ESP8266 Community Forum

- Thu Aug 31, 2017 12:44 pm #69612 I have a lot of 1F 5.5 volt supercaps with a rated discharge current of only 10mA. I saw that on the spec sheet and laughed. Ok for a RTC but useless for any power. I did try and test them with a 100mA draw and they couldn't do it. Totally useless. I was hoping to use them for a Raspberry Pi. If they could handle 100mA then I would have wired a bunch in parallel.

What seems to freak it out is the slow voltage rise on its power supply, going up from 0V through to 3.3V from the step-down buck regulator I have on it. It just can't seem to handle that.

Put a resistor in series with the supercaps to act as a current limiter. You don't need fast charging. Put a Schottky diode with a low forward drop across the resistor to allow higher current discharge. If you have 16V suppercaps charge them to 12-15 volts and use a buck regulator to take that down to 3.3v. You store a lot more energy by going to a higher voltage.

The Enable pin on the ESP8266 can be controlled by a voltage supervisor chip. If the voltage is higher than 3v then enable the ESP.

http://www.linear.com/product/LTC2935 one example.

There are chips designed for supercap backup use but you need to evaluate which is suitable for your application. One example http://www.linear.com/product/LTC3110

- Thu Aug 31, 2017 3:13 pm #69615 sorry to have to confront you with modern time parts (your supercaps are supercrap) but continuous current of 3A seem more than adequate to me ...

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- Thu Aug 31, 2017 3:21 pm #69616 I assume you will be placing two in series because of the low voltage rating of the capacitors.


They were designed for a specific purpose and that is the way we use them in our products. I hoped I would be able to use them as they would have been a no cost component for me. So I'll continue to use batteries since they are my other no cost option.

- Fri Sep 01, 2017 5:24 am #69632

you have to be cautious not to mix up old "goldcaps" with new "supecaps" (e.g. nesscaps),
the new kind have realy low esr.

I have the new kind. The low esr must be helpful as far as providing bursts of power goes?

The cap is not the problem here. If I short it out even with a relatively thick wire, the wire gets very hot. I guarantee it can power the ESP8266

(level control) cct == circuit e.g. DS1233 (stone age part I remember as DS application engineer)

So a part that takes a floating voltage between 0..X and provides 0 on the output until the input is logically high? I could use something like that. I looked for the DS1233 but found mostly technical specifications. I'd like to see some example wiring or use cases if you happen to know where I can find something like that.

Or better yet a convenient SparkFun/Pololu breakout board )

-Michael