xtal_01
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I have read a few posts on this forum (and other forums) ... looked at data sheets .... found a good description on PowerStream ... but still have a few questions I am hoping someone can answer.
First, I should say I only dabble in electronics. I usually build industrial control panels .. anything from a simple starter to a PLC / touch panel HMI monitored and controlled via the web.
I was asked to duplicate a simple box that monitors air flow with a differential pressure switch.
The originals were made some 25 or 30 years ago and have started to fail.
The person who build and designed these (I worked with him) has long since retired and passed away ... so I can't just ask him what he did.
The circuit is simple ... transformer supplies a 12 volt regulator .... a relay is held on and alarms if it looses pressure or if it looses power.
The factory almost never looses power ... and if it does, there are three generators to bring it back up within about 10 min.
There is an adjustable voltage regulator charging a 9 volt NiMh battery.
The client wants to keep the design .... they say if it worked for 25 years, they don't want to change it.
Anyway....
So, if I understand the circuit correctly .... R4 (1K) limits the charging current.
R2 (1K) is listed as "optional" on the drawing but it is installed on all the boards. I am not sure if it is needed ... it actually causes a problem (from what I can tell) jumping around the diode D5 as it will "bleed" power back to the Yellow power LED (about 3 mA).
My best guess is that R2 is there to "force" a trickle charge onto the battery .. about 1 mA .... as the battery reaches the supply voltage, some power will still flow through the resistor as a result of the 1 volt drop across the diode.
So questions:
1) do I need R2 ?
2) What voltage should I charge the battery at .... rated voltage is 8.4 (7 cells at 1.2 volts ?) ... charge limit is 10.5 .... if I assume 7 cells @ 1.4 V each when charged then 9.8 volts ....discharge -off is 7 volts
3) where do I measure the voltage ... at the regulator output or at the battery (after the diode) ?
4) when setting the supply, do I have the battery in or out of the circuit?
Just as a side note .... I am still scratching my head over the D6 (it is across the contacts of the pressure switch) and there is a 1K resistor (R&) that does not show up on the drawing.
The "see note 2" is interesting as there is no note 2 ... there are lots of traces on the PCB that are not use ... even an unused 6 pin IC socket !
Any help would be greatly appreciated!
First, I should say I only dabble in electronics. I usually build industrial control panels .. anything from a simple starter to a PLC / touch panel HMI monitored and controlled via the web.
I was asked to duplicate a simple box that monitors air flow with a differential pressure switch.
The originals were made some 25 or 30 years ago and have started to fail.
The person who build and designed these (I worked with him) has long since retired and passed away ... so I can't just ask him what he did.
The circuit is simple ... transformer supplies a 12 volt regulator .... a relay is held on and alarms if it looses pressure or if it looses power.
The factory almost never looses power ... and if it does, there are three generators to bring it back up within about 10 min.
There is an adjustable voltage regulator charging a 9 volt NiMh battery.
The client wants to keep the design .... they say if it worked for 25 years, they don't want to change it.
Anyway....
So, if I understand the circuit correctly .... R4 (1K) limits the charging current.
R2 (1K) is listed as "optional" on the drawing but it is installed on all the boards. I am not sure if it is needed ... it actually causes a problem (from what I can tell) jumping around the diode D5 as it will "bleed" power back to the Yellow power LED (about 3 mA).
My best guess is that R2 is there to "force" a trickle charge onto the battery .. about 1 mA .... as the battery reaches the supply voltage, some power will still flow through the resistor as a result of the 1 volt drop across the diode.
So questions:
1) do I need R2 ?
2) What voltage should I charge the battery at .... rated voltage is 8.4 (7 cells at 1.2 volts ?) ... charge limit is 10.5 .... if I assume 7 cells @ 1.4 V each when charged then 9.8 volts ....discharge -off is 7 volts
3) where do I measure the voltage ... at the regulator output or at the battery (after the diode) ?
4) when setting the supply, do I have the battery in or out of the circuit?
Just as a side note .... I am still scratching my head over the D6 (it is across the contacts of the pressure switch) and there is a 1K resistor (R&) that does not show up on the drawing.
The "see note 2" is interesting as there is no note 2 ... there are lots of traces on the PCB that are not use ... even an unused 6 pin IC socket !
Any help would be greatly appreciated!