Alternator Help/Suggestions....

[xumFJ40]

Hey gang,

I got stranded the other night on my why home when my truck died, and I couldn't get it started....

Anyway, a simple jump allowed it to start right up, but as soon as I would "draw too much power" as in honk the horn...the truck would die.

Once I got it home, and hooked the battery charger up, the charger showed that the battery was just about drained....

So, I assume that my alternator has not been working and I have been running off of battery (new red top) power for the last couple of trips.

The only thing that confuses me is that my "ammeter" gauge has showed dead middle while the truck is running and at idle. This gauge is the stock gauge...and I assumed that it would show me that the alternator was charging correctly....but I guess not.

So....to the questions:

1) What should I expect this gauge to tell me?
2) Any other ideas as to my problem, or am I correct that my alternator is bad?...I plan on having it tested anyway.
3) If the alternator is bad...what are some good alternative replacements? Anyone have some good experiences to share?

Thanks

 

[CruisinGA]

1) Ammeters show whether the alternator is matching current draw. needle to the (+) side means that the alternator is more than matching current draw, and thus charging the battery. Needle to the (-) side means that the alternator is not matching current draw and the battery is being drained. Needle in the center (if ammeter is working and truck is running) means battery is charged and ammeter is matching current draw.

2) Your alternator very well may be bad. But something is also wrong with your ammeter.

3)I've always grabbed 2F used ones from the local cruiser shop, nets me more power (45 vs 35 amps) and cheaper. Napa remans are ok. Toyota is best.
My first alternator to go just needed new brushes. A few dollars and 2 hours of work and the alternator was fine.
Do not leave the voltage reg out of the equation. I would go ahead and replace it now. $27 may save a lot of headache.
You need to check out the ammeter and associated wiring. I think something is up there.

 

[xumFJ40]

Bailey,

Now that you mention it, when I turn on my lights, it would drop to the (-) side a fair bit...but would be fine at Idle with Lights off....

Supposedly the VR was tested before I bought the truck, but I will check it and my alt out...

So, would I be best served by a toyota replacement, or one of the high output aftermarket ones?

 

[PabloCruise]

I don't know if the HO ones fit w/out mods. I don't know if you want the HO current running through your dash...

Having a GM unit putting out 90 amps is sweet. But so is having an all Toy rig.

It is up to you!

 

[CruisinGA]

When the truck is running with no accessories on, there is nothing drawing current but the ignition system and idle solenoid. Neither of which need much current at all.
Case in point: My grandfather told me that back in the 50's someone figured you could drive across the country on a battery with no alternator as long as nothing but the coil was drawing current.

The fact that the needle stayed on the negative side with lights on and engine running means that your alternator is not compensating like it should. Does not mean necessarily that alt. is bad. Check wiring, volt reg, and first of all have alternator checked out at auto parts store.

Unless obviously replaced recently, I would not ask questions and just replace the voltage reg. It may still work, but chances are you will get more regular charging and a more stable system with a new one. It is also one thing to check off the list as bad.


I do not like hi-po aftermarket alts. They do not put out those big amps until you get them up to big RPM's-which will not happen often in a cruiser. They sacrifice low RPM amps to produce the big ones later on. As TJ said, you should not run more than the 45 amp 2F alts through the factory wiring. It is dangerous to have that kind of current inside the cab.

So, you really should not install anything other than a factory rated replacement until you change around the charging system, IMO not necessary for most. Do you really need 200 amps, or even 100? Not often.

Honestly, I've found that the properly operating, stock, charging system I have now can easily handle all my needs, and best of all it is reliable toyota. I prefer used Toyota over new aftermarket. So new toyota is first choice. pm cruiserdan and see what he can do.

EDIT: If you do want to run a higher output toyota alt (up to 65 amps I believe) you can add either an external shunt to the ammeter, or double the shunts inside it. Search for posts by Pin Head for the procedure. The external shunt is probably what I will do when I install my winch and need more amperage.

 

[JasonH]

Ryan, I think I have a couple extra alternators. I can bring them Thursday if you want to see if one of them will work for you.

 

[RUSH55]

CGA, WTF is a shunt?
I have a 100amp alt I got from Specter about 2 or 3 years ago, and it's always been quirky. At idle, with lights on, the needle bottoms out on the (-) side. Can an alternator shop repair this? It'll reach dead center at about 1100-1200 rpm's. Another thing it does is surge. The needle will bounce from low on the (-) to high on the (+) and lights/accessories will go dim, bright - dim, bright... I heard that this could be caused by the stock amp meter. True? What do you think could be done to modify the electrical system to handle the increase in amps. Anyone know of an informative website?

 

[Dave E]

A shunt is basicaly a bypass. Lets say that the shut is sized the exact same size as your ammeter, your ammeter would indicate 1/2 the number of amps it does now, because it only receives half the amps the alternator put out. The shunt receives the other half. I've never measured the ammeter on my cruiser, but if you knew the resistance of the meter, you could calculate the nessary size shunt to efffectivly resize your ammeter.

Dave

 

[RUSH55]

What it the unit of measurement used to measure the "size" shunt or shut? What does it look like?
So now I see there is both a "shut" and a "shunt", how are they hooked together, or how is it configured so that one recieves half the amperage, and the other part bypasses it? I guess I'd have to see the schematic of an ammeter to get the picture, but I'm enjoying the lesson.

 

[sherwood]

Hi Rush,

let me take a stab at it. First, you must understand that I barely got out of high school :whoops:

The ammeter movement is a fairly sensitive device. It takes very little current to move the needle.... usually milliamperes or microamperes. The shunt's job is to bypass the bulk of the current and send it on it's way to do it's regular, everyday duties.... and deliver a tiny portion of the total to the meter movement. The ammeter just monitors the flow.... kind of a sampling device.

The shunt is a resistor and it is measured in ohms. The other significant factor in selecting a resistor is it's current handling ability. It does, of course pass all the current used in your Cruiser..... minus the wee little amount consumed in wiggling the needle on your ammeter. So, it must be a rather stout little resistor or it will melt/explode/evaporate !

To calculate shunt value, you must know the maximum current flow to be expected in your everyday usage of the cruiser. You must also know how much current it takes to move the ammeter needle to full scale...... IOW.... a multiplier "ratio". You must now the resistance of the meter movement.

Rs = Rm / n-1

Where
Rs = resistance of the shunt
Rm = resistance of the meter
n = multiplying factor

Or, you can do as most REAL engineers do........ experiment, experiment, experiment ;p

Knowing all the ballpark parameters will give you a good starting point.

Going to http://www.qsl.net/4s7vj/lessons/chapter7.htm and looking at paragraph 7.1.2, both methods, claculation and bench calibration are shown.

BTW, Shunt resistors are of very low ohmic value. They are usually found NOT with the regular resistors, but under their own heading of "shunt resistors".

john

 

[CRZRJames]

I have no electrical engineering degree or background, but here are a few things I have learned (by the seat of my pants) about my charging system:

1) The stock charging system runs all charging amperage through the large white wire that runs through the ampmeter. A long time ago I heard that it was good to take the ammeter out of the equation by taking the white wire (s) off of the posts behind the ampmeter and tie them together. I did that and for several years it has worked with no problems.

2) If you are caught on the side of a mountain and need to use your winch for an extended perior of time, a stock alternator will NOT keep up with amps your winch is eating.

I put in dual batteries and a GM 94 Amp alternator a few years ago and have had little problems with that setup. When installing the GM alternator, you eliminate the stock wiring harness to the alternator and also eliminate the external voltage regulator. With the GM alternator, you run a single charging wire to a splitter and then individual charging wires from the splitter to each of the batteries. This way, the charging amperage is not being carried through the gauge cluster.

If you don't plan to run a winch or welder, I would stick with the stock alternator because any other system will tend to be quirky. I have gotten a lot of good use out of my system, but am on my second splitter and sometimes have issues with the "excite" wire.

Good luck,
James H.

 

[sherwood]

About the dangers of the ammeter. As CRZRJames stated, routing the entire current loop through the dash to the ammeter would be a great concern to me.

In later cruisers, they wisely rectified this by passing only a fraction of the current to the ammeter. Under the hood, the current flows from the battery/charging system through a fusible link, and on to the rest of the Cruiser. The fusible link acts to protect the wiring from over-current conditions. A fusible link is a smaller than normal wire. A smaller than normal wire is inherently a pseudo-resistor. It is more difficult to pass current through a small wire.... so..... in comparison to the rest of the main trunk, that fusible link is a resistor.

The fusible link doubles as a "shunt" resistor or current divider. A small fraction of the total current passing through the fusible link is "shunted" to the ammeter circuit. On my '79, this smaller current is passed through two glass fuses to the ammeter.

I have no concerns as to fire/damage to wiring in my factory ammeter wiring.

I definitely would investigate a better method for the older LC systems.
It may be possible to "remote" the shunt resistor from the meter to under the hood... and add some fuses. I haven't looked into the older ammeters to see how they are mechanically arranged.

john

 

[RUSH55]

Sherwood, do you know the location of this resistor wire? Did you replace yours with the glass fuses?

 

[sherwood]

Sorry Rush,

It's stock on the '79. Don't know how it's done on your Cruiser.
On the '79, the fuses are just off the big power cable between the battery and the firewall.

john

 

[Dave E]

The shunt resister on a an meter is typicaly like 1 Ohm, maybe 0.5 Ohms. A easy way to figure out the size resister you would need to rerange, is measure the resistance of the meter you have and add a second resistor in parallel, the exact same size. BUT measureing that small of a resistance is hard. I will say that while this will allow your ammeter to measure a larger current, it is dangerous to put this extra current through the OEM wires. These were sized for the lower currents and fire can result from overloading them. If you wanted to put new wire from the high power alt to the battery, and install a shunt resistor in line, you could connect an ammetter to this shunt resistor without it being in the dash. This appears to be what is discribed in the 79 model above. I do agree with the fuses from the shunt to the meter.


Ok, now back to the origional thread....


I'd keep a stock alt, unless you have added a lot of power hungrey accessories. The wires are not build to handle the extra current.

Easy test for the ammetter. Park on a hill. Leave your lights on for a couple hours. If you cant restart it, roll start it. The ammeter should indicate heavy charging. If not, you have a bad meter.

Boy... think this is about $.04 worth.


Dave

 

[Pin_Head]

Wow, all this talk about shunts is pretty impressive. The stock OEM shunt is just a strip of brass between the two lugs on the ammeter. You can double or triple the capacity of the meter just by stacking 2 or 3 of these.

The resistance of most high current shunts is too low to measure. You can calculate its resistance from the diameter of the wire and its resistance per foot. A typical 0-10 mA full scale meter might have a coil resistance of 50 ohms. To use it in a meter that would read 100 amps full scale, you would need a shunt that has 1/10,000 of the coil resistance or .005 ohm.

 

[RUSH55]

Sorry Pin Head, until this thread, I'd never even heard of a shunt. Going thru ammeters isn't something we do alot in our shop.

 

[Pin_Head]

Sorry Pin Head, until this thread, I'd never even heard of a shunt. Going thru ammeters isn't something we do alot in our shop.

If you did more boats in you shop you would have heard about them. Most marine ammeters are external shunt because they are less of a fire hazard.