Guys where exactly is best place to fit a inline fuse when I install a new Alternator?
And what size fuse?
Wiring is in good condition.
20 AMP Fuse, and in the main power wire from the starter switch before it reaches the terminal block. It is typically yellow in color.
There is no simple answer to your question.
The wire sizes on an original Model T are based on a 25 amp system. Hence the 25 amp fuse recommended in the diagram above.
When you add an alternator to the Model T everything changes. The alternator has the capacity to produce significantly more power so the equation changes significantly.
Changes to the original Model T system need to be evaluated in the context of how much current is actually being handled. Since I do not know all the details of your modified system I cannot answer your original question, but I know this; the alternator under the right conditions has the capability of producing more than 65 Watts of power. This means you need to look at each load circuit and determine if larger wire sizes are in order.
Ron the Coilman
65 Watts divided by 12 volts equals 5.41 amps.
Thanks Ron, the wires were new in the 90's and look in perfect condition.
System is standard 6v but had a 12 v battery, ordinary 12v headlight bulbs, one tail light and one brake light fitted by previous owner. Its going to be a gear driven Alt so cant spin too fast.
Draw at most would be GPS & cell charging plus lights on and braking ( no indicators but if they come they would probably low amp)and I guess the engine if the mag was to fail one night.
I understand if battery is low I need to charge before starting up if possible as this is the high risk time.
I will fit a Volt meter (directly to the battery) and I have a 30 amp ammeter coming with the Alternator but not sure if I'll fit this at the start yet.
Oops my mistake.
That should read 65 Amps.
Ron the Coilman
Mike, when you say "Main Starter switch" do mean the Starter button on the floor?
A 12 volt system will use 1/2 the amps that a 6 volt system does. That is why wires for a 12 volt system are smaller. Wiring designed for a 6 volt system is heavier and therefore more than sufficient for a 12 volt system.
12 v gear driven alternators do NOT turn fast enough to produce dangerous current in a Model T Ford That is My experience.
P.S. what is the maximum currant You have observed
on a 12 v alternator T ?
Amen - Dean
To clear up a few things only I wish to state that:
The Model T and the Model A are both 20 amp systems - not 25 amp. Typical simple systems like these 2 cars have would be properly fused at 25% higher current than would be "normal". Thus 25 amps fuse is the correct fuse. Location is important and you don't put a fuse where it is convenient to change but rather you put it where it affords the most protection for your wiring. 12V or 6V has really nothing whatever to do with the actual fuse choice but rather the size of the wire determines the amount of current it can safely carry and you should fuse the system to protect the wiring since it is what will get hot and could melt and cause serious damage to car and property. The T and other Fords before 1939 used the adjustable 3rd brush type of generator which unlike alternators has the ability to set the 3rd brush for some maximum current. If that maximum is chosen too high then the generator can burn up but the main job of the single 25 amp fuse is to protect the wiring harness since the lightest gauge wire normally used in the harness is 16 gauge and it can typically handle higher amperage for the short time it takes to blow the fuse. Most repro harness' have replaced the 16 gauge wire with 14 gauge since the insulated modern 14 gauge cloth wire is the same O.D. as the older 16 gauge wire so it all looks more authentic with 14 gauge when you go with new modern harness.
Great so exactly where would you suggest I place the fuse?
I put my fuse at the battery side terminal of the starter switch which protects any load on the car, being in line with the supply to the terminal block. The alternator will generate more than 20 amps after start up so I throttle down until the battery is brought up. Just keep it below 20 amps. You will see a discharge at idle, like waiting at a stop sign. The 12v alternator set up works great for me. PK
Pat same Q as I asked Mike...is what you call the "Starter Switch" the starter button on the floor?
When we say starter switch we mean starter switch.
Thanks Royce, just thought I should clarify that.
Pat, thats a handy hint if you think the battery is well down and dont have access to a battery charger just keep the revs down if possible.
Be sure to get two alternators, you will need the second one sooner than you think.
Modern alternators are not designed to be installed on the Model T engine side mount. They also have the capability to produce far more current than the original model T wiring system can handle.
Ron the Coilman
How can a 20 or 25 amp fuse in the charging/lighting system, as this Forum explains, protect the wiring from a charging alternator pushing 65 amps ????
My experience with a gear driven 6V alternator, as shown on the car's ammeter, will not charge over 10 amps with a very low battery, using the hand crank to start engine. I have a 20 amp in-line fuse as suggested by a T parts specialty vendor..... NEVER had to replace fuse in 10 years.....running a Becker 6V gear sidemount unit.
Now, can someone with specific documentation explain how that 20 amp fuse has protected that wiring system using a dreaded high output alternator ????
Alternators are an option to the owner, to be used accordingly as an option, for whatever reason the owner has.
Alternators have no place in the mindset of the strict hardline original Ford parts owner.
You're looking at it wrong Bob. The alternator has zero to do with fuse rating. Assume a direct short to ground in your wiring (makes no difference whether it has an alternator or generator or nothing). Basically, the battery will try to send a few hundred amps through the wire to the point of the short. The 20-25 amp fuse just saved your house from burning down or at least from you having to buy a new harness for your car.
Now, with the alternator if the current goes too high your only out a fuse (maybe, if the excess was being sent to the battery through the fuse).
The warning is really to the guy that adds an alternator with no fuse. A gen with no fuse having it output limited to 10 amps isn't a problem as it can only put out 10 amps. (of course the battery can still burn it up)
That may not be "specific documentation" as your looking for but it is based on over 30 years experience with aircraft wiring and the wire size is selected based on load and length. You can't reasonably hook wiring designed for 20 amp load to something capable of putting out 60 amps without some safety such as a fuse or circuit breaker.
With respect to fuse location. I would likely run two with an alternator and for the following reasons. I would run one where everyone puts them right at the starter switch. In a short, it opens and prevents the battery from smoking your wire system. The second one would be at the alternator. Reason, if the short occurred say under the dash with the engine running (alternator putting out), the alternator is sending all of its output to the path of least resistance. If that short is before reaching the fuse under the floor and you push 60 amps through the wire, you won't like the outcome.
Alternator circuits don't use fuses, normally. The current fluctuates widely and using too large a fuse will burn wire. Too small a fuse and it will burn on startup. Alternator circuits use what's called a Fusible Link which is high temp wire of a smaller gauge than the rest of the circuit. For alternators, this is normally 12Ga. while the circuit is 10Ga.
Use two separate circuits for the alternator and the rest of the car (terminal block feed). Use a fuse on the car feed wire--20/25A.
Yes Ken, that is exactly what I was thinking and in the location shown.
Universal Fusible Links are available at most auto parts stores. These can be wired in at the alternator or at the starter switch, if the wire terminal is large enough.
Here's a typical universal fusible link.
Ken that sounds sensible & workable, going by your diagram does the fusible link wire from the Alt and the fuse wire to the terminal go on the same side of the starter button?
If I do this I would probably put a new wire from the Alternator to the fusible link and leave original in place sealed. What size/type do you suggest I use or order? Is this called 10 GA?
Ron, considering I drive my T an average of 30 mins a day, 6 days a week how long are you predicting my Alt will last?
Alternator arrived today So I fitted it. Battery was fully charged before I started it up, hand cranked and amp meter didn't show anything which is expected. At very low idle & with headlights on amp meter reads minus 8 but it only takes a few extra revs (basically a fast idle) for the amp meter to sit slightly above zero. Very impressed, clearly the extra speed provided by a pulley system is not required from what I can see so far. I'll do a road test using my GPS and see what speed I need to travel for charging. Great to have the ability to drive at night now.
Once the engine rpm's get beyond idle speed, the alternator "kicks-in" to start charging.... internal design in the Daryl Becker unit. Happy Motoring !!
Thanks Bob although I didn't get a Darly Becker unit soley because I couldn't contact them, via email or phone it was impossible. Ended up with a Delco Remy via "Macs", good price and great service. Went for a drive tonight and its impossible to drive in top gear without the Alternator charging...brilliant, very pleased so far.
Installed a 20 amp fuse yet ?
Not familiar what Mac sells as alternators, or who supplies them for Mac.
I can only relate my experience with the Daryl Becker alternator.
Keep us posted. Thanks !
Yes I installed a fuse today at the Alternator and I disconnect the battery when not using until I get the entire set up complete.
Your picture shows a paper fuel filter between the fuel strainer and the carburetor. Those can cause a lot of trouble. I would remove it.
Its brand new and i fitted it after cleaning the fuel tank a couple of days ago. I have a cleanable one on order.
Why can they cause a problem?
he thinks the slow the fuel flow
I originally had a hard plastic unit which did restrict a bit but it blocked with crap hence the removal of tank. I see this one is still running clear and not restricting flow...yet but I will monitor.
Since i have this pic up do you think the head is factory? It does have a "Z" on the water inlet.
The reason i ask is compression shows 90psi
From what you described, that cylinder head is not a Ford head, but a "Z" high compression head..... which is a good accessory. Have one on my '26 Runabout.
Looking at the commutator flag terminals at he top
of your coil box, I suggest re-installing them so the wire is positioned coming from the lower part of the terminal stud. ..... lessens chance of shorting flag terminal at coil box cover.
Ok Bob I will do thanks, do you mean loosen them and turn them so they are all at the bottom of each stud?
Head - You can see the Z in the photo but is there a difference in height over the standard head than can be measured? Or is there any other way I can tell for sure?
(Message edited by Rata Road on April 25, 2015)
If you just turn them so the wire is on the bottom you will have a bend in the wire. Remove terminal from stud & re-install so wire will be positioned straight in line, wire on bottom.
90 pounds compression and the "Z" casting are clues that it is a high compression head,,,,, gives better combustion & a peppier engine compared to a standard Ford T head.
So there is no way of telling by looking at the outside?
Its just that my research shows the head wasn't changed from 1988 on, were the high compression ones available before then?
Will change those wires over, thanks for the tip
Kevin, easy to tell, Z heads are aluminium and going by you photo, that's what you have, Z on the top and fitted with head bolt washers for a alloy head. Scratch some more paint off to make sure.
Check it with a magnet. If it doesn't stick to it, it is.
Did you ever figure out where the end play in your rear axle was coming from?
Will do thanks guys.
Les I havent started to look yet, I had a bad rust etc issue coming from the fuel tank causing flow problems so I removed the tank and spent 4 days cleaning etc. Then my Alternator arrived so have been setting this up.
I will update the original thread when I get around to having a look. I will probably get some basic parts in first so could be a month or so.
Yes its a high compression head.
Gary.. the magnet trick worked well. That will explain the compression.
Thanks for your help guys
Bob I had a go at adjusting the flag terminals but they are too hard to remove. I pulled a coil out and secured the terminal inside the box but it was going to brake off before it would allow the nut to loosen so they are staying as they are. The flags are attached to a strip of wood and I cant see how they can ever touch the metal case.
Thanks for the tip though.
Going to town to see Dr Hook next week so will pick up fusible link etc then.