AC timer circuit

What you want is a monostable 55 timer circuit. When the circuit is triggered it will activate a relay for a predetermined time. This page has a good schematic:

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You will need to change some of the values to get the time period to suit your needs. This circuit can also be brought as a kitset from most electronics stores if you don't feel comfortable building it from the schematic.

Reply to
tom
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Dave, look at Nuts & Volts issue September 2004, page 32. This circuit is exactly what you want. Regards Fred

Reply to
whru

Intermatic makes a switch that times up to 12 hours. It's on this page here:

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This would seem to be the simplest way to do it. Richard

Reply to
spudnuty

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You are insane.
Reply to
John Fields

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How about, instead, a box that when you press the button the charger
starts and when the battery gets to 14.5V the charger is
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Reply to
John Fields

I would like to build a device which turns an AC power outlet for a predetermined (ideally adjustable or programmable) time. I will use it to power a battery charger on my boat. I've got a fully automatic battery charger, but not a terribly expensive one. This charger charges the battery until a "full" indicator comes on, at which time charge voltage shuts off. However, the sensor that detects "full" is a simple voltage sensor, which appears to toggle at about 14.5VDC. Well, as the battery settles down after charging ceases the voltage drops over 10 minutes or so until it reaches

14.4VDC, at which time the charger turns on again. As the boat is unattended, I'd rather not have the charger turning on and off indefinitely.

Instead, I'd like a simple box with one button on it. I push the button, AC circuit that powers the charger is energized for, say, 8 hours, then shuts off. I have seen homemade versions of this device at a high-tech company I worked at, where the lab manager built a bunch and hooked up all of the solder stations to them so that when people forgot to shut them down, it would happen automatically.

Any help greatly appreciated.

Dave

Reply to
Dave

Buy a better charger. Hacking something like this together is a recipe for disaster, particularly in an unattended setting. Also, your battery will die if you let it self-discharge for too long; you need to keep lead acid batteries charged.

One idea would be to get a weekday timer, and set it up to charge every friday (before you go out).

Another idea would be a solar panel charger, like those dashboard auto chargers.

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Regards,
  Bob Monsen
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Reply to
Bob Monsen

battery

after

indefinitely.

AC

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You can go to a store like Lowes and get a water heater timer. There are also many other timers that can be bought for not too much. The water heater timer will probably have to be set to come on every 24 hours for a short time.

Reply to
Ralph Mowery

I'm probably being helpful but I'd spend the money on a better charger ... I think a decent unit will charge at a predetermined rate then drop to a small trickle charge to keep it topped off.

Reply to
JeB

Timing is not the best way to charge a boat battery.

I use a solar panel to keep my battery up. It will not charge enough to over-charge (and boil). It charges enough to keep it up, but every 6 months or so, I put a real charger on it, check the water, etc.

If you don't see your boat at least every six months, you need to sell it.

Reply to
Vey

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The best you can get out of a bipolar 555 depends on the bias
current of the 555\'s input comparator, the leakage current of the
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Reply to
John Fields

Both options are better than mine, although as other posters have noted, probably the best thing for me to do is just upgrade my charger. I know very little of timing circuits other than that they exist, hence my simple questions.

just out of curiosity, why did you say that the poster who advocated the "555 monostable circuit" or some such was insane?

dave

Reply to
Dave

Or any ordinary coffepot timer, albeit they're probably not rated for outdoor use. :-)

Good Luck! Rich

Reply to
Rich Grise

Probably because suggesting a 555 circuit in this application is insane. ;-)

Cheers! Rich

Reply to
Rich Grise

Yea, today the local paper had some timers on sale at Lowes for $ 7.95 reduced from $ 9.95.. Some things are just too inexpensive to reinvent. Unless one has a well stocked junk box the price of the parts are more than the whole thing can be bought for.

I used a water heater timer to keep a standby battery charged on a remote repeater site. The charger was a 10 amp charger that would cut to a trickle. Even at this the battery was not used much so I set the charger for about an hour each day.

Reply to
Ralph Mowery

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