YAVLiC - Fitting the Li battery

Received the battery. 42 CALB CA66Fi cells, 66Ah. 32 of them go into the battery compartment standing up as 2 rows of 16 and the remaining 10 will be stacked flat on top, most of them where the impellers used to be. Unfortunately the supplier forgot to send the interconnects. Next week then...

Battery cooling

I have satisfied myself that forced cooling will no be necessary with the cells I bought. As a contingency however, I have a plan B which will use conduction instead of forced convection. 2mm aluminium sheets between the cells would serve as the heat conductors. They would be thermally coupled to the bottom of the battery compartment. For the cells stacked horizontally, I would have to come up with a heatsink – maybe the plastic sides of the battery compartment could be replaced with aluminium sheet...

Battery mechanical fitting

I could not fit the cells side by side where the frame welds are. Some of the protruding welds will therefore have to be ground down by about 1 mm. Also interfering is the bracket for the rear temperature monitoring board and a rivet in the front center of the battery compartment. While I am at it, the big ventilation holes will also need to be covered – this will stop the battery from getting a shower when I ride in the rain.

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Re: YAVLiC - Fitting the Li battery

Hi Manfred, welcome to the forum!

That is an interesting project.

I think the lack of response from others might be due to the location where you posted it. Many of the regular Vectrix tinkerers on here may have set their home page to this one: http://visforvoltage.org/forums/vectrix Therefore, they may miss interesting posts that pop up elsewhere in the forum.

If I was you, I'd charge up the old NiMH battery to test if the scooter is in working order before investing much time and money into fitting a Lithium battery. It would only take a few hours and then you will know what other problems you may be dealing with.

I do not understand why you think that the battery data sheet means that the batteries are suitable. I would interpret them as unsuitable, because the maximum current draw will be exceeded by a large margin on a regular basis. If riding up a large hill or mountain, the maximum current draw can go on for many minutes at a time.

Good luck, Mik

Re: YAVLiC - Fitting the Li battery

Mik wrote:

I think the lack of response from others might be due to the location where you posted it. Many of the regular Vectrix tinkerers on here may have set their home page to this one: http://visforvoltage.org/forums/vectrix

Well, I posted to my blog – it wasn't supposed to be a forum post. It is meant as a record as much for myself as for others.

Quote:

If I was you, I'd charge up the old NiMH battery to test if the scooter is in working order before investing much time and money into fitting a Lithium battery.

Depends on your starting point. I have a very high confidence that the electrics and electronics of the bike are ok. I also have access to a full set of spares.

Quote:

I do not understand why you think that the battery data sheet means that the batteries are suitable. I would interpret them as unsuitable, because the maximum current draw will be exceeded by a large margin on a regular basis. If riding up a large hill or mountain, the maximum current draw can go on for many minutes at a time.

1.) The original Vectrix had a 125A fuse, so I think worst case, continuous discharge current can't be much more than that.

2.) There are already bikes out there which successfully run on this battery.

3.) The datasheet is a bit nebulous at best. The maximum discharge current as per datasheet actually has no time limit. I interpret that as the maximum continuous discharge current with the battery in free air. The limit in this case is determined by the battery's ability to dissipate internally generated heat. At 132A (2×C) with Ri=1mΩ, internally generated power is 17.4W. The internal temperature rise depends on the thermal resistance of the battery's internal structures and it's casing. 17.4W dissipated over a surface area of 840cm2 is not going to cause too much of a temperature gradient between the center of the battery and ambient.

Peak discharge current is not stated at all but would be much higher, limited by the thermal capacity of the battery and the current carrying capability of the battery's internal conductors. Any LFP battery will be able to tolerate a temporary discharge of several times it's capacity. At 200A each cell generates 40W of heat which is only 2.3 × what can be dissipated continuously. So some heat build-up will occur, raising internal temperature over time. What is needed is a graph showing internal temperature rise over time with a number of different currents. The battery manufacturer ought to have that data, but unfortunately CALB does not publish it. I have requested the data from them – let's see if they'll respond with something useful.

Edit 2013.09.01: CALB does not seem to reply to emails.

Edit 2013.09.01: ev-tv.me has some useful information about CALB CAxxFi cells.
According to that information, maximum discharge current is 10C for 30 seconds, i.e. 660A for 30 seconds &emdash; highly unlikely in the application at hand.

Quote:

Good luck, Mik

Thanks :-)

Re: YAVLiC - Fitting the Li battery

The max discharge at 2C is actually continuous, not peak - the new CALB's have higher power density than the older ones (which had higher power density than the thundersky's that came before them)

For what it's worth I have now done more than 60'000km on my Thundersky 60Ah pack

Matt

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