Discuss 12v car battery. How to lower amperage output for a device? in the New Member Introductions area at ElectriciansForums.net

ann58585

New EF Member
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4
Location
dublin
How do I lower the amperage output best for a device that will suck my car battery dry without loosing too much energy?
There are several methods but I would like to know a way to say get around 1 ampere max out to my device the most energy efficient way. Not loosing too much to heat.
The battery is a normal car battery charged normal so between 13.5 V and 10 V operating.
What method is best?
resistor?
capacitor?
Diode?
anything else?
I have a 1a schottky diode 1n5859. Could I just put that in between or should I put more than that? fuse?
 

telectrix

Scouser and Proud.
Respected Member
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cheshire/staffordshire
the battery will supply as much current as the load requires.it's the load that determines current draw, not some cock-up devices, unless you want to limit the load current, then will the load function at a reduced current level?
 

static zap

Regular EF Member
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1,830
Location
west midlands
Bulbs tend to stabilize the current (just resist staring directly)
..Next problem modern car batteries HATE / are not even designed to go below 12 / 12.1V without the " paste " inside dropping off the plates !
Its called Deep Cycle discharge - electric scooter batteries more appropriate.
--You need an appropriate fuse near battery -
-or inexperience may cause fire !--
 
OP
A

ann58585

New EF Member
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4
Location
dublin
ok so 12v battery fuse and then what? device.
The device wants to draw 6a and I do not want it to because it will not work for that purpose.
 

StephenRowley

Regular EF Member
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191
Location
Leeds
As Tele says it's the battery will just give what ever current download demands. But I would use a fuse as if something does short the car battery can deliver a lot of current.

really need a bit more detail about exactly what your trying to power and the exact charity battery arrangement to give proper advice. For instance if the device if particular sensitive to voltage variation some form of voltage regulator
 

static zap

Regular EF Member
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1,830
Location
west midlands
Re reading post sounds like you have a 9 -10V device , you believe only takes 1A .
( This is where experience takes over-need info about actual device -as plenty take a surge at startup )
Most efficient is more expensive ,but may have Auto shut-off ,
that may save you from a car that wont start !
 

Marvo

Admin and gender confused
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A battery is effectively a constant voltage driver, not constant current.

If you have a load (device) that requires current control you'll need to give us more info about the device.

Fusing of circuits supplied by a battery is essential because it will deliver 'unlimited' (not actually unlimited but enormous none the less) current if there's a fault or overload.
 
A

Adam W

There is more than likely a standard way of doing it without having to resort to ingenuity.
 

PEG

Respected Member
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4,873
Location
Manchester
If the device "wants" 6A,giving it 1A may cause other issues...

Tell us what the device is or you may start to get "tie a knot in the cable" type of advice...;)
 
OP
A

ann58585

New EF Member
Messages
4
Location
dublin
ok it is a 12V 6a device see it as a sort of a heater that I want to only draw around 1a or it will suck the battery dry in no time. it is a car battery that is not running a car but is loose. Also the device does not do what I want at 6 a but will do at 1 or 2 a or perhaps even lower than 1a.
I have the 'heating device' loads of car fuses of different sizes and diode.
I can buy anything else you come up with.
I need something that does not use up much so a bulb will not do.
I thought fuse resisistor diode device in that order but did not know the values or numbers of the particular ones to use.
Also I think there must be a more energy efficient solution out there as I am not exactly a rocket scientist.
So I looked up a bit and came up with the other crazy ideas as you see on the top of this thread.
Now I wonder if anyone can come up with a list of exact things to put this to work without setting the shed on fire.
battery is old 64Amp lead acid runs like a train will start a car in no time.
64A 12V battery------car fuse?A------?------Diode?-----output 12V around 1A going to the 'device'
Thanks in advance.

 
A

Adam W

In that case I suggest you purchase a device which has been specifically manufactured, tested and guaranteed to serve the purpose in question, thereby reducing the risk of setting your shed on fire, which nobody wants.
 

StephenRowley

Regular EF Member
Messages
191
Location
Leeds
If you restrict your heating device to 1amp you'll only have 12watt Maxish of heat which isn't much at all.

The diodes will not reduce current demand.


What exactly are your trying to do we may be able to offer up a better solution ?
 

Strima

Electrician's Arms
Messages
3,528
Location
St Neots
Reducing the wattage of the heater will reduce the heat output.
 

rsgaz

Regular EF Member
Messages
267
Location
UK
really need a bit more detail about exactly what your trying to power
Agree.

it is a 12V 6a device see it as a sort of a heater
Sadly, still not told us.

If you are in this vehicle at the time, then you yourself is a 100 watt heater, give or take, this extra 12 watts will hardly make a difference.

Your best bet is probably Pulse Width Modulation.
 

Jason Philip

Active EF Member
Messages
39
Location
USA
Buck is close to PWM ,
Potential divider !
(but where does the other 10V at 1A go with a potential divider)
(unless thats a 2nd low wattage heater)
Into the resistors, he says it's a 6amp draw at 12v, so the device uses 72watt, and has a 2ohm resistance. if he want's it to draw just 1a then he can put resistors in series, and make a potential divider that will have an overall resistance of 12ohm, including the heater device, the overall wattage will be reduced to 12w, 2 watt to the device and 10w dissipated into the resistors, the whole circuit now uses 1/6th of the device original consumption, honestly though, I am just theorising and given the OP lack of explanation or answer on this thread, I'm not sure this is even a real scenario.
 

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