Battery backed up 12v & 5v supply

[oliverb]

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

 

[ericgibbs]

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,
The basic layout is OK, it requires some extra components to make a practical sytem.

I'll mark up your dwg and repost.

 

[oliverb]

Thanks ericgibbs

 

[ericgibbs]

Thanks ericgibbs

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.

 

[oliverb]

Thanks ericgibbs have added your extra components and redrawn below.

I will of course add a fuse as near to the battery as possible.

I presume 2amp regulators with heatsinks will do?

Brett.

 

[ericgibbs]

Thanks ericgibbs have added your extra components and redrawn below.

I will of course add a fuse as near to the battery as possible.

I presume 2amp regulators with heatsinks will do?

Brett.

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.

The LM317 may a heatsink, try it first.

 

[Hero999]

How long do you want it to last for?

The 5V output could last twice as long if you used a switching regulator.

 

[oliverb]

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.

 

[Hero999]

I think you've misunderstood me, it will last for years run off the 16V supply.

I was asking you how long would you like it to run from the lead acid battery?

 

[oliverb]

I have an 18ah battery and the power tends to be out for 2 to 4 hours on average. There will be 800mA max through the 5v reg.

I presume a switching regulator is more efficient?

I have never used one before do you have an example I could look at?

 

[Hero999]

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.

Official Home Page of Roman Black

 

[oliverb]

May be worth taking a look at as the PSU will be on 24/7 and when the mains fails I will get a bit more out of my battery.

The devices seem to be very hard to get hold off. I found this 5V 1A Switching Voltage Regulator [DE-SW050] - £7.83 : Total Robots, Robotics, Control and Electronics Technology £12 odd including postage.

I think I will build with the 7805 and see what power it draws then I can always pop one of the above in as it is pin for pin compatable.

 

[Hero999]

Did you look at the schematic I linked?

It's much cheaper to build than that.

You can buy ICs that will do it, i.e. MAX649, try searching Linear Technology, Maxim and National Semiconductor websites for many more.

 

[ericgibbs]

May be worth taking a look at as the PSU will be on 24/7 and when the mains fails I will get a bit more out of my battery.

The devices seem to be very hard to get hold off. I found this 5V 1A Switching Voltage Regulator [DE-SW050] - £7.83 : Total Robots, Robotics, Control and Electronics Technology £12 odd including postage.

I think I will build with the 7805 and see what power it draws then I can always pop one of the above in as it is pin for pin compatable.

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.?

 

[oliverb]

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.

 

[oliverb]

Did you look at the schematic I linked?

It's much cheaper to build than that.

You can buy ICs that will do it, i.e. MAX649, try searching Linear Technology, Maxim and National Semiconductor websites for many more.

Just checked it out looks interesting. Will look into MAX649 as well.

 

[ericgibbs]

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.

hi,
Been looking at the technical specs for your weather station, quite impressive.
Not suprised it takes that much power to operate.

Can you say where you are located in the UK.?

What use do you put all this weather data too.?

 

[shokjok]

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.

 

[oliverb]

hi,
Been looking at the technical specs for your weather station, quite impressive.
Not suprised it takes that much power to operate.

Can you say where you are located in the UK.?

What use do you put all this weather data too.?

Hi My weather station is in Kenley Surrey.
It's online here **broken link removed**

It's used for personal use / anyone who lives in the area or who wants to view it.

 

[ericgibbs]

Hi My weather station is in Kenley Surrey.
It's online here **broken link removed**

It's used for personal use / anyone who lives in the area or who wants to view it.

hi Oliver,
Looked at your site, now thats a professional looking website, well done.