solution to get 12 hour battery life?

[Red Squirrel]

Anyone know of a good solution that would enable to get at leats 12 hours of battery life on a PC (probably would be a laptop). Basically this is for hospital PCs that are on carts and get moved around from room to room. They're wanting a solution where at the end of the shift the nurse can swap out the battery and let the other charge. So there would be 2 batteries per cart. Would be preferable if the PC does not need to be shut down for the switch over.

The laptops take 19.5 volts which is a weird number, so something like a boat battery or similar would not work (and would probably not be safe anyway), almost need something that will either produce 120V AC so the adapter plugs straight in, or something where the voltage can be set.

I was looking on batterygeek.net and there's interesting stuff there.

We're also trying to stay away from any chemical based battery such as lead acid, so is there even anything out there that could work? 12 hours is long expectation but that's what they want.

Edit: Also what does watt hours mean? Is it that it can produce 1 watt for that time? So 200 watt hours would mean it can last for 200 hours if it's powering a 1 watt item? So if I want to power 2 watts, then I just divide?

 

[Turbonium]

Isn't this largely dependent on what PC system you are running, rather than the battery?

Say an Atom-based netbook, versus a 17-inch, Core 2-based behemoth?

 

[Red Squirrel]

Well I don't know exactly how much watts I need, but lets just assume a standard laptop with like a centrino chip or something. Though the atom seems like a good idea... if we switch all the laptops to that it would be easier to get a high battery life.

It's only to run Meditech and maybe a few other clinical apps anyway, it does not need lot of power.

 

[Turbonium]

I see a potential problem in that they might need a large screen for the clinical apps, and to my knowledge, no laptops with larger, more standard-sized screens are built on Atom platforms by default. And even if you could find a larger screen paired with an Atom, the larger screen will eat up the battery faster than would a small screen.

But yea, 12 hours is a really long time to go on a single battery. And if you're going to be sending the batteries through a full charge/discharge cycle every 24 hours, they will wear down quickly and lose their maximum capacity over time.

As for netbooks, I'm fairly certain even the most energy-efficient ones paired with the largest batteries run no longer than around 10 hours while averaging say 1-10% load. Someone correct me if I'm wrong.

 

[Red Squirrel]

another thing I was also thinking is if there is a way to add multiple batteries in parallel. Personally if it was my choice I'd go with a deep cycle marine battery and a laptop that takes 12 volts, as that could probably last quite a while and live through the abuse of being completely discharged and recharged. But I can see why they don't want a bunch of lead acid batteries on wheels around patients.

NiCad is probably the best bet here, I would think.

 

[brblx]

generally nicad < nimh < lithium ion.

and you would need a hell of an industrial battery backup solution to get 12 hours of battery, especially in some sort of hot swappable solution.

you would be much better off with a standard battery backup and the nurse can simply plug the cart in in the room. that's how i've generally known computer carts to work, and it's a lot cheaper and easier.

 

[JAG87]

You can get a Dell latitude + a 12 cell slice and that should last you 12 hours easily, Dell rates it up to 19 hours with an SSD.

HP also makes the Elitebook, rated up to 24 hours with SSD and their ultra capacity 12 cell slice.

Depending how much your budget is, this would cost around $1500-2500 per cart. You might need to purchase extra batteries and slices for the swaps.

 

[Modelworks]

There are a couple ways to approach this. The easiest to set up is to use one large 12V battery connected to an inverter that the laptop plugs into. That bypasses any need for worrying about the voltages the laptop power adapter outputs as most laptops want 18VDC . You could adapt this by using 24VDC and a DC-DC converter , but a inverter is much easier to do and more reliable.
Laptops generally use about 18VDC @ up to 4A. So 72 watts total. So for 12 hours you need 72AH battery. If the inverter is 90% efficient you would need a 80AH battery.

Battery types :
Gel Cell - cheap and is sealed so no chemical issues. Electrolyte is a gel , less likely to leak.
Lithium - expensive, but small, requires a proper charger though and does pose a risk of fire if not treated properly.
SLA - same as type battery in a car, but sealed so no leaks.
NiCd - terrible for this application, would take a cart full of them
NiMh - good but again would take a cart full.

Lithium Ion would be the smallest but would also run in the thousands of dollars to do right.

I would go SLA. They work well and can handle the abuse. They are used in powered wheelchairs, hover rounds, so they must be ok for use around patients.
What I would buy:

Inverter - http://www.batteryspace.com/in...n=VIEWPROD&ProdID=4181 $55
charger - http://www.batteryspace.com/in...n=VIEWPROD&ProdID=4506 $36
Battery - http://www.batteryspace.com/in...n=VIEWPROD&ProdID=3509 $300

The biggest problem I see is that you want something the nurse can swap out. Any battery you use for this is going to weigh A LOT ! It isn't something most people can just pick up and charge. I think you would be better to have two carts , each with a battery and its own inverter + supply .

Set up an area for the cart to be charged and have the one charger there. Get the charger above and replace the leads with a jack, so they can just move the cart there and connect the jack. That charger could recharge a 100AH battery in about 10 hours.



About the amp hour stuff.
With batteries if you have a battery that is 12VDC and rated for 20AH that means the battery can supply 12V @ 20A for one hour. Or 12V @ 1A for 20 hours. The exceptions to this are the batteries max current. That is listed as the most the battery can supply at any one time regardless of its overall capacity. That is where people get confused about car batteries. They often rate them as CCA or cold cranking amps as currents as high as 600A . That is because they are designed to provide all the current for a very short period of time, try to use them for a application like this and the plates would buckle. So if you wanted to discharge that same 20AH battery by trying to draw 100A in one minute, it would fail.

When I did the math on the inverter I looked at how many watts the laptop needed, 72 watts. Divided by 12vdc that is 6A for every hour, or 6A x 12 hours, 72AH. Then add in the loss of 10% from the inverter.

 

[Hacp]

Originally posted by: RedSquirrel
Anyone know of a good solution that would enable to get at leats 12 hours of battery life on a PC (probably would be a laptop). Basically this is for hospital PCs that are on carts and get moved around from room to room. They're wanting a solution where at the end of the shift the nurse can swap out the battery and let the other charge. So there would be 2 batteries per cart. Would be preferable if the PC does not need to be shut down for the switch over.

The laptops take 19.5 volts which is a weird number, so something like a boat battery or similar would not work (and would probably not be safe anyway), almost need something that will either produce 120V AC so the adapter plugs straight in, or something where the voltage can be set.

I was looking on batterygeek.net and there's interesting stuff there.

We're also trying to stay away from any chemical based battery such as lead acid, so is there even anything out there that could work? 12 hours is long expectation but that's what they want.

Edit: Also what does watt hours mean? Is it that it can produce 1 watt for that time? So 200 watt hours would mean it can last for 200 hours if it's powering a 1 watt item? So if I want to power 2 watts, then I just divide?

Have you taken a physics class?