lbenson
Senior Member
I'm looking for a simple charger for a 12V backup SLA, say 10Ah, from mains (e.g. 18V laptop charger)--LM317 with appropriate components seems simple enough, as in this 6V charger thread: http://www.picaxeforum.co.uk/showthread.php?27999-6-VOLT-1Ah-SLA-Charging-problem
The conditions of use are as follows:
1 criticality of operation: not critical, merely desirable.
2 frequency of use probably much less than .5% of the time, maybe 2 days per year, usually in smaller chunks.
3 duration of use: minutes to days, shutoff when < 11.9V (by picaxe, not shown in circuit below).
4 safety of charger to prevent damage to battery: important
5 efficiency of charger: doesn't really matter (within reason)
6 need to be fully topped off at end of charge: not very important
The devices powered are picaxe 14M2, cable modem (internet), wireless router (the latter two have 12V 2 amp and 1 amp wall warts respectively). The most important thing the picaxe will do once mains go off is send an email that it has, but it will also monitor temperatures and door openings in the vacant house and send email updates.
I have used a UPS in the past, but think that an inefficient way to go (as far as runtime for a given 12V SLA goes). The UPS battery died, so I figured this would be a good time to start this project.
Here is a thread which has the following LM317 charging circuit: http://www.circuitstoday.com/battery-charger-circuit-using-lm317
In the comments, the author says this circuit is really for 6V charging, but changing the value of R4 to 1K2 would make it work for 12V (Note in image to that effect added by me). Also, I don't have for R1 a .56 Ohm resistor, 1 Watt or 5 Watt, for current limiting, but think I have a 1 Ohm 5 Watt resistor, which would allow less current.
Would this circuit with the change to R4 and R1 be suitable for my purposes? (The circuit by which the picaxe switches from mains to battery is a different matter--I also want to be able to power-cycle modem and router since they occasionally lock up).
The conditions of use are as follows:
1 criticality of operation: not critical, merely desirable.
2 frequency of use probably much less than .5% of the time, maybe 2 days per year, usually in smaller chunks.
3 duration of use: minutes to days, shutoff when < 11.9V (by picaxe, not shown in circuit below).
4 safety of charger to prevent damage to battery: important
5 efficiency of charger: doesn't really matter (within reason)
6 need to be fully topped off at end of charge: not very important
The devices powered are picaxe 14M2, cable modem (internet), wireless router (the latter two have 12V 2 amp and 1 amp wall warts respectively). The most important thing the picaxe will do once mains go off is send an email that it has, but it will also monitor temperatures and door openings in the vacant house and send email updates.
I have used a UPS in the past, but think that an inefficient way to go (as far as runtime for a given 12V SLA goes). The UPS battery died, so I figured this would be a good time to start this project.
Here is a thread which has the following LM317 charging circuit: http://www.circuitstoday.com/battery-charger-circuit-using-lm317
In the comments, the author says this circuit is really for 6V charging, but changing the value of R4 to 1K2 would make it work for 12V (Note in image to that effect added by me). Also, I don't have for R1 a .56 Ohm resistor, 1 Watt or 5 Watt, for current limiting, but think I have a 1 Ohm 5 Watt resistor, which would allow less current.
Would this circuit with the change to R4 and R1 be suitable for my purposes? (The circuit by which the picaxe switches from mains to battery is a different matter--I also want to be able to power-cycle modem and router since they occasionally lock up).
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