what voltage do you expect from cig lighter? 12 or 14v?

hi there, using a voltmeter logger i have taken voltage measurements from both the cig lighter and the accessory socket. for a kia they give 12.1-12.

5v when engine is on or off. while engine is running if you turn on headla mps or fan etc, momentarily it will spike up to 13.8 and then go back to 12 .5. i guess the alternator might be a smart type which disengages with a cl utch if not needed.

on other cars i tested this on ( e.g. ford, peugeot) i found that with car engine is off you get 12.5, with car on you get a steady 14-14.1v , regard less of if you turn on headlamps etc.

i suspect that certain electronic accessories meant for plugging into the cig outlet might expect 14v if they are intended to work with engine runnin g, and might not work as intended with the pure 12v. i am finding this issu e with a navigator which has a internal 12v battery which is charged from t he accessory socket.

anyone else observe this? thanks K

Reply to
beerismygas
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both the cig lighter and the accessory socket. for a kia they give 12.1-12.5v when engine is on or off. while engine is running if you turn on headlamps or fan etc, momentarily it will spike up to 13.8 and then go back to 12.5. i guess the alternator might be a smart type which disengages with a clutch if not needed.

engine is off you get 12.5, with car on you get a steady 14-14.1v , regardless of if you turn on headlamps etc.

outlet might expect 14v if they are intended to work with engine running, and might not work as intended with the pure 12v. i am finding this issue with a navigator which has a internal 12v battery which is charged from the accessory socket.

You can always put one meter lead on the battery + and the other on the live side of the socket. In theory you should get zero volts reading.

What satnav is it, they usually (always?) run on five volts once the juice gets past the input stabilizer.

Reply to
James P

Most car electrics batter side when the engine is running will be between 12.5 and 14.5 volts most in car toys are built o accomadate this.

Some usb charger inserts can not supply enough power to charge these toys , my blackberry cant pull enough with third party adaptors, oem kit and its fine

Reply to
steve robinson

Are you sure? It would be quite unusual for a GPS receiver to have a 12v in ternal battery.

Are you using the charging cable supplied with the device? If not, and it i s actually running off 5v (e.g. it has a USB socket on the side), then it m ay be that the charger isn't providing enough current. Many USB chargers ca n often only output (upto) 500mA whereas a lot of devices these days need u pto 1A so you need to pick your charger carefully.

Mathew

Reply to
Mathew Newton

internal battery.

is actually running off 5v (e.g. it has a USB socket on the side), then it may be that the charger isn't providing enough current. Many USB chargers can often only output (upto) 500mA whereas a lot of devices these days need upto 1A so you need to pick your charger carefully.

its a marine model. but my main curiosity is this voltage disparity. i wond er on other makes what is the voltage to be expected. is there a standard f or engine on , engine off ? thx

Reply to
beerismygas

internal battery.

actually running off 5v (e.g. it has a USB socket on the side), then it may be that the charger isn't providing enough current. Many USB chargers can often only output (upto) 500mA whereas a lot of devices these days need upto 1A so you need to pick your charger carefully.

on other makes what is the voltage to be expected. is there a standard for engine on , engine off ? thx

It is very common to do the job cheaply and cheerfully by having a resistor in series with the lead. Usually inside the plug a resistor inside the plug that goes into the car socket.

Of course putting a meter on the lead without the device connected will give the full voltage so you'd be better off measuring the inline current.

Reply to
James P

The battery voltage might be as low as 7v (while cranking) and up to about 16.5 (a dynamo with a mechanical regulator). The acceptable on-charge voltage varies with temperature.

Anybody designing car electrics should know this.

BUT - taxi drivers (generally dealing with diesel engines) are known to connect two 12v batteries in series when trying to start recalcitrant engines. So that's well over 26v !!!

Years ago I worked on a project designing electronic taxi meters; and this was one of the design considerations - the electronics should work normally from about 7v to about 30v.

Larger vehicles use 24v electrics. I'm sure there are some which use greater voltages - as well as the obvious milk floats.

Reply to
Graham J

Your readings are entirely expected and likely fairly typical across all cars.

What model GPS is it?

Reply to
Mathew Newton

Some modern cars use 42v - IIRC, BMW 7-series were the first. Allows higher power demands with lower currents.

Reply to
Adrian

Never ever seen a battery go down to 7v when cranking. Anything under 9 suggests it's fooked.

Reply to
Dave Plowman (News)

Did it really reach the road with a paying owner?

There were supposed to be at least 3 cars on market with 42V by 2002, it never happened. Only Toyota did it for real, with a Japan market only Hybrid, dunno if any are left.

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There was a 2nd round of bullish "We are gonna deliver it (this time)" in 2005 but that was a damp squib too.

HID headlamps all run at 42V from DC-DC ballast converter but nothing much else.

But higher voltage systems not entirely dead. Hybrids use much higher generator, battery, motor voltages, in a separate dedicated system. So the car is still 12V. Other power recovery systems may push to higher voltages.

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To go from 6V to 12V Lucas quoted the British bike industry twice as much for everything. I believe that included the 12V bulbs they were already making by the million for cars, bikes needed "special" ones. Bulb life on British big singles and parallel twins was quite short.

Reply to
Peter Hill

My father was in the motor trade selling trucks. Cab and chassis units were often driven from factory to specialist body makers in those days - and they'd often arrive without a single bulb still working due to vibration. 24v electrics having bulbs more delicate than 12. Shouldn't be a problem these days with LEDs.

Reply to
Dave Plowman (News)

That's because you can't see the meter display flash for 40ms. That assumes it takes analogue samples faster than 1/25th sec. I suspect many only sample 2-10 times a second. 1/25th sec an analogue meter needle wouldn't achieve the full deflection. Fig 3 on page of link below shows it's used as a crank test waveform. It may be a bit over the top but testing usually uses the extreme case.

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Special constant current devices for LED drivers. E-bay is full of LED bulbs that use nothing more than a series resistor.

240V household LED bulbs do have complex electronic controllers and some can vary the LED current and brightness depending on the waveform chopping of a Triac dimmer.
Reply to
Peter Hill

So you're assuming the sampling frequency of the meter always coincides with the low 'peak' of starter current?

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Quite. It's one of those technical articles designed to sell a product.

Which is fine if they're not being driven close to their limit.

And tend to fail well before their claimed life.

Reply to
Dave Plowman (News)

NO. I'm pointing out how very unlikely it is to observe these rapid short duration transients with normal multi-meters.

The only way to see such fast transients is a storage tube oscilloscope. I have a HP 1741A here (gift), where is yours? Yes they have gone digital these days.

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OK you may see them on high end workshop equipment with an oscilloscope like SUN.

Reply to
Peter Hill

Maybe I'm missing something but surely cranking a cold engine isn't *that* transient an event? You could be looking a several seconds with some engines.

If a transient drop is only detectable with an oscilloscope because of it's brevity, surely in real world terms (and normal real world measurements), it's irrelevant?

Tim

Reply to
Tim+

If you look at the graph I referred to, you will find it has non-linear time and voltage scales. 40ms initial at 5-6V, 20 seconds at 6-9.5V. During the sustained 20 seconds cranking the voltages are stable enough to be measured with a multimeter. It takes that initial 1/25th second time for the battery to begin the chemical reaction that permits 100A to flow.

For a load like a filament bulb nothing much will happen in 1/25th sec. It takes longer than that for it to cool below the temperature it glows white hot at. Even at 1/2 rated volts it will glow quite brightly - that's how dim dip worked, the two dip headlamps bulbs were put in series.

For transistors and LEDS it's effect is seen and responded to very quickly. LEDs are used as transmitter in opto isolators on signals with frequencies in the MHz, the LED flashes to microsecond pulse, an opto transistor detects. It would have to to be a very poor electronic device to have a frequency limited to 25Hz. Even vacuum tube computers had 10's of KHz clock frequency.

My car's ECU has a "brown out" detection. If the system volts drop below a critical voltage it shuts down, storing learnt parameters in non-volatile memory, when power is restored it does a full re-boot. It would be pretty useless if it shut down during cranking.

Cars modular wiring systems are now full of PIC/ATMEL and other micro controller chips running at 20-40 MHz. CAN Bus and everything attached to it has to keep running when the supply voltage drops to 6V. Then there is the USB stick, SD card or iPhone plugged in the stereo.

Reply to
Peter Hill

Well, yes, but they run on tiny amounts of power. A small smoothing cap would easily hide a 25ms voltage dip, without designing the circuit to actually run on 6V. (Whether they can or not, I don't know.)

Reply to
David Taylor

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