# [EVDL] battery balancers



## EVDL List (Jul 27, 2007)

Has anybody had any experience with the battery balancing modules on the
Tradin' Post?
http://evtradinpost.com/index.php?method=showdetails&list=advertisement&rollid=5416&fromfromlist=classifiedscategory&fromfrommethod=showhtmllist&fromfromid=31

The company information says they will work with different battery
chemistries= lithium or lead acid. The information they sent me includes
this: Product name: single cell equalizer for lithium battery. Product
model: QNBBM-4S.
LGBBM equalizer module adopts distributed ,parallel,two-way,energy
transferring type which is
the ideal balance solution.Using the latest circuit technology and devices,
such as synchronous
rectification, soft switches, etc., to achieve high efficiency and high
product reliability.

I wonder what LGBBM is?

Michael B
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## EVDL List (Jul 27, 2007)

I haven't but looking at the ad and the picture I wonder what their
current drain is, if it is even across the pack, and what happens if
you only have 1-2 cells hooked up to the "last" module in your pack.
The ad says that you need this device because BMS systems typically
have low current shunting and that your batteries need more than this.
My experience so far doesn't support this. In another thread Travis
posted about how the warmer batteries in his pack reach full before
the cooler ones do but he didn't indicate what the shunting current
was or how much energy difference there was. It may be that if you
have a large temperature differential you will need some regular
balancing but I still don't think it needs to be as much as the ad
implies.

FWIW, my Black Sheep Technology BMS boards only have a 1mA draw when
not shunting or in an alarm state. I built my batt-bridge circuit so
that it only has a 0.3mA current draw.



> Mike Beem <[email protected]> wrote:
> > Has anybody had any experience with the battery balancing modules on the
> > Tradin' Post?
> > http://evtradinpost.com/index.php?method=3Dshowdetails&list=3Dadvertiseme=
> ...


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## EVDL List (Jul 27, 2007)

Danger. Claims with no back up to the claim is a very very dangerous thing.
Typed claims or typed words saying its so is not proof. I'd not bother. I am
BMS free with LiFePO4 Cells. Doing just fine and with a split pack. No
issues with differing temps either. Hot, cold or warm. 

Pete  

-----
If you don't understand, be patient, you will. Now I understand. 
--
View this message in context: http://electric-vehicle-discussion-list.413529.n4.nabble.com/battery-balancers-tp3711266p3711456.html
Sent from the Electric Vehicle Discussion List mailing list archive at Nabble.com.

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## EVDL List (Jul 27, 2007)

> gottdi wrote:
> >
> > I am BMS free with LiFePO4 Cells. Doing just fine and with a split pack.
> > No issues with differing temps either. Hot, cold or warm.
> ...


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## EVDL List (Jul 27, 2007)

Dan,

Do NOT use a PakTrakr on LiFePO4 cells if you are not going to top
balance on every charge. The PakTrakr pulls its power from only the
first three cells in a monitor group and you will put them way out of
balance in a relatively short period of time. You absolutely must NOT
put anything on your pack which will put an uneven draw on it unless
you have a BMS system to correct for it.

If you are not going to go with a cell level BMS then you might want
to go with a Lee Heart Batt-Bridge type circuit. I went with a
modified version of what is posted in the EVDL Library. Basically I
did this:

Bat Neg -- 100k resistor at post -- wire to one side of a 1K 15-turn
pot -- oposite side of pot -- wire -- 100k resistor at post -- Bat Pos

I then installed a digital volt meter with an isolated power supply
(9V battery) to the center post of the pack and the wiper of the pot.
I have the volt meter calibrated to display double the input voltage
so I know the actual difference in 1/2 pack voltages. When the voltage
of each half of the pack was exactly the same I adjusted the pot so
the voltage read zero. I did install a 10k resistor at the middle
terminal before the wire to the volt meter as a safety in case of a
short. I chose the resistors so the current drain in my case is under
0.35mA and a worst case short of one of the wires is only going to
draw 0.7mA for a + or - lead and 3.5mA for the center tap. This was
easier than trying to find high voltage, low current fuses in a small
package to mount to a battery post.

If you wish you can see pictures on my blog at
http://2003gizmo.blogspot.com/2011/07/battery-pack-balance-monitor.html.




> Danpatgal <[email protected]> wrote:
> >
> > gottdi wrote:
> >>
> ...


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## EVDL List (Jul 27, 2007)

Thanks for the link to that meter. I've heard about Fair Radio but
forgot about it. Maybe you were the one who told me about it, even. I
did go correct your name misspellings in my blog. I will say, however,
that you do have a heart! 

I'll have to keep looking for a 50uA or so meter. At that point,
however, I will have to select the resistors to match my pack voltage
and what I want the meter to display for a given condition.



> Lee Hart <[email protected]> wrote:
> > On 8/3/2011 8:09 PM, David Nelson wrote:
> >> If you are not going to go with a cell level BMS then you might want
> >> to go with a Lee Heart Batt-Bridge type circuit. I went with a
> ...


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## EVDL List (Jul 27, 2007)

I went another route for this solution. I got an RC charger that can put
out about 5A or 50 watts. It can charge 1 to 5 lithium cells. It's also
adjustable for a couple types of lithium, NiCd, or lead-acid. The RC
charger does a good job of tapering off when needed and doesn't overcharge
the cells. Even when charging 5 cells in a serial string, it never caused
my BMS to alert.

Rather than trying to transfer charge from high cells to low cells, I just
charged them all up with the RC charger. That brought them up to a common
point. (Obviously, I'm top balancing). Once I got them all to the same
state of charge, the pack was balanced enough that the charger's taper at
the end of charge, working with the BMS shunts, was enough to balance the
pack.

Before I "topped up" all the cells, the pack was so far out of balance that
the highest cells would start to go over-voltage and the BMS would shut off
the charger before the charger had left its bulk charge mode and started the
low-current taper. In that situation, I wasn't getting enough shunting to
equalize the pack.

The Elcon charger now gets through its full taper cycle and shuts itself off
and I haven't used the BMS alert to stop charging for a few months. 

The other advantage of the RC charger is that it tells you how many Ah it
put into each cell to get them up to that fully charged state. That can
help you understand how far off your cells were.

I bought the Sky Charger B6AC DUAL POWER Charger from the Xheli store,
through Amazon. (It can be powered either through 110VAC or 12VDC.)

Mike

P.S. One thing that makes me nervous about that ad is that it sounds like
it's trying to throw in every important-sounding buzzword possible. That
always concerns me.

> -----Original Message-----
> From: [email protected] [mailto:[email protected]] On
> Behalf Of Mike Beem
> Sent: Monday, August 01, 2011 9:40 PM
> To: Electric Vehicle Discussion List
> Subject: [EVDL] battery balancers
> 
> Has anybody had any experience with the battery balancing modules on the
> Tradin' Post?
> http://evtradinpost.com/index.php?method=showdetails&list=advertiseme
> nt&rollid=5416&fromfromlist=classifiedscategory&fromfrommethod=showh
> tmllist&fromfromid=31
> 
> The company information says they will work with different battery
> chemistries= lithium or lead acid. The information they sent me includes
> this: Product name: single cell equalizer for lithium battery. Product
> model: QNBBM-4S.
> LGBBM equalizer module adopts distributed ,parallel,two-way,energy
> transferring type which is the ideal balance solution.Using the latest
circuit
> technology and devices, such as synchronous rectification, soft switches,
> etc., to achieve high efficiency and high product reliability.
> 
> I wonder what LGBBM is?
> 
> Michael B
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## EVDL List (Jul 27, 2007)

>
> What I was looking to use these for now would be to balance AGM batteries.
> They have a 10amp current capability, and this is where I have run into
> problems in the past with AGM's and Regulators. Too many times the bypass
> current exceeded the regulator's capacity to shed it.

I would also be interested if they turned out to work for Lithium.
Michael B
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