# [EVDL] active balancing



## EVDL List (Jul 27, 2007)

I had an idea last night as I was dropping off to sleep about a method
to actively balance batteries.. 
I think it would involve stopping the car and diconnectiong the pack
from the controller but the idea is as follows:


You have a much larger than normal aux battery. 

A bms monitors all cells for undervoltage.. a simple system tells you
when you are undervolting one or more batteries. Once this is occurring
regularly (not just on hard acceleration) you pull over, and the aux
battery provides a top up charge to the batteries that are flagged as
sagging most. A circuit could measure the average voltage of the pack
and charge the rogue batteries until they hit that average. This could
be quite a fast process if the cells can accept a fast charge. Once
this process is completed you carry on driving (the aux battery is
recharged again once you set off.)


The main flaw in this theory, that I can see is the need to disconnect
the pack, unless someone with more than a passing knowledge of
electronics can correct me, this is necessary before charging an
individual cell.


Would there be *any* benefit to this technique? Or is it a complicated
waste of time?

Any thoughts? 





-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Cor van de Water
Sent: 17 February 2009 11:47
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] YEE-HAA! It works!

Another way to get a "series resistor" for current limiting is the
infamous
stainless steel rod, for example a threaded rod so you select its
resistance
in a mechanical way (where are the nuts to hold the lug connecting to
it) 


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

Please consider the environment before printing this e-mail.
-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Tom Parker
Sent: Tuesday, February 17, 2009 4:56 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] YEE-HAA! It works!

On Sun, 2009-02-15 at 03:41 +0000, [email protected] wrote:

> 2. Since I have a clutch, I went without a speed controller. My idea
> for a two stage resistive load speed controller did not work (but
> makes a great space heater). The second contactor (both Kilovac
> EV200AAANA) bypasses the resistor. So basically it was all-or-nothing
> today. Kinda herky-jerky. I could use a suggestion for a speed
> controller. 

Instead of a resistor as your first stage, look into using your
contactors to connect your pack in parallel for lower voltage and then
series when you want to go faster. Do not connect just half the pack as
this will seriously unbalance your battery. Search for "contactor
controller" to get some ideas. You might need more contactors than the
two you have.

Others will no doubt suggest a suitable solid state motor controller.

> Although the shunt meter showed 400 amps when I let the clutch out,
> that quickly (3 sec.) decayed to less than 200 a. then settled to just
> a needle width over 100 amps while cruising along (in 1st at 27 mph). 

27mph sounds awfully fast for 1st gear. With your motor name plate
rating at 90V and your battery at 72V, you should have less chance of
exploding your motor, but I would still be careful at high speed in low
gears (especially downhill) and also at no load with the clutch in. If
the motor goes too fast it will explode.

> I have a 150 amp fuse (Bussman LKN150 NSPP) in the power circuit and
> that did not blow today (but then again it was just above freezing).

Is this your fuse family? http://www.bussmann.com/pdf/1028.pdf The fuse
curves in that document don't make any sense, as the 150A fuse appears
to melt in one second at 50A. What am I missing here? These fuses also
appear to have no DC rating. The 600V AC rated fuses in this family
might work on 72V DC, but I'm not sure. How many volts is your fuse
rated for?

Congratulations on the getting your car going, your work looks very
clean and tidy.

_______________________________________________
General EVDL support: http://evdl.org/help/
Usage guidelines: http://evdl.org/help/index.html#conv
Archives: http://evdl.org/archive/
Subscription options: http://lists.sjsu.edu/mailman/listinfo/ev


_______________________________________________
General EVDL support: http://evdl.org/help/
Usage guidelines: http://evdl.org/help/index.html#conv
Archives: http://evdl.org/archive/
Subscription options: http://lists.sjsu.edu/mailman/listinfo/ev


_______________________________________________
General EVDL support: http://evdl.org/help/
Usage guidelines: http://evdl.org/help/index.html#conv
Archives: http://evdl.org/archive/
Subscription options: http://lists.sjsu.edu/mailman/listinfo/ev


----------



## EVDL List (Jul 27, 2007)

Hi Robin,

Your theory has a lot of merit and it has been
available for a long time in a slightly modified
version, called Lee Hart's balancer, which uses
a DC/DC converter to take power from the entire
pack to recharge the weakest battery out of the
pack, so it is a form of energy shuttling from
stronger to weaker batteries.
It is fully automatic and you can get the 
details and boards from Lee when he has time to
build another batch and not spending his spare
time on BEST or the Sunrise project or answering
our perpetual emails ;-)

Therefor, please dig in the archives to find the
interesting information and post a link to it
(or quote it) for the follow-up, that helps
everyone here.

Success,

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

Please consider the environment before printing this e-mail.
-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Robin Lawrie
Sent: Friday, February 20, 2009 4:50 PM
To: Electric Vehicle Discussion List
Subject: [EVDL] active balancing

I had an idea last night as I was dropping off to sleep about a method
to actively balance batteries.. 
I think it would involve stopping the car and diconnectiong the pack
from the controller but the idea is as follows:


You have a much larger than normal aux battery. 

A bms monitors all cells for undervoltage.. a simple system tells you
when you are undervolting one or more batteries. Once this is occurring
regularly (not just on hard acceleration) you pull over, and the aux
battery provides a top up charge to the batteries that are flagged as
sagging most. A circuit could measure the average voltage of the pack
and charge the rogue batteries until they hit that average. This could
be quite a fast process if the cells can accept a fast charge. Once
this process is completed you carry on driving (the aux battery is
recharged again once you set off.)


The main flaw in this theory, that I can see is the need to disconnect
the pack, unless someone with more than a passing knowledge of
electronics can correct me, this is necessary before charging an
individual cell.


Would there be *any* benefit to this technique? Or is it a complicated
waste of time?

Any thoughts? 





-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Cor van de Water
Sent: 17 February 2009 11:47
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] YEE-HAA! It works!

Another way to get a "series resistor" for current limiting is the
infamous
stainless steel rod, for example a threaded rod so you select its
resistance
in a mechanical way (where are the nuts to hold the lug connecting to
it) 


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

Please consider the environment before printing this e-mail.
-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Tom Parker
Sent: Tuesday, February 17, 2009 4:56 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] YEE-HAA! It works!

On Sun, 2009-02-15 at 03:41 +0000, [email protected] wrote:

> 2. Since I have a clutch, I went without a speed controller. My idea
> for a two stage resistive load speed controller did not work (but
> makes a great space heater). The second contactor (both Kilovac
> EV200AAANA) bypasses the resistor. So basically it was all-or-nothing
> today. Kinda herky-jerky. I could use a suggestion for a speed
> controller. 

Instead of a resistor as your first stage, look into using your
contactors to connect your pack in parallel for lower voltage and then
series when you want to go faster. Do not connect just half the pack as
this will seriously unbalance your battery. Search for "contactor
controller" to get some ideas. You might need more contactors than the
two you have.

Others will no doubt suggest a suitable solid state motor controller.

> Although the shunt meter showed 400 amps when I let the clutch out,
> that quickly (3 sec.) decayed to less than 200 a. then settled to just
> a needle width over 100 amps while cruising along (in 1st at 27 mph). 

27mph sounds awfully fast for 1st gear. With your motor name plate
rating at 90V and your battery at 72V, you should have less chance of
exploding your motor, but I would still be careful at high speed in low
gears (especially downhill) and also at no load with the clutch in. If
the motor goes too fast it will explode.

> I have a 150 amp fuse (Bussman LKN150 NSPP) in the power circuit and
> that did not blow today (but then again it was just above freezing).

Is this your fuse family? http://www.bussmann.com/pdf/1028.pdf The fuse
curves in that document don't make any sense, as the 150A fuse appears
to melt in one second at 50A. What am I missing here? These fuses also
appear to have no DC rating. The 600V AC rated fuses in this family
might work on 72V DC, but I'm not sure. How many volts is your fuse
rated for?

Congratulations on the getting your car going, your work looks very
clean and tidy.

_______________________________________________
General EVDL support: http://evdl.org/help/
Usage guidelines: http://evdl.org/help/index.html#conv
Archives: http://evdl.org/archive/
Subscription options: http://lists.sjsu.edu/mailman/listinfo/ev


_______________________________________________
General EVDL support: http://evdl.org/help/
Usage guidelines: http://evdl.org/help/index.html#conv
Archives: http://evdl.org/archive/
Subscription options: http://lists.sjsu.edu/mailman/listinfo/ev


_______________________________________________
General EVDL support: http://evdl.org/help/
Usage guidelines: http://evdl.org/help/index.html#conv
Archives: http://evdl.org/archive/
Subscription options: http://lists.sjsu.edu/mailman/listinfo/ev


_______________________________________________
General EVDL support: http://evdl.org/help/
Usage guidelines: http://evdl.org/help/index.html#conv
Archives: http://evdl.org/archive/
Subscription options: http://lists.sjsu.edu/mailman/listinfo/ev


----------



## EVDL List (Jul 27, 2007)

Hello Robin,

This method has already been done and still may be in use today. In Germany 
they have city bus lines that drive a certain length route, with large 
battery cases that look like rack panels that slide into compartments on 
both sides of the bus under the passenger compartment floor much like are 
Greyhound buses do for storage.

These heavy plastic boxes have two prongs that plug into a center buss bar 
that goes down the center line of this compartment. Each battery case also 
have a buss connection where each cell can plug into it. When all the cells 
are plug into this case, this container looks like one smooth white plastic 
box with two handles on the front.

Now when any one cell goes bad, it is ejected up which is now higher then 
the others. The buss connection below the battery then closes which 
completes the circuit for the rest of the cells.

When the bus get backs to the bus terminal, a worker slides out the battery 
case with the pop up cell onto a roll around carrier. He then install 
either a new cell and reinstall the battery case.

After so many runs, they then slide all the battery cases out for charging 
and install charge up batteries if the bus still have to make more runs or 
they can charge the batteries in the post after the final run.

Roland


----- Original Message ----- 
From: "Robin Lawrie" <[email protected]>
To: "Electric Vehicle Discussion List" <[email protected]>
Sent: Friday, February 20, 2009 3:19 AM
Subject: [EVDL] active balancing


> I had an idea last night as I was dropping off to sleep about a method
> to actively balance batteries..
> I think it would involve stopping the car and diconnectiong the pack
> from the controller but the idea is as follows:
>
>
> You have a much larger than normal aux battery.
>
> A bms monitors all cells for undervoltage.. a simple system tells you
> when you are undervolting one or more batteries. Once this is occurring
> regularly (not just on hard acceleration) you pull over, and the aux
> battery provides a top up charge to the batteries that are flagged as
> sagging most. A circuit could measure the average voltage of the pack
> and charge the rogue batteries until they hit that average. This could
> be quite a fast process if the cells can accept a fast charge. Once
> this process is completed you carry on driving (the aux battery is
> recharged again once you set off.)
>
>
> The main flaw in this theory, that I can see is the need to disconnect
> the pack, unless someone with more than a passing knowledge of
> electronics can correct me, this is necessary before charging an
> individual cell.
>
>
> Would there be *any* benefit to this technique? Or is it a complicated
> waste of time?
>
> Any thoughts?
>
>
>
>
>
> -----Original Message-----
> From: [email protected] [mailto:[email protected]] On
> Behalf Of Cor van de Water
> Sent: 17 February 2009 11:47
> To: Electric Vehicle Discussion List
> Subject: Re: [EVDL] YEE-HAA! It works!
>
> Another way to get a "series resistor" for current limiting is the
> infamous
> stainless steel rod, for example a threaded rod so you select its
> resistance
> in a mechanical way (where are the nuts to hold the lug connecting to
> it)
>
>
> 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
>
> Please consider the environment before printing this e-mail.
> -----Original Message-----
> From: [email protected] [mailto:[email protected]] On
> Behalf Of Tom Parker
> Sent: Tuesday, February 17, 2009 4:56 PM
> To: Electric Vehicle Discussion List
> Subject: Re: [EVDL] YEE-HAA! It works!
>
> On Sun, 2009-02-15 at 03:41 +0000, [email protected] wrote:
>
> > 2. Since I have a clutch, I went without a speed controller. My idea
> > for a two stage resistive load speed controller did not work (but
> > makes a great space heater). The second contactor (both Kilovac
> > EV200AAANA) bypasses the resistor. So basically it was all-or-nothing
> > today. Kinda herky-jerky. I could use a suggestion for a speed
> > controller.
>
> Instead of a resistor as your first stage, look into using your
> contactors to connect your pack in parallel for lower voltage and then
> series when you want to go faster. Do not connect just half the pack as
> this will seriously unbalance your battery. Search for "contactor
> controller" to get some ideas. You might need more contactors than the
> two you have.
>
> Others will no doubt suggest a suitable solid state motor controller.
>
> > Although the shunt meter showed 400 amps when I let the clutch out,
> > that quickly (3 sec.) decayed to less than 200 a. then settled to just
> > a needle width over 100 amps while cruising along (in 1st at 27 mph).
>
> 27mph sounds awfully fast for 1st gear. With your motor name plate
> rating at 90V and your battery at 72V, you should have less chance of
> exploding your motor, but I would still be careful at high speed in low
> gears (especially downhill) and also at no load with the clutch in. If
> the motor goes too fast it will explode.
>
> > I have a 150 amp fuse (Bussman LKN150 NSPP) in the power circuit and
> > that did not blow today (but then again it was just above freezing).
>
> Is this your fuse family? http://www.bussmann.com/pdf/1028.pdf The fuse
> curves in that document don't make any sense, as the 150A fuse appears
> to melt in one second at 50A. What am I missing here? These fuses also
> appear to have no DC rating. The 600V AC rated fuses in this family
> might work on 72V DC, but I'm not sure. How many volts is your fuse
> rated for?
>
> Congratulations on the getting your car going, your work looks very
> clean and tidy.
>
> _______________________________________________
> General EVDL support: http://evdl.org/help/
> Usage guidelines: http://evdl.org/help/index.html#conv
> Archives: http://evdl.org/archive/
> Subscription options: http://lists.sjsu.edu/mailman/listinfo/ev
>
>
> _______________________________________________
> General EVDL support: http://evdl.org/help/
> Usage guidelines: http://evdl.org/help/index.html#conv
> Archives: http://evdl.org/archive/
> Subscription options: http://lists.sjsu.edu/mailman/listinfo/ev
>
>
> _______________________________________________
> General EVDL support: http://evdl.org/help/
> Usage guidelines: http://evdl.org/help/index.html#conv
> Archives: http://evdl.org/archive/
> Subscription options: http://lists.sjsu.edu/mailman/listinfo/ev
>
> 

_______________________________________________
General EVDL support: http://evdl.org/help/
Usage guidelines: http://evdl.org/help/index.html#conv
Archives: http://evdl.org/archive/
Subscription options: http://lists.sjsu.edu/mailman/listinfo/ev


----------



## EVDL List (Jul 27, 2007)

> Robin Lawrie wrote:
> > I had an idea... to actively balance batteries... have a larger than
> > normal aux battery. A BMS monitors all batteries for undervoltage...
> > when you are undervolting one or more batteries... the aux battery
> ...


----------



## EVDL List (Jul 27, 2007)

Hi Steven,

I would like to resurrect the idea I exposed to the group a week ago: to 
use small, standard individual chargers to separately and independently 
manage the charge of each battery.

I thought it was a dumb idea at first but after reading about all the 
difficulties, the complexity and cost associated with most battery 
management systems, I started looking differently at this simple solution.

Although I did not get much feedback on this idea (maybe because there 
were no small, inexpensive and sophisticated charger available until 
recently) I will be implementing this solution no later than next week: 
I will install a standard off the shelf microprocessor-controlled 
charger (6 by 1.6 by 2.8 inch, $40 each) on top of each of my sealed 
lead acid batteries (with suitable protection against possible fumes 
release). Each charger will manage its own battery, regardless of the 
other batteries state of charge or condition. I am hoping for an 
extended battery life since the management of the charging process 
applies to each battery, individually, and is not affected by the other 
batteries.

By the way, I have verified that these individual chargers are fully 
isolated from the AC power.

The only drawback I can see is the relatively low charging current I can 
get from these chargers (8Amp).
Should I need a quick charge, I will keep my original 10 Amp charger 
ready to bulk recharge the pack until I reach let's say 80% SOC, but I 
will let each small charger gently and precisely equalize it own battery.
The total cost of the 12 small chargers ($480) is slightly less than the 
big 144 V charger ($500+). One of the benefits is that the heat 
dissipated by the small chargers will keep the batteries warm - a good 
thing in winter- and the battery boxes I have installed are big enough 
to hold the chargers. 

Again, I have no guarantee that this is the best solution, but so far I 
have not seen any major flaw in the reasoning.

I will keep you posted on the results..

Michael

PS: you can have a look at these chargers at: 
http://www.tempestbatteries.com/html/BC-12-8000F.html

> Message: 1
> Date: Fri, 20 Feb 2009 05:00:43 -0800 (PST)
> From: Steven Ciciora <[email protected]>
> Subject: Re: [EVDL] active balancing
> To: Electric Vehicle Discussion List <[email protected]>
> Message-ID: <[email protected]>
> Content-Type: text/plain; charset=us-ascii
>
> Yes, this is a good idea. It's what Lee Hart's BMS does, and the zivan smoother. I'm sure others as well. It gets complicated though, which is why simple bypass regulators are often used (and a lot of people complain about the cost of the simple solution...).
>
> The Zivan Smoother (and Lee's BMS, if you program it that way) scans each battery in the pack (using mechanical relays) and then attaches a DC-DC charger to the lowest battery. This DC-DC converter is powered by the entire pack, vs just the aux battery in your proposal. The disadvantage to what you proposed (using the aux battery with no electronics between it and the low battery) is that as the two batteries get closer to each other in state of charge, it takes exponentially longer for them to equalize. And the entire reason for a BMS is to keep all the the batteries as close together as possible. So to make your proposal more efficient, a DC-DC (boost) converter is usually used to make charging of the low battery quicker.
>
> Don't be discouraged that someone already came up with your idea; I am most impressed when people come up with good ideas that are outside their field of expertise. It shows that you are starting to think like an expert 
>
> Steven Ciciora
>
> - Steven Ciciora 
>
> 
>

_______________________________________________
General EVDL support: http://evdl.org/help/
Usage guidelines: http://evdl.org/help/index.html#conv
Archives: http://evdl.org/archive/
Subscription options: http://lists.sjsu.edu/mailman/listinfo/ev


----------



## EVDL List (Jul 27, 2007)

> Michael Bonard wrote:
> > Again, I have no guarantee that this is the best solution, but so far I
> > have not seen any major flaw in the reasoning.
> 
> ...


----------



## EVDL List (Jul 27, 2007)

Michael,

As Josh alluded to, if one of the chargers quits, or becomes
disconnected, that battery gets beat up on the next short run, or killed
over several short runs or one long run. Lee Hart devised the following
quick and simple solution to let you know one battery is low on charge
http://www.evdl.org/pages/battbridge.html 

At 8 amps, your sealed lead acid batteries may not be getting enough of
a quick charge to give a full life. If I have it correct, they like a
strong charge, but an occasional strong charge may work. Your idea of
running a larger charger once in a while may help out a lot with
longevity.

Good luck! I would like to hear of your results. I have thought about
your set up, and had several 1.5 amp chargers, so have thought about
doing something similar, but much less practical. Your progress, and
the work of others, inspires me to keep going.

Alan 

-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Michael Bonard
Sent: Friday, February 20, 2009 1:09 PM
To: [email protected]
Subject: Re: [EVDL] active balancing

^Hi Steven,

^I would like to resurrect the idea I exposed to the group a week ago:
to 
^use small, standard individual chargers to separately and independently

^manage the charge of each battery.

Snip

^I will be implementing this solution no later than next week: 
^I will install a standard off the shelf microprocessor-controlled 
^charger (6 by 1.6 by 2.8 inch, $40 each) on top of each of my sealed 
^lead acid batteries (with suitable protection against possible fumes 
^release). Each charger will manage its own battery, regardless of the 
^other batteries state of charge or condition. I am hoping for an 
^extended battery life since the management of the charging process 
^applies to each battery, individually, and is not affected by the other

^batteries.

^By the way, I have verified that these individual chargers are fully 
^isolated from the AC power.

^The only drawback I can see is the relatively low charging current I
can 
^get from these chargers (8Amp).
^Should I need a quick charge, I will keep my original 10 Amp charger 
^ready to bulk recharge the pack until I reach let's say 80% SOC, but I 
^will let each small charger gently and precisely equalize it own
battery.
^The total cost of the 12 small chargers ($480) is slightly less than
the 
^big 144 V charger ($500+). One of the benefits is that the heat 
^dissipated by the small chargers will keep the batteries warm - a good 
^thing in winter- and the battery boxes I have installed are big enough 
^to hold the chargers. 

^Again, I have no guarantee that this is the best solution, but so far I

^have not seen any major flaw in the reasoning.

^I will keep you posted on the results..

^Michael

^PS: you can have a look at these chargers at: 
http://www.tempestbatteries.com/html/BC-12-8000F.html 


_______________________________________________
General EVDL support: http://evdl.org/help/
Usage guidelines: http://evdl.org/help/index.html#conv
Archives: http://evdl.org/archive/
Subscription options: http://lists.sjsu.edu/mailman/listinfo/ev


----------



## EVDL List (Jul 27, 2007)

To remain very frugal but efficient, I plan to implement Lee Hart's 
beautiful battery bridge balance alarm. It is incredibly simple (3 
LED's, two resistors), of negligible cost and very reliable!

If one battery is not charged properly I should be able to detect it 
using this balance alarm circuit. Then I will be able to look at the 
individual battery chargers which have a built-in LED monitoring, 
confirm the alarm by measuring the voltage of the corresponding battery, 
and eventually replace the charger.

I hope that this answers the question!

Michael





> Josh Wyatt wrote:
> > Michael Bonard wrote:
> >> Again, I have no guarantee that this is the best solution, but so far
> >> I have not seen any major flaw in the reasoning.
> ...


----------



## EVDL List (Jul 27, 2007)

> On 20 Feb 2009 at 3:55, Cor van de Water wrote:
> 
> > please dig in the archives to find the interesting information and post
> > a link to it (or quote it) for the follow-up, that helps everyone here.
> ...


----------



## EVDL List (Jul 27, 2007)

> Michael Bonard wrote:
> > I would like to resurrect the idea I exposed to the group a week ago:
> > to use small, standard individual chargers to separately and
> > independently manage the charge of each battery.
> ...


----------



## EVDL List (Jul 27, 2007)

> On Friday 20 February 2009 02:45 pm, Bill Dube wrote:
> > It is much more cost-effective to flag a weak battery
> > for replacement before it reaches a critical point than it is to
> > "prop up" a weak battery with energy transfer from the rest of the
> ...


----------



## EVDL List (Jul 27, 2007)

> It is important to weigh the cost of such a system against the benefit.
>
> While it seems like a good idea to prop up a weak battery, the cost of 
> doing it can be much more than the cost of simply replacing the weak 
> battery. It is much more cost-effective to flag a weak battery for 
> replacement before it reaches a critical point than it is to "prop up" 
> a weak battery with energy transfer from the rest of the pack.

I am gonna disagree with this statement for AGM lead batteries only. I 
think this will help them age together.
I am on my second pack of exide orbitals that have failed the same way, 
diverging capacity using bypass regulators.
The first pack was replaced under warrantee and after a year, i replaced 
4 weak ones. now I have 3 more that are weak.

>
> Batteries fail in two ways: They fail prematurely, or they wear out in 
> the normal fashion at the normal rate.
>
> When they fail prematurely, they generally decline quickly. This is 
> for two reasons: There is something wrong with the weak battery. This 
> is also because the weak one is getting cycled at a greater percentage 
> of its capacity than the rest (and has been for some time.)
Amen, well said.
>
> Since premature failed batteries decline quickly, moving amp-hrs to 
> them will not add many cycles before you must replace the weak battery 
> anyway. 
but by shuttleing charge while you drive, this weaker bettery makes the 
trip with the same relative discharge depth as the rest int he pack; ie 
all batteries go to 80% DOD and not all batteries go 24ah down.
> When you calculate the cost per amp to "prop up" any of the many 
> batteries in the string, and compare it with the number of additional 
> cycles you will get from the week battery, you discover that it is 
> much much much cheaper to simply replace the weak battery (or to 
> manually by-pass it) than it is to supply it amps automatically from 
> the rest of the pack.
>
> In a nutshell, an energy-transfer style system can extend the cycle 
> life of a weak battery and also of an aged pack, but the additional 
> cycles you will get are not worth the cost of the energy-transfer 
> system. It is much cheaper to replace the worn-out or defective 
> batteries than it is to buy and maintain the energy-transfer balancing 
> system.
But then you are always replacing 2 or 3 batteries and you end up with a 
pack that has capacity all over the map. ( I have this situation, again)
I think transfering charge will reduce the cycle depth on the weaker one 
by taking from the stronger ones. This means that each cycle brings them 
closer to being the same "cycle age". They should all die at the same 
time. Assuming normal wear and not a cell short.

The question I have is How does LiFePo4 age? Bill, you got to have the 
best data on that?
>
> Bill Dube' 

_______________________________________________
General EVDL support: http://evdl.org/help/
Usage guidelines: http://evdl.org/help/index.html#conv
Archives: http://evdl.org/archive/
Subscription options: http://lists.sjsu.edu/mailman/listinfo/ev


----------



## EVDL List (Jul 27, 2007)

alan said...
> At 8 amps, your sealed lead acid batteries may not be getting enough of
> a quick charge to give a full life. If I have it correct, they like a
> strong charge, but an occasional strong charge may work. Your idea of
> running a larger charger once in a while may help out a lot with
> longevity.

I have noticed that when I can charge at higher amps it really helps, but I was never sure if that was just the warming effect.

Here is something the charge shuttling charger can do that my pack charger cannot.
If I have available to me a 110V 20A plug I can at most pull 12A from it
becasue of the charge voltage on a 288V pack being 300V+ that is a max of 4A (12A/3) into the pack. 
(5A runs for a few mins then pops the breaker. even 4A pops some breakers)

Off the same 110V plug, I plan on the opportunity charging capability of the Lee Hart Battery Balancer to push

up to 30 amps into each battery one at a time to help wake them up. since 110V/14 ==> 8 * 12A = 96A (max avail from wall) 

I obviously takes the a little more time at 30A per battery vs 4A per pack 


if 30ah down
1H * 24 = 24h vs 30/4 =7.5h

but I only use 2500wh to get to work, about 10ah

.3H * 24 = 7.2h vs 2.5h 

2.5h is what I see, so this checks, but I am at my desk longer than 7h. I plan on bulk charging when I get there for an hour then let the balancer have a go for a few days to get things woken up and stabilized.

I will automate this, the balancer has some outputs for just this but I wonder if it wouldn't be better to hit each battery with 20A for 10 min each first? That is 4 hours(walk out at lunch and switch), then bulk charge them at 4A until full then kick the balancer back on to finish.

_______________________________________________
General EVDL support: http://evdl.org/help/
Usage guidelines: http://evdl.org/help/index.html#conv
Archives: http://evdl.org/archive/
Subscription options: http://lists.sjsu.edu/mailman/listinfo/ev


----------



## EVDL List (Jul 27, 2007)

I have a proposed pack of 28 12V DEKA Gel batteries. How does the use 
of a balancing unit apply or differ for this type battery ?
John



> Jeff Shanab wrote:
> > alan said...
> >
> >> At 8 amps, your sealed lead acid batteries may not be getting enough of
> ...


----------



## EVDL List (Jul 27, 2007)

> Bill Dube wrote:
> >> It is much more cost-effective to flag a weak battery
> >> for replacement before it reaches a critical point than it is to
> >> "prop up" a weak battery with energy transfer from the rest of the
> ...


----------



## EVDL List (Jul 27, 2007)

> On 21 Feb 2009 at 13:36, John M. Salmon III wrote:
> 
> > I have a proposed pack of 28 12V DEKA Gel batteries. How does the use
> > of a balancing unit apply or differ for this type battery ?
> ...


----------



## EVDL List (Jul 27, 2007)

> On Saturday 21 February 2009 03:13 pm, Lee Hart wrote:
> ---< other good stuff (and details) snipped >---
> > So the Balancer saved me money.
> 
> ...


----------



## EVDL List (Jul 27, 2007)

Bill, you're right, but this is based on engineering approach, not
bin counters' one. ACP demonstrated what they can build and
thus how technologically advanced they are, so they will get more
business in general and recover costs of *this* non-profitable BMS
that way.

The bet is on the fact that chemical storage (Li cells) is the
only disposable item in the pack, electronics will stay and supposedly 
outlive many
cell replacements, thus amortizing the cost. If you build $50 cell 
balancer to balance $5 cell and throw away whole system after cells wore 
out, it makes ony academic sense - to learn or test. No business. But if 
you do the same
and replaced $5 cells 50 times over next 75 years, you've used
$50 balancer for $250 worth of cells now. That *might* make sense
(depending on bin counter's calc), but you have to look far beyond your 
nose, and too few people these days do.

People rather buy cheap than good and lasting. BMS included.
Thus everyone wants cell electronics 30 cents worth since [chinese] cell 
is just $5. Nobody cares that balancer serves many cells over its life
and some day will pay for itself. That day is too far away to think 
about it, you know how people are, they want all future benefits *now*,
or the product is no good.

Victor




> Bill Dube wrote:
> > Again, it sounds like a great idea until you must shell out the cash
> > for the system.
> >
> ...


----------



## EVDL List (Jul 27, 2007)

> Lee Hart wrote:
> 
> > 1. With Balancer:
> > Initial pack cost 12 x $158 = $1896
> ...


----------



## EVDL List (Jul 27, 2007)

> John M. Salmon III wrote:
> > I have a proposed pack of 28 12V DEKA Gel batteries. How does the use
> > of a balancing unit apply or differ for this type battery ?
> 
> ...


----------



## EVDL List (Jul 27, 2007)

> Victor Tikhonov wrote:
> > Lee Hart wrote:
> >
> >> 1. With Balancer:
> ...


----------



## EVDL List (Jul 27, 2007)

> John M. Salmon III wrote:
> > I have a proposed pack of 28 12V DEKA Gel batteries. How does the use
> > of a balancing unit apply or differ for this type battery ?
> > John
> ...


----------



## EVDL List (Jul 27, 2007)

> Bill Dube wrote:
> > There is a _huge_ difference between a typical battery balancing
> > system, and an energy transfer system.
> 
> ...


----------



## EVDL List (Jul 27, 2007)

I should of probably added that the number of modules makes a difference.

10 244ah cells for a 120V pack is only 10 bypass regs. ~350.00
24 50ah cells for a 288V pack is 24 regs $~840

The charge shuttleing system costs less than the regulator system 
systems with more modules.

1/2 my regs have died, one took out a battery when it did. They have no 
feed back unless you are looking at them.

I think the Lee Hart Battery Balancer will be a bargain for the price.

It should be able to
control the Bulk charger,
Balance the batteries on charge AND on discharge.
Provide drive time information on state of charge and voltage and 
warnings.
Control a heater and or fan for the box during charge
Charge the Aux battery
Test the capacity of all the modules
Provide opportunity charging

Provide history of battery capacity and let me see which ones are 
headed south. 


_______________________________________________
General EVDL support: http://evdl.org/help/
Usage guidelines: http://evdl.org/help/index.html#conv
Archives: http://evdl.org/archive/
Subscription options: http://lists.sjsu.edu/mailman/listinfo/ev


----------



## EVDL List (Jul 27, 2007)

> Jeff Shanab wrote:
> > Bypass regulators don't work unless the charger can't or is prevented
> > from over-powering them.
> >
> ...


----------



## EVDL List (Jul 27, 2007)

Well I would Victor. Of course, I start by replacing his $1896 cost with my
$10,600 cost for LiFePo4s and his balancer starts to look pretty good.

Jack Rickard




> Victor Tikhonov wrote:
> >
> > Lee Hart wrote:
> >
> ...


----------



## EVDL List (Jul 27, 2007)

> Lee Hart wrote:
> >
> > B
> > My battery balancer uses a $500 control board, plus one $195 relay board
> ...


----------



## EVDL List (Jul 27, 2007)

> Jack Rickard wrote:
> > I have a pack with 16 batteries. So where do I send the check?
> 
> Me; but not yet! I've been doing an update to the design for the past
> ...


----------



## EVDL List (Jul 27, 2007)

> Bill Dube wrote:
> > A typical BMS for a Li-Ion battery pack does not do charge transfer.
> > If you look up "BMS" and go through the commercially available
> > products, only a few are charge transfer type.
> ...


----------



## EVDL List (Jul 27, 2007)

> Jeff Shanab wrote:
> >> Bypass regulators don't work unless the charger can't or is
> >> prevented from over-powering them.
> 
> ...


----------



## EVDL List (Jul 27, 2007)

> Jeff Shanab wrote:
> 
> > The idea was a 6S5P group 24 sized module.
> > What if we had a common toroid with 6 LV and 1 HV in a ZVS
> ...


----------



## EVDL List (Jul 27, 2007)

> Bill Dube wrote:
> 
> > A typical BMS for a Li-Ion battery pack does not do charge transfer.
> > If you look up "BMS" and go through the commercially available
> ...


----------



## EVDL List (Jul 27, 2007)

> Roger Heuckeroth wrote:
> > I had a similar type plan. I actually went so far as to get some
> > quotes on toroidal transformers similar to the above. In low qtys <10
> > pc they were over $200 each. That's just for the transformer. Then
> ...


----------



## EVDL List (Jul 27, 2007)

- Make sure Balancer is tailored for Li cells!

- Balancer is a device transferring energy from the pack to a weaker 
cell. So you know then you have a weak cell, yet keep using it
in a hope the balancer makes problem go away.

Keeping weaker Li cell is quite more potentially troublesome than
keeping weaker lead battery - a Li cell must have serious internal 
problem to be "weak".

I'm not suggesting abandoning balancer idea for the lithoum pack,
but consider rather buying extra cells for the cost of the balancer,
then less powerful hardware can maintain it.

No hardware can fix bad battery - it is just wrong approach to the 
problem. Balancer may be good idea for lead battery which is not as 
demanding as Li one. I would be scared to drive with bad Li cells,
no matter what hardware is sitting on top of it.

I just had one NuMH cell raptured under hard acceleration releasing
pressure and so toxic substance that liner on the roof of the car
got "burned" (kind of eaten) by it. Thanks god I had a hat on my head
and cranking windows I could open quickly. That was weakest NiMH cell.

It wasn't pretty. It would not make any difference balancer or not -
I demanded too much for this cell during acceleration. Li *could* be
worse - FePO4 or not. Bad Li MUST be replaced, not pumped extra into.

Just a food for thought.

Victor




> Jack Rickard wrote:
> > Well I would Victor. Of course, I start by replacing his $1896 cost with my
> > $10,600 cost for LiFePo4s and his balancer starts to look pretty good.
> >
> ...


----------



## EVDL List (Jul 27, 2007)

> > Jeff Shanab wrote:
> >> Bypass regulators don't work unless the charger can't or is prevented
> >> from over-powering them.
> >>
> ...


----------



## EVDL List (Jul 27, 2007)

> A typical BMS for a Li-Ion battery pack does not do charge transfer.
> If you look up "BMS" and go through the commercially available 
> products, only a few are charge transfer type. 

For lithium-ion I am planning on bypass regs. Because of the individual 
cell monitoring and need for faster reaction to low voltage or over 
voltage than Lead-acid.

Before this sounds like we are beating up a dead horse, they both are 
viable balancing systems for lead. The implementation is what sets one 
bms apart from another. I have lived with bypass regs and I will try the 
LHBB, I hope I have better luck than the regs, I was hard on them and 
they responded in kind.



_______________________________________________
General EVDL support: http://evdl.org/help/
Usage guidelines: http://evdl.org/help/index.html#conv
Archives: http://evdl.org/archive/
Subscription options: http://lists.sjsu.edu/mailman/listinfo/ev


----------



## EVDL List (Jul 27, 2007)

>
>
>


> Jeff Shanab wrote:
> >
> >> The idea was a 6S5P group 24 sized module.
> >> What if we had a common toroid with 6 LV and 1 HV in a ZVS
> ...


----------



## EVDL List (Jul 27, 2007)

>


> Jeff Shanab wrote:
> >
> >> The idea was a 6S5P group 24 sized module.
> >> What if we had a common toroid with 6 LV and 1 HV in a ZVS
> ...


----------



## EVDL List (Jul 27, 2007)

I think we need to separate differences from normal aging and the effect 
a BMS has on helping with that, from defective cells.
It appears in lead that if you ignore the small differences at the 
beginning of their life you amplify it creating what we are calling here 
a weak battery.

I think a passive balancing system is a good first order protection. It 
protects against overvoltage and overcharge making the whole pack act 
like the weakest module.

I think an active system is a possible 2nd order system. It adds the 
ability to balance on discharge to help balance the ageing also.

Obviously if you have a large capacity difference in the first month, 
there is a problem.
So how do we know a month after installing 20+ batteries in every 
little cubby hole what there capacity is ?
It looks like a simple bypass regulator system cannot tell you that, you 
need a pack tracker or something. The regs do latch a red LED, so you 
can go look and see which is lowest. that tells you one batteries 
capacity. (~ emeter / average pack voltage)

I think Lee's active balancing implementation can deal with one battery 
at a time during charge and discharge. It can give you the balancing and 
the pack-tracker functionality. More because of Lee's design than Active 
vs Passive balancing it can be easy to extend. Battery capacity 
tester/cycler., Opportunity charger, shoring up week battery, aux 
battery charger, bulk charger controller, battery box heater and fan 
controller, It seems our imagination is the limit, The beauty of an open 
design!


> - Make sure Balancer is tailored for Li cells!
>
> - Balancer is a device transferring energy from the pack to a weaker 
> cell. So you know then you have a weak cell, yet keep using it
> in a hope the balancer makes problem go away.
>
> Keeping weaker Li cell is quite more potentially troublesome than
> keeping weaker lead battery - a Li cell must have serious internal 
> problem to be "weak".
Everything I have been talking about is for lead, I don't know if 
Lithium ion has same aging issues.
>
> I'm not suggesting abandoning balancer idea for the lithoum pack,
> but consider rather buying extra cells for the cost of the balancer,
> then less powerful hardware can maintain it.
>
> No hardware can fix bad battery - it is just wrong approach to the 
> problem. Balancer may be good idea for lead battery which is not as 
> demanding as Li one. I would be scared to drive with bad Li cells,
> no matter what hardware is sitting on top of it.
>
> I just had one NuMH cell raptured under hard acceleration releasing
> pressure and so toxic substance that liner on the roof of the car
> got "burned" (kind of eaten) by it. Thanks god I had a hat on my head
> and cranking windows I could open quickly. That was weakest NiMH cell.
>
> It wasn't pretty. It would not make any difference balancer or not -
> I demanded too much for this cell during acceleration. Li *could* be
> worse - FePO4 or not. Bad Li MUST be replaced, not pumped extra into.
>
> Just a food for thought.
>
> Victor
>
>


> > Jack Rickard wrote:
> >> Well I would Victor. Of course, I start by replacing his $1896 cost
> >> with my
> >> $10,600 cost for LiFePo4s and his balancer starts to look pretty good.
> ...


----------



## EVDL List (Jul 27, 2007)

> Jeff Shanab wrote:
> 
> >> On Feb 22, 2009, at 10:34 AM, Jeff Shanab wrote:
> >>
> ...


----------



## EVDL List (Jul 27, 2007)

I guess I disagree Victor. 

And in this application, there is nothing special about Lithium Ion. Energy
transfer is energy transfer.

What I'm seeing is that the cells actually stay in balance pretty well. But
during normal charge and discharge, small imbalances start to creep in. 
They get progressively worse, not because of a bad cell, but just from
cummulative imbalance. It's sort of like making 10,000 copy iterations with
a photocopier. Small errors start to grow larger, and larger, and larger.

They really aren't that hard to keep in balance. I'm having some success
using little bitty things designed for radio controlled helicopters on
relatively huge cells. They are active, but they really work by bleeding
off energy from all the other cells to reach the lowest common denominator. 

Lee's concept of using whole pack voltage to charge individual "batteries"
is very appealing to me. The problem isn't so much a cell going bad, that
is just as you say. The problem I want to address with balancing is just
the creeping imbalance. As it creeps, it gets worse. And it's just a
problem based on impedence variations that are inevitable.

I'm also quite comfortable dealing with "batteries" instead of cells. I'm
working on a 20 segment visual LED bargraph display that will allow me to
see variations at the 4-cell "battery" level at a glance. If I have one
battery that is out of line with the other, I would pull it out of the car
and off to the bench to deal with it at the individual cell level. So I'm
pretty comfortable with balancing and monitoring at the battery level,
including the charge balance. Nobody deals with individual cells in the
lead acid world, and it's actually an advantage to be ABLE to using
LiFePo4s. But I think on the car, I can think of them as "batteries" pretty
much as I have them configured - 4 cell packages. 

It might be that a truly effective balancer might mask problems from being
detected visually for awhile, but I'm guessing not for very long if you
really have a cell go bad. 

The goal is life extension. I think the better you keep them in balance,
the longer they will last - as Lee pretty much demonstrated with lead acids. 
The other life extension concept pretty much revolves around buffering using
Maxwell Ultracaps. I just haven't done a vehicle with enough ROOM
physically to place them. But I did do a bank at 72 volts for a GEM - no
fancy electronics at all. Just a big tank buffer between the batteries and
the controller. It changed performance PHENOMENALLY, which wasn't really
what I was after. But the caps can produce a huge amount of current without
the voltage sag, and it shows up in the driving. But the concept there is
to level out the current demand on the batteries from the start/stop/go like
hell/stop/start time constant of normal driving. It appears to be working. 
WITHOUT dc-dc converters, etc. I can measure large swings in current to the
controller, with much smaller swings in current between the batteries and
caps.

So I'm eschewing the computer in the car thing for the most part. I've got
3x5 inch Linux computers laying around. But they lead to keyboards, and
monitors, and software errors. 

I divide the BMS function into two fairly simple things: Active Balance and
Effective Monitoring. Effective monitoring is something I can look at WHILE
ACCELERATING - a 1/3 second glance, and tell if any battery is not a team
player and which battery it is. The second element is active balancing. I
want a device that actively shuttles charge between "batteries" 24x7, while
charging, while driving, and most importantly, during the majority of the
time when the car is sitting in the garage. It doesn't have to do 50 amps. 
It can do 50 ma. But it should be moving the charge around, not just
bleeding it off as heat.

My best effort was a flying cap design. And I like it. But I wound up with
TEN MOSFETS on a PCB with some capacitors, drivers, a 555 etc. It started
to look remarkably like a CONTROLLER and I had $400 in parts, more in
reality but assuming a board cost based on 16 boards, instead of 2. 

There has to be something simpler and less expensive. Mechanical relays are
a little retro, but I can get used to the idea - I think.

Jack Rickard









> Victor Tikhonov wrote:
> >
> > - Make sure Balancer is tailored for Li cells!
> >
> ...


----------



## EVDL List (Jul 27, 2007)

> Lee Hart wrote:
> >
> > Jack Rickard wrote:
> >> I have a pack with 16 batteries. So where do I send the check?
> ...


----------



## EVDL List (Jul 27, 2007)

Jack,

Are you saying that you simply put a ultracap bank in parallel with 
the battery on you GEM? So the ultrcaps charged up to the same 
voltage as the battery, and only gave up the energy between full 
battery voltage and the voltage to which the pack sagged to when 
accelerating?

What was the capacitance of the ultracap bank?

Roger


> Jack Rickard wrote:
> 
> > The other life extension concept pretty much revolves around
> > buffering using
> ...


----------



## EVDL List (Jul 27, 2007)

> Lee Hart wrote:
> >> But it will take another month or two if I have to build and test them
> >> for you, because there are a bunch of people in line ahead of you.
> 
> ...


----------



## EVDL List (Jul 27, 2007)

Michael and All,
If you search the archive's for modular charging, you'll find a lot of
posts about this. Before going with 16 of the Soneil brand chargers, I bought another brand to test, but it had an algorithm like the one you mention below. It didn't take too much research to realize that the 14.8 volts is too high as the batteries age. I've written plenty about the Soneil's in the RX-7, the algorithm, etc.
Suck Amps,
BB

>Date: Fri, 20 Feb 2009 22:40:50 -0600
>From: Lee Hart
>


> >Michael Bonard wrote:
> >> I would like to resurrect the idea I exposed to the group a week ago:
> >> to use small, standard individual chargers to separately and
> >> independently manage the charge of each battery.
> ...


----------



## EVDL List (Jul 27, 2007)

> Roger Heuckeroth wrote:
> >
> > Jack,
> >
> ...


----------



## EVDL List (Jul 27, 2007)

Jack,
Have you looked at Tavrima?
http://www.tavrima.com/home.html
They have a fully integrated high-voltage solutions.

I've yet to contact them for pricing, but I've been reconsidering caps since
I'm going with Gels in my EV and will want to keep the batt current lower.

-Nick





> Jack Rickard <[email protected]> wrote:
> 
> >
> >
> ...


----------



## EVDL List (Jul 27, 2007)

> Roger Heuckeroth wrote:
> >
> >
> > Other than the room and cost issue it sounds like a great idea.
> ...


----------



## EVDL List (Jul 27, 2007)

Nick

I looked at them about 9 months ago. Sent them an Email... no 
response. Gave them a phone call... left message... no response.

Roger

Sent from my iPhone

On Feb 23, 2009, at 9:31 PM, nicolas drouin <[email protected]> 


> wrote:
> 
> > Jack,
> > Have you looked at Tavrima?
> ...


----------



## EVDL List (Jul 27, 2007)

On Mon, Feb 23, 2009 at 6:07 PM, Roger Heuckeroth


> <[email protected]> wrote:
> > How do you engineer a capacitor bank? For example, say if your
> > running a 64S battery of LiFePO4 cells that have a nominal voltage of
> > 205V. When you hit the accelerator you want to be able to feed the
> ...


----------



## EVDL List (Jul 27, 2007)

> Roger Heuckeroth wrote:
> 
> > How do you engineer a capacitor bank? For example, say if your
> > running a 64S battery of LiFePO4 cells that have a nominal
> ...


----------



## EVDL List (Jul 27, 2007)

> Nick Drouin wrote:
> >
> > Jack,
> > Have you looked at Tavrima?
> ...


----------



## EVDL List (Jul 27, 2007)

> Nick Drouin wrote:
> >
> > Jack,
> > Have you looked at Tavrima?
> ...


----------



## EVDL List (Jul 27, 2007)

> Jack Rickard wrote:
> > However, to some degree we're going the wrong direction here. They have a
> > 300 volt 2 farad package. But it's 9 x 22 inches - the size of a Warp9
> > motor and it weighs 77 lbs. And it would take 15 of them for 30 F. The
> ...


----------



## EVDL List (Jul 27, 2007)

I got an answer in a couple of hours. $2200 for their 300v 90kW unit plus
shipping.

It's a thought.

Jack Rickard




> Roger Heuckeroth wrote:
> >
> > Nick
> >
> ...


----------



## EVDL List (Jul 27, 2007)

> Roger Heuckeroth wrote:
> >
> >
> >
> ...


----------



## EVDL List (Jul 27, 2007)

> Jack Rickard wrote:
> 
> > Roger Heuckeroth wrote:
> >>
> ...


----------



## EVDL List (Jul 27, 2007)

> Roger Heuckeroth wrote:
> >> Oh, to find a 1.2 F 250v electrolytic with a low ESR - at ANY price.
> 
> It's not likely to be a single can; it would be the size of a trash can!
> ...


----------



## EVDL List (Jul 27, 2007)

Jack,



> Jack Rickard wrote:
> > I guess I disagree Victor.
> >
> > And in this application, there is nothing special about Lithium Ion. Energy
> ...


----------



## EVDL List (Jul 27, 2007)

> Lee Hart wrote:
> >
> > Roger Heuckeroth wrote:
> >>> Oh, to find a 1.2 F 250v electrolytic with a low ESR - at ANY price.
> ...


----------



## EVDL List (Jul 27, 2007)

> Lee Hart wrote:
> >
> > Roger Heuckeroth wrote:
> >>> Oh, to find a 1.2 F 250v electrolytic with a low ESR - at ANY price.
> ...


----------



## EVDL List (Jul 27, 2007)

> Victor Tikhonov wrote:
> >
> > Jack,
> >
> ...


----------



## EVDL List (Jul 27, 2007)

> Victor Tikhonov wrote:
> 
> > I did experiment with ultracaps bank in my ACRX some 5 years ago:
> >
> ...


----------



## EVDL List (Jul 27, 2007)

Roger,

A higher voltage on the controller side means a lower current drawn for the
same power.
So starting current is lower.
Since the caps can be full cycled, for the same amount of acceleration (ie
energy drawn over a few seconds) the average amps drawn from the batteries
are *lower* than if the caps were wired in parrallel.

The battery pack also is burdened with having to charge the caps up again.
This is done on regen.

Matt 

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf
Of Roger Heuckeroth
Sent: Thursday, 26 February 2009 3:20 AM
To: [email protected]; Electric Vehicle Discussion List
Subject: Re: [EVDL] active balancing




> Victor Tikhonov wrote:
> 
> > I did experiment with ultracaps bank in my ACRX some 5 years ago:
> >
> ...


----------



## EVDL List (Jul 27, 2007)

A minor typo correction.
When the caps are wired in series, the battery isn't burrdened with charging
the caps up again. 

Matt

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf
Of matt
Sent: Thursday, 26 February 2009 9:55 AM
To: 'Electric Vehicle Discussion List'
Subject: Re: [EVDL] active balancing

Roger,

A higher voltage on the controller side means a lower current drawn for the
same power.
So starting current is lower.
Since the caps can be full cycled, for the same amount of acceleration (ie
energy drawn over a few seconds) the average amps drawn from the batteries
are *lower* than if the caps were wired in parrallel.

The battery pack also is burdened with having to charge the caps up again.
This is done on regen.

Matt 

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf
Of Roger Heuckeroth
Sent: Thursday, 26 February 2009 3:20 AM
To: [email protected]; Electric Vehicle Discussion List
Subject: Re: [EVDL] active balancing




> Victor Tikhonov wrote:
> 
> > I did experiment with ultracaps bank in my ACRX some 5 years ago:
> >
> ...


----------



## EVDL List (Jul 27, 2007)

Sounds like it only provides a benefit if you have regen, and then 
only for short regen cycles. Long downhills would overwhelm the caps. 
Charging the caps from the battery through a DC-DC would just waste 
energy.

Sent from my iPhone



> "matt" <[email protected]> wrote:
> 
> > A minor typo correction.
> > When the caps are wired in series, the battery isn't burrdened with
> ...


----------



## EVDL List (Jul 27, 2007)

Matt summarized this quite well. Basically, if you wire the caps
directly in parallel, you can reduce current out of batteries
during acceleration only, and for very short time (until caps voltage
drops below what the battery would have alone, then battery takes over).

The caps have no impact on cruising.

With series connection, my initial voltage is 2x of the battery voltage
(say from the prior deceleration to stop). So accelerating at this 
conditions results in 2x less current as well, but for much longer
since I can discharge capacitors to zero instead of 10-15% in case of
parallel connection. Side benefit is - far better performance at 2x as 
high voltage (during acceleration). Once you're cruising, caps as before 
have no effect. But during next stopping they entirely absorb regen 
current charging from zero to full voltage. In case of parallel 
connection it doesn't take that much to replenish 10-15% you spent, so 
the rest of regen is "wasted" in that respect. (Wasted in a sense that
battery still gets it in either case, but the caps don't.)

Charging caps from the battery through DC-DC does not waste energy,
it just transfers it from one place to another (it's of course wasted in
conversion process, but DC-DC is 97% or so efficient).

Also you don't need to charge the caps while cruising. Next regen
when you'll stop will take care of it. DC-DC is to fill them up
and can be controlled on and off as needed. Schematic shown on my
site is just a concept illustrating an idea clearer, many irrelevant
for understanding details are not present there. For instance, battery
bypass when I don't want entire regen current to run through the
battery but still want 100% of it through the caps.

Victor

Roger Heuckeroth wrote:
> Sounds like it only provides a benefit if you have regen, and then 
> only for short regen cycles. Long downhills would overwhelm the caps. 
> Charging the caps from the battery through a DC-DC would just waste 
> energy.
> 
> Sent from my iPhone
> 
>


> "matt" <[email protected]> wrote:
> >
> >> A minor typo correction.
> >> When the caps are wired in series, the battery isn't burrdened with
> ...


----------



## EVDL List (Jul 27, 2007)

Victor,

Will you be integrating this into your Audi, or CRX?

Roger

Sent from my iPhone



> Victor Tikhonov <[email protected]> wrote:
> 
> > Matt summarized this quite well. Basically, if you wire the caps
> > directly in parallel, you can reduce current out of batteries
> ...


----------



## EVDL List (Jul 27, 2007)

[ OT for this thread, but we have been for a while... ]

Given the following:
- 12x 12V Group31 Deka Gels
- Logisystems 144-156V 1000A controller

What would you think of putting a 12V cap in series with the battery pack to
bring it from 144V nominal to 156V nominal (sorry, my controller can swing
350V to 700V!) and either using a DC/DC to charge the 12V cap, or the aux
battery, or an alternator which can be clutched in for regen.

A large enough cap could still take a bit of the hit off the Gels on
accelerations? Or does the current flow thru them anyway... I'm a little
out of my depth here.

Basically, would it be a form of hardening, but taking full advantage of the
Caps, instead of just (V1-V2)*F = C, we get V1*F Coulombs.
To put some numbers to it:
Say my 144V pack is resting at 165V and sags to 140V under load.
Say we have lots of those Maxwell 3000 Farad 2.7V caps on hand.

When charging, the 144V pack can get nice and high, so for a safety margin,
you design the paralled capacitor bank for 192V, or 192V/2.7V= 72 caps.
These will provide, in series, 3000F/72 = 41.67F

Under the hard accelleration, the caps will yield:
(V1 - V2 ) * F = C
Where:
V1=165 the resting voltage, fully charged
V2=140 the sagged voltage of the pack, when the caps are providing nothing
for you.
We have:
(165-140)*41.67= 1041.75 Coulombs

Under, say, a 200A load, using C=A*dt, this will carry you 1051.75/200A =
5.25 seconds.
(not sure the sag versus amp draw is realistic for the 8G31's but whatever)


Instead, if we just add the 12V to the end of the pack for 156V nominal, for
the same 72 caps we get:
12V/2.7=5 caps in series, so 3000F/5 = 600F per series.
There are 72 caps, so we can get 14 parallel sub-strings out of these.
That gives us 600F*14 = 8400F
[Someone double check this math please, I'm venturing out of my comfort
zone]
Now we have:
V1=12
V2=0
We don't care what the pack is doing under load, or the initial voltage,
simply that the caps get drained to 0V
And we have:
(12-0)*8400F = is this really 100,800Coulombs ? 100 times the amount !?
28Ahr ?

This would carry you, under the same 200A load, 100,800C/200A= 504 seconds =
8.4min ? You'd be at warp speed ;o)

My math / knowledge must have fallen apart somewhere along the line here...
help!


-Nick




>
>


> Victor Tikhonov <[email protected]> wrote:
> >
> > >
> > > With series connection, my initial voltage is 2x of the battery
> ...


----------



## EVDL List (Jul 27, 2007)

Victor,

Once the caps discharge does battery current flow through them or is there some kind of bypass? Does this pose any kind of restriction? Do they get hot?

Thanks for a great explanation of the benefits of series connection.

Frank




________________________________
From: Victor Tikhonov <[email protected]>
To: Electric Vehicle Discussion List <[email protected]>
Sent: Thursday, February 26, 2009 8:19:02 PM
Subject: Re: [EVDL] active balancing


<With series connection, my initial voltage is 2x of the battery voltage.......>



_______________________________________________
General EVDL support: http://evdl.org/help/
Usage guidelines: http://evdl.org/help/index.html#conv
Archives: http://evdl.org/archive/
Subscription options: http://lists.sjsu.edu/mailman/listinfo/ev


----------



## EVDL List (Jul 27, 2007)

Frank,

There is bypass, and actually more than just bypass - there are means to 
maintain few volts in forward direction - else some of the caps
will inevitable reverse if you discharge the pack to exactly zero
as they are never identically balanced. Some caps of 0V pack will have
little positive voltage on them (OK) and others - some negative
(not OK). Positively biased (about 12V) bypass assures no cap is reversed.

There are fine details that will take too long to explain and
that are probably is too boring for general EVDL.

Victor



> Frank John wrote:
> > Victor,
> >
> > Once the caps discharge does battery current flow through them or is
> ...


----------



## EVDL List (Jul 27, 2007)

Was planning for Audi, but I have issues with HV inverters
and may look for alternatives. If those will not be
750...900VDC capable, it makes no sense to use caps in this
configuration. Side benefit (goal) was to have only 400V
battery while having 750V performance, but again, I'm unsure
which inverters I will end up with.

The ACRX has mid voltage 350VDC system, so it cannot use
series caps connection concept, at least with 350V Li battery
I'm planning to install one of these days.

Victor

Roger Heuckeroth wrote:
> Victor,
> 
> Will you be integrating this into your Audi, or CRX?
> 
> Roger
> 
> Sent from my iPhone
> 
>


> Victor Tikhonov <[email protected]> wrote:
> >
> >> Matt summarized this quite well. Basically, if you wire the caps
> >> directly in parallel, you can reduce current out of batteries
> ...


----------



## EVDL List (Jul 27, 2007)

Victor,

Does a higher battery side voltage help an AC controller as much as it 
does a DC controller? I was under the impression from things that I 
have read that AC motors are not quite as "amp hungry" starting from 
stall as a DC motor is. My understanding is that an AC induction 
motors torque is proportional to slip (difference between the rotor 
speed and the stator winding felid speed). With a DC motor controller 
your controlling voltage (and thereby amps) at the motor. With an AC 
motor controller your controlling both voltage and frequency. Have I 
been mislead on this?

The industrial variable frequency drives that I use in my business 
provide a nice smooth high torque start without drawing a lot of 
amps. I also understand that where high voltage is required for AC 
motors is at the high speed end to extend the point at which torque 
starts to fall off. If that is the case, your series capacitors would 
be sucked dry at that point and give no advantage.

I just wonder if all the expense of the caps and related circuitry 
really provide much of an advantage on an AC system. In your case you 
own them, but would you advise this set up to anyone. I believe you 
said once before that the money would be better spent on the battery 
pack.

Roger



> Victor Tikhonov wrote:
> 
> > Was planning for Audi, but I have issues with HV inverters
> > and may look for alternatives. If those will not be
> ...


----------



## EVDL List (Jul 27, 2007)

> Jack Rickard wrote:
> 
> > Roger Heuckeroth wrote:
> >>
> ...


----------

