OK, the BC548 has the opposite pinout of the KST2222--these things get confusing...

http://www.futurlec.com/Transistors/BC548.shtml

 

Would be either the transistor or the zener diode. Correct? The 1.8k ohm is definitely correct and connected to 12v+, and the other side to pin 2 and the zener.

Right now, the base emitter junction appears to be open, or the emitter is not connected, because you're getting ~3.9v at the junction of the 10k and 22k resistors when you press S1.

In reality, with a battery that measures 12.6v, you should see about 8.66v at the junction of the two resistors when the base or emitter is disconnected and S1 is closed, not 3.9v. You have the 22k and 10k resistors swapped. Or maybe you've connected the battery backwards? That would explain why the transistor is damaged. It would also mean that the LM358 is toast.

I can try the 7.5k ohm resistor in series with the POT and neg terminal.

I've attached a schematic & simulation of the circuit. Note that I've added R9, a 100k resistor from the output of the opamp to the noninverting input; that provides hysteresis, which helps the MOSFET turn off much more quickly. Without the hysteresis, the MOSFET may stay in a resistive state for a period of time; if there is significant current flow through it, the MOSFET will get very hot, and possibly burn up.

 

I love this circuit you made. Electronic wise, it is totally functional. However, from what you described, it appears that Q1, for some reason, is not conducting. When everything is working, you should have around 5 volts at pin 2 of your op-amp. That is where you need to concentrate your troubleshooting at. For a test of the remainder of the circuit, you could jumper the emitter and collector of the transistor together to effectively take it out of the circuit, and see if the voltage at pin 2 drops to around 5. That would be my starting point.

 

I am going to remove the transistor from the circuit and test it, then swap out the lm358. If one of these things works, I will then modify the circuit as posted.

 

and tested it out of the circuit....FAILED! I installed a new one and now it works. I must have damaged the emitter from soldering the heavy gauge wire to the mosfet source/battery negative. I was too lazy to put the heat sink clip on. I knew I had it wired exactly to the schematic. When the mosfet gets ready to turn off, I notice it does not do it quickly at a set point. It starts to dim the lamp, then eventually goes out. The solution is the 100K resistor across pin #1 and the junction of the POT & 22k resistor? So you can use a mosfet as a dimmer by varying the voltage/current to the gate?

 

was too low. The circuit would not activate. I did trial and error until I found the perfect resistor. 270K prevents the power from gradually going off/dimming, and allows me to reset the circuit. This circuit is perfect for a scooter/motorcycle/small engine to prevent the lead acid battery from draining down below a safe level of around 12.15V - 12.25V. The circuit only draws 1.2ma. If you wanted to use it on a car, all you have to do is have the mosfet power a heavy duty relay/contactor.

Thanks Again for all the help.

 

The circuit is not suitable for an automotive environment.

The components are not rated for an automotive environment.

When a transient occurs during normal operation, the battery will become disconnected, and the alternator will cycle wildly due to operating without a load; likely destroying any electronics in the system before destroying the regulator.

As you have now declared that this is an automotive modification topic, the thread will be locked, and I will suggest to the Moderators that your future threads be moderated, as you have intentionally violated the Terms of Service, paragraph 6.

 

Sigh, did it have to end in this? I 'll talk with the other mods about the fate of this thread.

 

Okay, Dave says the thread stays as is, but in the spirit that the community helped build a non automotive circuit.

As SgtWookie says, this circuit is not specified for automotive use and any conversation to make it so will result in a closed thread.

 

My sealed lead acid battery which is charged by a solar panel for powering lights at night. I wanted this circuit for protecting the battery from over-discharge at night due to a couple cloudy days in a row not allowing a full recharge. Only problem is, the circuit needs me to press the reset button after the charge rises back up. The scooter/motorcycle battery idea was an afterthought. Many people have scooters/motorcycles that have a tendency to get a dead battery. I thought this would have been another good use for this circuit, but obviously more modification was needed to make it reliable. For whatever purpose someone is making a circuit, that should be no issue for getting help here.(Unless it is highly illegal) We are here for help with circuits. What we decide to use it for is our business.

 

My sealed lead acid battery which is charged by a solar panel for powering lights at night. I wanted this circuit for protecting the battery from over-discharge at night due to a couple cloudy days in a row not allowing a full recharge. Only problem is, the circuit needs me to press the reset button after the charge rises back up.

Then it needs some more work.

The scooter/motorcycle battery idea was an afterthought. Many people have scooters/motorcycles that have a tendency to get a dead battery.

I am not unfamiliar with this problem, as I have owned them in the past. The best thing to do is disconnect the battery when not in use, and keep the battery float charged.

I thought this would have been another good use for this circuit, but obviously more modification was needed to make it reliable.

There are many reasons why we don't discuss automotive modifications on this site, but what most of them boil down to is safety and/or legal reasons.

If someone attempted to use the circuit that we have been discussing in an automotive environment, it would be very unreliable, and could plausibly fail at a critical moment - such as going around a curve at night, the circuit fails, the system loses power and the headlight(s) go out.

What do you do then?

Automotive engineers with years of experience make mistakes that cost people's lives and property every day, and their parent companies billions of dollars in lawsuits and recalls. What chance do you think we non-automotive engineers have of remotely developing a circuit for automotive use, which is one of the most brutal environments on the planet, that a neophyte can build and install, and have a snowball's chance in a hot place of working for any period of time?

About ziltch-point-diddly, which is one of the big reasons WHY we don't support such discussions, which leads back to the safety and legal reasons - because riding a motorcycle at night without lights is both unsafe AND illegal.

For whatever purpose someone is making a circuit, that should be no issue for getting help here.(Unless it is highly illegal) We are here for help with circuits. What we decide to use it for is our business.

The point is that we want our members to live long, happy and productive lives in as safe of an environment as we can advise.

You are duly cautioned that the circuit is not suitable for use in an automotive environment, and due to its' very nature of operation, cannot be made safe or suitable for such use - even if every part in it were qualified for automotive use, was built on a professionally designed board, assembled by an experienced technician, tested in a lab over the full range of temperatures for a month, conformal coated, and placed in a liquid-tight housing on shock-absorbing mounts with a suitable harness and waterproof connections.

It would still not be safe nor suitable.

We don't tell you things like this because we simply want to deny information to you, or keep you from doing some mod to your wheels that would be "cool".

It's because we have many years of experience, and have learned that it's just not plausible for a casual hobbyist; even an experienced one, to make such modifications without a very large probability of it failing, and possibly having severe consequences.

We don't want anything bad to happen to our members, their property, nor to anyone around them. We also realize that we are not experienced automotive engineers, and on top of that, we cannot watch over your shoulder to ensure that you are doing everything according to how we think it should be done - and since we're not automotive engineers to begin with, it may not be exactly how it should be done anyway.

We're not the "bad guys".
We are just trying to keep bad things from happening to our members.

 

As I said before, your help was well appreciated, and I fully understand all of your concerns. Your 100% correct when you say engineers with years of experience make mistakes when they design a circuit, so what makes me think I won't make a big mistake on a circuit with only a fraction of their experience. I do agree that it should not be used on a car because you have no guarantee that the circuit won't cut off power when it should not. All this being said, there is no guarantee that my scooter would not lose all power due to some other reason(loose fuse holder/loose wire etc), which it has before. I did want this circuit to be able to handle intermittent heavy loads where the battery would normally drop in voltage, but that would trigger the circuit to cut off power. I have lots of other useful ideas for this circuit. I came up with an idea to modify it, and tested it out several times with total success. I took the battery + which feeds the circuit and added a schottky diode in series with that line to the board. I then added a 15,000UF 25v electrolytic capacitor across the power supply to the circuit. Now when the circuit experiences an intermittent voltage drop of up to 3 seconds, the circuit no longer triggers a cutoff due to the reserve in the capacitor which powers the circuit. The circuit does not see the drop. This can be used for pumps connected to a 12V battery which for some reason fail to turn off and end up draining your battery.

 

Automotive engineers with years of experience make mistakes ...........non-automotive engineers have of remotely developing a circuit for automotive use, which is one of the most brutal environments on the planet, that a neophyte can build and install, and have a snowball's chance in a hot place of working for any period of time?

I like the snowball example.

Yes you are right. I work in a company that develops and manufactures electronic components for the automotive sector, like electric power steering units, pedal sensors etc.
These circuits are tested and tested and then tested again, under all imaginable and unimaginable circumstances, undergo temperature shock tests, ESD tests, all possible short circuits and wrong wire harness connections, a lot of stuff.... and they still fail. Because there is something the developers didn't consider.


So yes, it is dangerous, especially because there is always this little something that you didn't think could happen.

 

As I said before, your help was well appreciated, and I fully understand all of your concerns. Your 100% correct when you say engineers with years of experience make mistakes when they design a circuit, so what makes me think I won't make a big mistake on a circuit with only a fraction of their experience.

You still don't understand.

This is going to sound rather unkind, but the photos you posted of the circuit that you built show a disaster in the making.

Two of the resistors have cracked ends.

The board has a corner broken off, and the physical connection for the components is compromised.

The board layout is poor.

You used generic perf board rather than a proper board.

The soldering leaves much to be desired.

You used heavy gauge wire to connect to the board without proper terminals or connectors; it is highly likely that the connection is physically weak, and will come apart after being vibrated.

There is no proper stress relief for the wiring.

There is no service loop for the wiring.

Zip-ties are not the way MOSFETs are secured to heat sinks.

The nut holding the MOSFET tab to the heat sink will vibrate loose and fall off.

Components are not held in position in a mechanically stable and supported fashion. Minor movement of certain components will cause shorts, and circuit failure.

It might be OK if it were simply used on a bench and never disturbed; as long as it was fused. If an attempt were made to use it in an automotive environment, it would quickly fall apart and fail, perhaps catastrophically.

I am not just guessing here, either. I have, a long time ago, built projects that looked pretty much the same as yours, and I saw how they failed.

I do agree that it should not be used on a car because you have no guarantee that the circuit won't cut off power when it should not.

I can pretty well guarantee that the circuit you built will fall apart at any random moment, particularly if subjected to an automotive environment.

All this being said, there is no guarantee that my scooter would not lose all power due to some other reason (loose fuse holder/loose wire etc), which it has before.

This goes back to proper maintenance. It is your responsibility as the owner of said vehicle to ensure that it is maintained in a manner to keep it corrosion-free and roadworthy. Since many electrical parts of a scooter are exposed, it requires much more maintenance than an automobile does to ensure that the connections, sockets, etc. are clean, corrosion-free and sealed using appropriate materials. "electrical tape" is NOT an appropriate material for anything on a vehicle, unless it's just to cover a rip in the seat.

I did want this circuit to be able to handle intermittent heavy loads where the battery would normally drop in voltage, but that would trigger the circuit to cut off power.

It's not just that the power would be cut. The alternator would no longer have the stabilizing factor that the battery provides, and the output voltage would fluctuate wildly. At best, this would lead to being stranded, and very possibly some quite expensive repairs.

I have lots of other useful ideas for this circuit. I came up with an idea to modify it, and tested it out several times with total success. I took the battery + which feeds the circuit and added a Schottky diode in series with that line to the board. I then added a 15,000UF 25v electrolytic capacitor across the power supply to the circuit. Now when the circuit experiences an intermittent voltage drop of up to 3 seconds, the circuit no longer triggers a cutoff due to the reserve in the capacitor which powers the circuit. The circuit does not see the drop. This can be used for pumps connected to a 12V battery which for some reason fail to turn off and end up draining your battery.

I guess you're talking about a bilge pump in a boat while one is away.

If a leak develops in a boat while no one is around and there is no bilge pump, the boat will sink.

If there is a battery-powered bilge pump, the pump will run until the battery is dead, and the boat will sink.

If there is a battery-powered bilge pump with a battery-low cut-off circuit, the pump will run until the cut-off circuit disconnects the battery, and the boat will sink - perhaps the battery will be worth diving for.

But I digress.

If you're going to use it to disconnect your SLA from the outdoor lighting when the battery discharges down to just above 12v, that's a very good use for it.

 

Your like a broken record.

"the photos you posted of the circuit that you built show a disaster in the making."

That is your opinion, which I TOTALLY disagree with. Just because a circuit was not assembled on a nice computer generated circuit board does not mean it will not work just as good. Especially since it is not an RF circuit.That I know for a fact. I have never had a board fail, and I have assembled many circuits. If yours did fail, then obviously it was not done like mine. The soldered connections were all done extremely well. No cold soldered joints, board properly cleaned before soldering, proper flux, proper cleaner, proper bus wire. As for the heavier gauge wire soldered directly to the mosfet, I would prefer that connection over a socket which can become loose or corroded. The one resistor you see with a chip in the epoxy at one end....is meaningless. If the chip was in the middle where is counts, you would have a valid point. As for the board being cut off....I had it laying around and did not want it going to waste, so I made it work. Obviously if I decided to use this circuit in a boat/car/scooter or anywhere else......It would be placed in a housing where NO damage would be done to the circuit. The nylon tie was only temporary! I could not find my robertson screwdriver to tighten the nut on the small bolt. So I held it in position with that tie until I found the screwdriver later. Oh yeah, Loctite 242 works extremely well on that nut if your so worried about it becoming loose. I also would not bet on my circuits, "falling apart". You would lose. I see you are still stuck on the alternator / battery issue. LOL. I agreed with you on that already. Get over it, I know its tough. Maybe you need therapy to get over it. If the circuit were used on a boat bilge, then it would not be recommended to use it if you were not going to be around on a daily basis to see your boat.(Example - In your backyard) Use common sense. I have seen countless boats have their batteries destroyed due to deep discharge by stuck float switches, or bilges that were manually activated, and they forgot to turn it off. Oh yeah, even if you don't use this on a boat, your battery will still end up going DEAD if the above happened and your boat will still sink! It will just take longer to do it. LOL This is turning out to be a comedy.

I'd love to see how you treat your friends, after seeing how you attacked me(someone you barely know) over a simple suggestion on how a circuit can be used. You really are a miserable person. What's really bothering you? Money troubles? Your home value in the toilet? Regret voting for that fraud Obama?". I'm done with this forum. I will make sure I tell others to stay clear, especially in all my future Youtube videos.

 

Your like a broken record.

"the photos you posted of the circuit that you built show a disaster in the making."

That is your opinion, which I TOTALLY disagree with. Just because a circuit was not assembled on a nice computer generated circuit board does not mean it will not work just as good. Especially since it is not an RF circuit.That I know for a fact.

And your qualifications are? Training? Certifications?

I have never had a board fail, and I have assembled many circuits. If yours did fail, then obviously it was not done like mine. The soldered connections were all done extremely well. No cold soldered joints, board properly cleaned before soldering, proper flux, proper cleaner, proper bus wire.

Here, this brief guide should help you improve your soldering considerably:
http://www.elexp.com/t_solder.htm
You should try to get some 63/37 solder. It looks like you're trying to use lead-free solder; it's much harder to get decent-looking joints with that. The iron you're using is the wrong size, wrong tip, or just not hot enough to solder the larger gauge wires.

You're using far too much solder.

As for the heavier gauge wire soldered directly to the mosfet, I would prefer that connection over a socket which can become loose or corroded.

It's not the fact that it's soldered. It's how it was soldered.

The one resistor you see with a chip in the epoxy at one end....is meaningless. If the chip was in the middle where is counts, you would have a valid point.

It's damaged. The body of the resistor is supposed to be hermetically sealed. Since the epoxy is chipped, that also means that the component was subject to stresses that makes its' physical integrity suspect.

As for the board being cut off....I had it laying around and did not want it going to waste, so I made it work.

It must've been quite a challenge to center the component leads in the vias that were broken in two while you were trying to solder them.

Obviously if I decided to use this circuit in a boat/car/scooter or anywhere else......It would be placed in a housing where NO damage would be done to the circuit.

It should be obvious by now that just "a housing" would not correct the deficiencies that have been pointed out thus far. However, it would make it easier to find the parts that will fall off due to shock, vibration and metal fatigue.

The nylon tie was only temporary!

Now that, I believe.

I could not find my robertson screwdriver to tighten the nut on the small bolt. So I held it in position with that tie until I found the screwdriver later. Oh yeah, Loctite 242 works extremely well on that nut if your so worried about it becoming loose.

Loctite is pretty good stuff.

I also would not bet on my circuits, "falling apart". You would lose.

Don't be so sure about that. Your scooter motor would vibrate it to death in short order.

I see you are still stuck on the alternator / battery issue. LOL. I agreed with you on that already. Get over it, I know its tough.

You didn't seem to get it the first time around, like a lot of other stuff.

Maybe you need therapy to get over it.

I don't seem to be the one with a problem. On the other hand, I'm trying to help you to not cause yourself injury or damage to your property, which is what the overriding concern of the forum is. We talk a lot about electronics, but we try our best to make certain that things are going to be safe for our members.

If the circuit were used on a boat bilge, then it would not be recommended to use it if you were not going to be around on a daily basis to see your boat.(Example - In your backyard) Use common sense. I have seen countless boats have their batteries destroyed due to deep discharge by stuck float switches, or bilges that were manually activated, and they forgot to turn it off. Oh yeah, even if you don't use this on a boat, your battery will still end up going DEAD if the above happened and your boat will still sink! It will just take longer to do it. LOL This is turning out to be a comedy.

That was deliberate not-so-dry humor. My dad and I had a discussion about bilge pumps many years ago; it seemed the foregone conclusion that bilge pump or not, the boat was still going down.

I'd love to see how you treat your friends, after seeing how you attacked me(someone you barely know) over a simple suggestion on how a circuit can be used.

There was no attack.
The thread started off as a simple low-battery cutoff circuit.

After it was more-or-less working, you suddenly tried to suggest that it was an automotive circuit, when it is absolutely not suited for such a purpose; and discussion of automotive modification topics are against the Terms of Service paragraph 6 - which, by the way, you agreed to abide by when you first signed up here, and also every time you hit the "Submit Reply" button. It went straight from a perfectly innocent thread, to safety issues and ToS violations.

You really are a miserable person.

By the way, ad hominem aka personal attacks are not only in violation of the ToS, they are also a demonstration of your inability to present your case in a logical fashion. As I have made in excess of 20,000 posts here in the last several years with better than 90% of them being helpful to people, while you are racking up an impressive record of being argumentative and violating ToS, I'm not terribly concerned about what you think.

I'm done with this forum.

At this point, it's still your choice to leave. If you continue to violate ToS, it won't be your choice for long.

I will make sure I tell others to stay clear, especially in all my future Youtube videos.

Danger, danger - people might actually learn something here!

Are you done ranting yet?

Good.

I have not attacked you; I have simply given my professional opinion on some of the problems with the design, fabrication/assembly/workmanship/etc., but it was not to berate you. It was simply to point out that your assembly leaves much to be desired.

I started out experimenting with electronics over 40 years ago when I was a teenager.

After spending nearly two years in training on avionics, I was a radar systems/missile fire control technician on the McDonnell-Douglas F-4J/S Phantom II multirole fighter/interceptor/bomber for a number of years. They don't let you work on them if you don't know what you're doing.

I then went to work for Hughes Aircraft Company, where I worked in engineering and manufacturing on the F-14, F-15, F/A-18, AN/AXQ14 weapon data link and GBU-15 glide bomb, Advanced Synthetic Aperture Radar, the Advanced Medium Range Air to Air Missile, the YF-22 prototype, a number of other experimental programs, and even a few spacecraft. They don't let you work on those if you don't know what you're doing, either.

I'm still working in aerospace.

But, I don't consider myself an automotive engineer.

And, my vehicle is completely stock. So have been my last several vehicles. They're really quite reliable that way.

 

You handled the situation all wrong. There is a correct way of handling things, and then there is the wrong way. You chose the wrong way. You jumped on me after one reply to a thread, and then I got the insults about my soldering, the layout, components I used, and any intended use for the circuit. Like I need you giving me advice on how to solder after 20yrs of assembling circuits....Tip size/heat/solder wire....LOL. Did it ever occur to you that I may live in a remote area of the world where it is not possible to get electronic supplies? That I have to make do with whatever I have laying around (soldering irons-tips/solder/pc boards...etc). I guess not. You should be so skilled to use the supplies/equipment I have to work with here. Considering what I used, this soldering job came out excellent. I could care less what you say, because I am completely satisfied with the job. I know a lousy soldering job when I see one. I'm the one who has to be happy with the job, not you. Done wasting my breath here.

 

Enough ranting. Nothing useful to be said anymore here. We might think of deleting the useless part of the thread too.