I have gotten the data sheet it will put it in my notes. Thing is the LM555 is a very standard part and very easy to get.

 

Of course you could always eliminate the long pulse trigger with a high power high current transistor

What long pulse trigger are you speaking of?
Trigger pulse has nothing to do with the timing circuit.

 

I’d use a PIC. Fewer parts and accurate delays of years possible.

 

There are a variety of Capacitor charging circuits to choose from however some circuit constraints are universal.
A project with large or medium size capacitors can be planned with the help of an online calculator.
The known and unknown circuit values are accessed and the time constant for your application can be determined.

Capacitor Charge Time Calculator
A common sense approach without a 555 might give some hint toward using a 555 timer in some novel way.

A basic large capacitor or supercap charging circuit uses a comparator and a mosfet.
The circuit can be analyzed by making a simulation.
3-17.jpg (663×370)

 

35 years ago I worked at a company that sold a safety product that included a 555 timer with about a half hour delay. The time was consistent within a minute and that was adequate and I have no recollection of how it functioned, but the delay was just a 555 timer IC, NO, it was not cycling, it was just a delay that was required occasionally. So the reset was not at all an issue.

 

Enthusiastic past user of 555 timers as I am, I have to agree with BobTPH that these days, at a cost of just a few pennies, I would use a PIC in this application. Just as simple, more accurate and with far greater range possibilities.

 

You can only get so far trying to beat electrolytic capacitor leakage currents. Using a resistor in parallel shunts the leakage - but unless it is lower than the leakage current, there will be variability in the timing as the leakage will affect the net charge-discharge currents.
For long delays I prefer using a JFET or MOSFET opamp, where input currents of <1nA or so are specified, allowing the use of film capacitors and resistors of 100M to 1G with reasonable accuracy over several hours. For more precise timing I've used a 32768Hz crystal oscillator (they're easy to build and very low power) and one or more CMOS divider(s).

 

Just as simple

Keeping in mind the skill level of the TS, maybe you've forgotten how much fun it is to decipher Microchip's documentation of the Special Function Register, the Option Register, the I/O control register, and the Timer Register.

ak

 

My preference for long delays without having to program a micro is the CD4060, configured as an oscillator-counter (example here).
It's a fairly simple circuit, and can give long delays with relatively small RC values, and the part's cost is likely comparable to using a 555.