Autometer pyro

[Dodge man]

Been looking to put a pyro in my deuce. I saw this one on ebay AUTOMETER Z-SERIES ELECTRIC PYROMETER GAUGE KIT 2654 : eBay Motors (item 260327149788 end time Jan-28-10 14:29:04 PST) and it seemed like a good price so I bought it.

The problem is that I didn't pay good enough attention to the description. It requries 12v to the gauge for it to work. Is there a way to get this thing to work short of getting a 24/12v converter? I thought about wiring the light and the gauge in series but I'm concerned that it will either destroy the gauge or it won't work right. I know you can wire two 12v bulbs in series and make them work but I'm thinking this gauge is a little more sensitive to voltage than a bulb is. Another possible problem with a series connection is that the gauge may draw more or less current depending on the EGT which would cause a voltage change.

Any ideas other than getting another pyro?

How much power does it pull? If it's not too much you can use a 7812 regulator IC to drop 24V to 12V. Depending on the particular model they'll handle up to 1 1/2 amps but will probably need to be heatsinked to handle the total POWER dissipation ((~27v charging voltage -12V out ) X current draw). The Autometer manual will probably specify the peak current but you need to find out the average current and not the peak current. You can hook it to a single 12 volt battery and measure the current with a multimeter. The 7812 is a three lead device, the first (left) lead is power in, the middle lead should be connected to ground, and the third lead will be regulated 12V out. The tab is connected to the center lead (ground) and should be well fastened to a clean metal surface that can act as a heat sink. As long as the tab is well grounded then you don't need to connect a ground to the middle lead. If you're running very low power then the tab alone may be a sufficient heat sink. They generally recommend putting a small capacitor (.1 to 1 uF) on both the input and output to eliminate any AC ripple but you can probably get away without using them. I would recommend that you buy decent parts and not the trash that RS sells. The caps shouldn't be more than about 35 cents ea and the regulator a dollar or two. Let me know if you can't find them and I'll send you some.

 

[Dodge man]

why not a 24v to 12v transformer

can pick them up online for 10$

Transformers only work on AC power, not DC.

 

[Autocar]

Anytime you put electronics on a vehicle, you really need to add some protection circuits. First, you need reverse voltage protection in the form of a diode in the input wire(this could be a 1N4001 up to a 1N4007-the 1N4007 is best because it has the highest voltage rating). Second, you need a current limiting resistor(10 ohm 1 watt should do) in series with the input wire followed by a surge suppressor(either a 24 or 26 volt transorb or a 30 volt zener diode tied to ground). Then, on the input to the voltage regulator you need a 470 micro farad electolytic capacitor in parallel with a .1 microfarad ceramic capacitor. On the output of the voltage regulator, you need a .1 microfarad capacitor in parallel with at least a 270 microfarac electolytic capacitor. The above will make a bullet proof power supply that will never burn out. All this stuff is available thru the mail order electronic places and should cost less than $10 total. Could draw up diagram and parts list if you needed.

 

[m16ty]

How much power does it pull? If it's not too much you can use a 7812 regulator IC to drop 24V to 12V. Depending on the particular model they'll handle up to 1 1/2 amps but will probably need to be heatsinked to handle the total POWER dissipation ((~27v charging voltage -12V out ) X current draw). The Autometer manual will probably specify the peak current but you need to find out the average current and not the peak current. You can hook it to a single 12 volt battery and measure the current with a multimeter. The 7812 is a three lead device, the first (left) lead is power in, the middle lead should be connected to ground, and the third lead will be regulated 12V out. The tab is connected to the center lead (ground) and should be well fastened to a clean metal surface that can act as a heat sink. As long as the tab is well grounded then you don't need to connect a ground to the middle lead. If you're running very low power then the tab alone may be a sufficient heat sink. They generally recommend putting a small capacitor (.1 to 1 uF) on both the input and output to eliminate any AC ripple but you can probably get away without using them. I would recommend that you buy decent parts and not the trash that RS sells. The caps shouldn't be more than about 35 cents ea and the regulator a dollar or two. Let me know if you can't find them and I'll send you some.

I can tell you didn't read the whole thread.

Been there, done that. The gauge is powered through a 7812. Nothing else was added and it's working fine.