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YAEBU! (Yet Another Emax Battery Upgrade) project

Posted: Wed, 23 Jan 2019, 23:40
by xphread
Hi All.

Have been an EV lurker for a while and popped in to the occasional EV meeting or event, but most of my EV plans and projects have taken a back seat until now.

A little while ago, I acquired an eMax "sport" scooter - sans batteries. Fingers crossed this is a largely uneventful process of buying new batteries & a suitable charger, connect it all up, re-licence and go. (haha... I project has been without unforeseen detours)

So, without wanting to burdening one person in particular any more with my "brain dumps", I thought I'd post up my current thoughts to confirm I am on the right track... and hopefully learning from others if I am going astray, or learn from others experience if there is anything I should be watching out for.

I have a fairly strong knowledge of electrickery (I think) - but most of my work has been in very low voltage and current applications I am concerned that there is quite likely some knowledge blind-spots in regards to high power applications. (This project is just part of my continued learning)

My current thoughts from other's projects (mainly the "similar" eMax 90/110S etc) are :
I probably want to bump battery voltage up to ~60V and between 40 to 60Ah - depending on space and cost.

I have the "safe" option of purchasing a pre-used battery pack known to work in a emax 110S (which would probably set me back about $2K with a charger, or closer to $2.5k for new LiFePo4 batteries)

...but I was thinking that this might be a promising alternative option:

------------------------TLDR; version start here...--------------------------------------------------

10x 12.6V, 30Ah -"high power" Battery pack ... st=ae803_3 (5 in series to get 63Volts, and 2 of these in parallel to get 60Ah and half the current draw from each "half pack") The continuous current draw is quoted as 60 Amps, so that means the "5S2P" configuration should be happy with 120A continuous (which should be plenty for this scooter, so the battery back will not be overly stressed (no???) Advert claims: Built-in BMS protection,With overcharge, over discharge, short circuit protection (so that means nothing else is required apart from a relatively simple, voltage regulated charger?)

Then a suitable(?) charger: ... st=ae803_3 (15S as the individual packs are 3 cells in series, and I am putting 5 individual packs in series?)

Am I missing something? (price will end up closer to $1000 - which seems more reasonable/justifiable in relation to the value the scooter will have once running)

Thoughts? (I know these are cheapish chinese cells, but they are given a fairly high rating and somewhat technical specs are claimed, (when other "local" sellers of imported cheap cells (eg Ebay shops) often won't give technical specs and are very vague on ratings etc)

Are those wires attached (as per the photos) sufficient? (Should I cut them back and attach more heavy gauge wire from the cell?)
I have to double check the physical dimensions of the packs fits in the original space - but I can sort that. (reduce capacity by using 20Ah packs, or even fit a top box etc if needed...)

Anyway... this is a start. Please hit me with any knowledge/suggestions/reality checks.
Thanks in advance!

Re: YAEBU! (Yet Another Emax Battery Upgrade) project

Posted: Thu, 24 Jan 2019, 07:19
by Adverse Effects
that charger wont work with the packs built in BMS's, so you will have no balancing

and if you just use the BMS's that are built in to the packs then you will need 10 smaller chargers

Re: YAEBU! (Yet Another Emax Battery Upgrade) project

Posted: Thu, 24 Jan 2019, 07:41
by xphread
Hmm.... At first I was thinking of using similar packs of 48volts in parallel, (that came paired with their own chargers) but I couldn't find any that could guarantee the current required...

When I found these that had the right current supply, I thought it would be easy to bump the voltage to 60... But maybe not.

The intricacies of BMS is something I know is what I don't know... :(

I can only at a high level appreciate that the internal BMS's in series might not work with a charger at the full series voltage (which is why I am here, thanks!)... But if using 10x 12v chargers (which would be a bit of a hassle as 10 plugs or a very unwieldy single connector) would the batteries need to be isolated from each other during charge? (for example if the negative of each charger has the same reference voltage with respect to the mains... Would it not cause shorts/alternative current pathways?... Or are the low voltage/DC side of (all?) chargers isolated or floating(for a lack of a better word) ?

Re: YAEBU! (Yet Another Emax Battery Upgrade) project

Posted: Thu, 24 Jan 2019, 07:49
by xphread
Would it be better/doable to buy the packs for salvaging the cells, rip out the BMS and install a different BMS with a new configuration?

Re: YAEBU! (Yet Another Emax Battery Upgrade) project

Posted: Thu, 24 Jan 2019, 12:39
by Richo
I don't know about the e-max but the similar scooter I have does fit 8 Leaf cells with a bit of modifying.
8 x 7.6 = 60.8V nom
But they're a bit harder to get these days :(

Re: YAEBU! (Yet Another Emax Battery Upgrade) project

Posted: Thu, 24 Jan 2019, 12:46
by Richo
xphread wrote:
Wed, 23 Jan 2019, 23:40
10x 12.6V, 30Ah -"high power" Battery pack ... st=ae803_3
That link took me to a battery that is either 1C or 2C at best and in no way "high power".
Realistically you could only assume ~500 cycles.
So working out the $/L equivalent you'd be better off buying premium for a petrol scooter.

Re: YAEBU! (Yet Another Emax Battery Upgrade) project

Posted: Thu, 24 Jan 2019, 15:41
by antiscab
I have a bit of a hate hate view of the old Emax sport.

You'll need to add a torque arm or similar to the hub motor. If you don't, it will rotate in its housing one day.

The speedo cable tends to get pinched between the forks and the frame.

The original motor controller is a bit hit and miss. You can run 60v, but the dc-dc won't support it. If going for more speed and power, I'd recommend a better controller. You can do a shunt mod to get more acceleration out of the present one.

In stock form, the controller draws Max if 75A from the battery. With a shunt mod you can get this as high as 170A. Don't do this without the torque arm, as that fails even at 75A.

The original chargers also had a high failure rate, though not so difficult to replace.

The battery box is an odd shape, so panel cutting is needed to get anything useful to fit. Though if you don't need much range, that might not be as much of an issue.
My old Emax used from memory 0.75Ah/km at 60v, from memory