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[tobyker]

I have a number of Nicad powered workshop and garden tools. They come with fairly unsophisticated chargers and instructions to charge for 1, 2, 3 or 12 hours. I have mains timer plugs that I can set to pass current for a specified time, but they all work continuously - If I forget to unplug the thing within 24 hours they cycle again. What I want is a timer I can set for however long I want to charge the battery for, which will cut the current and stop at the end of the specified time. Has anyone heard of such a thing?

[Shipmate60]

Security timer plug.
You set the time you want power and plug in.
Time not duration eg midnight to 8-00 am.

Bob

[FullLeatherJacket]

Sorry to be obtuse (well, I'm not really) but have you thought of pouring a glass of wine at about ten PM and then wandering round the workshop with it in your hand, planning the things you'd forgotten to do today? That way you're bound to spot things which should have been taken off charge before.
The TT brigade can always drink tea - it's the event which is important, not the bevvie.
Works for me, every night 

Suit yourself

FLJ

PS You could always buy 7-day timers and avoid the ceremony for six days a week..................

[Shipmate60]

Wine?
What is up with Lager?   :)

Bob

[FullLeatherJacket]

Wine?
What is up with Lager?   :)
Bob

It makes me f*rt! 
FLJ

[anmo]

Wine?
What is up with Lager?   :)
Bob

It makes me f*rt! 
FLJ

If you have that problem with lager, I suggest you never try eating Jerusalem artichokes.

[tobyker]

Thanks shipmate and FLJ, but 1. all the security timers I can find repeat next day, and 2. mine is not the sort of shed you wander round with a glass of wine in your hand. All I need is a simple 12-hour timer once on once off. Part of the problem is the charging of a lawn mower at a location a mile away.

[tigertiger]

Thanks shipmate and FLJ, but 1. all the security timers I can find repeat next day, and 2. mine is not the sort of shed you wander round with a glass of wine in your hand. All I need is a simple 12-hour timer once on once off. Part of the problem is the charging of a lawn mower at a location a mile away.

I think there are chargers that switch themselves off when done.
This does entail buying another charger though.

Another thought. This will require some electrical knowldge to make it work.
The only timer I can think of that might help you is a central heating timer. Some have a weekday and weekend cycle. If you can frig one of these to a main power supply and then set it as Sunday, when you switch on, you will then have 5 days before it goes on the weekend cycle again.
Just a thought.

[malcolmfrary]

Sounds like a job for an extra box with a momentary switch and relay. 
Set the timer, press the switch to arm the relay, relay remains operated through its own contact allowing power to the charger until the timer switches it off and releases the relay.  Subsequent re-operations by the timer do nothing until the switch is re-operated with the timer active.
There is probaly a Health and Safety person having a kitten or an orgasm as you read this.

[dreadnought72]

Sounds like a job for an extra box with a momentary switch and relay. 
Set the timer, press the switch to arm the relay, relay remains operated through its own contact allowing power to the charger until the timer switches it off and releases the relay.  Subsequent re-operations by the timer do nothing until the switch is re-operated with the timer active.
There is probaly a Health and Safety person having a kitten or an orgasm as you read this.

Who cares? I love the solution! Thats MY kind of electrics!!!!

Andy

[tobyker]

Thanks - I had wondered if there was away of making the timer switch itself off. But why doesn't anyone make something like that? now to the Maplins catalogue to find mains relays.

[malcolmfrary]

There is an alternative to FLJ's solution - that is to have the routine of the glass of wine after looking at the workshop.  Sort of a reward and incentive for remembering.  Having the glass before might annoy the HSE by putting you in charge of a lightswitch while under the influence.  We can't have that, can we?

[OMK]

Tobyker,

Here's an older analogue-type timeclock. This will do the job. Those red and blue tabs simply press on the face of the dial at your needed times of operation... from 15 minutes to 24 hours.

Holler if it's any use to you.

[OMK]

Hmm... on second thoughts, forget it.
I thought this was a one-time on/off unit. It's not though. Seems it will cycle continuously, which is what you don't want.

Sorry 'bout that.


Let's build a one-shot PIC or crystal-controlled timer... what it the maximum 'On' time you require?... 6 hours?... 7 hours?... more?...

[Model Boats Website]

I have a number of Nicad powered workshop and garden tools. They come with fairly unsophisticated chargers and instructions to charge for 1, 2, 3 or 12 hours. I have mains timer plugs that I can set to pass current for a specified time, but they all work continuously - If I forget to unplug the thing within 24 hours they cycle again. What I want is a timer I can set for however long I want to charge the battery for, which will cut the current and stop at the end of the specified time. Has anyone heard of such a thing?

tobyker,

It's a good idea to stop the charge after so many hours to stop the battery getting overcharged, however as a note of caution (because it's happened to me) you don't want to leave the battery connected to the charger for any length of time.

The battery will backdrain (discharge) back into the charging unit, although it may be a small amount of current I wouldn't leave it connected up for more than a couple days or you'll end up with a duff battery.

[Model Boats Website]

Hmm... on second thoughts, forget it.
I thought this was a one-time on/off unit. It's not though. Seems it will cycle continuously, which is what you don't want.

Sorry 'bout that.

PMK,

You could use this as a one-time on unit by switching it on manually and just having the "off" pin in for approx 4 hours later. As long as you leave out the "on" pin the unit should stay off.

(does that make sense?)

[Colin Bishop]

Brilliant Fireboat! That's what I call lateral thinking. 

[OMK]

(does that make sense?)

Not sure that I follow.
Unless you're there to pull out the 'on' tab, then the damn thing will cycle forever. I presume that he (Tobyker) wants a unit that can be left unattended, knowing it'll switch itself off after the battery charging cycle has timed out.
Can't do that if that 'on' tab is there.
It needs something along the lines of Malc'Frary's suggestion... a simple one-shot timing cycle that cannot be retriggered again unless a manually-operated 'start' button is pressed.

[Colin Bishop]

The way I understand it is that on the timer you have two rings of holes, an "on" ring and an "off" ring. You can also switch the timer on manually via another control - my plug in hot water timer works that way. So, you set the timer to "now" and put a peg in the "off" ring at the time you want to switch off. You don't put a peg on the "on" ring". Then you trigger the manual "on" control which starts the charger. When the "off" peg comes around it will swich off at the designated time and stay off because there is no "on" peg to switch it on again. Simple and elegant! QED...

[tobyker]

Thanks for the offer, PMK, but that is almost exactly what I've got already. I think Fireboat gets the cigar, though - why didn't I think of that? There's a little black pin you can use to switch it on.  As to the backdrain through the charger, could that be stopped by putting a diode in the charger lead, or isn't it that sort of backwards? And if so where do I put it, pointing which way? The batteries in question -for remote charging - are 12v and 24v - dedicated chargers for each.

[OMK]

The way I understand it is that...

By Jove - you're right! Simple, elegant AND it works.

Toby:
In order to prevent that 'backdrain' you could, as you say, stick a diode in series with one of the wires to the battery. This is only effective if your charger is NOT of the peak-detect flavour. You might try a bog-common 1N4001... 1N4002, etc. Stick it in series with the red (positive) wire. The Anode should be at the end towards the charger; the Cathode (the end with the stripe) should go to battery positive... not forgetting the ubiquitous fuse(!).
This may be a moot point, though. For the charger itself has either half-wave or full-wave rectification already there. In other words... it's not likely that the battery will discharge itself back through the charger unit. Although, an added diode will cause no harm -- it merely ensures that no current will flow should you accidentally reverse-connect the  wires to the battery.

[malcolmfrary]

Back draining depends on the circuit of the charger.  
A car type charger  (real car, that is) usually just has a transformer to drop the mains vpltage, and a rectifier to turn it into rather lumpy DC.  The only circuit the battery "sees" is the wrong end of the rectifier.
A regulated charger might well have a DC path back from the battery, as some voltage regulators require that a load always be present, and if no power is being supplied, this load is presented to the battery.  A sufficiently knobbly diode will cure this, but most commercially available chargers will probably have the problem pre-solved.
Remembering to switch off before the glass of wine still gets my vote.  Especially if it's nice wine.

Hi PMK we both weote together.  Snap!

[FullLeatherJacket]

Thank goodness that's been settled. I almost lost the will to to drink.  :'(
FLJ

[OMK]

It's a good idea to stop the charge after so many hours to stop the battery getting overcharged, however as a note of caution (because it's happened to me)...

Hey, Fireboat, apologies if my previous post sounds like I contradicted you. Don't worry, bud - I'm having a bad hair day.

Monsieur Jacket:
Return email heading your way... as soon as I've finished me shandy (hic!).

Hi to you too, Malc'F. Yep - seems we did. In actual fact, you just reminded me of something... Took me a godly age to fathom-out why I couldn't get any juice from a modified computer PSU. You're right... I was forgetting that it needs to detect a load across the output.


Well that's me redundant. I'm about as helpful as a chocolate soldering iron today. Who fancies coming down the pub?..............

[HS93 (RIP)]

I have one of these for charging batteries that I don't want to fast charge as it is so universal  Nice job and easy to use,NO GUESS WORK OR TIMERS.. Peter


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