Ammeter 30A - 2 Questions

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Dhugalmac

10 Year
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While I have benefited from reading previous posts, this is my first one that I have done.

I have 2 questions regarding the 30A Ammeter in my 72 FJ40 Project vehicle.

1. Before I got the vehicle, one of the previous owners did a V8 conversion - it works.
But they used a generator (alternator ??) that is not stock.
Somewhere along the line the 40A fuse between the generator <-> Ammeter <-> Battery blew.
How can I find out what amperage this needs to carry so that I can determine if my dash's 30A ammeter is adequate?

2. When I put an ohmmeter across my ammeter's leads I read almost a short.
But when I took it out and looked at its guts it looks as though the metal (from post to post) intentionally runs all the way across with a resistor (??) block mounted onto it.
How can I tell if this meter is Shot and needs replacing? Or if it is OK?

Your advice and/or suggestions would be greatly appreciated.

Thanks
 
Your fuse was 40 Amps so replace it with the same.
The resistance of the Ammeter is 0.4 ohm, so yes, your digital multi meter will read close to 0 ohm.

Rudi
 
Thanks for the info.
Yes, not knowing any better, I already went ahead and replaced the fuse with the same type (40A).

Before putting it back into the instrument panel, is there any way of knowing if the ammeter will handle the current from the new generator without the trial and error of just blowing it up?
 
The alternator charges only the "used" amps for cranking, so if your battery is in a good condition you'll see maybe a 15 to 20Amp charge which drops rapidly in the direction of 0 Amps.
If your battery is empty, you're not able to crank the engine. You'll use jumper cables and at that same moment the donor vehicle is charging your battery.

Did it work before? What numbers did you get when it worked? Why did your fuse blow?
BTW..... a fuse is not the smartest thing to use. A fusible link is what Toyota used in these Cruisers.
The difference between a fuse and a fusible link is that:
A fuse pops at a certain value, so if you have a short high current draw the fuse will pop.
A fusible link can handle a temporarily high current where a fuse would pop.

Rudi
 
Again, thanks for the info.

Yes, the vehicle worked when I bought it 6 months or so ago, but I never paid any attention to the ammeter reading then.
As you say, it is usually reads 0 when everything has been working fine. And it is 0 when it isn't working at all.

At least the vehicle was driveable, although the dash lights, etc were not coming on with the lights.

I am not sure why or when the fuse blew.
After having the vehicle work OK for a month or so, one day it wouldn't start - no cranking, nothing.
I was troubleshooting it when I came across the blown fuse.

On my 72 FJ40 wiring diagram, the location is labeled "fusable link", but there is now a 40A blade-type fuse there. It does not look like original equipment. I think that it must have been put there by the previous owner who did the V8 conversion.

What you are calling a "fusible link" sounds like what I have previously called a "Slow-Blow Fuse"
And it makes sense that it is what should be there.
When looking on line for a "fusible link" for my FJ40 I see units out there, but I am not finding the housing for it.
Maybe that is why they went with a simple blade-type fuse.

I am wondering if I replace the simple blade fuse with something like the following would it work just as well
0299040.ZXNV: 299 Fuse 40A 32 Volt Slow Blow Acting 2 Pin Bulk: Littelfuse

But for now, after replacing the fuse, getting a new battery and temporarily jumpering the wires that used to go to the ammeter, the vehicle is starting again.

However, not knowing what blew the fuse caused me to wonder if something was wrong in that part of the circuitry.
And reading an almost-short across the ammeter, caused me to wonder if that was SHOT - thereby causing the fuse to blow.

But from what you indicate, the ammeter is most likely OK.

My newest concern about it is its capacity.
If the fuse is 40A shouldn't the ammeter also have that same capacity instead of its current -30 to +30 ?
 
The OEM fusible link handles all of the power in and out of the battery to the chassis. It might see considerably more than 40A if everything was on at the same time. You really don't want a fuse in this situation, even a "slow blow", because if it blows you have no power to anything, including your engine which is dangerous.

A fusible link is a short piece of wire that is smaller than the rest of the wire so it will burn out first. No housing is used.
 
fusible link - "is smaller than the rest of the wire so it will burn out first"

Wouldn't that result in the same thing as a Slow-Blow fuse -- "if it blows you have no power to anything"
 
A fusible link can handle a start-up or run-in current much bigger than the nominal value of a fuse.
If you have a 40Amp fuse (even when it's a slow blow) that fuse blows at 1.2 x 40 Amps = 48Amps.
A fusible link needs time to burn up so it can handle a run-in current of 80 to 100Amps for a short time.
Another example; you're working on the electrics and by accident you touch ground with a live wire. FLASH! there goes the fuse.
A fusible link doesn't care about that.

A fusible link is 4AWG numbers smaller than the wire(s) it protects. So if your main wire between alternator and battery is, let's say, 6AWG, your fusible link is 10AWG.

Long story short...... your choice; fuse or fusible link.

Rudi
 
Rudi - thanks for the excellent clarification.

I'll begin looking to find a "fusible link" to replace the existing fuse.

Any advice regarding the ammeter capacity:
* OK to stay with the current 30A?
* Or, considering the fuse/fusible link 40A rating, should it be changed to a 40A?
 
Stay with the 30A meter. There is no upgrade possible unless you want to install an external Ammeter and upgrade your wiring.
Order a FL from @Coolerman he will respond to this.
The one thing you never mentioned is: What is the capacity of the Alternator? 40A or more?

Rudi
 
I'll have to check the Alternator.
I never mentioned its capacity because I don't know.
Where would I find the capacity?
Would it be on a label or somewhere else?

Also, while looking for Fusible Link I am having a tough time finding anything for the FJ40.
However I am finding some 'raw' Fusible Link Wire
Catalog
Fusible Link Bulk (Wire & Cable) ~ All Battery Sales and Service
If I were to get the wire to use somehow, it is not listed by Amperage.
Instead it is listed in wire gauge - so what gauge should I get?
 
Generally the fusible link size should be 4 sizes thinner than the wiring it is going into.
Let's say the wire size you have on the harness is 16ga. , then you would want a 20ga fuse link.
The thinner the wire ,the higher the number.
You can buy fusible wire at NAPA auto parts. If you need I can probably find a part number..
BTW If it helps, I probably even have what you need. I have it in small spools, but I can snip off a piece.
 
djcfj40 -- Thanks for the info. and thanks for the offer of some fusible link wire.

Since there is a NAPA store pretty close to the house, I'll check there first.
If I run into any problems I will most certainly contact you to see if the offer is still available.

It is hard to imagine using a 20ga wire in the circuit from the Battery + to the rest of the vehicle.
Since a wire's current carrying capacity is proportional to the wire's diameter, 20ga seems pretty small.
But I did find another reference: Weather Pack Environmentally Sealed Connectors | Weatherpack Terminals and Seals | White Products Cleveland Ohio and it agrees with the 4ga smaller recommendation.

Thanks
 
First off, my question for Rudi is about fusible links, but not related to this thread or Toyota. So, if the OP would prefer I will start a new thread, but will give a quick overview of what my question is so you can decide.

I have a 94 Chevy pickup with a 6.5 diesel and dual batteries, which came stock with a CS 130 alternator. I changed out the stock battery cables for some bigger welding cable (don't remember the size at the moment), except for the charging wire to the batteries. I also changed to a CS 144 alt that puts out 140 amps instead of the 100 amps that the CS130 puts out. My question pertains to what is the minimum size charge wire, and fusible link, that should be on there now.

Again, to the person that started this thread, if you prefer, I can start a new thread for this. It's just that my questions do pertain somewhat to the thread subject matter.

Don
 
Don (a.k.a. handcannon) - I don't have any objection to your jumping onto this thread, but you might get more targeted suggestions/advice by starting a new thread with your question.

Pin_Head - thanks for the info. 20ga did indeed seem TOO SMALL to be carrying the full electrical load of the vehicle. 14ga seems more likely. Regardless, I will get a wire gauge and measure the primary wire before I do anything else.

Rudi (bj40green) - I went out to the vehicle last evening and looked at the alternator. There is no label on it, merely a manufacturer stamping of their name - Delco Remy. However after going to their website and looking at the form factors of their various models it looks like the alternator is a Model 10SI

The site: Catalog says:
"There were 10SI alternators with 37amp, 42amp, 55amp, 61amp, and 63amp ratings. The smaller amp output rated alternators were installed on cars with no air conditioning, and few electrical accessories. The 61amp output rated 10SI was very commonly installed on 8cylinder cars, with factory air conditioning option. "

So I am still guessing, but it seems likely that my alternator is the 61 amp unit.

Thanks
 
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