12 volt power source?

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It's quite a DRAIN!

Yup!!

In the past, when I have been using a 'decent' multimeter on the electrical system, I haven't noticed any great (or even consistent 'minor' differences. Just the difference you would expect comparing readings on a 'multimeter' with a 90deg full range for 15 volts scale, with a dashboard 10 degree for 16 volt scale.)

Chuck D.

Not in any of the cars that I have had over the years Ray.

Unless you are saying that by supplying all the power need to operate the car, AND some extra to charge the battery, there is some magical "Firewall" between those parts of the system.

Chuck

Nope! "Sitting" = Engine off, no accessories in use, only drain on battery --- 'chemical "self discharge" (What drains a 'charged battery' over long periods of time.)

Chuck D.

Nope, the 'stator' current comes from whatever is available. Witness the FACT, that once a car is started, IF the RPM of the engine is high enough, the 'Battery' may be removed --- WITHOUT killing the engine.

Depending on the car, hours to days.

Just where is this 'Magical Switch' circuitry or relay. there isn't anything like this available in any of the 'Voltage Regulator' circuits that I have ever worked with. Chuck D.

The battery is wired directly into the secondary side of the automobile's electrical circuit. If any part of the circuit beyond the alternator/regulator is at 13.8 volts then the battery is at 13.8 volts. (give or take the fractional voltages caused by resistances within the wiring) After starting, the battery could be down as low as 10.5 volts. The rest of the secondary side circuitry will also be down at battery voltage because there is nothing in normal car wiring that disconnects the battery.

There is _nothing_ in normal car wiring that seperates the battery from anything but the alternator - therefore _all_ wiring beyond the regulator is at battery voltage. (ignoring subsequent voltage regulation for electronic equipment and the small internal resistances of the battery and wiring.

Greg.P.

What component in a car's wiring do you imagine isolates the battery from everything downstream of the regulator???

The "magical switch" is 4 diodes (or more) used both to rectify the alternator's output and to stop the battery-alternator-battery discharge loop. Beyond that, the battery and internal resistances are the voltage regulator. (check the voltages at different rpms without the battery in circuit ! =8^O)

On Wed, 26 Dec 2007 07:30:19 +1300, I said, "Pick a card, any card" and Greg Procter instead replied:

Baloney. You've been spewing from the mountaintops that a 12 volt battery will measure 13.8 volts and that's simply wrong. Don't try to weasel out of it now. Everyone here has been trying to convince you that the CHARGING circuit is 13.8 volts and now you pretend you knew it all along.

A 12 volt battery will not ever measure 13.8 volts as you stated.

Because a 12 volt battery will never, ever measure 13.8 volts. Ever.

This one bears repeating. You simply don't understand batteries, Greg.

-- Ray

On Tue, 25 Dec 2007 14:52:44 -0500, I said, "Pick a card, any card" and Charles Davis instead replied:

Without a battery, the stator is not powered.

That's a short while.

Get real. It should be in the engine compartment. Depending on the car, it may also be under the dash.

-- Ray

On Wed, 26 Dec 2007 07:34:12 +1300, I said, "Pick a card, any card" and Greg Procter instead replied:

The nominal voltage is the one you want.

Greg, do you know what that means? Clearly not. I'll try to explain. That rating means that the battery charge voltage may be floated to

13.8 volts safely for long periods of time for keeping the battery charged. It doesn't mean that the battery itself will ever maintain a potential of 13.8 volts all by itself without an external charger being applied. 12 volt lead-acid batteries under charge do not limit the voltage to 12 volts in the overall circuit when external potential is applied. That's what the "floating" voltage means.

You seem bent on dying in this ditch today, Greg. Press on.

-- Ray

That battery company I cited is going to be very disappointed!

In that case the car electric connected to said battery will never measure 13.8 volts. Ever. The information that voltages above 13.8 volts will cause gassing is sort of wasted really.

Fair point - care to design my current electric car design for me?

Spooky!!!

Your cited battery data said that batteries at 13.8 volts will drop to

13.2 volts in a short time - that's days!?!

So all the other factual data is meaningless and irrelevant??? I guess they had to fill the page with something?

Go read it again - they said 14.2-14.5 volts.

Well, a small change of tack here - I originally stated that a commonly used circuit for operating a model railway (1930s-60s) was a trickle charger and an automotive battery - giving 13.8 volts.

With any electrical/electronics circuit, the _maximum_ voltage is important.

I'm on my 2nd-10th time round with every point - I've given you a manufacturer's cite, I've pointed out your mistakes and flawed thinking. I'm a practical person rather than an theoretical engineer and I know I make the occassional mistake, but you're talking a load of bollocks. The figure that counts is not the nominal voltage, the average voltage, the mean voltage, the minimum voltage, the charging voltage or the static voltage - we were discussing the _maximum_ voltage that could be seen on a model railway from a supply containing an automotive battery at the time when "12 volts DC" was set as the norm (by the NMRA) In an automotive or model railway situation the voltage at the battery terminals and the attached loads cannot be higher than the terminal voltage - the difference between generator/alternator/charger output and battery terminal voltage _MUST_ be lost in the resistance of the circuit. Voltages above 13.8 volts applied to battery terminals will result in high currents which will cause out-gassing and heating of battery plates with consequent distortion and probable destruction of the cells - but what do _I_ know.

Regards and a Merry Christmas to all!

Greg.P.

On Wed, 26 Dec 2007 10:13:33 +1300, I said, "Pick a card, any card" and Greg Procter instead replied:

They're on the same page as me, Greg. Why would you believe otherwise?

Exactly. Not without external potential added. A battery circuit, including the battery, can be driven to a higher voltage but that process is known as charging. When used as a source of power, a battery will never be at 13.8 volts. It's a physics thing.

That's what the float limit is all about. Gassing causes the electrolyte's hydrogen to leave the battery. It's a serious issue. If you charge at too high a voltage, the electrolyte outgasses and you get spidering between the cells which can cause cell failure. Water vapor also escapes during gassing which lowers the levels. Gel batteries don't suffer that same fate but an overcharge voltage on them can cause swelling and cell failure from heat.

No thanks, mate. I'm converting one now. A Dihatsu Mira-J. I'm so pleased about how clean the car has become since the engine is gone. I've got 3 years invested in it and don't expect to finish for at least another 3. Batteries (huge power sources) are getting cheaper and different every day.

Have you looked at the commercially available fuel cells? Brilliant!

Look in the middle column, third one down. The best part? They're literally a few miles away from me.

Now, Greg, I'm offering you a Boxing Day olive branch. Can we end this seemingly endless debate and get back to trains?

-- Ray

On Wed, 26 Dec 2007 10:16:10 +1300, I said, "Pick a card, any card" and Greg Procter instead replied:

I never cited any battery data. Also, I have never stated and never will state that a 12 volt lead-acid battery will ever reach a charge potential above 12 volts by any significant amount.

You must be thinking of someone else.

-- Ray

On Wed, 26 Dec 2007 10:35:23 +1300, I said, "Pick a card, any card" and Greg Procter instead replied:

It all has its uses, Greg, but not as you believe.

Greg, that's a theoretical maximum and the 13.8 volt charge limit has become a defacto standard. This is a red herring here. The battery itself will not go over 12 volts. You clearly stated that the voltage on train power supplies was 13.8 volts because that is what a battery is. It's not. Quit trying to rearrange your own claim. It's very dishonest, Greg.

For CHARGING, Greg. For CHARGING ONLY. Not for replacement of a 12 volt battery as you originally stated.

For charging, yes. For eliminating a 12 volt battery, no. The voltage that is important is the nominal voltage.

Which you have misinterpreted.

I'm just a lowly electronics design engineer. What would I know?

What, Greg? That a 12 volt lead-acid battery will actually be a 12 volt power source? That's fact, not your brand of fiction. In your world, batteries reach any voltage you want even outside of their physical ability.

That would be 12 volts DC. Or, as pointed out by others here, a maximum of 12.6 volts in an absolutely perfect world. Never will it reach the 13.8 volts you suggested.

So, you can be educated after all. It has to be beaten in, but you can be helped.

The same back at you, Greg.

-- Ray

snip

Most (if not all) of the automotive alternators that I've seen are 3 phase units, needing 6 diodes to convert to DC.[4 diodes would work quite well for a 2 phase unit.] The feed/ connection for the 'Stator (Field) control circuitry' being after these diodes (the same connection point as what goes to the battery), the diodes only prevent reverse current flow through the armature windings, nothing else.

Chuck D.

Well Ray, it seems that you haven't ever actually measured a battery voltage while it is being charged! [And for the few microseconds AFTER removal of the charging voltage.] The voltage RAPIDLY drops, but there IS a finite time where the voltage is STILL at the 13.8 volt level.

Chuck D.