How do I determine a fuse that I need for a circuit?

[EasyGoing1]

Re: How do I determine a fuse that I need for a circuit?

The negative of the battery will be connected to cathode of the diode, the positive will be connected to GND when battery is put in backward.
BTW, that is how crowbar circuit works, it seems like you did not read the links to learn about the circuits.
May I ask how much understanding you have about diode, MOSFET, transistor, and circuit?

So here's a picture of this setup with the battery connected backwards and the diode in line ... now how does the negative of the battery connect to the cathode?

This is pure theoretical obviously ... as i think we all agree this is a worthless setup for this goal.

[Curious.George]

Re: How do I determine a fuse that I need for a circuit?

I have these very cheap but very useful 18650 battery chargers. However, if you accidentally put the battery in backwards, it immediately frys the chip on the charger and lets the smoke out. Someone at one time suggested that I use a fast acting resettable fuse inline between the battery and the charger and ive been looking at them but I don't know what kind of fuse to get.

Put a little (active) current limiter in series with the charger's output. In the event that the charger's output is exceeded (for whatever reason: reversed load, short circuit, etc.) the current draw on it will be limited as per the design criteria of the limiter.

Note that fuses have non-zero response times -- often many seconds at 2X their rating to open. (and, then you've got to buy a replacement!)

[You may need more voltage compliance from the charger to accommodate drops in the limiter, depending on your design]

[EasyGoing1]

Re: How do I determine a fuse that I need for a circuit?

May I ask how much understanding you have about diode, MOSFET, transistor, and circuit?

I took electronics when I got my AS degree between 1990 and 1993 ... got my CET back then ... BUT I went on to do what I had been doing as a hobby since 1982 - computers! I became a network engineer in 1996 and have been doing that ever since ... I have recently (about two years ago) picked up electronics again just to have fun and have logged a lot of hours doing it ... love playing with microcontrollers ... back in the early 90's, I went all the way through electrical calculus ... do I remember all of that crap? Hell NO! But I'm not an idiot and can understand pretty much anything if I take the time to look at it.

[budm]

Re: How do I determine a fuse that I need for a circuit?

You have diode in the low side, then in this case the Anode is connected to the positive of the battery that is put in back ward.
Now redraw your diagram and have diode on the high side instead by connecting the Anode of the diode on the positive output of the charging instead.
It is very obvious that you refuse to learn from the links I provide, I do not understand why I am wasting my time here.
RJ understands it after looking at the link.
BTW, do the experiment by putting DCA meter in series with the battery when it is connected in reverse to the charger to see how much current will be when charger is off and when charger is on, try that with fully charged battery and low charged battery, observe the direction of the current flow.

[EasyGoing1]

Re: How do I determine a fuse that I need for a circuit?

It is very obvious that you refuse to learn from the links I provide, I do not understand why I am wasting my time here.

I do apologize, I meant no offense ... I wasn't paying close enough attention but that's no excuse.

I just went and read that second link and I see exactly what he's talking about ... specifically where he said:

If the battery is reversed, the current will not be reversed: it will still flow "clockwise", but both the battery and the charger will "push" it the same way, and the diode will happily let that happen of course

The battery being a voltage source is what I was missing in my thought process ... I was thinking of it purely as a load ... he is obviously correct.

[EasyGoing1]

Re: How do I determine a fuse that I need for a circuit?

In fact, that link is EXACTLY what I am trying to accomplish ... same exact battery charger too ... im going to go back and see what his conclusions were.

[EasyGoing1]

Re: How do I determine a fuse that I need for a circuit?

OK Thats interesting ... he used a resettable fuse in series but then a diode in parallel acting as a shunt if the batter is plugged in backwards... which then heats the fuse and causes it to close ... which offloads enough current from the charger to protect it and when he did this, the current that he measured in reverse through the charger was less than 300mA and we know from my test that it takes 1.6 amps to blow that chip so I think we have a winner!

I would further like to connect something up so that when the battery is plugged in backwards, it makes a noise through little piazzo so that the user is alerted ... or perhaps just a red LED in parallel with the diode with a current limiting resistor would do the trick...

I even have some of those fuses around here somewhere ... lets see if I can get this going by half past lunch time ;-)

[budm]

Re: How do I determine a fuse that I need for a circuit?

"which then heats the fuse and causes it to close" Close? You men blowing the fuse open. One thing about OTC is that once it goes HIGH RESISTANCE and cool down it will conduct again. Do the experiment that is how you will learn, hands-on.
http://www.littelfuse.com/about-us/e...s-vs-ptcs.aspx

[EasyGoing1]

Re: How do I determine a fuse that I need for a circuit?

You men blowing the fuse open.

Yes, that is what I meant

One thing about OTC is that once it goes HIGH RESISTANCE and cool down it will conduct again. Do the experiment that is how you will learn, hands-on.
http://www.littelfuse.com/about-us/e...s-vs-ptcs.aspx

While reading that, I'm curious ... have these "fuses" ever been used for their current limiting abilities, by designing a circuit in such a way that it would only 'partially' open the fuse thus slowing the flow of current without actually going full blown open? Kinda like a variable choke in the right conditions?

[EasyGoing1]

Re: How do I determine a fuse that I need for a circuit?

"Do the experiment that is how you will learn, hands-on.

I can't seem to locate the PTCs that I purchased at the moment ... was looking on some old scrap boards to see if I could find any and I know these are not it, but I'm wondering ... is the component that starts with a 'C' - a capacitor and the one marked 'L' and inductor?

[budm]

Re: How do I determine a fuse that I need for a circuit?

https://www.dcode.fr/capacitor-color-code
http://amateurradio-world.blogspot.c...-codes_07.html
Just lift up one leg off the board and use the cap meter to read its capacitance.

[eccerr0r]

Re: How do I determine a fuse that I need for a circuit?

You could also do it the roundabout way like my 1/2 cell Li-ion chargers, they auto detect polarity and use an H-tree to switch the polarity to the correct orientation...

... but this might be a bit tougher than the original problem statement...

[budm]

Re: How do I determine a fuse that I need for a circuit?

From post #1: I have these very cheap but very useful 18650 battery chargers.
So what kind of charge controller is used in this cheap charger?

[brethin]

Re: How do I determine a fuse that I need for a circuit?

Best solution is don't put the battery in backwards, problem solved.

[EasyGoing1]

Re: How do I determine a fuse that I need for a circuit?

From post #1: I have these very cheap but very useful 18650 battery chargers.
So what kind of charge controller is used in this cheap charger?

The TP4056 ... You can buy 10 of them for around $5

[eccerr0r]

Re: How do I determine a fuse that I need for a circuit?

says 7.99/10 for me. I hate amazon, and this isn't worth $0.50 if it's so easily destroyed as a battery charger...

Technically it's probably for permanently attached batteries most likely and not a generic battery charger.

[EasyGoing1]

Re: How do I determine a fuse that I need for a circuit?

Technically it's probably for permanently attached batteries most likely and not a generic battery charger.

You're probably right about that ... because I've seen similar modules centered around that same chip that are meant to be used as a portable power source - like those things you get that you can plug into your cell phone if you have no access to electricity ... and with those modules, you are supposed to connect two 16550 batteries to the charger permanently so that when you plug it into a power source, it charges those batteries but when its disconnected from power, then it can be used to power other devices that use 5 volts ...

But with this particular module, I'm not sure how you could use the batteries if they were permanently attached to the charger... which doesn't mean there isn't some way to do it, I just can't think of any applications..

But at that price, its too tempting to NOT use them as a general 16550 battery charger...

[Per Hansson]

Re: How do I determine a fuse that I need for a circuit?

This popped up in my feed yesterday: https://www.youtube.com/watch?v=7Tk5ghH_U2s

[budm]

Re: How do I determine a fuse that I need for a circuit?

HT3582DA Charger IC with Battery reversing protection:
https://www.codrey.com/electronic-ci...rger-teardown/