Voltage regulators - how do they work?

Richard53

One for the techies. I'd be interested to know how a car's voltage regulator works. I know what it does, but how does it do it?

Reason for asking - I am trying to sort out an electrical problem with my Land Rover. One thing I have noticed is that when I set off from home (unlit country lane) I can see the light from the headlights betting brighter and dimmer, roughly with changes in engine revs. The change seems to happen in distinct steps, rather than smoothly, if that makes sense. These are small changes that you wouldn't notice under street lighting. My Mondeo did the same, and the charging system was 100% fine on that, so I am really trying to find out if that is how VRs work (regulating system voltage within a given range, hence the steps) or if there is a fault and the lights should brighten and dim smoothly or not at all.

This might be a stupid question, but it has made me realise that I don't know what goes on inside a VR at all.

(The problem with the LR is almost certainly a poor chassis earth, which I am sorting, but I was just curious.)

Gloomendoom

Solenoids with some spring loaded contacts.

You need to set it correctly or you can get all sorts of issues. I had a problem with my LR cutting out after 17 miles. Turned out that the new voltage regulator wasn't adjusted properly and I was over-volting the ignition coil. I had incorrectly assumed that new voltage regulators were plug and play. They aren't, you need to tune them to your car.

https://www.youtube.com/watch?v=UxXuKOQTASE

https://www.youtube.com/watch?v=UxXuKOQTASE

Richard53

That's the kind fitted to a Series vehicle, I think. Mine's the modern type (1996) built in to the alternator, but I assume it works to the same principles (electronically rather then mechanically). In general, it is allowing voltage to vary over a limited range, hence the apparent steps in brightness as it switches in and out. I'm guessing that 'tuning to the vehicle' is no longer possible. It's right or it's not.

Thanks for digging that out. Curiosity satisfied and, more importantly, confirmed it's normal behaviour.

Cheers.

phillw

Richard53 wrote: »

Mine's the modern type (1996) built in to the alternator, but I assume it works to the same principles (electronically rather then mechanically).

http://www.carparts.com/classroom/charging.htm#VOLTAGE%20REGULATOR

"The voltage regulator controls the field current applied to the spinning rotor inside the alternator. When there is no current applied to the field, there is no voltage produced from the alternator. When voltage drops below 13.5 volts, the regulator will apply current to the field and the alternator will start charging. When the voltage exceeds 14.5 volts, the regulator will stop supplying voltage to the field and the alternator will stop charging. This is how voltage output from the alternator is regulated. Amperage or current is regulated by the state of charge of the battery. When the battery is weak, the electromotive force (voltage) is not strong enough to hold back the current from the alternator trying to recharge the battery. As the battery reaches a state of full charge, the electromotive force becomes strong enough to oppose the current flow from the alternator, the amperage output from the alternator will drop to close to zero, while the voltage will remain at 13.5 to 14.5. When more electrical power is used, the electromotive force will reduce and alternator amperage will increase. It is extremely important that when alternator efficiency is checked, both voltage and amperage outputs are checked. Each alternator has a rated amperage output depending on the electrical requirements of the vehicle."

System

Gloomendoom wrote: »

Solenoids with some spring loaded contacts.

Maybe in the 1960s and 70s but they moved onto solid state over four decades ago when they moved from dynamos to alternators.

Ganga

If the lights are going brighter/dimmer with the change in engine revs i would check the fan belt/alternator belt is adjusted properly

Gloomendoom

Tarambor wrote: »

Maybe in the 1960s and 70s but they moved onto solid state over four decades ago when they moved from dynamos to alternators.

I know that but it didn't occur to me that the OP wanted to know how an electronic circuit worked. Electro-mechanical is so much more fun.

Jackmydad

Gloomendoom wrote: »

I know that but it didn't occur to me that the OP wanted to know how an electronic circuit worked. Electro-mechanical is so much more fun.

And if it wasn't working properly, there was always the starting handle!

Ectophile

Regardless of the voltage regulator, the amount of current the alternator can put out depends on the engine revs. On a cold day, the engine will be harder to start, and will draw more power out of the battery. Then once the engine is running , you turn on the lights, heater, demister and so on, putting a huge load on the electrics.

When the engine's revving, the alternator can produce enough amps, and the electrics will be at about 13.8 to 14.4V. If the revs drops to idle, the alternator can't keep up, and you're running on battery. If you've only just started the car, that may be down to 12V.

Richard53

Ganga wrote: »

If the lights are going brighter/dimmer with the change in engine revs i would check the fan belt/alternator belt is adjusted properly

First thing I checked - all OK.

Gloomendoom wrote: »

I know that but it didn't occur to me that the OP wanted to know how an electronic circuit worked. Electro-mechanical is so much more fun.

Actually, I had forgotten about the wonders of the electromechanical switch. It's been a while ...


But the principle is the same, switching in at one value and out at another, giving a small range of acceptable values that appear to the driver as a discrete step in brightness.


Interesting info, and thank you all.

arcon5

Ectophile wrote: »

When the engine's revving, the alternator can produce enough amps, and the electrics will be at about 13.8 to 14.4V. If the revs drops to idle, the alternator can't keep up, and you're running on battery. If you've only just started the car, that may be down to 12V.

Well that's not true at all. Otherwise the battery light would come on everything it falls to idle. The alternator will always produce sufficient voltage unless faulty.

The only exception being absorption stage of a smart charge system