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Discussion Starter · #1 ·
A question to the forum:
Any concerns combining a lead acid battery pack with a Lithium pack?
I have 108v electric escort currrently equipped with 18 6v lead acid
batteries.
I would like to upgrade it to 144v by adding twelve 100aH Lithium Cells.
Most likely I will need a separate charger for the Lithiums and an ethilon
BMS
to monitor them.
The advantages are clear notably less money spent(buying only 12 Li cells)
and it gives me
a preliminary working experience with the Lithiums as to how to balance and
monitor them.
When the Li technology gets better, cheaper, and easier to monitor then I
can invest in a
whole pack.
However what are the disadvantages and potential pitfalls?
Thanks,
Hazem
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Discussion Starter · #2 ·
I have 46 LiFP cells 90Ahrs (TSs) in parallel with 12 off 50Ahr spiral wound
Chinese copies of yellow tops. I have no BMS on either set. They are charged
together with a contemporary NG3 Zivan charger that has user- adjustable
programs. Occasionally I check the balance manually with individual cell or
12V chargers after a full charge but the cells/batteries are always close to
full so the check interval is much longer now. This hybrid pack was
designed to allow high motor currents without exceeding the TS limit. I am
happy with this arrangement and have taken my EV on two long trips of 1600ks
& 1800ks respectively as testament to the success of the philosophy. I dont
take the pack volts below 120V which yields 2.6V/cell , above the lower
limit. Normally my pack volts are around 145V even after 100ks of driving.
When the lead bats wear out Ill probably get another set of LFPs as the
technology is improving. David

--------------------------------------------------
From: "hazemsedra" <[email protected]>
Sent: Tuesday, February 22, 2011 12:37 AM
To: <[email protected]>
Subject: [EVDL] combining Lead Batteries with Lithium

>
> A question to the forum:
> Any concerns combining a lead acid battery pack with a Lithium pack?
> I have 108v electric escort currrently equipped with 18 6v lead acid
> batteries.
> I would like to upgrade it to 144v by adding twelve 100aH Lithium Cells.
> Most likely I will need a separate charger for the Lithiums and an ethilon
> BMS
> to monitor them.
> The advantages are clear notably less money spent(buying only 12 Li cells)
> and it gives me
> a preliminary working experience with the Lithiums as to how to balance
> and
> monitor them.
> When the Li technology gets better, cheaper, and easier to monitor then I
> can invest in a
> whole pack.
> However what are the disadvantages and potential pitfalls?
> Thanks,
> Hazem
> --
> View this message in context:
> http://electric-vehicle-discussion-list.413529.n4.nabble.com/combining-Lead-Batteries-with-Lithium-tp3317351p3317351.html
> Sent from the Electric Vehicle Discussion List mailing list archive at
> Nabble.com.
>
> _______________________________________________
> | REPLYING: address your message to [email protected] only.
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>

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Discussion Starter · #3 ·
I don't think I'd put lithium in series with lead. It is probably better to
put them in parallel.
But then you would need 108/3.2~34 lithium cells to have equal voltage
packs.
You better have some instrumentation that will let you keep a close eye on
things, especially the lithium.
If not, at best you'll kill the lithiums, at worst you'll burn your car
down.

Al

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Discussion Starter · #4 ·
Hi Hazem,

As the others say, the idea can work but the devil's in the details.

I would avoid Hi-Power batteries as they are low quality, have high
variability, and have high internal resistance. The minor savings over
quality TS or CALB cells is not worth it if you plan to actually use the
cells.

Cory

hazemsedra wrote:
> A question to the forum:
> Any concerns combining a lead acid battery pack with a Lithium pack?
> I have 108v electric escort currrently equipped with 18 6v lead acid
> batteries.
> I would like to upgrade it to 144v by adding twelve 100aH Lithium Cells.
> Most likely I will need a separate charger for the Lithiums and an ethilon
> BMS
> to monitor them.
> The advantages are clear notably less money spent(buying only 12 Li cells)
> and it gives me
> a preliminary working experience with the Lithiums as to how to balance and
> monitor them.
> When the Li technology gets better, cheaper, and easier to monitor then I
> can invest in a
> whole pack.
> However what are the disadvantages and potential pitfalls?
> Thanks,
> Hazem
>

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Discussion Starter · #5 ·
I run a lithium pack in series with a NiMH pack and I charge them both
in series. Since the charge efficiency is better for Li than NiMH, the
Li will always fill up first, at that point I switch the charger over
to finish charge the NiMH pack only. The same scheme should work with
lead but it requires a bit of a custom BMS.

If you use two separate chargers you'll need to think a bit about
what happens if one charger does not charge its half of the pack and
how to detect that situation before driving off.

Other than that, I say go for it! It's a good way to get your feet wet
with lithium without spending too much money.


hazemsedra <[email protected]> wrote:
>
> A question to the forum:
> Any concerns combining a lead acid battery pack with a Lithium pack?
> I have 108v electric escort currrently equipped with 18 6v lead acid
> batteries.
> I would like to upgrade it to 144v by adding twelve 100aH Lithium Cells.
> Most likely I will need a separate charger for the Lithiums and an ethilon
> BMS
> to monitor them.
> The advantages are clear notably less money spent(buying only 12 Li cells)
> and it gives me
> a preliminary working experience with the Lithiums as to how to balance and
> monitor them.
> When the Li technology gets better, cheaper, and easier to monitor then I
> can invest in a
> whole pack.
> However what are the disadvantages and potential pitfalls?
> Thanks,
> Hazem
> --
> View this message in context: http://electric-vehicle-discussion-list.413529.n4.nabble.com/combining-Lead-Batteries-with-Lithium-tp3317351p3317351.html
> Sent from the Electric Vehicle Discussion List mailing list archive at Nabble.com.
>
> _______________________________________________
> | REPLYING: address your message to [email protected] only.
> | Multiple-address or CCed messages may be rejected.
> | UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
> | OTHER HELP: http://evdl.org/help/
> | OPTIONS: http://lists.sjsu.edu/mailman/listinfo/ev
>



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www.electric-lemon.com

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Discussion Starter · #6 ·
Al wrote:
> I don't think I'd put lithium in series with lead. It is probably
> better to put them in parallel.

I would worry more with them in parallel than I would in series.

In parallel, what one battery does affects the other (you could say they
"argue" with each other. Any difference in voltage leads to a current
flow between them. The higher voltage pack discharges to charge the
lower voltage pack. If this current is uncontrolled and unmonitored, it
can become dangerously high.

Under load, the current in parallelled packs tends to divide
unpredictably. Each string has its own voltage and internal resistance,
which also change with state of charge, temperature, age, etc.

Cells in series don't "talk" to each other. Each delivers exactly the
same current regardless of what the others are doing. This makes it a
lot easier to predict what's going to happen. You can monitor the
voltage of each cell, and estimate its state of charge to prevent damage.

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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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