# [EVDL] A123 balancing with TL431



## EVDL List (Jul 27, 2007)

Last year I noticed that Viktor designed a circuit with this
regulator to regulate the max voltage on his Li-Ion batteries 
and taper the charger back using an opto-isolated bus.
I bet it will show on the Metric Mind website.

Only thing I did not like is that the transistor he
specified maxes out at 10A while he uses 20A fuse.
But I guess his concern was to blow a fuse and burn
his batteries, he rather burn up the regulator and
keep the battery.

Regards,

Cor van de Water
Systems Architect
Proxim Wireless Corporation http://www.proxim.com
Email: [email protected] Private: http://www.cvandewater.com
Skype: cor_van_de_water IM: [email protected]
Tel: +1 408 542 5225 VoIP: +31 20 3987567 FWD# 25925
Fax: +1 408 731 3675 eFAX: +31-87-784-1130
Second Life: www.secondlife.com/?u=3b42cb3f4ae249319edb487991c30acb

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Mark Hanson
Sent: Friday, May 02, 2008 5:24 AM
To: [email protected]
Subject: [EVDL] A123 balancing with TL431


Hi,

I made a balancer using the TL431, goto www.digikey.com and put in the TL431 and click on the data sheet. Look at page 26 Figure 21 "High Current Shunt Regulator".

First note that the shunt regulator must be set to 2X the final current taper of the charger, if the final charger current is 200ma then the regulator must handle 400ma.

The TL431 will handle 100ma by itself or 200ma with a 6.8 - 10 ohm resistor in series with the cathode as in the previous example on page 25 at the top of the page Figure 17 "Shunt Regulator". Siunce I'm doing a UPS and my final taper is only 50ma I can use this circuit with a single 10k trimpot instead of R1/R2. Also note that the R1 (or high side of the pot) should go out directly to the battery after the resistor (the schematic in Fig 17 is in error) as it will not regulate well unless you tie the pot directly to the battery. Adjust for 3.6V if cyclic charging at 2x final taper current (100ma in my case since my charger taper is 50ma) or 3.45V if float charging for an UPS application.

If > than 150 - 200ma then use the figure 21 schematic and again tie the hi side pot to the other side of the load resistor *and* the load resistor should be on the collector side of the PNP transistor *not* where it is shown. Use a 2N2907A for 600ma or if more current is needed a TIP125 or TO-220 type will be needed. Also there should be a 1k resistor in series with the base and I didn't need the pull-up shown (from the top of the cathode to V+. (so this schematic had some errors too). This circuit will work for 3.45V, 3.6V or for higher voltage sealed batteries, 14.5 for Optimas, Hawkers etc. Size the load resistor/wattage acordingly to drop about half the voltage of the transistor at the desired shunt current (2x of final charge taper for effective clamping).

Have a voltage clamped day,
Mark
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## EVDL List (Jul 27, 2007)

Mark Hanson wrote
> I made a balancer using the TL431...

This is a good part; accurate and widely available. However, it draws 
about 400uA, which could be a problem with low capacity cells. A123's 
are about 2.3 amhours, so 400uA drains it in 5750 hours or 8 months. 
Since fully discharging a lithium cell is fatal, you'll have to be 
careful, especially if there are other parts of your circuit that 
increase this current consumptions.

> I can use this circuit with a single 10k trimpot instead of R1/R2.

This is another 320uA of load.

> This circuit will work for 3.45V, 3.6V or for higher voltage
> sealed batteries, 14.5 for Optimas, Hawkers etc. Size the load
> resistor/wattage accordingly to drop about half the voltage of the
> transistor at the desired shunt current (2x of final charge taper
> for effective clamping).

Good advice. The idle supply current is less of a problem with high 
amphour batteries.



> Cor van de Water wrote:
> > Last year I noticed that Viktor designed a circuit with this
> > regulator to regulate the max voltage on his Li-Ion batteries
> > and taper the charger back using an opto-isolated bus.
> ...


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## EVDL List (Jul 27, 2007)

[No message]


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## EVDL List (Jul 27, 2007)

Well... If you discharge with REALLY small load the cell to 0V (or near, 
but still at positive side) You will be able to resurrect LiFePO4 cells.

LiCo will die for sure.

I have had several TS LFP cells sitting in zero for several months. 
After few cycles they gave nearly the original capacity but had 
remarkably better performance. So internal resistance drops after this 
kind of "murder attempt".

I'm testing this now on my drag bike. To get more out of the LFP-40s <GRIN>

-Jukka

Lee Hart kirjoitti:
> Mark Hanson wrote
> > I made a balancer using the TL431...
> 
> This is a good part; accurate and widely available. However, it draws 
> about 400uA, which could be a problem with low capacity cells. A123's 
> are about 2.3 amhours, so 400uA drains it in 5750 hours or 8 months. 
> Since fully discharging a lithium cell is fatal, you'll have to be 
> careful, especially if there are other parts of your circuit that 
> increase this current consumptions.
> 
> > I can use this circuit with a single 10k trimpot instead of R1/R2.
> 
> This is another 320uA of load.
> 
> > This circuit will work for 3.45V, 3.6V or for higher voltage
> > sealed batteries, 14.5 for Optimas, Hawkers etc. Size the load
> > resistor/wattage accordingly to drop about half the voltage of the
> > transistor at the desired shunt current (2x of final charge taper
> > for effective clamping).
> 
> Good advice. The idle supply current is less of a problem with high 
> amphour batteries.
> 


> > Cor van de Water wrote:
> >> Last year I noticed that Viktor designed a circuit with this
> >> regulator to regulate the max voltage on his Li-Ion batteries
> >> and taper the charger back using an opto-isolated bus.
> ...


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## EVDL List (Jul 27, 2007)

Cor,

Because transistor collectors are connected directly to the
heat sinks and sinks were installed on the TS cells about
1cm apart http://www.metricmind.com/ac_honda/images/bms_finished2.jpg
intent for 20A fuse is to protect the cells in case two sinks short
together; such short would bypass the clampers and has nothing
to do with it's circuitry and components ratings. Fuses were not
meant to protect clampers.

Victor
'91 ACRX - something different




> Cor van de Water wrote:
> > Last year I noticed that Viktor designed a circuit with this
> > regulator to regulate the max voltage on his Li-Ion batteries
> > and taper the charger back using an opto-isolated bus.
> ...


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