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Homemade solid state 6V regulator
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herbie1200
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PostPosted: Wed Feb 22, 2017 12:40 am    Post subject: Homemade solid state 6V regulator Reply with quote

I put on and tested my homemade solidstate 6V regulator...

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It is tuned to max 7,4-7,5V measured at battery terminals - engine cold.

Due to its position, on the generator, it reacts to engine temperature increase.

So when engine is hot voltage drops to about 7,2V.

100km on it, all right.

I'm in doubt to apply following improvements:

- a current sensing circuit;

- to use for cut off an "ideal diode" diode instead of the present schottky diode (less voltage drop, 0V against 0,3V)

- a PWM field regulation; now it is "natural" feedback, like the original electromechanical, the frequency is governed by generator voltage waveform. A pwm should give a perfectly stable output voltage.

P.S. I travel with a well tested NOS spare regulator under my back seat Laughing
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gt1953
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PostPosted: Wed Feb 22, 2017 6:59 am    Post subject: Re: Homemade solid state 6V regulator Reply with quote

Nice to see something like that for the 6 volt crowd...I only bet you have an interest in electronics.
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bluebus86
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PostPosted: Wed Feb 22, 2017 10:31 am    Post subject: Re: Homemade solid state 6V regulator Reply with quote

pretty cool!!!! would you mind sharing a schematic and a brief explaination of how it operates? electrons are not my first thing, Im a bit more mechanically inclined than electrically. very neat idea.
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Wayne S. Johnson
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PostPosted: Wed Feb 22, 2017 11:36 am    Post subject: Re: Homemade solid state 6V regulator Reply with quote

Hi herbie1200,

Its great to see you are working on a 6V generator regulator.

This is my ALTERNATOR REGULATOR prototype, built in 1974. It ran for about 10 years without any problems. Over the 10 year test period, the ambient temperature range was 25° F to 105° F. The regulator is designed to allow the alternator voltage and current limit to be adjustable. It’s the only solid-state alternator regulator with current limit, which is for output diode protection.

6 volt generator regulator issues:
The goal is to package a solid state regulator in an original mechanical regulator case. The alternator regulator circuit was used for a 6 volt generator prototype. The main issue is with the revers current diode the heat dissipation. Looking for the lowest forward voltage rating of a Schottky diode rated at 30 A we find the specification of 600 mV @ 30A. The power while operation at full current is W=30X.6 which is 18 W. The thermal path included 1.5° C/W R JC, 1.5° C/W R CS, 20° C/W R SA (without the regulator cover), total = 20° C/W add the ambient temp at the generator of 50° C the total is 20x18+50 = 410° C which is almost 4 times the max junction temp.

Any ideas for solving this design issue?
More info on generator regulators:
http://ludens.cl/Electron/dynareg/dynareg.htm

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This is a typical schematic, this will work for 6 or 12 V generators. For 6 volt operation change ZD1 to 6.5 V.


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http://webspace.webring.com/people/qp/pravg/solidsta.htm
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herbie1200
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PostPosted: Thu Feb 23, 2017 12:41 am    Post subject: Re: Homemade solid state 6V regulator Reply with quote

Hi Wayne

I used an array of 2x(2x20A) Schottky diodes, normally the measured voltage drop is 0,2-0,3V, and diodes (you can see one of them in my photo under the board, they are TO220 cases) are almost cold.

Anyway I've ordered a set of "ideal diodes", they are a sort of small PCB with a MOS circuitation that will drop 0,00...Volts.

My circuitation uses a MOS to control the generator field instead of a bjt for 2 main reasons:

1) MOS has a very low RDon, ~0ohm, on a 6V generator this helps a lot for a correct field current instauration

2) The field coil controller should be ON also when ignition is off. BUT with a bjt you should keep a BJT on for a lot of time and this drains battery. MOS is voltage controlled so only 0,1mA are drained from the battery.
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herbie1200
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PostPosted: Mon Feb 19, 2018 1:21 am    Post subject: Re: Homemade solid state 6V regulator Reply with quote

This is the schematic.

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The regulator itself is the center part of the schematic.

The left is a model of a charged 6V battery plus a variable load 0..27A.

The right is a dynamo model.

The schematic is inspired by bosch solutions, please note the strange BF394B position, but... it works!
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Zorba2.0
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PostPosted: Mon Feb 19, 2018 5:40 am    Post subject: Re: Homemade solid state 6V regulator Reply with quote

Grazie!
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Wayne S. Johnson
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PostPosted: Mon Feb 19, 2018 4:51 pm    Post subject: Re: Homemade solid state 6V regulator Reply with quote

The reverse voltage of the BF394B Base Emitter junction is being used as a Zener diode. This forms a voltage reference of about 4V.

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herbie1200
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PostPosted: Tue Feb 20, 2018 1:25 am    Post subject: Re: Homemade solid state 6V regulator Reply with quote

Dear Wayne

Yes, in fact in the first versions I used a zener diode, like on alternator circuitries.

The issue is that low voltage zener (we are in the 6V world, not 12V) have the wrong temperature drift.

Plus the regulator itself in a stock 6V engine is mounted on top of the generator, so it works at almost engine block temperature.

When using zener I had to observe a regulated voltage drop, from 7,2V (ideal for an optima battery) down to 6,7 when hot. This drop is the same that I observed in the LT-spice temperature simulation (see my schematic).

Looking at the schematic: the Veb0 value of Q2 instead is a perfect compensation of Q1 Vbe drop, so voltage is perfectly stable.

Bosch made the same arrangement on the popular 12V solid state regulator.
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Wayne S. Johnson
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PostPosted: Tue Feb 20, 2018 1:03 pm    Post subject: Re: Homemade solid state 6V regulator Reply with quote

Temperature drift is a factor of the voltage reference, gain amplifier Q1 (-2mV/°C Base Emitter voltage times the circuit gain), gain resistor TC times the voltage gain of the circuit. Replacing Q1 with an Op Amp and the voltage reference, which will reduce the temperature drift.

Consider the following changes.
1. Replace the zener with an LM325 voltage reference, 150 ppm/° C (0.015% /° C) temperature coefficient.
2. Replace the Q1 gain stage with an Op Amp (TLC272 2uV/° C or any 5V powered OP Amp.)
3. Replace the gain resistors with 100 ppm or less resistors.

Optional:
1. My regulator design used a shunt to measure current, the second op amp was used to limit the alternator (or generator) current. I have seen a generator be destroyed in seconds with a faulty regulator.
2. The reveres current diode can be used in place of a shunt, with some variation in the current limit point due to operating temperature. Some variation in the current limit point is much better than no protection.

You can bench test the temperature drift by replacing the field coil with a resistor (R1 in the circuit below) and using a 7V power supply for Vin. Use a 1K base resistor for stability issues. RL is not used.

Place the circuit and a small fan in a Styrofoam cooler, the fan will circulate the air and provide a small amount of heat. To control the temp set point, get a Digital Temperature Controller $13 on eBay. Use a 50W light bulb for a heating element inside the cooler. Wrap the light bulb in aluminum foil for even heating; don’t let it touch the Styrofoam.

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herbie1200
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PostPosted: Wed Feb 21, 2018 1:04 am    Post subject: Re: Homemade solid state 6V regulator Reply with quote

Dear Wayne

My criterium has been to stay "low" with complexity, also to have a good control on:

- power consumption; in my arrangement the circuit is always on, and with discrete components I can be sure on how much current is drawn with engine off, exactly the R7+R10 (less than 3mA); operational amplifiers I cannot be sure about their consumption, especially if they are prone to auto-oscillating.

- also I wish the regulator to "start" also with discharged battery, I don't know the way an operational amplifier works when far from its correct DC feeding. In my arrangement the only issue is to have enough voltage >VGth to put MOS in ON state via R3+R4

- for now I did not implement a current control; I don't like shunt, but I've bought a small IC with a sort of iron conductor with an hall sensor on it. I will test something. I'm also thinking to simply put a 30A fuse inline.

Respect to the schematic I posted, made a couple of adding:
- a MOV 80V between MOS drain and source, for protection
- a big schottky diode in parallel with ideal diode, I'm not so trusted into chinese ideal diodes PCB, they are for solar panels not rated for automotive.

On the car an oscilloscope shows that the regulator works normally at about 15-30Hz.

The tricky part was to make good mechanical and electrical arrangement into original bosch case, making them affordable against thermal mechanical and electrical threats.

And... your schematic???
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Wayne S. Johnson
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PostPosted: Wed Feb 21, 2018 1:49 am    Post subject: Re: Homemade solid state 6V regulator Reply with quote

Regulator power consumption is not an issue when using the ignition switch to turn on the regulator. If the regulator is on when the engine is off, field current would be several amps.

I do not have a schematic of my regulator design, I built it almost 50 years ago.

For design ideas take a look at the LM723 data sheet, the part was designed in the 60's and is still the predominant regulator in most linear power supplies today. Unfortunately it requires at least 9.5V to operate, but all the functions can be duplicated with 5V parts. All your design goals can be met using the parts I listed.

Good luck with your design.
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