Battery Safety

[llile]

Got a brand new battery from Ping (PING batteries is a great company)

I very carefully wrapped the ends of the cable in electrical tape, and set about terminating them with anderson connectors. Very soon I pulled off the tape to work on the second terminal. I watched, in slow motion, like Bruce Willis running away from an exploding car, as the two bare terminals wagged closer to each other, and I realized a moment before they were going to touch - POW! Dammit! I took all kinds of precautions too. Such a spark is bad for the battery, and can ruin the BMS. Not immediately, the FETS will blow up after a few weeks use, right in the middle of a big ride. This also ends up ruining your charger, and you are stuck in the middle of no where with a charger that smells like a campfire. BTDTGTTS.

What do people do about battery safety? Do you use fuses, if so where, what fuse? Do you use safety disconnects? If so, what kind? How do you go about working on a battery without shorting it out? What procedures? I am getting ready to build a 72V pack, 2X as dangerous as a 36V pack.

[biohazardman]

I use an on off switch for the battery power viewtopic.php?f=3&t=32463 as well as an inline fuse and always tape any loose wire to battery connections, I am working on, until I have them securely soldered or screwed down. Otherwise showers of sparks and plasma spew everywhere. I use an automotive fuse that is right at or just under my max controller amperage. Have only blown one in 5K thusfar.

[dnmun]

if you disconnect the sense wire ribbon cable from the BMS, then the BMS will turn off and it cannot short out to the positive terminal.

if you look at the BMS, you will see a white rectangle printed on the pcb near the charging FEt on the v2 signalab. in the middle of the rectangle are 2 through holes for a thermal switch not used on this BMS but which would turn off the BMS if the battery overheated. the rectangle is on the other end next to the sense wire plug on the v1 signalab.

in between the two holes you can see the trace that connects the two holes. the circuit current for the BMS runs through that trace and if you cut the trace open and then install a switch, remotely on the dashboard of your bike, with a wire connected to the two holes, then you can turn the battery on and off at the BMS with that switch.

then you can short it out all you want while the BMS is turned off and nothing will happen. also you can use that as the main power switch for the entire system and the switch doesn't have to carry more than a few milliamps to control all the current the battery can provide. or it can be a tiny micro switch that is activated when you sit on the seat. so when you get thrown off the bike, it will turn off the battery.

[CamLight]

If possible, I never have more than one terminal exposed at a time. If I do, it's inevitable...BANG!
Even with only one terminal exposed, I always wear glasses just in case. I've picked tiny balls of copper out of my shirt too many times to want a doctor have do that to my eyes.

Once I get the pack connected to the BMS, I have no worries about anything happening to the pack unless it's physically damaged. I can even dead short the wires and only about 60A flows and that's only for 250 microseconds or so. Without the BMS, over 1,100 amps would flow. Found that out the hard way during a capacity test that happened to have the right equipment in place. Now THAT was an interesting flash!

[dogman]

Well, you just learned lesson one. One bare wire at a time, never two.

Lesson two, after you put the color coded covers on, check polarity one more time. Amazing how many times I've mixed em up, though I was positive I had it right.

[llile]

Well, you just learned lesson one. One bare wire at a time, never two.

Lesson two, after you put the color coded covers on, check polarity one more time. Amazing how many times I've mixed em up, though I was positive I had it right.

Thanks for stating a very obvious, but hard to follow rule! It gets worse, I wasn't just applying Andersons (that would be relatively easy), I didn't mention that I am working on a series-parallel battery pack, so there are two 36V batteries in series and eventually another such pack in parallel. The reason for this is to keep swappable batteries for all my E-bikes - one is 36V and the other is 72V. In order to do this you neet a couple of Schottky diodes, one in series and one antiparallel with the pack. (Li Ping sez so, don't argue with him. He tells me that the series diode helps protect the BMS from overvoltage and is required if you do this with his batteries, the antiparallel diode deals with surges due to motor inductance. I have a long thread explaining the physics behind this.) So it is a tricky operation, and there is a point where you almost have to have two bare (shudder) wires.

I think the first step from now on will be to install a fuse, and pull the darn thing before working on anything else. Then I can work on the diodes and stuff "Cold".

Oh Yeah, I always wear safety glasses in the shop, even if I am sweeping the floor. I was born with dust magnets in both eyes. I have a 14 year old buddy that sometimes helps with hacking, and I regularly upbraid him for not having his safety glasses on, or propping them up on his head. The first act, before entering the shop, is to put on the specs.

[dnmun]

i would be interested in understanding the physics of this like you mentioned. i have asked several times for people to explain to me how the lack of the diode will cause the pack to be damaged if the output mosfets turn off. it just seems that if they are off, then no current can flow so i don't understand how they can be reversed charged as richard said.

the irfb 3055 mosfets can withstand 55V so if there is still some voltage, say 36V in the pack then it should withstand up to 91V applied to the terminals. and where does the 91V come from?

[dnmun]

really, i would like it if you posted up the thread about why the diodes are needed.

does the diode have to be high voltage equivalent to the battery voltage?

when combining dissimilar chemistries in parallel, the diode only had to be rated at the difference in voltage between the two packs when discharged, so how do you know what value to use for the lifpo4 packs, and really why are they needed. i really would like to know.

even with graduate degrees in physics and EE, i still don't understand how it works to damage the battery. so please post up the thread if you will.

[dogman]

Fails to understand the need to have + and - bare at the same time. Work on one wire, cover it, uncover the other wire, work on it.

I do repeat commonsense stuff like this a lot, because commonsense is not common.

Re the diodes, perhaps Ping started this originally, just as a cover his ass kind of approach when asked about connecting bms protected batteries. With diodes, he could be sure nothing could possibly happen. No chance of a dufus connecting a charged battery to a discharged one causing a problem with the diodes in place.

[John in CR]

really, i would like it if you posted up the thread about why the diodes are needed.

does the diode have to be high voltage equivalent to the battery voltage?

when combining dissimilar chemistries in parallel, the diode only had to be rated at the difference in voltage between the two packs when discharged, so how do you know what value to use for the lifpo4 packs, and really why are they needed. i really would like to know.

even with graduate degrees in physics and EE, i still don't understand how it works to damage the battery. so please post up the thread if you will.

Here's a quote from Fechter's post from 4 years ago. This is the topic to put it in context http://endless-sphere.com/forums/viewtopic.php?f=2&t=4046&p=59990&hilit=diode+series#p60076. I don't know much now, and certainly didn't know anything back then, so if a guru tells me put a diode, then I put a diode...in this case a reverse diode.

John

...In series, you need the reverse diodes across the battery to protect the BMS from the other pack. You would also need to check to see that the chargers were isolated or disconnect the packs for charging. Otherwise, I don't see any issues with putting them in series.

[d8veh]

One other point about battery connectors: Always put a female connector on the battery so that you don't have live prongs exposed that can touch a bit of metal and short out. The same if you have a Cycle Analyst, Speedict or Wattmeter shunt in line: On the side that connects to the battery, male connector, and female on the controller side, then male on the controller.

[dnmun]

ok, i thought the guy had a thread to explain why.

i have followed richard's comments, including the recent one about reverse charging the pack that shuts off. i even wrote ping and explained i thought he was introducing diodes for no reason, but he didn't reply either.

it just seems that when the mosfet is open, there is nothing that can happen to damage the pack. that's how i see it. even if the controller is a dead short, should not cause current to flow imo. stumped.

i do know that the diodes prevent regen and they also get hot and soak up power, and nobody else uses them from what i have seen.

but this guy can be safe just by disconnecting the sense wire plug, and short it out to his hearts content with no risk. i still like using the switch on the BMS circuit current trace though. better than expensive contactors. jmho.

[rodney]

I have a similar problem, id need some help with..
Ive done what i thought i'll never do:
connected my battery to itself... Big spark, some bad smell, connectors (4mm bullets) toasted..
I checked may pack (4x 6s 5000mAh lipo) with cell log immediately, 3 batteries were fine, last one
said cell error.. Using a multimeter it was still 25v (i charge the whole pack at 50v, and it was hot
off the charger when i blew up)...
Couple minutes later cell log did read the last pack, and all cells were fine, balanced and not dead..
I made some new wireing (or is it wiring?), tried to make sure this wont happen again, but now i am scared for my
pack.. Its only couple days old... Is it possible that it wasn't damaged? Or it will just blow something
when i try to charge/discharge them?
I have put car fuse (25A) on + side of my pack, but that wire on fuse looks so thin...

Sorry for my english, bad student

[Alan B]

Use fuse holders and fuses rated for the proper voltage and current. No thin wires or shoddy fuse holders or inadequate voltage fuses.

Plan your work. Tie things down, cover them up and work cold when possible. Bullet connectors are very dangerous due to their polarization issues. Shorts are easy to form with bullets. Procedures and color coding are helpful, but not always adequate. Minimize this type of work, don't require it for every charge cycle. Only do this type of work when alert and focused.

Safety is a combination of Planning, Engineering and Procedure. Try to minimize the Procedure part, Engineered safety is more reliable than procedural protections. Planning is key.

Powered connectors should always be shrouded. Loads can be exposed when unpowered. But when charger meets battery there are two power sources. Normally the charger is current limited and the battery may not be so the battery needs the greater protection. But dual shrouded connectors are best so both sides can be protected.

Have fun and be safe,

[bigmoose]

I was making two new batteries for my portable scopes last night... If I were working with LiPo I would have a couple of KFF this morning!

Lessons learned:
1) The batts came with shrinktube on the positive tabs. I should only have removed the one that I was trimming/soldering at the time. Would have been first KFF.

2) Watch where the trimmed tabs fall. Remove each piece as you cut it from the work area. Mistake was tooling picked up a piece of trimmed tab and dropped it into a partially finished stack. This would have been KFF #2.

3) How did I forget to take my wedding ring off? Stupid... stupid... would have been vaporized ring and KFF #3.

I survived the stupidity of my actions, and was saved only by the meager power in 4/3A size cells and not by my safe practice of battery assembly.

[rodney]

Thanks for advices..
Cells do seem to be fine ,discharged them to 3.74-5v, all still balanced... Charging them now,
will see how it goes.. I ordered bms (same time as batts) it should come in a week or two, then
i will build battery box and hopefully make sure that this doesn't happen again...