Voltage regulator insides

[SeanB]

Tore apart an alternator today, on it's way to being a scrap pile addition. Was not charging, probably a combination of worn brushes, and a dead diode or two, along with corroded contacts.

Anyhow, here is the insides of the voltage regulator. 3 wire bonds are from left to right input, output and ground.

Nicely encapsulated in a soft jelly coating.

[RCMR]

Automotive voltage regulators are very simple devices -- I recall replacing a friend's burnt-out VR on their old 1970-something Toyota HiAce with something I knocked up using a 2N3055 and some passives.

Worked for years and was still working perfectly when he sold it.

The VR simply varies the current in the rotor to ensure the voltage from the field windings is held constant regardless of load and RPMs.

Basic electronics 101 stuff.

[SeanB]

I don't have any of the older regulators around any more, nothing electronic in there other than resistors and very finely calibrated relays. You can still buy them.

This one is nice in that it is big enough to see the actual regulator circuit, along with the trim laser cuts on the thick film resistors.

[Psi]

Good timing, i was just wondering about whats inside an alternator.

2 days ago i replaced my car battery with 6x 2600Farad 2.5V super capacitors (sick of having to replace my battery every 2 years)

There's an interesting side effect where as soon as you start the car the capacitor have been discharged a little and have a lower voltage, so the alternator immediately tries to pull the voltage back up.
Since they're capacitors and have almost no ESR they don't pull up to 14V instantly like a battery would so the alternator puts the full 30A into the caps while the engine is idling. It tends to stall the engine just after starting unless you give it some gas for 3 seconds.

So i was wondering how exactly the alternator works internally as i might have to add some resistance into the alternator charging line.

[Rerouter]

hmm, that sounds like a biggy of an issue if you are ever jump started aswell, you would have to make absolutly sure they clamped there negative on the case or you could well pop a conventional lead acid,

an altenator is like a conventional generator, it generates an AC voltage, however the larger the load it has to drive, the more force it requires to turn, and the lower the voltage drop from its esr,

so it could be that its demanding so much current that your motor simply cannot turn it, so yes either adding some resistance (moving your alternator negative to chassis may help add 0.05 ohm)
or use some type of mosfet switch to soft start the alternator, where it increases a pwm voltage from it until a certain voltage is met, to stop the current stalling your motor, and the mosfet acts as a tiny series resistance,

[Psi]

hmm, that sounds like a biggy of an issue if you are ever jump started aswell, you would have to make absolutly sure they clamped there negative on the case or you could well pop a conventional lead acid,

yeah, being jump-started is an issue. If the caps are flat it's like shorting out their battery
I'll probably mount a resistor somewhere to jump-start from.

Really there isn't a need to jump-start in the typical way. I don't need their battery connected in parallel while cranking, i just need to steal some energy to bring my cap voltage back up then i can start the engine myself.

[muvideo]

2 days ago i replaced my car battery with 6x 2600Farad 2.5V super capacitors (sick of having to replace my battery every 2 years)

Just curious, but is it "safe" to have the equivalent of few (2-3) Ah battery?
Did you try how many start attempts before the capacitors voltage become low?
Another candidate for car starting is Li-Fe chemistry, 4 cells are centered around car
working voltage (3.2-3.6V), but I dont know how is high temperature life .

Fabio.

[Simon]

Interesting idea, I did not know we had caps powerful enough to start a car. Thing is now you will need to rub the engine anytime you need power or you will not be starting again. No more using stuff plugged into the cigarette lighter socket unless the engine is running.

Have you considered a battery and capacitor combination ?

[SeanB]

Bigger issue with the supercaps is that the diodes inside the alternator will die in short order, as they really are not rated for 30A continuously, more like 30a for 5 seconds. You might want to add some more 4mm wire to the alternator output, about 2m should do to increase the output resistance enough to keep them happy. I often find that one or more of the 6 diodes is either open circuit or dead short.

The battery and added capacitor is good, it combines both good points, as even a near dead battery will eventually charge the cap enough to start the engine.

I just replaced my car battery yesterday afternoon as it silently died during the day. Went at 4 to go home, turn key and click. Voltage was 10.5V, so one dead cell. R800 ($100 near enough) later and 5 minutes later new battery was being quickly changed by me, carpool was getting noisy. Have to give the old one in Monday, will check it and see if recoverable as UPS battery, and give in a very dead one.

[Kevin.D]

quote : - "2 days ago i replaced my car battery with 6x 2600Farad 2.5V super capacitors (sick of having to replace my battery every 2 years)"

You can't really do that , you need a charge/discharge regulator, because as you pull charge from the caps the voltage will quickly drop below  12 volts  ,so all that remaining energy in the caps becomes unusable without a high power step up converter which you don't want  . You  are better with a larger number of 2.5V caps in series then charge to a much higher voltage via a low power step up  converter  then use a high power step down switching regulator to get your 12 V out so much more of available cap energy is usable.
Also Those 6 caps your using here are going to be energy equivalent to a  1 Ah@12 v battery .
Not great but would give you a good starting current for 35 or so seconds  ,that would allow you to fit a much smaller car battery than usual say 10 Ah instead of 60 Ah .

But is expense of the super capacitors and regulators required worth it .? Probably not,your not going to save that much on battery costs over car lifetime .

[Psi]

You can't really do that

Sure you can, you don't have to use all the capacity if you don't want to. There's plenty of energy between 8 and 14.5 volts.
Which is enough to start the car. It would probably start on 6V even. A normal lead acid voltage is quite low during cranking.

I have no plans to build a regulator for it. It has enough power to start the car at least 16 times and i've never needed more than 1 time. (except for aforementioned stall issue i need to fix)

Obviously if i leave the lights on its going to run flat real quick but i never do that.
I can't say i've ever use the cigarette lighter for anything.

Adding a smaller battery in parallel would defeat the purpose. I want to stop having to buy replacement batteries.
The caps should outlast the car.

Yeah, the caps are expensive if you buy them new, i'm using 2ndhand caps from electronic goldmine which were $15 each.

[Hypernova]

You probably want to keep a small 12v battery around in your trunk Psi, doesn't have to be lead acid. Nobody really knows how well those Maxwells age as well as their self discharge rate. If you find them flat at least you can hook up the backup and wait for an hour or so and charge it back up for 1 start.

[Psi]

You probably want to keep a small 12v battery around in your trunk Psi, doesn't have to be lead acid. Nobody really knows how well those Maxwells age as well as their self discharge rate. If you find them flat at least you can hook up the backup and wait for an hour or so and charge it back up for 1 start.

Yeah, some sort of recharge pack would be a good idea for an emergency.
Maybe something that can take AA's Since its easy to find/buy those.

The maxwell datasheet says 20% after 10 years. I suspect they will last 20 years easy before the capacity gets too low for my application.