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 ...

Attachments

nesscap.pdf

(595.66 KiB) Downloaded 357 times

- 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