DC to DC UPS (Help!)

Hi i am trying to build a sort of DC TO DC ups for my modem/router, please look at the image attached for my project plan. I was able to find many charging circuits online but i cant understand what value relay and capacitor should be used. can any one help me with this project. Thanks in advance.


Picture of DC to DC UPS (Help!)
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Goodhart6 years ago

As you can see "in this over simplified schematic" the need for a "relay" is eliminated (would be too slow anyways) BUT that the "switching circuitry" is included within the diode configuration.
spooge (author)  Goodhart6 years ago
This is exactly what i needed, Thanks. Can you please tell me what transfer will go well with this circuit or I can just pick up an after market adapter to hook up with it in that case what voltage/amps should i get?
spooge (author)  spooge6 years ago
I forgot to add does this circuit has overcharge protection, if not how to i add that?
Goodhart spooge6 years ago
I don't see it in the one I supplied;  to "add" it may mean a bit of modification (but then, since that schematic IS just a basic example, it will need adjusted anyways), to accommodate something like this maybe...
Goodhart spooge6 years ago
It was just an example of "how" they are made; specifics would need to be worked out per each type of load and such. One thing though, the faster the switching diodes used the better it is at "picking up without dropping" too often :-)
A relay switchover setup should not actually be needed. I think you could power the modem from the battery, with the charging circuit attached all the time.

This would be somewhat akin to your cars electrical system, where the electrical loads are connected to the battery, and so is the "charger" (alternator) which keeps the battery charged, at least while the vehicle is running. If you turn off the vehicle, you can continue to power the loads, but if you deplete the battery to far you won't be able to start the vehicle again.

The charging circuit output would need to be sufficient to handle the load of the modem and still keep the battery "topped off" during normal operation.