Anyone ever made a voltage reducer before? I see them advertised in catalogs for a high $$$$ amount. A freind of mine told me to go to Radio Shack and buy the reducers. If anyone has done this before or is interested in the schematic he gave me, let me know. I will put it together this week and check it with a volt meter and then get back to you. Going from a 12 V into a 6V gauge.

 

Hi Doug,

Just to make sure I understand what you are doing, I need to ask a couple of questions.

1. Are the gages from a 6V positive ground application, like a 1948-1955 truck?
2. Are the senders attached to the gages from a 6V positive ground application?
3. Are you using a complete, 6V positive ground system including all 6V senders? (I've never heard of a system like that but then, there are a lot of things I've never heard of)

If the answer to #3 is yes, then a simple, fixed, three-wire voltage regulator like a 7806 will work fine.

If the answers to #1 and/or #2 are yes, you have to generate two voltage sources from your 12V system - 12V (easy - already there) and -6V. Since there is no way to produce voltages outside the 0-12V range from your current system using linear electronics, you will need something like an inverter. I did some research a while ago and found a unit that will probably work. it's a very simple module with no external circuitry. Should provide enough current for a standard set of gages with no problem. If you are interested I can dig out the part number and post it.

 

Excellent question. Let me tell you what I'm working with. I have a beutifull 1951 truck that has been converted to 12 V battery with alternator and all. The gauges have never been hooked up and the wires have all been cut. I'm guessing that I have a 6V positive ground application, like a 1948-1955 truck. Thanks to your reply It seems I need to to generate two voltage sources from your 12V system - 12V (easy - already there) and -6V.

I am interested in the part number, place you purchased and cost.

Thanks
Dlarson

"Since there is no way to produce voltages outside the 0-12V range from your current system using linear electronics, you will need something like an inverter. I did some research a while ago and found a unit that will probably work. it's a very simple module with no external circuitry. Should provide enough current for a standard set of gages with no problem. If you are interested I can dig out the part number and post it."


__________________

 

Finally found the chip, it's a Maxim unit but now that I look at my notes I specified it for generating 12V positive on a 6V negative ground system. Seems that's a more common request - using newer 12V sensors/gages on a 6V system.

I've looked to try to find a DC-DC converter that will work the other way 'round for you but couldn't find an inexpensive commercial IC. I think you are stuck with whatever you can get from the vendors. Sorry 'bout that.

 

I think you're making this all too complex. I assume you're using the original senders and gauges. I also assume your truck has been converted from 6V positive ground to 12V negative ground.

The gauges don't care about polarity, except the ammeter which doesn't have a sender anyway. The gauges are bi-metalic heater type, so the deflection is proportional to the current through them.

The original senders are bi-metalic switches with heater elements in them also. The current through them heats the bi-metalic which opens the switch. The sensed value (pressure, temperature or level) determine the duty cycle of the switch. Half full might be on/off equal amounts. 3/4 full would be on more and off less. The current passes from the battery, through the gauge through the sender to the chassis. This clever system is somewhat voltage insensitive. Think of your generator going from 6V to 8V and the gauges seeing a 33% voltage increase. Actually they would see a 33% current increase, but this would be compensated for by the switch in the sender heating faster and opening sooner.

To calibrate the gauges, connect them to a variable resistor where the sender would be. Measure voltage across the gauge and adjust the resistor for 1.5 volts across the gauge. The gauge has an adjustment with a small screw driver and should be set at 50%.

To cut the current produced by connecting your gauges to 12V, go to radio shack and get something close to 30 ohm resistors. I connected two 15's in series. Should be about 5 watt size. You'll need one for each of the gauges. Connect them in series between the gauge and the sender. I put mine on the back of the instrument cluster between the gauge terminal and the wire that goes out to the sender.

Works great for my '49 F1 and I think your original gauge setup is identical.

Good luck,
Johann