I need to build a battery backup circuit for my Oregon WMR 928 weather station.
The weather station itself runs at 12v max 300mA and the weather server runs at 5v max 800mA.
I would like to run it from a 12v sealed lead acid battery so the circuit must have trickle charge built in for this type of cell.
I first thoughts are to get rid of the 2 ac adaptors that came with the devices and build a new combined 12 & 5v PSU using voltage regulators. The trouble is where do I connect my battery?
Have uploaded a pic of my basic thoughts without any major details.
Any ideas, suggestions or circuits would be appreciated.
Brett
I need to build a battery backup circuit for my Oregon WMR 928 weather station.
The weather station itself runs at 12v max 300mA and the weather server runs at 5v max 800mA.
I would like to run it from a 12v sealed lead acid battery so the circuit must have trickle charge built in for this type of cell.
I first thoughts are to get rid of the 2 ac adaptors that came with the devices and build a new combined 12 & 5v PSU using voltage regulators. The trouble is where do I connect my battery?
Have uploaded a pic of my basic thoughts without any major details.
Any ideas, suggestions or circuits would be appreciated.
Brett
hi,
Have a look at this dwg, sorry its a bit rough, any questions please ask.
Dont forget to remove the dry batteries from the units before you connect the external 12/5V supplies.
I have added an LED to show when charging.
If you cannot get 12.8V then reduce the 220R to 180R on the LM317.
hi,
The LM317 is rated at 1.5A max and the 7805 is 1Amp.
I would consider this would be good enough for a trickle/float charge, I dont expect the modules take much current.
I need it to last for years.
How long is twice as long?
I have regulators on some of my clocks that have been on for 10 years continuously and are still working.
This simple switching regulator has an efficiency of 77% at 800mA when run from 15V, the LM7805 has an efficiency of just 39% at 12.8V. At 12.8V it's likely to be slightly more efficient and the current consumption will be about 400mA. You could probably tweak the efficiency up a bit by using a better higher powered transistor and altering a few component values.
hi Oliver,
Question is, how long do your mains failures last.?
Worst I've known in the UK is about 30 minutes.
I would think the amount of current the two weather modules take
[ as they were designed for dry battery use] will be milliamps.
EDIT: how long do they last on internal batteries and what type are they.?
hi Oliver,
Question is, how long do your mains failures last.?
Worst I've known in the UK is about 30 minutes.
I would think the amount of current the two weather modules take
[ as they were designed for dry battery use] will be milliamps.
EDIT: how long do they last on internal batteries and what type are they.?
Both units are mains powered. The WMR928 has internal batteries that will last a day on mains failure but it will stop outputting data during this time. This needs 300mA at 12v.
The server has no provision for batteries and shuts down as soon as the mains goes off. I have measured this at 800mA at 5v.
My last mains fails was 2 days ago and lasted 2 1/2 hours and this was the 3rd power fail this year. People at work lost it for 2 days solid. According to the BBC it's due to get worse as 4 power stations are due to go off line soon with the replacements not due until I think 2018. I have got so fed up with it I now have an inverter powered from a car battery to keep my gas boiler running while the power is down.
Both units are mains powered. The WMR928 has internal batteries that will last a day on mains failure but it will stop outputting data during this time. This needs 300mA at 12v.
The server has no provision for batteries and shuts down as soon as the mains goes off. I have measured this at 800mA at 5v.
My last mains fails was 2 days ago and lasted 2 1/2 hours and this was the 3rd power fail this year. People at work lost it for 2 days solid. According to the BBC it's due to get worse as 4 power stations are due to go off line soon with the replacements not due until I think 2018. I have got so fed up with it I now have an inverter powered from a car battery to keep my gas boiler running while the power is down.
I am working on an AC detector using a 4N25 opto. When AC is present, the opto is on and the relay N.O. contacts allow the solar panels to charge the battery through a diode triangle. When the sunlight is low enough to disable the relay, the N.C. contacts enable the battery to power the unit until the mains are restored.