Just to make sure. All I really need to do it turn the field on below 14.5 volts and off above 14.5 volts. Or in the case of two 8 volters in series 19.3 volts?

 

Just to make sure. All I really need to do it turn the field on below 14.5 volts and off above 14.5 volts. Or in the case of two 8 volters in series 19.3 volts?

Yes. An olde electromechanical regulator does that. Modern PWM regulators (such as I described earlier) do that much more efficiently and accurately.

 

Yes. An olde electromechanical regulator does that. .

As per post#3
Max.

 

I'm trying to figure out how PWM would be better. Seems like as it approaches the final value it is kind of PWM anyway as it pops above and below 14.5 volts..

 

PWM has a fixed switching frequency just the pulse width varies, whereas the older basic method the frequency varies, it is still effective though, just offers the possibility of the varying EMI if you had a radio etc hooked up to it..
Max.

 

I'm trying to figure out how PWM would be better. Seems like as it approaches the final value it is kind of PWM anyway as it pops above and below 14.5 volts..

Duty cycle varies. As the demand goes up, the ratio of ON/OFF time is increased to as high as 99%. When I worked w/ CO2 Lasers driven by RF power, the drive for the Class E RF drivers were also controlled using PWM.

PWM has a fixed switching frequency just the pulse width varies, whereas the older basic method the frequency varies, it is still effective though, just offers the possibility of the varying EMI if you had a radio etc hooked up to it..
Max.

The PWM regulators I mentioned don't appear to make any noticeable noise. At least, I've never noticed any in my '69 Plymouth's AM/FM radio, even when DX-ing on AM BC or on my ham HF transceiver. IIRC, the switch rate is actually pretty low.

Sure, your comparator idea would get the job done. However, considering the excellent availability and low cost of an off the shelf unit, I don't see a reason to reinvent the wheel. Unless someone wants to tinker.

Bryan

 

Ahh, the noise. I started out thinking pwm, but could see no advantage and a lot of added complexity.
Sure I like to tinker and I don't see an off the shelf one that will do both 12 and 16 volt batteries.

 

The PWM regulators I mentioned don't appear to make any noticeable noise. At least, I've never noticed any in my '69 Plymouth's AM/FM radio, even when DX-ing on AM BC or on my ham HF transceiver. IIRC, the switch rate is actually pretty low.

As I mentioned, the PWM type replaced the electronic version of the mechanical regulator that came out as an intermediate measure after RFI was experienced, the PWM type came on the scene as a noise free replacement.
I used the Comp. circuit in a short production run to regulate the field of mobile 200amp 230vdc generators that did not have on board circuit supply, the field residual was used for it to pull itself up by its boots straps.
Max.

 

Hey Ronv,
I don't think you will have any problems with a 12V regulator, but a 16V regulator is going to be a tall order. I don't recall ever seeing anything for that voltage as it is not a common DC voltage used in industry. If you wanted, you could call someone at WAI Global and see if they have anything that might meet your needs. They purchased Transo Electronics a few years ago and are pretty much the largest VR manufacturer/supplier in the world. Here is a website for you to go to.
http://www.waiglobal.com/contactus.html
Good luck

 

I want to build a regulator for my little portable generator. (battery, small engine, alternator) In looking on the internet it looks like they just turn the field on below 14.6 volts and off above 14.6. Is it really that simple?

Yep, 100,000,000 automobiles cant be wrong...

Here is an alternator voltage regulator simulation I did several years ago. It matches what happens in a real automobile (or aircraft) very closely. Note how simple the Voltage Regulator, Alternator, and Battery models are.

The VR is modeled as a voltage-controlled switch, which closes when the bus voltage V(bus) drops below 14.245V and opens when V(bus) is greater than 14.255V.

The alternator is a (field) current-controlled current source, where 1A of field current makes 30A of output current. The field resistance is ~7Ω, so even if the VR is fully turned on, the max field current is about 2A, and therefore the maximum output current is about 60A. This models the Ford Prestolite alternator in my Cessna... The field inductance is approximate.

I was investigating how long it takes the alternator system to recover when a large load is suddenly added to a smaller steady load, in this case 45A is added to an existing 5A load. Note that because of the field inductance, the alternator cannot instantaneously supply the step increase in load, so until the alternator catches up, the current comes from the battery.

When the big load is switched off, again because of the field inductance, it takes a while for the alternator to stop producing output, so V(bus) overshoots, a classic example of "load dump"!

Note that the VR coupled with the field inductance and the snubber diode form a Pulse Width Modulator, where the average field current is just the right amount to keep the bus voltage near the set point. Note that the pulse rate is not constant, but in a real system runs at about 30 to 50Hz.

Note how the battery acts as a giant filter capacitor...

Play with the .asc file to see all the subtleties of this deceptively simple circuit..., and how closely it matches what happens in your car....

 

Thanks Mike!
It was good to have some better numbers for field inductance and the battery.
One of the things it showed me was that I could use a smaller clamp diode because the inductor current doesn't drop to zero at the high currents.
Kind of like an elecro-mechanical buck regulator.