The Stovebolt Site Forums The Shop Area The Electrical Bay Ammeter Wiring Update

I have been checking with every electrical engineer who will listen about the issue of what to do to protect your electrical system from a catastrophic fire event when installing a higher amp alternator than your ammeter gauge is capable of handling. Ammeter Shunting is what you hear is the answer. Problem being, there is no shunt product that is matched for a 50 amp meter (that is in our trucks) and a larger alternator. The ones that are available are expensive and very LARGE. The reason has to do with metallurgy, resistance values in the micro-ohm range, and its just not feasible to address.

So, one of my more down to earth friends (yes I have a few), told me about his late 60's Chevy car. They put a 40 amp charging system with a 30 amp gauge. To make sure they didn't burn down the vehicle, all that is required is to put in a 30 amp fuse in line with the ammeter. In OUR case, the gauge is 50 amps max. So, the prudent and safe thing to do is put a 50 amp fuse in line with the ammeter. Just a beefy 8 gauge fuseholder with at least a 40 amp fuse in it will make sure you are safe from your truck burning down to the ground!

It's an easy solution to a complex problem that will give you the same peace of mind you had before you went to a larger alternator.

This is the fuseholder that supports the AGU Fuses:

http://www.amazon.com/gp/product/B007WX0NMS?refRID=4V6G9Y71M23XFH5AY3NR&ref_=pd_rhf_ee_p_img_4

This is the 50 amp fuses to match your 50 amp gauge:

http://www.amazon.com/gp/product/B001JYPD12?psc=1&redirect=true&ref_=od_aui_detailpages00

For those of you who use that extra Alternator amperage for Inverters, etc, there are Shunts available but they are 6 inches long by an inch and a half wide.

http://www.summitracing.com/parts/sww-407616?seid=srese1&gclid=CPv-6OWoosgCFYM_aQodpoYK4A

(they do not look that large in the picture) Hope this helps!

What you propose is indeed a way around the problem. The only problem is you could be trading one problem for another.
Since a number of electrical takeoffs are located on the input lug of your amp meter, when you blow this large fuse you will lose most if not all power to everything else. Now, you are replacing the fuse...but for what reason? Did you just over amp your meter or have you had some sort of short develop? If it's the second reason then when the fuse is replaced, it blows again. As the old saying goes, "Now whatta ya going to do?"

Yes. That's true. It is not the elegant solution I had hoped for. But in reasoning this out, it was also brought to my attention to think about how many amps 50 amps represents... how much of your wiring is capable of handling 50 amps? The entire wiring system is a fuse at that point right?

So, we figured that if the fuse blows, put another one in to see if it was just a one time event (like a lightning strike?), and if not, its troubleshooting time. Does that make sense?

I've been running a 10si for several years without a problem using just the stock amp gauge on my '40 with a 235. I don't draw that much amps but what happens if I discharge the battery a lot? Like if I have starting problems and have had to crank it too much. Or, if I left the lights on for a while? Would that make the alternator put out its max trying to charge the battery?

Dennis

I hope someone else chimes in Dennis. My unsure thought on this is no, the battery is only capable of charging at a lower rate, however, GOOD QUESTION. In perusing the internet for an hour so far, I have been unable to answer the question. I'll keep looking. The answer is out there. I do not want any monkeys in the wrench!

Maybe I missed seeing it in this post, but doesn't an alternator only charge the amount it is needed to charge? I may be confused or am misunderstanding, but isn't the amount of the output of an alternator only what the battery is requiring at the time the alternator is putting it out? So, wouldn't a 60 amp alternator need to be supplying 60 amps only if battery was "taxed" 60 amps. If all the equipment on a vehicle is "turned on", the alternator puts out what it needs to keep the battery charged just like it doesn't if none of the equipment is on. A limiter of sorts - right? So, how could it really ever put out the full amount it is capable of putting out unless the battery was fully discharged or the system was basically being over taxed. Most of the time a battery is down, you usually put a charger on it, so the alternator really never puts out it's full capability and in at least the case of my truck, the starter is not hooked to the alternator, but the battery. So, finally, how could the Amp Meter really be taxed any more than the battery needs or wants even if the amperage goes through the amp meter?

Deve, just sitting around watching a ball game and a thought hit me. If you were to put the big fuse on the down stream side of your amp meter (between the meter and battery), then if It popped you would only lose the charging circuit to the battery. It should be easy to spot as your amp meter needle would never move. Just a thought you understand
On the other questions...once the engine is started the alternator takes over the job of supplying electrical power to all running circuits plus bringing the battery back to a fully charged state, if possible. There are many ways to wire a amp meter incorrectly but only one way to wire it correctly.

Yes. I was taught to dedicate your alternator-ammeter-battery line and not to connect anything else to it. Not sure if it's right, but there is nothing else in that circuit on my StartKart. That is not how an AD is wired according to the wiring diagram. But the diagram does show a clean path between the ammeter and stater terminal (battery). I like the idea of putting it between the battery and ammeter. What does everyone else think?

All the angst about high capacity alternators is misplaced concern. Nice to discuss, but totally superfluous in the real world. An internally-regulated alternator is smarter than all drivers, and most mechanics, sort of like an automatic transmission. Untold millions of electrons have been needlessly slaughtered by self-appointed experts who like to waste gigabytes of self-congratulatory bandwidth, though. Cheap entertainment, I guess- - - -we could be doing something really stupid like playing golf!
Jerry

I was on a conference call with a few electrical engineers in California about this the other day. I know it is a real concern beyond a shadow of a doubt. The problem exists if you go higher in amps than the ammeters internal protection which is 50 amps.

When I told them the idea of using a radiator clamp in a horseshoe configuration, one of them laughed and said its something he would have done when he was 14, but now that he understands the need for a balanced system, no way.

Mr Herbison, if you choose to tell people not to worry about it, and they take your advice and go about their lives and their house burns down, that's on you. I do not want that on my conscience.

The problem with just stuffing any old piece of metal back there is it changes the accuracy of the meter. You want full deflection of the meter. Since these trucks didn't come with a shunt, and the late 60's Impala was set up with a fuse to fix that problem then I feel the next best thing is to fuse the circuit. But I do not know if these higher amp alternators would go to their max output under any conditions we might run across.

I know its easier to just move on, but its not serving anyone. Lets try and get to the bottom of this. This right here is why I do not EVER take one persons word for anything. Jerry in this case you are just dead wrong and dangerous at the same time. Today's crop of new admirers/owners of these trucks will just blow it off and then cry when their entire family is wiped out in a fire. I couldn't sleep at night and probably won't until I figure this out.

Why don't you take another identical ammeter, remove the guts and wire it across the existing ammeter. If they are the same design, they should share the current. You will then get 1/2 the deflection for a given current but it should handle twice what the original did.

It's not a bad idea Fred. Still looking for that perfect solution that doesn't halve the deflection. Maybe try and find a 100 amp gauge and transfer the guts into ours? That's what it's all about, bantering ideas back and forth until a solution presents itself.

If I knew these high output alternators would never reach more than 50 amps fusing it would work too. Or a way to limit the output of the alternator? Congrats on getting your GMC finished.

Engineers- - - -highly intelligent people with no common sense. My brother is one, with a Master's in EE and a Doctorate in Plasma Physics, although he is also an ASE-certified Master Mechanic. At least he got a trade education first.
Jerry

I'm torn about that. I have worked with some of the foremost geniuses of our time at Sandia National Labs. Some of them couldn't tie their own shoes. No social grace either. Then I came from Kansas farmers who lived on common sense or died from lack of it. They were all about social grace. I think if you can see both sides of the equation you are better off for it. I agree that the trade education puts you further ahead from a well rounded standpoint and its how I taught my kids, but it is pretty cool to watch a real scientist working on really hard to understand concepts and they just zip right through it. But there is always a good technician standing right beside him keeping common sense at the forefront.

This particular problem we are dealing with in this thread is about both. A very knowledgeable engineer or just good electronic guru can unlock the storehouse of ideas and the common sense guys can step in and keep things flowing in a straight line. There is always the question of why the guy purchased an alternator too large for his gauge, but that's sort of a copout and doesn't provide an answer. Lots of people doing it too.

I've been running a 66 amp Delcotron on my Farmall tractor with a 20A meter for around 20 years. When the battery is low, it pegs the needle for a short time, then swings back to a lower reading. After a normal start, it will not even peg and will swing back toward zero in just a few seconds. Most of the output in a modern vehicle goes toward running all the gadgets. They use high-output alternators so they can do that and still charge the battery in a reasonable length of time.
Generally speaking, you won't be charging the battery at anywhere near the full output of your charging system unless you are jump-starting another vehicle, and then not usually.
As far as burning your house down, the alternator only puts out current while the engine is running. I don't know of many folks who run their automobiles inside their houses.
Another thought, this may be one reason they switched to volt meters in newer models.

What do you think about the idea of an inline 50 amp fuse (50 amps is the gauge rating)? I am wondering under what circumstances the fuse could blow. If the car came with a high output alternator I wouldn't worry about it since the manufacturer would have balanced the system with the appropriate gauge or yes, a voltmeter.

So Ed, if you put in a 20amp inline fuse, how often would it blow and under what circumstances is the question.

I have met Jerry and know he has cleaned more grease from under his fingernails than most of us will every put in a grease gun. I think he is trying to say this is a non problem and we are beating it to death for no other reason than we don't play golf, at least I don't.
If you don't want to use a volt meter in place of the amp meter which most people do, including me, then you leave yourself few options. You have covered most already. BTW, I'm retired from making a living doing instrumentation and instrument design and it bugs the heck out of me when a meter reads incorrectly as I believe it also does you. But you got to see the big picture in the fact these amp meters were not built to be percise to begin with. They are there to give the driver just an ideal of what is going on, not what the exact charge/discharge rate is/was. If that is what you must have then pull the amp meter, sent it to one of your engineering buddies. Using the test equipment any engineer worth his salt has, he can build you a shunt which will allow you to correctly read your meter IF there is not to much non linearity involved.
I also know Jerry wants no one or any equipment to be harmed by some of the stupid things we do, that's one reason he's here. Now a pesky fly or mosquito is another matter.
Jerry, have I used up my allotment of gigabytes yet?

I wouldn't know, Deve. My point is that in all the years I have had that set-up, the ammeter has never overheated, let alone caught fire.

"Measure it with a micrometer- - - -mark it with chalk- - - -cut it off with an ax!" Dash mounted ammeters are notoriously inaccurate, and they're so over-built it would take a dead short to ground to damage one or heat it up enough to burn wiring. This discussion, like a LOT of others on similar subjects has gotten ridiculously silly.

Beltfed, you've summarized my thoughts exactly. I'll get fussy about a thousandth of an inch of extra clearance on a rod or main bearing, or a couple of ten-thousandths on a wrist pin bushing. That stuff is important. Getting anal about an ammeter reading is stupid!
Jerry

Its not like I do not hear what you guys are saying. It has to do with we are not dealing with 60 amps. We are talking about anywhere between 80 and 150 amp alternators.

(1) What size wire do you have to have to run 100 amps through it?
Answer: 4 gauge. Nobody I know has a truck with 4 gauge wire going through the charging system. Some of us even have 65 year old 10 gauge wires under the dash in questionable shape.

(2) What circumstance would ever cause 100 amps to go through your completely inadequate wiring/gauge?

Answer that and then we can say we are done here. I do not have to tell anyone that has contributed so far what would happen if 100 amps went thru a 10 gauge wire. It would evaporate as fast as a fast blow fuse. If you caught it in time, you might be able to save your truck. I hope its not running inside the attached garage. I know you think this is alarmist, but it's prudent to be on the safe side.

Shunts are the best answer but unfortunately, there are no custom shunts available for our old gauges. At least in my extensive search I haven't found any that are feasible. The engineers that I have talked to say that isn't about to happen either due to the expense in creating metal combinations that have low enough resistive qualities.

To early for a football game so here goes...
The current carrying capacity of a wire is not determined by the size of the copper or aluminum conductor. It's the insulation! Using building codes for example, code says for a 30 amp circuit use a #10 gauge wire with something like THHN insulation. What that means is at a 30 amp draw the insulation will not degrade, melt, etc. NOW, hang a bare #10 wire in free air between two post. Feed it current, lots of current. See how much current it takes to melt that #10 wire. I'd say you will be surprised.
Car manufactures do not use building codes for automotive wiring. The first time I really noticed this was when I was installation a Spal electric fan on my Hotrod. The instructions said it needed a little less than 20 amps. Sounds like #12 wire by building code standards right? The pigtails from the motor were #18 at best. What the hey, I said. I wish the rest of my car ran as good as that fan.
No doubt you need good wire with good insulation, clean connections, etc. But you will see what many would consider undersized wires all over your ride.
I run a #8 wire from my high output alternator with a fuse link. Some people hate fuse links but I still run one. As for insulation I only use GLX type which is cross-linked polyethylene.
I don't think I really answered your questions but maybe someone smarter than me will.

GM uses 10 gauge wire for an output lead on their 100 amp compact alternator, the one that wears out the Torrington bearing at the rear of the case and causes vehicle-destroying short circuits from the alternator rotor grinding itself into the stator when the bearing fails. I have load-tested several of them to maximum output for several minutes without the wire even getting warm. Now, our resident expert is going to call me a liar, I'm sure!
Jerry

You may test a wire gauge and it holds, but you yourself would NOT recommend that wire size as the one you use in a real world application. You would go to 8 gauge. You know it. Especially when lives were on the line. This isn't about a few minutes of testing, or the ammeter, its about a balanced system when someone unbalances it by purchasing an alternator too big for the application. I have never represented myself as an expert at anything. I get whatever I have learned here. It's what gripes you to no end. Here is someone who doesn't proclaim to be anyone special (like you). Just someone seeking answers.

Jerry, rather than keep sending more and more wasted text, say the answer if you know it. Is there ever a time when a 100 amp alternator would actually charge at that rate, and if no, what rate is its top? Its okay if you don't know. The only thing that matters is the answer to the question. Then you can go back to your regularly scheduled programming.

Use a simple self-holding relay circuit to isolate power to your buzzer silliness until the engine starts. You can use oil pressure to activate the self-holder, which will continue to provide power until the engine is shut down again. A freshman electrical engineering student knows how to wire a self-holding relay.

The only time a 100 amp alternator would even approach supplying its full output to the battery would be during a deliberate load test using a carbon-pile battery load tester to confirm the capacity of the alternator. If you had an ounce of practical experience to go with your theoretical pipe dreams, you would already know that.
Jerry

Now you are finally getting it! I have no practical experience and I failed Freshman relay class. You still keep talking, but no answer as to what the max output under any stress this 100 amp alt output is. please do not disappoint your disciples. LOL

You're not as dumb as you're desperately trying to seem.
Jerry

It must be past beer-thirty. I can relate to that. But dumb has nothing to do with it. It has to do with real inexperience and the HOPE that someone actually KNOWS the answer. Not someone who likes to portray themselves as an expert when everyone knows there is no one single person that can boast all of the BS you claim. But, BUT, I appreciate what you DO know. I do not appreciate, and NOBODY ELSE DOES EITHER, the way you like to tell everyone else how stupid they are! And I am here for you folks! This will NEVER be over until Mr Herbison sees the value of treating everyone and the experience they have with decency and humility. WOW do you have NO idea what you are up against. Keep it up! No way does this end without you being found out for exactly who you are. DO YOU HAVE THE ANSWER TO THE QUESTION OR NOT? Watch closely folks to the next retort and find out who this idiot really is.

Deve, No one here seems to be able to satisfy your quest for knowledge on this subject and the 'flaming' has started. The forum moderators take a dim view of this and we, the population of this forum, don't want anyone tossed as this is our hobby, not our job. All information, good and bad is necessary if we are going to separate the good from the bad.
My advice to you since your engineering friends nor we can answer your questions is to go to the source. Contact the manufacturer of these hi output alternators like "Powermaster" and ask them. If they don't know then I guess no one will.
I noticed your place of employment. I have been there several times for conferences as my place of employment was the Oak Ridge National Lab. I was involved in nuclear reactor research (Neutron science). I remember eating lunch a few years back sharing a table with two senior nuclear physicists. They were discussing Quarks (look it up if you don't know what they are). One physicist ask the other how he would measure a Quark. He response was, "why I would use a Quark meter". I almost choked on my food.
I also turned wrenches on aircraft for a number of years in the National Guard.

I would like the right to post a question without people coming in and driveling all over it. Question is asked, question is pondered, question is answered or not answered based on the knowledge we have here. I expect as the original poster for off topic conversation to be taken to the Greasy Spoon. I get very frustrated when people who claim to be the Son of God just yap yap yap. BLAH BLAH BLAH and in the end, we have NOTHING to show for it. The very least he could do is just not reply to anything that I post and life would be just fine. But if he insists on taking that tact where all he does is clown up the works, and the moderators sit there and don't do a darn thing about it, it's up to ME to keep MY topics on track. I am doing the best I can with the tools I have.

Warning though, I lose my sense of humor real fast when people think they can clown things up and here I am trying to get serious answers to a serious problem. Next thing you know I will be following this [censored] all over the forums retorting every single post he makes. All I ask is to be left alone to work with those who actually DO know a portion of the answer so I can help put the pieces together. If he survives his hangover, hopefully he will have the decency to just stay away. We can elevate this beyond belief or we can get along. I am very good at both.