Replacing a CMOS battery with a Super Capacitor? 

why is elmo teaching me electronics

A clever idea. I do feel like the coin cells have proven to be a reliable option though.

Interesting. Look forward to updates!

I had a laserdisc player built around 1994 with a supercap like this in it. It had some apparent surface corrosion so I replaced it in 2020, but there was no apparently damage to the board or nearby components

The original XBOX uses a supercapacitor to power it's clock chip. It's notorious for leaking and eating the motherboard. Whether that's because it has the same issues as other cheap capacitors made during the "plague" era I do not know.

You do amazing work good sir

NiCd and NiMh batteries weather overcharging very well compared to Li-ion batteries. From what I have learned from watching electrician youtubers, the liquid electrolyte simmers inside the battery and converts to a gas which returns to a liquid over and over again while it is overcharged. Excess storage is converted into heat and dissipated. As long as you don't feed the battery a dangerous voltage it can handle it. This is why NiMh batteries are used in garden solar lights and such. No need for an overcharge protection circuit.

It's a great idea! And well implemented there!!! But super caps do leak eventually!

Two years ago i tinkered with SuperCaps too and observed exactly the same problems. Fast selfdischarge and after 48h all your cmos dats are gone. So i used a CR2032 on the external batterie pins of the boards.

How about stacking two or three and solder pins in parallel?

Hmmm.. interesting idea.

The 5v rated capacitors are quite bad at holding the charge.It's better to use 2.5-2.7v rated capacitors as they often have much lower self discharge - you can use a very efficient low current step up regulator to boost the voltage to 3v needed by the circuit. For example, TLV61224 is a step-up regulator that outputs 3v and works with 0.7v...3v input voltage. Or, another example, MAX1724 can do 3.3v out with as little as 0.8v.. You could use an ideal diode chip like LM66200 to automatically switch between 3v or 3.3v from PC and 0.7v...3v from a supercapacitor or battery with minimal losses. In fact you could probably just use a AA or AAA or even AAAA battery instead of a super capacitor with this step-up regulator and get more life than a CR2032, but alkaline batteries may leak. You could get a lithium based AA or AAA battery, those don't leak and last a long time. I've used a 20F 2.7v super capacitor to power a multimeter for around 40 minutes - used a 1A linear regulator to charge the supercapacitor to 2.5v within a minute, then used a LT1037 step-up regulator to boost the voltage to around 5.8v the multimeter needed to be above the low battery threshold and the multimeter averaged around 3-5mA of power consumption. Another option would be batteries in the CR123A format - you get 3v at up to 1.55Ah and they're not that expensive at around 3 dollars..

it's also leaking (xbox original for example), I'm using barrel battery but with connectors (m/female) to unplug when mb on the shelf

Would an 18650 be an option? I hate having to replace the non-rechargeable CMOS batteries!

Reverse current of common diode like 1N4148 would be

Personally I prefer CR2032s as I have been though the nightmare of dead super capacitors in Sega Naomi boards.

What voltage range does the CMOS want?

Oh yes, it's a catch! NiCd they dissipate redundant charging current into heat, but for LiOn or Capacitor is a death.

Why would they purposely choose a voltage of 9v?! No wonder the barrel batteries would leak...

Scrap Computing: triggering armchair 'electronics engineers' since july 1 2023

i have see the super capacitor leaking

If the charge of the capacitor lasts for a few months then it is not sufficient, an ordinary battery keeps the clock running for ages. When I switch on a computer that was on a shelve for a very long time, often the clock still runs, most the time it is a few minutes off. Most computer clock chips are not that accurate, they really need the time server to synchronise, if the clock chip doesn't get its weekly or daily correction he wanders off to the future or the past.

The proper drop-in replacement would be a NiMH battery in the same form factor as the original NiCd. Not sure if NiMH batteries leak but they should last many years as the original batteries did. Personally I'd just use CR2032, they're cheap and simple.

Not a good idea. The components are over volted

It is an idiot*c idea. The thing called "supercapacitor" is not a capacitor, but downgraded chemical rechargeable battery. The difference is that a complete battery has chemical conversion, which support the balance of ions. The ion battery (which is the correct name as opposed to marketing BS "supercapacitor") behaves more like a capacitor - actually it behaves as a normal chemical rechargable battery discharged beyond exhaustion of chemical oxidizer and reducing agents, when there is nothing left to support the minimum amount of voltage. It discharges almost linearly to 0V, meaning that a huge amount of charge is wasted just because it is difficult to utilize it at lower voltages, meaning that a normal rechargable battery would last way longer and support the minimum required level of voltage.

Why is your voice so high? Are you eunuch, buddy? I'm so sorry, if that's the case.