Lima Delta Posted February 2, 2021 Share Posted February 2, 2021 After spending some time recently troubleshooting a charging problem in the freezing cold, I've been thinking about a 3G swap... If I were to go ahead with this upgrade, I would like to have the ammeter function as a voltmeter. I've considered the RCCI voltmeter conversion but I can't help but wonder if it isn't something I can do myself, and whether or not anyone else has had success making a DIY conversion? I understand the general theory of converting an ammeter to a voltmeter, but I need to figure out the particulars. I have three spare ammeters to play with, but I don't want to waste any by making avoidable permanent mistakes. I also have a friend who works at an avionics shop that can test the ammeter with a variable power supply to determine it's specifics so that I can work out what kind of resistor to add. Can anyone tell me whether or not the RCCI converted units have any external modifications at the back of the gauge, or was it all done internally? Lucas Link to comment Share on other sites More sharing options...
Gary Lewis Posted February 2, 2021 Share Posted February 2, 2021 I saw no external mods on my ammeter converted to a voltmeter. As for what it would take, I think you could do it with a resistor in series - except that the ammeter's needle rests in the middle of the scale. But if there's an easy way to make it rest at that left edge then the resistor trick should work. I did some testing on four ammeters and recorded the results on the page at Documentation/Electrical/Ammeter. But here are the results. As you can see, it only takes about .25v to make it go full scale, assuming starting at the left edge. If you assume the meter is a .17 ohm resistor and put it in series with an 18 ohm resistor the combination will pull .79a at 14.4 volts. And the drop across the meter's .17 ohm will be .135v, which is about right to take the thing to half scale. Please let us know what you find! Link to comment Share on other sites More sharing options...
Lima Delta Posted February 2, 2021 Author Share Posted February 2, 2021 I saw no external mods on my ammeter converted to a voltmeter. As for what it would take, I think you could do it with a resistor in series - except that the ammeter's needle rests in the middle of the scale. But if there's an easy way to make it rest at that left edge then the resistor trick should work. I did some testing on four ammeters and recorded the results on the page at Documentation/Electrical/Ammeter. But here are the results. As you can see, it only takes about .25v to make it go full scale, assuming starting at the left edge. If you assume the meter is a .17 ohm resistor and put it in series with an 18 ohm resistor the combination will pull .79a at 14.4 volts. And the drop across the meter's .17 ohm will be .135v, which is about right to take the thing to half scale. Please let us know what you find! Thanks Gary, I did see your numbers earlier, and the variation was what got me thinking I should test my own to see how it compared. The photos I've seen of what I presumed to be unpowered converted gauges (like the one on the RCCI site) also had me wondering because they've all seemed to show the needle resting in the middle. Is this the case with your voltmeter, or does it in fact rest to the left? If do this myself, my plan will be to do like you've suggested: somehow modify the gauge so the needle rests to the left, then add the appropriate resistance. I'm curious to open the case and see how much space there is inside. Cheers, Lucas PS It's been said before I know, but you've done a real service by setting up all these resources. Thank you! Link to comment Share on other sites More sharing options...
Gary Lewis Posted February 2, 2021 Share Posted February 2, 2021 Thanks Gary, I did see your numbers earlier, and the variation was what got me thinking I should test my own to see how it compared. The photos I've seen of what I presumed to be unpowered converted gauges (like the one on the RCCI site) also had me wondering because they've all seemed to show the needle resting in the middle. Is this the case with your voltmeter, or does it in fact rest to the left? If do this myself, my plan will be to do like you've suggested: somehow modify the gauge so the needle rests to the left, then add the appropriate resistance. I'm curious to open the case and see how much space there is inside. Cheers, Lucas PS It's been said before I know, but you've done a real service by setting up all these resources. Thank you! Welcome! Glad it is helping. My voltmeter rests to the left just like the other gauges when off. So if you can get it to rest there then the resistor trick should work very well. There are plenty of 40 ohm potentiometers available, some that have 22 turns, which would you let you dial any ammeter in so the top reading would be what you want. Link to comment Share on other sites More sharing options...
JimsRebel Posted February 2, 2021 Share Posted February 2, 2021 I have three spare ammeters to play with, but I don't want to waste any by making avoidable permanent mistakes. Lucas He will buy your cores. So it's really a freebie for you. Just mail all 3 to Rocket Man, assuming all 3 are usable, let him keep 2 cores and convert one for you. When I did it I mailed in 2 cores, just in case 1 wasn't usable. He gave me credit for the other core, so for me it was almost free. I also bought the orange needle paint from him and paint all the needles to match. Jim Link to comment Share on other sites More sharing options...
JimsRebel Posted February 2, 2021 Share Posted February 2, 2021 I have three spare ammeters to play with, but I don't want to waste any by making avoidable permanent mistakes. Lucas He will buy your cores. So it's really a freebie for you. Just mail all 3 to Rocket Man, assuming all 3 are usable, let him keep 2 cores and convert one for you. When I did it I mailed in 2 cores, just in case 1 wasn't usable. He gave me credit for the other core, so for me it was almost free. I also bought the orange needle paint from him and paint all the needles to match. Jim Here is a link to some testing I did about 10 years ago on the amp meter. https://www.ford-trucks.com/forums/1122070-replace-amp-meter-with-dvm-update-with-photos-2.html#post11204855 This was before I knew about Rocket Man Voltmeter. He replaces the guts of the meter and does not reuse the stock meter movement. The nice part about his voltmeter is it only reads the voltage in the range you need, compared to a 0-20 volt scale. More info in the link below, encase you haven't read it yet. https://www.ford-trucks.com/forums/1339746-how-to-swap-amp-meter-to-volt-meter.html Jim Link to comment Share on other sites More sharing options...
Lima Delta Posted February 3, 2021 Author Share Posted February 3, 2021 Here is a link to some testing I did about 10 years ago on the amp meter. https://www.ford-trucks.com/forums/1122070-replace-amp-meter-with-dvm-update-with-photos-2.html#post11204855 This was before I knew about Rocket Man Voltmeter. He replaces the guts of the meter and does not reuse the stock meter movement. The nice part about his voltmeter is it only reads the voltage in the range you need, compared to a 0-20 volt scale. More info in the link below, encase you haven't read it yet. https://www.ford-trucks.com/forums/1339746-how-to-swap-amp-meter-to-volt-meter.html Jim Hi Jim, Thanks for the advice. I may end up going with a unit from RCCI in the end, in which case I'll send him two cores (pretty sure he won't buy the one I started playing with last night lol). I was able to modify the movement so that the needle wants to rest to the left now. I removed the "U" shaped magnet that keeps the needle centered and replaced it with small magnet on the left side. Getting the placement right was a bit tricky but I've got it all tacked back together with hot glue for now and it looks pretty good so far. I wish I had my own power supply. Lucas Link to comment Share on other sites More sharing options...
Gary Lewis Posted February 3, 2021 Share Posted February 3, 2021 Hi Jim, Thanks for the advice. I may end up going with a unit from RCCI in the end, in which case I'll send him two cores (pretty sure he won't buy the one I started playing with last night lol). I was able to modify the movement so that the needle wants to rest to the left now. I removed the "U" shaped magnet that keeps the needle centered and replaced it with small magnet on the left side. Getting the placement right was a bit tricky but I've got it all tacked back together with hot glue for now and it looks pretty good so far. I wish I had my own power supply. Lucas Changing out the magnet and getting it to rest on the left is a big step. Now if you can map out what voltage/current it takes to make it hit the various marks you can figure out what resistance to put in the circuit. But a variable power supply is ideal for that. I found mine on Craigslist years ago for $35 and have used it extensively. The ability to bring the voltage up slowly from 0 is a huge help. Link to comment Share on other sites More sharing options...
Lima Delta Posted February 3, 2021 Author Share Posted February 3, 2021 But a variable power supply is ideal for that. I found mine on Craigslist years ago for $35 and have used it extensively. The ability to bring the voltage up slowly from 0 is a huge help. Yes, now including a scan for a decent used power supply in my morning rounds through fb marketplace lol. L Link to comment Share on other sites More sharing options...
Gary Lewis Posted February 3, 2021 Share Posted February 3, 2021 But a variable power supply is ideal for that. I found mine on Craigslist years ago for $35 and have used it extensively. The ability to bring the voltage up slowly from 0 is a huge help. Yes, now including a scan for a decent used power supply in my morning rounds through fb marketplace lol. L In the interim you could put a pot from your battery to the voltmeter and slowly turn the pot up and record the voltage shown on your DVM at the voltmeter when it moves. Link to comment Share on other sites More sharing options...
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