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Hello and thank you in advance for pointing me in the right direction.

I finally started designing my own PCBs. If I set up a PCB with a 110 to 5v power source (HLK-PM01), could I then add another 5v from a different power source that has battery backup connected directly to the HLK-PM01?

The goal here would be for the PCB to get its main source from the HLK-PM01 using the 110v source, but if 110v goes out it would draw from the other source also connected.

The other question is similar. I have a 110v to 24V 40A power source. To it I connected a 24v battery pack that I made. If I wanted to get more battery, seems the "usual" way is to replace the current battery pack with a larger one.

Would it be a bad idea to have multiple 24v packs all connected to the same 24v power source? When 110v is working, it is providing 24v to all battery packs and connected devices, but when 110v all battery packs would be sharing the load of the connected devices, at least that is my goal.

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    \$\begingroup\$ Welcome! Please draw a schematic of what you are proposing. \$\endgroup\$
    – winny
    Commented Jul 13 at 7:57

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Assume first question is: Suggest a circuit to connect both a primary and a backup DC voltage supply to a load with preference to the primary? The answer depends on the voltages and reverse current characteristics of the two supplies. Probably the easiest way is choose the AC-mains-fed primary supply output to be at a slightly higher voltage than the battery-fed backup supply. If either supply can't tolerate having the other supply back feed voltage onto the supply that is lower or off, then place a diode in series with the intolerant (possibly both) supply's positive output with the two diode cathodes connected together and to the load, while directly connecting the grounds of the supplies and load together. This is commonly called a diode-OR power-sharing circuit, because power comes from supply A OR B depending on which has higher voltage output. Other fancier ways exist to do similar with less power loss by using FET switches to steer the current, some of which are described in the linked question/answer.

Assume your second question is: Can I combine two batteries of the same voltage in parallel for extra capacity, both for charging and discharging? The short answer is that you can safely connect two battery packs with the same chemistry and voltage in parallel if you first charge them independently to the same final voltage before the initial connection. After the parallel connection, they will operate as one larger battery for both charging and discharging, and the resulting capacity is the sum of the two individual capacities (which do NOT need to be identical). Read some relevant Q&A on such systems. However, if the battery packs contain an internal Battery Management System (protection electronics) like many modern Lithium-based bulk storage battery packs, then first consult the battery instructions for details if parallel connections are supported. Do not ever connect different battery chemistries in parallel, even if they are same voltage range (e.g. a lead-acid 12V battery in parallel with a 12V LiFePO4 battery is not going to work well, because the term "12V battery" actually describes a range of operating voltages that is not identical between chemistries, and no battery charges or discharges at just 12.0V).

You mentioned you have a 24V power source from AC-mains full-time connected to a 24V battery pack you made. Just take care that if the power source is not intended as a 24V battery charger, but rather is a constant-voltage AC-DC supply, that you adjust the output voltage to a proper "float charge" for your battery chemistry, which will not be 24.0V. And please be aware when building your own series cell battery pack, that you should appropriately match cell capacities and balance the cells as needed.

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  • \$\begingroup\$ Thank you so much. I can say I understood 80% of your reply. Confident with a quick look at the link you shared I will be able to fully understand. To expand on the second answer you gave me. I have an 18 cell pack 6 sets of 3 connected in sequence. I am using a hx-6s-12a BMS. Will check data sheet for parallel connection info. In general do BMS take care of the "float charge". I am pretty sure I do have a constant-voltage AC-DC supply. \$\endgroup\$
    – Cancun Manny
    Commented Jul 13 at 23:50
  • \$\begingroup\$ Oddly enough, I do/did know what parallel connection meant, but in my head I picture parallel connections "together", but in essence yes I am connecting in parallel just with longer connections in between the packs. Just got to make sure correct size wire for the amount of load I want to put \$\endgroup\$
    – Cancun Manny
    Commented Jul 13 at 23:57
  • \$\begingroup\$ With regard to BMS and charging, the BMS will cutoff when the any monitored battery cell voltage or the string reaches a maximum voltage or if the current exceeds maximum rating, and will help balance the cells. The battery charger is generally responsible for changing charging mode from initial constant current, to later constant voltage, and then if appropriate, reducing the voltage to a float charge. Float charge is not recommended for Li-Ion batteries, as extra time spent at full charge tends to degrade life and they don't self-discharge very quickly. \$\endgroup\$
    – BK303
    Commented Jul 15 at 1:29

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