Any suggestions as to wiring a one wire(single load wire, self fielding internal regulating) alternator to a dash voltage light? There is no threaded post to draw off the field windings on the case.
Wiring a one wire alt. with a low volts dash light
- Thread starter rohach
- Start date
Seymour Snerd
Lifetime Supporter
A bit pricey but it does what you want: http://www.periheliondesign.com/moreproductsfiles/LV_Annunciator Manual.pdf
The only other simple way to detect a voltage threshold that I can think of would be a relay with a low-voltage coil (they can be found as low as 1.5 v) with the coil in series with a zener diode with a value of around 11 volts. Thus the relay would operate somewhere between 11 and 12.5 volts. With a double throw relay, connecting the lamp through the normally closed contact pair would turn the lamp on when the voltage drops through ~ 11V and go out when it rises to about 12.5V. And it you want the threshold somewhere else you just choos a zener with a different voltage. They tend to come in one volt increments.
Example parts:
Relay: Digi-Key - 255-1356-5-ND (Manufacturer - AGQ2001H)
Zener Diode: Digi-Key - 1N5348BGOS-ND (Manufacturer - 1N5348BG)
Total: $5!
Let me know if you want a drawing of how to wire that up.
The only other simple way to detect a voltage threshold that I can think of would be a relay with a low-voltage coil (they can be found as low as 1.5 v) with the coil in series with a zener diode with a value of around 11 volts. Thus the relay would operate somewhere between 11 and 12.5 volts. With a double throw relay, connecting the lamp through the normally closed contact pair would turn the lamp on when the voltage drops through ~ 11V and go out when it rises to about 12.5V. And it you want the threshold somewhere else you just choos a zener with a different voltage. They tend to come in one volt increments.
Example parts:
Relay: Digi-Key - 255-1356-5-ND (Manufacturer - AGQ2001H)
Zener Diode: Digi-Key - 1N5348BGOS-ND (Manufacturer - 1N5348BG)
Total: $5!
Let me know if you want a drawing of how to wire that up.
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Thanks for the input, a diagram would be essential for me to wire it up. Will it work with a light that is designed to light off of alt. field, or do I have to rewire at the dash also?
Seymour Snerd
Lifetime Supporter
Here's a diagram of the relay with zener diode idea. The way I've laid it out it assumes that grounding the lead to the dash ALT light turns it on (which is how my SPF is wired for a 3-wire alternator), so it should work in your case. If that's not how your car is wired let me know.
In terms of physical construction you could solder the zener diode between pins 8 and 3. Then all you need to do is connect switched 12V to pin 1 (switched because this thing draws about 100 mA all the time so it would eventually drain your battery). Connect pin 3 to ground and pin 2 to the wire to your ALT light. You could foam tape the relay upside wherever is convenient, presumably in back of the dash near the ALT light, or you could put it back near the alternator where the ALT light wire presumably shows up; then you just need a switched 12V wire back there.
Having said all that, I ordered the parts for this and will test it when they arrive in a few days. I hope you can wait that long so I don't end up sending you on a wild goose chase, in case there's something wrong with the idea.
In terms of physical construction you could solder the zener diode between pins 8 and 3. Then all you need to do is connect switched 12V to pin 1 (switched because this thing draws about 100 mA all the time so it would eventually drain your battery). Connect pin 3 to ground and pin 2 to the wire to your ALT light. You could foam tape the relay upside wherever is convenient, presumably in back of the dash near the ALT light, or you could put it back near the alternator where the ALT light wire presumably shows up; then you just need a switched 12V wire back there.
Having said all that, I ordered the parts for this and will test it when they arrive in a few days. I hope you can wait that long so I don't end up sending you on a wild goose chase, in case there's something wrong with the idea.
Thanks again Alan, I can put it on the back burner for now. My biggest concern was if it was possible to accomplish in the first place. I'll keep my eye on this thread to see what outcome is.
Terry Oxandale
Skinny Man
Just a rambling comment;
I ran a one-wire off the driveshaft in my 240Z years ago. The alternator sat behind the passenger seat. Whenever the alternator was not outputing (low speed below about 20 mph), it would whine almost like a siren, pitch was proportional to the rational speed. Once the output threshhold was reached, it went silent, and the dash LED went out. The reverse would happen when I slowed to a stop...silent until the threshold, at which the LED would come on, and the alternator whine started abruptly at a high pitch and would "whine" down in pitch until a dead stop. Even with the loud track exhaust, one could hear this whine. It would always tell me if it was charging or not, simply by sound.
Just a little tid-bit of central Arkansas experience.
I ran a one-wire off the driveshaft in my 240Z years ago. The alternator sat behind the passenger seat. Whenever the alternator was not outputing (low speed below about 20 mph), it would whine almost like a siren, pitch was proportional to the rational speed. Once the output threshhold was reached, it went silent, and the dash LED went out. The reverse would happen when I slowed to a stop...silent until the threshold, at which the LED would come on, and the alternator whine started abruptly at a high pitch and would "whine" down in pitch until a dead stop. Even with the loud track exhaust, one could hear this whine. It would always tell me if it was charging or not, simply by sound.
Just a little tid-bit of central Arkansas experience.
Seymour Snerd
Lifetime Supporter
Mike --
While waiting for the parts it occured to me that the addition of a variable resistor would allow you to fine tune the thresholds. Furthermore I think I can add a second one so you can fine tune the turn on threshold independent of the turn off threshold. This is getting interesting....
BTW I agree that three wire alternators are superior from an engineering perspective, mostly because they allow remote sensing and thus do a better job of keeping the battery charged without relying on heavy cabling between it and the alternator.
But, like you, a one wire is what I have so, thanks to your question I'm going to go ahead and make myself a battery voltage idiot light. Will probably steal the fan override light since I already stole the Alt light to serve as an oil pressure light.
I'll let you know when it's all working (should be by early next week).
Alan,
Have you made any headway on your Voltage light creation? The anticipation is killing me!
Have you made any headway on your Voltage light creation? The anticipation is killing me!
Seymour Snerd
Lifetime Supporter
Yes I have, just this morning. The relay triggers at a far lower voltage than I expected (and the spec sheet describes), so with the 11V zener it basically tells you when the voltage has dropped below 11. Too low; that just means the battery's dead.
So I ordered some higher value zeners. My thought is that you want it to trigger somehwere between 12.5 (which is what the battery will rest at with the engine off) and 13.5 or so (which is abouit the lowest you should have with the alternator running). So I suspect the 13V zener will get us what we want. Also with the zeners I'll have some variable resistors of the right size to make it adjustable within about a 1V range. Unfortunately the parts take a few days to get here.
Very cool, keep me posted!
Seymour Snerd
Lifetime Supporter
Mike --
Now it works much better...
Here is the updated circuit diagram and top and bottom views of "the prototype" built on a Radio Shack (Tandy) 276-159 prototype board. I changed the zener to 12V, and added a variable resistor ("trim pot") so the threshold can be adjusted from about 12.3 to 15V. I think 13V should work pretty well for telling whether your alternator is working or not.
PM me your postal address and I'll send this thing to you.
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Seymour Snerd
Lifetime Supporter
There's an error in the drawing: the circuit grounds the indicator lamp when the voltage is too low, so the indicator lamp should have been shown with it's filament tied to +12 on the other side, not ground.
Allen, I have finally gotten around to soldering this rig together. I am planning to use the alt+ as my 12 volt switched source. It is a convenient location(near the dash light wire and source+). Can these componants handle direct 100 amp alternator output or will it cook them? I am planning to silicone the board into a plastic box and mount it away from any heat source. I will keep you posted on its performance. Thanks
Seymour Snerd
Lifetime Supporter
It should be fine up to about 16V, and normally you would never see that. So you can connect it to anything that is "12V".
Seymour Snerd
Lifetime Supporter
I built this first version and tested; the zener needs to be 12v, not 11V, and with that the light comes on at around 12.2V, which I think is a little low. (So then I built the one further down with the variable resistor and it worked great, but USPS threw it away rather than delivering to Mike). The new one is on its way to the beta tester.
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