Whole house fan motor

change: [1K]

it was just a guess, and your're right it's probably bit low for a BC557 about 18ma in from base would would be better than about

180 so use 1K instead.

as you can see I'm not trying to get precise results transistors vary but upto a factor of 3 in their gain ratio so ignoring the small details often doesn't hurt the result.

yeah but i'm not desiging an analogue circuit my goal is to over bias the transistors so they go into saturation, stay there and stay cool.

I woudn't trust a cheap digital meter on a PWM signal, I'd add a low-pass filter or envelope detector circuit depending on what I wanted to measure.

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100K seems high, a but BC557 does have quite a lot of gain and can only handle 100mA, hoever the MJE3066 has much more gain then the venerable 2N3055 so it hard to predict how strong that transistor need to be.

A stronger transistor may be better suited there, eg BC327 or MPSA56, or an even bigger one like BD78 or TIP42

If you want to increase the current just connect a load in parallel with the battery, eg. a a car headlamp, or other dummy load.

Hmm, mysterious. You're not pluging the '3055 into a solderless breadboard, or using long jumper wires to hook this up are you?

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if you want to switch the 3055 by turning on a current to ground (where the microconttoller is connected) you need to make the top NPN transistor look like a PNP

The Sziklai pair arrangement does that almost perfectly

That would work, but would also make monitoring the battery voltage using the microcontroller much harder.

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I have the app notes for the LM338 and such, which show simple charger circuits like that, but the fact of the matter is I have a couple of

3055s and this project is as much about learning some basics as it is about charging a battery. For my requirements it is easier to use what I have on hand than try to select among parts that I don't really understand. If there were a fundamental reason why the 3055 is bad for this application I might consider a mosfet, but I don't see why I should bother.

Regards,

Uncle Steve

--
There should be a special word in the English language to identify 
people who create problems and then turn around and offer up their own 
tailor-made bogus non-solutions designed to completely avoid the root 
causes of the situation under consideration.  'Traitor' might be a 
good choice, but lacks the requisite specificity.  One of the problems 
with contemporary English is it lacks many such words that would 
otherwise categorically identify certain kinds of person, place, or 
thing -- making it difficult or impossible to think analytically about 
such objects.  These shortcomings of the English lexicon are 
representative of Orwellian linguistics at work in the real world.

After figuring out that it seems better in this case to have the battery on the emitter side of the 3055 (probably doesn't really matter, but this way seems easier) I rebuilt this configuration with

2.2k on the base of the 2n2222 (to reduce the drain on the uC pin, perhaps for no good reason) and used 220 ohms on the base of the BC557, which sets the current into the 3055 base at about 35mA and 10mA for the LED.

That's the bit I haven't yet figured out. When I understand how to do that reliably, or at least to requirements, with arbitrary transistors and without fooling around on a breadboard so much I'll be happier.

There's no PWM yet, just a mechanical switch. The weird readings I got on a couple of occasions were perhaps pathological cases where broken transistors were doing something stupid.

I have a couple of wrinkles to figure out yet before I start finalizing the software and begin testing the uC. I probably should put a LM338 on the p/s to set the voltage to the bulk charge rate, etc.

Regards,

Uncle Steve

--
There should be a special word in the English language to identify 
people who create problems and then turn around and offer up their own 
tailor-made bogus non-solutions designed to completely avoid the root 
causes of the situation under consideration.  'Traitor' might be a 
good choice, but lacks the requisite specificity.  One of the problems 
with contemporary English is it lacks many such words that would 
otherwise categorically identify certain kinds of person, place, or 
thing -- making it difficult or impossible to think analytically about 
such objects.  These shortcomings of the English lexicon are 
representative of Orwellian linguistics at work in the real world.

You need a B-E resistor on the 3055. The lack of that probably accounts for your observed instability.

I'm out this A.M., will post embellishments when I return. ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| Phoenix, Arizona  85048    Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.

I have enough gain at the moment, so this is a non-issue until I have an excuse to make another run to the local electronics retailer.

Grin. I have just such a dummy load (25W or so) but it won't tolerate

13.5V (or more) so I'll have to be careful about how it gets hooked up.

It is a TO-220 package so fits in the breadboard, however I have been wondering a little about the power rating of the breadboard rails... The transformer is 55W so I suspect this might not be an entirely academic issue.

Regards,

Uncle Steve

--
There should be a special word in the English language to identify 
people who create problems and then turn around and offer up their own 
tailor-made bogus non-solutions designed to completely avoid the root 
causes of the situation under consideration.  'Traitor' might be a 
good choice, but lacks the requisite specificity.  One of the problems 
with contemporary English is it lacks many such words that would 
otherwise categorically identify certain kinds of person, place, or 
thing -- making it difficult or impossible to think analytically about 
such objects.  These shortcomings of the English lexicon are 
representative of Orwellian linguistics at work in the real world.

I first tried that because I was having difficulty getting two 2n2222s to produce enough gain. I believe I was not setting them up properly, and is on my to-do list to understand how two NPN stages should work in this kind of arrangement.

How so? I have a high-impedance resister-divider network hooked up to the +ve battery terminal and ground, eventually going to a uC pin configured for ADC. I'd just have to move it to span the battery terminals instead of +batt and supply ground. The current arrangement does have the advantage that all three r/d networks will have the same scale.

Regards,

Uncle Steve

--
There should be a special word in the English language to identify 
people who create problems and then turn around and offer up their own 
tailor-made bogus non-solutions designed to completely avoid the root 
causes of the situation under consideration.  'Traitor' might be a 
good choice, but lacks the requisite specificity.  One of the problems 
with contemporary English is it lacks many such words that would 
otherwise categorically identify certain kinds of person, place, or 
thing -- making it difficult or impossible to think analytically about 
such objects.  These shortcomings of the English lexicon are 
representative of Orwellian linguistics at work in the real world.

The 3055 has a minimum beta of 20 at 4 Amps, which you spoke of at one point in this thread, which means the base current that must be supplied is 200mA... not a big deal EXCEPT the driving device will see considerable dissipation.

You ought to go buy the TO-3 version of the LM317 for the circuit I suggested and avoid the magic smoke ;-) ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| Phoenix, Arizona  85048    Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.

I'm starting to appreciate these factors. Yet, after removing the

4004 diode as superfluous and changing the .5 ohm sense resistor to .1 ohms, I'm seeing 3A output which is pretty much the capacity of the power supply. The 3055 runs cooler as well; not sure what that means.

Now I have to use an op-amp comparator to measure the current to get decent resolution.

The literature doesn't specify the switching frequency, rise time, etc. for that part.

Regards,

Uncle Steve

--
There should be a special word in the English language to identify 
people who create problems and then turn around and offer up their own 
tailor-made bogus non-solutions designed to completely avoid the root 
causes of the situation under consideration.  'Traitor' might be a 
good choice, but lacks the requisite specificity.  One of the problems 
with contemporary English is it lacks many such words that would 
otherwise categorically identify certain kinds of person, place, or 
thing -- making it difficult or impossible to think analytically about 
such objects.  These shortcomings of the English lexicon are 
representative of Orwellian linguistics at work in the real world.

I'm curious why you need to "switch" it? Isn't your only concern the _average_ current, as determined by the PWM?

All you need is a low-pass R/C between the micro and the base of Q1 (as noted in the text box on the schematic).

I'll run a simulation of that and repost later (under this same link).

...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| Phoenix, Arizona  85048    Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.

And you don't need to measure the current via a high-side OpAmp kludge, it's calculable from the voltage at the emitter of Q1.

(If you want it to be super precise, just add an OpAmp between your micro and Q1.) ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| Phoenix, Arizona  85048    Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.

Reposted with those features added...

Non-linearity at low end is due to bias current from LM317 adjust pin. Scaling both R2 and R3, proportionately to lower values, will lower that break point.

Diode is necessary as a safety in the case where battery is connected, but 18V supply is set to zero. Diode can be moved in front of LM317 if desired. ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| Phoenix, Arizona  85048    Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.

You're probably correct, except the rating of the LM317 is half of what I need. It's an interesting idea to use PWM to control a voltage regulator, but it's a completely different approach from what I intended to build. Perhaps it will be worthwhile to refactor your design and substitute a LM338, which has the requisite capacity. For now I think I will fool around with the existing arrangement.

Even at 3A output, the 3055 doesn't appear to be saturated as Vce is only .9V. I picked up a couple of BC517 which have a beta of 30000 and 1A current capacity. Perhaps that will be more effective than the BC557 in the pseudo-Sziklai arrangement.

Regards,

Uncle Steve

--
There should be a special word in the English language to identify 
people who create problems and then turn around and offer up their own 
tailor-made bogus non-solutions designed to completely avoid the root 
causes of the situation under consideration.  'Traitor' might be a 
good choice, but lacks the requisite specificity.  One of the problems 
with contemporary English is it lacks many such words that would 
otherwise categorically identify certain kinds of person, place, or 
thing -- making it difficult or impossible to think analytically about 
such objects.  These shortcomings of the English lexicon are 
representative of Orwellian linguistics at work in the real world.

I would't go over 200mA per contact on an unknown breadboard. especially where an open circuit or unexpected resistance could cause a problem.

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Too late! I have already determined that the conducters are capable of handling 12V at 4A without melting anything. The battery is another matter with a listed capacity of 180 Cold Cranking Amps, and I am quite certain a short would cause major damage.

Regards,

Uncle Steve

--
There should be a special word in the English language to identify 
people who create problems and then turn around and offer up their own 
tailor-made bogus non-solutions designed to completely avoid the root 
causes of the situation under consideration.  'Traitor' might be a 
good choice, but lacks the requisite specificity.  One of the problems 
with contemporary English is it lacks many such words that would 
otherwise categorically identify certain kinds of person, place, or 
thing -- making it difficult or impossible to think analytically about 
such objects.  These shortcomings of the English lexicon are 
representative of Orwellian linguistics at work in the real world.

not melted anything, but you've destroyed a few transistors in mysterious circumstances.

If the Q1 (MJE3055) collector contact gets a bit loose all current will go through Q2 (BC557) and destroy it.

Melt some solder, take the main current path off the breadourd.

100CCA, so it's just a little one (motorcycle?)

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Mainly due to bone-headedness.

Almost there.

It's a "lawn and garden" battery. $20.00 on sale, so a good deal even if it doesn't tolerate actual use all that well. As a backup power solution it will be used only rarely.

Regards,

Uncle Steve

--
There should be a special word in the English language to identify 
people who create problems and then turn around and offer up their own 
tailor-made bogus non-solutions designed to completely avoid the root 
causes of the situation under consideration.  'Traitor' might be a 
good choice, but lacks the requisite specificity.  One of the problems 
with contemporary English is it lacks many such words that would 
otherwise categorically identify certain kinds of person, place, or 
thing -- making it difficult or impossible to think analytically about 
such objects.  These shortcomings of the English lexicon are 
representative of Orwellian linguistics at work in the real world.

I would urge you to follow JT's advice. Build his circuit.

It is easy to add a pass element to get higher current later on. Here's an example diagram to give you an idea how it's done:

MJ2955 Vin ---+----> ------------------+-----------> Vout | e\ /c | [3R] --- | | | ----- | +------+---Vin|LM317|Vout---+-------+ | ----- | | | Adj [240R] | | | | | | +----------+ | | | | [.22uF] / [.1uF] | \ | | 5K / regulator, but it's a completely different approach from what I

In reading your various posts it seems clear to me that you are expending a lot of effort and have a lot of interest in this, which is all to the good. But I also see that you are speeding by some points where you could benefit by working to understand them, rather than passing them by - which is what prompted me to reply.

No perhaps about it, it is definitely worthwhile. The earlier part of my reply suggests how you can do it with parts on hand, then later on add a pass element, or, as you mention, substitute a 338.

Well, you may get it to work, but you won't learn why it does, or why the previous attempts didn't. It is my impression that you are leap frogging some of the basics. Sometimes throwing bigger/better/stronger parts at a problem is not in your best interests.

Ed