Portable power - part II

[Adrian]

HI Folks

Regular readers may remember the discussions last week about powering a combination of things like laptops, wireless internet aerials and so on from a portable power source...

All was fine at the weekend - managed to scrounge the use of a little

650W Honda 'suitcase' genny - which worked well...

This evening I finally found the spare DC plug for the laptop (ancient Toshiba Portege 7020TC) - and had a quick play with feeding it from a variable DC source.

Turns out that, with the internal battery fitted to the laptop, running with less than 15V input will flatten the internal battery.

However.... if you remove the battery, the laptop will boot & run from as little as 11.5V (though it does object if the volts drop to 11V). Also - the power consumption without the battery fitted is much lower than with it installed - in the region of 200 - 250mA, rather than 2A

So - as the wireless internet 'antenna' will also (allegedly - haven't tried it) run from 12V dc - what's to stop me from running the whole lot at 12V from dryfit or leisure batteries ?

FWIW - the laptop battery (which is probably part-defunct anyway) is rated at 10.8V / 3000mAh

Provided the laptop runs OK at the reduced voltage, I can't actually damage it at the lower voltage, and without the battery fitted, can I ??

Still sort of DIY - as the next step will be constructing some kind of enclosure / wiring harness for either dryfit or leisure batteries

Thanks in advance for any comments

Regards Adrian

[George]

High amp batteries is potentially dangerous on lappys should you accidently short something when powering it up? I'm sumising these dryfit are of the alarm type? which carry a heavy amperage.

I've rigged up 12v to 5v converter using a flat type laptop battery,the converter is just a 5v regulator attached to two spade terminals and the spade terminals plug onto the battery as they would in the lappy. I use this for when I'm going to be out and about with the digital camera and have the battery in my back pocket with leads long enough for movement to the camera...sure I can buy quite a few rechargables but this way I can go all day snapping without changing batteries.

[meow2222]

dont think so. If the onboard reg is failing to regulate then the internals can run below rated voltage, but that wont damage any circuits. If the fan is 5v no change, if its 10.8v then the fan will run slower, and thus run more of the time... laptops are pretty tolerant of that though, the fan not on at all most of the time.

All lead acids can indeed deliver high currents, and a fuse should be fitted close to the battery. Problem solved.

NT

[Adrian]

HI George

Thanks for the comments....

George wrote:

Yes - the particular item I'm looking at is rated 12V 12AH - sealed lead acid (heavy little blighter!) - and no doubt has a terrifying lagre short-circuit current - but then, don't they all....

This laptop came originally in a little samsonite briefcase (think it belonged to some financial insitution or other) and so I was going to see about fitting it all, plus the battery, back into the same case - so there'd be no need for anything to be plugged or unplugged out in the field..

I'm always surprised by the battery life on my little Fuji F10 digital camera - seems to run forever before the battery starts to sag. My first digital camera (one of the 'Flip-up' Ricohs - quite a few years ago) used to eat rechargeable AA cells for breakfast - but technology has clearly moved on!

Regards Adrian

[Adrian]

I wish that was true of this one ! - theres two fans (one on the laptop and one in the docking station) and while they're not 'angle-grinder'-noisy, you certainly know they're running.....

The little battery / power monitor is even smart enough to know that the battery is 'not present' - so I guess it's not that unhappy about it...

..running quite happily now at a shade under 11.5V - so I guess the next step is to rig up the antenna and see how much 'juice' that wants. The lappy can spend much of its time on the Markets 'asleep' - so long as it can spring into life when asked.... don;t know if the antenna (which is a little 5gigs transciever that looks like a network connection to the laptop) also 'dozes' - we'll have to see....

My thoughts exactly ! Thanks Adrian

[Adrian]

HI All

Correcti> HI Folks

[meow2222]

does the fan run non stop? That would be unusual for a lappy. P1s generally have a reduced clock speed option to prolong battery life and by running stuff cooler it avoids the fan running, I dont know whether you've tried that or whether its still fast enough. Its a BIOS setting.

NT

[Adrian]

It's an unusual lappy . Came to me in a waitrose carrier bag, as a tangle of wires and circuit boards, with a duff display. Found a similarly broken machine on eBay, cannibalised the two to make one, then sold the remaining bits (with appropriately hones description) back on eBay.

Didn't actually cost me anything - and it's worth every penny

It usually lives out in the glass studio as a sort of jukebox - playing mp3's from a big hard disk on the network....

Had a delve in there - the fan is already set to 'quiet' (yeah - right !) but have dropped the CPU speed down to see if that makes any difference..

Fans probably want cleaning - but that's a fairly major strip-down - and life's too hectic to do that right now...

Laptop, docking station and antenna together pull a maximum of about 2A at about 12V, dropping to 9/10 of nothing when the laptop goes to sleep

- so battery operation from an SLA is looking like an option....

It's not as though the web link is going to be in constant use througout the day - more a matter of having it 'available' from the publicity point of view....

Many thanks Adrian

[The Natural Philosopher]

Thats a 3 cell Li-ion pack: 12.6 v fully charged, about 9v at deaths door. If you want to charge rarer tha replace it, if its a bare cell with no electronics, never ever go above 12.6v.

If its got electronics, your figure of 15v to get it to charge is reasonable.

Nope. It will be probably regulating that lot down to +-12v and a 5v for most of the guts, maybe less.

[The Natural Philosopher]

Ah! 24W sounds not nresanable to me.

[Adrian]

Yes - generally between 1.5 and 2A - going up to 3 when the (flat) battery is installed and the volts are cranked up to 15....

Adrian

[Adrian]

Darn decimal points ! See other post for 'real' data

Ah - I see.... Modern replacements are available - but about 50 UKpounds - so I think I'll stick with this one

Right....

Have been runningth alaptop all afternoon on about 11.5v from a stabilised PSU - seemed happy. Much below that and it's not reliable at booting....

Any idea what the volts on a dryfit-type SLA look like over time on load

- are they like nicads in that they have a flattish 'volts against time' graph until they suddenly go downhill....?

I have this old 12v 12Ah dryfit kicking around - guess the next step is to try that running the laptop and see how long it lasts. Really only need 4 or maybe 5 hours running time from the kit between re-charges - so might just get away with it - depending on how 'virile' this old SLA is.... - I see that serious Ah-rated sla aren't cheap..... so let's hope that there's some life in this old one !

Many thanks Adrian

[The Natural Philosopher]

I think like mosts batteries they start off pretty high, rapidly decay to a sloping plateau, where 90% of the charge is, before falling off a cliff and buggering themselves.

But I do not have chapter and verse..more familar with Li and Ni chemistries really.

[Adrian]

I did some googling last night - saw some graphs which tend to support what you said (though no mention of falling off cliffs )

I guess the proof of the pudding will be to rig it all up (with a fuse!) and see how it runs. Might do that today - was going out to the local Saturday market - but today's weather forcecast is drizzle interspersed with heavy rain - so I'm not sure it's worth the bother... ..don'cha just love the Irish summers !

The 12Ah dryfit is part of a mains-to-50v switching power supply/ups that I bought as surplus a few years back - seems to have a fairly 'clever' charging circuit for the dryfit - so might just extend the battery leads from the charger to croc clips for easy charging of the dryfit..

Thanks again for the thoughts Adrian

[Andrew Gabriel]

That's exactly my experience with them in low end UPS's. However, in other applications such as alarms, I've got several which have been replaced after their routine 5 year replacement intervals. Some of these are now over 15 years old, and still have their original full capacity. I had one which went from working at full capacity to death in a very short time, but that did encompass me lending it to someone and I suspect they overcharged it.

My conclusion is that UPS's treat their batteries very badly, and given people know who to treat batteries well, I have to conclude they do it deliberately to maintain sales. The excuse I hear is that they have to fast-charge them to be ready for another power cut quickly, but I suspect they continually over-charge them. This only applies to UPS with integral batteries though -- our

80kW UPS with separate battery cabinets has original 10+ year old batteries, and they apparently aren't ever expected to need replacing in the lifetime of the UPS, but they get a checkup from time to time.

[Adrian]

Yes - they don;t like being overcharged - the 'seal' allows the excess gas out, and the battery dries out....

These particular UPS's were intended for telecomms applications - and seem to consist of a mains-driven switcher producing 50v dc and trickle-charging a 12v dryfit, which cuts in and (though another switcher) provides the 50v when the mains is out...

Nice piece of kit - if you happen to need -50v dc....

Rainy day here - so I'll split my time between some glasswork and seeing how long the laptop will run from the fully-charged dryfit. As the laptop's also pretending to be an MP3 jukebox in the glass studio - shouldn't be too hard to do

Regards Adrian

[Dave Liquorice]

I don't think the the routine on load self test that many have is particulary kind to the batteries either. Pull out a few % of capacity and immediatly recharge every week. The current set of batteries in my UPS went in in Sep05, they preformed fine when the grid fell over the other month and have lasted longer than previous sets but I have now switched off the auto self test...

And the fairly high temperature that the cells are living at inside the UPS probably doesn't help either. 38C is the temp of the UPS ATM, I've seen it >40C fairly often.