Satnav/GPS

'Morning Gents
    Slightly off topic....but at least I'm not selling shoes and it is engineering of a sort.
    I have a good friend who has several modern vehicles and even more older ones (pre-war Austins). Said friend is getting married soon and I thought of giving them a vehicle-type satnav system as a wedding present. I assume these things need 12volts, but I don't know the current draw?
     The older cars have six volt systems, without the convenience of cigar lighter sockets. Would it be feasible to run a decent GPS system off a (12v by 12Amp/hour?) sealed lead acid battery, the sort of things used in a burglar alarm system? I'm imagining a small brick-sized battery on the floor of the car, couple of spade connectors to a cable which terminates in a cigar lighter-type socket and I've got a system which is portable between vehicles.......or have I?
--
Chris Edwards (in deepest Dorset) "....there *must* be an easier way!"

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Chris Edwards wrote:

My relatively old tomtom Go says on it 5v 2amps. I strongly suspect the 2 amps is absolute worst case to run the unit and when the battery is charging at max rate. You will still need a regulated supply as a nomimal 6 volt car will vary from below 5 to 7 or more complete with spikes etc and modern electronics won't accept that wide range. Nice little switch mode supply project for an electronics expert. you will need a two stage design as most configurations do not like the input range being both sides of the desired output range.(no I've got too much on before you even think about it!!).
Bob
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TomToms run of regulated 5V ( built into the cigar adapter.) If you build a 5V Low Dropout regulator then the 6V will be fine. This is only really needed for charging the TomTom although it will drive the TT if connected. My advice, start the car and then connect the TomTom supply.The regulator may not like Load Dumping! The TomTom will happily run a few hours on its internal Lithium cell. When almost flat, the Lithium will draw 1- 1.5 amps from the external 5V supply. Hope that helps.
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Greetings Chris, Having reached the age to claim both 6v and ancient cars, wasn't the other question -polarity?
Regards
Norm
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On Sat, 26 Apr 2008 10:48:37 -0700 (PDT), ravensworth2674

Sorry Norman....I don't understand your point about polarity? I'm getting some good stuff by way of response, but since I barely know a watt from a widget I'm still absorbing all the advice being offered. I assume any incoming advice re 6v car battery use would apply equally to my idea of a self-contained, stand alone system using a small sealed lead-acid battery for use when installed in the Austins? I must ask Bob Minchin about that later.
Keep taking the tablets
--
Chris Edwards (in deepest Dorset) "....there *must* be an easier way!"

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Chris Edwards wrote:

The point Norman is making is that most early vehicles used a positive earth system. ie the positive side of the battery is connected to the chassis. Modern cars have the negative side of the battery. I don't feel this makes too much difference as the tomtom is in a plastic case. It will be important when moving the power supply from car to car to ensure that the correct polarity is used. A simple rugged solution, avoiding possible accidents, would be to go back to your idea for a 12v lead acid battery fitted with a cigar lighter socket and thenuse the power supply that comes with the tomtom. Note that this sort of lead acid battery needs a special charger designed for sealed batteries. A standard car charger will not do.
HTH
Bob
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     Gentlemen
    Many thanks to all those who offered advice with my satnav/GPS query. I now have a much clearer idea of the way forward - I must confess, it hadn't really dawned on me, not ever having seen a satnav system 'close up', that they generally use their own on-board batteries in addition to taking power directly from the vehicle's system. (In Dorset we still get our directions by reading lichen on tree trunks and watching crows circling the rick field).
    It therefore looks like what I need then is a system which can be plugged into a modern car's 12v cigar lighter for routine use, or into a cigar lighter socket fed from a 12v 12Ahr dry battery when used in the pre-war Austin, supported by a special charger for the dry battery.
    As ever, my thanks to one and all....I shall proceed accordingly.    
    
--
Chris Edwards (in deepest Dorset) "....there *must* be an easier way!"

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On Sun, 27 Apr 2008 15:50:38 +0100, Chris Edwards

Just a quick note. We use an HP HX4700 with a TomTom Mobile5 GPS.
The input supply is regulated by the supply leads in most of these and means you need two supply sockets if you want to go that route.
We fitted the 5V regulated supply for the TomTom inside the Seidio cradle and brought the lead out to plug into the TomTom5 unit. Just one supply cable needed now.
Peter -- Peter & Rita Forbes Email: snipped-for-privacy@easynet.co.uk http://www.oldengine.org/members/diesel http://www.stationary-engine.co.uk http://www.oldengine.co.uk
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I have a pen-cell operated unit which works just fine. I use re-chargeable cells and carry a spare set for emergency. Thus it is non-voltage-specific so far as the car is concerned.
Mike
--
Mike Whittome
in the north of Hampshire
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Just a thought, but do they make GPS suitable for motorcycle 6V systems ? Might be easier to use with gloves as well.
--
Boo

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On Sun, 27 Apr 2008 14:06:11 +0100, Boo

    Thanks Boo...I think they may do...I'll look at that too.
--
Chris Edwards (in deepest Dorset) "....there *must* be an easier way!"

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