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| Speco Gauges when they're NOT Speco gauges (update) https://www.ausmini.com/forums/viewtopic.php?f=2&t=33544 |
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| Author: | Wombat [ Wed Jul 04, 2007 11:43 am ] |
| Post subject: | Speco Gauges when they're NOT Speco gauges (update) |
Got some second hand Speco Gauges off an Ausmini member a while back and thought I'd check out the Voltmeter. It is reading high but can't find any 'adjustment' anywhere - anyone know if they can be adjusted? Also there is a terminal labeled 'S' along with '+' and ground and lights Anyone know what the S is? |
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| Author: | Marvin [ Wed Jul 04, 2007 12:42 pm ] |
| Post subject: | |
The 'S' is usually an input/connection for the Sender if it has one, which from memory the voltmeter doesn't use. I have a Speco voltmeter in mine, and can't remember using anything other than the + and - terminals. I may still have the instructions, I will look when I get home as I didn't drive my car to work today. What would you call 'reading high'? |
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| Author: | Mick [ Wed Jul 04, 2007 1:03 pm ] |
| Post subject: | |
Paerhaps inside there may be a adjustment pot to mechanically trim the needle, but generally if there is none, then no. |
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| Author: | Wombat [ Wed Jul 04, 2007 2:05 pm ] |
| Post subject: | |
Marvin wrote: What would you call 'reading high'?
About half a division across the scale |
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| Author: | Matt68 [ Wed Jul 04, 2007 2:06 pm ] |
| Post subject: | |
From memory, you can loosen the screws that hold the 'face' in place from the rear, and adjust it accordingly. But that is just a memory of what i did a few years ago. Might be wrong. |
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| Author: | Wombat [ Wed Jul 04, 2007 2:18 pm ] |
| Post subject: | |
Also does anyone have the wiring diagram for the 2" tacho? |
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| Author: | Marvin [ Wed Jul 04, 2007 4:24 pm ] |
| Post subject: | |
This is the speco voltmeter I have, it's a 2" one from the Auto & Marine range 
The instructions say that the + goes to the accessories and the - is earth. That's all you need to do. When I turn the ignition to ACC or start my car the gauge reads just under 12v mark then when the alternator kicks in at about 3800 rpm it jumps to around the 14v mark. |
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| Author: | Wombat [ Wed Jul 04, 2007 5:03 pm ] |
| Post subject: | |
Same dial but white - when I hook up my variable Lab power supply and crank the voltage through 10-15 volts it reads about 1 volt more than the Lab supply. |
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| Author: | Marvin [ Wed Jul 04, 2007 5:14 pm ] |
| Post subject: | |
AFAIK there is no adjustment. Contact [email protected] and ask them. They were pretty helpful with the questions I asked them a while ago. |
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| Author: | Mick [ Wed Jul 04, 2007 6:27 pm ] |
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You could try a variable resistor inline, but it would need to be a very high resistance to be comparable to the gauge's own resistance. Make it adjustable and you can trim it to the correct value. without any maths being done, my end, start with a variable resistor 1/13th the value of the guage's resistance (try and make this so that there is room to move above and below this value). But there are other things going on here with reactance and impedance so this is very rough. Another one would be to make a pair of resistors in series accross the voltage supply from pos to neg. One would need to be 1/13th the value of the other. Choose an arbitrary resistance, but make it in the hundreds of ohms to limit current draw. Make the other one variable and wire the voltmeter accross this one. This would be rather accurate once done accross the range. Other than that, learn to read the gauge for the 1 volt error or mechanically adjust the gauge inside the unit somehow (why not just bend the needle??). |
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| Author: | Wombat [ Wed Jul 04, 2007 8:36 pm ] |
| Post subject: | |
Had a real close look - they are not Speco - but Swoosh written in the style of speco and look very much like speco and I'd say come out of the same OEM manufacturer in Hong Kong - Not that happy Jane  Teach me to look at the product when I receive it. They were advertised on here as Speco so I didn't bother checking - Thanks guys for the input - i'll go and sit in the corner and sulk now 
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| Author: | slinkey inc [ Wed Jul 04, 2007 9:36 pm ] |
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The mechanical oil pressure in my dad's mini once went silly, it was reading 100psi at normal, decent rpm driving, and when switched off it went and sat at 20psi. It normally went from 0 to 80psi. Undoing the back and turning it fixed it appartly. I didn't fix it though, so I can't say how hard it was, but yes they are adjustable, kinda. |
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| Author: | Mick [ Thu Jul 05, 2007 8:10 am ] |
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The old smiths gauges are different, they are a bourdon tube arrangement where the oil pressure bends a semicircular hoolw tube by some known amount per PSI of oil pressure. The voltmeter uses electromagnetism to deflect a coil attached to a needle against a spring load. They're fairly different scenarios. But I still think you could bend the needle in the voltmeter to read closer to the correct voltage..... |
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| Author: | Traumatic Rover [ Thu Jul 05, 2007 7:54 pm ] |
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You could use a diode (avaliable for any electronic store) in line with the volt meter, each diode will give you a 0.6 voltage drop. ie 2 in line will drop your reading by 1.2 volts. typical diode part number 1N4004. Oh yeah make sure you get them the wright way around, other wise the meter won't work. |
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