Car Alternators - how much are they overdesigned ?
I recently bought a cooler which can operate in my car. I have some worries :
1> The alternator in the car must be designed (assumed :D) for supplying power to the car Stereo, Air Conditioner, all lights, etc. How much is it overdesigned, that is how much more power can it provide safely without overheating the wires or the alternator ? There is no info on this in the car manual.
2> Assuming that the electrical system can provide the power, is it alright to plug all the gadgets (Cooler, Charger, etc.) to the cigarette lighter outlet ? I mean do the wires to the cigaretter lighter outlet designed to handle power more than a cigaretter lighter does ?
3> I know that the alternators generate AC voltage (If you had a DC generator it will give varying voltages with speed) which is then rectifed and regulated to give the correct voltage to keep charging the battery. So even if the alternator were to provide more power is the rectifying unit capable of handling it ??
4> In the same line - is it a good idea to use the new jump start wires which connect to the cigarette lighter plug. Are the cigarette lighter wires designed to handle the high current required during jump starts ?
5> Also on the same lines, is it alright to start the car with the air conditioner ON. Are cars designed inherently to not supply current to the air conditioner when starting ? I ask this because everything else (lights, stereo etc.) works even when the enginer is not running except the air conditioner.
Any help is appreciated.
PS = I am also posting this question to the Click and Clack bros
From what I have seen, the cigaretter lighter is not individually fused. So the fuse will blow up - when the combined power of the lighter and other connections exceed the limit. The wire to the cigaretter lighter can still get damaged.
Ditto
ALternators definitely don’t generate DC voltage. Alternators generate Alernating Current (AC) hence the name. The AC is rectified.
Fuses in Cars are quick acting. Also, refer above.
Putting a simple automatic switch can easily cut off all other supply accept the supply to the starter. I’m not sure if this is done though ??
It’s not overdesgned too much. People who like to put huge freaking stereos in their car (possibly to bounce the car down the road if the engine dies? just kidding) also upgrade their alternators when they add in the amplifiers.
The cigarette lighter is fused, and the wires are sized bigger than the fuse. This doesn’t mean it is safe to just put a bigger fuse in there, but if you stay within the rating of the cigarette lighter you won’t overload the wiring or the alternator.
Despite what crazy horse said, alternators do in fact put out AC which gets rectified by the “regulator.” Quite often the regulator in a car is just a rectifier, and the car relies on the battery to provide both regulation and filtering. Older cars may have a DC generator, but no modern car I’m aware of does.
The cigarette lighter jump start wires don’t actually jump the car the way the old jumper cables did. All they do is provide a low current connection between the two vehicles, which allows you to slowly charge the battery of the dead one from the live one. The whole thing seems like a bad idea to me.
The air compressor usually has an electric clutch which won’t engage while the engine is starting (since it is wired to the switched portion of the electrical system, same as your stereo). The compressor’s mechanical parts spin because of a belt which is attached to the front of the engine. If the engine isn’t running, the compressor isn’t turning, and the air conditioning doesn’t work. While the engine is starting the electric clutch is disengaged which means the compressor still isn’t spinning (in other words it is safe to start it with the AC turned on).
While click and clack have probably forgotten more about cars than I ever will know, their knowledge of all things electrical is somewhat lacking. To their credit they do a lot better than most auto mechanics, but even they admit that electrical things are kind of beyond their understanding. Coincidentally, their latest show (which you can listen to on their web site) contains a segment about a car with some rather humorous electrical problems. Click and clack seemed to have missed the possibility of a faulty ground, but otherwise they are definately on the right track of what the problem is (not bad for mechanical guys if you ask me).
On my truck it is. On our van the cigarette lighter is also on the same circuit as the horn but nothing else. On one of the cars I have the dome light and the radio are on the same circuit as the cigarette lighter.
Usually just about everything except the lights and the connection to the radio’s memory (but not the radio’s main power) is switched.
Alternators generate AC Voltage. It’s why they are called “alternators”, after all. DC generators are called “generators”.
As far as design power output - the amperage that an alternator can put out is roughly proportional to the rotational speed (it levels off at a point, according to the chart for my car…). You should note that very often the alternator is a component where the manufacturer puts in the absolute minimum size that will suffice to operate the car, to save the most money. To help out in this situation, I have seen overdrive pulleys for alternators, where the alternator speed is increased over stock by about 15-30% (this is in opposition to the “underdrive” pulleys that racers often must use, so their alternator works at the higher rpms they are running at…it also saves a little power for them at lower rpms too).
IME, I have seen situations where the alternator size even goes up and down - in one case, Subaru put in a 45-amp alternator one year, then bumped it up to 60 amps two years later (when they had a rash of complaints of dead batteries in the first couple years afterwards), then dropped it back down to 55 amps the next year. Like they were “iterating” towards a balance.
FIAT and Ford have done the same thing - IIRC, the 1998 Mustang GT has a higher output alternator than the 1997 or the 1999 for this reason, but I may be mis-remembering. I thought they went from 110 amp to 130 amp to 120 amp.
>> Quite often the regulator in a car is just a rectifier
Nope. Never. An Alternator is a source of current and has a feedback circuit which senses voltage and adjusts the field current to produce the desired current output.
This (sizing) problem arises continually in sailboats where you want to recharge batteries fast running the engine as little as possible. There are indeed oversized alternators in the market. Standard alternators are in the 55 Amp range and often boats will upsize to 110 Amps and even install several. When installing very large alternators you need to interrupt the field current until the engine is running as you do not want the huge alternator loading your starting motor.
Thank you sailor. Its regulated and not just rectified. In fact if you did’nt sense the battery voltage and charge it accordingly, you’ll surely screw up the battery or the alternator or both.
BTW, the nominal AMPs are just that: mominal. I do not believe a 55 Amp alternator can output 55 amps indefinitely, only for a short time and with good luck and favorable wind and tide.
The first thing I’d want to know is how many amps the cooler uses. If it’s 5 or less, I wouldn’t worry much. If it’s 15 or more, I’d be hesitant to use it. Presumably this is something you’d need to leave running for long periods. Any additional electrical load will shorten the life of the alternator. Whether this life-shortening is linear or geometric proportional to the amperage of the load, I don’t know. Which component of the alternator (rectifiying diode, windings, internal connection, etc.) is likely to fail first varies with different alternators.
It’s not uncommon for electrical connectors to suffer with sustained high-amperage loads. This is most commonly seen in blower motor and radiator fan circuits. It’s possible that extended use of the cig lighter socket could cause some damage. Fuses typically blow at about twice the expected load on the circuit. If you’re using 90% of the fuse rating, it probably won’t blow, but the socket or its connector could be overstressed.
Any accessory that doesn’t operate with the key off is also not going to operate (and thus not use power) with the key in the start position. It’s the moment the key is released to the on/run position that these will start to use power. Although it’s not a bad idea to turn off everything possible when jumper-cable starting, for normal use purposes it’s not necessary. Items that operate with the key in the off position (headlights, etc.) should be turned off when starting.
With some cars, it’s not too hard to find an optional higher-rated alternator; with others, there’s only one model available. The nominal rating is peak power, although testing specs are to look for +/- 10% of this. Constant use at peak power will fry one in short order. Even constant use at more than a small percentage of peak power will shorten its life noticeably. Alternators are designed to keep a battery’s charge topped up, not to charge a significantly low battery.
Now that automotive DC generators are mainly historical curiosities, some car manufacturers are calling alternators “generators.” It may be a more technically accurate description of their purpose, but I can’t see a compelling reason for the terminology change, which I believe may cause some confusion. Ah well, they didn’t ask me.