18 volt charger

The 2n3055 conducts 130 mA. Divide that by the gain of the transistor, and you have the base current. Ry has to allow at least that much current to flow into the base. Size Ry to allow twice that much. To do the arithmetic you need to know the voltage across Ry. It is supply voltage minus two diode drops (the base-emitter junctions of the transistors). So if the base of the 2n3055 needs say 13 mA, and the voltage across Ry is 22 or 23 volts, Ry is in the 15 or 20 kilohm ballpark.

It's a tiny attachment, so yes it's fine. But you will no doubt get silly perfectionists calling it wrong because it's an attachment, even though it's smaller than a large text post.

If it was my drill, I'd insist on a fast charger, which is what they come with. The drill is always flat at the point where you need it most.

Hi, Nels. The answer for your question is:

Rx =3D 5 ohms Ry =3D 1500 ohms

Here's how we got there. Looking at your circuit redrawn with component values added (view in fixed font or M$ Notepad):

I'd recommend a much simpler design: the basic circuit uses two parts. I'll show 3 circuits below. The first is the basic circuit. The second is the same circuit modified to include the LED indicator you want. The third is an automatic shut-off circuit.

-------

Gnd -------------------- Gnd to battery -

With a 10 ohm (1/2 watt or higher) resistor for R, you'll get 125 mA constant charging current.

Now, I'll draw the circuit again, but this time it will include an LED to show both that power is on and that the battery is drawing current.

How it works: The circuit will always conduct .125 amps when

The circuit will not shut off when the battery is fully charged. When charging at C/10, automatic shut-off is not required.

If you decide an automatic shut off circuit is a must:

Ooops - I forgot to include the turn on pushbutton. You need to press the button to start the charge cycle.

Before we get too far, I should mention that this circuit was found here:

Understood. I'll scratch up 1500-1600 ohms

It is a linear, and has an adjustment. I can get about 28 volts max.

Absolutely. We can't regulate that much current without making some heat. That heat has to go somewhere.

That is simple enough.

Yes. That LED is for a power-on indicator only. I may skip the charge indicator just to keep it simple.

I will look into that ASCII art program you used. Thanks.

Nels

Thank you for your reply, Ed. What an elegantly simple design! By my original post, you can see that I am a little weak on transistor theory, but this I can understand. Since this project is on the cheap, I will forgo the relay shutoff, but the rest is good stuff. One question -- I know the 317 is an adjustable regulator, but in this case the output remains constant. Could I calculate and install a fixed resistor instead? Thanks!

Nels

Yes. You could use a fixed resistor, but then it would be current limited, not constant current as you originally wanted.

What happens may best be seen by considering the start of charge, when the battery is at 18 volts, versus the end of charge, when the battery is at 21.45 volts. Using a 20 ohm resistor: supply 24 V --->20 ohm resistor ---> 18v battery There will be 6 volts across the resistor, meaning 6/20 or 300 mA current. As the battery charges, the voltage across it increases. At end of charge, there will be 2.55 volts across the resistor (24 - 21.45) for 127.5 mA current (2.55/20). As you can see, the current is not constant. But it will work just fine.

If you don't want constant current (or any other "bells and whistles") just use a 20 ohm, 5 watt resistor in series with your 24 volt supply. Add a 3 amp fuse to protect against a short circut. You'll be good to go. And Radio Shack # 271-132 is 2 10 ohm, 10 watt resistors for $1.79. Put those in series and you have the 20 ohms of resistance you need.

A simple current limited 1 resistor charger is not the best way to charge NiCds, but it does not overly abuse them, either. Just take the pack off the charge after about 10 hours and you should be fine.

You could add one "bell and whistle" - a LED charge indicator, like this:

Gnd --------------------------------------------- Gnd to battery -

The LED would glow brightly at start of charge when the battery voltage was 18 volts, and get progressively dimmer as the battery charges. The 150 ohm resistor can be 1/2 watt - no need for a power resistor. The Diode can be a 1N4001.

The auto shut-off circuit can be added later, if you like.

Ed

perfectionists calling it wrong because it's an attachment, even though it's smaller than a large text post.

perfectionists calling it wrong because it's an attachment, even though it's smaller than a large text post.

worked. I've never known a news feed that filters to that extent stuff that's already on the news network. If I did find one, I'd close the account promptly!

perfectionists calling it wrong because it's an attachment, even though it's smaller than a large text post.

Incorrect. Perhaps some won't allow them to SEND it. But that obviously worked. I've never known a news feed that filters to that extent stuff that's already on the news network. If I did find one, I'd close the account promptly!

I've been on the internet (and newsgroups) since 1994. Try getting your facts straight before making an even bigger ass of yourself.

Allowed indeed. This is a public group, not an over-policed admin-ridden forum.

perfectionists calling it wrong because it's an attachment, even though it's smaller than a large text post.

worked. I've never known a news feed that filters to that extent stuff that's already on the news network. If I did find one, I'd close the account promptly!

perfectionists calling it wrong because it's an attachment, even though it's smaller than a large text post.

worked. I've never known a news feed that filters to that extent stuff that's already on the news network. If I did find one, I'd close the account promptly!

Then it didn't hurt you did it?

I've heard other terrible things about Giganews though.

If a text group becomes full of 100 p*rn pictures a day, complain. But the odd

facts straight before making an even bigger ass of yourself.

Authority should be illegal :-P

If you're going to post a number of large ones perhaps.

Your rules made sense back when everyone had a 1200 baud modem, but not now.

forum.

But there is a difference between a slight bending of the rules and outright flouting them.

worked. I've never known a news feed that filters to that extent stuff that's already on the news network. If I did find one, I'd close the account promptly!

hassle to go get it.

extra hassle to go get it.

worked. I've never known a news feed that filters to that extent stuff that's already on the news network. If I did find one, I'd close the account promptly!

If someone posts the text to one group and the binary to another, it's an extra hassle to go get it. So I simply skip those messages. A web link wouldn't be so bad I suppose, but for 5kB which is textpost sized, I'd much prefer it was sat right here!

I didn't state my opinion (which happens to be none). I only hold opinions on things that I use myself, or several people agree on.

odd 5kB gif which is to do with the topic? That's just being petty.

Which is pedantic.

facts straight before making an even bigger ass of yourself.

Hence the :-P

I was being imprecise again :-P I meant the rules you quoted.

They're guidelines, not rules.

forum.

flouting them.

You don't appear to understand what bending the rules is. If there is a sign saying no overtaking, and a queue of traffic stuck behind a tractor doing 2mph, I suppose you'd call overtaking it breaking the law?

extra hassle to go get it.

My newsreader won't do that. Anyway you still have to load something extra. If the attachment is included, it's right there in front of you, without flipping between two posts.

If I've read enough to know I'll be interested by that point.

I'd much prefer it >was sat right here!

Stop showing your stupidity. I can only laugh so much in one day.

I did. Twice. What's your meaning then? But as you are a pedant, you will have a meaning which is 0.0001% different to mine, so call mine completely wrong.

A pedant with no sense of humoUr. You're getting worse.

Says who?

Menstruation has nothing to do with it.

Nope, I want to be vague. Rules are precise, guidelines are vague.

As a general rule.

saying no overtaking, and a queue of traffic stuck behind a tractor doing 2mph, I suppose you'd call overtaking it breaking the law?

The no overtaking sign would mean it is dangerous to overtake another car. When a tractor or bicyle is involved, the speeds are much lower.

extra hassle to go get it.

I used to use Agent (full version), but changed to Opera because Agent has other things missing. I've yet to see a program that does everything.

Granted, you may diminish your audience slightly. But from what I've seen the number of people who ignore messages with attachments are few and far between. Plus you get a good argument for free.

And I'm not the one who makes at least 5 childish insults in every reply.

have a meaning which is 0.0001% different to mine, so call mine completely wrong.

Stop being slippery and answer the question. I'll set Jeremy Paxman onto you.

I told you they are GUIDELINES, and I'm not a sheep.

Just pointing out you Americans have got your words mixed up. I believe the term you were looking for was "fullstop".

Since when is a guideline more precise than a rule? It's like saying an apple is more precise than a banana. They are just different.

I observed your poor attempt at misguided humoUr.

Don't be absurd.

sign saying no overtaking, and a queue of traffic stuck behind a tractor doing

When a tractor or bicyle is involved, the speeds are much lower.

The signs have no words, it's a picture.

I apologize for the attachment. I also apologize for being the impetus of yet another episode in the continuing saga of the debate between John Fields (whose advice I have so far come to respect) and Peter Hucker (who was unknown to me until these recent exchanges).

The charger problem is solved. Thanks (sincerely) to all who contributed. This thread is now dead to me.

Nels

John Fields wrote: > >>>On Wed, 23 Nov 2005 18:32:34 -0000, "Peter Hucker" >>>wrote: >>>

--- Another post, another look into that diseased little mind of yours. Who are you to tell _anyone_ what to do?

If someone feels like apologizing, they should apologize and you should have the good manners to keep your mouth shut.

-- John Fields Professional Circuit Designer