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24/7 Notebook Power?
RobPiano asks: "Help! I am working at a health care facility that may be expanding its network to have eight Fujitsu wireless notebooks. These notebooks would be required to run nearly 24/7 with minimum downtime. Unfortunately, charging and replacing lithium-ion batteries is expensive, and cost is definitely an issue. The notebooks are placed on carts, so an 'on-cart power supply' is an option, but having it plugged in is not. I considered a car battery, but most of the nurses would have trouble pushing both cart and battery. How have you readers kept your systems powered?"
You're right. And of course I knew that. I'm constantly amazed at how moderation works on slashdot. I have (4, Informative) for that post so far when it was essentially a troll. But people don't seem to have gotten the joke.
What this guy should really be doing is not considering laptops in the first place, but using something like simple, liquid-proof, touchscreen "webpad" terminals (wireless if the hospital allows.) Like the ones used by waiters.
You don't need all the extra junk in a laptop to perform data entry. Not to mention the maintenance headaches, and the practical impossibility of what he wants to do, short of cold fusion. Wouldn't everybody like to have our laptops running 24/7 without ever needing to recharge the batteries?
Laptops are almost ridiculously not suited to this application. To me it sounds like the guy just got his hands on a technology budget for the first time and is itching to spend it. If he's budgeted enough money for a bunch of wireless laptops but not enough to keep the batteries charged (is that really such a huge expense?) something is wrong with the whole picture.
Or maybe the original post was a joke and I didn't get it.
I see you harshly and in the second case unjustly criticizing someone for attempting to be helpful. Instead of merely pointing out problems in logic, your response would have been better used offering suggestions. In my opinion, the only solution to this problem is a high capacity battery. All other forms of electricity, solar, friction, etc are not suitable for this use. Since the laptops need to be used continually, having an extra battery setup for each laptop would be appropriate. The only downtime in this case would be switching the batteries out, however you have to ensure that it takes the batteries longer to drain during use, than it takes to charge. Also, the user should be sure that as many power saving features as possible are enabled to cut down on any unnecessary use.
this is a great resource for deepcell batteries
http://www.uuhome.de/william.darden/dcfaq.htm
also one almost identical for car/motorcycle batteries
http://www.uuhome.de/william.darden/carfaq.htm
these references will be all you will ever need to know about charging/discharging times, how many cycles to expect and to what extent you can discharge the batteries and still retain a viable performance.
pay specific attention to
#12 (in the DC or 16 in the car faq) HOW CAN I REVIVE A SULFATED BATTERY?
for help in keeping costs down, it contains specific information to revive the battery by "cleansing it" and replacing electrolyte.
Good luck!
--Meat
--I use a lot of solar and maintain almost 60 deep cell batteries (of various kinds) on 5 different arrays total. I know a smidgen of this subject
;^)
Put a sealed glassmat agm battery on the bottom level of the cart. cheaper just use a gelcel. A cheap sealed 12 volt gelcell will cost about what a tiny new laptop battery goes for, hold like 50 times the amp hours in it, something like that anyway, a lot. Use carts with larger wheels if pushing is a problem. Stuff rolls easy if the wheels are cool, don't be cheap there. Any normal human can roll around several hundred lbs no sweat if the casters are decent. Small wheels ="bad", larger diameter wheels ="good", easier to roll. Even a 4 foot 6 nurse can still push the cart. Don't let thembuffalo you with "they can't do it". That is BS. Even a 50 lb batt on a cart is doable. Even with all their other gear. One of those batts will run a laptop for a LONG time, I know I can run one of my old powerbooks for more than 24 hours without completely discharging a normal 12volt semi deep discharge battery. Piece of cake really. Look at laptop batteries, weigh zip, look at an industrial deep discharge battery-massive. Plenty-o-juice. In fact, when you go to work, take a peek at the batteries the maintenance guys use in their electric floor scrubbers (if they are cordless) I bet you use in the hospital. Those will be industrial "traction" batteries designed for heavy extended use, and chances are they will be either crown brand or rolls/surrette. You'll be getting something very similar, in fact, the exact identical (if 12 volt) batteries in those floor polishers will probably work for you exactly as you need, simplifing supply and inventory and re-charging. Go ahead, go look at them.
Want to go a few more bucks, use two 6 volt agm batts wired in series for 12 volt, then use that input for the laptops.
BTW, use laptops that will TAKE 12 volts natively, or suffer a small loss with the car adapter/inverters. Not much, but some.
At your recharge station use a solar/alternate energy industry controlled 3 stage charger adjusted for the type of batt you get, don't use a one stage car battery charger, they are the worst way to charge batteries you can buy, and most of them don't even charge glass mat or gelled sealed batteries without 'sploding them. they are "adequate'for recharging your starter battery, and that's about it. Mostly they suck. heh.
Good rule of thumb for batt longevity is try not to deep discharge them, the closer to "full" you can keep them the better. Me, personally try to never drop below 80% or so charged, even though I have gone lower very occassionally. for your uses even 60% full is still quite doable and the batts should last for years. You should have zip problems with your batts running one laptop for an an entire shift. You will need extra carts and batts though, as recharge time can be long, just depends is all.
There also exists a device called a "desulphator", several brands out there now, they hook to the batteries and oscillate the sulphates from the acid electrolyte right back off the plates, and work VERY well. I recommend them to anyone who wants mileage out of their batteries.
There are other more exotic batteries on the market now, and even some fuel cells coming, but geez loeez they are 'spensive.
The batteries themselves can fit into nice neat plastic vented battery boxes from walmart, like 10$ apiece. Cabling for adding a female receptacle for the laptops male DC 12 volt plug you can do yourself, you're a tech, right? Female 12 volt (car-type) receptacles are on the counter at any auto parts store, 4$, 8$ for dual or triple.