PING Pack BMS cuts out early when > 100F

[mcstar]

I'm at just over 1000 miles on my 10AH 48V ping pack. Everything is just great with it except that I keep tripping the low voltage BMS cutoff after only 7ah whenever the temperature outside is over about 100F. In the mornings when the temp is below 80 or so, I easily can put 9AH+ on the pack, but on the way home this week the temperature is about 100F it cuts out at about 12miles. I'm thinking about adding a computer fan to the pack, maybe loosing some of the duct tape, I've even thought about changing out the resistors on the BMS with some higher quality ones. Has anyone else had to deal with this problem?

 

[dogman dan]

Not yet but I'm expecting it. I bought the 20 ah size to hopefuly avoid issues with the battery being able to deliver less power when at desert temps. I haven't had a 100 degree ride home yet, but have had some in the high ninteys. I did notice the battery was good and hot by the time I got home, an hour of hard ride. Since I heard you should not charge a real hot battery, I used a square aluminum cookie sheet to make a container for the battery. The aluminum was cut at the corners and folded, in such a way as to avoid sharp edges, into a sort of a bread pan shape around the battery. The battery now is cooler when I get home, and cools off much faster after a ride. The aluminum makes a kind of heat sink to transfer the heat away faster. I also ventilated the battery bag I carry it in better. An I put the BMS where it does not touch the battery directly. At hardware stores you can buy aluminum tape, for use on hot ducts. I just had the cookie sheet handier, and wanted some bash protection. Another Idea I did not do since it was harder to fit on the carrier, was to put the battey in an Ice chest, with a cold pack or two under it, and some type of way to keep the battery above all that, dry. That's two now I know of with 1000 miles on a duct tape pack. Hooray! I'm hoping for 5000 miles a year, for at least two or three years. Good luck and tell us how your solution works out.

 

[mcstar]

Those are some good ideas dogman. I'm thinking about a combination of some of what you said. I ecspecially like the idea of themally seperating the BMS from the battery. My suspision is that the resistors in the BMS are drifting due to the temperature and tripping off earlier than normal. If I disconnect for as little as 30seconds, then reconnect, the pack is usually at least 50V. I doubt it's really low on capacity. I'll update here of my progress in this issue.

 

[recumbent]

I used a square aluminum cookie sheet to make a container for the battery. The aluminum was cut at the corners and folded, in such a way as to avoid sharp edges, into a sort of a bread pan shape around the battery ...

That's a clever idea, dogman. I'm going to look for a bread loaf pan to fit over my battery pack tomorrow Great idea , thanks.

 

[dogman dan]

A lifetime in the desert has taught me to keep my cool. Here's a pic of the funky cookie sheet wrapped around my battery. I searched all over and couldn't find a bread pan that fit. So I just folded a big square cookie sheet around it. I could have bought some sheet aluminum, but the cookie sheet was allready in the kitchen. It's far from pretty, but the cookie sheet keeps my battery much cooler. It was getting pretty hot, and now it is just gets warm to the touch. When I ride home it's about 90% uphill for an hour, 12 miles, and one mile of it is very steep.

 

[mcstar]

I did what you suggested and found a used aluminum baking pan in the kitchen. It was just the right size so that it fits snuggly around the battery. I fastened it with a single strip of duct tape once I got it all wrapped up. After two trips into work and back I can say it definately helped a lot. The battery stayed much cooler on both trips. The wrapping is a very good heat sink. On the way home I did get one cutout, but it was near 100F and I was riding WOT the entire way. I don't think the whole thing gets much air flow inside the soft pack I have it in. After the first cutout, I unplugged then re-plugged in the battery made it another 5 miles at about 75% throttle with no further issue. This is much better than previous times that left me peddalling without assistance and an overheating battery. I think I'm going to design a mount for a CPU fan using some sheet metal and pop rivets this weekend. Then I'll cut some slots in the Al wrapping to get some good airflow through the battery.
Thanks for the ideas! Maybe this will help someone else. I'll post pictures of the solution I come up soon.

 

[mcstar]

I now think that one of my pack's cells my have lost it's connetion with the rest. I've noticed that the cutouts alwasy seem to happen at the same place, after about 4.8AH of discharge, whereas I used to get a solid 9.5AH or greater discharge. This has ocurred even with entire battery pack iced down and kept cold the entire trip. This pack is arranged in a 2p16s arrangement, so I'm starting to think that at least one of the cells in one of the 16 2P arrangements has come loose. Has anyone else trouble shot/fixed an issue like this. I plan to tear the pack down this weekend and look for loose connections. I'll post some pictures when I get in there.

 

[TylerDurden]

Has anyone else trouble shot/fixed an issue like this.

Checked here?
http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=4303

 

[mcstar]

Thanks TD, that thread is very helpful. I'll give the suggestions there a whirl this weekend.

 

[dogman dan]

Bummer, I've wondered how much abuse those little foil tabs could take when whacking the bumps. One of the reasons I went full suspension for the commuterbike. But hey, all I want is for the ping to last till something better doesn't cost more than a tho. If it lasts me the summer, I'll be happy enough. When it breaks, I can't wait to take it apart!

 

[mcstar]

Whew, that was work! I spent last night tearing the pack down and correcting the issue. I found 2 cells in 2 different places that had tabs that had come loose. Reconnecting them was tricky. Soldering directly was useless. The tabs were underneath pc boards which made access to them difficult. I had no intention of trying to remove the PC boards so, I was working with limited space and access. I tried several approaches to reconnecting them. Finally, I came up with something that seemed to work well. What I did was, I fashioned small clips out of a 1/4" strip of sheet metal and rolled one end of it up creating a clip with approximately the shape of a capital G. Then I slipped the tab into the open end of this clip and squeezed it onto the remaing tabs of the battery making a good electrical connection. Then I was able to solder the clip in place and finally I soldered copper wire to the clip. This seemed to create a strong firm connection. I tested all the connections I made and they all seem good. Now I just have to put everything back together.

 

[dogman dan]

We must have pics of that! Hooray for you!

 

[kbarrett]

Box these batteries up, people.

They are too fragile to be kicking around in a nylon bag.

Use a metal ammo can or something similar, and pad it in case the can gets shoved off the bike.

 

[dogman dan]

No kidding. That baking pan saved mine when I crashed . The battery was undamaged, but there was a road rash on the corner of the baking pan and a new hole in the bag. Finally i got the right size metal toolbox, but I'm keeping the baking pan since it fits so good.

 

[catfish]

Newbie here. Building my first ebike. Currently trying to anticipate issues of battery heat and potential vibration damage. I splurged most of my Bush economic stimulus check on a Yesa LiFePO4 36V 10ah battery. hope the check shows up soon.

kbarrett , glad to hear that someone else has used the idea of ammo can. i just bought one before reading your post. I also bought an army surplus tool bag which just fits snugly inside the 6 X 7 X 11 ammo can. My idea was to keep the battery in the bag and just lower it into the ammo can when riding, either drilling holes in the can for the wires or slightly propping the lid open for the wires. Then if i have to park somewhere, i can take the bag in with me to avoid battery theft and if i need to charge it. The ammo can will sit bolted onto my homemade rear rack made of angle iron.

So i guess my question is: Would the bag inside the can (with limited ventilation from the wire holes or lid slightly open) be too hot of an environment for the battery? I was also going to line the bag with about a half inch of spongy packing foam to reduce shock from bumps. Afraid this might be like a little Easy Bake oven. I am in Texas where it's been in the 90's and will surely hit 100 in July if not sooner.

My bike is an old Fuji mountain bike and has no shocks, so i'm trying to balance using cushioning spongy stuff in the battery container without creating a Thermos.

Thanks for any tips. This forum is great.

 

[e=mcsquared]

hey techs yet to have it be an issue but when i wrapped the pack in corrugated plastic that heat shrinked, first i am hearing of a hi temp issue with ducktap packs
should it be a prob some solutions might be wrapped in air tubing channeled threw even the existing infrastructure of the courigated plastic,
however i have a fan on my bag that might cool the pack,
sadly hence i haven't hit the heat of summer it remains to be seen how the pack with thrived.

have two packs like winter/ summer tires

anyway if it quits lags or disappoints keep you posted on any changes

first off i agree when 20ah should be 20ah, a constant drain on the pack might be a variable.

if user tops of the pack before the pack loses it charge?
a sitting pack does it lose capacity if not used shortly after being charged?


when the packs cuts out
at what voltage?

i have a 20ah ping 36v
so using the full 20 isn't impossible to do but rarely use it 4

 

[dogman dan]

Mcstar and I live where its HOT. Cool compared to Phoenix though, but 90 degrees F and in my case no humidity to help with air cooling. I tried to lean all I could about my new battery, and one thing I noticed was they said don't charge it hot, or in a hot place. So as it got warmer I began to wait a bit to start charging, and wait a bit more, and more. So I did the heat sink thing Just to speed up the process. Coming in from 12 uphill miles at 92 F my battery was at least that temp, and felt warm to my 98 degree hand. In the morning I could not feel heat on the battery but that was back in may. The battery is supposed to tolerate heat well while discharging, but the bms may be another story. I was just wanting to plug in to charge just a bit sooner and now when my battery is warm, it cools much quicker. We'll see after I heal a bit more how I do in 105 heat. I just got the doc to let me ride again yesterday but I'm sticking to cool mornings for now. Mcstar turned out to have a different reason for his cut out, and mine never has.

But box em up for sure! When I flipped the bike last month that baking pan sure saved my battery. I'd been hunting an ammo can too but all the good surplus stores here are gone. Fortunately my wife had the steel toolbox.

 

[mcstar]

Here's an update to my early cutout problem just so noone else is mislead. I started researching the LIFEPO4 chemistry and found how they are supposed to have such great stability even at higher temperatures. This started me thinking that maybe I was mis-diagnosing my problem. As it turns out, temperature was not really to blame. I opened up the pack and found that one of the cells had broke loose and was no longer connected on one tab. Since the batteries are wired in a 16s2p configuration, the other cell in parallel with it was taking all the load while one with the broken tab was not taking any. Well, I was able to come up with a way to reattach the tab but in the process broke another cell loose I became suspicious of this being issue after I realized that my cutouts always happened at around 4AH (ie 1/2 the pack's capacity). Eventually I got the tabs fixed and all batteries re-connected, but in the process blew my BMS! Uggg again. Now I'm waiting for Mr Ping to send me a new BMS (and a couple spare batteries).

 

[dogman dan]

Ouch! Now that I can ride agan, I'll take mine out on a 100 f day this weekend and climb some hills so we can put this to rest. I still think ventilating the bms is a good idea. When I start out , the pack will be at about 120 f from the garage so I can put it to a good test.

 

[fechter]

Eventually I got the tabs fixed and all batteries re-connected, but in the process blew my BMS! Uggg again. Now I'm waiting for Mr Ping to send me a new BMS (and a couple spare batteries).

Thanks for the report.

Got any blown Ping BMS's lying around you want to send me for reverse engineering?

 

[mcstar]

fechter, if you're willing to post your progress and some schematics for us all to use, maybe we can work something out. How ironic that we will be reverse engineering a Chinese circuit.... :lol: I cannot stop giggling! Kinda goes around and comes right back! They've taken the precaution of scraping the markings off the ic and Mosfets. Kinda silly since their functions are pretty obvious. It would be cool to make our own board like this one that didn't have the Mosfets, but instead had an output that could drive the controller's brake line. I know others have worked on this, but I've never seen the completed project.