I am going to be getting some SLABs to use in various portable, high power applications. This includes RC stuff, portable heating/cooling, and other projects. The SLABs are 12V 35Ah. I may discharge them at 100A in certain applications. While that may not be ideal, they should be able to handle it. They may be configured in series or parallel (still no more than 100A will be drawn). That means 12V and 24V. The batteries have an internal resistance of 10mOhms, meaning I can only really have a few milliohms of resistance in my protection circuits and wiring.
I need a circuit breaker in case of a short. It would be very dangerous if there was not one. Additionally, I need overdischarge protection to avoid damaging the battery. For overcurrent protection, there are many commercial solutions that are economical. But for overdischarge protection, I could not really find anything that can handle the current and is economical. Ideally, a board would integrate both protections and allow for 12/24V operation. But that is not really available. So I think I will have to go with a DIY solution for overdischarge. Given how catastrophic shorts can be, I will go with this reliable commercial breaker. Having two switches is certainly undesirable due to added resistance and cost, but seems like the only option here.
So here is my idea. I could use help finding the parts for certain things. I could also use feedback on it. This is a rough schematic.
I would first have the breaker. Then there is a linear reference of 6V. It would use some 27uF filtering caps, which may be overkill but should not hurt. But it can vary from 5-6V, based on a trimmer/divider. This represents an undervoltage of 10-12V, a reasonable range. If it is not adjusted properly, it will not destroy it completely. Then this is then compared to half or a quarter of the battery voltage. Two in series would have twice the cutoff voltage. If it is under that reference voltage, it turns on its output. This resets a s/r latch. It can only be set by a no pushbutton. When it is on, it turns a mosfet on that turns the main switch on (probably a relay). I did not put the mosfet in the schematic because it was getting kind of crowded.
I have no idea what to look for in a comparator or s/r latch. If people could give specific suggestions, from mouser, that would be very helpful.
For the switch, here are the requirements. I have looked around but the relays I found consumed too much power when on. The mosfets did not look like they could handle the current (puny leads) and had too high on resistances. Additionally, SMD would be hard and annoying to solder (and might overheat it dangerously), so leaded or another package is ideal.
-less than 800uOhm on resistance
-actually rated at least 140A, continuous
-less than 1/2 a watt consumed when on (meaning a large coil resistance for a relay). A latching relay would also be good, but I could not find any viable options. This is one of the major limiting factors I have found. The problem with NC is it would consume too much power from a dying battery. And it should fail open, not short, if something happens to the control circuitry.
-less than $20. Ideally cheaper.
This thread stems off of this one. It seems that after a few days, no one pays attention to your post anymore.
Thanks in advance for your help,
Live Wire
I need a circuit breaker in case of a short. It would be very dangerous if there was not one. Additionally, I need overdischarge protection to avoid damaging the battery. For overcurrent protection, there are many commercial solutions that are economical. But for overdischarge protection, I could not really find anything that can handle the current and is economical. Ideally, a board would integrate both protections and allow for 12/24V operation. But that is not really available. So I think I will have to go with a DIY solution for overdischarge. Given how catastrophic shorts can be, I will go with this reliable commercial breaker. Having two switches is certainly undesirable due to added resistance and cost, but seems like the only option here.
So here is my idea. I could use help finding the parts for certain things. I could also use feedback on it. This is a rough schematic.
I would first have the breaker. Then there is a linear reference of 6V. It would use some 27uF filtering caps, which may be overkill but should not hurt. But it can vary from 5-6V, based on a trimmer/divider. This represents an undervoltage of 10-12V, a reasonable range. If it is not adjusted properly, it will not destroy it completely. Then this is then compared to half or a quarter of the battery voltage. Two in series would have twice the cutoff voltage. If it is under that reference voltage, it turns on its output. This resets a s/r latch. It can only be set by a no pushbutton. When it is on, it turns a mosfet on that turns the main switch on (probably a relay). I did not put the mosfet in the schematic because it was getting kind of crowded.
I have no idea what to look for in a comparator or s/r latch. If people could give specific suggestions, from mouser, that would be very helpful.
For the switch, here are the requirements. I have looked around but the relays I found consumed too much power when on. The mosfets did not look like they could handle the current (puny leads) and had too high on resistances. Additionally, SMD would be hard and annoying to solder (and might overheat it dangerously), so leaded or another package is ideal.
-less than 800uOhm on resistance
-actually rated at least 140A, continuous
-less than 1/2 a watt consumed when on (meaning a large coil resistance for a relay). A latching relay would also be good, but I could not find any viable options. This is one of the major limiting factors I have found. The problem with NC is it would consume too much power from a dying battery. And it should fail open, not short, if something happens to the control circuitry.
-less than $20. Ideally cheaper.
This thread stems off of this one. It seems that after a few days, no one pays attention to your post anymore.
Thanks in advance for your help,
Live Wire