NickB6

I don't salvage AGM or lead acid batteries. Those have dangerous chemicals (sulfuric acid) and lead oxides in them. You can have explosive gases, and not to mention the risk of severe chemical burns and environmental damage. I recommend taking them to a recycler who properly disposes of them because once a AGM or lead acid battery won't take a charge anymore or has significant capacity loss, it's not worth salvaging. Some places will actually pay you for them since the lead inside has some value.

I don't have a diagram of a 4s4p, but the same principle applies. You cabn search Google and probably find one. Best

There's a safety feature in the balance board that cuts the battery voltage at a certain point to prevent over discharge. You should be able to charge the battery with the balance charger, but it may be that the batteries have dumped below what the charger will allow for lithium ion batteries (around 2.2 or 2.3 volts). Most balance chargers won't allow it so you need to find a way to safely raise the pack voltage to the point where the charger will allow charging. Are you using an appropriate charger? If your battery is 46.8v you need to charge it at 48 volts at least, so you need either a power supply that will output that voltage at a constant current, or a charger for that battery pack. Ideally, you need to charge the series cells in parallel, so they are all at the same voltage. The p…

There's a safety feature in the balance board that cuts the battery voltage at a certain point to prevent over discharge. You should be able to charge the battery with the balance charger, but it may be that the batteries have dumped below what the charger will allow for lithium ion batteries (around 2.2 or 2.3 volts). Most balance chargers won't allow it so you need to find a way to safely raise the pack voltage to the point where the charger will allow charging. Are you using an appropriate charger? If your battery is 46.8v you need to charge it at 48 volts at least, so you need either a power supply that will output that voltage at a constant current, or a charger for that battery pack. Ideally, you need to charge the series cells in parallel, so they are all at the same voltage. The parallel cells should be okay, so long as your balance circuit is working properly.Let me know if that helps.Nick

Hi. You're right and thanks for the input. Increasing the capacity increases charge time, but we're talking about series cells, so the end charge voltage will be whatever the BMS amd charger allows (within tolerance of course). This is why we use a proper balance charger to prevent overcharging and keep track of cell voltages. The BMS is good, but not a reliable way to charge cells properly.

Wow that's a lot of batteries! Thanks for sharing the tip and glad you liked the tutorial.

Great! Glad to hear you got since good cells out of an otherwise dead battery.

So you got it to work?

Thanks Tony. I actually accidentally bypassed the balance circuit on cell 3 before by connecting the cells wrong and when I try to charge it my charger throws an error for cell voltage not matching. You could try omitting the 3rd and 4th cell and just connecting your balance charger with a 2S lead and that might work. Give it a short and report back. Thanks

Hey thanks!

At the very least you will need some kind of protection circuit. Your charger can balance charge them, but you run the risk of overcharging since the charger can't individually monitor the batteries. The bms ensures the batteries receive equal amounts of charge, so one doesn't finish charging before the other and get overcharged which can be really bad (overheating, venting, fire or at the leas your battery dies from overtemp). It also monitors individual battery voltage and cuts the power if one cell falls below the cutoff voltage of 2.5 to 2.9v instead of letting them continue discharging when one cell is already over- discharged which can damage that cell. If you're using a holder, you can charge them in parallel, but you still need a protection circuit.

No problem! Glad to help.

Hi Chad. So you're a 6S battery. On the balance board especially for 6S boards coming from China, which aren't well marked. The P- might not be marked clearly but It is usually parallel to the P+ solder pad . It might just have minus mark next to it. Kind of hard to see, but check there. Hope that helps!

Thanks for commenting. If you're careful, it will be okay. Quality batteries have safety features that prevent then from exploding except under extreme conditions. However, I wouldn't do it with cheap lithium batteries though since they may not have any anti burst or overheat protection (not to be confused with an internal pcb protection board) in the event you do cause an overheat or overpressure condition. The battery holders are good for low current things like you mentioned, but for anything over 1.5A I recommend spot welded connections or soldered with tabs rated for it.

Very true. The recycled cells won't have the "youthfulness" of when they were new, and won't handle as much load or current draw without experiencing voltage sag, excessive heating, and capacity loss. The aforementioned red Sanyo cells actually did really well and had nearly all of their specified capacity when I recovered them. All very consistent until I thrashed them with my high power flashlight (draws 9.5 amps at full power) and that reduced the capacity by about 35% after a month of light use and the voltage sag was so bad I couldn't run it at that high power for more than 10 minutes. When one cell gets under 2.7 volts the BMS will cut the power and you can't turn it back in until the cell(s) have recovered or you put it back on the charger. I have since put another batte…

Very true. The recycled cells won't have the "youthfulness" of when they were new, and won't handle as much load or current draw without experiencing voltage sag, excessive heating, and capacity loss. The aforementioned red Sanyo cells actually did really well and had nearly all of their specified capacity when I recovered them. All very consistent until I thrashed them with my high power flashlight (draws 9.5 amps at full power) and that reduced the capacity by about 35% after a month of light use and the voltage sag was so bad I couldn't run it at that high power for more than 10 minutes. When one cell gets under 2.7 volts the BMS will cut the power and you can't turn it back in until the cell(s) have recovered or you put it back on the charger. I have since put another battery in there and it's now worn out too, so I'll make another with new high drain INR cells which is really the kind to use for something like this. Anything over 4 amps draw needs needs new batteries if you want them to last and maintain capacity. Thanks

Great job. I made one similar to this. I recycled the housing from an old 3.6v rechargable rotary tool, pulled out the wimpy nicad batteries, and wired in a 5.5mm x 2.1mm barrel jack. I took the 42 volt power supply out of an old HP office jet printer and wired it to a barrel connector to plug into the tool. Voila, the thing ripped at probably 20,000 rpms, but that wimpy motor wasn't powerful enough and got too hot under load. So I took the paper feed and handling motor out of the printer (a lot bigger and had more turns), and modified the housing to hold it. I added a ball bearing to support the collet shaft. Now it really rips! Lots of torque and good power. Nowhere near my dedicated Dremel XPR, but for precise work it's amazing. Just needs a variable speed controler to be perfect.

Hi! You could use an external power supply to charge the battery through the BMS, but that's not ideal if you want your batteries to live a long life. The BMS is limited by the tolerances built into the protection IC, and it doesn't do a great job monitoring individual cells, which may result in overcharging the series cells before it reaches the cutoff voltage (16.8 volts for 4S). Some cells charge to 4.2, and others to 4.25 to even 4.3 volts before the cutoff is reached. That's not good and reduces lifespan and capacity. This is what the balance plug is for. The balancr charger limits and monitors current and voltage and is calibrated to closer tolerances than the actual BMS. I tested my BMS during charging and after with my multimeter and under load, and it indeed does pull the plug wh…

Hi! You could use an external power supply to charge the battery through the BMS, but that's not ideal if you want your batteries to live a long life. The BMS is limited by the tolerances built into the protection IC, and it doesn't do a great job monitoring individual cells, which may result in overcharging the series cells before it reaches the cutoff voltage (16.8 volts for 4S). Some cells charge to 4.2, and others to 4.25 to even 4.3 volts before the cutoff is reached. That's not good and reduces lifespan and capacity. This is what the balance plug is for. The balancr charger limits and monitors current and voltage and is calibrated to closer tolerances than the actual BMS. I tested my BMS during charging and after with my multimeter and under load, and it indeed does pull the plug when anything is exceeded, but you need a charger to get the most out of it. Thanks hope that helps!

Banesync, thanks for the suggestions! I added it to the write-up. I had forgotten that you can short out on the metal can of the battery if touching the positive or negative terminals.

Glad you liked it. Great suggestion. I had planned on it, but never got around to it until today so thanks for reminding me!

I followed your example and built this. I used an 8 quart stainless bowl from Ikea, a cookie tin for the base, and got some tiny drill bits and drilled hundreds of holes for stars and constellations. I used .5mm bits, and only broke 3 drilling the holes. I used my Dremel tool and cooling oil to keep the bits alive. I enlarged some of the holes with .8mm and 1mm bits as well. I ended up using a switch mode power supply/brick from a PC monitor and a DC-DC constant current, constant voltage driver. I tried a 5W LED, ran it at 11 volts and 1100 mA attached to a fan-cooled heatsink to keep the LED alive. It came out nice, except the LED emitter was square even though it seems the LED has segments of individual LED's on the emitter that I only saw when the light projected through the holes. Did…

I followed your example and built this. I used an 8 quart stainless bowl from Ikea, a cookie tin for the base, and got some tiny drill bits and drilled hundreds of holes for stars and constellations. I used .5mm bits, and only broke 3 drilling the holes. I used my Dremel tool and cooling oil to keep the bits alive. I enlarged some of the holes with .8mm and 1mm bits as well. I ended up using a switch mode power supply/brick from a PC monitor and a DC-DC constant current, constant voltage driver. I tried a 5W LED, ran it at 11 volts and 1100 mA attached to a fan-cooled heatsink to keep the LED alive. It came out nice, except the LED emitter was square even though it seems the LED has segments of individual LED's on the emitter that I only saw when the light projected through the holes. Did you have issues like that with the 3W LED? I'm thinking of downgrading to a lower-power LED like 1W or 3W to see if it gets rid of the strange light shape. I will post pictures when I can. Thanks for the great idea!

I was using the wrong capacitor. You need a large size one rated for at minimum 1000uf. Bigger is better. It was too small even though rated at 1000uf and 16v. I salvaged a larger (about 3 times larger) 10v 1000uf from an old power supply and it works fine, but I'm going to swap it out for a 1600uf or maybe a 2500uf I took off an old motherboard. If yours isn't turning on, you may have it wired wrong. The switch goes between the battery and step up board. I broke the circuit connection at the board, not battery. Follow his wiring diagram. It worked for me.

Very nice! I got all the parts together from China after a month and put the circuit together. I'm having some issues though. I was using a 10v 1000mf capacitor. It works fine without the capacitor (just can't turn up the volume without it shutting off) but as soon as I connect the cap to the step up board the voltage output goes from 6.5 to 1.2 and keeps falling until it's down to .5v the battery is still outputting 4.1v but at the output of the charging board it's the same as the output at the step up board. What's going on here? I'm lost. Any help is appreciated!

To get them free, you need to buy something at HC. It can be anything. I have several of these and the little black flashlights lying around that I got free. They work great. I buy small cheap stuff like a $1 set of utility knives or 50 cent box cutter and they give you the light free with the coupon.

Galvanized steel is coated with mostly zinc and tin, and every welder knows that welding galvanized metal releases zinc oxide fumes and other nasty stuff that makes you sick and can kill you you in short order without proper safety gear or a fume extractor/ventilation. "Welders fever" is real. I have heard of that milk trick before but don't know if it works. Wear a respirator made for metal fumes!