well...it was a fun build.

:-)

(04-27-2018 11:33 PM)mdunn Wrote: [ -> ]BTW, I haven't dug too deeply into LiPo either, but am told that charging to 4.1V instead of 4.2V will GREATLY extend its lifetime.

I don't know anything about LiPo batteries, but I wonder how you charge it. A dedicated LiPo-charger? How do you connect this to the battery?

Dieter

>how you charge it. A dedicated LiPo-charger?

A lab supply.

(04-28-2018 06:13 AM)Dieter Wrote: [ -> ]I don't know anything about LiPo batteries, but I wonder how you charge it. A dedicated LiPo-charger? How do you connect this to the battery?

Dieter

LiPo charger. You can buy or build them with just a handful of components. There is plenty of cheap stuff on the web for battery packs with chargers supplied. The trick will be if the charger can deal with the calculator being on while attempting to charge.

cheers

Tony

A battery charger module like this between the charger an the battery.

https://www.ebay.ch/itm/Micro-USB-5V-1A-...SwHHFY-OCI

the Maximum input voltage is 8V. Perhaps a diode in serie to limit the voltage.

(04-27-2018 08:40 PM)Dieter Wrote: [ -> ]The author of that article seems to be concerned about the voltage of the LiPo battery that is used instead of the original NiCd pack. But... why?

From my evaluation, the 4.2V of the LiPo will not harm the power supply, which is a switch mode boost power supply. Just do not exceed 6V at the battery terminals.