# Question on (not) converting voltage **URL:** \ **Category:** Factual Questions\ **Created:** [May 31, 2023, 1:58am UTC](https://boards.straightdope.com/t/question-on-not-converting-voltage/984802 "2023-05-31T01:58:22Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Saint\_Cad](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/saint_cad/32/18907_2.png) [@Saint\_Cad](https://boards.straightdope.com/u/Saint_Cad)\ **Post date:** [May 31, 2023, 1:58am UTC](https://boards.straightdope.com/t/question-on-not-converting-voltage/984802/1 "2023-05-31T01:58:22Z")
I have a radio charger I want to use in my car. It uses 14V at 1A. Is there anyway that the12V plug in the car will work or is 2 volts too much to make up? ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [May 31, 2023, 2:10am UTC](https://boards.straightdope.com/t/question-on-not-converting-voltage/984802/2 "2023-05-31T02:10:20Z")
An alternator typically produces around 14V. ---
**Author:** ![Saint\_Cad](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/saint_cad/32/18907_2.png) [@Saint\_Cad](https://boards.straightdope.com/u/Saint_Cad)\ **Post date:** [May 31, 2023, 2:30am UTC](https://boards.straightdope.com/t/question-on-not-converting-voltage/984802/3 "2023-05-31T02:30:26Z")
Tesla so assume exactly 12V DC ---
**Author:** ![echoreply](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/echoreply/32/3641_2.png) [@echoreply](https://boards.straightdope.com/u/echoreply)\ **Post date:** [May 31, 2023, 2:45am UTC](https://boards.straightdope.com/t/question-on-not-converting-voltage/984802/4 "2023-05-31T02:45:11Z")
> [@Saint\_Cad](#): > > Tesla I’m working on an unrelated project, so I was all set to measure this. On my 2018 Model 3 a cigarette lighter USB-C PD adapter reports the car is providing 14.2-14.4 volts. I put a 65 watt load on the USB-C PD adapter (the adapter is outputting 20v at 3.33amps), and the voltage from the car drops to a steady 13.6 volts. In my case the power is coming from the DC to DC converter, because the contactors have closed and the traction battery is online. Once the car goes to sleep, the cigarette lighter will not get power. Not a problem to charge while you’re driving, but otherwise you’ll need to have sentry mode or something else running to keep everything active. ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [May 31, 2023, 2:46am UTC](https://boards.straightdope.com/t/question-on-not-converting-voltage/984802/5 "2023-05-31T02:46:12Z")
> [@Saint\_Cad](#): > > Tesla so assume exactly 12V DC So you didn’t go for the aftermarket alternator installation to make it run forever? ---
**Author:** ![Saint\_Cad](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/saint_cad/32/18907_2.png) [@Saint\_Cad](https://boards.straightdope.com/u/Saint_Cad)\ **Post date:** [May 31, 2023, 2:47am UTC](https://boards.straightdope.com/t/question-on-not-converting-voltage/984802/6 "2023-05-31T02:47:35Z")
Burns too much gas. ---
**Author:** ![Saint\_Cad](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/saint_cad/32/18907_2.png) [@Saint\_Cad](https://boards.straightdope.com/u/Saint_Cad)\ **Post date:** [May 31, 2023, 2:50am UTC](https://boards.straightdope.com/t/question-on-not-converting-voltage/984802/7 "2023-05-31T02:50:37Z")
So what I need then is a cigarette lighter (I’m old) to that jack that all adapters seem to use. Make one or buy one? ---
**Author:** ![echoreply](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/echoreply/32/3641_2.png) [@echoreply](https://boards.straightdope.com/u/echoreply)\ **Post date:** [May 31, 2023, 3:29am UTC](https://boards.straightdope.com/t/question-on-not-converting-voltage/984802/8 "2023-05-31T03:29:49Z")
Do you mean how do you create a cable that goes from the round 12v auxiliary power receptacle (which I called a “cigarette lighter”) to your radio? That I’m not sure about. You could probably just build a cable that has an auxiliary power plug on one end, and the correct connector to go into your radio. Make sure you get the polarity right! I’m not sure if I’d do that, though. There may already be cigarette lighter adapters for your radio, and they probably are just straight through cables, but I’d really hate to give advice that blows up your radio or car. I looked through the appropriate junk drawer and found two different auxiliary plug to barrel plug cables. I have no idea what they went to. I also found some sort of step down device to convert the 12(14) volts from the car into a lower voltage, and a similarly device which can also broadcast a short range FM signal, too. I know none of that helps you, sorry. ---
**Author:** ![Francis\_Vaughan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/francis_vaughan/32/3093_2.png) [@Francis\_Vaughan](https://boards.straightdope.com/u/Francis_Vaughan)\ **Post date:** [May 31, 2023, 3:30am UTC](https://boards.straightdope.com/t/question-on-not-converting-voltage/984802/9 "2023-05-31T03:30:46Z")
Lots will depend on the nature of the charger and what assumptions have been made. It may be that it is designed for use in a car and they just chose to label it with what is close to the nominal voltage you would see. It the charger uses a switch mode regulator it won’t care much either way. If it uses a series regulator it might struggle. Just about everything modern uses some form of switch mode, but not everything. Heck, it might not even include a regulator, if it is cheap and nasty enough. Also, the battery voltage of the thing being charged is a clue. ---
**Author:** ![Saint\_Cad](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/saint_cad/32/18907_2.png) [@Saint\_Cad](https://boards.straightdope.com/u/Saint_Cad)\ **Post date:** [May 31, 2023, 5:57am UTC](https://boards.straightdope.com/t/question-on-not-converting-voltage/984802/10 "2023-05-31T05:57:25Z")
> [@Francis\_Vaughan](#): > > It may be that it is designed for use in a car and they just chose to label it with what is close to the nominal voltage you would see. No the adapter is made to plug into 110V AC and output 14V DC. I want a new adapter that goes directly from the cigarette lighter directly to the charger. ---
**Author:** ![Francis\_Vaughan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/francis_vaughan/32/3093_2.png) [@Francis\_Vaughan](https://boards.straightdope.com/u/Francis_Vaughan)\ **Post date:** [May 31, 2023, 6:22am UTC](https://boards.straightdope.com/t/question-on-not-converting-voltage/984802/11 "2023-05-31T06:22:21Z")
> [@Saint\_Cad](#): > > I want a new adapter that goes directly from the cigarette lighter directly to the charger. I meant the charger is specified as a nominal 14 volts input. It isn’t impossible it was designed with a car voltage in mind. That the adapter matches this is an element of accidents of history. I would bet that the charger will work perfectly run off a car. But some checking on the specifics of the device would tell you exactly what is possible. ---
**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\ **Post date:** [May 31, 2023, 9:49am UTC](https://boards.straightdope.com/t/question-on-not-converting-voltage/984802/12 "2023-05-31T09:49:15Z")
> [@Saint\_Cad](#): > > No the adapter is made to plug into 110V AC and output 14V DC. I want a new adapter that goes directly from the cigarette lighter directly to the charger. > [@Francis\_Vaughan](#): > > I would bet that the charger will work perfectly run off a car. But some checking on the specifics of the device would tell you exactly what is possible. It will not run perfectly off a car if it needs 110V AC input. However, does the _radio_ need exactly 14.0V input, which you could generate using e.g. an XL6009 module (or similar voltage regulator), or would it be directly OK with the 12 to 14+V coming from the car? ---
**Author:** ![RitterSport](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rittersport/32/6326_2.png) [@RitterSport](https://boards.straightdope.com/u/RitterSport)\ **Post date:** [May 31, 2023, 10:25am UTC](https://boards.straightdope.com/t/question-on-not-converting-voltage/984802/13 "2023-05-31T10:25:58Z")
How about a lighter-to-110 volt adapter for the car? Then, plug your existing charger into it. ---
**Author:** ![Saint\_Cad](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/saint_cad/32/18907_2.png) [@Saint\_Cad](https://boards.straightdope.com/u/Saint_Cad)\ **Post date:** [May 31, 2023, 1:31pm UTC](https://boards.straightdope.com/t/question-on-not-converting-voltage/984802/14 "2023-05-31T13:31:37Z")
Do they make those? I’ve only seen them go 110VAC to 12VDC ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [May 31, 2023, 1:40pm UTC](https://boards.straightdope.com/t/question-on-not-converting-voltage/984802/15 "2023-05-31T13:40:09Z")
You need to determine the minimum DC voltage it will work at, and then stay at least 0.5 V above that. If it’s not specified on the spec sheet, you need to perform a test using an adjustable DC power supply. If you don’t have one, get with a local amateur (“ham”) radio operator, whom I am sure would be more than happy to help you. ---
**Author:** ![RitterSport](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rittersport/32/6326_2.png) [@RitterSport](https://boards.straightdope.com/u/RitterSport)\ **Post date:** [May 31, 2023, 1:40pm UTC](https://boards.straightdope.com/t/question-on-not-converting-voltage/984802/16 "2023-05-31T13:40:16Z")
> **[Amazon.com: BESTEK 150W Power Inverter 12V to 110V Voltage Converter Car Charger...](https://www.amazon.com/BESTEK-Inverter-Charger-Charging-Shared/dp/B003SGJIRO)** > > Buy BESTEK 150W Power Inverter 12V to 110V Voltage Converter Car Charger Power Adapter with 2 USB Charging Ports (3.1A Shared) (150W): Power Inverters - Amazon.com ✓ FREE DELIVERY possible on eligible purchases ---
**Author:** ![Francis\_Vaughan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/francis_vaughan/32/3093_2.png) [@Francis\_Vaughan](https://boards.straightdope.com/u/Francis_Vaughan)\ **Post date:** [May 31, 2023, 2:10pm UTC](https://boards.straightdope.com/t/question-on-not-converting-voltage/984802/17 "2023-05-31T14:10:41Z")
There seems to be some confusion about how many devices and what they do in the chain. I’m assuming there is a 110 → 14 volt adapter that is then connected to a charger that accepts 14v and charges the batteries for a radio. The task is to eliminate the 110-\>14v adapter in such a manner that a car will successfully drive the charger, which will eventually allow the radio to work. Given a car battery is a nominal 12.6v, and a running car typically a volt or two higher, it is hard to imagine that the charger won’t work right away without additional effort. As noted above - it depends on the charger. One built using a switch mode regulation circuit will likely accept a much wider range of input voltages. But if it uses a simple series or shunt regulator (or worse) to set the charging voltage and current, the car supply might drop below the minimum needed to have it work. There exist a staggering range of possibilities, from the very sophisticated dedicated smart battery charging systems, all the way down to a current limiting resistor and nothing more. Something as simple as knowing what the batteries being charged are would probably settle it. ---
**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\ **Post date:** [May 31, 2023, 2:37pm UTC](https://boards.straightdope.com/t/question-on-not-converting-voltage/984802/18 "2023-05-31T14:37:07Z")
They make therm, but you need the little cigarette-lighter inverter; do not try to hook up a 110VAC → 12V adapter backwards. ---
**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\ **Post date:** [May 31, 2023, 2:43pm UTC](https://boards.straightdope.com/t/question-on-not-converting-voltage/984802/19 "2023-05-31T14:43:59Z")
If it is just a battery charger, the ones I have do not care about the precise input voltage, and they are not even that “smart” as you have to specify the chemistry of the battery you want to charge, number of cells, and the maximum charging current. ---
**Author:** ![andrewm](https://avatars.discourse-cdn.com/v4/letter/a/c57346/32.png) [@andrewm](https://boards.straightdope.com/u/andrewm)\ **Post date:** [June 1, 2023, 12:26am UTC](https://boards.straightdope.com/t/question-on-not-converting-voltage/984802/20 "2023-06-01T00:26:31Z")
Have you _measured_ or are you just assuming? I’d expect the “12V” accessory socket even in an EV to never output less than at least 13.8V, possibly higher. If the car isn’t keeping the 12V bus voltage at least that high at all times when it’s “on”, the battery will be drained by the loads on the 12V bus. I just measured by connecting a voltmeter to the accessory socket in my ID.4 and it puts out 14.3V. [Next page](https://boards.straightdope.com/t/question-on-not-converting-voltage/984802.md?page=2)