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#495662 - 03/19/08 03:25 PM
Best Alternatior for a 12V conversion - '50 Str8?
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Gary_N
Member
Registered: 10/19/04
Posts: 407
Loc: Maryland
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At some point in time I need to convert to a 12 V system. I'm wondering what some of you have used in your conversions.
Thanks!
Gary
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BCA #40969 '50 Special - "Yoda" '54 Roadmaster - "Frankie" '64 Electra Coupe - "Arthur" '48 De Soto S11 Coupe - "Bobo" '01 Z06 SCCA - T1 Racecar "Dragonfire" - For Sale ------------------- http://www.wrenchhappy.com
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#496904 - 03/24/08 09:25 PM
Re: Best Alternatior for a 12V conversion - '50 Str8?
[Re: Gary_N]
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51dyno
Member
Registered: 03/19/07
Posts: 27
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Theres an old timer that rebuilds ford ts & as motors ,he has 6volt altenaters.I believe he"s from minesota.he has a stand at Iola every year.If interested I can look for his flyer,there is someone building altenaters inside generater housings.
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#496982 - 03/25/08 06:12 AM
Re: Best Alternatior for a 12V conversion - '50 Str8?
[Re: 51dyno]
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simplyconnected
Member
Registered: 11/06/07
Posts: 147
Loc: Detroit (Royal Oak), Michigan
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I used a standard Mustang alternator on my '55 Ford. GM also has a one-wire alternator that's very popular. These alternators have the voltage regulators already built in. Good ones are salvaged daily.
Depending on your demand, you may want to go with a 6-volt alternator. Let's do the math. A 35amp 6-volt generator or alternator produces 210 watts (that's like two 100 watt light bulbs). Headlights and the heater max it out.
A 12-volt 55amp alternator produces 660 watts. That's three times the power of the 6-volt system. 55 amps is the smallest alternator you will find because they go over 100 amps for police, taxi, ambulance, etc.
If you do the 12-volt conversion, all your wire sizes are more than sufficient. All light bulbs need to be changed as well as horn relay, and starter relay. Your gauges need a separate regulator, distributor coil needs a resistor, and your radio needs to be reworked. Your 6-volt starter runs well on 12-volts.
Sounds like a lot of retrofit, but well worth a Saturday afternoon. Want electric wipers or fuel pump? An alarm? Remote start? Power windows/locks/trunk release? Try finding them in six-volt. You already know about stereo stuff. Your cell phone, GPS, and inverters don't do 6-volt.
There's real good reasons why all the car companies abandoned 6-volt back in 1955, and never looked back. I'm glad I changed mine.
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#497460 - 03/26/08 08:49 PM
Re: Best Alternatior for a 12V conversion - '50 Str8?
[Re: simplyconnected]
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Gary_N
Member
Registered: 10/19/04
Posts: 407
Loc: Maryland
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Simplyconnected: Thanks for the advice. I really can't live much longer with the 6V system. Right now it takes about two - five minutes for the car to actually start charging. The gauge shows a draw then eventually pegs to the plus side, and then comes back to a little above neutral on the gauge. I keep turning stuff off when I stop at a light, like the radio and heater blower.
Gary
_________________________
BCA #40969 '50 Special - "Yoda" '54 Roadmaster - "Frankie" '64 Electra Coupe - "Arthur" '48 De Soto S11 Coupe - "Bobo" '01 Z06 SCCA - T1 Racecar "Dragonfire" - For Sale ------------------- http://www.wrenchhappy.com
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#497606 - 03/27/08 11:55 AM
Re: Best Alternatior for a 12V conversion - '50 Str8?
[Re: Gary_N]
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Leif Holmberg
Member
Registered: 02/10/02
Posts: 372
Loc: Sweden
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Way not put a new AC 6 Volt (look like the old one) insted of your old DC generator.Sears for Gener Nator.
Leif in Sweden.
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#497630 - 03/27/08 02:11 PM
Re: Best Alternatior for a 12V conversion - '50 Str8?
[Re: Leif Holmberg]
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rlbleeker
Member
Registered: 06/13/02
Posts: 200
Loc: Spokane, WA
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The simplest solution is probably to fix whatever is wrong with your system. Surely a new 1950 Buick didn't have this problem? Nothing wrong with 12V (obviously), but it's a bit of work to convert. In my experience, 12V on a 6V starter is not a good thing.
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#497788 - 03/28/08 01:10 AM
Re: Best Alternatior for a 12V conversion - '50 Str8?
[Re: rlbleeker]
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simplyconnected
Member
Registered: 11/06/07
Posts: 147
Loc: Detroit (Royal Oak), Michigan
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Certainly, to be a 'purist' you must maintain original equipment. Back in the days of having one tail light, two headlights, and a heater motor, the 6-volt system worked marginally well. Generators only produce when they are turning VERY fast.
Long idle periods caused engine overheating. Vapor lock was very common on hot days. Some days, the ol' gal just wouldn't start. Bottom line is, these cars were built for specific service and for select areas of the U. S. Sustained mountain service demanded a re-jetted carb.
If a 12-volt system sensibly solves your electrical woes, then why not retrofit? Even at an idle, an alternator charges very nicely. It is hearty. Batteries and everything else in 12-volt is much cheaper and available everywhere. By the way, even after 1955, gauges were kept at 6-volts for many decades. The little 6v regulator is on the back of every Ford dash board built up to now.
I have run my 6-volt starter on 12-volts for three years now. The extra starting speed helps my engine start faster so I don't need to keep the key in "start" as long.
My choice was to retrofit and I am VERY happy I did. I come from experience; from both sides. If you feel strongly about keeping it stock, that is your choice.
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#497902 - 03/28/08 02:52 PM
Re: Best Alternatior for a 12V conversion - '50 Str8?
[Re: simplyconnected]
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rlbleeker
Member
Registered: 06/13/02
Posts: 200
Loc: Spokane, WA
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If you do go the 12V route and keep the 6V starter, it will crank very nicely; but remember that it will be drawing approximately twice the amps it was designed for and can overheat if cranked too long. I melted the armature in a straight 8 Chrysler doing this.
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#498567 - 03/31/08 03:20 PM
Re: Best Alternatior for a 12V conversion - '50 Str8?
[Re: simplyconnected]
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rlbleeker
Member
Registered: 06/13/02
Posts: 200
Loc: Spokane, WA
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Not an expert here, but my understanding of series-wound DC motors is basically that speed is proportional to voltage and torque is proportional to amperage. At startup there is no counter-voltage, so it's simply V = IR. Doubling the voltage doubles the current. So when you hit the key it will draw approximately twice the initial amperage. As speed increases, the counter-voltage increases; decreasing amperage and torque. Speed will increase until the torque matches the load. Turning your engine over faster, means doing more work (compressing air, friction) in the same length of time, thus more torque and hence more amperage.
Now, these old starters are definitely over engineered and may handle 12V indefinitely; particularly with reduced cranking time. But I still think they are going to be more prone to failure than a correct 12V starter.
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#498718 - 04/01/08 06:10 AM
Re: Best Alternatior for a 12V conversion - '50 Str8?
[Re: rlbleeker]
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simplyconnected
Member
Registered: 11/06/07
Posts: 147
Loc: Detroit (Royal Oak), Michigan
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Not an expert here, but my understanding of series-wound DC motors is basically that speed is proportional to voltage and torque is proportional to amperage.
When the starter first energizes, it's at "Locked Rotor Current" until motion begins. Locked Rotor Current is 400% of "Full Load Amps". This is at its strongest magnetism because current makes magnetism. An engines is hardest to turn when at a dead stop (cold-welded). As motion increases, counter electromotive force increases, current and magnetism decreases. Think of it this way, holding your key on when the pistons take over and the engine revs, current goes down so far your starter motor could turn into a generator (without a bendix gear).
At 6-volts, sometimes my starter would labor terribly, barely turning the engine fast enough to start (like on cold mornings). We've all been there. The starter is using so much current, the battery can barely supply the demand. Current in this case is enormous, for as long as it takes to start the engine (or until the bat dies). That kind of sustained work kills starters. (Flooding does too.)
We all know that starters have a short duty cycle. They aren't fan-cooled. If they overheat, that's it for either 6-volt or 12-volt. We could argue, because 12-v starters burn up, they are really designed to run on a lower voltage. Truth is, they will run on 6-volts using #2AWG copper.
6-volt batteries need more Cold Cranking Amps than 12-v (to do the same work). 800 CCA is typical. 6-v generators usually output 35amps (when they are run fast).
12-v batteries run ~450 CCA, and alternators put out 55-100 amps. It takes 1/4 to 1/2 the time to recover a 12-v battery. - Dave Dare, FMC (DAP)
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#498804 - 04/01/08 03:25 PM
Re: Best Alternatior for a 12V conversion - '50 Str8?
[Re: simplyconnected]
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rlbleeker
Member
Registered: 06/13/02
Posts: 200
Loc: Spokane, WA
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The torque the motor produces is the result of the opposing magnetic fields and is a function of the windings and current (amps) passing through the windings. A 12V starter will have twice the turns and produce the same torque at the same speed with half the current, watts remains the same.
torque = motor constant * amps
As the motor turns the fields will induce a counter-voltage (EMF) that opposes the supply voltage. The equation becomes:
amps = (supply voltage - counter voltage)/resistance
At locked rotor counter voltage is 0, so it simply becomes I = V/R. R is the resistance in the copper and is constant if we ignore heat. So doubling the voltage from 6 to 12, doubles the initial amp draw. Doubling the amps doubles the torque, which is why it accelerates to cranking speed so much faster.
As the motor speeds up, the counter voltage increases and the effective voltage (supply voltage - counter voltage) decreases and so amps and torque do likewise. It will accelerate to a stable speed where the load torque equals the motor torque. If we had a constant torque load, then doubling the voltage would double the speed. It would consume twice the watts (2 * volts * amps) and produce twice the mechanical power (2 * RPM * torque).
We don't have a constant load situation though. The torque required to crank the engine is greatest when the engine is not in motion, static friction. Once in motion the required torque will decrease significantly and then increase with speed. Cranking the engine faster than the 6V cranking speed will require more torque and therefore more amps, regardless of supply voltage. It will find a balance point (the 12V cranking speed) somewhere below 2 times the 6V cranking speed with amps somewhere above the 6V cranking amps.
I get your point that the increased torque is going to significantly decrease cranking time for a well tuned car. Heat is the enemy. The resistive heating is a function of the wire size, the amperage traveling through that wire (voltage doesn't matter) and the length of time it's doing so. The increase in heating due to the increased amps and the decrease in heating due to decreased duration my very well result in a net decrease if the car starts quickly.
My caution is that if you crank it as long on 12V as you would on 6V you will have increased heating and risk damaging the starter. Sometimes they don't start right up and if your running a 6V starter on 12V you should keep that in mind. Shorten your starting attempts and leave time for cooling in between.
The starter I melted didn't happen while cranking but on that 2X inrush when I hit the key. Melted the solder on two of the bars at the commutator. Maybe it was a weak joint in the first place, a little extra resistance. It was fine on 6V, melted in short order on 12V.
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#498946 - 04/02/08 03:43 AM
Re: Best Alternatior for a 12V conversion - '50 Str8?
[Re: buick5563]
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simplyconnected
Member
Registered: 11/06/07
Posts: 147
Loc: Detroit (Royal Oak), Michigan
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Thanks Mike. I don't mean to beat this horse, but knowing about starters is beneficial to all restorers.
Friction 101: When engine parts sit motionless for an extended time, strong adhesion occurs at the points of contact. The points of contact are in effect cold-welded, forming a continuous solid. The longer it sits, the worse it gets. If the materials are to be slid over each other, these junctions must be sheared. Breaking this bond requires tremendous torque (and causes engine wear).
The relationship of starter windings, polar patterns of the magnetic structures and other specifications have so much to do with the actual performance characteristics. The simple explanations you see in elementary textbooks and qualitative explanations grossly oversimplify how motors work and lead to confusion and misunderstanding by the novice technical person.
Consider, if your 6-volt starter cable requires #4 copper wire, how come your field windings don't burn up? All that current certainly goes through them, right? Field windings are heavy, but they aren't #4, they are more like #10 (which normally carries 200 amps only for a moment). Doubling to 12-volts couldn't possibly double field wire current. The answer is INDUCTANCE.
Inductance 101: The ability of a winding (inductor) to store energy in the form of a magnetic field (and consequently to oppose changes in current) is called inductance. When current through an inductor is increased or decreased, the inductor "resists" the change by producing a voltage between its leads in opposing polarity to the change. Confusing? Ohm’s law just got trashed.
Starting current as a rule of thumb (for all motors) is four times normal running current. It could be as high as TEN times for some motors. (Ever see your lights dim when a motor starts?) That's why we don't have a fuse on your starter motor wire. The AMP value would be so high, it's useless, so we let the wire be the fuse.
Changing to 12-volts doesn't double the starting speed, inductance won't let it. If it did, your engine would start at over 1,000 rpm! Realistically, speed goes up nearly 50%, but starting torque skyrockets; that's what we want.
Check your brushes for wear (on all starters). If the spring is weak or the carbon is short, a small gap will cause your commutator segments to burn. Starter motors are hearty and should last a very long time when properly maintained. As a side note, alternators have brushes too (on slip rings). They're really small and only feed the field windings. They normally last at least 100,000 miles. New alt brushes with the holder are about $15.
Here's a help for checking inductors (motors, transformers, solenoids, etc). Using a continuity light, if you scrape the test leads over the winding leads, you should see a little pretty blue trailing spark. If your light shines with no spark, you have a dead short. Try this on any inductor with the lights turned down. Make sure the power is off first. Those cheap penlight continuity testers work just fine for this. - Dave
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#499019 - 04/02/08 02:05 PM
Re: Best Alternatior for a 12V conversion - '50 Str8?
[Re: simplyconnected]
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rlbleeker
Member
Registered: 06/13/02
Posts: 200
Loc: Spokane, WA
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Yeah, this is definitely a bit geeky and I suppose we've gotten a bit off topic, but I'm finding it interesting. It's been a long time since I studied flux and all that stuff in college physics. I know I've over simplified my arguments.
So inductance is a relationship between flux (size and strength of magnetic field) and current. The current flow creates the magnetic field which creates the inductance which resists the flow of current until a balance is found. Correct?
Then doubling the voltage across a winding won't actually flow twice the current (due to inductance), but it will still flow more current and make more torque won't it?
I agree, it won't crank the engine twice as fast, it can't. I didn't want to take a guess at it, so just said "somewhere below 2 times". I'll buy your 1.5 number. Isn't it still generating more torque at that speed and using more amps to do so?
Am I correct that a 12V starter will, to over simplify, have twice the wire and generate the same torque with half the amps? It won't crank as fast as your 6V starter on 12V correct?
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