Simple circuit for 5v logic battery back up

[blort1961]

Is there a simple way to float charge 5 or 6 AA , or a 9v Nicads, to back up a 5v powered logic circuit. I dont need looong running times, just back up for the occasional power failure, or when Im moving the circuit to another outlet.

 

[alec_t]

If the back-up is for only low-current short-term use, couldn't you just use 4 AA (non-rechargeable) alkaline cells and a diode in series?

 

[blort1961]

ya know...I really didn't think bout that...I would still like to see if I could float some batteries...just so I can try it in other circuits. I haven't really found too much on a google search

 

[audioguru]

Ni-Cads are obsolete and are very toxic. The ones I used many years ago all became shorted. Does anybody sell them anymore? Even very cheap Chinese solar garden lights use modern Ni-MH batteries now.
Modern Ni-MH cells hold their charge for one year. If you trickle charge them it can be at an extremely low current.

 

[blort1961]

ok...my bad Audio Guru...My Canadian brother....you are absolutely correct.
I REALLY should have said NiMh... I actually have a lot of 'em around, as I use them for my RC stuff. I have dropped off all my NiCads out to the Hazardous Waste people at the dump a few months ago...I had a lot of those as well...most came with my Futaba stuff.
Now back to the question at hand.....

 

[cowboybob]

Is there a simple way to float charge 5 or 6 AA , or a 9v Nicads, to back up a 5v powered logic circuit. I dont need looong running times, just back up for the occasional power failure, or when Im moving the circuit to another outlet.

First, you might want to read this: https://www.powerstream.com/NiMH.htm. Note the paragraph under "Basics".

With that in mind, google: "ni mh battery float charger circuit" (what I used to find the above site - 4th entry). Be forewarned that many circuits posted on the web either do not work or are seriously flawed.

 

[blort1961]

First, you might want to read this: https://www.powerstream.com/NiMH.htm. Note the paragraph under "Basics".

With that in mind, google: "ni mh battery float charger circuit" (what I used to find the above site - 4th entry). Be forewarned that many circuits posted on the web either do not work or are seriously flawed.

Yes , thats why I come here for info...there are a million schematics on the web....and probibly 99.9% DONT WORK. Every schematic that Ive used from this site has been 100% correct