Re: Adjustable voltage regulator for car alternator

Thanks, Jim for the reply ~

I do have a temp. sensor setup already going into my Plasmatronics regulator, so I could use a temp. compensated circuit, at the risk of complexity/your time.

I haven't procured/scrounged the alt. yet, so I don't know about it's field - should I look for one setup in particular?

Thanks so much,

Marcus, in outback Oz @ 23.7VDC, so not too much juice left in batteries tonight!!

Reply to
marcus
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I'm going to say this before anyone else does: "Use a PIC"

This truely may be a good job for a micro controller witha built in ADC. I would use a good reference and a R-R op-amp and a few resistors to scale and offset the input to the ADC. Assuming 4 x 8 bit ADC channels, I would allocate them something like this:

Chan Meaning

0 0..255 = Battery voltage 26..32 1 0..255 = Battery voltage 0..32 2 0..255 = Thermistor 60C..-20C 3 0..255 = Charging current 0 .. 2xBattery rating

Channel 1 is used to look at the battery voltage in the non-charging state. Channel 0 is supposed to have the fast charge stopping point near the middle of its span.

You may also want a logic input to tell you that the alt. is spinning.

The field drive would be done as a PWM control at some fairly low frequency. The field coils have a very large inductance but it is very lossy at high frequencies.

The only part of the software that needs to be at all quick is the bit that regulates the charging current.

Reply to
MooseFET

It's a little easier if the field is tied to A+, then the switching can be done to ground via a power NMOS, or NPN... avoiding a high-side driver problem.

As for those who suggest a PIC... what a pile of crap. Analog is trivial in this application. Can a PIC provide 5A ?:-)

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

MooseFET ~

Thanks for the PIC idea - I have thought longingly about this, and I know it would have advantages - but as far as micros go, I'm only up to trying to decide which programmer to get and having received a few samples from Microchip, so I am resigned to a "dumb" design for the time being.

Marcus in Oz; 2:58AM and batteries now @ 22.9VDC - getting low!

Reply to
marcus

OK, I'll look for an alt. with an A+ field. Any ideas how to tell quickly if I have a suitable alt. with say my multimeter in the local junkyard. I can look up common models on the net of course.

thanks all,

Marcus in off-grid outback

Reply to
marcus

Measure resistance between field terminal to A+, and field terminal to ground.

Desired is resistance to A+ (field connected to A+ internally).

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

Sure just hook about 28V onto it. More than 5A will come out of whatever pin is connected to the expensive parts.

Reply to
MooseFET

Have you looked at Silicon Chip (AU)?

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If you are in Oz your library may have back copies you can read for free.

Reply to
Homer J Simpson

Thanks Homer, but these won't do what I want.

I already have a Plasmatronics regulator for my solar panels but I need an adjustable AVR to control a 24V alternator driven by a 3 - 6 HP stationary engine. It needs to handle 50A and sense the battery voltage.

I have just about every issue of SC - great magazine. It was a great shame about EA magazine - I wonder whatever happened to Graham Cattley the editor who ruined it in only a few issues?

marcus

Reply to
marcus

If it was me, I would look at controlling the engine speed to control the charging. This will give maximum efficiency per litre of gas - this is expensive electricity.

I subscribed for many years back when it was Radio, TV & Hobbies (I think). Eagerly awaited it every month - sad, but most all of the electronics magazines have died now.

Reply to
Homer J Simpson

If you want to squeeze every ounce out, I think you will end up controlling both. Strangely enough, I see an increase in field current when less charging current is needed.

Take the over simplified model of the generator's performance as:

Volts(Open ckt) = K1 * Field * RPM Amps = K2 * Torque / Field

Also over simplifying: Assume that the engine's torque for most efficient operation remains constant. ie: full throttle on an engine with no tuned ports.

To lower the current we actually want to increase the field. To make the current lower, we also need Volts to go lower so the RPM must decrease by more than the factor we reduced the current.

Reply to
MooseFET

YOU see an increase in field with less charging current - You really want to think about that statement moosefet. If the regulator is kicking in it does decrease the field current as the output voltage goes up - and increases the field as the output drops.

Is it just possible that there's enough "runout" (out of round or offset from the axis) in the slip rings? that may cause the brushes to press lightly on the rings, or to leave the rings entirely? as speed voltage and current try to increase - my own observation.

In your alternator - in theory (and from my own observation) the speed, number or turns, and magnetic field determine voltage - period (aside, perhaps, from winding temperature which is negligible).

You'd better state the exact conditions before you try to sell that idea. You're talking about the field (?) increase current (stronger field) and you increase output voltage - and with a load - output current - and torque load on the engine.

From my experience, if I see something like decreasing output power (current and voltage) as the speed increases it is just telling me that the brushes are "floating" (not tracking the slip rings at that speed). Either increase the spring tension or fix the out-of-round condition.

I'm guessing/thinking that you are seeing some anomaly and haven't pinned it down to the real cause. Like brush float, self-induced voltage in the rotor, etc..

My old Land Cruiser used a single coil electro- mechanical regulator. At slow speed, the contacts stayed "normally closed," really driving the rotor with a lot of current. At mid speed the contacts opened and a resistor supplied some current to the rotor (you could see the armature hover between contacts). At high speed the rotor was shorted

- I assume the self-induced magnetic field was keeping the output voltage up.

It was clunky and expensive and I replaced it with a solid state regulator - but I really really think that electro mechanical regulator was using a self-induced voltage/field at high speed.

BTW the '72 Toyota $60 mechanical regulator could be replaced by a '67 Dodge electro mechanical regulator for $ 6 (in '78). About once a year - until I used a solid state regulator.

Regulating engine speed is not trivial - since it requires some real engineering talent - but is the "only" good way to do it.

With batteries supplying the invertors(s) there's no need to regulate the field - unless the battery bank is small and the load changes rapidly and to extreme power requirements - better to regulate engine speed for efficiency.

And you'd want it "fail safe." - all the control circuits turn to mush - you'd still want to protect the engine, alternator and batteries. Easy enough - but necessary.

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Reply to
default

(snip)

I think this conclusion includes adjusting the engine speed and alternator excitation current, simultaneously, to obtain the optimum fuel to electric power conversion efficiency, not a fixed speed (governor controlled engine), variable excitation current situation.

I could be wrong about this.

Reply to
John Popelish

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