Battery backed up 12v & 5v supply

[oliverb]

Thanks Eric. All the hard work is done by Weather Display Software.

 

[carmusic]

i would go with something like that for the 5v regulator
**broken link removed**

 

[oliverb]

I built the circuit today with the 7805. The power consumption has gone up from 8watts with it's original PSU to 18watts. The 7805 gets really hot even with a large heat sink. I turned the voltage down to 7volts and the watt meter dropped to 8-9 watts. This confirms that it is the voltage drop across the 7805 that is using the extra power.

As an experiment I plugged the weather station and server into my old Belkin UPS. I took out the old 7ah battery and wired in my new larger 18ah battery. With the mains disconnected 0.6Amp was being drawn from the battery. Thats just under 8 Watts.

I would have thought using an inverter would be a very inefficient way of doing things.

 

[Hero999]

The power dissipation in a linear regulator is can be calculated with the following formula:
Pd = (Vin-Vout)/I

If you don't want to use a large heat sink then you need a switching regulator which might actually work out cheaper than a large heat sink.

 

[ericgibbs]

I built the circuit today with the 7805. The power consumption has gone up from 8watts with it's original PSU to 18watts. The 7805 gets really hot even with a large heat sink. I turned the voltage down to 7volts and the watt meter dropped to 8-9 watts. This confirms that it is the voltage drop across the 7805 that is using the extra power.

As an experiment I plugged the weather station and server into my old Belkin UPS. I took out the old 7ah battery and wired in my new larger 18ah battery. With the mains disconnected 0.6Amp was being drawn from the battery. Thats just under 8 Watts.

I would have thought using an inverter would be a very inefficient way of doing things.

hi Oliver,
A point to consider, they do make 6V SLA batteries.
Using a +5V VLO drop 1A regulator would help cut the losses and use a suitable mains adaptor charger for the 6Vbty.

 

[oliverb]

The trouble is I need 12 for the weather station. I could use a 12v and 6v battery though.

 

[ericgibbs]

The trouble is I need 12 for the weather station. I could use a 12v and 6v battery though.

hi,
Thats what I would consider, ie; dual batteries.
The amp hour capacity of the 12V and 6V chosen to suit the standby load.
Also by adding the 6V battery the overall 'running on battery supplies' period would be increased.

It would be a simple matter to use the 12V charge system, with a step down regulator tapped in to float the 6V.