Revising the control logic as follows:
Rather than shutting off the battery when voltage falls below a minimum threshold (11.9 volt), the battery will remain connected to power the preamp, however, the charger will be reconnected to prevent further draining of the battery. Under normal preamp load conditions this should prevent further draining of the battery since the charger is designed to deliver more charging current than the preamp draws thus the battery voltage should charge up.
The rationale behind this change is there's a potential downside to simply disconnecting power altogether from the Tortuga preamp while it's turned on and playing music. When power is removed from the LDRs there's a brief period (probably less than a second or so) when the loss of power causes in momentary jump in volume before shutting off. This is largely mitigated in preamps that have input switching but for those that have only a single direct wired input (no input switching relay), this volume surge can be disconcerting. So in an abundance of caution, best to not disconnect batter power and instead just reconnect the charger leaving the preamp powered.
Note, however, the following exceptions:
a) When the PS12B is connected to the preamp and controlled via the preamp 12 Volt Trigger output (the preferred control method), once the preamp is turned off and the 12 Volt Trigger signal goes off, the PS12B battery will also disconnect and remove power to the preamp until such time as the PS12B battery voltage increases to at least 12.1 volts.
b) When the PS12B gets powered up (connected to AC main) and if the battery voltage is below the safe 11.9 volt threshold, the battery will remain disconnected until battery voltage increases to at least 12.1 volts.
Here is the currently conceived operating parameters and control logic for the PS12B. If you have any questions, comments or suggestions I welcome your inputs.
Please note that the PS12B has not been released yet and is still in final development.
The PS12B is a nominal 12 VDC sealed lead acid (SLA) battery power supply combined with a "smart" charger system. The capacity will either be 5.7 Ah or 7.0 Ah - still finalizing battery selection.
The max current draw is 0.5 A above which a replaceable fuse will blow requiring the unit to be opened up to replace the fuse. The batteries should last for 2-5 year of normal usage, are replaceable and relatively inexpensive.
The objective is for the PS12B to be a hands-off automatic battery based power supply to the Tortuga preamps. Given that the normal current demand of the LDR3.V2 or LDRx is around 135 ma (~200 ma during auto-cal), the PS12B may be able to run the preamp for up to roughly 40 hours (5.7 Ah) to 50 hours (7 Ah) continuously before needing to be recharged. This is a best case scenario and actual time will likely be considerably less. Safe to say, there's more than adequate battery capacity to operate the Tortuga preamps for long listening periods lasting many hours if not all day before needing recharge. Even if almost fully discharged to minimum allowable voltage levels, the PS12B will fully recharge overnight.
The PS12B must be plugged into AC main power at all times in order to operate. The AC mains IEC input socket has an integral 1 A fuse. The PS12B can be pre-configured for either 120 VAC or 240 VAC mains power via an internal set of configurable jumpers.
Summary operational narrative:
The PS12B must be connected to AC main to operate. When not connected to AC main power, the battery output will remain disconnected to prevent over-draining and damaging the battery. In this respect, this is not a portable battery power supply. When connected to AC main power, the default state of the PS12B is for the battery to be connected to the charger and the battery to be connected and available to the user. To use the PS12B to power a Tortuga preamp you'll want to disconnect the charger and run off pure battery power. To disconnect the charger you connect the 12V Trigger out from the preamp to the PS12B. The 12V Trigger out will automatically disconnect the charger when you turn on the preamp and connect it again when you turn the preamp off. This is the preferred "hands off" method. You can also press the push button on the front panel to disconnect the charger. Press it again to connect the charger. If the charger remains disconnected, the battery will eventually discharge to the point where low voltage will automatically disconnect the battery and reconnect the charger. If this happens the PS12B won't be available to power the preamp until it's voltage level is back up above 12.1 volts.
When fully charged, the battery will be at between 13.5 and 14 volts. When voltage drops below 12.1 volts a warning light will come on. When it drops below 11.9 volts the battery will be disconnected and the charger will reconnect to the battery and the battery will remain unavailable until the voltage is back up above 12.1 volts. This automatic shutoff protects the battery from being damaged or shortening its useful life due to over-discharge.
Summarizing the front panel LEDs:
Green/Off - battery disconnected - not available (either because AC mains off or battery voltage too low)
Green/On - battery connected - available
Yellow/Off - charger disconnected
Yellow/On - charger connected to battery and charging battery
Red/Off - battery voltage ok (> 12.1 V)
Red/Blinking - battery voltage getting low (< 12.1 V) and needs charging - time to turn off the preamp
Red/On - battery voltage too low (< 11.9) - will automatically disconnect battery and turn on the charger
No LEDs lit - means the PS12B is not connected to AC main and the battery is not available