I could use a little help. I'm new to electronics, but i'm

I'm no expert... I thought you need breaker or some thing

Something to divert power away from fragile batteries.

I'm interested in this, too

I killed part of my car by using a 15 instead of a 10

>>1189156
I would just buy some overcharge/undercharge protection circuit and not have to worry about my batteries setting my house on fire.

What did you get the batteries off of? If you got it off a drill there should probably be a voltage control circuit in there, then again you can buy those circuits for less than whatever your tearing it out of.

>>1189156
I've got a lot to say about this and other li-ion questions, but I'm going to start my own thread soon.

To answer your question, yes, you can build a simple circuit to protect from 'overdischarge' condition. Basically, it's an op amp used as a comparitor between a reference voltage and the voltage of your battery pack. When your battery drops below the reference voltage, the output of the opamp, which is used to drive a mosfet, goes low and disables current flow. You really need one monitoring each cell which means, in your case, something like a quad opamp in a single chip, and a single voltage reference, which will be a second chip, and a quad mosfet in a third chip.

The question is though, why reinvent the wheel? There are battery management systems that will do all this and more for a couple of bucks, you just have to be patient enough to wait for shipping.

I'm assuming your using 4 cells in series? Search for "4S battery management circuit" these boards are only a few bucks and will monitor each cell individually, even though you are using them in series.

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>>1189156
A single li-ion battery has 3.6V (max. 4.2V min. 3.0V). Three in series get you 10.8V (9V..12.6V) and four in series 14.4V (12V..16.8V). 12V amps usually can handle that and undervoltage protection can also be done.

>>1189237
I'm guessing you'd get Vref from a 555 voltage booster hooked up to a 7812 or something?

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>>1189266
Not sure what a 555 voltage booster is, and no need for a voltage regulator. I'm really thinking something more like pic related.

Just feed it some voltage and it will output a stable reference voltage. You don't need much current from it since an op amp has a high input impedance. Again, you are better off using one op amp for each cell, but you only need one voltage reference. Although, by the time you purchase all the parts, it will be significantly more expensive than just ordering a 4S battery management circuit.

>>1189375
after looking them up. they do look easy to use.

One problem though. they all say for 18650 li-ion and i got 26650 same voltage but 3500 mAh.

Is that a big problem?

>>1189539
The battery size is no problem for the reference voltage, and for the rest of your circuit, which is ultimately a voltage meter, but it does being up another point about limiting the current in your application. If li-ion batteries heat up too much (due to draining current too fast) then they may catch on fire or explode. The way to protect against that is to figure out how much current your end application requires, then put a current limiting resistor in series between the battery output and the amplifier input. Many professionally designed amplifiers will already have an explicit or implicit current limiting function already designed in. It sounds like you may be designing your own amp though, so it's worth considering.

A better way to limit current from a li-ion battery is, again, to use a battery management circuit that limits the current that any particular cell can output, as well as monitor for the under voltage condition that you are already designing for. Seriously, you need a pretty good reason (senior design project, mil spec project, can't tolerate some other parameter of a pre-designed bms, etc) to not just pay the couple of bucks for a pcb that has already been designed, printed, populated, and tested.

What's your reason for reinventing the wheel here? Doing it to prove to yourself that you truly understand how the circuit works, or some professional reason?

>>1189553
A few years ago I picked up half a dozen 26650's from Radio Shack for next to nothing, and I just got tired of them sitting around. So I grabbed this amp http://www.ebay.com/itm/172306482262?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT#rwid some battery boxes and some 15 watt speakers from the trash at work.

And now I'm fucking around with it all.

The end.

>>1189156
Use a zener with an los