These lightweight alternators are more efficient. Ok, lets skip a bit… vehicles are now fitted with alternators. If they didn’t do this, just leaving your car idling in winter could flatten your battery! They have to ensure that even at tick-over, the output of the alternator is sufficient to put some charge back into the battery, power the engines electrical systems and power all the other things.
CAMPER BATTERY ISOLATOR RELAY WIRING DIAGRAM WINDOWS
Well, the old dynamo’s were rotating too slow at tick over or idle speed, the voltage was generated was around 9 or 10 volts… not enough to charge the battery, however at the higher end of the vehicles rev range, the output could be as high as 20 volts, so they had a box or regulator to control this excess voltage by switching the dynamo in or out of circuit.Ĭar designers have to take into account that in winter you will start your car, turn on the heated windows and mirrors, heater fan, stereo, and then maybe leave the car idling to warm up.
The old dynamo’s did need to have the engine going at a fast – 1800 to 2000 RPM idle speed to generate enough voltage to charge your battery but modern alternators will produce sufficient output to charge the vehicle battery at your engine normal tick over or idle speed. So this is where one of the myths comes from – “ you need to rev your engine to get your alternator to charge your battery!“Įrr… no you don’t.
The regulator was inefficient too and often caused overcharging and boiling of the battery and at slow speed, they just plain didn’t work. with car engines now revving up to 7000 RPM our poor old dynamo would be spinning at 14,000 RPM and lasting about a week as the centripetal force acting on those heavy copper coils rotating at that speed would pull them apart pretty quickly.ĭynamo’s had few other issues – not only were they heavy but the carbon brushes needed changing on a regular basis, the commutator needed cleaning and if it became pitted through arcing would usually need re-finishing in a lathe. Dynamo’s were usually geared so that the turned twice as fast as the car engine, which was great when you average Ford engine only managed to do about 4500 RPM…. that eventually went to the battery.ĭynamo’s typically had an output of around 25 to 30 Amps – which compared to modern alternators of around 120 to 160 amps was tiny. The output of the dynamo went to a regulator that controlled the DC (Direct Current) voltage…. It was heavy, it has a commutator that allowed the rotating coil to pass the output current via carbon brushes which required some regular maintenance. It had fixed heavy magnets wrapped round a rotating coil that was driven by the engine usually via the fan belt. Not too long ago, the only device to charge a car battery was a dynamo. don’t panic! We do need to look back a few years though. A better understanding of what’s happening will hopefully help you fault-find if there are problems. I’ve written this to try to remove some of the mystery (or should that be misery?) out of what happens when you plug your caravan into your tow car.
It is then easy to see how connecting your caravan allows the engine to charge the caravan leisure battery. To really understand whats going on, we have to understand how the tow vehicle’s battery and alternator work first. There is a lot of confusion and a lot of myths as to what actually happens when you plug your caravan into the tow vehicle and start the engine.
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