Battery choice

I want to be able to run a Garmin GPSmap 450 from batteries, for an hour or two at a time.

The GPSmap 450 is designed to run on a boat, and has a wide input range of 10 - 35 V and takes a maximum of 15 W, and I want to be able to show people how to use it without having to launch the boat.

Sealed lead acid is a possibility but it will be a bit heavy and I don't think that it will like being left discharged if someone is careless.

With Ni-Mh the cells will become unbalanced in storage so charging will have to be very slow.

I've been looking at Li-ion chargers but I can't find ICs that can limit the voltage on each cell if I have several in series. It seems odd as all the single cell chargers make a big thing about keeping the cell voltage below 4.1 or 4.2 V.

Any suggestions would be welcome.

Hi Diver300,

15W at 12V equals a current flow of 1.25A. For a 2 hour continuous operation you would require a 2.5Ah battery. After this time the battery would be completely depleted. To make it safe I suggest to use a 4.5Ah lead-acid-battery. Even if is not charged immediately after use it doesn't matter, since it still has safe capacity.

The weight of this battery type is 1.81kg. (brand name is Kung Long)

Panasonic makes batteries of 2.2, 3.4 and 7.2Ah.

Boncuk

I can give an idea that you can use big capacitor in place of battery. In this forum, some geniuses will help you in this matter !

Unfortunately a capacitor is a no go because one large enough would fill a room,

Hero999 said:

Unfortunately a capacitor is a no go because one large enough would fill a room,

Click to expand...

Hi Hero999,

not quite. WIMA has developed supercaps up to 700F (Farad). They are not bigger than a 470µF/350V electrolytic cap. (Check out https://www.wima.de and search for supercap)

The downside: they can just handle up to 5V.

For comparison: A 1F capacitor using two metal plates and air as dielectricum must have the plates separated by approximately 80m (height of the Cologne cathedral tower)

Hans

Boncuk said:

For comparison: A 1F capacitor using two metal plates and air as dielectricum must have the plates separated by approximately 80m (height of the Cologne cathedral tower)

Click to expand...

I think you're a little confused

Capacitance is inversely proportional to spacing - 80m spacing would be so small as to not be worth mentioning. Perhaps the 80m referred to the size of the plates?.

700F is small compared to a battery, a 1A load will last just 700 seconds (under two miniutes) and the voltage will drop by 1V.

can any one help me to convert the battery of car of 12v 40 amps to 5v?
pls. schematic and type of component to esy to analize.