# [EVDL] Temporary Cell Insertion



## EVDL List (Jul 27, 2007)

I've got two strings of LiFePO4 in parallel: a 100ah string and a 200ah
string. I actually have two additional 200ah cells sitting in the garage
that I'd like to take advantage of, so I'm thinking about trying an
experiment--put the two cells in the car, but charge them separately. Then
when I'm ready to drive, I'd like to flip the two additional cells into
series with the 200ah string. This wouldn't overcharge the 100ah string,
and would give me some additional amps out of the 200ah string, which has a
higher internal resistance (in daily driving, the 200ah string is supplying
only about 1/5 of the amps).

So what is the best way to connect/disconnect the two cells? My first
thought is a two-throw contactor, but the cells would be being
connected/disconnected under a small load due to the different string
voltages. Could a contactor handle that on a twice-a-day basis?

Thanks.

Bill

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## EVDL List (Jul 27, 2007)

I do not think any contactor has a problem breaking that 7V DC
difference unless you find a way to weld the contacts by massively
overloading it in current? 


Cor van de Water
Chief Scientist
Proxim Wireless Corporation http://www.proxim.com
Email: [email protected] Private: http://www.cvandewater.com
Skype: cor_van_de_water XoIP: +31877841130
Tel: +1 408 383 7626 Tel: +91 (040)23117400 x203 

-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Bill Dennis
Sent: Friday, August 24, 2012 11:53 AM
To: 'Christopher Darilek'; 'Electric Vehicle Discussion List'
Subject: [EVDL] Temporary Cell Insertion

I've got two strings of LiFePO4 in parallel: a 100ah string and a 200ah
string. I actually have two additional 200ah cells sitting in the
garage that I'd like to take advantage of, so I'm thinking about trying
an experiment--put the two cells in the car, but charge them separately.
Then when I'm ready to drive, I'd like to flip the two additional cells
into series with the 200ah string. This wouldn't overcharge the 100ah
string, and would give me some additional amps out of the 200ah string,
which has a higher internal resistance (in daily driving, the 200ah
string is supplying only about 1/5 of the amps).

So what is the best way to connect/disconnect the two cells? My first
thought is a two-throw contactor, but the cells would be being
connected/disconnected under a small load due to the different string
voltages. Could a contactor handle that on a twice-a-day basis?

Thanks.

Bill

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## EVDL List (Jul 27, 2007)

Are you wanting to put them in series with your full 300 AH pack, or just the
200 AH string?

If the first, you don't even need a contactor but the extra cells would be
the weak link; if the second, the 200AH string will be charging the 100AH
string whenever your foot is off (or light on) the accelerator. 

Seems like a lot of extra work/risk for an extra 640wH.



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## EVDL List (Jul 27, 2007)

1) In series with the 200Ah string.
2) It's not just for the extra Watt-hours in the two cells (1280Wh, by the
way, not 640Wh), but because the 200Ah string is currently supplying only
about 1/5 of the amps. I want the 200Ah string to supply more of the amps,
and also to recharge the 100Ah string when the car is at a red light, for
example. Let's say that when the car is stopped, the higher-voltage 200Ah
pack is charging the 100Ah string at 30A. That's 30A * 120V = 3600 Watts
going into the 100Ah string. Someone correct me if I'm incorrect.

Bill 

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf
Of Voltswagon
Sent: Friday, August 24, 2012 2:05 PM
To: [email protected]
Subject: Re: [EVDL] Temporary Cell Insertion

Are you wanting to put them in series with your full 300 AH pack, or just
the
200 AH string?

If the first, you don't even need a contactor but the extra cells would be
the weak link; if the second, the 200AH string will be charging the 100AH
string whenever your foot is off (or light on) the accelerator. 

Seems like a lot of extra work/risk for an extra 640wH.



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## EVDL List (Jul 27, 2007)

How are you measuring that the 200AH string is only carrying 1/5 of the load? 
They should be averaging 2/3 of the load already, unless you're not using
enough of the pack to bring the 100AH string down at all anyway. A voltage
matched pack in parallel will act as a single string, creating a voltage
imbalance can only do that, create an imbalance.

A 7 volt difference in the packs would charge the 100AH string much faster
than 30A. Unless the 100AH cells have room for an extra 5-10AH, I expect
they'll fry.



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## EVDL List (Jul 27, 2007)

Given that I measured with a 50A 50mV shunt nearly a 30A initial
current paralleling a TS-LFP40AHA cell at ~3.35V with one resting at
3V I think the current between your two parallel packs will be much
higher than you might think.

I also question how you determined that your 200Ah string is only
supplying 1/5 of the load? Something isn't adding up here.



> Voltswagon <[email protected]> wrote:
> > How are you measuring that the 200AH string is only carrying 1/5 of the load?
> > They should be averaging 2/3 of the load already, unless you're not using
> > enough of the pack to bring the 100AH string down at all anyway. A voltage
> ...


----------



## EVDL List (Jul 27, 2007)

I've got a shunt/meter on both strings, so I can see how much current each
is supplying. The 200Ah string is made up of older LCP cells, while the
100Ah string is LFP cells. The LCP cells have much higher internal
resistance. So I'm basically getting only about 40Ah out of the LCP cells
when the LFP cells reach empty. The LCP cells still seem to have plenty of
life in them, so I'm trying to find a way to keep using them before having
to spend another $10,000 for replacements. This seems to be an easy way.
Lee has also suggested the idea of putting a DC/DC converter in series,
which I might also try, but is a bit more complicated.

Yeah, the 30A was just for the purpose of illustration. Could be 50A.
Could be 100A. Won't know until I hook it up.

Hope this makes things a little clearer.

Bill 

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf
Of David Nelson
Sent: Friday, August 24, 2012 9:09 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Temporary Cell Insertion

Given that I measured with a 50A 50mV shunt nearly a 30A initial current
paralleling a TS-LFP40AHA cell at ~3.35V with one resting at 3V I think the
current between your two parallel packs will be much higher than you might
think.

I also question how you determined that your 200Ah string is only supplying
1/5 of the load? Something isn't adding up here.



> Voltswagon <[email protected]> wrote:
> > How are you measuring that the 200AH string is only carrying 1/5 of the
> load?
> > They should be averaging 2/3 of the load already, unless you're not
> ...


----------



## EVDL List (Jul 27, 2007)

Oh, then you don't have two strings of LiFePO4 as originally stated.
That does make a difference.



> Bill Dennis <[email protected]> wrote:
> > I've got a shunt/meter on both strings, so I can see how much current each
> > is supplying. The 200Ah string is made up of older LCP cells, while the
> > 100Ah string is LFP cells. The LCP cells have much higher internal
> ...


----------



## EVDL List (Jul 27, 2007)

Grrr. Just went back and read my original post. Hadn't meant to say that
they were both LiFePO4. Sorry about that. My bad. Fingers type faster
than the brain thinks, sometimes. 

Bill

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf
Of David Nelson
Sent: Friday, August 24, 2012 9:41 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Temporary Cell Insertion

Oh, then you don't have two strings of LiFePO4 as originally stated.
That does make a difference.



> Bill Dennis <[email protected]> wrote:
> > I've got a shunt/meter on both strings, so I can see how much current
> > each is supplying. The 200Ah string is made up of older LCP cells,
> > while the 100Ah string is LFP cells. The LCP cells have much higher
> ...


----------



## EVDL List (Jul 27, 2007)

could you run your charger with the lcp's ? losses would be there but then
you could keep all lcp cells in one string and you just keep supplying the
buffer pack of lfp's. what was the voltage of your pack. -jukka
lauantai, 25. elokuuta 2012 Bill Dennis <[email protected]> kirjoitti:
> Grrr. Just went back and read my original post. Hadn't meant to say that
> they were both LiFePO4. Sorry about that. My bad. Fingers type faster
> than the brain thinks, sometimes.
>
> Bill
>
> -----Original Message-----
> From: [email protected] [mailto:[email protected]] On
Behalf
> Of David Nelson
> Sent: Friday, August 24, 2012 9:41 PM
> To: Electric Vehicle Discussion List
> Subject: Re: [EVDL] Temporary Cell Insertion
>
> Oh, then you don't have two strings of LiFePO4 as originally stated.
> That does make a difference.
>
>


> Bill Dennis <[email protected]> wrote:
> >> I've got a shunt/meter on both strings, so I can see how much current
> >> each is supplying. The 200Ah string is made up of older LCP cells,
> >> while the 100Ah string is LFP cells. The LCP cells have much higher
> ...


----------



## EVDL List (Jul 27, 2007)

Yes, I've talked to Rich Rudman about that. He says that my PFC-30 could
supply about 40A running on DC running from the 120V of LCP cells. That's a
little better than I've got now, because the 40A would be fairly constant. 

Here's another idea that Lee's had, which is along the same lines (view
diagram with a fixed-width font). The isolated output of a Vicor MegaPac
PFC connects in series with the 200Ah string, boosting its output voltage.
I've bought a MegaPac with a 5V/80A output to give it a try if the
two-extra-cell scheme doesn't pan out.

D1 MegaPac PFC
100Ah ___|/|_____+---------------+ 
Pos. BR1 | |\| |+ ENA|-+ (enables MegaPac only 
<-------/ -| |out | \ K1 when car is running)
|___|/|_____|- + in - |-+
|\| | +---------------+ 
D2 |____~~____| |
| F1 | 
| | 
200Ah 200Ah----+---100Ah 
Pos. Neg. Neg.
| | 
| | 
+-PFC-30-+



> Jukka wrote:
> >could you run your charger with the lcp's ?
> >losses would be there but then you could keep all lcp cells in one string
> and you just keep supplying >the buffer pack of lfp's.
> ...


----------



## EVDL List (Jul 27, 2007)

Can you post a diagram showing how the strings connect and where the shunts
are?

I still don't understand the issue. I have some LiFePO4 boosters hooked to
a lead acid pack. The voltage equalizes very quickly when you get off the
throttle. If ran at a higher voltage (through extra cells or because the
LFP is doing all the work) the LCP cells should be dumping their guts into
the LFPs. 

How can the LFP get empty without draining the LCP if they are in parallel?



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## EVDL List (Jul 27, 2007)

Part of the issue is the different voltage ranges between the two cells.
For LFP, I take charging cutoff voltage to be 3.6V, while for LCP it's 4.2V.
So there are 36 cells in the LFP string, and 31 cells in the LCP string.
For 0% SOC, I use 2.8V for the LFP cells, and 3V for the LCP cells. This
would give 100V empty for LFP and 93V empty for LCP. But the discharge
profiles are also different. The LCP cells tend to discharge more linearly,
while the LFP cells discharge more flatly, with a steep knee at the end.
Because of this, when the LFP cells are at 10% state of charge, their string
voltage is still around 114V. At this point, I used only about 1/5 the
energy in the LCP cells. But, now both string have large internal
resistance. I really can't drive the car with either one. Step on the
accelerator and voltage sags to around 60V. So I've got this extra capacity
in the LCP cells that I really can't use.

Regarding letting up on the accelerator: Because the LFP cells recover
faster, they actually charge the LCP cells briefly when I let up on the
pedal. So I'm getting even less range out of them. I diode between the two
strings would solve that issue.

So this parallel string things of LFP/LCP isn't working out as well as I'd
hoped, and I'm wanting to experiment with some different ways to solve it. 

Bill 



-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf
Of Voltswagon
Sent: Friday, August 24, 2012 9:58 PM
To: [email protected]
Subject: Re: [EVDL] Temporary Cell Insertion

Can you post a diagram showing how the strings connect and where the shunts
are?

I still don't understand the issue. I have some LiFePO4 boosters hooked to
a lead acid pack. The voltage equalizes very quickly when you get off the
throttle. If ran at a higher voltage (through extra cells or because the
LFP is doing all the work) the LCP cells should be dumping their guts into
the LFPs. 

How can the LFP get empty without draining the LCP if they are in parallel?



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## EVDL List (Jul 27, 2007)

The setup with the MegaPac is no different than
adding 1 or 2 cells to the LCP string using a
separate contactor on that string, other than
that trimming the MegaPac allows you to dial in
a certain current to deliver to the LFPs.
I am not sure of the function of the PFC-30,
do you charge the LCP string with that or do
you want it to charge both strings or are you
using it to discharge the LCP string?


Cor van de Water
Chief Scientist
Proxim Wireless Corporation http://www.proxim.com
Email: [email protected] Private: http://www.cvandewater.com
Skype: cor_van_de_water XoIP: +31877841130
Tel: +1 408 383 7626 Tel: +91 (040)23117400 x203 

-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Bill Dennis
Sent: Friday, August 24, 2012 10:15 PM
To: 'Electric Vehicle Discussion List'
Subject: Re: [EVDL] Temporary Cell Insertion

Yes, I've talked to Rich Rudman about that. He says that my PFC-30
could supply about 40A running on DC running from the 120V of LCP cells.
That's a little better than I've got now, because the 40A would be
fairly constant. 

Here's another idea that Lee's had, which is along the same lines (view
diagram with a fixed-width font). The isolated output of a Vicor
MegaPac PFC connects in series with the 200Ah string, boosting its
output voltage.
I've bought a MegaPac with a 5V/80A output to give it a try if the
two-extra-cell scheme doesn't pan out.

D1 MegaPac PFC
100Ah ___|/|_____+---------------+ 
Pos. BR1 | |\| |+ ENA|-+ (enables MegaPac only 
<-------/ -| |out | \ K1 when car is running)
|___|/|_____|- + in - |-+
|\| | +---------------+ 
D2 |____~~____| |
| F1 | 
| | 
200Ah 200Ah----+---100Ah 
Pos. Neg. Neg.
| | 
| | 
+-PFC-30-+



> Jukka wrote:
> >could you run your charger with the lcp's ?
> >losses would be there but then you could keep all lcp cells in one
> >string
> ...


----------



## EVDL List (Jul 27, 2007)

Bill Dennis wrote
> 
> Part of the issue is the different voltage ranges between the two cells.
> For LFP, I take charging cutoff voltage to be 3.6V, while for LCP it's
> 4.2V.
> So there are 36 cells in the LFP string, and 31 cells in the LCP string.
> For 0% SOC, I use 2.8V for the LFP cells, and 3V for the LCP cells. This
> would give 100V empty for LFP and 93V empty for LCP. But the discharge
> profiles are also different. The LCP cells tend to discharge more
> linearly,
> while the LFP cells discharge more flatly, with a steep knee at the end.
> Because of this, when the LFP cells are at 10% state of charge, their
> string
> voltage is still around 114V. At this point, I used only about 1/5 the
> energy in the LCP cells. But, now both string have large internal
> resistance. I really can't drive the car with either one. Step on the
> accelerator and voltage sags to around 60V. So I've got this extra
> capacity
> in the LCP cells that I really can't use.
> 
> Regarding letting up on the accelerator: Because the LFP cells recover
> faster, they actually charge the LCP cells briefly when I let up on the
> pedal. So I'm getting even less range out of them. I diode between the
> two
> strings would solve that issue.
> 

Okay, that makes more sense. As Lee suggested, it's not difficult to
calculate the resistance for each string at various states of charge, and
use that to predict what the current flow would be between each pack. If
you haven't done so already, I'd recommend doing a typical drive with each
separately, using video or another logger to track amps, AH, V, and sag all
along the curve. 

You may be able to look at the discharge curves to see where a certain cell
count combo would allow them to play nicely. I don't think just switching
in 2 extra cells will help because it would just dump charge the smaller
string, but raising or lowering the cell count (changing the final charged
position on the curve) may help. 

If the two curves are really too different maybe the DC-DC is the way to go.



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## EVDL List (Jul 27, 2007)

When I hear that the LFP cells reach 90% DoD and are still at 114V
then that would be the number to shoot for, for the LCP string also.
The setup would be really just add LCP cells to shift the 90% DoD
point as close as possible to the 114V and verify that the current
is still within acceptable range (the high internal resistance of
the LCP cells will probably take care of that anyway) and have the
LCP string connect to the LFP string using its own contactor that
is engaged when the car is on.
The only additional thing you need to take care of is that the
BMS on the LFP string can trigger the LCP contactor to open when
it starts to overcharge the LFP string (low speed driving or waiting
with the car on)
Slightly more complex is a setup where you use a 2-stage rocket, in
case the discharge of the LCP string is too high at low DoD:
1. Initially when LCP is below 40% DoD or so, you have the LCP
string connect to the LFP string directly,
2. When the current from LCP to LFP gets too low, you engage a
"boost stage" with the MegaPac increasing the LCP string voltage
to virtually increase the number of cells in that string and
continue to supply current down to 90% DoD.

In essence this last is using Lee's idea for boosting when needed
because the LCP have such a large voltage drop compared to LFP.
For simplicity, presume the LFP is constant in voltage and the
LCP string goes from 4.2VpC to 3.4VpC (there is little energy
left when reaching 3.4V) then the delta in voltage in the LCP
string is:
(4.2-3.4) x 31
which is approx 25V.
To give you two "areas" of discharge (0-40% and 40-90% for example)
that means that you have to shift the voltage of the LCP string
by about 12V in order to get the second stage deliver approx
the same current as the first stage.
It also means that the resting voltage of the LCP string should be
more than 12V higher than the LFP string.
36 x 3.6V = 129.6 
31 x 4.2V = 130.2
These values, while allowing you to charge them with one charger,
*guarantees* that you cannot use much of the LCP string energy,
although the LCP string should give more than 50% of its energy to
the LFP string eventually when you parallel them long enough and
they stay at the 114V that the LFP plateau at. But if you want the
LCP to supply more of their energy from the get go, then you need
to add in between 2 and 4 cells to boost the current from LCP to LFP.
Again, you will need to monitor the LFP cells to avoid overcharging
them from the LCP string if the car is ever turned on but not driven.

This also means that you will need 2 chargers, one for each string.

As suggested before, the different discharge profile of the LCP
may be difficult to match to the LFP string and using a DC/DC
converter to bridge that and always deliver a constant current
into the LFP string independent of the DoD might be the solution
that allows you to use most of the available energy.

Cor van de Water
Chief Scientist
Proxim Wireless Corporation http://www.proxim.com
Email: [email protected] Private: http://www.cvandewater.com
Skype: cor_van_de_water XoIP: +31877841130
Tel: +1 408 383 7626 Tel: +91 (040)23117400 x203 

-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Bill Dennis
Sent: Saturday, August 25, 2012 7:10 AM
To: 'Electric Vehicle Discussion List'
Subject: Re: [EVDL] Temporary Cell Insertion

Part of the issue is the different voltage ranges between the two cells.
For LFP, I take charging cutoff voltage to be 3.6V, while for LCP it's
4.2V.
So there are 36 cells in the LFP string, and 31 cells in the LCP string.
For 0% SOC, I use 2.8V for the LFP cells, and 3V for the LCP cells.
This would give 100V empty for LFP and 93V empty for LCP. But the
discharge profiles are also different. The LCP cells tend to discharge
more linearly, while the LFP cells discharge more flatly, with a steep
knee at the end.
Because of this, when the LFP cells are at 10% state of charge, their
string voltage is still around 114V. At this point, I used only about
1/5 the energy in the LCP cells. But, now both string have large
internal resistance. I really can't drive the car with either one.
Step on the accelerator and voltage sags to around 60V. So I've got
this extra capacity in the LCP cells that I really can't use.

Regarding letting up on the accelerator: Because the LFP cells recover
faster, they actually charge the LCP cells briefly when I let up on the
pedal. So I'm getting even less range out of them. I diode between the
two strings would solve that issue.

So this parallel string things of LFP/LCP isn't working out as well as
I'd hoped, and I'm wanting to experiment with some different ways to
solve it. 

Bill 



-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Voltswagon
Sent: Friday, August 24, 2012 9:58 PM
To: [email protected]
Subject: Re: [EVDL] Temporary Cell Insertion

Can you post a diagram showing how the strings connect and where the
shunts are?

I still don't understand the issue. I have some LiFePO4 boosters hooked
to a lead acid pack. The voltage equalizes very quickly when you get
off the throttle. If ran at a higher voltage (through extra cells or
because the LFP is doing all the work) the LCP cells should be dumping
their guts into the LFPs. 

How can the LFP get empty without draining the LCP if they are in
parallel?



--
View this message in context:
http://electric-vehicle-discussion-list.413529.n4.nabble.com/Temporary-C
ell-
Insertion-tp4657442p4657468.html
Sent from the Electric Vehicle Discussion List mailing list archive at
Nabble.com.

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## EVDL List (Jul 27, 2007)

The PFC-30 would charge both strings: the LCP directly, and the LFP through
D2.

Bill

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf
Of Cor van de Water
Sent: Saturday, August 25, 2012 1:28 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Temporary Cell Insertion

The setup with the MegaPac is no different than adding 1 or 2 cells to the
LCP string using a separate contactor on that string, other than that
trimming the MegaPac allows you to dial in a certain current to deliver to
the LFPs.
I am not sure of the function of the PFC-30, do you charge the LCP string
with that or do you want it to charge both strings or are you using it to
discharge the LCP string?


Cor van de Water
Chief Scientist
Proxim Wireless Corporation http://www.proxim.com
Email: [email protected] Private: http://www.cvandewater.com
Skype: cor_van_de_water XoIP: +31877841130
Tel: +1 408 383 7626 Tel: +91 (040)23117400 x203 

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf
Of Bill Dennis
Sent: Friday, August 24, 2012 10:15 PM
To: 'Electric Vehicle Discussion List'
Subject: Re: [EVDL] Temporary Cell Insertion

Yes, I've talked to Rich Rudman about that. He says that my PFC-30 could
supply about 40A running on DC running from the 120V of LCP cells.
That's a little better than I've got now, because the 40A would be fairly
constant. 

Here's another idea that Lee's had, which is along the same lines (view
diagram with a fixed-width font). The isolated output of a Vicor MegaPac
PFC connects in series with the 200Ah string, boosting its output voltage.
I've bought a MegaPac with a 5V/80A output to give it a try if the
two-extra-cell scheme doesn't pan out.

D1 MegaPac PFC
100Ah ___|/|_____+---------------+ 
Pos. BR1 | |\| |+ ENA|-+ (enables MegaPac only 
<-------/ -| |out | \ K1 when car is running)
|___|/|_____|- + in - |-+
|\| | +---------------+ 
D2 |____~~____| |
| F1 | 
| | 
200Ah 200Ah----+---100Ah 
Pos. Neg. Neg.
| | 
| | 
+-PFC-30-+



> Jukka wrote:
> >could you run your charger with the lcp's ?
> >losses would be there but then you could keep all lcp cells in one
> >string
> ...


----------



## EVDL List (Jul 27, 2007)

If you use the two separate sets according their best performance
you'll get more out of them. The charging procedures are also a bit
different. Old-New, LCP-LFP... Be careful.

How does the BMS handle the different sets ?

I was thinking this charger connection in the way that you have two
chargers already. One on each string. But if you do not you can keep
pushing the LFPs until the BMS says stop. Then you charge LCPs full
with the same charger.

With constant easy load from LCP's you should get more drivable energy
out. They sag due their ticking clock and sagging generates more heat
which increases the resistance. Keeping them cool and unstressed you
can buy few more years of service.

I have just now one pack of LCP's that were made in 2005 (or so) in
the lab. Planing to test the pack to see how much they have got old.
Cells have been in a car and in use until now. They're going back if
they are still good enough.

-Jukka

http://www.google.com/profiles/jarviju#about


2012/8/25 Bill Dennis <[email protected]>:
> Yes, I've talked to Rich Rudman about that. He says that my PFC-30 could
> supply about 40A running on DC running from the 120V of LCP cells. That's a
> little better than I've got now, because the 40A would be fairly constant.
>
> Here's another idea that Lee's had, which is along the same lines (view
> diagram with a fixed-width font). The isolated output of a Vicor MegaPac
> PFC connects in series with the 200Ah string, boosting its output voltage.
> I've bought a MegaPac with a 5V/80A output to give it a try if the
> two-extra-cell scheme doesn't pan out.
>
> D1 MegaPac PFC
> 100Ah ___|/|_____+---------------+
> Pos. BR1 | |\| |+ ENA|-+ (enables MegaPac only
> <-------/ -| |out | \ K1 when car is running)
> |___|/|_____|- + in - |-+
> |\| | +---------------+
> D2 |____~~____| |
> | F1 |
> | |
> 200Ah 200Ah----+---100Ah
> Pos. Neg. Neg.
> | |
> | |
> +-PFC-30-+
>


> > Jukka wrote:
> >>could you run your charger with the lcp's ?
> >>losses would be there but then you could keep all lcp cells in one string
> > and you just keep supplying >the buffer pack of lfp's.
> ...


----------



## EVDL List (Jul 27, 2007)

My LCP cells are from 2005 also. Originally I had 290Ah in the car (200Ah
string and 90Ah string in parallel, 35 cells in each string). Due to sag
and heating, this setup, although providing 36Kwh to a small, 1000-kg car,
proved unusable. For my first extended test drive back then, I drove the
car 70 miles (112 km) in September (my daily commute was 90 miles/144km).
If I pulled many amps at all, the pack sagged from 144V to 80V. And when I
got home, the pack was at 70C degrees, which seemed too high. That's when I
replaced the 90Ah LCP cells with the 100Ah LFP cells. Performance got much
better: even though providing 4/5 of the current, the LFP cells don't sag
much, and never get over 45 degrees C, even in the heat of summer. But, of
course, I lost my range because the LCP cells aren't contributing much.

As for charging, I currently charge both strings in parallel, but
undercharge them slightly (only to 124.5V). Haven't had any problem. The
issue I've found with charging the LCP cells separately is that, because of
the cells' high internal resistance, if the charger supplies much more than
about 10A, the cells shoot up over the cutoff voltage and the charger turns
off. Have you had problems this way in charging the LCP cells, Jukka?

Thanks.

Bill =


-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf
Of Jukka J=E4rvinen
Sent: Sunday, August 26, 2012 10:13 AM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Temporary Cell Insertion

If you use the two separate sets according their best performance you'll get
more out of them. The charging procedures are also a bit different. Old-New,
LCP-LFP... Be careful.

How does the BMS handle the different sets ?

I was thinking this charger connection in the way that you have two chargers
already. One on each string. But if you do not you can keep pushing the
LFPs until the BMS says stop. Then you charge LCPs full with the same
charger.

With constant easy load from LCP's you should get more drivable energy out.
They sag due their ticking clock and sagging generates more heat which
increases the resistance. Keeping them cool and unstressed you can buy few
more years of service.

I have just now one pack of LCP's that were made in 2005 (or so) in the lab.
Planing to test the pack to see how much they have got old.
Cells have been in a car and in use until now. They're going back if they
are still good enough.

-Jukka

http://www.google.com/profiles/jarviju#about


2012/8/25 Bill Dennis <[email protected]>:
> Yes, I've talked to Rich Rudman about that. He says that my PFC-30 =

> could supply about 40A running on DC running from the 120V of LCP =

> cells. That's a little better than I've got now, because the 40A would be
fairly constant.
>
> Here's another idea that Lee's had, which is along the same lines =

> (view diagram with a fixed-width font). The isolated output of a =

> Vicor MegaPac PFC connects in series with the 200Ah string, boosting its
output voltage.
> I've bought a MegaPac with a 5V/80A output to give it a try if the =

> two-extra-cell scheme doesn't pan out.
>
> D1 MegaPac PFC
> 100Ah ___|/|_____+---------------+
> Pos. BR1 | |\| |+ ENA|-+ (enables MegaPac only
> <-------/ -| |out | \ K1 when car is running)
> |___|/|_____|- + in - |-+
> |\| | +---------------+
> D2 |____~~____| |
> | F1 |
> | |
> 200Ah 200Ah----+---100Ah
> Pos. Neg. Neg.
> | |
> | |
> +-PFC-30-+
>


> > Jukka wrote:
> >>could you run your charger with the lcp's ?
> >>losses would be there but then you could keep all lcp cells in one =
> 
> ...


----------

