Bosch 18v poor-man's BMS?

[LI-ghtcycle]

Hello, I'm looking for the least expensive way to protect my 18v Bosch Li-Ion batteries from damage via over-discharge. I have seen some posts on using BMS systems made for RC applications and such, so I am just looking for some form of preventing over-discharge, but everything seems to be so expensive that it's not really doable with my budget.

Maybe I am hoping against hope for some "pie in the sky" easy solution, I thought maybe there might be a rudimentary circuit that I could build or that would be salvaged off old electronics to offer this protection.

Thanks for reading!

Dayn

 

[gilnet]

are you using pks?or did you disassemble and rebuid pk?if so what is the config?I don't know the answers but I think for someone to help they will need more info.I also think pks have lvc considered in the pks circuitry.Otherwise tool users would be burning them up.no pun intended.much written on dewaults in many threads.

 

[LI-ghtcycle]

Oh sorry I am using the packs as made by bosch to use their charger. Oh, well if it has LVC in the battery, then I should be set, I was of the impression that all that was in the bosch tools (Dewalts have BMS in the batteries, but my understanding was that bosch do not have the BMS in the battery, just in the tool, and I assumed that LVC would be in the tool too?)

 

[docnjoj]

I know my 36 volt Fatpacks have an LVC of 24 volts absolute and cuts them off. I never go near that voltage in real life as I usually stop at about 36-37 volts.
otherDoc

 

[gilnet]

I use konions also.Makita. I got all my pks from an illustrious member of ES who has extensive posts on both bosch and mak.I am working on a pack now and am rereading the posts over(and over).Just put "doctorbass" "bosch" in search and you'll become an expert in no time.Me? I just keep rereading.

 

[John in CR]

I know my 36 volt Fatpacks have an LVC of 24 volts absolute and cuts them off. I never go near that voltage in real life as I usually stop at about 36-37 volts.
otherDoc

Doc,
I don't see how that is possible. The positive and negative slots are hard wired directly to the battery leads. While the LVC may be triggered by the pack's circuit board, it can only be effective when used with the tool, unless you figured out some way to use that 3rd slot in combination with a switch on your controller.

LI-ghtcycle,
Your poor man's LVC could be just to shut it down as soon as your bike begins to slow significantly. The increase in the voltage drop under even a light load once the pack runs low is not a subtle change. It's so significant and rapid, that otherDoc thought his packs turn off.

John

 

[TPA]

The easiest way is Cycle Analyst

 

[heathyoung]

Well, I'm playing with the Makita Konions at the moment, and they have a BMS/Battery monitor circuit, but the LVC is situated on the multipin connector - whose pins are not at all clear in function.

That said, there is a TL431 chip on board that can be used for LVC purposes - its SMD, so unless you are a major tightass you may as well buy a whole lot of normal ones in the 3 pin To-92 package - you can do a per-cell LVC this way + some optoisolators across your brake line ~ easy.If you put an led in series with the optocoupler LED, it wont drain your pack too low (ie. once the voltage dropped across the LED's exceeds the cell voltage, they turn off, removing the load). It also shows you which cell dropped first (handy).

This is where a few other designs fail to address the LVC load across the cells will eventually drain them to below the forward voltage of the LED.

 

[gilnet]

It would be great if you could draw a diagram of this.Does this in anyway have to do with why maks have 1cell pair that drains and causes them to not charge?this,I think was why they had the return epidemic.I have to go reread docs thoughts on that.I think it was that one cell pair was hooked up for info and had small,slow continuous drainage thus making the pk appear dead and nonrechargable.Most pks I get from him have 1-2cells(pr) w low v.and rest are good.OW,my brain hurts.

 

[docnjoj]

I know my 36 volt Fatpacks have an LVC of 24 volts absolute and cuts them off. I never go near that voltage in real life as I usually stop at about 36-37 volts.
otherDoc

Doc,
I don't see how that is possible. The positive and negative slots are hard wired directly to the battery leads. While the LVC may be triggered by the pack's circuit board, it can only be effective when used with the tool, unless you figured out some way to use that 3rd slot in combination with a switch on your controller.

LI-ghtcycle,
Your poor man's LVC could be just to shut it down as soon as your bike begins to slow significantly. The increase in the voltage drop under even a light load once the pack runs low is not a subtle change. It's so significant and rapid, that otherDoc thought his packs turn off.

John

Yep! that would be the way, John. I don't do it cause the sag is pretty obvious at around 34 volts and below. I get about 15 miles with the 4 in //, but wiring them thru the controller shut off would do it. All IMHO, however since I never followed thru on the trial.
otherDoc

 

[docnjoj]

Ya know, John, I may actually have to buy a Bosch 36 volt tool and try this out. From the factory drawings for parts there seem to be no electronics in the tools (drills, saws etc) except the ESC on the trigger. Maybe time for an experiment. And, of course, a new tool!
otherDoc