# AC timer circuit

D

#### Dave

Jan 1, 1970
0
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

T

#### [email protected]

Jan 1, 1970
0
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:
http://ourworld.compuserve.com/homepages/Bill_Bowden/page9.htm#555mono.gif
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.

J

#### John Fields

Jan 1, 1970
0
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:
http://ourworld.compuserve.com/homepages/Bill_Bowden/page9.htm#555mono.gif
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.

J

#### John Fields

Jan 1, 1970
0
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.

---
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
disconnected from the mains and stays disconnected until you press
the button again?

Maybe even disconnects the battery from the charger so it can't leak
back through the charger's output circuitry?

W

#### [email protected]

Jan 1, 1970
0
Dave,
look at Nuts & Volts issue September 2004, page 32. This circuit is
exactly what you want.
Regards
Fred

R

#### Ralph Mowery

Jan 1, 1970
0
Dave said:
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.

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.

J

#### JeB

Jan 1, 1970
0
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.

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.

B

#### Bob Monsen

Jan 1, 1970
0
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.

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.

---
Regards,
Bob Monsen

There once was a man from Hornepayne,
Who tried to transform the whole plane,
It bent a meridian
So it wasn't Euclidean,
And frustration drove him insane.
- Anonymous

V

#### Vey

Jan 1, 1970
0
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.

D

#### Dave

Jan 1, 1970
0
John Fields said:
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
disconnected from the mains and stays disconnected until you press
the button again?

Maybe even disconnects the battery from the charger so it can't leak
back through the charger's output circuitry?
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

R

#### Rich Grise

Jan 1, 1970
0
"Dave" <[email protected]> wrote in message
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.

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

Good Luck!
Rich

R

#### Rich Grise

Jan 1, 1970
0
just out of curiosity, why did you say that the poster who advocated the
"555 monostable circuit" or some such was insane?

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

Cheers!
Rich

J

#### John Fields

Jan 1, 1970
0
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?

---
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
timing cap and the resistance of the timing resistor. If you're
lucky you can get maybe half an hour out of the thing on a good day,
but there's _no way_ You'll get 8 hours out of it. The bipolar 555
and the CMOS 7555 have the same typical trigger current, 50pA, so
it's no better for the 7555. It's the capacitor's leakage current
that'll kill the long timeout for both of them.

R

#### Ralph Mowery

Jan 1, 1970
0
You can go to a store like Lowes and get a water heater timer. There
Or any ordinary coffepot timer, albeit they're probably not rated for
outdoor use.

Good Luck!
Rich

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.

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