Automotive 6 Volt Generator Transistor Voltage Regulator

[rjenkinsgb]

I enjoy helping with things like this, stuff with practical applications. It's good to see them become functional!

My main line of work is designing and repairing industrial control systems, anything from computer-based electronics through the motor drive systems and mechanics. I'm interested in just about anything relating to electronics, programming or technology generally, but especially computers, digital gear and audio.


Re. the main diode, I don't know of any really low voltage ones offhand. Once the rest of it is finalised, it could be an application for another FET possibly, but the control of that & change in feedback voltage would take some thinking about...

The field remanence is a problem, it seems a limitation of that field configuration, there is no easy way of providing a start-up bias. I wonder what a neodymium magnet stock on the outside over one of the field poles would do?? The casing may just be too thick for any significant field to pass through it.

 

[Danwvw]

I have been using a magnet to start it. even a novelty magnet will start it if I hold it through the slot to the side of the field coil however it doesn't work through the generators steel housing. A jumper from B+ to D+ works quite will. I thought about the FET and using the 6 volt gen lite wire to gate it, It probably won't be necessary if the Thermistor works? Still it's a fun idea.

Looks like a DC to DC converter would be needed to gate the MOSFET if I understand this correctly?
.

Maybe use SCR's:

 

[rjenkinsgb]

Remember it must only turn on when the dynamo voltage reaches or exceeds the battery voltage!

I was thinking of a circuit that detected the voltage 311 output going (pulsing) low, to show the output was working, and using that to pull down the gate of a P channel FET.

However that then also needs a change in the voltage feedback circuit, as it must regulate at two different voltages, depending if the FET is on or off...
Possibly a second FET switching a preset across the bottom of the reference voltage divider, to calibrate the lower output voltage?

 

[Danwvw]

Sounds pretty complicated! Hope I don't have to do that. I could put a 2n2222 or something in there too but I would rather keep it as simple as possible. As it is now the gen lite wire is bringing the unregulated LM311 supply to 4 volts with just the key on not started and 4.2 volts started not charging, there is even some pulse activity to the gate on the scope.
Generator drops out when returning to Idle and when it's cold it doesn't start charging again without revving the engine.

Note! The Un-Regulated when charging at 8 volts D+ is only 7 volts. I checked and it's not the gen wire that loads it.

Probably the unregulated supply could be improved, the super cap you mentioned or a diode to D+ instead of the 47 ohm resistor. Really when I think about it the field resistor is not what starts the generator anyhow, with the mechanical it's the field relay is normally closed at startup so DF is ground then. Our Electronic Regulator Design can't do that till it has D+ supplied.

Note! on the Mechanical Voltage Reg the NC is ground, C is DF, and NO is D+.

 

[Danwvw]

So I found a 2.5 Ohm Thyristor in an computer power supply and tried it in parallel with the 7 ohm field resistor, It did make it start charging a little easier but it stays cool and makes it overcharge, so that Idea is not going to work!
Here is what I am thinking now: GA-230 Super Capacitor 0.4F 4.5V 90m ohms

 

[Danwvw]

The .4F SuperCapacitor arrived however testing shows it's not going to work to start this generator charging. tried it on the D+ and DF and the unregulated and across the 7 ohm and it just does not help the generator to start charging. The only way to get this generator to start charging is to momentary jump B+ to D+. At least with the Electronic Design.

 

[Danwvw]

Ok, So the plan is to try this circuit next. I am thinking getting the resistor values correct, it will work. But all the working voltages are marginal because it's running the devices off of the generator indicator lamp power to avoid draining the battery.
When the engine is reved before it starts charging the D+ starts to go up to about 2 volts which could cause the MOSFET to not work, just have to try it. The field resistor not shown here but in the regulator schematic may need to change from 7 ohms to 5 ohms to help keep the D+ voltage before it starts lower.
See any problems? Have any suggestions?

 

[rjenkinsgb]

Remember the common mode range for the 311; the inputs should not be within 1.5V or whatever of the positive supply - that's why you need the dividers on all the inputs in the main reg circuit.

Can't you just provide an outside kick to the regulator 311, so that can turn on the main control FET?
That should be all it needs.

In fact, connecting the lamp via a couple of diodes to the "lower ends" of the 47 ohm power feeds, for the IC and reference, may be enough?

ps Very few supercaps are actually rated for high discharge current. Many generic ones have high internal resistance and are only suitable for milliamp level loads.

 

[Danwvw]

Wow your up must be morning for you. Midnight here. I need to go to bed! Yes these values will have the inputs at 2.5 volts and 2 volts and the supply at 4 volts when it's trying to start charging.
So I could start driving the car with the electronic voltage regulator and testing it in the real world I put a microswitch hanging on my bumper and I set the choke get it running above 900 RPM on the engine probably 1500 RPM on the generator. I have to press the switch for 2 seconds to start it charging. It just jumpers the field to ground. Probably a more robust start circuit could use B+ for the power supply but it would need to shut itself off somehow.
As far as kicking the 311, It's actually worked with about 4.4 volts with the gen lamp on it's supply, the real problem is the generator needs High current in its field to start to charge, It really does need the field grounded ideally to start charging. Thanks for continuing to help.

6 Volt Voltage Regulator Final Schematic:

 

[rjenkinsgb]

It really does need the field grounded ideally to start charging.

... But, if the 311 in the regulator is powered, it will turn the power FET on and ground the field!

 

[rjenkinsgb]

Or (and?) slightly re-arrange the FET drive - move the 330 Ohm pulldown to be a pull up to the 8V supply, 311 pin 1 to ground and 7 as output, then swap pins 2 & 3.

That puts the FET on with the highest possible gate voltage, until it starts to regulate, and then it should work the same as it does now.

 

[Danwvw]

I see what your saying, I did that on the start circuit design I think it probably makes a 1/2 volt more that way.
When I had the gen lamp wire to the un regulated supply it was making a gate pulse at idle however the mosfet was not firing or quit just about at the same time voltage drops from the generator, it's on that 7Ohm video just at the end it drops out. But I had the scope a little over on storage persistence or something. I should look at it on the scope again maybe power the unregulated correctly and see what the MOSFET can do.
I think the problem with the power mosfets is they need at least a minimum current Drain to Source to stay in and perhaps a minimum voltage Drain to Source to fire? It probably would self start with the field resistor much higher as that lets the generator build higher voltages before it starts charging . Perhaps I will try removing the field resistor altogether It may work that way if it gets revved way up, but my goal was to duplicate the behaviour of the mechanical voltage regulator.
Moved the start switch to inside the car and took the car out on the highway for a 25 mile trip . It always drops out at stop signs etc however worked flawlessly otherwise. .

 

[Danwvw]

x

 

[rjenkinsgb]

I think it probably makes a 1/2 volt more that way.

But more importantly, it will try to charge even without the 311 functioning!

The charging dropout at tickover is normal, it's one of the reasons alternators replaced dynamos...

A FET acts something like a voltage controlled resistor. If it has appropriate gate-source voltage, it will be low resistance regardless of drain voltage or current.

Using a fet with a lower gate threshold voltage could make a massive difference; these look promising, they start to turn on at around 2.5V:

https://www.onsemi.com/pub/Collateral/NTP60N06L-D.PDF

 

[Danwvw]

Definitely build my next prototype with the Voltage Comparator configured with pin 7 collector output, Yes those NTP60N06L Mosfets may be a better match, looks like their current comes up a lot quicker than the IRF540 Mosfet's also it starts conducting earlier. I don't see them available on ebay except from China though!

 

[rjenkinsgb]

That was just the first I found, which appears to be discontinued..

This is another possibility - it's just whatever type has the lowest gate voltage turn-on to pass enough current to get the dynamo to fire up..

N-Channel MOSFET, 47 A, 55 V, 3-Pin TO-220AB Infineon IRLZ44NPBF | RS

uk.rs-online.com

 

[Danwvw]

I can get these on e-bay out of New York. MTP75N03HDL

 

[rjenkinsgb]

That looks good!

 

[shortbus=]

I have a dumb question, as most of mine are. Why couldn't this be done by using the old magnetic regulator, but then using the points in it to control mosfets or transistors? Like when they add a solidstate circuit to a points ignition distributor? When I did that to one of my old Harley's the points never had to be messed with again, since they were only controlling a transistor base current not full coil current.

 

[Danwvw]

Sure I would like to see the design! One of the nice things about doing it all electronic though is very good control of voltage and the ability to set the output voltage and current the generator produces. . This design can adjust the output to go right up past 10 volts but that is dangerous.

The 12 Volt Mechanical Regulator Schematic:
**broken link removed**