1976 F250 Single Wire Alternator Conversion
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GoodiePop
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Re: 1976 F250 Single Wire Alternator Conversion
I forgot to also mention, I've ordered the 50-400A amp meter that I posted earlier, along with another 300A Amp and Voltage meter, so I will have 3 digital meters along with my factory ammeter when I'm done (I already have one in the truck that I have connected to the inverter). I don't have to be able to see all of the digital meters all of the time, but the factory one in the dash will be great to be able to glance at it and see what's going on. If something is not reading correctly, I will then be able to see with great certainty what's not right.
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zgerbic
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Re: 1976 F250 Single Wire Alternator Conversion
I would suggest that you read carefully the info from the sensor manufacturer about wire size and sensitivity of the sensor, if you are expecting to get a reading that means something. I suspect you will be ending up with the 200A setting to get something that is usable. Probably see 130A to 150A draw with the AC and accessories on in the trailer. That is a lot of power coming from the batteries, just below what a 6 cylinder typically draws for the starter. It will be interesting to see how long the batteries last if the AC has to cool down the trailer after it has been sitting in the sun.
Have you thought about attaching an AC compressor to a V twin motor sized for a typical 2500W to 5000W backup generator. Could be an interesting alternative but would require quite a bit of work to graft that into the trailer. I am not familiar with trailers and if you can retrofit them with a factory style AC unit that runs off 12v. Another thought would be a gas powered generator in the bed of the truck, maybe a quiet Honda inverter/generator, that could run several hours on its own fuel tank. Could end up using that on your house during a power failure to keep the refrigerators and some lights running during a blackout. Just bolt it down well as someone might want it more than you do.
Have you thought about attaching an AC compressor to a V twin motor sized for a typical 2500W to 5000W backup generator. Could be an interesting alternative but would require quite a bit of work to graft that into the trailer. I am not familiar with trailers and if you can retrofit them with a factory style AC unit that runs off 12v. Another thought would be a gas powered generator in the bed of the truck, maybe a quiet Honda inverter/generator, that could run several hours on its own fuel tank. Could end up using that on your house during a power failure to keep the refrigerators and some lights running during a blackout. Just bolt it down well as someone might want it more than you do.
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GoodiePop
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Re: 1976 F250 Single Wire Alternator Conversion
The A/C unit is behind my driver’s seat. I no longer have the travel trailer. I never removed all of the wiring and batteries after I sold the trailer.
I got the multi-meter connected appropriately. I’m not happy at all with the results. Toshiba states that this unit, draws 1380 watts, but the actual draw came up to 1555.
I have pictures on my phone, but I don’t know how to incorporate them here.
After about 12 minutes of run time, A/C on Cool, fan on High, the voltage dropped to 12.23. Amps at 127. The voltage continued to drop, so I shut it off. Voltage returned to 14.61 after 10 minutes of running at approximately 1600 RPM, and the amps went to 0.4, with the inverter switched off.
I did move the inverter positive cable to the battery farthest in the line.
I got under the hood and unwrapped all of the factory wiring so as to locate the 38A wire. Didn’t take but a minute. Storm clouds started gathering, so I covered everything up and put things away for the night.
I did notice on the wiring diagram from here, specific to the 73-79 truck, that the wire marked “I”, on the plug for the regulator, is the wire that leads to the ammeter in the dash. It first comes from the Blk/Red wire at the solenoid, then connects to the yellow “A+” wire in the regulator plug. I’m assuming that a direct-wire configuration from the A+ wire to the I wire isn’t intended nor suggested, but I’ve been able to locate these under the hood.
I got the multi-meter connected appropriately. I’m not happy at all with the results. Toshiba states that this unit, draws 1380 watts, but the actual draw came up to 1555.
I have pictures on my phone, but I don’t know how to incorporate them here.
After about 12 minutes of run time, A/C on Cool, fan on High, the voltage dropped to 12.23. Amps at 127. The voltage continued to drop, so I shut it off. Voltage returned to 14.61 after 10 minutes of running at approximately 1600 RPM, and the amps went to 0.4, with the inverter switched off.
I did move the inverter positive cable to the battery farthest in the line.
I got under the hood and unwrapped all of the factory wiring so as to locate the 38A wire. Didn’t take but a minute. Storm clouds started gathering, so I covered everything up and put things away for the night.
I did notice on the wiring diagram from here, specific to the 73-79 truck, that the wire marked “I”, on the plug for the regulator, is the wire that leads to the ammeter in the dash. It first comes from the Blk/Red wire at the solenoid, then connects to the yellow “A+” wire in the regulator plug. I’m assuming that a direct-wire configuration from the A+ wire to the I wire isn’t intended nor suggested, but I’ve been able to locate these under the hood.
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zgerbic
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Re: 1976 F250 Single Wire Alternator Conversion
Is the 1555W at the AC plug to the AC unit, or measured at the 12V input to the inverter? If before the inverter then you may be seeing the additional wattage draw from the inverter itself. Remember the inverter is not 100% efficent, more like 85% to 89%, depending on how much current is being lost in the 12V to 120V voltage conversion.
The voltage dropping while running is to be expected. Some drop will occur because the inverter and AC are running. The more current that is being drawn from the alternator as the batteries start to discharge is passing through the wiring from the front of the truck to the batteries at the rear. The more current, the higher voltage drop across the wiring. I suspect if you measure the dropped voltage at the batteries while running and immediately measure the voltage at the alternator output, you will see about 1 to 2.5V higher at the alternator. Remember the wiring has resistance and so will drop some voltage with these really high current levels passing through the wire. The further you move the inverter away from the alternator, the more wires and connections it probably has, each dropping a little voltage. This is one of the reasons I suggested you connect the inverter to the cable coming from the alternator and tie the batteries to the inverter/alternator connection. This will likely make a small difference in the voltage measured at the input to the inverter. This might seem like unnecessary changes as you normally could ignore voltage drops in wires and connections (except headlights and starter) in regular truck wiring. Since you are working with currents 10x to 30x of normal levels, wire resistance and connector connection resistance drops much larger voltage levels. A quarter volt here, a quarter volt there and maybe a half volt somewhere else starts adding up to a noticeable level. Another source of voltage drops you might be seeing is in the ground connections. If you are running a ground wire from the front of the truck to the 4 batteries and inverter, you will get the same voltage drops across this/these wires as you would for the positive wires. Remember it is carrying the same current in both the positive and negative wires. It would probably be better to ground the alternator/engine, the inverter and the batteries to the same metal structure. This will be either the cab body or the truck frame.
I looked at the 76 wiring diagram and instead of labeling the wire 38A, it is labeled 38 with shunt under it. On the 76 schematic the points are S-201 and S-202. Same wire, wired in the same place, side of starter relay (S-202) and the point where the truck power wire meets the alternator wire (S-201 vs. "the splice"), just like the older trucks. It may be easier to look at a schematic for an earlier truck 68 or 69 to see where the wires go as they are clearer to see.
Based on the 76 schematic wire 655 to ammeter effectively connects to the side of the starter relay and the regulator, just more segments of wire between the connections, and is connected to one side of the shunt. Wire 654 to ammeter connects to the junction of the other side of the shunt, the large wire that goes to the alternator and the truck under dash wiring. The large wire to the alternator from the junction is the piece of wire you need to make a large gauge. The large wire from the batteries at the back of the truck should either be connected to the junction point or to the connection on the back of the alternator. It should not be connected directly to the battery. If connected to the battery, too much current might pass through the shunt wire and overheat it or possibly burn it out due to the large current draw from the inverter batteries. The shunt should only be passing charging current to the starting battery and discharge current to the truck's normal wiring. This is what is being read by the trucks dash ammeter.
The shunt wire color coding has changed from the black/yellow of the older trucks to black/red. Problem with the 76 truck is that all the high current segments of wire from the alternator to the starter relay are black/red so it is not clear which is the shunt and which is something else.
If you move the 4G wires (alternator to battery and battery to back of truck) from the starting battery to the junction labeled S-201 (on 76 schematic) and make sure the regulator is removed, you should be done with the under hood changes. You will not need to touch the ammeter wiring or any other wiring to get the ammeter to work. The trick is to just make the ammeter to junction wire bigger and to connect the rear batteries to the junction or rear of alternator. This makes the wiring match the stock truck but thicker to carry more current.
The voltage dropping while running is to be expected. Some drop will occur because the inverter and AC are running. The more current that is being drawn from the alternator as the batteries start to discharge is passing through the wiring from the front of the truck to the batteries at the rear. The more current, the higher voltage drop across the wiring. I suspect if you measure the dropped voltage at the batteries while running and immediately measure the voltage at the alternator output, you will see about 1 to 2.5V higher at the alternator. Remember the wiring has resistance and so will drop some voltage with these really high current levels passing through the wire. The further you move the inverter away from the alternator, the more wires and connections it probably has, each dropping a little voltage. This is one of the reasons I suggested you connect the inverter to the cable coming from the alternator and tie the batteries to the inverter/alternator connection. This will likely make a small difference in the voltage measured at the input to the inverter. This might seem like unnecessary changes as you normally could ignore voltage drops in wires and connections (except headlights and starter) in regular truck wiring. Since you are working with currents 10x to 30x of normal levels, wire resistance and connector connection resistance drops much larger voltage levels. A quarter volt here, a quarter volt there and maybe a half volt somewhere else starts adding up to a noticeable level. Another source of voltage drops you might be seeing is in the ground connections. If you are running a ground wire from the front of the truck to the 4 batteries and inverter, you will get the same voltage drops across this/these wires as you would for the positive wires. Remember it is carrying the same current in both the positive and negative wires. It would probably be better to ground the alternator/engine, the inverter and the batteries to the same metal structure. This will be either the cab body or the truck frame.
I looked at the 76 wiring diagram and instead of labeling the wire 38A, it is labeled 38 with shunt under it. On the 76 schematic the points are S-201 and S-202. Same wire, wired in the same place, side of starter relay (S-202) and the point where the truck power wire meets the alternator wire (S-201 vs. "the splice"), just like the older trucks. It may be easier to look at a schematic for an earlier truck 68 or 69 to see where the wires go as they are clearer to see.
Based on the 76 schematic wire 655 to ammeter effectively connects to the side of the starter relay and the regulator, just more segments of wire between the connections, and is connected to one side of the shunt. Wire 654 to ammeter connects to the junction of the other side of the shunt, the large wire that goes to the alternator and the truck under dash wiring. The large wire to the alternator from the junction is the piece of wire you need to make a large gauge. The large wire from the batteries at the back of the truck should either be connected to the junction point or to the connection on the back of the alternator. It should not be connected directly to the battery. If connected to the battery, too much current might pass through the shunt wire and overheat it or possibly burn it out due to the large current draw from the inverter batteries. The shunt should only be passing charging current to the starting battery and discharge current to the truck's normal wiring. This is what is being read by the trucks dash ammeter.
The shunt wire color coding has changed from the black/yellow of the older trucks to black/red. Problem with the 76 truck is that all the high current segments of wire from the alternator to the starter relay are black/red so it is not clear which is the shunt and which is something else.
If you move the 4G wires (alternator to battery and battery to back of truck) from the starting battery to the junction labeled S-201 (on 76 schematic) and make sure the regulator is removed, you should be done with the under hood changes. You will not need to touch the ammeter wiring or any other wiring to get the ammeter to work. The trick is to just make the ammeter to junction wire bigger and to connect the rear batteries to the junction or rear of alternator. This makes the wiring match the stock truck but thicker to carry more current.