12v Cigarette socket is blowing my phone charger(s) - why ?

[aidancoughlan]

I wired up a cigarette socket to my batteries (battery to small bus-bar + and -, busbar positive to switch, switch positive to cigarette socket , and cigarette socket back to bus-bar negative terminal).

When I tried a phone charger it didnt work (ie. the light on the car charger didnt light, and the phone didnt charge). I've tested all along the circuit with a multimeter, and I was getting approx 14 volts right down to the +/- terminal inside the cigarette socket. (The voltage was high as the battery charger was running).

I noticed I had connected the +/- terminal at the back of the Cigarette socket incorrectly (wrong way around, the markings on the socket were extremely hard to see) - so I switched them, charger still didnt work. I tried a second car phone charger - it worked ok ! Puzzled, I reversed the polarity and tried again - the second charger now didnt work, and continued to not work when I corrected the +/- to the right terminals.

I didn't think it would make any difference, but It seems that connecting the +/- the wrong way around is damaging the chargers ? Can anybody help explain to me why this is ? Or was it that the voltage was at 14 volts instead of around 12v that did the damage, and it was just co-incidence that it happened when I switched the +/-?

 

[yoda]

There is electronics inside the chargers which are sensitive to polarity! Check and Check again (and then get a friend to check) before you blow up a third charger.

Yoda

 

[Steve Clayton]

At best you've blown the fuses within the charger heads; at worst you've blown the charger circuitry and rendered the chargers useless (or possibly both)

 

[aidancoughlan]

OK, thanks guys. The stamped polarity markings on the cigarette socket terminals are so miniscule as to be almost invisible - I didn't see them and thought it didn't matter which way around (as if wiring a light for example).

I'm curious though - what kind of circuit inside the phone could be damaged by reverse polarity? I understand (I think) that the polarity is important if there is a fuse involved - it needs to be on the positive side to be effective. If (by wiring the socket wrongly) I connected the postiive into the negative side of the phone charger, it should still work (shouldn't it?) - it's just that the internal fuse would not be protecting the charger.

If that description is accurate, does it mean that there was something else going on to actually damage the charger ? What could possibly blow the fuse - too much of a current draw ? - but the only load is the phone charger itself, which is presumably not too much for it's own fuse. Is the the fact that there was 14v on the circuit irrelevant or could it be part of the problem?

I'm keen to fully understand the issue if possible, as the intention is to connect our nice nice new portable Waeco fridge to the socket... miffed and all as I am having destroyed two (sealed) car phone chargers - I'm not prepared to dump the fridge !

 

[sailorman]

the cig socket should also be "Fused" to protect its circuit. the pwr would be better taken from your main switch panel & nor direct fron buss bar

 

[whipper_snapper]

[ QUOTE ]
I'm curious though - what kind of circuit inside the phone could be damaged by reverse polarity? I understand (I think) that the polarity is important if there is a fuse involved - it needs to be on the positive side to be effective. If (by wiring the socket wrongly) I connected the postiive into the negative side of the phone charger, it should still work (shouldn't it?) - it's just that the internal fuse would not be protecting the charger.

[/ QUOTE ]

There is no polite way of putting this! Your understanding is wrong in absolutely every respect. I suggest you get help with the next wiring project!

 

[Bilgediver]

Never a good idea to reverse the polarity of DC equipment as often it is polarity sensitive.

In future when in doubt stop.....and go back to first principles...if not marked then use logic and a test meter.

On a cigarett socket the pin is plus and the side connectors negative so check with a meter which terminal is going where as some sockets are not marked!!!!!

You battery chargers probably have a fuse which you will find if you unscrew the pointy end. Replace with fuses of the same rating and you should be OK.

Seems you want to set fire to your boat with your installation so please follow the advice given and at least put an inline fuse in the socket circuit . Hopefully you used something more substantial than bell wire but do get a second opinion that it will take 10 amps and use a fuse of that rating for starters.

 

[aidancoughlan]

Thanks for the responses guys, I know I'm still missing something though, and hoping to be enlightened ....

[ QUOTE ]
the cig socket should also be "Fused" to protect its circuit. the pwr would be better taken from your main switch panel & nor direct fron buss bar

[/ QUOTE ]
[ QUOTE ]
Seems you want to set fire to your boat with your installation so please follow the advice given and at least put an inline fuse in the socket circuit

[/ QUOTE ]
Yes, I have also fused the cigarette socket to protect the circuit. The wiring from the battery goes to a dual bus-bar with pos and neg sides, and then to a small BEP 4-way switch panel with 15-amp spade auto-style fuses protecting 2 of the 4 switches each.

I've then wired the cigarette socket to one of these switches, and further protected that wiring by an in-line AGC fuse rated @ 5 amps.
The Waeco Portable Fridge I intend to install consumes 35 watts at full load, which @ 12 volts is around 3 amps... hence the 5 amp fuse.

On my boat to take this particular feed from the main switch panel would have been an unnecessarily long route, but it is quite close to the batteries.. hence the small local bus-bar, switch and fuse.

[ QUOTE ]
Hopefully you used something more substantial than bell wire but do get a second opinion that it will take 10 amps and use a fuse of that rating for starters.


[/ QUOTE ]
I don't recall the wire guage size (I think it's 16AWG - and is tinned marine quality), but I did check it in Calders book at the time - it's a very short (2-3ft run).


[ QUOTE ]
There is no polite way of putting this! Your understanding is wrong in absolutely every respect. I suggest you get help with the next wiring project!

[/ QUOTE ]
Help me out here ! What in particular about my understanding is wrong... that's what I am trying to get to the bottom of. If you have a simple load on the circuit (eg. a light blub) it doesnt matter which way you connect the +/- , right? What exactly is inside the phone charger that makes it different - I believe there *is* something about it, I'm trying to learn/understand what. Can you enlighten me?

 

[Steve Clayton]

[ QUOTE ]
What exactly is inside the phone charger

[/ QUOTE ]
A LED that lights up when power is applied correctly.
A small printed circuit board with a specifically designed logic chip(s) that senses the status of the phone battery and applies charge as appropriate.
Probably a couple of resistors and capacitors that are balancing aids for the chip. (Some capacitors are "electrolytic" - this means that they expect power to be applied correctly; get it wrong and they can literally blow up!)
The chip is powered by the DC voltage. It expects to see + and -voltage applied correctly to the appropriate terminals; get it wrong and the chip fries it's internal components.

It clearly does not have a reverse polarity protection circuit /forums/images/graemlins/grin.gif

 

[aidancoughlan]

Many thanks Steve, I was more thinking in terms of 12v wiring inside the charger and trying to understand how it could damage itself. I suppose I didn't consider there would be sensitive electronics inside the phone charger (although in hindsight it seems obvious).

By the way, for my peace of mind can you confirm if my understanding of the following is correct (leaving aside the sensitivity of the chips etc. to polarity - ie. assuming a simple load on the circuit) ?
[ QUOTE ]
I understand (I think) that the polarity is important if there is a fuse involved - it needs to be on the positive side to be effective. If (by wiring the socket wrongly) I connected the postiive into the negative side of the phone charger, it should still work (shouldn't it?) - it's just that the internal fuse would not be protecting the charger

[/ QUOTE ]

 

[Steve Clayton]

[ QUOTE ]
I understand (I think) that the polarity is important if there is a fuse involved - it needs to be on the positive side to be effective.

[/ QUOTE ]
The fuse can be on either the pos or the neg side - if it blows then the circuit is broken. That said it is important that the fuse is on the positive side so that if it blows then the device/circuitry after the fuse is isolated from the power source (put it on the neg side and you will still have power being applied to the device so possibility of overheating/fire)

[ QUOTE ]
If (by wiring the socket wrongly) I connected the postiive into the negative side of the phone charger, it should still work (shouldn't it?) - it's just that the internal fuse would not be protecting the charger

[/ QUOTE ]
We've covered this - the answer is "No" in respect of devices that expect correct polarity. Stick the cigarette heater element in and it will work.

 

[aidancoughlan]

Thanks Steve, that clears it up for me. I realise putting the fuse on the negative side will protect the circuit itself (after blowing the device on the circuit).... while putting the fuse on the positive side protects the device as well. Although I've always followed the instructions for positive/negative connection on electronics such as VHF / GPS etc., I didn't fully realise the significance of the sensitivity to polarity for some devices connected to the cigarette lighter socket - Now I'm happy that that was the problem.

ps. While the phone charger is obviously damaged because of it's sensitivity to the polarity, is it likely that it (or any other polarity-sensitive device) could have caught fire ?

 

[William_H]

The concept of only fusing the positive connection is perhaps a carry over from motor vehicles where the negative is always connected via the metal body. A fuse in the negative line would alos protect the wiring from fire from a short circuit. However it is perhaps best to continue the fuse in the +ve wire rule for consistancy.

The idea that polarity doesn't matter is only applicable to light bulbs and other resistive devices. Some types of electric motor are not fussy but otherwise almost everything is polarity sensitive.

If for instance if you connect a battery charger around the wrong way to a battery you get in effect the battery voltage added to the battery charger supply so 30 odd volts connected to a short circuit. hence a lot of current and burnt wiring- boat fire. Hopefully the fuse will fail before the wire burns.

Some electronics will also die instantly. Some devices have a diode in the power supply which is a safeguard against reverse polarity but many don't.
So always double check the polarity of the supply.

I think you may end up with trouble with the cigarette lighter socket for powering the fridge. Permanent hard wiring is far more reliable at higher currents. I think you might need a 10 amp fuse for the fridge also.

Lastly as suggested the cigarette lighter plug type phone chargers probably have a blown fuse. They may seem difficult to open up. May be sealed as you say however many have a small screw holding two halves of the case together near the wire exit. The contact end will unscrew to allow the case to be parted. Note carefully where all the springs and contacts go as they can be tricky to reassemble. That is if they are the same type as I have a few of around here.

good luck olewill

 

[VicS]

Regarding your fridge it may take a much larger current when starting up than it does when running. You should therefore fuse the circuit in accordance with the manufacturers instructions. I agree with William H that a cigarette lighter plug and socket is a poor device for connecting a load like a fridge, however there are similar plugs and sockets around which do positively lock together (sorry but i cant provide any details although IIRC Ford supply one for connecting accessories in their commercial vehicles)

Regarding the phone charger fuse. It is most likely in the nose and accessed by unscrewing the centre contact assembly. I would not recommend that you dismantle the whole case in the way that William suggests. Plugs to fit cigarette lighter sockets are sometimes fused in the same way at least decent ones are.

As for catching fire, no its is not likely because the fuse would have prevented that. The intended implication was I think that your lack of understanding of these electrical gadgets could be a serious hazard.

You may find the "boat electrical notes" HERE useful

 

[nigelmercier]

[ QUOTE ]
A fuse in the negative line would alos protect the wiring from fire from a short circuit. However it is perhaps best to continue the fuse in the +ve wire rule for consistancy.


[/ QUOTE ]

In my new GPS chartplotter, the instructions specifically say to put the fuse in the negative. I've done both /forums/images/graemlins/laugh.gif

 

[Bilgediver]

What exactly is inside the phone charger that makes it different -
************************************************

The charger will have solid state devices in it IE transistors and chips and these are very sensitive to the abuse of incorrect polarity and easily destroyed.

Depending on the quality of the charger there may be built in protection and a fuse and the protection would be designed to protect the circuit agains reverse current and blow the fuse.

These fuses are usually under the spring loaded pin at the pointy end and could be quite a low rating and fast blow type.

 

[whipper_snapper]

[ QUOTE ]
Thanks Steve, that clears it up for me. I realise putting the fuse on the negative side will protect the circuit itself (after blowing the device on the circuit).... while putting the fuse on the positive side protects the device as well.

[/ QUOTE ]

As said above, that is not true. But it is amazing how many people believe it. I think it's because of the water analogy that is often used to explain electrical circuits. It's a pretty good analogy for most purposes but it does give the impression of electrons piling up at the end of the positive wire trying to get out!

In fact the electrons are flowing the other way, and anyway it is just not like that. A current will only flow given a potential difference and a conductor. The terms pos and neg are just conventions and could have been reversed. And they only have meaning relative to each other. So a neg potential is positive with respect to a more neg potential.

Has that helped or muddied the waters even more?!

 

[bedouin]

[ QUOTE ]

As said above, that is not true. But it is amazing how many people believe it. I think it's because of the water analogy that is often used to explain electrical circuits. It's a pretty good analogy for most purposes but it does give the impression of electrons piling up at the end of the positive wire trying to get out!


[/ QUOTE ]
I think people probably confuse Mains AC with low voltage DC. With mains AC the fuse must be in the Live - which people see as analogous to +ve in the DC sense.

I think being consistent in always fusing the +ve in a DC environment is a good thing. It means all -ves are effectively equivalent and can be commoned, and also avoids any possibility of creating a loop/short that is unprotected (e.g. by connecting the +ve from a -ve-fused circuit to the -ve of a +ve fused circuit)

 

[davidpbo]

Always assume that polarity/correcting the wires the right way round matters.

Plug in car chargers are cheap as chips, often made to a budget and unlikely to have much excess protection. Some D.C. equipment may have reverse polarity protection but it is not safe to rely on it.

Even if there are fuses in the circuit they will not necessarily protect the equipment against reverse polarity. You have had a lucky escape, two blown phone chargers ( which may as stated only be fuses) is a lot cheaper than say a VHF, Radar or GPS.

Hope they are allright.

 

[Drascomber]

[ QUOTE ]
however there are similar plugs and sockets around which do positively lock together (sorry but i cant provide any details although IIRC Ford supply one for connecting accessories in their commercial vehicles)

[/ QUOTE ]

"Marinco" brand plug and sockets will lock together, the socket will also take a normal cigar lighter plug (without locking), they are made for boats, not cars so don't corrode so easily and have a captive rubber bung (which you can leave off if fitting in the cabin. They are American but widely available in UK chandlers.