MMG-3 lithium ion battery overdischarge??? - Page 1
Forum section: electronics / repair

author: SKHILLBILLYSlures
author_rank: Regular Contributor
timestamp: October 06, 2019, 06:19:13 pm
content: PART A: i know it's a freaking motorcycle battery but im not here about the bike what iam here for is just how incredibly dumb i was to leave my key on overnight in the ole girlOf course without paying any attention i went right on ahead and plugged in a trickle charger/tenderIm about to get made fun ofI woke the next day after a full 24 hour charging session and realized it's lithium ion(Because i really like to pay attention)After it didn't crank my worst $88-$72 fear seems to be coming true i plugged my good ole nixie tube keithley DMM(I still haven't attended equipmholics anonymous) and received a 9.63V DC readingThe batteries maximum Voltage rating is 15V DCUsually i can find out this stuff my self BUUUTTTT i can absolutely not find the data sheetFor other charge characteristics im pretty i did over discharge but before i spend all the money I have, i thought i would Ask?and yes there appears to be a built in bms but i can't tell without a data sheetPART B: should i design my own BMS to go "infront of" the batteryI was thinking something simple like an op amp as a voltage reading that uses a comparatorAnd a small logic circuit to tell if the bike is on and a high current dc relayIntended function is as follows:If the battery were to reach too low of a voltage the op amp measuring would trigger the comparator to send a logic signal to a fet or something like that (i know im being lazy it's more than likely going to be a mosfet but I'm using "fet" as a general term for this rn) then the "fet" would disengage the relay cutting all current and voltage from the bikeI want it to work with my key and have a timer in the logic circuit say off for over 30 minutes and the relay auto disengageand when i turn the key on it will engage the relay if the battery has enough voltage

author: ogden
author_rank: Super Contributor
timestamp: October 06, 2019, 06:44:38 pm
content: I can't tell much about motorcycle batteries, but I know that usually lifepo type is used which have 2.5V per cell "discharged" voltage and 2.0V deterioration voltage (your battery have 4 cells). Your 9.63V was far from critical, seems like built-in BMS did it's job quite well. Just charge battery as soon as you can and it will be fine. Long stay at fully discharged state, especially at or below 8V - that is battery killer. One night at 9.63V will not do much harm. Building BMS with higher voltage treshold will be just waste of time and resources. Not worth it.

author: jogri
author_rank: Frequent Contributor
timestamp: October 06, 2019, 06:53:34 pm
content: Let me put it this way: You want to design something that can cut the power of your bike without warning? Something homebrew that has the potential to seriously harm you should it accidentally engage while you are on the freeway? Something that has to work in a humid, high vibration environment?Are you really shure about this?

author: SKHILLBILLYSlures
author_rank: Regular Contributor
timestamp: October 06, 2019, 07:44:03 pm
content: Well the bike is a KTM exc-F 500 which is outfitted with a computer complete with efiAnd TPS among other fancy electronic "doo dads" so a circuit with proper weather protection is not entirely out of this worldThe engage was a reference to it being in an on or off stateIt would just be a battery switch tied with basically a bms that in the event of failure the bike would just shut off and i pull in the clutch and presumably pop in a new relayNo matter what it's basically meant to be a slightly over engineered switch to combat my non attention paying in order to prevent a serious over discharge situationThey often are the culprit of failures

author: ogden
author_rank: Super Contributor
timestamp: October 06, 2019, 07:48:15 pm
content: Quote from: SKHILLBILLYSlures on October 06, 2019, 07:44:03 pmNah. Do **YOU** have experience of manufacturing automotive grade electronics that withstands wide range of temperature and acceleration?Quote from: SKHILLBILLYSlures on October 06, 2019, 07:44:03 pmYou did not experience serious over discharge situation. Also it is highly unlikely that your ~90$ battery have no built-in BMS. So no worries whatsoever.

author: SKHILLBILLYSlures
author_rank: Regular Contributor
timestamp: October 06, 2019, 07:53:35 pm
content: I think your right because funny enough under the strap it list on the battery that it need to be completely disconnected before chargingNice label location right??Am going try to charge it disconnected and test the voltage in say 3-4 hoursIf it goes up and works fine i will thank you endlessly if it doesn't im going to curse myself out for leaving the dam key on

author: mikerj
author_rank: Super Contributor
timestamp: October 06, 2019, 08:29:02 pm
content: Quote from: SKHILLBILLYSlures on October 06, 2019, 06:19:13 pmWhat kind of battery tender? The usual low current motorcycle battery maintenance chargers are ok to use with LiFe batteries.

author: SKHILLBILLYSlures
author_rank: Regular Contributor
timestamp: October 06, 2019, 11:07:59 pm
content: My neighbor's Harley Davidson tenderOut put:12V DC 750maUpdate my non attention paying knows no bounds [the battery actually has a max charging voltage of 15V and would be considered not fully charged at 14V(duh)]Thanks to the above mathsI realized i was merely hopefully when i tried charging todayOnly to achieve a peak DC V of 13.04 V DCTo then test it and have a half volt drop after load and being disconnected from the circuit and got a 12.4 V DC readingConclusion im going to have to use my warranty powersThanks for your help if you've been hereHaven't gotten to do a job repairing electronics literally everyone is throwing out their old crap instead of calling someone to fix it am totally competent at repair most my own but like the saying goes if you don't keep using it you'll start losing itI'll be back to post a circuit schem in this threadI need to have some jumper leads go off into my airbox so i don't have take my seat offSo i figured i would idiot proof my key in order to prevent this from occuring again whilst simultaneously making the battery chargable without having to disconnect anything other than my air box cover which snaps into place

author: ogden
author_rank: Super Contributor
timestamp: October 07, 2019, 07:16:14 am
content: Quote from: SKHILLBILLYSlures on October 06, 2019, 11:07:59 pmYes, 14V is "not full". Both lifepo4 and lead-acid batteries have surprisingly similar "fully charged" voltages. That's why lifepo4 is often marketed as direct drop-in replacement of lead-acid. How long did you tried to charge it? You may consider to charge for at least 12h and only then make any conclusions. Hopefully that "smart" Harley Davidson tender charger does not become frustrated about li-ion voltage curvesBTW what's capacity of your battery?

author: SKHILLBILLYSlures
author_rank: Regular Contributor
timestamp: November 10, 2019, 09:58:41 pm
content: I tried for over two days plus another symptom the battery had taken a piss was the new one had a night where the key was left on for roughly the same time and the bike cranked right upI know the following isn't a good circuit representation but is as follows to demonstrate logic requirements for the circuit I hope to conjure into existence

author: SKHILLBILLYSlures
author_rank: Regular Contributor
timestamp: November 10, 2019, 10:01:24 pm
content: Here's my crappy representationI'm trying to have the relay switch on only when all three other conditions are metIf one of these fails it must output a zero to the relay controller and therefore allow no current or voltage to flow