Hello all,
I'm currently in the process of rebuilding an alarm panel originally built with Picaxe chips. The power supply is one major area that I want to improve/get right this time.
I am feeding the entire project from a 48v 5A DC power supply. The alarm system is broken down in to smaller sections, where each section probably draws between 0.8-2A of current, but in total i'm sure it's less than 4.5A.
The 48v power supply voltage is dropped down to suitable voltages for specific parts:
48v In -> LM2596HV -> 24v out
24v In -> MP1584 -> 12v out (relays etc)
24v In -> MP1584 -> 5v out (Picaxe and other 5v IC's)
24v In -> MP1584 -> 5v out (Nextion HMI only)
24v In -> MP1584 -> 3.3v out (for 3.3v IC's)
I am going to use a Picaxe 18M2+ to monitor the voltages via divider circuits and Analog pins. Currently calculating the resistor combinations. No problems here.
I am wanting to add 2x 12v 7aH/12aH sealed lead acid batteries as a backup for when the mains fails.
I'd really appreciate some guidance and perhaps help designing the cheapest yet suitable and safe battery backup and charger circuit (I don't want an alarm starting a fire!) to kick in when the mains supply fails, in order to maintain 24v input to the other regulators- keeping my system alive.
I've found numerous guides detailing (see here) the use of an LM317 to make an independent charger- but I don’t know how to make the battery supply take over from the mains PSU and serve as the 24v supply. I guess the charger end might be taken care of with the above link...?
Concern 1: The LM2596HV is currently adjusted to output 24v when 48v is provided- I can't just attach the battery to this due to the output voltage dropping below 24v- so I need to prevent the battery voltage going backwards through this module and my mains PSU.
Concern 2: With the above link- It doesn't show if I can use the battery supply whilst connected but not actually charging.
Question: Has anyone accomplished battery backup from a primary mains supply with an LM317 or equivalent?
Looking forward to your help
Some nice features I'm wanting to add:
Things I know:
I'm currently in the process of rebuilding an alarm panel originally built with Picaxe chips. The power supply is one major area that I want to improve/get right this time.
I am feeding the entire project from a 48v 5A DC power supply. The alarm system is broken down in to smaller sections, where each section probably draws between 0.8-2A of current, but in total i'm sure it's less than 4.5A.
The 48v power supply voltage is dropped down to suitable voltages for specific parts:
48v In -> LM2596HV -> 24v out
24v In -> MP1584 -> 12v out (relays etc)
24v In -> MP1584 -> 5v out (Picaxe and other 5v IC's)
24v In -> MP1584 -> 5v out (Nextion HMI only)
24v In -> MP1584 -> 3.3v out (for 3.3v IC's)
I am going to use a Picaxe 18M2+ to monitor the voltages via divider circuits and Analog pins. Currently calculating the resistor combinations. No problems here.
I am wanting to add 2x 12v 7aH/12aH sealed lead acid batteries as a backup for when the mains fails.
I'd really appreciate some guidance and perhaps help designing the cheapest yet suitable and safe battery backup and charger circuit (I don't want an alarm starting a fire!) to kick in when the mains supply fails, in order to maintain 24v input to the other regulators- keeping my system alive.
I've found numerous guides detailing (see here) the use of an LM317 to make an independent charger- but I don’t know how to make the battery supply take over from the mains PSU and serve as the 24v supply. I guess the charger end might be taken care of with the above link...?
Concern 1: The LM2596HV is currently adjusted to output 24v when 48v is provided- I can't just attach the battery to this due to the output voltage dropping below 24v- so I need to prevent the battery voltage going backwards through this module and my mains PSU.
Concern 2: With the above link- It doesn't show if I can use the battery supply whilst connected but not actually charging.
Question: Has anyone accomplished battery backup from a primary mains supply with an LM317 or equivalent?
Looking forward to your help
Some nice features I'm wanting to add:
- 18M2 needs to know when the mains supply is lost, and that batteries are being used. Could do this if the LM2596HV output ADC value is 0 and the LED's from the LM317 charger circuit feeding Picaxe inputs.
- Battery voltage needs to be maintained and monitored via ADC (not sure if I do this in the same way as a standard DC supply)
- Fuse on the battery line to prevent surges (never selected or used them before)
- Fuses on the 48v and 24v supply as above (self resetting ones? - again, never selected or used one before)
Things I know:
- How to program Picaxe confidently and write code.
- Ohms law
- Voltage dividers and ADC
- Connecting batteries in series= double voltage, same current
- Connecting batteries in parallel= double current, same voltage
- C/10 as the current to trickle charge
- Too deep discharge cannot be recovered from (though I'm not sure how deep that actually is)
- When a battery is fully charged, the voltage drops slightly. Detecting this can help me stop doing a fast charge, but instead a trickle.
- Possibly some other things
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