12v lithium motorcycle batteries low voltage cutoff ?

[eHomer]

I'm still thinking about 12v lithium batteries for my small electric outboard on my canoe, and maybe supplementing my 36v Lithium battery to 48v for occasional ebike use.

In a previous thread I started, there was a suggestion of using a lithium motorbike battery as a complete self-contained ready made unit.

I was wondering if motorbike batteries have LVC functionality though.
I understand that draining a lithium pack below it's minimum voltage can kill the cells permanently. I know that ebike controllers have LVC circuitry, and a lot of ebike lithium pack BMS's have LVC too, but what about these lithium motorbike batteries ?

In Shorai's FAQ, at http://shoraipower.com/faq they warn "However, most modern street bikes have a draw even when key is off, to support clock, computer, alarms, or other devices. This draw will eventually drain the battery, which is damaging and could void your warranty."

So that sounds as though they don't have an inbuilt LVC, because if they did then they would shut off before the cells got too low ?

It still seems strange though, surely a motorbike battery could easily be run right down if the engine doesn't start while cranking ?

 

[Deleted member 4366]

It looks like those ones don't have a BMS, which is really bad news, and makes them very expensive for what they are.

I just bought another three of those 4S lipo hard-packs for my outboard. Mines 58lbs force I think, so a bit more powerful than yours. I've decided to try it at 16v instead of the previous 12v becuse it was OK in the harbour, but I could do with a bit more power for the open sea. My main boat's out for the winter, so it'll be April before I get a chance to try it.

 

[eHomer]

Yes, they're certainly expensive, especially without having a BMS.

I've been googling them and there's quite a lot of discussions going on in motor bike forums, where they are attractive mainly because of their very light weight compared to lead acid.

The Shorai batteries do have a 5 pin "balancing" port to give access to each cell for their dedicated external charger which does balance the cells correctly, but only when charged off the bike, via the mains.

When connected for discharge and onbike charging, via just the neg and pos 12v posts, there's no BMS protection at all, or LVC.

I suppose that's because they're primarily designed for motorbike starting, rather than deep cycle, so they should normally stay topped up.

The wiring of the balancing port is standard taps at 0v, 3.3v, 6.6v, 9.9v, 13.2v, so presumably an external BMS could be connected ?

I wondered if even a standard ready made BMS with LVC could be connected up somehow ?

I have visions of a neat little 2kg padded bag with about 30ah of 12v lithium in it for use with my outboard or as an ebike battery 36-48 "booster", complete with BMS, LVC, fuse, and one of those small digital voltmeters that I bought after advice from an earlier thread on here !

 

[eHomer]

Well I've jumped the gun now...

I tried an ebay bid on a Shorai 12v 27 AH PBEq LiFePO4 battery , and got it for £80, where the new price in the UK is getting on for £300.

http://www.batterystuff.com/batteries/shorai-lithium-lfx27l3-bs12.html

I've googled them quite a bit and I'm hoping that the built-in balancing port will allow me to connect a 12v BMS, to enable LVC protection, and cell balancing when recharging. Shorai use that port for a dedicated mains charger, but it has no LVC function because these batteries are normally fitted in motor bikes for starting, rather than deep cycle use.

I know it may sound daft, but it does weigh less than 2kg, giving me 27ah, of which hopefully 80% (21 ah) will be usable.

The balancing port is wired with a connection between each of the four cells, so I'm hoping that the 12v BMS from eclipsebikes should just connect up as is, giving me full BMS with LVC protection, just like my 36v ebike Lithium packs.

I was thinking of this one: http://www.eclipsebikes.com/lifepo4-144v-cell-50a120a-p-1061.html at £39.99

Do you think that would work ok ?

Or anything better or cheaper ?

 

[jateureka2]

I think that BMS would work.

I'm interested in using a couple of lithium motorcycle batteries as a replacement for my Aprilia 24V NiMh battery and stumbled onto this thread. The ones i was looking at are specified as safe for charging on a normal lead acid battery charger so I was thinking they must have built in protection for over charge. I was assuming the LVC on the controller would be enough for over discharge protection.
Here is a link to the one I'm looking at, it's an SSB PowerSport Litium prismatic cell battery
http://www.ebay.com.au/itm/SSB-12V-LH4L-BS-LITHIUM-MOTORCYCLE-BATTERY-YTX4L-BS-YTX4LBS-YTZ5-S-YTZ5S-HONDA-/281163288474?pt=AU_Motorcycle_Parts_Accessories&hash=item4176a34f9a

As this is for starting a MC, it only gives 130 CCA rating though, not Ah.. and only $85 AUD delivered.

 

[eHomer]

I'm afraid that purchase was a mistake on my part.

I was fooled by the advertised capacity as 27 ah, when in fact that was the somewhat devious PbEq rating, which evidently means the "same as" an equivalent rated lead acid battery, so the damn thing only has 9ah cells internally. Shorai then recommend that they be discharged by no more than 50%, so I'm only going to get 4.5ah per cycle.

Quite useless for the intended purpose, powering a very lightweight canoe electric outboard motor.

I posted my tale of woe on a subsequent thread, here: http://pedelecs.co.uk/forum/threads/watch-out-for-pbeq-ah-ratings.16688/

Lithium motorcycle batteries are ideal for starting motorbikes, with the high CCA and long standing charge life, but pretty useless and overly expensive for anything else. !