Ammeter Amped

[Wildergarten]

This post is pursuant to the magick experienced that led to the Wirring Error thread (viewtopic.php?f=21&t=44286). Out of the four trucks I've disassembled, two of them had come with 10AWG wires run straight through a hole in the firewall (with no grommet) directly to the ammeter and bypassing the harness. This suggested that the high current loop from the alternator to the ammeter and back out to the big lug on the relay had fried at some time in the past.

Before frying the harness, I had noted a high resistance connection to the lugs on the ammeter (they were a bit loose and when I wiggled the connector I saw a small spark at one of the nuts. Upon cleaning the studs and hooking it up with new nuts and washers, I found to my dismay that the line had been feeding a dead short under the dash. What made the magnitude of the failure so nasty is that I had failed to notice that the person who had made this bypass modification had blown off the fusible link wired the #10 directly to the relay lug. So, where was the short? From what I can tell, it was the ammeter itself. Hence this post.

In removing the failed ammeter, I thougth I might salvage the insulator plate with the buss bar on the back of the instrument housing. I planned to us the buss bar on the back insulator plate to power a push button switch run the electric fuel pump to prime the carburetor before starting (the power comes off the breaker on the windshield wiper switch). When I checked the buss bar, there was no continuity between the bar itself and the channel with the lugs, probably due to accumulated corrosion. So I pullled out a spare instrument panel and the loose spare ammeter to solder up all three buss bars at the same time.

Please look at the first photo of the back side of a spare instrument panel. Note the carbon between the stud and the edge of the insulator plate. I suspect that the combination of windshield leaks and repeated high current had slowly oxidized the insulating material. If it cracked at the stud, that pathway would eventually form a direct short.

Now look at the second photo. After soldering up the buss bar, I took the back plates to the sandblasting cabinet and gave each a VERY quick dusting to take off that carbon. The one on the top blew apart instantly, revealing that it was likely cracked with a similar carbon buildup in the crack. That was from the ammeter that had shorted I actually spent more time blasting the one on the bottom to take off the carbon residue in the first photo.

In looking at the ammeter that had fried (third photo), there was no melting at the studs that would indicate a short to the back of the instrument housing. Hence is my conclusion is that should consider this insulator plate suspect. If there is any carbon on it at all, or if one intends to use a higher amperage alternator, one might wish to replace it with a better material similar to FR5 circuit board material.

[nutz]

nice detective work
makes me wounder if i can make an inductive amp gauge so don't have to have all the power running threw my dash
guess that why they went to volt meters

[Wildergarten]

nice detective work

Thanks, just trying to help.

makes me wounder if i can make an inductive amp gauge so don't have to have all the power running threw my dash
guess that why they went to volt meters

With my last truck with a stock alternator, it couldn't keep up with the combination of the heater blower, wipers and lights. One wonders how much current was leaking out those studs into the dashboard.

With alternators putting out over 100A these days, I am certain the ammeter is even more problematic. For my current build, I want one even bigger to power work lights, inverter, compressor, etc. run on dual batteries with an isolator. I do like the look of the dash, but if I make one it will have a vacuum gauge between a speedo and tach. I used to want an ammeter simply for diagnostic reasons, but have slowly changed my mind. This was probably the final straw.

[martincom]

With my last truck with a stock alternator, it couldn't keep up with the combination of the heater blower, wipers and lights. One wonders how much current was leaking out those studs into the dashboard.

I'm not so sure that black discoloration is carbon tracks. Carbon tracks usually occur when there is arcing involved. You indicated there was some arcing from loose wires, on the studs. However, that wouldn't leave carbon tracts on the fiber board insulator. I'm more incline to believe the discoloration was from heat generated by the high current flow, through the poor connection created by loose connections.

The stock alternator, assuming a 40 amp, should have kept up with that load, above idle. A pitfall of the mechanical regulators was they resulted in low to no output at idle and idle RPMs alone result in low output. Voltage drop in the wiring, particularly a bulkhead connector is a known issue, as well.

With alternators putting out over 100A these days, I am certain the ammeter is even more problematic. For my current build, I want one even bigger to power work lights, inverter, compressor, etc. run on dual batteries with an isolator. I do like the look of the dash, but if I make one it will have a vacuum gauge between a speedo and tach. I used to want an ammeter simply for diagnostic reasons, but have slowly changed my mind. This was probably the final straw.

Our earlier several trucks had Econoline E350 stripped chassis under them, which came with Ford instrumentation. In the '70s, both GM and Ford had moved to shunt type amp meters --- which never worked. They were just an instrument cluster ornament. Having a functioning amp meter was pretty critical for our application. I ended up salvaging the amp meter from '70 B-body Mopar instrument clusters and mounting them upside down, to match the graphics, in place of the Ford amp meters. These were not shunt fed amp meters and were much like the amp meter in my '71 D100. They were pretty robust and we never had an issue with them.

The build on these trucks was near identical to what you describe for your current build, with the exception that we utilized a 90 amp alternator and didn't have a compressor. We utilized #6 from the alternator output to the battery isolator. One side of the isolator fed the starting battery, which pretty much just served the stock electrical system of the truck, with the addition of four heater blower motors. We utilized #8 from the alternator output to and from the amp meter. We also utilized relays for the blower motors, so we didn't have to run that current through the ignition switch contacts, which would have been problematic, but they would still power on/off with ignition. We didn't utilize any type of amp meter on the auxiliary output of the isolator, which fed two auxiliary batteries, the inverter, and the service bench. We did have a voltmeter incorporated into the service bench. I also had added switches/wiring to serve an idle solenoid, to increase idle speed. This was to increase idle speed, in part for full alternator output, but more significantly to circulate the coolant through the heater cores quicker. We had three heater cores in these trucks and we worked in sub-zero temps. At idle, the heater blower motors alone would more than dissipate all the heat from the circulating coolant.

I did away with the battery isolator in my last service truck build. I had issues with isolator failures and they're not a cheap piece. We simply utilize a relay to disconnect the auxiliary batteries from the starting battery when the ignition is off. Relays have come a long way since our first service truck builds. They're smaller, can have significant ampacity, can be weatherproof, and low cost. I've had zero issues with the isolation relay.

[Wildergarten]

I'm more incline to believe the discoloration was from heat generated by the high current flow, through the poor connection created by loose connections.

Yours is a better description of what I meant. We agree there as to the cause being overheating oxidizing the material long term, with the initiation of the process being a combinaton of water, corrosion, and contact resistance. I had put the VOM on that patch on the insulator and it read in the double digit ohm range. Not good.

Having a functioning amp meter was pretty critical for our application. I ended up salvaging the amp meter from '70 B-body Mopar instrument clusters and mounting them upside down, to match the graphics, in place of the Ford amp meters.

In the immortal words of a T-shirt once given to me: "Does anal retentive have a hyphen?" To which I responded, "It should, but it's not on this T-shirt."

The build on these trucks was near identical to what you describe for your current build, with the exception that we utilized a 90 amp alternator and didn't have a compressor. We utilized #6 from the alternator output to the battery isolator.

I calculated #4, particularly because the compressor is to be at the back of the truck. I even have some welding jacks I was thinking of putting on the back of the truck. So that cable might have to be bigger. Do you think a battery and small compressor could run a carbon arc? (engineers call it, "Creeping Elegance.")

One side of the isolator fed the starting battery, which pretty much just served the stock electrical system of the truck, with the addition of four heater blower motors. We utilized #8 from the alternator output to and from the amp meter. We also utilized relays for the blower motors, so we didn't have to run that current through the ignition switch contacts, which would have been problematic, but they would still power on/off with ignition.

I have two relay blocks for the truck with Bosch style relays and ATO fuses, one in the engine compartment and the other in back with the compressor.

We didn't utilize any type of amp meter on the auxiliary output of the isolator, which fed two auxiliary batteries, the inverter, and the service bench. We did have a voltmeter incorporated into the service bench.

Good thought!

I also had added switches/wiring to serve an idle solenoid, to increase idle speed. This was to increase idle speed, in part for full alternator output, but more significantly to circulate the coolant through the heater cores quicker. We had three heater cores in these trucks and we worked in sub-zero temps. At idle, the heater blower motors alone would more than dissipate all the heat from the circulating coolant.

As you know, I'm in (what's left of) California.

I did away with the battery isolator in my last service truck build. I had issues with isolator failures and they're not a cheap piece.

Have you looked into Blue Sea Systems? That stuff is for marine applications. I'm planning to use their stuff all over the truck for high current fuses, distribution fues blocks, etc. Their stuff is sealed, with beefy buss bars and solid brass connections.

We simply utilize a relay to disconnect the auxiliary batteries from the starting battery when the ignition is off. Relays have come a long way since our first service truck builds. They're smaller, can have significant ampacity, can be weatherproof, and low cost. I've had zero issues with the isolation relay.

Well now you've got me thinking. As long as they're electromechanical I'm interested. Got a brand you can recommend?

[martincom]

We utilized #6 from the 90 amp alternator output to the isolator and from the isolator to the auxiliary batteries. We utilized #2 welding cable from the batteries to the distribution bus bars under the work bench.

I've utilized Potter & Brumfield, Bosch and Tyco or TE (whatever they're calling themselves this week) all without issue.

In my last service truck build, we ordered the chassis with a 140 amp alternator, which was the largest available as a factory option. It was more than adequate for what we required. I utilized #4 from the alternator, to relay, to the auxiliary batteries in that truck. I utilized the heavy duty, weatherproof Bosch circuit breakers at each end of the #4. I had 60 amp units on-hand, so that's what I utilized. They're the manual reset type and they've never tripped. I would have went larger if I had to order them.

FYI: Ford offered quite a bit info on a public web page for third party body-builders. They had output verses RPM graphs for all the alternators they offered. The 140 amp produced maximum output at 900 RPM. The truck idled at 750 RPM, as regulated by the engine control module/fuel injection. Ford also incorporated some firmware/hardware in their ECM whereas the body builder could increase the idle RPM when required for such things as PTO driven options. They had extra wires flagged off in the wiring harness for this. By providing a switch closure on one lead the RPM would increase. What it increased to was controlled by a specific resistor value placed across another pair of wires. So we utilized this to increase idle speed, when needed. I utilized a two position switch and two different resistor values, one yielded a 900 RPM idle and the other position 1200 RPM. The ECM interlocked the increased idle speed with the transmission being in park and the emergency brake being sent.

I shared all of this so you may want to research/calculate at what engine RPM your selected alternator will produce maximum output and plan some type of mechanism to achieve that.

Have you given any thought to a belt driven air compressor in the engine compartment? What, exactly, were you planning for?

I don't have any data on the power requirements for a carbon arc.

[Wildergarten]

Have you given any thought to a belt driven air compressor in the engine compartment? What, exactly, were you planning for?

Pressurizing a water tank for a hose.
Tires.
Maybe the very occasional blow gun for chainsaws and such.
Maybe a bladder jack.

While I was doing this job, I came up with a handy dandy way to help keep rats out of the cab.
The neodymium ferrite magnets do a good job. The shift boot has hardware cloth under it.