**Building a Custom Hardcase to Power Your Projects**

To take your projects to the next level, you need a reliable and safe way to power them. One solution is to build a custom hardcase that protects everything and provides easy charging options. The author of this article has successfully built such a hardcase using a 3-cell battery and a latching changeover switch.

**The Latching Changeover Switch**

To build the hardcase, we first need to create a latching changeover switch. This switch is used to control the flow of power from the battery to the device that needs it. The author explains that they broke off five PCB pins and soldered colored wires to them, matching those of the battery's balance lead. The five-pin switch is limited by the number of poles or switches available, so it can only work with four-cell batteries or less. To keep things neat, heatshrink was used to cover the joints.

The author then soldered the other ends of these wires to the middle pin of each pole on the latching changeover switch. Next, they attached a PCB socket and soldered five colored wires to it, using the same wire colors in the same order as the previously made connector. To protect against shorts, electrical tape or heatshrink was wrapped around the joints. The leads of this new connector were then soldered to the latching changeover switch, wired up to the rear pin of each pole so that when the switch is on, they are connected to the wires of the previous connector.

**Reversing the Voltage Applied to the Second Coil**

However, once the relay is on, turning the switch off doesn't turn the relay off, meaning that the battery is left connected. To fix this issue, we need to reverse the voltage applied to the second coil when the switch is turned off. The author soldered a new wire to the circuit's ground output, which goes to the device that needs the power, rather than the one that goes to the battery. This new wire can then be soldered to the middle pin of the last remaining pole on the switch.

Another wire of the same color was then soldered to the first pin of the same pole, so that when the switch is off, it is connected to the other wire. The author notes that this wire should actually be soldered to the top pin of the switch because these pins just go straight through, and it doesn't matter which one you solder them to.

**Adding a Wire to Trigger the Relay Off**

The author also needed to add a wire to trigger the relay off when the push button is pressed. This wire needs to be inserted between the push button and the relay's second coil. The other end of this wire should be connected to the last cell of the battery, which in this case is the fourth wire (red) for a 3-cell battery. If using a 4-cell battery, it would need to be connected to the balance lead's fifth wire.

To avoid overloading the coil, the author used an 82 ohm resistor to drop the voltage from 12V to 5V, which is the rating for the coil. Now that the circuit is complete, we can test it by turning on the multi-pole switch and triggering the relay with the push button.

**Testing the Circuit**

When the voltage drops below the set value, the battery disconnects just as before. However, if you want to turn it off beforehand without unplugging the battery, it's just a case of turning the circuit off, which also now disconnects the battery. This means that you can safely power your projects without worrying about damaging your batteries.

**Building a Custom Hardcase**

To build the hardcase itself, the author used 6mm MDF and added an additional balance lead and power connector to make it easy to charge the battery. These are essentially extensions of the original connectors on the battery, before any circuitry. The case can safely hold everything, including the latching changeover switch, PCB socket, wires, and resistors.

**Conclusion**

Building a custom hardcase to power your projects is a great way to ensure that you have a reliable and safe solution for powering your devices. With this article, you should now know how to build such a hardcase using a 3-cell battery and a latching changeover switch. The author hopes that this video was particularly helpful, and they invite viewers to consider donating to support the creation of more videos like this one.

"WEBVTTKind: captionsLanguage: enPowering homemade projects with rechargeablebatteries is actually more difficult thanit sounds.This is because most battery types cannotbe over-discharged, as doing so may damagethe battery and make it unstable.Consumer electronics overcome this issue byusing clever battery protection circuitrythat constantly monitors the battery's voltage,automatically switching the device off ifit gets too low.Unfortunately these protection circuits arenot readily available separately, so in thisvideo I'm going to show you how to constructone yourself, allowing you to make your ownprotected battery pack to use in your ownprojects.To make the circuit you'll need the followingitems.The finished circuit is compatible with mostlithium based batteries, which is a very commonbattery type used in devices from smartphonesto radio controlled models.I'll be using a 3 cell 8000mah battery packfor this project.It cost only $42 from Hobby King, so it'sa lot of power for the money.It's intended for use with RC models, whichmeans it has an extremely high current capability,making it ideal for use with high power projectslike my 100w LED light panel.One thing to keep in mind is that lithiumbatteries are usually wired in series to increasetheir voltage.Each battery is referred to as a cell, usuallyhaving a nominal voltage of 3.7v. As minehas got 3 cells, and each cell has a voltageof 3.7v, the total pack voltage is 11.1v.Lithium batteries like this usually have balanceconnectors.They're basically little wires going to thepositive end of each cell, and are requiredfor this build.If you want to learn more about battery packsand how to calculate how long they'll poweryour project for, Afrotechmods has an excellentvideo on the subject, a link to which is inthe description.To keep the project simple we're going touse a battery voltage alarm as the circuit'sbase.This alarm beeps loudly when the battery dropsbelow a value you select, so we're going torepurpose this action to trigger a latchingrelay, which when triggered will disconnectthe load from the battery.Before we begin it's important to note thatlithium batteries if abused can be dangerousand even catch fire in some circumstances.You must always use a proper charger and setit up correctly for your battery pack, andexercise extreme caution against short circuits,using a multimeter to check everything beforeyou hook it up to a battery.I've put a link in the description to an articleall about how to care for these batteriescorrectly, so I highly suggest giving it aread if you're new to them.So, with that out of the way, let's begin!The circuit has two options.One is the simple option, which just includesthe cutoff circuitry, while the other addsan on-off button, which is ideal for selfcontained packs but makes things more complicated.Many of you will be fine working of this diagram,which you can also find in the description,but for those of you who are less confidentI'll walk you through it step by step.So the first thing to do is prepare the batteryalarm by removing the two buzzers.To do this without any desoldering tools,grab the buzzer and touch your soldering ironto each of its contact points whilst pullingthe buzzer away from the circuit board.You'll need to alternate between each contactpoint until it comes free.Now it's time to solder some wires to thesecontact points.As the buzzers were wired up in series, weneed to use these two contact points.So solder on a black wire to the negativepad, and a red wire to the positive pad.Next trim down your breadboard to measure13 holes wide by 28 holes long, with the tracesrunning the longer length of the board.Now you can bend the pins on the alarm downwardsusing a pair of pliers and insert it intothe breadboard.Make sure that its far left pin is in thethird hole from the bottom and the fourthhole from the left, and solder it in place.Now we need to break nine pins off our PCBheader strip and solder it inline with thealarm but on the bottom row of holes.Because the alarm beeps when it's first pluggedin, we need to add a push button to act asan on trigger.This pin on the left is the negative pin ofthe alarm, so we'll push the momentary pushbutton in line with this pin above the alarm.We can now flip the board over and use a knifeto break the copper strip between the button'spins, and then solder it in place.Now it's time to add the latching relay.This particular relay has six pins.Two are the switched contacts, and the othersare coils.If either of these coils is given brief power,it will switch the relay either on, or off,depending on the polarity.As we want the push button to turn the relayon, we need place the relay on the board abovethe alarm, with the second set of coil contactsin line with the push button.When the button is pressed, a circuit willbe made with the second cell, sending a currentto the coil and switching the relay on.So we'll again scratch the copper off betweenthese pins, extending the cut right to theedge of the board, and solder it in place.To complete the circuit we need to bridgeto the third pin of the alarm, which is thepositive contact of the battery's second cell.As the relay is rated at 5v, but the secondcell is 7.4v, I used a diode to drop the voltagedown slightly.You can also use a 10 ohm resistor, or evenjust a wire bridge if you want, as it shouldstill be able to handle it for brief periods.We can also cut through the four copper stripsbelow the switched contacts, but we won'tsolder them quite yet.Now we can wire up the alarm to the othercoil, so trim down the wires we added earlierand poke them through the board, with thepositive wire going next to the upper coilpin, and the negative wire going next to thelower coil pin.We can now bridge the wire contacts to theadjacent coil contacts.To smooth out the alarm's voltage pulse, weneed to add a 100uf capacitor.It just goes parallel to the coil, with thepolarity matching the wires we just added.So now we can give it a go.So if we plug the battery's balance connectorinto our circuit, we should hear a littleclick as the relay switches 'off', assumingthat it was on to begin with.This is because the alarm beeps when it isfirst given power, and we've configured thebeep pulse to trigger the relay off.So to switch the relay on, we can press thepush button.Again, we can hear a little click as it switcheson.So with the basic circuit complete, we cannow solder a power wire to each side of therelay's switched contacts.One of these wires connects directly to thebattery's negative terminal, and the othercan continue on to the device that needs thepower.The battery's positive wire can just be connecteddirectly to the device without anything inbetween.So we'll plug in the battery's balance lead,and press the push button to trigger the relayon.The alarm has been set to trigger at 3.7v,and sure enough, as soon as the alarm detectsthat one of the cells has dropped below thisvalue, it trips the relay and the batterysuccessfully disconnects from the load.For general use you should set the voltagecut off to 3.5v, at which point you can simplydisconnect the battery and recharge it.So this is a really practical circuit thatwill protect lithium based batteries frombeing over-discharged.But what if you want to take it to the nextstep by adding a switch to turn it on andoff, rather than having to unplug the battery?Well, to do this we need to add a six polelatching changeover switch between the balanceconnector and our circuit.The idea is that when in the off position,it disconnects all of the balance leads fromthe circuit, and also triggers the relay offso that the battery is also disconnected fromits load.So to add a switch for this we need theseextra components, the most important of whichis the six pole latching changeover switch.A six pole latching changeover switch basicallyhas six completely separate on-on switchesinside it.Each switch has three sets of pins.When it's turned on, the middle pin of eachset is connected to the pin just behind it.When it's turned off, the middle pin getsconnected to the pin just in front of it.The first thing we'll do is break off fivepcb pins and solder some coloured wires tothem, preferably matching those of your battery'sbalance lead.Why five pins?Well, as we've only got six poles, or switches,to work with, it means we have to limit theswitch to work with four cell batteries orless.You can always use a nine-pole changeoverswitch if you need to use it with a highercell count battery.To keep it neat we can use some heatshrinkto cover the joints.Now we can solder the other ends of thesewires to the middle pin of each pole on thelatching changeover switch.Now we can get the pcb socket and solder fivecoloured wires to it, taking extra care touse the same wire colours in the same orderas the previously made connector, with theblack ground wire on the outer edge.Just like with the previous connector, wecan we can wrap some electrical tape or heatshrinkaround the joints to protect against shorts.The leads of this new connector can then besoldered to the latching changeover switch.They need to be wired up to the rear pin ofeach pole, so that when the switch is on theyare connected to the wires of the previousconnector.We need to match the colours too.So the finished switch should look like this,and when connected to the alarm and balancelead, it should turn the circuit on and off.However, once the relay is on, turning theswitch off doesn't turn the relay off, meaningthat the battery is left connected.What we need to do is get the switch, whenturned off, to trigger the relay also off.We'll do this by reversing the voltage appliedto the second coil.To do this, all we need to do is solder anew wire to the circuit's ground output.This is the one that goes to the device thatneeds the power, rather than the one thatgoes to the battery.This new wire can then be soldered to themiddle pin of the last remaining pole on theswitch.Another wire of the same colour can then besoldered to the first pin of the same pole,so that when the switch is off it is connectedto the other wire.Here you can see that I've actually solderedit to the top pin of the switch - this isbecause these pins just go straight through,so it doesn't actually matter which you solderthem to.The other end of this wire can then be solderedto the circuit, above the relay and in linewith the second coil.Now we have one last wire to add.This wire needs to be inserted between thepush button and the relay's second coil.The other end of this wire needs to be connectedto the last cell of the battery to triggerthe relay off.As I'll be using a 3 cell battery, that meansI'll have to connect it to the balance lead'sfourth wire, which in my case is red.If you're using a 4 cell battery, it wouldhave to be connected to the balance lead'sfifth wire.Again, I'm going to connect it to the upperpin as it's getting a bit cramped on the otherside.Remember, it needs to be connected to thepole's front pin, so that it only carriescurrent when the switch is turned off.To avoid overloading the coil, we can usean 82 ohm resistor to drop the voltage, whichis around 12v for a 3 cell battery, to 5vwhich the coil is rated for.So now the circuit is complete!Let's give it a test.We'll turn on the circuit with the multi poleswitch, and then trigger the relay with thepush button.When the voltage drops below the set value,the battery disconnects just as before.But now if you want to turn it off beforehandwithout unplugging the battery, it's justa case of turning the circuit off, which alsonow disconnects the battery.So the last step is to build it into a customhardcase to protect everything.I used 6mm MDF to make mine, and as you cansee, I've also added an additional balancelead and power connector, so that it can becharged easily.These are basically extensions of the originalconnectors on the battery, before any circuitry.Now you can safely power your projects withoutworrying about damaging your batteries.If you've found this video particularly helpful,I've actually set up a PayPal donation accountif you feel inclined send a tip my way.All donations go straight back in to buyingthe resources needed to make more videos likethis one, and are warmly appreciated.So, thanks for watching, and I hope I seeyou in my next video where I'll be showingyou how to build a solder fume extractor tohelp keep you safe when soldering.Bye for now!\n"