[EVDL] Thundersky Lithium Batteries

<[email protected]> wrote:
> Looks like Thundersky is making a 12V model of their Lithium Batteries.
>
> Anyone using these or know the price ?
>
>
> http://www.thunder-sky.com/products_en.asp?fid=66&fid2=82
>
>
> Thanks;
>
>
> Dennis
> Elsberry, MO
> http://www.evalbum.com/1366
>
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Bill Dube <[email protected]> wrote:

> Don't use them in series.
>
> There is certainly a big internal transistor that disconnects the
> battery from the load/charger when the battery is full or empty. This
> will not allow the other batteries in the series to fully charge.
>
> This big transistor probably has a voltage rating of 20 to 30 volts,
> maximum. If you put several of these batteries in series, then you
> will exceed the voltage rating of that big transistor. When one of
> them opens up under load or under charge, the transistor will be
> ruined. It could catch fire. It will certainly never function again.
>
> Bill D.
>
> At 12:01 PM 2/16/2011, you wrote:
> >There are so many errors in their datasheet,
> >who says that this is correct? There may be
> >a reason, but I do not expect that they have
> >found a Li-ion cell that does not like cycling
> >and thus this must be avoided.
> >I'd more expect that their continuous current
> >spec of 3C will not allow but the lighter EVs
> >or those with high voltage packs.
> >We also know that long strings (high voltage
> >packs) are notoriously difficult to keep in
> >balance and avoid over charge or over discharge...
> >
> >The datasheet seems to indicate that the charge
> >voltage goes above 17V which would indicate they
> >are still at their game of charging to 4.2V per
> >cell (or even above!)
> >While the discharge stops at 2.5V per cell, *if*
> >they are balanced.
> >
> >Serious errors in their datasheet are that the
> >90Ah cell gets charged and discharged with 90A
> >for *two* hours. That would make it a 180Ah cell.
> >The Cold cranking discharge at 600-ish Amps at
> >various temps suggest that the battery is
> >completely discharged (2.5V per cell) after
> >6 seconds, which would make it an approx 1Ah battery,
> >so I expect that the scale is actually in minutes,
> >even thought the specs say not to discharge 10C
> >for more than 10 sec.
> >
> >Really weird is that their charge curve starts
> >with 1 volt per cell (4V on the battery) and very
> >reduced charge current. I do not know what they
> >intend to say with that.
> >
> >Cor van de Water
> >Director HW & Systems Architecture Group
> >Proxim Wireless Corporation http://www.proxim.com
> >Email: [email protected] Private: http://www.cvandewater.com
> >Skype: cor_van_de_water IM: [email protected]
> >Tel: +1 408 383 7626 VoIP: +31 20 3987567 FWD# 25925
> >Tel: +91 (040)23117400 x203 XoIP: +31877841130
> >
> >
> >
> >-----Original Message-----
> >From: [email protected] on behalf of J Bills
> >Sent: Thu 2/17/2011 12:12 AM
> >To: Electric Vehicle Discussion List
> >Subject: Re: [EVDL] Thundersky Lithium Batteries
> >
> >hmmmm...
> >
> >"WARNING: This cell is not suitable to be used as a traction battery.
> >It is designed to replace lead acid starter batteries in ICE
> >vehicles."
> >
> http://kostov-motors.com/tractionmotors/kostovevmotors-and-kits/lithiumbatteriesbmsandchargers/lp12v90ah/
> >
> >
> >On Tue, Feb 15, 2011 at 8:24 AM, Pestka, Dennis J
> ><[email protected]> wrote:
> > > Looks like Thundersky is making a 12V model of their Lithium Batteries.
> > >
> > > Anyone using these or know the price ?
> > >
> > >
> > > http://www.thunder-sky.com/products_en.asp?fid=66&fid2=82
> > >
> > >
> > > Thanks;
> > >
> > >
> > > Dennis
> > > Elsberry, MO
> > > http://www.evalbum.com/1366
> > >
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> >
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Bill Dube <[email protected]> wrote:
>> Don't use them in series.
>> There is certainly a big internal transistor that disconnects the
>> battery from the load/charger when the battery is full or empty.
>> This will not allow the other batteries in the series to fully
>> charge.

Dennis Miles wrote:
> Wow isn't that nice a built in BMS... Or is that just a great piece
> of humor? Bill I love your Humor, er "BS" [:^)}

I have no idea what Thundersky is using in their lithium replacement for
a 12v starting battery. But, I designed the BMS for a client for just
such an application.

The 12v electrical system in a car can easily exceed the maximum safe
voltage for the lithiums. People also routinely connect their own 12v
chargers, which go even higher. They also forget and leave things on, or
keep cranking an engine that won't start until the battery is way below
the minimum safe voltage for the lithiums.

Since the battery can *start a fire* if abused like this, I felt that
you *must* include a BMS that can disconnect the battery from the system
if an overvoltage or undervoltage occurs. Like Bill said, this means a
big transistor or contactor in series.

I chose to use transistors. I had six MOSFETs, three in parallel, and
these two groups in anti-series to act as a switch that can stop current
flow in either direction. These transistors can handle starting currents
(hundreds of amps). But due to space and lack of cooling, they can only
do it for seconds.

Also, these transistor have to be low voltage (30v) to get the extremely
low on-resistance needed.

Such a battery can't be connected in series for EV use. The transistors
would overheat from sustained high current, and if they had to turn off,
they would be breaking the *total* voltage of the pack, not just that
one battery's worth.
--
Lee A. Hart | Ring the bells that still can ring
814 8th Ave N | Forget the perfect offering
Sartell MN 56377 | There is a crack in everything
leeahart earthlink.net | That's how the light gets in -- Leonard Cohen

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