LocostUSA.com

I want a clock for my car. Plumb out of room for a conventional clock, but I have a Timex Indiglo alarm clock that I can find room for. The thing has been running about 15 years on a AAA battery (expired in 2005), so I figured it would be a good application for a voltage splitter. Long story short, I can get the clock to run, but when the Indiglo is turned on, the screen goes black. If I install the out of date AAA battery, it operates just fine!

Any ideas what I'm missing?

Bill

So let me be the first to ask, If the light ran for 15 years on one aaa battery, why not just put in a new battery and be done??

Obviously, the resistor values you are using are not right, When you turn on the light, the voltage drops which is normal for resistor vased voltage divider. Do you know the current draw for the clock with the indiglo light on?

Also, what resistor values are you using? I can run some numbers.

_________________
Chuck.

“Any suspension will work if you don’t let it.” - Colin Chapman

Visit my ongoing MGB Rustoration log: over HERE

Or my Wankel powered Locost log : over HERE

And don't forget my Cushman Truckster resto Locostusa.com/forums/viewtopic.php?f=36&t=17766

First up, the clock does not really fit the space, dropping the battery would make a nice installation. Also, the Indiglo was on for maybe a minute during that 15 year time. I want to run the Indiglo whenever the lights are on. So two 1.5v power feeds seemed logical.

Current draw. Now your getting into the vast world of stuff that puts my inadequacies on full display. I don't know what I'm doing and I get lost in all the zeros. The best I can tell you is that with the VOM set on 2000k, the clock resistance is 155 with the light "On". Xero with th elight off.

Battery voltage is currently 1.4. I have tried several tries at voltages. The clock will run as low as .9v. I've tried voltages all the way up to 1.8. Initially I was using a small battery charger and decided that maybe there was some AC leakage screwing things up, so went to car battery as power source. Thinking perhaps the voltage was correct but the amperage was too low, I've varied V1 resistance from 1,000 to 15,000.

Thanks for the interest in my problem. While it may seem I have avoided some questions, I've done the best I can to describe the situation. Your educated guess as to proper resistance values would be very much appreciated.

Bill

Wear a watch...

_________________
JD, father of Quinn, Son of a... Build Log
Quinn the Slotus:Ford 302 Powered, Mallock-Inspired, Tube Frame, Hillclimb Special
"Gonzo and friends: Last night must have been quite a night. Camelot moments, mechanical marvels, Rustoleum launches, flying squirrels, fru-fru tea cuppers, V8 envy, Ensure catch cans -- and it wasn't even a full moon." -- SeattleTom

you trying to run the clock off the car battery? IF so I would use a LM317 to drop the voltage, or a 20ohm resistor.The LM317 would be a better solution IMO. A couple solder joints and a few components would work.

Bill, Measuring the resistance of the clock is not the proper way to determine the load of the clock. Since you can't measure current draw, I'll try a different approach:

What values of R1 and R2 are you using when the clock works but you don't try to light the display?

Measure the voltage across R2 when the clock is working and the light is off.

Measure it again when you try to light it up?

A crude voltage regulator can be made by replacing the R2 with a pair of diodes and choosing R1's values appropriately. Maybe adding a cap across R2. I'll make my recommendations after seeing your voltage readings.

_________________
Chuck.

“Any suspension will work if you don’t let it.” - Colin Chapman

Visit my ongoing MGB Rustoration log: over HERE

Or my Wankel powered Locost log : over HERE

And don't forget my Cushman Truckster resto Locostusa.com/forums/viewtopic.php?f=36&t=17766

Sorry. I have changed my recommendation to buying a DC-DC converter on eBay rather than building a voltage divider circuit. Not that what I had in mind won't work, but this will be much easier to implement and has no real downside.

In my circuit, the resistors may get hot, essentially being a linear regulator and selecting the optimum dropping resistor (R1) might take some trial and error. The LM317 would also work but could get just as hot. The biggest unknown is what does the clock draw with the light on. And this you cannot answer. With your minimum electronic experience, I really feel the buck converter module is the best option.

The 3A output of the module will certainly supply enough current for your clock and light from the get-go. And who can complain about 90 cents (US) delivered price? All you have to do is wait ~ 3 weeks or so for delivery from China. Simply adjust the module's output 1.5 volts on the test bench, the same voltage from your AAA battery. Then attach it to your clock. Done! I recommend adding an input fuse of ~1A rating to protect the input wiring and putting it in a safe enclosure of some type.

http://www.ebay.com/itm/1-DC-DC-Buck-Converter-Step-Down-Module-LM2596-Power-Supply-Output-1-23V-30V-/181409861491?pt=LH_DefaultDomain_2&hash=item2a3cdecf73

If you would rather not deal with a China supplier, then you can get the equivalent assy from the US for just under 4 bucks.

_________________
Chuck.

“Any suspension will work if you don’t let it.” - Colin Chapman

Visit my ongoing MGB Rustoration log: over HERE

Or my Wankel powered Locost log : over HERE

And don't forget my Cushman Truckster resto Locostusa.com/forums/viewtopic.php?f=36&t=17766

Chuck, here is what I bought:
http://www.ebay.com/itm/Digital-LCD-Das ... 2c7271c6a5

Once again, thanks for input.

Bill

That'll work!

No problemo.

_________________
Chuck.

“Any suspension will work if you don’t let it.” - Colin Chapman

Visit my ongoing MGB Rustoration log: over HERE

Or my Wankel powered Locost log : over HERE

And don't forget my Cushman Truckster resto Locostusa.com/forums/viewtopic.php?f=36&t=17766