viven44 Posted March 4 Author Share Posted March 4 I had 4 different ammeters on the bench to test. I hooked my lab power supply up with a DVM measuring voltage and another measuring current. On gauge #1 when the voltage got to .125v in the positive direction the gauge was at full scale and pulling .75 amps. And when I reversed the voltage the gauge was at full scale at .147v and was pulling .88A. As for the shunt, the largest alternator the Bullnose trucks came with could put out 70A from what I read, although Jim and I've debated this and he's pointed out that there were 100A 1G alternators available. But most of the documentation I have suggests 70A was the max used in the pickups & Broncos and, if so, the shunt was probably sized for that. I probably have an intact shunt around here some place and ought to run a test some day to see how hot it gets at various amounts of current and we'd know - for that one shunt. But my here's some math: P = I * V so let's assume the shunt is sized such that it'll drop .132v (the average of my 8 full-scale readings) @ 70A and you have 9.27 watts. So if you put in a 130A 3G alternator you'll see 18 watts in a piece of wire maybe a foot long? Just to confirm, the voltages you were were voltages at the power supply correct .. assuming the ammeter is the only element in the circuit, all the voltage drop happened through it... right ? There should be a minor drop on the other multimeter you had in series to measure current, but maybe that be ignored. Also, if I understand correctly, only a fraction of the voltage drop that happens at the ammeter would occur through the shunt itself. Since you have a shunt wire itself, could you measure its resistance, should be 1/100th of the ammeter itself. Since you measured ~170mOhm resistance on the ammeter itself, the wire should measure 1.7mOhm. Link below says 1 meter of 14 gauge Cu wire should measure 8mOhm https://learnemc.com/EXT/calculators/Resistance_Calculator/wire.html For determining if something is too hot, a better calculator would be a "fusing current" estimate of different AWGs, lengths. I do agree that changing the shunt wire may be necessary, but that would affect the ratio of resistance between the shunt and ammeter, and hence the reading, right ? Link to comment Share on other sites More sharing options...
Gary Lewis Posted March 4 Share Posted March 4 Just to confirm, the voltages you were were voltages at the power supply correct .. assuming the ammeter is the only element in the circuit, all the voltage drop happened through it... right ? There should be a minor drop on the other multimeter you had in series to measure current, but maybe that be ignored. Also, if I understand correctly, only a fraction of the voltage drop that happens at the ammeter would occur through the shunt itself. Since you have a shunt wire itself, could you measure its resistance, should be 1/100th of the ammeter itself. Since you measured ~170mOhm resistance on the ammeter itself, the wire should measure 1.7mOhm. Link below says 1 meter of 14 gauge Cu wire should measure 8mOhm https://learnemc.com/EXT/calculators/Resistance_Calculator/wire.html For determining if something is too hot, a better calculator would be a "fusing current" estimate of different AWGs, lengths. I do agree that changing the shunt wire may be necessary, but that would affect the ratio of resistance between the shunt and ammeter, and hence the reading, right ? The voltage drop is across the ammeter. Said another way, the voltage at the ammeter is the same as at the power supply. But the voltage across the shunt is exactly that across the ammeter. The wire size used to connect the ammeter to the shunt is plenty large enough to handle the ~1A of current w/o appreciable drop. As for measuring resistance, I don't own any tools that would allow measuring of that small of a resistance. Very few people do. My earlier post said the .167 ohm was 'calculated resistance". Said another way, I = E/R = .147/.88 = .167. I can't measure a shunt's resistance directly, but I can measure the current through it and the voltage drop across it and, therefore, calculate the resistance. As for the heat, fusing current determines when the conductor fails. But it doesn't determine when the insulation fails. I know that the fuse links have high-temp insulation but don't know about the shunt. But you could replace the shunt, which is exactly why I included that table on our page at Documentation/Electrical/Ammeter. All you have to do is to have a wire that drops whatever voltage your ammeter requires to take it to full scale. Ammeter #1 just needs a .167v drop, and it doesn't care if the current through the shunt is 70A or 700A. As long as it sees .167V it'll go to full scale. Link to comment Share on other sites More sharing options...
viven44 Posted March 4 Author Share Posted March 4 The voltage drop is across the ammeter. Said another way, the voltage at the ammeter is the same as at the power supply. But the voltage across the shunt is exactly that across the ammeter. The wire size used to connect the ammeter to the shunt is plenty large enough to handle the ~1A of current w/o appreciable drop. As for measuring resistance, I don't own any tools that would allow measuring of that small of a resistance. Very few people do. My earlier post said the .167 ohm was 'calculated resistance". Said another way, I = E/R = .147/.88 = .167. I can't measure a shunt's resistance directly, but I can measure the current through it and the voltage drop across it and, therefore, calculate the resistance. As for the heat, fusing current determines when the conductor fails. But it doesn't determine when the insulation fails. I know that the fuse links have high-temp insulation but don't know about the shunt. But you could replace the shunt, which is exactly why I included that table on our page at Documentation/Electrical/Ammeter. All you have to do is to have a wire that drops whatever voltage your ammeter requires to take it to full scale. Ammeter #1 just needs a .167v drop, and it doesn't care if the current through the shunt is 70A or 700A. As long as it sees .167V it'll go to full scale. OK thanks for the explanation! I agree fusing current is over-aggressive in automotive space. I'm intrigued though. If the stock shunt wire isn't making the ammeter go full scale, would that mean not much voltage drop is occurring through that shunt wire i.e. is the stock shunt wire oversized ? I think I'm missing something... Edit below: If shunt wire resistance is directly proportional to how much the ammeter can swing, then the stock shunt wire is plenty big because the gauge doesn't swing much.. if picking another shunt wire makes the gauge swing more, then i've reduced the amount of current the shunt can handle. I am going to need a lab power supply Link to comment Share on other sites More sharing options...
Gary Lewis Posted March 4 Share Posted March 4 OK thanks for the explanation! I agree fusing current is over-aggressive in automotive space. I'm intrigued though. If the stock shunt wire isn't making the ammeter go full scale, would that mean not much voltage drop is occurring through that shunt wire i.e. is the stock shunt wire oversized ? I think I'm missing something... Edit below: If shunt wire resistance is directly proportional to how much the ammeter can swing, then the stock shunt wire is plenty big because the gauge doesn't swing much.. if picking another shunt wire makes the gauge swing more, then i've reduced the amount of current the shunt can handle. I am going to need a lab power supply If my understanding is correct the stock Bullnose gauge will go full scale when 70A is conducted through the shunt, it either direction. I don't have an easy way to create that amount of current as most of my loads would be way under that, and my winch and inverter would be way over it. But if you want to run a test then figure out how to put a load like that on the system and you should see the ammeter swing. Link to comment Share on other sites More sharing options...
viven44 Posted March 4 Author Share Posted March 4 If my understanding is correct the stock Bullnose gauge will go full scale when 70A is conducted through the shunt, it either direction. I don't have an easy way to create that amount of current as most of my loads would be way under that, and my winch and inverter would be way over it. But if you want to run a test then figure out how to put a load like that on the system and you should see the ammeter swing. Okay, that makes sense. No safe, easy and cheap way to test that. The test you did makes the most sense. Link to comment Share on other sites More sharing options...
viven44 Posted March 4 Author Share Posted March 4 Jim and I've debated this and he's pointed out that there were 100A 1G alternators available. I have for a long time seen 90A alternators available for my 460 pickup on Rockauto. I always wondered if these worked fine and if they did then why 3G (shunt needs to be oversized, but any other reason why this wont work) ? https://www.rockauto.com/en/catalog/ford,1984,f-350,7.5l+460cid+v8,1126257,electrical,alternator+/+generator,2412 Would something like this work fine ? https://www.rockauto.com/en/moreinfo.php?pk=1000263&cc=1126257&pt=2412&jsn=1237 https://www.rockauto.com/en/moreinfo.php?pk=12526901&cc=1126257&pt=2412&jsn=1242 Link to comment Share on other sites More sharing options...
Gary Lewis Posted March 4 Share Posted March 4 Jim and I've debated this and he's pointed out that there were 100A 1G alternators available. I have for a long time seen 90A alternators available for my 460 pickup on Rockauto. I always wondered if these worked fine and if they did then why 3G (shunt needs to be oversized, but any other reason why this wont work) ? https://www.rockauto.com/en/catalog/ford,1984,f-350,7.5l+460cid+v8,1126257,electrical,alternator+/+generator,2412 Would something like this work fine ? https://www.rockauto.com/en/moreinfo.php?pk=1000263&cc=1126257&pt=2412&jsn=1237 https://www.rockauto.com/en/moreinfo.php?pk=12526901&cc=1126257&pt=2412&jsn=1242 It isn't that it won't work, but that a 3G puts out 105 amps at idle. The others don't give much until 1500 engine RPM. Link to comment Share on other sites More sharing options...
viven44 Posted March 4 Author Share Posted March 4 It isn't that it won't work, but that a 3G puts out 105 amps at idle. The others don't give much until 1500 engine RPM. If that would be sufficient to run an electric fan that would be sufficient for me. No plans to run fancy sound or anything else of that kind Link to comment Share on other sites More sharing options...
Gary Lewis Posted March 4 Share Posted March 4 If that would be sufficient to run an electric fan that would be sufficient for me. No plans to run fancy sound or anything else of that kind Check out Scott/kramtocs thread where he tested electric fans. Some draw more than others and some pull far more than others. Me, I'll stick with an engine-driven fan. Jim will probably be along to tell you why it is a bad deal to turn mechanical energy into electrical and then turn it back into mechanical, thereby having 2X the efficiency loss. Link to comment Share on other sites More sharing options...
viven44 Posted March 5 Author Share Posted March 5 Check out Scott/kramtocs thread where he tested electric fans. Some draw more than others and some pull far more than others. Me, I'll stick with an engine-driven fan. Jim will probably be along to tell you why it is a bad deal to turn mechanical energy into electrical and then turn it back into mechanical, thereby having 2X the efficiency loss. I have never used an electric fan before but that seems to be the hip thing to do so I wanted to see a path to potentially doing it. This Bronco is new to me overall, I don't know the condition of the transmission but I know it was running and used by a 'kid' for mudding a couple of times. It is in too nice a shape to be used for mudding, but hey I'm glad he did otherwise I wouldn't have acquired it as a 'project'. Last time it ran was when he went mudding deep at "rednecks with paychecks" and I think the engine (400) had got a big hot potentially and it was in the process of being rebuilt but the rebuild stopped due to his personal circumstances. It was parked for about 3 years and then I acquired it. I sold the never-started/non-running long block for a good chunk with all the fancy heads since my plan was to do a 460 swap anyway. Also when I had acquired it the Bronco had sat for approx 3 years and when I got it, the transmission dipstick wasn't in all the way and it wouldn't even go in all the way even with force so I have always been concerned about rain water and debris from being parked out for 3 years. Long story short, transmission is my biggest worry, not to mention the additional stress that the 460 will be placing on it. I would assume it was good before the engine work had commenced. I went ahead and decided to do a pan / filter change today. Had no idea that I would be getting out ~7 quarts from the pan only. The 4WDs use a deep pan I guess. Found a lot of black sediment at the bottom but fluid was clean and red. Link to comment Share on other sites More sharing options...
Recommended Posts