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Old 26-02-2019, 01:45   #1
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Cigarette lighter voltages

I have a cigarette lighter adapter similar to the one pictured. Since my yacht is wired for 24V I assume the female sockets will always be 24V.


But what about the USB(?) socket? Will that always be 5V if it was wired for 12V or 24V. (I'm a bit puzzled)
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Old 26-02-2019, 03:30   #2
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Re: Cigarette lighter voltages

Since the female sockets are marked for 12 as well as 24V, my guess is that the dc/dc converter installed for the USB port will absorb both voltages and produce the 5V in both cases. Many modern mobile phone chargers will accept an input range of 110V to 240V AC and still have a 5V DC output.
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Old 26-02-2019, 03:50   #3
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Re: Cigarette lighter voltages

Sailormed

Thanks for that. I thought voltages were reduced by resistors so my logic says the USB terminal would be 10V/24V and 5V/12V. But no?

Here is something relevant but of course a cigarette lighter wouldn't be 10A.

DC Converter 12V-24V to 5V
10A Power Supply Step Down Module

50W Waterproof USB

Here is a DC to DC converter.
Converts 12V or 24Vdc (or any voltage between) commonly used in trucks, buses & machinery to 5Vdc so that you can power your 5V equipment and devices.
Industry grade DC 12/24V to 5V step-down converter
Specs:
Input voltage: 12/24V DC
Output voltage: 5V DC
Output current: 10A (max), 50W
Module type: Non-isolated reducer (BUCK)
Rectifying method: Synchronous rectifier
Minimum differential pressure: 2V
Transfer efficiency: up to 96%
SS (Soft Start) time: Approx. 500mS
Output ripple: 50mV (MAX), 20M bandwidth


https://www.ebay.com.au/itm/DC-Converter-12V-24V-to-5V-10A-Power-Supply-Step-Down-Module-50W-Waterproof-USB-/132078873245
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Old 26-02-2019, 04:07   #4
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Re: Cigarette lighter voltages

Could I use one of these to power my base station 5W UHF, VHF radio?

DC-DC Buck Converter Step-Down Power Supply Regulator 24V/36V/48V to 12V MA1045

Specifications:
Material: plastic
Color: black & white
Input: 15V-58V
Output: 12V/3A(36W)
Transform efficiency: 96%
Peak current: max 6A
Over-heat protection: 150°C
Cable length: 15cm
Mounting hole: Φ4mm
Mounting distance: 56mm
Dimensions: 46 x 32 x18mm


https://www.ebay.com.au/itm/DC-DC-Bu...k2tz:rk:1:pf:0
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Old 26-02-2019, 05:07   #5
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Re: Cigarette lighter voltages

Quote:
Originally Posted by coopec43 View Post
But what about the USB(?) socket? Will that always be 5V if it was wired for 12V or 24V. (I'm a bit puzzled)
I think your question is a good one, especially given that the price of such devices is low, the reputation (or even name and location) of the manufacturer is often unclear, and the specification/description of the internals often not supplied with the device.

The solution is obvious: a USB Type A socket is large enough so standard multimeter probes can enter and be put to the contacts.

Some other of the USB sockets require finer probes.

The pinout for USB A (and the other varieties) are public (see e.g. https://en.wikipedia.org/wiki/USB).

So as a matter of course (or at least when in doubt) measure the voltage across pins 1 and 4. Your meter should read 5.0VDC plus or minus 5% (so 4.75V - 5.25V)

For just supplying 5VDC for charging, pins 2 and 3 in a USB Type A socket are likely tied to ground (or not connected at all?).
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Old 26-02-2019, 05:33   #6
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Re: Cigarette lighter voltages

Quote:
Originally Posted by coopec43 View Post
I have a cigarette lighter adapter similar to the one pictured. Since my yacht is wired for 24V I assume the female sockets will always be 24V.
Even if the USB Type A sockets are regulated to within 5% of 5.0VDC by that
adaptor, I doubt that the cigarette lighter sockets are regulated at all.

In 12VDC vehicles (e.g. a car), the cigarette lighter socket is 'nominally' 12VDC but fluctuates up and down (e.g. usually at a low when starting the engine and ranging up to some high depending on how well regulated the alternator is - I expect at least 13.8VDC or more if the alternator is poorly regulated or if regulation is set up for, say, AGM batteries or other battery chemistry).

I would guess much the same unregulated behaviour in a nominal 24V system. In the case of your build, you could of course choose to regulate your 24VDC system, including to suppress spikes (and so protect your electronics).
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Old 26-02-2019, 07:37   #7
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Cigarette lighter voltages

Nominal voltage for a 12V automotive alternator is 14V plus or minus .2.
Nominal voltage for a 24V aircraft using an automotive alternator is 24V plus or minus .4.
I for years plugged in a USB adapter meant for US cars and 12V into cigarette plugs for an aircraft we made that was 24V.
By some magic that is over my head, they all worked and outputted apparently 5V or maybe all the phones, etc that I plugged in didn’t mind 10V.
I’m pretty sure though that they outputted 5V.
I never checked though.
The lighter plugs to lighter plugs were unregulated, they just passed though whatever was put into them, they were just wire, no electronics.
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Old 26-02-2019, 08:38   #8
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Re: Cigarette lighter voltages

50% chance of working and 50% chance of catching fire and burning the boat down.

Read the input voltage specs on unit.

FYI 500ma is a useless USB plug. Many things won't even work. You need a 2.1a one.
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