0
\$\begingroup\$

I'm playing a lot with solar powered systems using ultracaps for energy storage. I'm also powering some small ~3.3V systems directly from LiFePO4 cells, charged by solar power.

In both cases I'd like to be able to power on the load when the ultracaps / battery reaches a specified voltage V(on), keep it on until the voltage falls below a second voltage V(off), and then keep it off until it rises back to V(on). V(on) > V(off)

Ideally, the circuit to achieve this should be as simple as possible (fewest components), cheap and all components readily available. It must also not draw much power itself (max. a couple of mA).

So what would people recommend? I've searched online and found microcontroller based solutions, but this seems like overkill and simple Schmitt triggers, but these don't quite fit the bill either - at least the simple implementation I tried never worked reliably.

Thanks!

\$\endgroup\$
7
  • \$\begingroup\$ Frankly, a microcontroller is probably your quickest and easiest design path. \$\endgroup\$
    – Scott Seidman
    Aug 1, 2018 at 15:07
  • \$\begingroup\$ Seconding Scott. If you really want to do it without one, though, a Schmitt trigger switching a relay is your best bet in general, though you could use a transistor instead of a relay depending on specific needs. \$\endgroup\$
    – Hearth
    Aug 1, 2018 at 15:07
  • \$\begingroup\$ do you have a stable supply for the components which would sense and switch on and off? \$\endgroup\$
    – Navaro
    Aug 1, 2018 at 15:20
  • \$\begingroup\$ @Navaro Not as such, they need to run off of the same powersuply as the main load, however if they opperate at a suficciantly lower voltage then I guess sticking them behind a LDO would give a stable supply throughout the intended opperating range. \$\endgroup\$
    – Prosthetic Head
    Aug 1, 2018 at 15:40
  • \$\begingroup\$ @ScottSeidman and Felthry, are you aware of any online guide / instructions for doing this as simply and cheaply as possible? \$\endgroup\$
    – Prosthetic Head
    Aug 1, 2018 at 15:41

3 Answers 3

Reset to default
1
\$\begingroup\$

I'd search for "under voltage lock-out circuit" like this: -

enter image description here

Image can be found in this pdf document entitled "Li-Ion Battery Protection Circuit Draws Only 4.5 μA".

\$\endgroup\$
0
\$\begingroup\$

There are purpose-made ICs for battery protection. Seiko Instruments has a good range of them.

\$\endgroup\$
1
  • \$\begingroup\$ Thanks, but I'm not looking for just battery protection. Essentially, I have an application which I want to run as much as possible, powered by LFP (not the ususal lithium battery chemistry) battery or ultracapacitors which are in turn charged by a solar pannel as and when there's enough light. I don't want the system to rapidly switch on and off, so want an independent "cut out" and switch on voltage. \$\endgroup\$
    – Prosthetic Head
    Aug 20, 2018 at 15:41
0
\$\begingroup\$

RF Diagnostics produces a lil' IC that's purpose-built for this. "RFD88A". $18.

https://www.rfdiagnostics.com/store/rfd88a-solar-engine-module

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.