replacing lipos by headways

[TheBMallory]

hey all,

I've built an electric drift trike that is using a 48v hub motor+esc.
https://www.youtube.com/watch?v=ReGFIBujli4

It is my first serious build and coming from the RC hobby, I powered it with the lipos I had laying around.

It is currently running of a 12S2P 5800mah lipo battery pack with no BMS (which is just a pain to balance, and I'm not too comfortable having this much lipo in my house). I've been reading this forum a lot lately and wanted to know this headway battery pack would be suitable for a 20A or so continuous discharge current (30A max) :
http://www.greenbikekit.com/lithium-battery/lifepo4/headway-48v-15ah-40152-lfiepo4-pack.html

Unless there's a big no-no that I haven't noticed, I think I'll give this a go...

 

[friendly1uk]

Says 150 so 20 should be nothing to it.

Look at the weight though. About double your lipo, or any other chemistry for that matter.
Headways will pay if you use them to commute every day for about 4 years

 

[TheBMallory]

yeah I know about the weight. My lipo pack is about 4Kg so yes it's the double, but I'm willing to have this trade off if it's really safer and less of a hassle to charge with a bms... Allright pulling the trigger right now !

 

[dnmun]

why not just use a BMS to balance the 12S lipo pack when you bulk charge? or go to 15S or 16S with a BMS by adding pouches.

if you have the balancing charger now then you can balance it initially and then the BMS will keep it balanced after that and protect you from over discharge and short circuits on the output.

the BMS will protect it from overcharging so you will not have to worry about fires from overcharging. that is really a red herring anyway. fire is more likely to be caused by shorts on the output.

 

[dogman dan]

Yes, shorting the leads of any battery is a big danger. And there are other ways to set a lipo pack on fire, like dropping a pack that was just overdischarged. Or having a hole develop from rubbing in the battery box.

If you want more safety, lifepo4 is a smart choice, but if you want to keep the battery light and small, then the now popular 18650 NMC pack is a good choice too.

Both tend to come with bms protection too.

 

[TheBMallory]

actually I already spotted a damaged cell in one of my 4S pack ( I put all my packs in a military ammo case when not in use so I guess it's good to go... for now). And yes, even though i Put some foam in my box, vibration and mounting and unmounting them for charging tend to produce some wear on wrapping of the packs. If Lifepos are like friendly1uk said "you put it and you're good to go for 4 years", then I'm ok with that...
I did research about the NMC chemistry but did not find a proper 48v pack supplier (i'd rather not having to solder everything myself), I'll keep this option for future projects but the lifepo is allready bought now

 

[dnmun]

what do you mean by damaged? has the pouch swollen and ruptured and is leaking electrolyte?

 

[TheBMallory]

when balancing, one cell jumps back and forth from 3.3 to 4.2 volts or so
edit: also the pouch is a little bit more swollen than the other ones. but no leaking that I could find

 

[dnmun]

that is a bad connection in the JST plug and not the pouch itself. since you do not use compression on the pouches there is always gonna be swelling with no compression to prevent it.

 

[TheBMallory]

I thought of that too and tried moving the pack a little but it didn't seem to have any effect (voltage still jumping). I saw that this week so I didn't have the time to open the pack itself to if the was any loose solder... I may give it a try this weekend (already did that once or twice in some of my smaller packs) but, having to deal with this is partially why I'd like to switch to safer and better packaged batteries

 

[dnmun]

lipo is safe. it takes a lot of overcharging and having the pouches all wrapped up in 'insulated by foam' boxes to force it into thermal runaway. but if you have a balancing charger that will keep it from overcharging.

you can take your pack with the bad pouch apart by stripping the shrink wrap back from the top by cutting with scissors in the corners and then peeling it down the pack. remove the white plastic strip that wraps around the pack and that exposes the top of the pouches.

if the white plastic piece is glued to the sides of the end pouches then just cut the white shielding plastic at the top and that will give you access to the top of the pouches. then you can resolder the loose sense wire to the top of the pouch if that is where it is disconnected.

 

[TheBMallory]

I indeed have a serious charger that does balancing (this is the only way I charge my batteries)... I don't think I'm a beginner with lipos, I used them when building an electric longboard, some fixed wing RC planes and multirotors... but yeah for some reason that giant pile of 6 4S pack seems like a bit too much for me... I'll investigate that broken pack this weekend and keep you posted

 

[dogman dan]

The larger the pack, the bigger the fire if it does all go off at once. That's for sure.

I'm not trying to be a fear monger. But people with no experience at all will read stuff, and think they can abuse their packs in other ways and be safe just because they have a BMS. That's not what people said, but being green, they will read it that way.

So I keep saying over and over, Don't store or charge RC lithium cobalt in a place you wouldn't build a fire. When I harp like this, the comment is not aimed at you, the creator of the thead. It's for the zillion 12 year olds out there reading this.

Really scary to me, is guys that permanently build the RC shitpacks into the frame buried in inaccessible battery containers, then would never have any clue if one cell started puffing, or got a corner squashed rattling around in the box.

Protecting the pack with some rigid material that adds compression is a super smart idea.

 

[MrDude_1]

Really scary to me, is guys that permanently build the RC shitpacks into the frame buried in inaccessible battery containers, then would never have any clue if one cell started puffing, or got a corner squashed rattling around in the box.

I am also annoyed by when manufacturers do that with phones, mp3 players and other devices... they're also the exact same cells.

 

[dnmun]

no they are not. the cell phone pack is 1S and is only about 400-600mAh. these batteries are 50X to 100X in capacity.

 

[MrDude_1]

no they are not. the cell phone pack is 1S and is only about 400-600mAh. these batteries are 50X to 100X in capacity.

I am still annoyed I cant get to them without the risk of destroying the device. Especially if the battery is bad, and I can just replace the pouch... IF I COULD TAKE IT APART.

 

[dogman dan]

Worth noting as well, the quality of manufacture of phone batteries is supposedly a lot better than RC packs. There are still phone fires, but less likely, and a smaller fire than a big bike battery.

Re that damaged cell, As long as the corners aren't crushed, and chafing just damaged the shrink wrap, you should be ok. Big dings or holes in the actual cell foil could be dangerous. If it stinks, it's leaking.

I like the idea of protecting the cells, either by compressing them in hard materials, or at least putting some coroplast around a pack assembly. The idea is rub something thick that can tolerate some chafing. Shrink wrap doesn't cut it.

It's just about impossible to prevent all movement of a big heavy battery as you ride, crash, tip the bike over, etc. But you can make a box so tight fitting that the cells never move around in the box. Then the inner box goes in the bag, pannier, or battery container.

Hard shell packs are popular, but the cells can still chafe inside the little box. Once they puff some, they'll stop moving in there.

 

[TheBMallory]

quick follow-up : my lipo was indeed leaking (stinking + I could actually see the electrolyte sheets). I put it in a fireproof place in my backyard while waiting for the "garbage collector" (is that the right word? English isn't my primary language) to come.
and I finally received the 48v lifepo pack : it is indeed bigger and heavier, but it looks like I could do a cleaner job with it than I did with the lipos.
I think my mistake was not having an appropriate housing for the lipos. you have to make sure they don't move, but you also have to be able to check them once in a while.

 

[dnmun]

if you post up a picture of your old lipo pack we can show you how to salvage the remaining good pouches. they need to be in compression just like the lifepo4 pouches. only the cylindricals in metal cans can live without compression.