Waldi Posted December 13, 2018 Report Share Posted December 13, 2018 I have bought an original 12V Smiths voltage gauge, type ACV 2201/00, it is the same design as my other CP instruments, black rim with hanging needle. I cannot get it to work however. It has two connections, numbered "1"and "2" (and a light bulb holder, which works ok, by the way). Cearbond shows a wiring diagram, indicating connection "1"is for earth and "2"is for positive ("connect to fused side of ignition"). I have connected the gauge like that but then the needle shoots to "full scale" immediately, as if it is shorted. Battery voltage is 12,6V, the needle should be in the middle of the scale, where it is indicated as "normal" Any ideas what might be the cause of this? Thanks, Waldi Quote Link to post Share on other sites
ed_h Posted December 13, 2018 Report Share Posted December 13, 2018 Hi, Waldi. Just a shot in the dark here, but if someone had swapped the guts with a fuel gauge, which I believe looks identical, it would read close to full scale when connected to 12.6 volts. When you say it "shoots to full scale immediately", do you mean a lot faster than, say, the fuel gauge when the tank is full? Due to the way the gauges work, they don't normally move very quickly. A peek inside might give a clue, too. Ed Quote Link to post Share on other sites
astontr6 Posted December 13, 2018 Report Share Posted December 13, 2018 2 hours ago, Waldi said: I have bought an original 12V Smiths voltage gauge, type ACV 2201/00, it is the same design as my other CP instruments, black rim with hanging needle. I cannot get it to work however. It has two connections, numbered "1"and "2" (and a light bulb holder, which works ok, by the way). Cearbond shows a wiring diagram, indicating connection "1"is for earth and "2"is for positive ("connect to fused side of ignition"). I have connected the gauge like that but then the needle shoots to "full scale" immediately, as if it is shorted. Battery voltage is 12,6V, the needle should be in the middle of the scale, where it is indicated as "normal" Any ideas what might be the cause of this? Thanks, Waldi Hi Waldi, When you measured the battery voltage was the engine running as I would expect the charging voltage to be a minimum of 13.5 volts with engine running and only go to 15 volts on a very low state of charge battery. where the needle points is purely controlled by the battery state of charge Bruce. Quote Link to post Share on other sites
Waldi Posted December 13, 2018 Author Report Share Posted December 13, 2018 Hi Ed and Bruce, thanks for helping problemsolving. Ed, the needle moved very quick, as if wrongly connected, not like a fuel gauge would do with full tank. Bruce, the battery was on my desk, not charged at that time, so 12.6 V was what I measured with my multi meter. Regards, Waldi Quote Link to post Share on other sites
ed_h Posted December 13, 2018 Report Share Posted December 13, 2018 Moving that quickly is not normal. I think I'd break into it to see if there is anything obvious. Since the gauge works by heating a coil of wire, it shouldn't be polarity sensitive, so I'm not sure there is a way to wrongly connect it. Ed Quote Link to post Share on other sites
Phil M Posted December 13, 2018 Report Share Posted December 13, 2018 Hi Waldi I believe Ed is right, your gauge is either faulty or probably not a volt meter, I have recently refurbished an old classic Smiths Volt gauge and tested it with a volt/current generator. The classic Smiths Volt meter (and probably the new ones) use a winding round a bimetallic strip as the volts increase he coil generates more heat and the needle moves slowly. I’ve taken a couple of photos to help Regard Phil Quote Link to post Share on other sites
Waldi Posted December 13, 2018 Author Report Share Posted December 13, 2018 Thanks Phil, I will contact the seller first before I dismantle, I prefer to send it back to him and look for a correct volt gauge. although dismantling it is tempting:) Regards, Waldi Quote Link to post Share on other sites
SteveB21 Posted December 14, 2018 Report Share Posted December 14, 2018 Hi Phil i just saw your post and wondered if you could provide any guidance on calibration of a smiths voltmeter as mine is reading low (confirmed with 2 different multimeters). Many Thanks Steve Quote Link to post Share on other sites
peejay4A Posted December 14, 2018 Report Share Posted December 14, 2018 I calibrated mine to 12v by judiciously bending part of the mechanism inside. I can’t recall which bit though, sorry. Quote Link to post Share on other sites
ed_h Posted December 14, 2018 Report Share Posted December 14, 2018 (edited) In Phil's picture, you can see two oval slots. These are accessible from the back of the instrument by removing little cork plugs. These are undoubtedly for calibration. A small straight blade screw driver can be used to move the respective brackets a little. One of the adjustments seems to shift the range of readings up or down, while the other would expand or contract the range. I've never seen any instructions on how to do the adjustments, but a little trial and error seems to work fine. Ed Edited December 14, 2018 by ed_h Quote Link to post Share on other sites
Phil M Posted December 14, 2018 Report Share Posted December 14, 2018 Hi Steve I calibrated mine using a simple Volt/Current generator so I can accurate set the required voltage, (now days they are relatively cheap I think mine was about £40),if the connections are clean and the winding ok and the correct resistance its just a case of a finite adjustment of the needle or if that does not work, as Ed mentions you can tweak the bi strip from the back. But I don't think thats not going to help you if your gauge is permanently low. Visual inspection may show the problem, for a start the winding heating the bimetallic strip should be 120ohms( nor sure how this differs from gauge to gauge) , as the gauges get old the winding can separate from the strip (but rare), more likely there is a bad connection on the winding to the terminals or the needle is bent or come loose from the bi strip. Best Regards Phil Quote Link to post Share on other sites
Peter S Posted December 15, 2018 Report Share Posted December 15, 2018 Morning Ed et al, Do these help? Smiths small gauges - last 3 paragraphs and Calibration instructions Pete Quote Link to post Share on other sites
ed_h Posted December 15, 2018 Report Share Posted December 15, 2018 What great links, Pete! I hadn't seen either of those. In the Jensen-Healy link, the last paragraph applies to temp and fuel gauges, but probably not to voltmeters. Also, on interchangeability, I think the voltmeter may have a different coil, since it has a 15 volt full scale, while the fuel and temp gauges would be less than 10 volts full scale. The other link from Randall pretty much describes how I calibrated my voltmeter. Ed Quote Link to post Share on other sites
Waldi Posted December 15, 2018 Author Report Share Posted December 15, 2018 Thanks Pete, I will test mine and let you all knw tge outcome. Waldi Quote Link to post Share on other sites
SteveB21 Posted December 15, 2018 Report Share Posted December 15, 2018 Thanks All I had found one of those links, but not the other. I will be interested to hear how you get on Waldi as my voltmeter is not yet at the top of my "to-do" list! Gives my time to butcher an old screwdriver in preparation. Cheers Steve Quote Link to post Share on other sites
Peter S Posted December 15, 2018 Report Share Posted December 15, 2018 Glad to be able to help. Pete Quote Link to post Share on other sites
Waldi Posted December 15, 2018 Author Report Share Posted December 15, 2018 Just measured the resistance across the 2 terminals: 138 Ohm, so “close” to the 160 mentioned in the JH forum. when I connect the battery across the terminals (12.6 V) it shoots straight to the other corner. It is a 12V gauge, it says 12V on the front. to check internals and hopefully adjust, I will need to open it, so that’s next. thanks, Waldi Quote Link to post Share on other sites
Waldi Posted December 16, 2018 Author Report Share Posted December 16, 2018 Today I opened the gauge. I did not see a bi-metallic strip or so, see below picture. The spool is not dark and looks ok. Any idea’s? All connections look ok. Thanks, Waldi Quote Link to post Share on other sites
Phil M Posted December 16, 2018 Report Share Posted December 16, 2018 Hi Waldi I believe you have the workings of a electric oil pressure gauge, and it makes sense if you connect a Batt and Eth to the terminals it will shoot to full, personally I have not taken one apart so I could be wrong. Quote Link to post Share on other sites
ed_h Posted December 16, 2018 Report Share Posted December 16, 2018 (edited) Well, that certainly isn't a bi-metal based gauge. It looks like a wound-field galvanometer. There is probably a small permanent magnet attached to the pointer. The small cylindrical component to the right is likely a diode for reverse polarity protection. The resistors set the range of the instrument. I'll bet you could just change the resistance and get to work OK. The top resistor looks like 51 ohms, but I can't really resolve the colors on the other one. Since the gauge is reading too high, you need more resistance. Try disconnecting one of the resistors or adding another 50 ohms in series with the others and see how it works. Some trial and error should get you pretty close. Ed Edited December 16, 2018 by ed_h Quote Link to post Share on other sites
Waldi Posted December 16, 2018 Author Report Share Posted December 16, 2018 Hi Phil and Ed, Actually I was just looking at Ed's site, and note your instrument internals look different. I will ask an electrical better educated friend here to help me with the resistors, I know about color codes (that they exist), but that's about it for me. He will know how to test this for sure. Best regards, Waldi Quote Link to post Share on other sites
Peter S Posted December 16, 2018 Report Share Posted December 16, 2018 Hi all, it looks like Phil is correct re it being an oil pressure gauge... How an oil pressure gauge works Pete Quote Link to post Share on other sites
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.