I am new here and i came because i seek an answer. I have a device that draws 3.5Amps and i have a 6v sla 4.5Ah battery that i can run it from, problem is the device is of a 1964 vintage and i dont want to dammage it as it was designed to run from a 4.5v battery that is no longer produced and i can not find anything suitable so i would lie to add a component in the positive side of the supply circuit that wil reduce the voltage to around 4.5v and still keep the current. Please can someone help me to select the correct component?
Hi Hero999
I am in UK , i am a collector of Soviet opto electronics and related items. yes this item includes an Infra red illuminator so that the viewer can detect the infra red light and convert it into an image that can be seen .
i run the **broken link removed** website.
would you expect a 3.5 amp device to run from a 6v battery?
it is said that either can be used but i had 3 x 4.5v lantern batteries in series and it was brighter than just 2 in series so i need a much higher capacity.
I though you said it's rated for 20W which, at 6V, is a higher current than 3.5A?
If you measure the voltage across the lantern batteries it will probably drop to 4.5V because they're overloaded.
If you go for the diodes then make sure they're rated for at least 5A.
Does it need to be portable?
You could use a 5V, 5A (25W) mains power supply and a single diode, if you're worried about the voltage being too high, although I think you'll be fine with 5V.
the actual lamp has 4.5v 20w marked on it. When we tested the draw of this item with the viewer and lamp turned on it was drawing 3.5amps i want to run it at 4.5v from a 6v battery and yes it has to be mobile as the battery compartment is belt mounted.
It's not possible for a device to draw 3.5ADC from a 4.5VDC supply and the power rating be 20W, it violates Ohm's law - a fundamental law of physics.
20/4.5 = 4.44A
If it's 20W when the current will be 4.44A.
My guess is the voltage is dropping below 4.5V so the current is also dropping, or the rating of 20W is a conservative estimate and the actual power draw is much less.
when we tested this i had 3 of the 4.5v lantern batteries in series to give greater capacity and the voltage was 4.5v , the draw was confirmed as 3.5A but although the lamp is marked as 20w it was not lighting very bright, it was lit but nowhere near its correct brightness so this may explain the problem with violating ohms law.
yes you are correct , it is an incandescent lamp with an IR filter, there is no visible light comming through the filter. it works well for an old device.