Amp Gauge Blow Up

[lippy]

Perfect replacement http://www.summitracing.com/parts/sww-82391/overview/

[Hotfingrs]

Originally Posted by lippy

Perfect replacement http://www.summitracing.com/parts/sww-82391/overview/

That's the one I have.

[Mongoose930]

Hi Patrick,

I plan on running a ammeter when I wire my Hi-Tech and I would be very interested to know how you ran a parallel line with the ammeter. I think that is a great idea and adds a measure of safety.

Thanks - Kevin

[patrickt]

Originally Posted by Mongoose930

Hi Patrick,

I plan on running a ammeter when I wire my Hi-Tech and I would be very interested to know how you ran a parallel line with the ammeter. I think that is a great idea and adds a measure of safety.

Thanks - Kevin

It is very simple to do. On an ERA, there is a 50 Amp master circuit breaker that sits right in front of the battery that protects the system in case something goes big time wrong. From that circuit breaker, a wire runs through the firewall to the ammeter and then back out the firewall to the fuse box. To run the parallel line all you do is a run a wire, I chose a 12 gauge wire (for a very good reason), and ran it directly from the circuit breaker to the fuse box. That wire is "in parallel" with the ammeter and its line. Current will run through both lines and will be apportioned based on the respective resistances of the two paths. But note that the current will still add up to whatever it was before you added the parallel line. Now, in most ammeters all the current is not actually going through the little measuring device in the gauge. A portion of it is and then that value is multiplied for display. But, a poor connection at the ammeter or some other malfunction, can, and does, create a good bit of heat, because the resistance increases and the current has no other path. But with a parallel line, the current will now increase through this "path of least resistance" and you will notice that the ammeter gauge no longer shows you the readings that it once did (because the current going through there is less). A parallel line will not only prevent a big problem from occurring, it will also tell you if your ammeter, or ammeter line, is having a problem -- you just have to pay attention. But even if you don't, you'll still avert a catastrophe.

[Mongoose930]

Thanks Patrick. Is the wire going to the Ammeter 10 gauge or 12 gauge? I am thinking that most of the current would run through the 10 gauge wire (if that is what it is) and only go through the 12 gauge parallel wire if there is a problem with the ammeter / 10 gauge wire. Great information.

[patrickt]

Originally Posted by Mongoose930

Thanks Patrick. Is the wire going to the Ammeter 10 gauge or 12 gauge? I am thinking that most of the current would run through the 10 gauge wire (if that is what it is) and only go through the 12 gauge parallel wire if there is a problem with the ammeter / 10 gauge wire. Great information.

Right. The resistance of the new 12 gauge line is just a wee bit higher, but not much more, than the existing ammeter line. That allows the ammeter to still work very nicely. I do notice that when you turn on all the fans the "peg" of the needle does not go nearly as far as it once did. Other than that, the readings are just a bit more subdued, but still tell you pretty much everything that they always did. If I disconnected the ammeter entirely and just ran the car on the 12 gauge parallel line, it would probably be alright, certainly for a while, but it might also heat up and you wouldn't want to run it that way forever by any means, but maybe you could. The thing is, if all of a sudden I note my ammeter is acting differently than it has for the last seven or eight years (and it acts very consistently), then I know to stop and investigate. I have to say that's one thing nice about these cars, they tend to give you a little advance notice before they crap out on you. But sometimes that advance notice is really subtle....

[patrickt]

To answer your question on what percentage of the current goes through what path, let's say your ten gauge ammeter line has a total resistance of .003 ohms, which is what one of the internet calculators says a three foot span of ten gauge wire has, and let's say your new parallel 12 gauge line has a resistance of .005 ohms. Now, the difference of .002 ohms is hardly anything, but it results in 62% of the current going through the ammeter and 38% going through the parallel line. Now, let's say something happens and that ammeter goes up to just .01 ohm (in one way, that's still not much). Now the current going through the ammeter will only be half as much as the current going through the parallel line. Move the ammeter up to just 1 ohm of resistance and now the parallel line carries 99.5% of the current. I think I did that right...

[Mongoose930]

Thank you so much. I really want to run an ammeter for the sake of originality and having a parallel wire as a safety back-up makes me feel a lot better about it.

Now about that non-isolated fuel pressure gauge...

[DanEC]

Patrick - I think you missed your calling in not becoming an electrical engineer - but it probably pays less than your current occupation. I'm drawing a blank on that 50 amp circuit breaker sitting in front of the battery. Being too warm and comfortable to walk out into the cold garage to study my car some more - I wonder if that circuit breaker is on the firewall now, just to the right of the starter solenoid in this picture? The wiring diagram appears to show it connected to the positive battery terminal at the relay.

[patrickt]

Yes, that's it. The battery is connected to the starter solenoid with the large cable. From there, it is connected to the 50 amp circuit breaker. You do it that way so the starter motor's draw does not go through the circuit breaker but everything else that draws from the battery does. All charging of the battery goes through that circuit breaker as well.

EDIT -- and it's always been there, I just consider that to be "next to the battery."

[awfink55]

Thank You ! Thank you! Patrick, A wiring fire is always one of my main concerns when it comes to my older cars. My ERA is nearly 20 years old and has an Ammeter that seems to functioning fine. I'm extremely interested in this discussion and the ability to protect my car any way I can. A simple fix like this is great to know. I'll make the wire change asap. Again, much thanks, all the info from the CC Members is priceless.

[patrickt]

Originally Posted by awfink55

Thank You ! Thank you! Patrick...

Well, that's the nicest thing anybody around here has said to me in a long time.

Here's how you can check your work after running the parallel line. Of course, if you happen to have an inductive ammeter, that takes all the guess work out (mine below cost about $100 or so, IIRC). Before you run your parallel line, with the car engine off, turn your head lights on and turn your fans on, and snap a pic of your ammeter. The needle should be a good bit over to the negative side. Run your parallel line, now repeat the test and snap another pic. Post both of the pics here and keep them for future reference. Your ammeter should still behave pretty much as it always did, just with less movement. If you find that your ammeter begins to move less than it did, or if your ammeter should stop working entirely, then you will need a meter to correctly diagnose the problem (because you want to know how much current is really going through the ammeter line, regardless of the fact that the dash ammeter says it's zero). It could be that the ammeter line is perfectly intact, there are no bad connections causing resistance, and everything is flowing normally... but the gauge just doesn't work anymore. On the other hand, if you clamped an inductive ammeter around the old existing ammeter line, headed up under the dash, and it reported that only 1% of the current was going through that dash ammeter and 99% of the current was now going through the parallel line, that tells you that you may have avoided having a very, very bad day (and, of course, you'll now need to fix whatever it is that's creating all the resistance in your dash ammeter circuit).

[RICK LAKE]

GUYS Here's the problem with a curcuit breaker, It protects the wiring curcuit from over load. Downside. IF you have a wiring problem like the amp gauge problem here and the power wire shorts to ground, it will blow and open the curcuit. HERE'S the problem the curcuit breaker cools off and resets. These thing will reset from 10 - 50 times. Each time the problem is grounded and burns the wire coating. Over time you get a melted wiring harness.
Slow blow glass fuses worked for alot of years in a car or truck. They are now plastic and cheaper to make but still do the same thing. If you want to save your wiring harness from burning up, install a maxi fuse and holder. It's not orginial but will protect the wiring harness of the car. You have them on most new cars and truck. They range from 80 amps to 250 amps. It only blows once. Have to find the problem but alot less damage to wiring harness. I have a 100amp for my wiring system and a fusible link of 125 amps on my ALT.
Side note all fuses are measured for ampage ratings of constant load. The problem is when a curcuit is turned on, like lights the amp spike instead of 10-15 amps is 30-40 amps for a split second. This is the reason for slow blow fuses.
Late note IMO wouldn't recommend running parallel curcuits. If you run 2 wires to and from the same terminals and one shorts out. Unless you cut it out of the curcuit it's only going to burn up the other curcuit too. ERA wiring harness is just fine. Issue again is the insolators of the amp gauge from SW or Smith. Theses gauage where not designed to handle 60 amps constant and spikes of over 100 amps on startup if your system is wired that way.
If you want to run the oem look of an amp gauge, leave it unhooked and run a voltage either under the hood or in the glove box to keep a check on the battery and charging system Rick L.

[vatdevil]

Originally Posted by RICK LAKE

GUYS Here's the problem with a curcuit breaker, It protects the wiring curcuit from over load. Downside. IF you have a wiring problem like the amp gauge problem here and the power wire shorts to ground, it will blow and open the curcuit. HERE'S the problem the curcuit breaker cools off and resets. These thing will reset from 10 - 50 times. Each time the problem is grounded and burns the wire coating. Over time you get a melted wiring harness.
Slow blow glass fuses worked for alot of years in a car or truck. They are now plastic and cheaper to make but still do the same thing. If you want to save your wiring harness from burning up, install a maxi fuse and holder. It's not orginial but will protect the wiring harness of the car. You have them on most new cars and truck. They range from 80 amps to 250 amps. It only blows once. Have to find the problem but alot less damage to wiring harness. I have a 100amp for my wiring system and a fusible link of 125 amps on my ALT.
Side note all fuses are measured for ampage ratings of constant load. The problem is when a curcuit is turned on, like lights the amp spike instead of 10-15 amps is 30-40 amps for a split second. This is the reason for slow blow fuses.
Late note IMO wouldn't recommend running parallel curcuits. If you run 2 wires to and from the same terminals and one shorts out. Unless you cut it out of the curcuit it's only going to burn up the other curcuit too. ERA wiring harness is just fine. Issue again is the insolators of the amp gauge from SW or Smith. Theses gauage where not designed to handle 60 amps constant and spikes of over 100 amps on startup if your system is wired that way.
If you want to run the oem look of an amp gauge, leave it unhooked and run a voltage either under the hood or in the glove box to keep a check on the battery and charging system Rick L.

Rick L...who makes 100 amp maxi fuse holders?

[patrickt]

Originally Posted by RICK LAKE

GUYS Late note IMO wouldn't recommend running parallel curcuits. If you run 2 wires to and from the same terminals and one shorts out. Unless you cut it out of the curcuit it's only going to burn up the other curcuit too.

That would only be true if there was a catastrophic fault to ground on the dash ammeter line, not with a continuing increase in resistance on the gauge condition. And a possible catastrophic fault to ground occurrence exists on any configuration, ammeter or volt meter or no gauge at all. But I do agree with you on the 50 amp circuit breaker. There should never be a time that circuit breaker clicks off, ever, for any reason. If it does click off, chances are the problem is not going to clear itself during the short "reset" period. So, all things considered, a one-time slow-blow 75 amp fuse is probably better and just carry a spare in case the short was caused by something innocent, like bumping a wrench from the fuse box to the firewall, or the like. The more I think about it, the more I like the idea of replacing that circuit breaker with a fuse.

[DanEC]

If Bliss is continuing to monitor - I'm still curious if the connections at the amp gage were good and tight when he disconnected them?

[Mongoose930]

Blue Sea makes excellent Fuse Products and I used them exclusively to wire my Contemporary Cobra and will be using their products on my Hi-Tech Cobra:

https://www.bluesea.com/products/category/Fuse_Blocks

They have an AMI fuse box that goes from 30A to 200A and Maxi Fuse holders up to 80A.

I don't think you would be disappointed with any of their products - very high quality.

[patrickt]

... or just change out the auto-reset circuit breaker for a manual-reset circuit breaker. I should of thought of that in the first place. Even ol' Rick might agree with me on that. Maybe not, though... he's a toughie.

[vatdevil]

Originally Posted by Mongoose930

Blue Sea makes excellent Fuse Products and I used them exclusively to wire my Contemporary Cobra and will be using their products on my Hi-Tech Cobra:

https://www.bluesea.com/products/category/Fuse_Blocks

They have an AMI fuse box that goes from 30A to 200A and Maxi Fuse holders up to 80A.

I don't think you would be disappointed with any of their products - very high quality.

Blue Sea also makes ANL fuse holders, which also work with fast blow ANN fuses
https://www.bluesea.com/products/550...r_-_35_to_750A
Since I'm mounting this in the engine bay, a breaker isn't suitable for the heat and vibration. These also look appropriate for a Cobra and accept up to 2/0 wire.

[patrickt]

Originally Posted by vatdevil

Since I'm mounting this in the engine bay, a breaker isn't suitable for the heat and vibration. These also look appropriate for a Cobra and accept up to 2/0 wire.

Cooper has an amp-temp chart for their automotive circuit breakers, you just adjust the rating for the under-hood temperatures. Vibration is the same as anywhere else on the car. ERAs have had their circuit breakers mounted on the engine side of the firewall for almost 30 years now without any problems, but I do think a manual-reset is better than an auto-reset.