LiFePO4 for EVT?

[lemmiwinks]

G'day!

I've got an EVT 168 which is currently running 4 50Ah SLA batteries (approx 14kg each for a total of 56kg for the pack). I'm wondering what Ah capacity LiFePO4 battery I could replace them with? I'd go for a drop in replacement something like this:

which happens to be a 20Ah unit.

Would 20Ah LiFePO4 be comparable with the capacity of 50Ah SLA? The range I have currently with SLA is fine for the use the scooter gets, I'm not looking to increase that, but if I can get the same range and cut the weight of the battery pack from 56Kg down to 11.2kg I'd be pretty darn happy.

According to the website they're made from a bunch of 18650's and a BMS but it doesn't say if I need a special charger or not. The EVT comes with a 3 stage 48V charger (actually I suspect it charges as 2 24V strings, but I've not 100% verified that) for the SLA, does anyone know if these can be used with LiFePO4, are the BMS that good? What about battery equalisation? Using PowerCheq's right now but I know they're not needed for lithiums, so can the BMS take care of that too or would I need a separate 12V charger for each LiFePO4 pack?

Sorry for all the dumb questions.
Cheers.

 

[TylerDurden]

Long time...

Those units should be ok with sla chargers... but only time will tell.

Do you know the max amps you pull? That will be key to judging the longevity of the LiFe, for a particular size.

 

[Battboy]

Is your Scooter a 24V. or a 48V. System. What is your current spec for the whole package i.e. ? Volts / ?Amps = SLA.

Best,

Don Harmon

 

[commanda]

The EVT, as sold in Australia, came with 48volt 50AHr of SLA. The EVT motor specs says 43 amps stall current, although the controller says 120 amps.

But, even if the peak amps are 120, that's still only 3C for a 40 AHr pack, perfectly doable with Thundersky.

I have just ordered 16 of the TS 40AHr cells from Trev at Foundry and Fibreglass
http://thebackshed.com/foundryandfibreglass/listing.asp?intpage=1&action=%3E&Cat=EV+Conversions

and got $1.80 per AHr as part of a much larger order he was placing. That's AU $1152 all up, plus shipping from Qld when they arrive.

The cells should fit in the EVT battery space by laying them on their side, and weigh about 25 Kg, saving about 30Kg.

I'm building my own BMS following Bob McRee and Gary Goodrum's original circuit here;

http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=3345

although they are now working on a newer version, which they plan to offer as a kit.

For a charging source, I picked up 3 switch mode chargers from Soanarplus, 24 volt 6.5 amp (MP-P225) for $36.12 each plus 10% gst plus shipping, about $128 all up. The similar looking 4.5 amp version I have for something else has an adjustment pot which varies the output from 19-27 volts.

Maybe I'll have the first lead-free EVT in Australia?

Amanda

 

[Battboy]

Commanda - Are you sure you are buying LiFePO4 from Thundersky and not Li-Ion ?

Don

 

[commanda]

from Trevs website: LFP Lithium Ion cells designed for electric vehicles.

from Thundersky:
Models : TS-LCP , TS-LFP , TS-LMP

Electrochemical system : Lithium , Phosphor , Iron , Fluorine Compound

Electrodes


Negative electrode
Carbon/Graphite
Nano Cellulose


Positive electrode
LiFCoO 2
LiFFePO4
LiFNiMnCoO2

So, to answer your question; Yes.

Amanda

 

[Battboy]

OK, it's just that the link you posted went to a page showing Lithium - Ion not LiFePO4 ? Just wanted to make sure you are getting what you want because there are big differences between the two chemistries which have been explained on this forum already.

Best of luck with your scooter!

Don Harmon

 

[safe]

LFP is correct in that it's their LiFePO4 cell.

I think he got it right.

Patrick was selling these here a while ago "on the side" (not as a business).

 

[Battboy]

I think Amanda is a she Don't think it's the same cell as Patric was selling either, but who knows - she didn't show any pictures of the actual cells. Thundersky makes their own LiFePO4 packs. You are right they call them LFP. I wish everyone would just say LiFeP04 especially companies that do make multiple chemistry offerings !

Don

 

[safe]

I think Amanda is a she

Oops! My apologies....

 

[Patrick]

Back to Lemmiwinks question.

Figure you'll get about 35 Ah out of your 50 Ah SLA. More if you go real slow, but as I remember, that isn't your style . . .

In terms of size, here are some good data points. The cylindrical cells (PSI or LiFeBatt) are a little smaller than equivalent lead. As an example, you can fit 8 x 10 Ah cells in the same space as an EB-20 (B&B 20 Ah, 12V SLA), so they are about the same.

On the ThunderSky, you can fit 20 LFP40s (i.e., 60 volts worth) in the same space as 4 12 V, 50 Ah SLAs. So you can certainly fit 16 LFP40s in the 168. It would be sweet to put in the 20 and do a 60V conversion for an extra 25% more speed - but not if you have hills. That upgrade can burn brushes.

You will need a BMS, or a very healthy bank account. The EVT charger is 2 24 v chargers with half taps, so the idea is that each 12 V batt gets it's own charger. Good idea, poor execution. Many failures with that charger. Anyway, it doesn't matter - convert to Lithium and get rid of it. The PowerCheqs can be sold - you won't need those either. Gary and Richard are building a nice BMS/LVC for 16 cells that should be available by the time you need it.

Either way is good. The PSI cells have higher peak discharge, but you don't need it. The TS will hit 120A no problem, and most of the time you be pulling much less. Given the price of TS these days, they are about 1/3 the price (TCO) of lead even with the worst scenario.

Good luck!

 

[lemmiwinks]

Hi everyone, thanks for the replies! It's been quite a while, but I find myself at home with some time on my hands which naturally leads to plotting wacky upgrades...

Max current not known for sure as I've not measured it, but as Amanda says the stall current for the motor is supposedly 43A so I would have to assume it couldn't be more than that.

Patrick, you recall correctly I've been tempted by the 60V upgrade, but it's pretty hilly where I live and combined with my riding style the brushes would be toast in no time flat for sure. I figured that the weight saving of about 45kg would probably be worth it just for the simple fact that it would bring the weight closer to that of a 50cc ICE scooter, so the thing should actually ride better, as well as accelerate and climb better too.

I don't really want to build my own pack, which is why I like the idea of the SLA sized drop in replacements like the ones here:
http://www.ev-power.com.au/-Lithium-Ion-Batteries-for-Electric-.html even though they're certainly not the best value for money (though they do include a BMS). The theoretical budget won't extend to the 36Ah drop ins so I might need to shelve it. The other thing I liked about using the 20Ah units was the fact that I should be able to fit 2 in the space where one 50Ah SLA used to be which would give me a whole lot of underseat storage 8)