1976 F250 Single Wire Alternator Conversion

[GoodiePop]

Hello all, It's been quite some time since I've needed to search for information on my truck, and I find myself now needing the expertise of some of you here to help me solve an issue I am faced with.

I have searched the posts here, so as not to duplicate anything, and I can't find anything specific. If I am wrong, please point me in the right direction, and I will delete my post.

I now have a new, single-wire, 220 amp alternator, straight 4ga wire going to the battery, and I would like to have my ammeter in the dash working again, but a), I don't know if the factory wiring will handle those elevated amps, and b), since my original 3 wires are no longer connected, which wire was the one that actually allowed the gauge to read charging or discharging? My former alternator was the one that originally came with my truck, but I had it raised to 150 amps, and that wasn't sufficient for the draw I have now.

The guys at the alternator shop who built this alternator for me said that since this was now just a single wire from the alternator to the battery, I would need a minimum of 4ga (done), and nothing else. I do have a regular Autometer Volt meter under my dash, but my go-to gauge has always been the factory ammeter, so I'd like for that to continue to function.

For anyone wondering why the alternator with such a high amperage output, my truck never came with A/C, and I have a service dog who rides in the back where the SuperCab jump seat folds out flat, and because of where I live, we see summer temps of 125-130 degrees. I had to put a 5000 watt power inverter in the bed to power the Toshiba 8000btu Portable A/C unit (not window unit - floor unit), along with mother's stationary oxygen concentrator, so here I am asking you all questions. I also have 5 - group 31 batteries in the truck for providing sufficient storage.

I am carrying my old 150 amp in the side box as a spare, (I have severe OCD and redundancy is a must), so I don't want to remove any of the factory wiring that goes to my former alternator.

I'm thinking that it's unlikely that the engine I have now would make any difference, but I have a 1994 GM 6.5L Hummer diesel, so if that is either good or bad, that would be for you who know about these things to decide.

Help? Thank you all for taking the time to read this. Take care.

[zgerbic]

Yes, you should be able to get the dash ammeter going again. It can be made to work with the 220A (or any other amperage) alternator. The engine used has nothing to do with the ammeter. I am assuming you still have the wiring in place from the existing dash ammeter out to where the battery/alternator are located. The problem you will run into is that if you restore the wiring exactly like it originally was from the factory, the ammeter will peg when you are drawing or charging over whatever the maximum current the factory alternator could put out (probably 60A). You need to make an adjustment so the indication across the ammeter is the same at 220A as it was at 60A. When this adjustment is made, the ammeter will still work the same as when the truck was new but the markings will now show 0 to + or - 220A, instead of 0 to - or + 60A.

Please look at my writeup in the following thread:
http://www.fordification.com/forum/view ... hp?t=96570
This explains how the ammeter circuit actually works.

I still don't have a factory ammeter or a factory 38A wire to measure in my lab so I will need to do some additional research to figure out what you actually need to do to re-scale the ammeter to match your 220A alternator.

There are at least four ways that I can think of to make the ammeter read correctly for the alternator installed:
1. Change the points where the ammeter wires are connected to the shunt to make them closer together to make the voltage at the ammeter correct when larger amounts of current are passing through the shunt.
2. Increase the wire diameter (less resistance per foot) to change the voltage dropped across the shunt to make the ammeter read correctly.
3. Install a small value resistor in line with the ammeter gauge to drop some of the voltage coming from the shunt. The resistance will probably be about 3.5X (~220/60) the resistance of the ammeter itself. A low resistance rheostat or potentiometer could be used which would allow you to just dial in the maximum value you would feel comfortable with.
4. Install a current shunt across the ammeter terminals which will shunt away about 3.5X of the current flowing through the ammeter to make it closer to the amount that would normally pass through the ammeter.

All four of these methods will individually correct for the increased alternator maximum current. The upside of getting the ammeter to work with the 220A alternator is that the ammeter will read full scale when the alternator is putting out maximum current. The downside is that the ammeter will be harder to read any fine variations in current flow. Keep in mind that the meter needle will move about 1/4 as far as it originally did to for any given amperage. I suspect the headlight current draw will hardly move the needle with the engine off and not move it at all with the engine running. Another thing to think about is that the ammeter will only read full scale discharge if all your electrical stuff is on and the alternator fails or the engine is off, and the ammeter will only read full scale charging if the batteries are all almost dead and the truck is trying to keep everything going and charge the batteries at the same time. If you think this is a little far fetched then you probably should try to setup the ammeter to peg for a little lower current measurement, perhaps 175A or so. There are ways to set this up which will allow the ammeter to read a lower, more realistic, full scale but keep the voltage across the ammeter from burning out due to too much voltage.

With regard to the increase in wire size (lower gauge) for the new ammeter, besides a large wire to the battery, you will need larger wires from the battery to some of the other electrical circuits that will be pulling the extra current. You will also need bigger fusible links or fuses under the hood or dash. Keep in mind that current leaving the battery connection to the rest of the truck will be the sum of the maximum alternator current plus whatever the batteries can provide. You will also need almost battery cable sized wires going back to the inverter if it is really pulling 5000W for more than a few seconds. 5000W / 12V = 416A. I suspect you need the 5000W inverter just for the startup current for the air conditioner, then it drops back to some reasonable value your wiring can handle.

If i can find out more about the gauge resistance and full scale voltage, and the resistance of the 38A wire, I will post some additional info on how I would get the ammeter to read correctly.

[GoodiePop]

Absolutely excellent information! Thank you very much for this. I also had a look-see at your post about the circuitry. I'm sure I will be able to get everything working now. I did learn that my A/C unit is rated at 12 amps, 1380 watts, so my 5000 watt inverter is a little over-kill, but as I mentioned earlier, I have OCD really bad, and I have to have peace of mind that I can not only provide cold air for everyone, but also that mother's oxygen concentrator will operate normally.

Incidentally, is there any one of the 3 specific wires that went to the factory alternator that I should be using to connect to the single-wire post on the new alternator? I saw that they are marked Battery, Field, and Stator on the back of the factory alternator, so I wasn't certain if just one of those connected to the new alternator would give me the starting point of making the ammeter function again, and then making the adjustments you mention after that.

The new alternator, I am told by the guys at the shop, is the same as the new Nippondenso style single wire units that are being widely used today, and while there is a plug on the back of the alternator that would facilitate connecting to the internal components, they filled it with silicone to make sure that I didn't connect anything to it, as they said I would damage the internal regulator. So what I am left with is just the single post for the 4ga wire going to the battery.

I took pictures to show everyone what I'm working with here, but I don't know how to imbed them here.

Thank you again. This is really terrific information. Take care and be well.
James.

[zgerbic]

James,

The inverter is not necessarily overkill. While the AC unit might only pull about 1380 watts when running, it has a compressor motor in it that likely pulls more than double that when starting up. Consider when you turn on a table saw or other large piece of machinery in a home environment. In many cases you will see the lights flicker for an instant. That is the huge current draw off the mains when the motor first starts. If you sized the inverter at, let's say, 1500W, it is unlikely you could get the AC motor to start or the inverter would immediately fail because it could not provide that initial surge of current.

The two small wires that connect to the dash ammeter (passing through the instrument panel connector) are not specifically connected to the alternator or regulator. They are connected to the section of wire labeled 38A that runs from the connection on the starter solenoid to an additional length of wire that goes to the alternator. This is the wire shown in Figure 2 or the write-up. I suspect you no longer have the 38A wire since you connected the new 4G wire from the alternator to the terminal on the side of the starter solenoid. I would assume the wire that goes toward the firewall, which would have been connected to point B in Figure 2, has been moved to the side of the starter solenoid as well. If this is the case let me know and I can give some advice as to what to do next if you want to get the ammeter working again. As a teaser for the answer, I suspect you will need to move the wire going to the firewall to a point along the 4G wire so you have the two segments as shown in Figure 2. One of the ammeter sense wires will have to be attached to the starter solenoid connection where it would normally go. The other sense wire will have to be attached at or near where you tap into the 4G wire for the wire connection going toward the firewall. This creates a setup that matches what comes from the factory and is shown in Figure 2. Now where you add the connection for point B along the length of the 4G wire is want has to be determined. The closer the new point B is to the alternator, the higher the ammeter will read for a given current draw (charge or discharge). The closer the new point B is to the starter solenoid connection, the lower the ammeter will read for a given current draw. Why you need to add the new point B attachment point for the wire going to the firewall is because the ammeter actually measures the current coming from the battery or going to the battery. This is what the ammeter is supposed to show, not the actual amount of current that is being used by the truck, AC and accessories.

[zgerbic]

You have a an interesting setup here so I have been thinking about it a bit and have some questions. I can see the value of having an ammeter. What do you want it to actually show? Do you want the needle to move enough to represent a normal charge/discharge you would see in a stock 60A alternator vehicle? What I mean is if you have the engine off and turn on the headlights, do you want to see the needle move 10% to 20% away from the 0 mark towards discharge? If the engine is running and you are driving down the road, do you expect to see the needle stay near zero unless the batteries were low and are now charging, and how far do you want the needle to move when charging? When the engine is off and you turn on the AC and some accessories, drawing let's say 20A, do you want to see the needle move to 10%, 50% or 75% discharge.

The behavior of the gauge is pretty simple when you have a 30A to 60A alternator and the truck draws typically no more than 30A. The needle position can tell a lot about what is happening in detail. When you spread that narrow gauge movement over 220A or more, turning on the lights will hardly show anything and 30A is hardly a flicker. I think it is a good idea to decide what you really want to show, so it tells you something useful you were expecting.

[GoodiePop]

Do you want the needle to move enough to represent a normal charge/discharge you would see in a stock 60A alternator vehicle?

Precisely. It had just been common practice over the years, to be able to glance at the ammeter and see that everything is just ok, by that meter showing charge or discharge. If something were to go wrong, then I would have an indicator immediately in front of me to let me know I have an issue.

I've been doing some rootin' around on the internet, looking at different ammeter configurations, and I see that there is a Bayite DC 5-120V 400A Mini Digital Current Voltage Amp Meter Gauge with Hall Effect available, but I also immediately thought of how I could possibly utilize the sensor from that device to gain my ultimate goal here. Here's the device:

https://www.ebay.com/itm/195405287721?h ... BM-tTOvvhg

Because I am not an electrical engineer, I can only assume and ask questions to those in-the-know, but with the 38A wire you're speaking of, would I be able to utilize the wire from the harness this device comes with, (3 wires, they are marked 100A, 200A, 300A), the one marked 300A, to run in place of the factory 38A wire, being connected to the sensor? I plan on ordering 2 of these devices, one for the new alternator and one for the inverter, just for satisfying my brain while I'm driving.

I should point out as well, I didn't connect the new 4ga wire to the starter solenoid, I just went straight to the battery, because I didn't want to remove anything from the solenoid without first knowing what I could safely remove. All factory connections are still intact. Now that you have mentioned connecting the single terminal from the new alternator to the battery terminal of the solenoid, I will do this.

[basketcase0302]

zgerbic
James,

The inverter is not necessarily overkill. While the AC unit might only pull about 1380 watts when running, it has a compressor motor in it that likely pulls more than double that when starting up. Consider when you turn on a table saw or other large piece of machinery in a home environment. In many cases you will see the lights flicker for an instant. That is the huge current draw off the mains when the motor first starts. If you sized the inverter at, let's say, 1500W, it is unlikely you could get the AC motor to start or the inverter would immediately fail because it could not provide that initial surge of current.

The two small wires that connect to the dash ammeter (passing through the instrument panel connector) are not specifically connected to the alternator or regulator. They are connected to the section of wire labeled 38A that runs from the connection on the starter solenoid to an additional length of wire that goes to the alternator. This is the wire shown in Figure 2 or the write-up. I suspect you no longer have the 38A wire since you connected the new 4G wire from the alternator to the terminal on the side of the starter solenoid. I would assume the wire that goes toward the firewall, which would have been connected to point B in Figure 2, has been moved to the side of the starter solenoid as well. If this is the case let me know and I can give some advice as to what to do next if you want to get the ammeter working again. As a teaser for the answer, I suspect you will need to move the wire going to the firewall to a point along the 4G wire so you have the two segments as shown in Figure 2. One of the ammeter sense wires will have to be attached to the starter solenoid connection where it would normally go. The other sense wire will have to be attached at or near where you tap into the 4G wire for the wire connection going toward the firewall. This creates a setup that matches what comes from the factory and is shown in Figure 2. Now where you add the connection for point B along the length of the 4G wire is want has to be determined. The closer the new point B is to the alternator, the higher the ammeter will read for a given current draw (charge or discharge). The closer the new point B is to the starter solenoid connection, the lower the ammeter will read for a given current draw. Why you need to add the new point B attachment point for the wire going to the firewall is because the ammeter actually measures the current coming from the battery or going to the battery. This is what the ammeter is supposed to show, not the actual amount of current that is being used by the truck, AC and accessories.

It's referred to as LRA (locked rotor amps is what every compressor pulls when it first starts and will be listed on the nomenclature plate, (35+ yr retired HVAC tech).
Been trying to get that through some old skool hard headed folks down here that think their wimpy 3000 watt generator will run a lot...more than it will safely.

Good response on the Amp meter wiring, I never had it in me to go that far to get my original working.

[zgerbic]

GoodiePop,

Just be careful you don't fall into the trap of "analysis paralysis". I have created several telephony network management systems and always try to keep the main screen very simple with only a general, high level, picture of the state of things. It is easy, especially in my field, to get lost or overwhelmed in too much information at too high a detail, or the feeling that you need to constantly look at readings to decide if something is bad or not. That is one of the beauties of the ammeter gauge it does not give more info than necessary but just enough, at a glance, to let you know if something is wrong or if everything is ok.

[GoodiePop]

This is why I prefer to be able to glance at the ammeter and see that it's either to the positive side, or if something is wrong, the negative side, but all the same, just a simple glance is best for me.

[GoodiePop]

No reply on my questions there about using the sensor inline with the 38A wire? Does this sound like it may work? I can't think of anything else that will read the current flow from the 4ga cable. The sensor is large enough in diameter to pass the 4ga cable through, this is why I figured it may allow the gauge in the dash to read positive or negative from center.

Yes/No?

[zgerbic]

It is not going to work the way you want by measuring the 4G wire with a magnetic sensor. The problem is that the alternator is directly connected to the battery. What you will see is how much current is going from the alternator to the battery (charging current) plus some of the current being supplied by the alternator. You will not be able to see any current being supplied from the battery to the truck. It cannot show discharge since the current will only be one way (out from the alternator). You will not be able to tell what is coming out of the battey or going into it.

In order to make either the dash ammeter work or make a magnetic sensor work, the wiring must be the same style as the original truck had. All the wires from the truck that are consuming power (dash, lights, coil, AC, accessories, etc.) must be connected to the alternator and the wire for sensing must be connected between the alternator and the battery.

You will need a heavy wire coming from the alternator to a connection point (as shown in the trucks wiring diagram). From that point all the trucks power needs have to come from that point (the starter is an exception). A smaller gauge wire needs to be put between that connection point and the battery (that is what the 38A wire is). That smaller wire is where any measurements are taken (which is what the 38A wire is used for). If you use the dash ammeter, it will need to be connected across that smaller wire. If you use a magnetic sensor, it has to be measuring that smaller wire. The smaller wires gauge and length determines the amount of voltage drop that either method measures to determine how much current is going into the battery (charging) or coming out (discharging).

In reality you may end up using a wire between 10G and 6G as the smaller wire in order to get enough voltage drop to make the ammeter move or the magnetic sensor show anything. While this may seem counter intuitive to what you think you need for the current produced by the alternator, when the truck is running, only current from the alternator is expected to used by the truck, not current from the battery so the alternator to truck power system would require a large wire. The current to the battery will only need charging level current as it is mainly used to run the (which already has a huge wire) and ignition system during the time you are starting the truck. The current levels should be significantly smaller through the 38A wire when the truck is running, in theory it should hover around zero amps while driving down the road after a few minutes (time to recover from cranking the engine). If there is any significant draw from the battery while the truck is running the battery will eventually discharge so low the truck will not be able to start after the truck has been turned off and you try to restart it.

It is possible you can use the existing alternator shunt wire (#38A) and ammeter wiring as it exists in the truck, but you will need to change the gauge of the wire from the alternator to Point A and the wire from Point A back to the rest of the truck to handle up to 220A. The battery charge current and any temporary current from the main (used for starting) battery while the engine is off should be able to be handled by the shunt wire. Current supplied by the rest of the four or five batteries need to be handled as a separate task since they should be isolated from the main battery. Not doing this risks ruining the batteries, over charging the batteries or allowing the batteries to drain the main battery, stranding you somewhere.

We have not talked about any of the additional wiring for the AC or the additional batteries (how they are connected, if you are using an isolator and where they are located). This is an additional discussion but the initial discussion needs to be settled first.

[GoodiePop]

The engine starting battery under the hood, is connected to a battery disconnect switch in the bed of the truck, approximately 7 feet away, via 6ga cable. My initial configuration for the 4 batteries in the bed of the truck, was because I had no battery storage in my travel trailer. The batteries in the bed are connected via a 6ga, stranded copper wire, running from the disconnect switch with a length of approximately 2 feet, and then there is positive/negative terminals via a male quick-connect plug on the bumper that connected to the female half on the wiring loom coming from the trailer. The disconnect switch is one of the simple, twist On/Off switches, so there is no specific current-flow isolator in this line.

The power inverter is located directly next to the 4-battery bank in the bed of the truck, connected with a 24" 6ga positive and negative cable. I am using a 15', 12/2, extension cord for powering the A/C unit, as well as the oxygen concentrator. I have only a remote On/Off switch panel inside of the cab for controlling the inverter.

All of the 6ga battery cable connecting the batteries in the bed to the engine compartment are housed in 1/2 inch PVC conduit, open on all ends, to allow air flow and heat dissipation.

The 4-battery bank is connected in parallel, with 6ga cable loops, from one battery to the next. The inverter is connected to the 1st battery in the bank, instead of the last, and I think I just told on myself, in that the inverter should most likely be connected to the last battery, so the 1st battery doesn't take the brunt of the power draw.

I hope this helps.

[zgerbic]

There are a few ways to hook this system up. It is correct to have a starting battery that is normally (or at least when parked) disconnected from the other batteries. Switch or isolator will work. Ammeter should be for the starting battery as I described above. The connection point I mentioned is where the power should go toward the rear batteries. I would have run the wire from the connection point directly to the inverter and then run a wire from the inverter to the batteries. Four individual wires, one to each battery, would be better but if you run only one then you can monitor the current charging and discharging the batteries across that single wire, or, you could run all four wires through the current monitoring sensor if the hole is big enough to get them through. What you would end up with is a dash ammeter that monitors the charge/discharge activity related to your starting battery and separately monitor the charge/discharge activity for the rear 4 batteries when charging or while in use. A simple voltmeter next to the rear batteries could be useful to see the state of the batteries when parked, when the trailer is using power, and what voltage you are getting when charging the batteries (with all the cable length and connections, there will be some voltage drop by the time the power gets from the alternator to the batteries themselves).

The idea here is to treat the front of the truck as a system and the back of the truck as another system. While charging, driving down the road, they may be connected as one, but once stopped they are independent. In this way you should be able to assure you can start the truck, be able to charge all the batteries and be able to monitor what is going on at any time.

[zgerbic]

Just to be clear...

...related to your starting battery and separately monitor...
should be
...related to your starting battery and a display to separately monitor...

Each system independently displays the charge and discharge for its batteries. While this may see a bit like overkill, but considering your investment in batteries/alternator/wire, and criticality of having the AC/concentrator working, you should make it easy to understand if it is all working as possible.

[GoodiePop]

This is excellent!! Thank you for taking the time to explain this in as great of detail as you have. I planned on using this morning to go out there and do all of this wiring, as we're only supposed to get up to 90 degrees today. I'm going to print all of this out, take pictures as I go, and post back on here the results. I'm sure I'll be successful. Be back soon!

And yes, you are correct in having an investment here. I'm in this $1700 now, and I know I could have bought a knee-knocker A/C unit, but that would have meant having to install an A/C compressor on my engine, and that was entirely what I wanted to avoid. My engine, even with the Banks turbo, is only around 220hp. To add another component to the engine that would drag hp and fuel mileage away from it was something I had to avoid. I'm getting 21 mpg now, so I didn't want to disturb that.