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Old 31 March 2004, 13:49   #1
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electrical question

hi guys + gals, me again. got a electrical question that i would like some advice on, just bought a new digital depth unit, that i will fit through my console dash, and also a new digital speed +temp unit also for dash mounting, at the moment i have no power on board, ie battery,as i have not needed it before.
the depth display is 12 volt dc with a power consumption of 60ma and works between +9 to+15v.
the speed display is also 12 volt dc and has a power consumption of 70ma and works between 8 to 16.5vdc.
my question is this ?- what type of battery should i buy, i was just going to buy a motorcycle batt, which i could disconect and recharge using my standard car batt charger(switched to 12v) after i have been out on the water, i only use my boat occasionally(unfortunatly), i also relise that i will have to put a fuse in the positive wire somewhere, what size fuse and how do you do it.



all sunshine makes a desert ?



cheers
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Old 31 March 2004, 16:44   #2
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Using a wee battery for the limited usage you have seems like an ok idea. However, I would recommend you use a gel battery of the type used for backup of alarm systems. They hold their charge for a long time, they have a long life and they will not spill. They come in various shapes and capacities so you will probably get one which is convenient for you. The only thing you'll need to be careful about is, they have a limited charge rate and your auto battery charger may charge at too high a rate. There are ways around this.

Fuses; add up your working current and choose a fuse a good bit higher capacity. The reason for this is that many pieces of equipment drain a surprising amount of current when they are switched on. You can use slow blow or delay fuses to overcome this but I wouldn't be fussy here. The reasoning is that it's very rare to have a piece of equipment fail by drawing excess current which is still below a typical, realistic, fuse rating. Normally, the fuse protects from short circuits, accidental or otherwise, and under these conditions even a relatively large fuse is going to fry. For the current consumpton you have stated, I'd try a 1amp fuse. If it takes any switch on surge without problem I'd stick with it.
If you want the minimum fuse possible, simply go down in size until you get a blow and then increase it a bit.
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Old 01 April 2004, 14:10   #3
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How old is your engine? You may be able to buy a kit (if its not already fitted) that would allow to connect it to a battery and charge it as you are motoring along. This would save you having to keep on removing the battery to charge it, or risk it going flat whilst your out at sea.
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Old 02 April 2004, 02:10   #4
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You could do worse than get a....

Sealed lead acid battery from http://www.maplin.co.uk/

ref:
MM22Y 12V 1.3Ah SLA In Stock 4.99

There on a promotional offer.

That would give you 10 Hrs at 130ma.

Cheers

Phil
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Old 02 April 2004, 08:28   #5
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thanks

thanks for all the replies people, what i have done is, i have an old but perfectly servicable 12v batt from black and decker drill, i will solder 2 wires on to the terminals, inside the batt +/- , and bring 1 wire out each side, on the poss wire i will use an in-line fuse from an old car radio rated 3 amp, then finish both wires of with a female crimp fitting, making sure both wires can not touch, then it should be a case of crimping all the wires with male crimps, and connect up. then when it comes to re-charge i can just disconnect the wires, and place the batt in the charger- hey presto.

what do you think-- good or what ? any comments good or bad please.

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Old 02 April 2004, 08:34   #6
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Hi Seaskimmer.

I've got a question for you...

Why the green extinguisher? Noticing that you're a fireman, I guess there's a good reason for it! (and before anyone gets smart, yes, I know it's for putting out a fire )
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Old 02 April 2004, 11:08   #7
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Quote:
Originally posted by Richard B
Hi Seaskimmer.

I've got a question for you...

Why the green extinguisher?
I spotted that too. Its green 'cos its Halon or BCF and it is now illegal in europe, thanks Brussels, who say it is not Green (note capital G). Best extinguishant around. Some people might spray the cylinder red so it does not draw any attention. Not that any one would do that of course.
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Old 03 April 2004, 11:33   #8
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[QUOTE=seaskimmer] then finish both wires of with a female crimp fitting,




Great idea love the recycling aspect and no worries about over charging the battery.

Why dont you finish the terminal one male & one female then plugging in would be less colour critical. Make sure cable from battery couldnt be plugged into each other though (tell who has a four yr old boy )
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Old 04 April 2004, 05:08   #9
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Quote:
Originally Posted by philip
Sealed lead acid battery from http://www.maplin.co.uk/

ref:
MM22Y 12V 1.3Ah SLA In Stock 4.99

There on a promotional offer.

That would give you 10 Hrs at 130ma.

Cheers

Phil
cheers for the reply phil, are you sure this will be the correct batt for my needs, as i am going to buy one on tue, and i will be able to re-charge using my normal car batt charger.

regards
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Old 04 April 2004, 10:34   #10
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Quote:
Originally Posted by seaskimmer
cheers for the reply phil, are you sure this will be the correct batt for my needs, as i am going to buy one on tue, and i will be able to re-charge using my normal car batt charger.

regards
I think you'll find your auto charger will overcharge it. If you buy a 10amp diode while you're there and put this in series with the battery, it'll drop the voltage by approx. 0.7v and that won't be far away. Test it for heat once you start charging. You may need to strap it onto a wee heatsink.
Personally, I'd go for one with a larger capacity.
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