Electrics electronics expert required..

[mark69sheer]

Hi, I have a need to design some electrics...

I need to power two devices from a battery for a number of weeks.
I am wanting to use a car type battery to feed power to two devices.

one device requires 9v dc rated at 0.5 4.5VA

the other device requires 12v dc rated at 1000mA

I am not bothered what Amp hr rating the feed battery is the only proviso is that I need the two devices be powered for a minimum of ten weeks , preferably 20 weeks from one charge.

Its to recreate the output of a couple of chargers using some form of 12v battery as there is no power in the building the devices require.

Many thanks for any help... I haven't a clue.

[miniman]

Well, I would say the simplest solution would be to connect an inverter and simply plug the 240v chargers into it. I'm no expert, but I would say the current draw isn't going to be significantly different to any other transformers plugged into the battery to achieve the same thing. A pair of batteries in parallel would increase the lifespan.

[Mikey G]

mark69sheer said:

Hi, I have a need to design some electrics...

I need to power two devices from a battery for a number of weeks.
I am wanting to use a car type battery to feed power to two devices.

one device requires 9v dc rated at 0.5 4.5VA

the other device requires 12v dc rated at 1000mA

I am not bothered what Amp hr rating the feed battery is the only proviso is that I need the two devices be powered for a minimum of ten weeks , preferably 20 weeks from one charge.

Its to recreate the output of a couple of chargers using some form of 12v battery as there is no power in the building the devices require.

Many thanks for any help... I haven't a clue.

Just taking that one into consideration you would require a battery with a capacity of 1680Ah just to last the 10 weeks (24x7x10) Not many of those size batteries kicking about!

[mark69sheer]

Cheers miniman.
I have an inverter and could do this but inverters are expensive and I may need to replicate it if possible a number of times. Also the inverter seems to get very hot and must use a fair amount of energy meaning the battery would drain rather quickly.
I need to design a custom circuit so I can build it for around £35 including spending around £20 for the 12v battery.

[eliot]

Use an LM7809 and LM7812 respectively, simple 3 legged device - battery in, ground, 9v out

http://www.cdil.com/datasheets/lm7809.pdf
http://www.cdil.com/datasheets/lm7812.pdf

[mark69sheer]

Mikey G said:

mark69sheer said:

Hi, I have a need to design some electrics...

I need to power two devices from a battery for a number of weeks.
I am wanting to use a car type battery to feed power to two devices.

one device requires 9v dc rated at 0.5 4.5VA

the other device requires 12v dc rated at 1000mA

I am not bothered what Amp hr rating the feed battery is the only proviso is that I need the two devices be powered for a minimum of ten weeks , preferably 20 weeks from one charge.

Its to recreate the output of a couple of chargers using some form of 12v battery as there is no power in the building the devices require.

Many thanks for any help... I haven't a clue.

Just taking that one into consideration you would require a battery with a capacity of 1680Ah just to last the 10 weeks (24x7x10) Not many of those size batteries kicking about!

jeez thats took me by surprise. It only powers a gsm module.

so 1000ma = 1 A doesn't the rating of the battery make a difference to how long it lasts?

[mark69sheer]

eliot said:

Use an LM7809 and LM7812 respectively, simple 3 legged device - battery in, ground, 9v out

http://www.cdil.com/datasheets/lm7809.pdf
http://www.cdil.com/datasheets/lm7812.pdf

Any suggestions as to which 12v battery or rating to get the length of service?

Do I need to do anything to alter the draw of the units or will they just take what they need without frying?

Edited by mark69sheer on Friday 17th October 20:55

[esselte]

mark69sheer said:

Mikey G said:

mark69sheer said:

Hi, I have a need to design some electrics...

I need to power two devices from a battery for a number of weeks.
I am wanting to use a car type battery to feed power to two devices.

one device requires 9v dc rated at 0.5 4.5VA

the other device requires 12v dc rated at 1000mA

I am not bothered what Amp hr rating the feed battery is the only proviso is that I need the two devices be powered for a minimum of ten weeks , preferably 20 weeks from one charge.

Its to recreate the output of a couple of chargers using some form of 12v battery as there is no power in the building the devices require.

Many thanks for any help... I haven't a clue.

Just taking that one into consideration you would require a battery with a capacity of 1680Ah just to last the 10 weeks (24x7x10) Not many of those size batteries kicking about!

jeez thats took me by surprise. It only powers a gsm module.

so 1000ma = 1 A doesn't the rating of the battery make a difference to how long it lasts?

Yes, a 40 amp/hr battery will supply 1amp for 40 hrs.So you're looking for something that will supply 1amp for 1680 hours....

[eliot]

nope.
I would actually measure the drawn current with a digital multmeter, 1amp seems quite a bit for a gadget, i bet you its only pulling a few milliamps. Just because the wall adapter is "rated" at 1a (1000ma) - doesn' mean it uses it.

- my megasquirt ECU draws a few hundred milliamps and you can run it of a 9V PP9 battery.

[dilbert]

Mikey G said:

mark69sheer said:

Hi, I have a need to design some electrics...

I need to power two devices from a battery for a number of weeks.
I am wanting to use a car type battery to feed power to two devices.

one device requires 9v dc rated at 0.5 4.5VA

the other device requires 12v dc rated at 1000mA

I am not bothered what Amp hr rating the feed battery is the only proviso is that I need the two devices be powered for a minimum of ten weeks , preferably 20 weeks from one charge.

Its to recreate the output of a couple of chargers using some form of 12v battery as there is no power in the building the devices require.

Many thanks for any help... I haven't a clue.

Just taking that one into consideration you would require a battery with a capacity of 1680Ah just to last the 10 weeks (24x7x10) Not many of those size batteries kicking about!

He's right, you're looking at about 80 car batteries to do that for twenty weeks.
If you're just reading the numbers off the paperwork, then you can probably do better than that, but you need to measure the actual consumption.

You also need to bear in mind that a switch mode psu will only be about 80% efficient.

Edited by dilbert on Friday 17th October 21:08

[john_p]

That 1A may be while it's transmitting at full power, so if a) you're in an area with good signal and b) your device only transmits every 5min/30min etc then you may find the average load is much reduced.

Otherwise you'll struggle to get 20 weeks out of a battery supplying 1A, even with a whacking great marine battery.

[Zad]

I make that 2,443 Ampere hours.

A heavy duty battery like a Varta 644 is 90 Ampere hours. You would need 20 of them to power that lot for 20 weeks.

[mark69sheer]

Looks like back to the drawing board.
I wrongly assumed a car type battery fully charged would easily power a gsm module for a number of weeks.

Then I remembered how your mobile needs charging every two days..

I assume using an inverter and plugging the chargers in would simply be worse.

[Roger McLittriss]

Autostarting diesel generator?

OK, sorry...


The talk of amp/hour ratings is slightly erroneous and assumes a number of perfect situation factors; in practice a 1000A/h battery would NOT give you 1A for 1000 hours no matter what the makers may claim.
Even loaded intermittently (eg 50mA standby for 5 minutes then 1A for 1 minute) the cells will gradually deteriorate, recovery getting slower until the battery has no time to get back up to full volts from the last loading, which speeds up the deterioration etc etc.
Also have to allow for such factors as ambient temperature (presumably a building with no power has no heating either); cold batteries get sluggish.
Whatever you do, don't use anything by Uniross...

[dilbert]

mark69sheer said:

Looks like back to the drawing board.
I wrongly assumed a car type battery fully charged would easily power a gsm module for a number of weeks.

Then I remembered how your mobile needs charging every two days..

I assume using an inverter and plugging the chargers in would simply be worse.

You'll probably find that you can get pretty close to what you want, but I doubt very much that you could use your mobile phone constantly for more than an hour two so without charging it.

You just need to make some measurements, and then estimate the duty.

I think my mobile is about 76 mins talk time, but if you don't use it, it stays charged for about a week.

You can probably use a solar panel to keep up with idle use, so that you can get the best out of your batteries.

Edited by dilbert on Friday 17th October 21:20

[Deva Link]

mark69sheer said:

Looks like back to the drawing board.
I wrongly assumed a car type battery fully charged would easily power a gsm module for a number of weeks.

Then I remembered how your mobile needs charging every two days..

The very first one I had in my car, in 1987, would flatten the battery (the car battery, that is) in half an hour.

mark69sheer said:

I assume using an inverter and plugging the chargers in would simply be worse.

Yep. As you said earlier, that heat generated is produced by power from the battery.

[Roger McLittriss]

Deva Link said:

mark69sheer said:

I assume using an inverter and plugging the chargers in would simply be worse.

Yep. As you said earlier, that heat generated is produced by power from the battery.

Still, it'd keep his shed warm

[spikeyhead]

mark69sheer said:

Hi, I have a need to design some electrics...

I need to power two devices from a battery for a number of weeks.
I am wanting to use a car type battery to feed power to two devices.

one device requires 9v dc rated at 0.5 4.5VA

the other device requires 12v dc rated at 1000mA

I am not bothered what Amp hr rating the feed battery is the only proviso is that I need the two devices be powered for a minimum of ten weeks , preferably 20 weeks from one charge.

Its to recreate the output of a couple of chargers using some form of 12v battery as there is no power in the building the devices require.

Many thanks for any help... I haven't a clue.

It may be possible if you can get some 48V batteries used to back up telephone exchanges and a suitable switch mode power supply.

A decent antenna on the gsm module will also reduce the power required if you're in a low signal area.

However the solution won't be cheap.

[Rebuilda]

Mark
I have a couple of gel batteries you can have to experiment with if thats any help. They are replacements for a large UPS from a computer rack. I am near Bolton.
Silly questions time.
Do you have access to a multimeter to measure the current drain of the devices when operating? As Eliot says the supply may be rated a lot higher than the actual consumption figure especially is it is being used to charge an internal battery as well as power the device.
Once you have the figure for the total current consumed then a solar trickle charger with double (or higher) rating, coupled with one or two of aforementioned gel batteries would keep the devices going for ever providing they get more than 12 hours light a day.

The other alternative if, for example, it was for a lock up would be to fit a normally closed microswitch to the door, wire that to a battery with a coil on the other end and run the HT to the door handle on the inside, just a deterrant of course...

[polus]

mark69sheer said:

Looks like back to the drawing board.
I wrongly assumed a car type battery fully charged would easily power a gsm module for a number of weeks.

Then I remembered how your mobile needs charging every two days..

I assume using an inverter and plugging the chargers in would simply be worse.

How did you arrive at those figures, from the supplies of the 9V and 12V device? What are these devices?

Ive knocked up a prototype tracking system, the GPS module and microcontroller used 50mA 3.3V average. Switch mode regulator at about 80% odd efficiency from 12V... Not sure how much a car battery is but 50A/hr will last (erm) around 18 weeks. If your figures are correct your going to need several but I doubt the actual devices use anywhere near that amount.

I used a switcher in my design, similar to this:
http://www.national.com/pf//LM/LM2734.html

Both http://rswww.com/ and http://www.farnell.co.uk/ do some "DC to DC converter"s in boxes which is what you want (Im presuming that going down the electronic design route is not on the cards).

You'd need the inverter spec and the two supply specs to work out the efficiency but I wouldnt bother as its too inefficient.

mark69sheer said:

Looks like back to the drawing board.
I wrongly assumed a car type battery fully charged would easily power a gsm module for a number of weeks.

Then I remembered how your mobile needs charging every two days..

I assume using an inverter and plugging the chargers in would simply be worse.

GSM module, yep, it will as they are only 20-200mA depending on what its doing (sleep, idle. tx data). Is it a mobile phone your using and not a GSM module? The killer in mobile phones is the fact that they have a couple of hundred Mhz processors and an LCD with a backlight.

Edited by polus on Friday 17th October 23:04