We currently use a LiFePO4 40A battery charger to charge a bank that will provide sustained power to our main DC bus in cases of power outage at a rural location. I want to modify this system to take the 120VAC input power to utilize a more appropriate and regulated DC switching power supply source for all the downstream 24V DC instrumentation and electronics.

I would preferably like the 24V battery power to be available immediately and not switched like you see on some budget UPS systems. Just dropping a 480W AC/DC regulator we have on the shelf is an option, but I have reservations about that. Even with a diode added to prevent the charger from backfeeding into the output of the new regulator, I am concerned that the regulator being added would potentially trigger into an overloaded fault state if the bank charge fell too low and it attempted to charge the bank with the regulator during normal use. What is the traditional approach here without utilizing complex, custom circuitry and still allowing for a seamless transition between the switched source?

Right now, all the downstream instrumentation can handle the max DC output voltages from both regulator and charger, but it seems more appropriate to ensure a reliable 24V DC bus with less voltage variance since new DC instrumentation with a narrower input voltage threshold isn't out of the question. I was thinking a Zener diode across the DC bus to regulate excess voltage would address this, but it would not address the overloading of the regulator.

Thanks

 

Another simple possibility in my mind is to put an additional diode -- a power Schottky diode with an ultra-low Vf, for example -- in between the battery charger's positive junction and the positive on the DC bus. The quiescent losses would be about 25W, but I'm not sure that's a bad thing if cost and simplicity are favored over efficiency and heat dissipation (in this case.)

 

I used a 1000W 48VDC power supply into a MPPT solar charge controller (up to 100vdc input) set for a 24VDC LiFePO4 battery bank for my system. You can set the bulk and float voltage, while the charge controller handles isolation issues.

You also need to get the correct type of power supply. Don't get one with hiccup current limiting. You need a power supply with Constant Current Limiting or fold back current limiting.
https://www.power-supplies-australi...Q8LAJMcxB5YcAff3xqMyeEHOiGKyZbz5_zzpugkCBNHku

 

I suggest thst FIRST, you investigate the circuit of the battery charger to understand exactly what it will do when it loses mains power while charging the battery. If all current between the charger and the battery ceases, then you are OK. By "all current ceases" I mean no current at all flowing in either direction, back into the charger or from the charger. As for the effect on the system from the added power supply, you would need to also verify that it will not draw current from the battery when the supply is not powered. I HAVE SEEN an otherwise very good power supply emit smoke when it was connected to a battery while not powered.
With the battery directly connected to the load, as shown, there is no delay or disturbance of the voltage when the mains power to the charger is lost.