EfunA (Sakura S50) SLA->Lithium conversion

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wookey
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EfunA (Sakura S50) SLA->Lithium conversion

I've upgraded my E-fun A/Erato 1500W/48V/36Ah SLA machine to Lithium (48V/30Ah). The pack is built from headway 38120S 10Ah cells in 16S3P format. Physically each K-long SLA battery is replaced by one 4S3P pack of lithiums. The bike got 30Kg (66lbs) lighter and is now nippier away from the lights (no need for 1st gear any more) and there is no performance drop as the batteries discharge there way there was with SLAs. Range appears to be significantly increased. Overall I'm very pleased, and would say that lithium is much better and worth the extra cost, assuming the longevity is in practice somwhere near what is marketed (2000 cycles).

The actual replacement onvolved taking off quite a lot of rear trim as one pack is quite enclosed. I have created a pictorial to show how this is done because it's not at all obvious. http://wookware.org/pics/moped/lithbatts/

More details of the upgrade are here: http://electricmotoring.forumup.co.uk/viewtopic.php?t=166&postdays=0&postorder=asc&start=15&mforum=electricmotoring

I have also added a cycle analyst which is reporting 33Wh/km (52Wh/mile).

One unexpected benefit is much more efficient charging. LiFePO4 seems to have much better charge acceptance (nearly 90%) than SLA so I am using about 800Wh to recharge rather than the >1kWh I was using to charge the SLAs.

jdh2550_1
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Re: EfunA (Sakura S50) SLA->Lithium conversion

One unexpected benefit is much more efficient charging. LiFePO4 seems to have much better charge acceptance (nearly 90%) than SLA so I am using about 800Wh to recharge rather than the >1kWh I was using to charge the SLAs.

That's a pretty significant efficiency improvement!

Congrats on the conversion. Did you install a BMS? If not, do you plan on doing this? Or are you going to monitor things manually?

John H. Founder of Current Motor Company - opinions on this site belong to me; not to my employer
Remember: " 'lectric for local. diesel for distance" - JTH, Amp Bros || "No Gas.

wookey
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Joined: Wednesday, April 8, 2009 - 06:12
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Re: EfunA (Sakura S50) SLA->Lithium conversion

Yeah, I was a bit surprised about the charging improvement. I've actually also changed the charger so the comparison is not entirely fair. The new one is a cheapo Meanwell power supply with the current limit adjusted. That appears to be 90% efficient @ 350W. The old SLA charger is a bit fancier (charge-state LEDs!) but is based on the same chip so one might think they are similar, but I didn't really measure it.

Currently I don't have a BMS because the one I want (a G/F as developed on Endless sphere) is currently unobtainium (previous version PCBs ran out, new model has had teething troubles and not yet finalised). So I'm operating with 'manual BMS' which turns out to be quite dull. I have posted about that here:
http://endless-sphere.com/forums/viewtopic.php?f=14&t=15247&start=180#p247682

The short version is that yes, cells do go quickly out of balance enough for a few to be above recommended voltages at end-of-charge. I've just turned my chargers down from 56.6V to 54V to try to reduce the risk of overcharging some cells. Clearly one needs to monitor fairly carefully if you want to avoid battery-harm whilst running without a BMS for more than about 6 charge cycles.

I guess some cell types may naturally (or by manufacturer binning) be better matched than others.

Wookey
Sakura s50 (Efun A)

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