Milwaukee battery question.

[b7100]

I have a 9.0 aftermarket battery that I have replaced the 15-18650 cells with 2800ma 30a cells. Now the charger won't charge and the fuel gauge is lit constantly. Did I mess up the bms or do I have something else wrong. My knowledge is limited so I hope I've explained it right

 

[amberwolf]

It's possible the BMS is one of those types that detects if any cell goes out of whatever limits it's designed to check for and then bricks itself (permanently disabling the output and input). Disconnecting cells and then connecting new ones would cause it to do this, because at disconnection the BMS would read nothing.

It's also possible that there's simply a poor connection from the BMS to the cells on one of the balance wires (if it has these).

Other things are also possible, but we'd need more detailed info on how the system was setup / wired / etc before the modification, what cells it had before, and how it is setup / wired / etc now, and what cells it has now, and what testing has been done so far.

 

[b7100]

Thanks for the reply. I don't have nor know how to provide that information. Is it possible to just jump from another 18 volt battery to charge it or use another charger. Would replacing the bms work? I have an 18 volt porter cable charger-could that be used somehow.

 

[docw009]

Since you mentioned 18V, I am guessing this battery is arranged in a 5X3 matrix. That would be five series groups, with three cells in parallel per group. At full charge, you would have 21.0 volts from positive to negative. At nominal charge, each group is at 3.6V, for 18 volts, which is why they call it an 18V battery,

The BMS will shut the battery down if any of the five groups are below 3 volts, although this number varies with the BMS. it is typically set at 2.9 to 3.0 volts. This is a safety requirement. Most cell makers set the absolute low point at 2.5V. You want to measure all five series groups and see what you have.

If any of the groups are above 4.2 volts, that is the max charge voltage, and the BMS will inhibit charging if it is working right,

 

[amberwolf]

Is it possible to just jump from another 18 volt battery to charge it or use another charger. Would replacing the bms work? I have an 18 volt porter cable charger-could that be used somehow.

If you don't know why it isn't charging normally, then continuing to try to charge it risks starting a fire.

BMSs are primarily intended to prevent cell damage that can lead to that kind of problem.

 

[amberwolf]

I don't have nor know how to provide that information.

I'm confused: If you don't know how it was wired before, or what type of cells it had, how did you replace the cells and know they were the right kind, and wired the right way?

If you replaced the cells yourself, then how do you not know how it is wired now, or what cells are in it now?

 

[calab]

On some tool batteries you have to do fine surgery replacing the bad cell, putting the new good one at the right voltage to parallel connect with the bad one, then disconnect the bad cell. The pcb smart board consistently monitors and if anything is out of whack it bricks itself. Like if the pcb smart board cant balance a cell because its too low, the tool battery bricks itself in the name of bottom line and safety.

 

[Slowchris11]

You should, at least, have a voltmeter. Measure the voltage of each parallel cell pack. Remember, you have 5 times 3 cells in parallel which are connected in series to give 5x 3.6V which makes it a 18 Volt battery. So we need the actual voltage of each of these 3.6V packs.
If you are lucky, these are far appart. In this case you can charge the low ones to match the higher voltag and a conventionel BMS will work again.

 

[b7100]

I'm confused: If you don't know how it was wired before, or what type of cells it had, how did you replace the cells and know they were the right kind, and wired the right way?

If you replaced the cells yourself, then how do you not know how it is wired now, or what cells are in it now?

The cells that were in it had no markings other than 19650. Beeing from China its hard telling what they were. I assume they might be recycled from dead powertool batteries. Original 9.0 Milwaukee batteries would have been 3000mah 15a. I used 2800mah 30a replacements. The drill does run a bit slower than the original 8.0 battery. I labled the old ones before I took them out. They were 5 banks of three and they were welded with nickel strips so it would be hard to cross wires.. Forgive me for the confusion. This is a learning thing as much as anything.

 

[b7100]

You should, at least, have a voltmeter. Measure the voltage of each parallel cell pack. Remember, you have 5 times 3 cells in parallel which are connected in series to give 5x 3.6V which makes it a 18 Volt battery. So we need the actual voltage of each of these 3.6V packs.
If you are lucky, these are far appart. In this case you can charge the low ones to match the higher voltag and a conventionel BMS will work again.

All cells were replaced with new. All measured 4.1 VOLTS. If I replace the bms board would that get it going?

 

[b7100]

On some tool batteries you have to do fine surgery replacing the bad cell, putting the new good one at the right voltage to parallel connect with the bad one, then disconnect the bad cell. The pcb smart board consistently monitors and if anything is out of whack it bricks itself. Like if the pcb smart board cant balance a cell because its too low, the tool battery bricks itself in the name of bottom line and safety.

Can I replace the pcb and get it going?

 

[docw009]

Sounds like it is partly going, if it runs your drill. Perhaps your meter is off, and the pack is at full charge already? Also sounds like you have crappy cells that cannot supply the required current, if the drrill no longer has its original speed.

 

[b7100]

Sounds like it is partly going, if it runs your drill. Perhaps your meter is off, and the pack is at full charge already? Also sounds like you have crappy cells that cannot supply the required current, if the drrill no longer has its original speed.

Cells are molicell p28a 2800mAh 35a. The fuel meter stays lit all the time. Drill runs ok although slower. And the charger flashes red and green when plugged in. Original 9.0 Milwaukee battery used Samsung 30q 3000 mAh 15a cells.

 

[b7100]

Can a porter cable charger somehow be used to charge a Milwaukee battery if they are both 18 volt?

 

[Slowchris11]

Do all the 3.6V tripples have the same voltage, now, while they are connected? Only then will the charger start.

I suppose the battery is a cheap copy part. In this case the BMS does not have a fault memory function and should work after simple reconnecting.
If you did anything right, the BMS may be defective, too. Sometimes you can't say who killed what first. Defective BMS the cells or defective cells the BMS. You need a 5S BMS.

 

[b7100]

Do all the 3.6V tripples have the same voltage, now, while they are connected? Only then will the charger start.

I suppose the battery is a cheap copy part. In this case the BMS does not have a fault memory function and should work after simple reconnecting.
If you did anything right, the BMS may be defective, too. Sometimes you can't say who killed what first. Defective BMS the cells or defective cells the BMS. You need a 5S BMS.

They all have the same voltage. Im assuming that it is the bms. The fuel gauge stays lit.

 

[calab]

Can I replace the pcb and get it going?

I have no clue, I just know that some major, reputable, tool companies have batteries with bms/pcb that "brick" themselves on purpose so they do not work anymore making them non-functional.