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#### Functional Artist

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Batt-Bridge "Battery Pack Balance Monitor" (wiring diagram & instructions)

This is (IMHO) how a Batt-Bridge works (Lee Hart's Battery Balance Analyzer)

...& (IMHO) how they are to be wired up.

I, like to, call it a "BPBM" (Battery Pack Balance Monitor)

http://www.evdl.org/pages/battbridge.html

Here is the description:

"The Batt-Bridge is about as simple as you can get; that's why it is so inexpensive. If all you want is an 'idiot' light to say, "Stop driving, your batteries are dead," I can't imagine anything any simpler. You really don't need dozens of ICs and hundreds of components just to light a light.
The Batt-Bridge divides the pack in half, and compares the voltage of each half. It lights an LED when one of them is 1v less than the other.

If a cell dies somewhere in the pack, it typically causes a 2 volt change. So the Batt-Bridge warns you that a cell went dead. There are two LEDs, so they indicate which half-pack contains the bad cell.

R1 and R2 are chosen to draw about 10-20ma from the pack. For example, if you have a 120v pack, R1 and R2 each have about 60v across them. At 15ma, they would be R = 60v / 0.015a = 4k ohms. They need to be identical values (1% or hand picked or trimmed). And they must be power resistors; 60v x 0.015a = 0.9 watts, so use at least a 2 watt resistor.

Use an ordinary low brightness green LED. Its purpose is just to indicate that power is on, and to act as a low-voltage 2.4v "zener" diode. However, the red LEDs should be high brightness types -- the brighter the better, so you can see them even in daylight.

Here's how it works. All voltages are relative to the pack center tap. If +pack == -(-pack), then the green LED lights. The green LED's anode is at +1.2v, and its cathode is at -1.4v. The red LEDs don't light because they only have 1.2 volts across them (they need over 1.5v to light).

Now, suppose you have a dead cell in the upper half of the pack. Then +pack is 2v less than -pack. R1 and R2 form a voltage divider, so both ends of the green LED are 1v more negative; its anode is at +0.2v, and its cathode is at -2.4v. This means there is now 2.4v across the lower red LED; so it lights! Likewise, if the dead cell is in the lower half, then the upper red LED lights.

The total resistance of R1 and R2 sets the sensitivity, and the ratio of these resistors sets the desired center-tap voltage of the pack. If both LEDs light, then the resistors are too low a value; increase the resistance of both of them proportionately. Ten milliamps through the resistors is low sensitivity (over 2v difference to light an LED); 20ma is normal sensitivity; 40ma gives you high sensitivity (less than 1v difference to light an LED).

If one LED lights when the half-pack voltages are correct, then adjust the value of one of the resistors. This is also how you deal with packs with an odd number of batteries, where the "center tap" is off by one."

From personal testing,

...this seems to work good for monitoring "simple" pack imbalance

...but, I have NOT been able to duplicate the claim, that it will indicate or tell you to "Stop driving, your batteries are dead,"

Here is a video to help explain the concept in a bit more detail

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#### Functional Artist

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Re: Batt-Bridge "Battery Pack Balance Monitor" (wiring diagram & instructions)

Here is another video

...testing a 24V version of a Batt-Bridge "BPBM" Battery Pack Balance Monitor

...for functionality (to make sure it works)

...& use data (to see how it works)

#### alvin

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Re: Batt-Bridge "Battery Pack Balance Monitor" (wiring diagram & instructions)

I have never seen the claim that it monitors SOC , just that there is an imbalance. And you should stop driving or charging until you find out why.

http://www.sunrise-ev.com/LeesEVs.htm#battbridge

#### Functional Artist

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Re: Batt-Bridge "Battery Pack Balance Monitor" (wiring diagram & instructions)

I have never seen the claim that it monitors SOC , just that there is an imbalance. And you should stop driving or charging until you find out why.

http://www.sunrise-ev.com/LeesEVs.htm#battbridge

I simply got it from:

"Here is the description:"

"The Batt-Bridge is about as simple as you can get; that's why it is so inexpensive. If all you want is an 'idiot' light to say, "Stop driving, your batteries are dead," I can't imagine anything any simpler."

...or more specifically:

Maybe I understood it wrong

#### john61ct

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Re: Batt-Bridge "Battery Pack Balance Monitor" (wiring diagram & instructions)

Stop driving, your imbalance within the series string shows something is wrong.

Would be more accurate.

The side LEDs in that video should be high power Red, the yellow is too weak.

#### Duncan

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Re: Batt-Bridge "Battery Pack Balance Monitor" (wiring diagram & instructions)

...or more specifically:

Maybe I understood it wrong
I took that as meaning that you have an imbalance - STOP and fix it!

You need something in addition to stay - STOP your batter is too low

With a Chevy Volt pack I'm simply using voltage as that chemistry has quite a respectable voltage/charge slope

When I had my headways I used the Amp hour facility on my Cycle Analyst

#### Functional Artist

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Re: Batt-Bridge "Battery Pack Balance Monitor" (wiring diagram & instructions)

I took that as meaning that you have an imbalance - STOP and fix it!

You need something in addition to stay - STOP your batter is too low

With a Chevy Volt pack I'm simply using voltage as that chemistry has quite a respectable voltage/charge slope

When I had my headways I used the Amp hour facility on my Cycle Analyst

Thank you all for the replies,

Layman's terms

We need to be CRYSTAL CLEAR about things

... the average joe, probably 50% of DIY folks (me included)

...to mean "your batteries have been discharged"

Like, "left the lights on till the battery went dead"

...or when you used to crank your old ICE auto till the "battery died"

That's kinda why I started this thread

Because while doing research on Chevy Volt batteries, I have found many vague references to Batt-Bridge's & their use but, not a lot of CRYSTAL CLEAR specifics

...on their actual construction

...or what to expect while using

(I assumed that when an imbalance was detected the green LED would go off & either of the red LED's would light up, that's not what actually happens)

So, I did some experimenting

...to document the building of a Batt-Bridge

...& use of this kool little contraption

* I wanted to make it CRYSTAL CLEAR that "from my experience" a Batt-Bridge will NOT tell you to "Stop driving your batteries are dead"

** I agree, adding an amp/volt meter would make a Batt-Bridge a more useful tool

*** Working on that next

#### Functional Artist

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Re: Batt-Bridge "Battery Pack Balance Monitor" (wiring diagram & instructions)

Stop driving, your imbalance within the series string shows something is wrong.

Would be more accurate.

The side LEDs in that video should be high power Red, the yellow is too weak.

Yes, exactly

...it's labeled as a "Out-of-Balance Battery Detector"

...NOT any type of a gauge

I was just going by the description

Another vagueness I have found

...in the diagram http://www.evdl.org/pages/battbridge.html it specifies D2 & D3 are "red high-efficiency LED" & D1 is just a green LED.

...in the written description down below it says: "Use an ordinary low brightness green" & "the red LED's should be high brightness types -- the brighter the better, so you can see them even in daylight."

...& your recommendation: "should be high power red, the yellow is too weak"

So, we have

...a. "red high-efficiency LED"

...b. "the red LED's should be high-brightness types"

...c. "should be high power red"

...d. looking on-line I have found LED's labeled as "ultra bright"

All say about the same thing (I think) but, it's NOT CRYSTAL CLEAR for the lay person (your average DIY guy or gal)

So, for the record, which LED's are the "right" ones for a Batt-Bridge?

* The yellow LED's are to help make it "idiot proof" for me.

My twins are running 24V motors on their karts.

I have 48V motors on other karts & my motorcycle.

The Batt-Bridge's, that I made, with the red LED's are to check the balance of 48V battery packs.

The Batt-Bridge with the yellow LED's are to check 24V battery packs.

...this way I can always "easily" tell which one is which

#### Functional Artist

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Re: Batt-Bridge "Battery Pack Balance Monitor" (wiring diagram & instructions)

I have assembled a couple of different "mobile" Batt-Bridges for doing "spot checks" on different voltage battery packs

I want to mount one permanently on to "El Moto" my electric motorcycle

...so, I can monitor battery pack balance while riding

They could also be mounted

...to the steering support of go karts & golf carts

...or even on the dash of cars & trucks

But, what if you do NOT want your Batt-Bridge on all of the time?

The ability to turn it off when not in use would be important

...it would probably take like forever & a day for them little LED's to drain the battery pack but, still, it's not good to have a constant drain on your battery pack, even if it's dinky

Well, to be able to turn it off ya, gotta add a switch

...but, not just any switch

Remember a Batt-Bridge has (3) legs or leads

...a positive (+) leg

...a center tap

...& a negative (-) leg

So, the switch will have to sever (2) of the legs/leads to "actually" turn it off

A (double pole single throw) dpst switch will accomplish this

...it is a switch that controls (2) separate circuits at the same time

I have started making a Batt-Bridge with a switch

...it will have the LED's & the switch on the face instead of on the end like I did on the "spot checker" units

I drilled (3) holes for the LED's & (2) others for the switch

...gonna skip the LED bezels on this one for comparison purposes

...drilled the (2) holes for the switch a bit bigger

...then, used a razor knife to connect them holes

...& whittled a little more off each side at a time

...till the switch fit snuggly

* What is the "proper" size/guage wire to be used on Batt-Bridges?

(It will carry pack voltage but, only ~10 - 20ma)

#### john61ct

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Re: Batt-Bridge "Battery Pack Balance Monitor" (wiring diagram & instructions)

Just email the guy, post his answers back here

#### Functional Artist

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Re: Batt-Bridge "Battery Pack Balance Monitor" (wiring diagram & instructions)

I sent this question on on EVDL:

"I am assembling a few Batt-Bridges.

In the description it specifies D2 & D3 are "red high-efficiency LED" & D1 is just a green LED.

...in the written description down below it says: "Use an ordinary low brightness green" & "the red LED's should be high brightness types -- the brighter the better, so you can see them even in daylight.

All say about the same thing (I think) but, it's NOT CRYSTAL CLEAR for the lay person (your average DIY guy or gal)"

** OK, here is what Mr. Lee Hart replied:

Yes, they are all saying the same thing. There are no good definitions

for LED efficiency and brightness, so I had to use generic terms.

* My next question:

"...for the record, which LED's are the "right" ones for building a Batt-Bridge?"

Electrically, what matters is the voltage drop across the diodes. The

*color* (or more precisely, the wavelength in nanometers) of an LED

largely determines this. The green LED should be about 565nm and drop

about 2.1v at 10ma. The red LEDs should be about 635nm and have drop of about 1.8v at 10mA.

Visually, the LEDs can be whatever color and brightness you want, as

long as the voltage drops are about right. Since the green LED is on all

the time (it just tells you the Batt-Bridge has power), you don't want

it to be annoyingly bright. The red LEDs indicate trouble, so you want

them to be bright enough to notice, even on a sunny day.

* My next question:

"...what is the "proper" size/gauge wire to be used on Batt-Bridges?
(It will carry pack voltage but, only ~10 - 20ma)"

The current is low, so just about any size wire will work. Choose it for

mechanical strength and insulation quality rather than wire size.

Be sure the insulation on the wire is good enough. You're connecting

these wire to your high voltage pack! Good wire will have its voltage

rating printed on it, or in its data sheets.

Also, put the resistors at the battery terminal end of the wire. That

way, if there is a short in the wire, the resistor will safely limit the

current.

#### Functional Artist

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Re: Batt-Bridge "Battery Pack Balance Monitor" (wiring diagram & instructions)

Did ya 'all notice that little gem at the end?

"Also, put the resistors at the battery terminal end of the wire. That
way, if there is a short in the wire, the resistor will safely limit the
current."

I have been putting the resistors at the LED end of the wires

...not at the battery terminal ends of the wires

...which does NOT "safely limit the current" coming up to the "monitor"

I guess if it's a "mobile" monitor, it's NOT that big of a deal

Hmmm

I wonder,

...if the switch I added to the last one (to be able to turn it off when not in use)

...will affect the functionality or sensitivity?

It seems to work OK

We'll see

#### PStechPaul

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Re: Batt-Bridge "Battery Pack Balance Monitor" (wiring diagram & instructions)

A few years ago I came up with a more efficient version, by adding an NPN and PNP transistor. It draws only about 1 mA while balanced, and will drive an LED at 5 mA with about 2.2V imbalance, 3 mA at 1.7V imbalance, and 1 mA at 1.4V imbalance:

#### Functional Artist

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Re: Batt-Bridge "Battery Pack Balance Monitor" (wiring diagram & instructions)

Very kool & Interesting!

Thanks for sharing

That's Great! improvements, enhancements & upgrades

I'd like to see more of it

Sometimes you just gotta think about stuff-n-try to make it

...better

...or simpler

What do you call your balance monitor with transistors?

Can you provide

...links, drawings, pictures & videos of it's construction &/or use?

#### PStechPaul

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Re: Batt-Bridge "Battery Pack Balance Monitor" (wiring diagram & instructions)

I have not built it, but only simulated it in LTSpice. The schematic is shown. I tried some other enhancements that made it a bit more sensitive, and used higher voltage transistors (150V) 2N5550 and 2N5401 to handle a 200+ volt pack. For even higher voltage, maybe split the pack into more sections. I don't show LEDs in my circuit, but they would be in series with the 10k resistors R3 and R4. Instead of LEDs, you could use optoisolators that would make it safer, and the warning lights could be on the 12V accessory circuit.

Here is a simple modification that will detect an imbalance as low as 500 mV, but could be a bit "touchy":

Adding a 10k resistor between the bases makes the circuit more reliable and stable.

#### EVfun

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Re: Batt-Bridge "Battery Pack Balance Monitor" (wiring diagram & instructions)

I have not built it, but only simulated it in LTSpice. The schematic is shown. I tried some other enhancements that made it a bit more sensitive, and used higher voltage transistors (150V) 2N5550 and 2N5401 to handle a 200+ volt pack. For even higher voltage, maybe split the pack into more sections. I don't show LEDs in my circuit, but they would be in series with the 10k resistors R3 and R4. Instead of LEDs, you could use optoisolators that would make it safer, and the warning lights could be on the 12V accessory circuit.
The LED does seem to be missing from your posted model...

#### Functional Artist

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Re: Batt-Bridge "Battery Pack Balance Monitor" (wiring diagram & instructions)

A few years ago I came up with a more efficient version, by adding an NPN and PNP transistor. It draws only about 1 mA while balanced, and will drive an LED at 5 mA with about 2.2V imbalance, 3 mA at 1.7V imbalance, and 1 mA at 1.4V imbalance:

**"A few years ago I came up with a more efficient version"

***"I have not built it, but only simulated it in LTSpice"

NOT to be rude but,

What are you waiting for?

Build it, test it, share the results

then, show others how to make 'em.

"on with the show"

#### Functional Artist

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Re: Batt-Bridge "Battery Pack Balance Monitor" (wiring diagram & instructions)

Did ya all know

Mr. Lee Hart has a web site full of interesting info

He also sells his Batt-Bridges & a lot of other kool stuff

check it out

http://www.sunrise-ev.com/index.htm

Batt-Bridge parts kit -- \$10. Includes LEDs, resistors, lamp holder, and detailed instructions. Specify pack voltage. \$5 for US shipping and handling.

Batt-Bridge, Assembled -- \$20. Assembled Batt-Bridge in panel mounted lampholder, with resistors and detailed instructions. Specify pack voltage. \$5 for US shipping and handling.

#### Functional Artist

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Re: Batt-Bridge "Battery Pack Balance Monitor" (wiring diagram & instructions)

I finished up the 48V Batt-Bridge with a switch

...& tested it over the weekend

As far as I can tell,

...adding a switch does NOT seem to affect the performance

While I was posting the video I came across this:

He calls it a "Battery Charger Controller Module"

The guy sells them & other stuff

https://www.ebay.com/itm/12V-24V-36...Switch-Control-Protection-Board-/122706296131

Does it look like it has any potential?

#### PStechPaul

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Re: Batt-Bridge "Battery Pack Balance Monitor" (wiring diagram & instructions)

I'm not really interested in building, testing, and selling simple circuits like the balance monitor. I don't have an EV, although I am still planning to complete an electric lawn tractor some day, and I will need some sort of BMS and charger. But I also have a couple of EMW chargers that I have been trying to improve upon, and other projects of higher priority. Now I have an idea for a modular BMS/charger designed for single cells (or 6-8-12 volt SLA batteries).

I also have a PCB designed and built for a four-cell BMS with shunt balancing and bottom cell charging, but I have not done much with it. I tend to devote time to projects while they present a challenge, and then lose interest when I am satisfied that the issues are resolved.

You, or anyone, are welcome to use my designs and run with them to make products for your own use or offered to the EV community.

Lee Hart's products look interesting, but are generally too simplistic for my taste. The video that shows various means to limit charging is also interesting, but I would use a PIC instead of the discrete and analog components he uses. I also commented on your video, suggesting you show the voltages of the batteries when the imbalance light glows.

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