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



## Functional Artist (Aug 8, 2016)

*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) 


https://www.youtube.com/watch?v=I8TX8guUsM4&t=2s


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## alvin (Jul 26, 2008)

*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


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## Functional Artist (Aug 8, 2016)

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



alvin said:


> 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


 
Thanks for the reply,


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:

"Stop driving, your batteries are dead,"


Maybe I understood it wrong


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## john61ct (Feb 25, 2017)

*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.


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## Duncan (Dec 8, 2008)

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



Functional Artist said:


> ...or more specifically:
> 
> "Stop driving, your batteries are dead,"
> 
> ...


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


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## Functional Artist (Aug 8, 2016)

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



Duncan said:


> 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
> 
> ...


 
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)

Would comprehend the phrase "your batteries are dead"

...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


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## Functional Artist (Aug 8, 2016)

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



john61ct said:


> 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

...if you think about it

...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


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## Functional Artist (Aug 8, 2016)

*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)


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## john61ct (Feb 25, 2017)

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

Just email the guy, post his answers back here


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## Functional Artist (Aug 8, 2016)

*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?"



** Mr. Hart's answer:

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)"


** Mr. Hart's answer:

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.


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## Functional Artist (Aug 8, 2016)

*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."


So, the Batt-Bridges I have already made up are "technically" wrong


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


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## PStechPaul (May 1, 2012)

*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:


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## Functional Artist (Aug 8, 2016)

*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 

...or add features


What do you call your balance monitor with transistors?

Can you provide

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


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## PStechPaul (May 1, 2012)

*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.


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## EVfun (Mar 14, 2010)

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



PStechPaul said:


> 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...


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## Functional Artist (Aug 8, 2016)

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



PStechPaul said:


> 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"


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## Functional Artist (Aug 8, 2016)

*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.


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## Functional Artist (Aug 8, 2016)

*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

https://www.youtube.com/watch?v=DmwDpcugV-U


While I was posting the video I came across this:

He calls it a "Battery Charger Controller Module"

https://www.youtube.com/watch?v=nJKWCVg1mLs

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?


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## PStechPaul (May 1, 2012)

*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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## Functional Artist (Aug 8, 2016)

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

Aw, come on 

It's your "baby", can't you conjure one up for us?

It only looks like, a couple of transistors &/or resistors, some LED's, a little bit of wire, some solder & maybe an hour (or so) of your time.

You don't need an EV, just to test & prove your theory or improve up on it.

You could build & test it on your kitchen table with some old batteries & a light or motor, like I did. 


I am NOT trying to give you a hard time, I really appreciate your taking the time to share your idea.

But,

"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"

The (2) diagrams are different & there are items missing?

Does it "actually" work in the "real world"?

This is NOT challenging to you?

How can you be "satisfied that the issues are resolved"?


Until it's built & tested, it's just theoretical.


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## john61ct (Feb 25, 2017)

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

Entitled much? Perhaps you could offer to pay someone to service your request.


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## Functional Artist (Aug 8, 2016)

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



john61ct said:


> Entitled much? Perhaps you could offer to pay someone to service your request.


Entitled? NO, I work all day long, everyday.


WOW! It's your idea. 

I thought you would be excited to show & prove that your idea works.


You want someone to pay you, to prove your ideas?

Me too. 


I am very sorry, that you took that the wrong way.

It's only ~$10.00 worth of parts & an hour of your time?

& you would get

...the glory

...the satisfaction

...the acclaim

...maybe even, your name in the history books


No one is paying me

I'm in it for the knowledge 


* I am still very interested in your work, 

...please share when you have more info


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## Functional Artist (Aug 8, 2016)

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

I received another message with some interesting info 

from "Cor van de Water" on the EVDL


"Looking at the Batt Bridge circuit:

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

You can see that it connects to the pack at 3 points:

bottom, mid and top.

So, in order to cut the current, you need to disconnect at least 2.

This can easily be done adding a reed relay in series with the two resistors so the pack+ flows through the resistor, then through the contact of the reed relay, then to the red and/or green LED. From the bottom of the green LED, you go through the contact of the second reed relay, then through the second resistor and to pack-.

The two coils of the two reed relays can be connected to IGN (Ignition) and ground.

Make sure they are 12V reed relay coils.

Note that the resistors are suggested to be dimensioned for 20mA.

That was a good value for older, low efficiency / low brightness LEDs.

Today you can buy LEDs that you cannot look at directly, lest you risk eye damage at 20mA.

So you may need to design for a lower current through the green LED.

One way to do this is to add a resistor in parallel to the green LED, so most of the current bypasses the LED and the LED will be less bright.

You can also increase the resistance of the two resistors R1 and R2 but this makes the circuit less sensitive to imbalance because there is less current change per Volt of imbalance.

This sensitivity can be improved again by adding a zener in series with the resistor, but now we are starting to design a more complex product again...

Cor."


I am going to do some more research 

...on Reed Relays

...& what size resistor will work?
("One way to do this is to add a resistor in parallel to the green LED, so most of the current bypasses the LED and the LED will be less bright.")


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## PStechPaul (May 1, 2012)

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

With my circuit, the current draw is very low, and for higher voltage packs, the resistors can be much smaller. The imbalance LEDs could be powered from +12 and -12 volt taps, or even 3V from lithium cells. I made some further improvements such that for a 144V pack the nominal current draw is about 700 uA when balanced, and the error LEDs light at 1 mA with only 800 mV imbalance. The LED is fully ON with 3.4 mA with 1 volt of imbalance. Here is the simulation:










Note that I have added the error LEDs, but I used ordinary silicon diodes to replace the power ON LED. The models in LTSpice seem to be for white LEDs with 2-3 volt forward drop. The three diodes have adrop of about 1.7 volts which should match a red or yellow LED. The circuit could be further optimized, and built and tested, but I'm satisfied that it will work as per the simulation and I'm not all that excited about proving it. The parts are only pennies, and the circuit would not take long to build, but I'll leave that someone else who wants to do it.


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## Functional Artist (Aug 8, 2016)

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



PStechPaul said:


> With my circuit, the current draw is very low, and for higher voltage packs, the resistors can be much smaller. The imbalance LEDs could be powered from +12 and -12 volt taps, or even 3V from lithium cells. I made some further improvements such that for a 144V pack the nominal current draw is about 700 uA when balanced, and the error LEDs light at 1 mA with only 800 mV imbalance. The LED is fully ON with 3.4 mA with 1 volt of imbalance. Here is the simulation:
> 
> 
> 
> ...


 
I thought about it a bit

I even started a parts list


It's a lot more complicated (part count, connections etc.)


What does it improve on? (accuracy?, power draw?, both?)

How much more accurate?

How much less power will it draw?

What is the level of improvement? (5%, 10%, 20%, 50%)

...is it worth all of the extra effort?

...or, after all is said & done, it's just a fancier, more complicated device that still only has the ability to monitor for a "simple" cell imbalance?

https://www.youtube.com/watch?v=WhUARTHlpH8


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## Functional Artist (Aug 8, 2016)

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

I did some more testing of the Batt-Bridge with a switch, so I can become more familiar with how they operate

I also hooked up some meters to help gather more accurate data


https://www.youtube.com/watch?v=Fi_1ti4D7-s

After testing, I recharged the battery & tested some more

I also, connected the "round" Batt-Bridge I made a few weeks ago
(to confirm my results but, ran into some issues)

...the (2) Batt-Bridges did NOT produce the same readings 

https://www.youtube.com/watch?v=1N8JjeAPSOo


* Evaluation

I know, that the BPBM with a switch is assembled, as per the diagram

So, my "round" BPBM 

...must NOT be assembled correctly


I am going to have to assemble another to confirm


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## PStechPaul (May 1, 2012)

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

I wrote some comments on your videos. To get better sensitivity, the green LED should have just a little lower forward voltage drop than _two_ of the red LEDs. It might be better to use a white LED with about 3V drop, and make sure the red LEDs are high efficiency types with about 1.8 Vf. The typical voltages are listed here:

https://en.wikipedia.org/wiki/Light-emitting_diode










As you can see, there is quite a bit of variation, but for best sensitivity, the red LEDs should be just under their conduction voltage. Then when an imbalance occurs, the green (or white) LED will keep the total voltage the same, but the center tap will cause one to conduct while the other turns off. It might be possible to design a circuit where the green LED turns off when one of the red LEDs turns on, but that will add complexity, and eventually you get to the point where you might as well use a BMS, or at least a PIC.

If you are serious about building a balance monitor, you should get the right parts, or perhaps just build one like I showed in my last simulation. It's really not all that complicated, especially if you use actual NPN and PNP Darlingtons like MPSA14 and MPSA64.

Many choices:
https://www.mouser.com/Central-Semi...stors/MPSA-Series/_/N-ax1sb?P=1yat5x1Z1z0zl5v


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## PStechPaul (May 1, 2012)

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

Here is a simulation of a balance monitor using a dual op-amp. Essentially the same thing could be designed using a small PIC in place of the op-amp. It may look complex, but the principles are quite simple. The PIC could eliminate some of the components as well. Enjoy!


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## PStechPaul (May 1, 2012)

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

I built my version of the Battery Pack Balance Monitor using a PIC12F1822:










It's not pretty, but it works:



















Here are two rough videos (about50 MB each). The first shows a simple program that just flashes the two red LEDs alternately. The circuit draws less than 1 mA with two 12V batteries. For the second video I added the ADC which reads the tap voltage and will cause one or the other red LED to flash if an imbalance of about 160 mV is detected. The white LED flashes off when the red LED is on, because it drops the supply voltage below that needed for the forward voltage.

http://enginuitysystems.com/pix/electronics/Battery_Pack_Balance_Monitor_3777.AVI

There are two 10k resistors across the 24 VDC supply to simulate two 12V batteries. I add a 100k resistor across each of them to drop the voltage to about 11.5 VDC, which is enough to show imbalance.

http://enginuitysystems.com/pix/electronics/Battery_Pack_Balance_Monitor_3780.AVI


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## Functional Artist (Aug 8, 2016)

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

Super Kool! I really like it! Nice Job! 

I (probably a lot of folks) would like to see more.

When you have a minute, can you show it in action?

...monitoring a battery pack


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## PStechPaul (May 1, 2012)

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

Here you go:


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## Duncan (Dec 8, 2008)

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

Maybe its just me - BUT the advantage of the Battbridge is that it is EASY - trivially easy for even an electronic moron like me to put together

Making it more complicated is silly

It uses a lot less power than anything else in the system and if it's connected after the contactors it uses zero when the system is off

Paul's system is smarter but it is also 100 times more complicated


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## PStechPaul (May 1, 2012)

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

Well, so far Functional Artist's videos of the Lee Hart Batt Bridge don't seem to work very well, needing several volts of imbalance to light the red LEDs as indication. Better components may work better, but I haven't seen any demonstration of just how well it might work. Closest thing I found was this video:






The red LED was reasonably lit, but there was no measurement of the voltages of the top and bottom half of the pack.

My circuit is a little more complicated, only 13 components compared to 5 for the Lee Hart circuit, and it uses 1/10 the current. The sensitivity can be programmed to whatever you wish, and the bright blinking white LED is immediately noticeable. If there is enough interest, I can design a PCB and have a quantity made - I think I'll try that www.pcbway.com company that is unbelievably cheap. I can use a PIC12F1571 or PIC12F508 which are only 50 cents in quantity 25, and the other parts are just a few pennies.


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## Functional Artist (Aug 8, 2016)

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



PStechPaul said:


> Well, so far Functional Artist's videos of the Lee Hart Batt Bridge don't seem to work very well, needing several volts of imbalance to light the red LEDs as indication. Better components may work better, but I haven't seen any demonstration of just how well it might work. Closest thing I found was this video:
> 
> 
> 
> ...


 
Hey Duncan & Paul

I too like the simplicity of the Batt-Bridge

but, he's right, from my testing, it doesn't seem to be all that sensitive

(how sensitive do yours seem to be, Duncan?)


*full disclosure

...maybe the ones I have made & tested are still NOT right

From my calculations, to construct a Batt-Bridge for a 48V battery pack you are supposed to use 

...(2) 1.6Kohm x 1W x 1% tolerance resistors

But, the resistors I used (I already had some in a box) are 1.5Kohm x 3W x 1% resistors (close but, no cigar)

...that could be affecting my readings


I have ordered some of the proper resistors & some ultra bright red LED's

...more testing to come


I like the sensitivity adjustment feature on the "PS tech monitor"

Thanks again, for taking the time & the effort

...yes, make more 

...refine your design

...& do more testing 



Simplicity comes with knowledge & repetition

...once you learn how to do something

...then, do it many times

...it becomes simple


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## PStechPaul (May 1, 2012)

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

Try putting one (or more) silicon diodes in series with the green LED to get a higher voltage across the two red LEDs. That should boost sensitivity.


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## Functional Artist (Aug 8, 2016)

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

Still trying to figure out these Batt-Bridges 

-so simple a cave man can do it, really? 

The first Batt-Bridges I made (going by the original version):

I divided the 48V pack voltage in half. (48V /2 = 24V) 

24V / .015 = 1,600 Ohm

24V x .015 = .36 W 
(then doubled the wattage to be able to handle the whole pack voltage)


So, I used 

...(2) 1.5Kohm 2W 1% resistors (because I already had them)

...(2) standard brightness red LED's

...& (1) standard brightness green LED


But, it didn't seem to work right

So, I made another (this time going "by the book") & used

(2) 1.6Kohm 1W 1% power resistors

(2) ultra bright red LED's

(1) standard green LED


But, it still didn't seem to work right.

...while going over everything, double checking & trying to figure this thing out.

I noticed that that the description has changed, on the web site, a little bit.

Now, it says, 
R = packV / 0.02A Ohms 1% (48V / 0.02A = 2,400 Ohm 1%)
P = packV 0.01A Watt (48V x 0.01A = .48W)


* Well huh, 
...does this mean that I should have used (2) 2,400Ohm .5W 1% resistors instead of the 1,500Ohm 1W 1% resistors?


So, I sent another message to Mr. Hart, 

...explaining the issues that I was having & asked if I should be using 

...1.6Kohm 1W 1% resistors (according to the old version)

or 

...2.4Kohm .5W 1% resistors (according to the the new version) 


His response:

"That all sounds correct. What problem are you having?

The LED current is not critical. Anything from 10ma to 20ma is usually 
fine, and the resistors can vary over a range of values -- they just 
have to be the *same* value.

I would suggest testing your batt-bridge. This is pretty easy if you 
have (or can throw together) a small adjustable-voltage power supply. 
With your setup, I would use a 24v battery (any kind; it only has to be 
able to supply 10-20ma), and an adjustable 24v power supply. Connect the 
24v battery and 24v supply in series. Connect the Batt-bridge to it as 
if it is your 48v pack.

The green LED should always be on. it just tells you there is power. 
When you adjust the 24v supply, you should see

23v - upper red LED on (and green LED)
24v - only the green LED
25v - lower red LED on (and green LED)

The precise threshold where the red LED begins to glow is adjusted by 
the choice of LEDs. Picking red LEDs with a higher voltage makes the 
+/-1v threshold get bigger. Picking green LEDs with a higher voltage 
makes the +/-1v threshold get smaller.

The resistor values basically set the brightness. You want it bright 
enough to notice in the daytime; but not so bright that it's painful at 
night. You also don't want to use up a lot of battery current 
continuously (if the Batt-Bridge is on all the time -- though I think 
you were going to use a switch or relay to turn it off when parked?)

Does this help?"


* I thought to myself, Not really, 

...it was an "either" - "or" question

...800 Ohm's is quite a difference 

...if the LED current is NOT critical

...why bother doing the math?


----------



## Duncan (Dec 8, 2008)

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

_...why bother doing the math?_

Because while it's not critical to be exact - if you get it too far out it won't work!


----------



## Functional Artist (Aug 8, 2016)

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



Duncan said:


> _...why bother doing the math?_
> 
> Because while it's not critical to be exact - if you get it too far out it won't work!


I was being sarcastic 

but, I asked a simple "going by the actual Batt-Bridge description, math" question (1.6K or 2.4K)


So, I went at it from a different direction
...& did some other testing

I tested the individual resistors, that I have been using 
...800 Ohm, 1.5K Ohm, 1.6K Ohm & even 3K Ohm
[email protected] 12V, 24V & 48V 

Just, to see (for myself) how many milliamps each size was letting thru @ the different voltages

According to my tests
12V
...800 Ohm = 16mA
...1.5K Ohm = 8mA
...1.6K Ohm = 8mA

24V
...800 Ohm = 32mA
...1.5K Ohm = 16mA
...1.6K Ohm = 16mA

48V
...800 Ohm = 63mA
...1.5K Ohm = 32mA
...1.6K Ohm = 32mA

...& 3K Ohm = 17mA

https://www.youtube.com/watch?v=OnWLNoCSE5I

So, it seems, according to my testing that @ 48V 

...a 1.6K Ohms resistor lets 32mA thru

...& I believe, extrapolating from the test results, that a 2.4K Ohm resistor would let ~21mA thru

So, they all seem to let more than the recommended 10mA - 20mA thru

* It looks to me that the 3K Ohm resistors, letting 17mA thru, are the only ones that put us in the recommended range 

...or maybe even use a bit higher Ohm resistor for a lower mA output (closer to 10mA's) would be better, for a lithium pack


----------



## PStechPaul (May 1, 2012)

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

I tried more simulations, and couldn't get any good results. I don't have models for green and high efficiency red LEDs, so I made do with what I had. The forward voltage and equivalent series resistance of the LEDs are critical for success. Or, you can use one of the options I proposed, and know it will work.










Remember, a high efficiency red LED is not necessarily a bright LED, and certainly not a high power version.


----------



## Functional Artist (Aug 8, 2016)

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

I also noticed that the new version does not mention that each of the resistors are monitoring only 1/2 of the battery pack voltage

So, if I use 1/2 pack voltage...like the "old version" 

& the math ...from the "new version" 


Like this,

R = 1/2 PackV / 0.02A Ohm's 1%
P = PackV x 0.01A Watts

So, for a 48V battery pack that would be,

48V/2 = 24V
24V/ 0.02 = 1,200 Ohm's
48V x 0.01 = 0.48W @ 1%


Now, it looks like I should have used 1.2Kohm .5W 1% resistors 


Well, lets go at this from yet, another direction


I went ahead & ordered a couple of Batt-Bridge kits, right from Lee Hart


...we'll see what size resistors he sends me 


.


----------



## PStechPaul (May 1, 2012)

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

As I show in the simulation, the function of this circuit is highly dependent on the LED characteristics, and not so much on the choice of resistors. I tried some more simulations and the results were very disappointing. At best I could get the green LED to light at about 10 mA while the red LEDs would have less than 1 mA at an imbalance of 4 volts. Maybe some LEDs are better than others. But if you look at the circuit, you will see that there are direct loops through the top of the pack, the top resistor R3, and the top red LED D1, and another similar loop through the bottom. The green LED D3 has to draw enough current to "starve" the red LEDs. Here's another simulation:










So at about 2 volts imbalance, the red LED has only 200 uA to light it. A high efficiency LED might be reasonably bright, and an inefficient green LED might not be too bright, but I think the circuit is essentially flawed, at least compared to one using a pair of transistors:


----------



## PStechPaul (May 1, 2012)

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

I made a prototype of the battery balance monitor, which I made even more sensitive by adding another diode between the bases of the NPN and PNP transistors. 



















Here is a video






The circuit:


----------



## Functional Artist (Aug 8, 2016)

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

Nice! 
Good to see your still working on it 
...& improving it

Can other LED's be used?
...so it can be mounted in a box?
...or on a dash board?

It's very sensitive 
...possibly too sensitive?

You don't want it to signal an imbalance 
...just by applying a load (motor)
...or increasing the load (accelerating)

Have you done any testing? 
...on a battery pack?
...or with a load?


----------



## PStechPaul (May 1, 2012)

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



Functional Artist said:


> Nice!
> Good to see your still working on it
> ...& improving it
> 
> ...


Yes, any LED can be used. Brightness can be adjusted by changing the resistors.



> It's very sensitive
> ...possibly too sensitive?
> 
> You don't want it to signal an imbalance
> ...


Sensitivity can be decreased by removing one or both of the diodes *D3* and *D4*. It's probably good to have it this sensitive, so dynamic imbalance conditions can be detected. With the load only on the entire pack, there should be no significant imbalance, unless one or more cells are weaker or stronger. 



> Have you done any testing?
> ...on a battery pack?
> ...or with a load?


No, I don't have a battery pack, and the tests I show in the video prove that it works. You are welcome to build one of your own and test it. The components are common, cheap, and non-critical, although the NPN and PNP transistors should be complementary (similar in characteristics). R3 and R4 should be 1%, or well matched, and can be 1/8 watt. The entire circuit uses only about 5 mW when balanced, and 50 mW when indicating an imbalance.

Another feature is that it can perform some self-balancing, since the LED on the higher voltage half drains current and eventually will balance the pack. You can use higher power LEDs or even power resistors to provide more of a load.


----------



## Yabert (Feb 7, 2010)

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



PStechPaul said:


> Another feature is that it can perform some self-balancing, since the LED on the higher voltage half drains current and eventually will balance the pack. You can use higher power LEDs or even power resistors to provide more of a load.


That sound like a disadvantage to me.
This electronic is supposed to be there to let us know when there is an imbalance.
If one cell in an half of the battery is weak, your electronic will continuously recharge the weakess half of the battery until the weakess cell die...


----------



## PStechPaul (May 1, 2012)

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

No, the LED for the higher half of the pack will light, causing a greater current drain and a discharge that eventually will bring it down to match the lower half. Certainly one or two mA won't do much, but you could use a *1 watt* LED that will draw *300 mA* (although for a *48* volt pack that will be about *15* watts in the resistor. For that, it would be better to use Darlingtons or maybe MOSFETs.


----------



## PStechPaul (May 1, 2012)

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

Just for fun I simulated a circuit using MOSFETs. The *IRF7343* is actually a dual *NMOS* and *PMOS* device in an *SOIC-8* package and rated at *55V*, with a gate turn-on of *1 volt*, and costs about *$1*. There is enough difference between the devices to shift the center operating point, but a *500 ohm* resistor at the top (*R5*) adjusts the balance perfectly. This is only a 1% difference, so you can see that resistors of at least *1%* are needed, or an adjustment trimpot could be added. I used *1k* resistors for the LEDs so they draw *10 mA* fully on when an imbalance of *0.5* volts is present, and will be very visible with even *100 mV* difference. Removing diode *D5* lessens the sensitivity.


----------



## Functional Artist (Aug 8, 2016)

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



Functional Artist said:


> I also noticed that the new version does not mention that each of the resistors are monitoring only 1/2 of the battery pack voltage
> 
> So, if I use 1/2 pack voltage...like the "old version"
> 
> ...


*Quick Update*

It's been (2) months now 
...& I am still waiting for the Batt-Bridge kits that I ordered, from Mr. Lee Hart back, in March 

I have sent him a few friendly reminders

...now he doesn't even respond 

*Do these things really work?*
*...in the real world (or just in simulations)*

I am starting to wonder

*Has anyone ever done any successful (real world) testing?*

...or does everyone just assume they work because their so simple?

* During my unsuccessful tests, if the center tap came loose (disconnected) the Batt-Bridge would still show that the battery pack was "in balance" 
...even when there is no way possible that could "know" that with the info it has access to, at the time


----------



## PStechPaul (May 1, 2012)

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

Maybe he has been following this thread, and gave up and crawled under a rock? If you really want something that just works, why not use one of the designs I have proposed. I think I have proven that the Lee Hart design does not work very well, unless perhaps you select special LEDs. 

Stuff I found written by Lee Hart:

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

http://www.evdl.org/pages/battbridge.html (says it detects a dead cell with a 2 volt difference)

https://www.youtube.com/watch?v=a-Ke_k0Dcoo (shows imbalance but voltages are unknown)

http://www.sunrise-ev.com/balancer.htm (complete balancer for sale)

http://www.sunrise-ev.com/LeesEVs.htm (Lee's main page)

http://www3.telus.net/nook/balancerland/balancer/index.htm (Lee Hart balancer)

http://www.mpoweruk.com/papers/lees_wisdom.htm (Lee Hart's battery as a dog)

http://www.electric-cars-are-for-girls.com/battery-charger-schematic.html (Lee Hart interview on bad boy chargers)


----------



## Duncan (Dec 8, 2008)

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

Personally I have been using his design for the last five or so years
It has successfully detected the times I had a failed cell

Works absolutely GREAT - and it works in such a way that you can't miss it when you are driving

If you want to detect a failed cell it's excellent

And detecting a cell just before it fails is no advantage as you can't do anything about it!


----------



## PStechPaul (May 1, 2012)

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

Could you run a test on your unit to see what the thresholds are for imbalance indication? It seems to me that it would be helpful to detect a weak cell, which would probably show itself on a heavy current load. If you saw the imbalance light flash, it might allow you to take it easy until you can get the pack balanced, or perhaps bypass the weak cell. I think it would be good to have a sensitivity of about1 volt.


----------



## Duncan (Dec 8, 2008)

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

Paul
when a cell is weak and it has any noticeable deviation in voltage then its DEAD - stuffed - knackered 

Basically its already too late !

What the BattBridge does is tell me that I need to get it fixed BEFORE I CHARGE IT

Which is what I need to know

The various battery fires all seem to have gone
Cell dies
Owner does not know
Owner charges to the old voltage
Kills other cells and goes on fire

The Headway cells I started with had random cell death -
I did kill some with over discharge as they were actually a lot smaller in capacity (12Ah) than labeled (16ah)

But when they died - they died - there was no half way - no coming back from the brink


----------



## Functional Artist (Aug 8, 2016)

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



PStechPaul said:


> Maybe he has been following this thread, and gave up and crawled under a rock? If you really want something that just works, why not use one of the designs I have proposed. I think I have proven that the Lee Hart design does not work very well, unless perhaps you select special LEDs.
> 
> Stuff I found written by Lee Hart:
> 
> ...


Hello Paul,

I am very interested in your ideas
I am not disregarding them 
...& I'm glad your still working on & refining them

I am just trying to prove "to myself" that this "super simple devise" 
...works 
...or don't & isn't worth wasting any more time on 
...before I move on (I'm about there)


----------



## Functional Artist (Aug 8, 2016)

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



Duncan said:


> Personally I have been using his design for the last five or so years
> It has successfully detected the times I had a failed cell
> 
> Works absolutely GREAT - and it works in such a way that you can't miss it when you are driving
> ...


Hello Duncan,

I thought we were talking about a battery pack balance monitor
...just to detect a simple "out of balance" situation
(either while driving-as to avoid "damaging" the battery pack or "for safety"-before charging)

When I first got on this forum Lee Hart's Batt-Bridge was mentioned or referred to many, many times 
"It's so simple, a caveman can do it"
...but, I could not find much documentation of their assembly or actual use

That's why I did all of the research & started this thread

* I just want to "safely" upgrade my electric motorcycle from lead battery's to a section of a Chevy Volt lithium battery 

But, also 

I thought that it would be beneficial, to the forum

To have a DIY thread that shows
...step by step "how to assemble" 
...& some testing to help demonstrate "how it works" 

*Now, it's been over 50 posts & **I look like a moron*

...& you keep saying that they work "absolutely great"

Not to be disrespectful 
...but, could you please show me (& the rest of the class)


----------



## john61ct (Feb 25, 2017)

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

I doubt if anyone thinks you look like a moron.

Only kudos from here


----------



## steveob (Nov 10, 2017)

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

what is wrong with using a couple $0.99 led voltmeters like here and a couple switches (or ignition controlled relays)?

http://www.diyelectriccar.com/forum...-pack-balance-monitor-batt-bridge-165953.html

The problem w/the batt bridge is that it was probably designed for lead, and the tolerance for imbalance was much greater. But for pennies you can monitor the actual pack half voltages anyway and see if they are equal.

Or do the microcontroller thing, and tie it into your controller and charger if it sees a "significant" imbalance at the half tap. "significance" is missing from pauls design, how much imbalance do you need before you alert the user?


----------



## PStechPaul (May 1, 2012)

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

I think your problem was your choice of "bright" red LEDs instead of high-efficiency red. Here is some info on various LED types:

http://donklipstein.com/ledc.html

https://learn.sparkfun.com/tutorials/light-emitting-diodes-leds

http://www.gizmology.net/LEDs.htm

http://www.radio-electronics.com/info/data/semicond/leds-light-emitting-diodes/characteristics.php

That last resource shows rough curves for several LEDs, and it is apparent that LED voltage varies greatly at lower current. Thus, the Lee-Hart Batt-Bridge probably works best with lower resistance and higher wattage resistors.










I didn't find much specifically for high-efficiency red versus standard red, but it likely means higher lumen output for less current. And low power LEDs will probably reach their sharpest V/I curve sooner. If you used high brightness, high power red LEDs, that is probably your problem. 

It's a shame that Lee Hart has been ignoring you. Maybe you can find forums where he hangs out, or add comments to his web site. I appreciate the simplicity of his circuit, but just a few more cheap components greatly improve the performance.


----------



## Duncan (Dec 8, 2008)

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

Hi Functional
As I said at the start they work fine - exactly as Lee Hart said 

They tell you what you need to know - in other words they tell you if a cell has gone bad

There is nothing else that you need to know!

If you want more details - then you use your multimeter!

As far as using two meters - yeah right! - watch the road - and watch two meters while subtracting two rapidly changing numbers from each other to see the balance
And that is better than a nice bright red LED coming on!

No need for complex circuits!


----------



## Functional Artist (Aug 8, 2016)

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



PStechPaul said:


> I think your problem was your choice of "bright" red LEDs instead of high-efficiency red. Here is some info on various LED types:
> 
> http://donklipstein.com/ledc.html
> 
> ...


Hello Paul,

In the beginning, I was trying to build a Batt-Bridge as per the directions

But, as I have documented in this thread, there were differences in Mr. Hart's original terminology "ultra bright", "high efficiency" etc. & in the latest version, there were differences in calculating the necessary resistors

I also found that there are many different types of LED's 
...& even more different types, Ohm's & wattages of resistors

So, ya I agree that 
...my choice of LED's may have been an issue
...or my math, figuring the right resistor for a battery packs specific voltage
...or even my choice of type of resistor 

I have asked several times, openly on this forum, for Mr. Hart, Duncan or whoever
...what would be the "right" resistors to monitor a 45V battery pack?
...or even a 48V battery pack?
...& what are the "right" type of LED's to "work" with this set up?

Unless I missed it, I never got a "crystal clear" answer
...from anyone

So, fumbling around, trying to figure this thing out on my own, I have now bought
...several different types of LED's
...several different Ohm & wattage resistors
...& assembled many versions
...& done a lot (lots & lots) of testing, to see if I got it "right"

But, all I got was inconsistent readings

...That's why I went ahead & ordered one, right from Mr. Hart
...to get the "right" resistors
...& the "right" LED's


----------



## steveob (Nov 10, 2017)

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



Duncan said:


> As far as using two meters - yeah right! - watch the road - and watch two meters while subtracting two rapidly changing numbers from each other to see the balance
> And that is better than a nice bright red LED coming on!
> 
> No need for complex circuits!


Well, plenty of people seem challenged to glance at their fuel and temp gauges too, I don't seem to have that problem fortunately. Idiot lights are fine, but really you want a microcontroller to shut down the charger or back off the throttle or whatever.

If you can glance at it, you can see trends though. But looking at your gauges sounds like it is asking too much...


----------



## PStechPaul (May 1, 2012)

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

I admire your tenacity, but question your motives and methods. If you are serious about testing your various Lee Hart Batt Bridges, you should use a variable power supply so you can quantify the sensitivity. You should also purchase LEDs of known characteristics with datasheets and V/F curves. The resistors are not critical - just select them to obtain no more than the max rated current (probably 20 mA), reasonable tolerance (1% best, 5% marginal), and high enough wattage to avoid burning up. 

My simulations are imperfect because I don't have good models for red and green LEDs, but they essentially prove that the circuit is only good for about 2V sensitivity, which Duncan declares "good enough". 

I don't know if you are just intent on (1) proving that Lee Hart's design is bad, or (2) you really just want to make something that works for your new battery pack. I think you have succeeded at #1, but failed at #2. I don't know why Lee Hart has not sent you your kit, but I think you should demand action or refund. Whining about it here serves no useful purpose.


----------



## Functional Artist (Aug 8, 2016)

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



Duncan said:


> Hi Functional
> As I said at the start they work fine - exactly as Lee Hart said
> 
> They tell you what you need to know - in other words they tell you if a cell has gone bad
> ...


Hello Duncan,

There are so many variables 
...o so confusing

Are we "currently" talking about 
...detecting a cell imbalance (within a volt or so) 
...or an actual cell failure
within a battery pack?

I remember reading when you had issues with (IIRC) Headway cells
...but, were (or I am) talking about a section of a Chevy Volt battery

Which from my research
...is a much better "matched" set of cells (resistances, DOM etc.)
...& professionally assembled to exacting specifications

Which IMO seems to make a much more "stable" battery pack
...than a DIY assembly of mismatched cells

Have you had any "cell failures" or even detected an "imbalance" since you began using the Chevy Volt batteries?


----------



## Duncan (Dec 8, 2008)

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

Hi Steve

Looking at a gauge is one thing - looking at two gauges that have rapidly changing vlues and subtracting one value from the other is something else again!!

And when I am severely abusing my batteries - which is when I really NEED to know then I am on a race track and all of my attention is on driving on this side (but only just) of the available traction


----------



## Duncan (Dec 8, 2008)

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

Hi Functional
My Chevy Volt cells have stayed exactly the same to within 11 mV of each other - and as a result no red lights from my BattBridge

But if one did fail the BattBridge would tell me BEFORE I stuck it on charge and overvolted it's mates


----------



## steveob (Nov 10, 2017)

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



Duncan said:


> looking at two gauges that have rapidly changing vlues and subtracting one value from the other is something else again!!


For some reason, you make it sound like it is a lot harder than it is (are they equal or not?!?), and make the case for using a microcontroller in the same breath, yet champion this particular balance monitor, but don't provide any LED part numbers...


----------



## Functional Artist (Aug 8, 2016)

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



PStechPaul said:


> I admire your tenacity, but question your motives and methods. If you are serious about testing your various Lee Hart Batt Bridges, you should use a variable power supply so you can quantify the sensitivity. You should also purchase LEDs of known characteristics with datasheets and V/F curves. The resistors are not critical - just select them to obtain no more than the max rated current (probably 20 mA), reasonable tolerance (1% best, 5% marginal), and high enough wattage to avoid burning up.
> 
> My simulations are imperfect because I don't have good models for red and green LEDs, but they essentially prove that the circuit is only good for about 2V sensitivity, which Duncan declares "good enough".
> 
> I don't know if you are just intent on (1) proving that Lee Hart's design is bad, or (2) you really just want to make something that works for your new battery pack. I think you have succeeded at #1, but failed at #2. I don't know why Lee Hart has not sent you your kit, but I think you should demand action or refund. Whining about it here serves no useful purpose.


I don't have a variable power supply

I thought about getting one but, why?

A battery pack balance monitor is supposed to monitor a battery pack

I want a battery balance monitor that will "actually" monitor a "real" battery pack
...not a variable power supply 
...or in "simulations"

Bench tests & simulations are great but, if it "really" works
...it should work on a "real" battery pack too

That's why I did all of my testing on a "real" battery pack

I am NOT trying to give Mr. Hart a hard time
...or crack on his ideas

I don't want or need a refund

I simply wanted to get this "right" or move on

* If you "really" want to see if your ideas work, you should test them out on "real" battery packs too


----------



## steveob (Nov 10, 2017)

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



Functional Artist said:


> I don't have a variable power supply
> 
> I thought about getting one but, why?


Yah simulations have their limits, but voltage is voltage and current is current. If you are going to dabble in electronics you should have a variable power supply and a decent vom, a scope and function generator would be next on the list.

Really the only thing that would change is the resistor values if the pack is higher voltage than the ps, but once you confirm the expected behavior at a certain current (voltage difference), then predicting the right resistor to use at a higher voltage is trivial.

I agree it works, if a cell fails open or shorted, or is otherwise off by some yet undetermined amount, but the gauges tell you how much it is out, possibly before it becomes a problem (better find the high/low cell and bring it back into alignment), or just do the microcontroller thing. What a lot of people are doing now is monitoring every single cell, which is a bit of diy overkill unless you regularly visit 100% and %0 charge levels, but I think the usefullness of the batt-bridge is very limited, compared to gauges or actual logic. 

But that is what idiot lights are, they make some assumptions about how much is too much and turn on.


----------



## Functional Artist (Aug 8, 2016)

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



steveob said:


> Yah simulations have their limits, but voltage is voltage and current is current. If you are going to dabble in electronics you should have a variable power supply and a decent vom, a scope and function generator would be next on the list.
> 
> Really the only thing that would change is the resistor values if the pack is higher voltage than the ps, but once you confirm the expected behavior at a certain current (voltage difference), then predicting the right resistor to use at a higher voltage is trivial.
> 
> ...


 
I am not trying to "reinvent the wheel" here

I was just trying to duplicate someone else's "supposedly proven" technology

You don't need a laboratory to boil water


I saw this guy once that put some water in a pot, set the pot on a heat source & in a few minutes the water began to boil

I was like WOW! 
I asked, how did you do that? 
His reply was, "once the water gets to ~212* it will boil".

It looked simple enough, so I went home, put some water in a pot, set on my regular old home stove 
...& sure enough in a few minutes the water began to boil

No smoke, No mirrors
...no special pots
...no special heat source

Crystal Clear...if you do this...this will happen...everytime


* Thinking about your "twin volt meter" idea
...(1) meter would be connected to 1/2 of the battery pack (lets say the left)
...& the second would me connected to the other side (the right)

So, on a 48V pack, (when in balance) each meter should show 24V
...& if a difference between the (2) meters appears
...the operator will know there is an issue that needs to be addressed

That seems simple enough & would give consistent readings, every time without any "special" LED's or resistors 

Just
...(2) simple, low cost meters
...a DPST switch 
...& (4) wires

Kool


----------



## john61ct (Feb 25, 2017)

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

Arduino / rPi could easily be set up to alarm at a difference setpoint.


----------



## steveob (Nov 10, 2017)

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



Functional Artist said:


> I saw this guy once that put some water in a pot, set the pot on a heat source & in a few minutes the water began to boil


That comparison might be a reduction to absurdity. And these LEDs are kinda analog in this application, not "boiling vs not boiling", which is challenging in itself to define.



Functional Artist said:


> Just
> ...(2) simple, low cost meters
> ...a DPST switch
> ...& (4) wires
> ...


It is a large improvement over the LED design IMHO, stupid simple and cheap, and infinitely more information. Well, kinda, IIRC the led would have varying amounts of brightness depending on the imbalance (and part numbers), and paul wants to get rid of that.



john61ct said:


> Arduino / rPi could easily be set up to alarm at a difference setpoint.


wouldn't be my first choice, want something that can do simultaneous adc, preferrably x3 so you can have amperage, and lots of adc bits, been looking into it. 10 bits is ok for 48 volts (~0.05v resolution, though the top half will be at ~0.1v resolution in a 96v pack) though, and even non-synchronous readings are probably useful, so probably fine w/arduino, maybe add some sample and hold circuits. Mostly I want the extra bits to extend the voltage range trivially.


adding: a piezo for an alarm isn't a bad idea, if it isn't incessantly going off.


----------



## Functional Artist (Aug 8, 2016)

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



steveob said:


> That comparison might be a reduction to absurdity. And these LEDs are kinda analog in this application, not "boiling vs not boiling", which is challenging in itself to define.
> 
> 
> It is a large improvement over the LED design IMHO, stupid simple and cheap, and infinitely more information. Well, kinda, IIRC the led would have varying amounts of brightness depending on the imbalance (and part numbers), and paul wants to get rid of that.


My point was that if something "really" works "as described"
...it should function, at home, on an "actual" battery pack

Exactly the same (or at least pretty close)

As it functions, in a lab, on a power supply 
...or in a simulation even

Kinda like the requirements for a patent
...it should be easily duplicatable
...& others should get the same "end" results

* My original plan, when I upgraded my motorcycle to Lithium, was to use an Amp/Volt meter in conjunction with the Batt-Bridge

This way I could
...monitor pack voltage (almost, like a fuel gauge)
...the amp draw (to monitor power consumption)
...& (rudimentarily) monitor pack balance (for safety)

So, now I'm leaning toward just using (2) meters
...simple & accurate


----------



## Functional Artist (Aug 8, 2016)

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

I figured that a Batt-Bridge along with an Amp/Volt meter would make a great DIY Lithium battery pack monitor

So, I did (just as much) research & worked on/with an Amp/Volt meter, as I did with the Batt-Bridge
...to learn how they operate & what they are capable of

http://www.diyelectriccar.com/forums/showthread.php/amp-volt-meter-192457.html

& here I some videos, I made, to help explain it more

https://www.youtube.com/watch?v=WMmLiqFFuUg
https://www.youtube.com/watch?v=icIeGdwQRvY
https://www.youtube.com/watch?v=97pbo2jKBA4
https://www.youtube.com/watch?v=1J8S26PM-f0

The Amp/Volt meter tests came out good & were consistent

It's the Batt-Bridge tests where I ran into the problems 
https://www.youtube.com/watch?v=hadjiVV3b18
https://www.youtube.com/watch?v=I8TX8guUsM4
https://www.youtube.com/watch?v=GLVD7VyVr8g
https://www.youtube.com/watch?v=DmwDpcugV-U
https://www.youtube.com/watch?v=Fi_1ti4D7-s
https://www.youtube.com/watch?v=1N8JjeAPSOo
https://www.youtube.com/watch?v=5OS24SHZ85Q

...& is why we/I am here


----------



## john61ct (Feb 25, 2017)

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

Seems pretty likely you've spent more time, money and effort on the concept than he has.


----------



## PStechPaul (May 1, 2012)

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

I am probably wasting my time continuing to reply to this thread. I looked at some of the videos, but they are way too wordy with unnecessary "information" as well as "disinformation", such as saying the longer lead of an LED is the negative (cathode), whereas the opposite is actually true. Then connecting the LED directly across a 12V battery, causing a momentary flash and magic smoke, which actually proves that the long lead is positive (anode). 

It seems the videos go on and on about simply making the connections, soldering, heat shrinking, and encapsulating with silicone, which is totally unnecessary for quantizing the sensitivity of the Batt-Bridge. Then showing that the yellow LED (which should be red), barely glows with about 1 volt imbalance (as predicted by simulation), and finally getting it to glow brightly by deep discharging the 12V battery to 6 volts. That will damage the battery, and it is also the same result that would be found using a power supply or simulation. 

I'm not wasting my time looking at all the videos. They should be identified by stating their contents along side the links. 

It is silly to complain that you don't have a power supply (which costs less than the battery you ruined), and even sillier to assert that a power supply cannot provide a definitive result. Following that "logic", you should use the actual lithium battery packs you plan to use, and discharge one or more cells until the idiot lights show imbalance. Of course, you will definitely damage the cells, but maybe that's the price of your "science".


----------



## Functional Artist (Aug 8, 2016)

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

I agree (this is becoming a waste of time) but, I learned a lot (thanks everyone) 
...so, this will also be my last reply to this thread 

FYI:

Most of my videos are DIY videos
...that's why I try to explain everything in detail

My videos are not geared toward electricians & other professionals
...they are for DIY'ers

I have seen many (I used to be one) who just twist wires together then use lots of electrical tape & think that is a good/permanent connection 
...so, I show some things over & over (trying to lead by example)

But, I am also learning as I go
...which I make pretty clear

I don't hide mistakes
...if I do something wrong - I show it
...so, hopefully others DON'T do the same thing

The flash & magic smoke looked kool 
...so, I wanted to show it (kinda like back in science class)
...but, it was mainly a way to show, DON'T do this 
(do NOT run 12V thru one of these little LED's...or you will cause permeant damage )

Before these experiments, I did not know 
...that LED's needed to be connected in a specific way (unlike many 12V automotive type, incandescent bulbs)
...that these little LED's must have a resistor in series to reduce the voltage 
...to assemble a Batt-Bridge, the LED's must be connected in a specific order (important detail) 
...the (3) LED's could (potentially) be connected in many different ways (I learned that the hard way too...but, I showed it)...& the correct way (as far as I know) too 


* If I had the LED's cathode (-) & anode (+) backwards
...it would not have worked ('cause it's a diode)


----------



## steveob (Nov 10, 2017)

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

problem is the signal to noise ratio with that sort of thing. We've all done lots of homework, that is really what diy is, you may or may not save a few bucks, but you are gonna pay for your education with time/money either way. Other people don't want to pay for your education with their time (or money).


----------



## Functional Artist (Aug 8, 2016)

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

I'm done with that STUPID idiot light
...steppin' it up a notch (or at least movin' on to newer, more accurate technology)

I assembled a Batt-Bridge alternative

It's a Dual Digital Battery Balance Monitor

It's just (2) simple digital voltage meters (~$10.00 ea.)
(one connected to each 1/2 of the battery pack)

Here is a quick demo video 

https://www.youtube.com/watch?v=cMP0OtKo6ao


----------



## john61ct (Feb 25, 2017)

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

Also built into Victron 702 or 712 BMV, if you wanted to buy a good AH counting bank monitor anyway.


----------



## Duncan (Dec 8, 2008)

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



Functional Artist said:


> Thanks for the reply,
> 
> 
> I simply got it from:
> ...





Functional Artist said:


> I'm done with that STUPID idiot light
> ...steppin' it up a notch (or at least movin' on to newer, more accurate technology)
> 
> I assembled a Batt-Bridge alternative
> ...


Totally useless for actual driving but a nice project for you


----------



## steveob (Nov 10, 2017)

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

we aren't all on a race course duncan, I use a similiar setup, no harder than looking at a fuel gauge like I said. 

It is like saying a temperature gauge is useless, well sure, if you never bother to look at it.

Don't know why you hate the idea so much.


----------



## Duncan (Dec 8, 2008)

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



steveob said:


> we aren't all on a race course duncan, I use a similiar setup, no harder than looking at a fuel gauge like I said.
> 
> It is like saying a temperature gauge is useless, well sure, if you never bother to look at it.
> 
> Don't know why you hate the idea so much.


Because it is a stupid idea 

You have to read two rapidly changing four digit numbers and subtract them to see if you have a problem - and keep doing that all of the time that you are driving

And those numbers are being updated but two different systems which are not synchronised so they could be different purely because of update times

A gauge - like a temperature gauge is GREAT for something that changes reasonably slowly - useless for something that changes fast

A nice bright red LED is much much better
Having dual voltage gauges AS WELL - makes sense but not INSTEAD OF


----------



## PStechPaul (May 1, 2012)

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

As I posted on the video:


> However, this requires you to read the voltages while you are driving, and the battery voltages will likely fluctuate, which makes a digital readout difficult to read, and you might be dangerously distracted. I demonstrated a much simpler device that works like the batt-bridge but is much more sensitive and accurate, that can be built for less than a dollar.
> 
> Did you ever receive your "genuine" batt-bridge kit from Lee Hart?



I know the OP thinks using actual SLA batteries with a load is better than a power supply, but neither is actually "real conditions", where the batteries will be powering a motor under varying load conditions.


----------



## steveob (Nov 10, 2017)

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

but it isn't like magic pixies that make it drop when you aren't looking, that is ridiculous. If it is getting out of wack it will be obvious under load and at "idle". I mean I appreciate the simple LED design, but this takes out all the guesswork, and is also quite simple to validate if it is hooked up and working correctly (if you even select the right part numbers, or get the polarity right). The cheap meters approach is infinitely more foolproof.


----------



## Duncan (Dec 8, 2008)

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



steveob said:


> but it isn't like magic pixies that make it drop when you aren't looking, that is ridiculous. If it is getting out of wack it will be obvious under load and at "idle". I mean I appreciate the simple LED design, but this takes out all the guesswork, and is also quite simple to validate if it is hooked up and working correctly (if you even select the right part numbers, or get the polarity right). The cheap meters approach is infinitely more foolproof.


Hi Steve
There are a number of issues that my Batt Bridge will detect that will NOT be seen unless you are at full power

Bad connector, Weak (high internal resistance) cell - lots of things that may not show up unless you are giving it death

And when I'm giving it death I am far too busy to read two four digit numbers and subtract them!


----------



## steveob (Nov 10, 2017)

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

that just isn't a true statement, don't know what to tell you. It will tell you infinitely more info than a light will.


----------



## Moltenmetal (Mar 20, 2014)

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

I had a cell drop in capacity mysteriously- I suspect it lost electrolyte through a leaking vent over time as I smelled electrolyte from time to time in my trunk.

My cell by cell BMS caught it when I was nowhere near the bottom of my expected pack capacity.

My Lee Hart LED battery bridge never said a peep.

I subsequently installed six cheap LED voltmeters, each monitoring an equal number of cells- 6 vs 6, 5 vs 5, 5 vs 5. They are handy for checking balance at high SOC and low SOC, and definitely capable of being used to verify that a BMS alarm while driving is real versus a loose wire etc.


----------



## Functional Artist (Aug 8, 2016)

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

Hey Duncan, 
How many times have you thought one of the red lights was on (kinda or just a bit) but, didn't know for sure. (could it have been just sunlight or a reflection?) 

How many times did you look at/check it?
...now, that's a distraction

This dual digital set up would tell ya for sure.

Why is it so hard to glance at (2) gauges that are right next to each other?

Why would anyone have to do any math?

In a "balanced" battery pack both meters should continuously show like numbers 

Like for 48V pack 
...the left meter, monitoring the left 1/2 would show ~25V
...the right meter, monitoring the right 1/2 would show ~25V too 

If (1) of the meters ever show more than 1V difference than the other meter 
...you would know CLEARLY that YOU HAVE A PROBLEM 

I am not an EE (like many of you guys) but, IMO hard acceleration (or racing conditions) should not unbalance a "good" battery pack
...or Duncans Volt packs would/should of been way out of wack (technical term) by now


----------



## PStechPaul (May 1, 2012)

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

If the error LEDs are bright white, as mine are, they are very easy to see just using peripheral vision. It should also be possible to add a couple capacitors so the LED will stay on for a few seconds after a transient voltage drop is detected. Battery pack voltage may fluctuate rapidly enough that the digital meters could not be read easily, especially at transition from, say, 29.8V to 30.2V. You might be able to simulate this by using a relay to switch a load on and off to one side of the battery pack, at a rate of 2-4 times per second.

I'm not really interested in selling my improved version of the batt-bridge, but the complaints expressed by Functional Artist are not really valid:



> I have watched your videos. I've told you I like your design & initiative but, that's still (10) little dinky parts, that need to be specifically chosen (for the specific bat pack voltage) & then assembled (correctly). These little digital meters come assembled, are easy to mount (in a dash board or even a hand held meter), they give more info (tells you exactly what's happening in your battery pack) & only require a (2) wire connection per meter/battery half. Short, sweet & to the point. You don't like EZ & having more info?



You can use larger thru-hole parts, if you prefer. The part values are not critical, and can be used for a wide range of pack voltages, although there are advantages to choosing certain values. A simple cheap PCB makes it easy to assemble, and the LEDs could be mounted on the dash or in a little box with just a couple small round holes, rather than two large rectangular cutouts.


----------



## Functional Artist (Aug 8, 2016)

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



PStechPaul said:


> As I posted on the video:
> 
> 
> 
> I know the OP thinks using actual SLA batteries with a load is better than a power supply, but neither is actually "real conditions", where the batteries will be powering a motor under varying load conditions.


IMHO 
First step is to do some bench tests using a "real" battery pack, to get a feel for how it works & what to expect (using faux load on 1/2 of the bat pack to create an imbalance) 

Second, do some "unloaded" load tests (motor mounted on a kart with a chain connecting the rear wheel but, the rear wheels are off of the ground) 

Third, do some "actual" load tests (with total weight of the kart plus an operator & rolling resistance etc.)

* The Batt-Bridge never got passed the first stage of testing. 

Want to see these little meters in action? 

Here is a video (from last summer) where I use one of these digital meters (while doing some overvoltage tests) to help gather some amp & voltage data.

https://www.youtube.com/watch?v=H-704ZyJkaU

...& here is another (from just a couple of days ago) where I use one of these meters (while doing some motor "load" tests) to gather some "Max Amp draw" data

https://www.youtube.com/watch?v=aVip7AKtHZg


----------



## Tony Bogs (Apr 12, 2014)

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

I'm going to apply a similar circuit in my packs on module level (2P12S) with two resistor arrays and the addition of a lot of very cheap (US$0,25) bimetal temperature switches and infrared optocouplers (about the same price). 

In the end it is all about a low cost solution for the prevenion of fire or at least the reduction of the chance of fire to the level of winning the jackpot in the National Lottery.

Three optocouplers, 12 bimetal switches and two precision resistors add up to about US$6 per 2P12S module.


----------



## Functional Artist (Aug 8, 2016)

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



Tony Bogs said:


> I'm going to apply a similar circuit in my packs on module level (2P12S) with two resistor arrays and the addition of a lot of very cheap (US$0,25) bimetal temperature switches and infrared optocouplers (about the same price).
> 
> In the end it is all about a low cost solution for the prevenion of fire or at least the reduction of the chance of fire to the level of winning the jackpot in the National Lottery.
> 
> Three optocouplers, 12 bimetal switches and two precision resistors add up to about US$6 per 2P12S module.


Kool, but, it sounds kinda complicated (~15 separate parts, per module)
…& a lot of work (plus assembly)

My low cost solution is "simple" & digital 
...to monitor the balance of my battery pack

I used (2) voltage meters (~$2.00 ea.) & a switch
…& it's "super" easy to assemble 

https://www.ebay.com/itm/Mini-DC-5-...e=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649

There are just (4) wires coming from the meters (a positive (+) & negative (-) for each meter)

...& (3) connections to the battery pack (positive (+), center tap & negative (-) 

Here is a video explaining it

https://www.youtube.com/watch?v=uzwUiSl0Azg


----------



## Tony Bogs (Apr 12, 2014)

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

Yeah, good starting point, but it just doesn't provide enough protection.


The arguments have been brought forward here.


One single static LED indicator or (worse) two meters is definitely not adequate.
A full blown BMS is the other end of the spectrum. I want to be somewhere in the middle.


Hardware that can capture (record) dynamic voltage differences ( due to impedance imbalance) has to be added.


PS. Forgot the temperature sensors: must have for NMC.


----------



## Functional Artist (Aug 8, 2016)

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



Tony Bogs said:


> Yeah, good starting point, but it just doesn't provide enough protection.
> 
> The arguments have been brought forward here.
> 
> ...


It's job is not to provide protection 
...its just a "simple" display (just like a Batt-Bridge) to give the operator information about what's going on inside of the battery pack

When I wanted to convert my (converted) motorcycle from SLA's to lithium
...I also, wanted/was looking for "something in the middle"

I didn't want to use a complicated & "expensive" BMS 
(I've read, on this forum many, many times, "BMS kill more battery's than they protect")
&
I didn't want to go "rogue" & just "wing it" either
(some folks are just connecting a "big 'ol" lithium battery to their vehicle & "hoping for the best") 


So, I did like (at least) a years worth of research on lithium battery technology, the proper care & use, monitoring/BMS's & charging
...before settling on the concept/system I am using

Then, I specifically, chose to use, a section of lithium battery pack from a Chevy Volt 
...to avoid any "impedance imbalance" (these batteries are well balanced & have been reported to maintain their balance)
...& temperature issues (these batteries have not been reported to "ever" get "dangerously" hot @ these voltages)
...&/or having to monitor them.


The concept I am working with
...is to start off with a "good" professionally designed & manufactured battery

1.) Never discharge it get below ~3.2V per cell (~38V)

2.) Never charge it above ~4.1V per cell (~49V) 
...3.7V nominal for this specific chemistry

3.) Monitor the "balance" of the battery pack 
...& periodically if necessary "manually" balance the pack


I am just sharing "how I am doing things" 
…& will, also, share/post the results (how well things work or don't work) along the way


----------



## Tony Bogs (Apr 12, 2014)

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

And I am just sharing that your setup provides very little protection,

But you're right, keeping an eye on the static voltages of bottom and top sections of the pack is always better than doing nothing (going rogue).

Nevertheless, the imbalance detection between sections of a pack is a good starting point for a pretty safe "early warning" setup when combined with bimetal circuit breakers.


----------



## steveob (Nov 10, 2017)

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

I love the dual meter approach, super simple install, cheap, super simple to use (if you know how to use a gas gauge, you can use this) infinitely more accurate than some random LEDs, and zero pack drain (check your one switch approach). I mean BMS's have killed more than a few DIY packs that were waiting for their owners to get back to them, there is no such thing as Idiot proof, better to just not be an idiot IMHO.

If you are like duncan and two voltage meters makes your brain explode, try some video games, i.e. a good FPS with health and ammo and etc displays (*coughTF2cough*), learn to pay attention to more than one thing at a time. Also spend some time on a motorcycle if you thought you were paying attention before. Real life isn't a closed and nicely controlled race track.

The next step I think is to just use an MCU (and some small relays), and show pack voltage and current and resistance and first level balance info (perhaps graphically) and set up the controller/charger interface. Still looking at super simple install and dirt cheap next to a cell by cell bms, and that is a huge win in the DIY sphere.


----------



## Tony Bogs (Apr 12, 2014)

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

Ah, but don't take your eyes of those meters. Don't even blink.


----------



## Functional Artist (Aug 8, 2016)

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



Tony Bogs said:


> Ah, but don't take your eyes of those meters. Don't even blink.


Why does everyone (well a select few) seem to think that these meters need to be constantly "stared at"?

Do you'all stare "don't even blink" at your Batt-Bridges?

Its just displaying info, like a temperature gauge, turn signal indicator, clock etc. 

Do you'all stare, "don't even blink" at clocks too? 

I will monitor my meters "quite often" for the first couple of rides after that, I only plan on looking at the meters "occasionally" like
...before a ride (to "mainly" check pack voltage but, also balance)
…& after a ride but, before charging (to also check pack voltage but, "mainly" to check pack balance)
…&/or if I ever sense/notice a problem


----------



## PStechPaul (May 1, 2012)

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

You can fairly easily (and cheaply) add a minimum voltage function to the two DVM balance monitor system, using a 5 uF capacitor, a 470 K resistor, and a Schottky diode on each meter. Under normal conditions, where pack voltage remains fairly constant, the RC network will read the nominal voltage with a time constant of 2.5 seconds. If the pack is subjected to a heavy current drain, the diode will discharge the capacitor to the lowest voltage of each section of the pack, and hold it long enough to read when you are not too busy. The long TC also tends to stabilize the meter readings. 

The switches could be replaced by tiny MOSFET SSRs that cost only about $1 each and draw only 2 mA when turned ON. They could be energized only when the vehicle is running. You could also use a CMOS circuit consisting of an LMC555 timer (150 uA at 12V), to turn the relays ON for perhaps 1 second every 20 seconds or so, to provide a reading while the vehicle is parked. Or just use a pushbutton to read the pack voltages as desired. 


After watching your video, I realize that the two wire voltmeters would draw too much current to implement the minimum voltage circuit as described above. It would require separate power and signal connections. That might be possible by opening the meters and adding the circuit internally.


----------



## Duncan (Dec 8, 2008)

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



steveob said:


> If you are like duncan and two voltage meters makes your brain explode,.


Some of us have cars that have enough power that we need to actually drive them!
And concentrate on things like hitting the apex - 
We don't have time for watching multiple meters - that probably don't update fast enough anyway


----------



## steveob (Nov 10, 2017)

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

nobody said they had to be digital meters, you can morph the concept into an analog meter, or analog meter with LEDS or do the MCU thing, or throw a bunch of logic chips at it, the meters are just the $3.00 quick and easy version. You are hung up on the LED version for some reason (but don't even have part numbers...)

What are you expecting to happen so immediately that you will miss it? And if/when you happen to notice such a brief blip on your LED thingie, what do you do about it anyway? 

If you need fast digital, then do fast digital, keep track of min/max all that fun stuff. Or mix and match analog/digital/led/piezo/?? The hookup should still be dirt simple and cheap.


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## Duncan (Dec 8, 2008)

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

Hi Steveob

Please STOP waffling about things you don't understand - when you finish primary school you will understand these things much better 

When you actually get to drive something other than a pedal car then you will understand


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## steveob (Nov 10, 2017)

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

Lol, you have an LED batt-bridge, and you can't understand why anyone would want anything else, what is there to understand?


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## Duncan (Dec 8, 2008)

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



steveob said:


> Lol, you have an LED batt-bridge, and you can't understand why anyone would want anything else, what is there to understand?


NO!
I have something that actually works - and plonkers like you keep telling me to go to something that would not work

Still if you want to install gauges on your pedal car taking you to kindergarten then go to it


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## john61ct (Feb 25, 2017)

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

Is that little crown icon mean you're a mod so rudely belittling a member?


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## Duncan (Dec 8, 2008)

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



john61ct said:


> Is that little crown icon mean you're a mod so rudely belittling a member?


No I'm an Admin - basically a spam buster - nobody has ever accused me of being "moderate" !

And I feel that reasonable criticism of plonkers is fine


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## Functional Artist (Aug 8, 2016)

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

I'm not familiar with the term "plonkers"
...but, it sounds kinda negative (LOL)

On a lighter note, I took my El Moto out today for the first test ride with the "new" lithium battery 
…& I didn't even hardly look at the meters

It was GREAT! 
...check it out

https://www.youtube.com/watch?v=5vRUdxZ334g


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## Tony Bogs (Apr 12, 2014)

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

Nice set of meters. Do they come in blue? 

I think I can squeeze one of them in between the audio system and the information display of my senior citizen EV


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## Functional Artist (Aug 8, 2016)

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



Duncan said:


> Some of us have cars that have enough power that we need to actually drive them!
> And concentrate on things like hitting the apex -
> We don't have time for watching multiple meters - that probably don't update fast enough anyway


Hey Duncan,

What do you do when your Batt-Bridge "lights up"?
...connect a "digital" meter to help figure out what's going on & gather more info?

According to the specs, the refresh rate is "about 300mS/time", is that fast enough?

The operating current for these meters is anywhere from ~13mA for blue meter, to ~18mA for green meter & ~23mA for red meter 
(very similar to a Batt-Bridge) but, you can turn these off & only use when needed


Hey Tony,
Of course they come in blue (must not have seen the photo)
...& as an added "bonus" it will also draw less energy too


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## Duncan (Dec 8, 2008)

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



Functional Artist said:


> Hey Duncan,
> 
> What do you do when your Batt-Bridge "lights up"?
> ...connect a "digital" meter to help figure out what's going on & gather more info?
> ...


300ms - so 600ms to be sure both are on the same time - nothing like good enough - that would give lots of false alarms as I am changing throttle

As to what I do when I get an alarm - same as if I had an oil light flash - back off and investigate later

Your two gauge system is OK for a tortoise - but no bloody use at all for a performance machine 

Maybe I should start calling you a plonker as well - you do seem to behave like one


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## Tony Bogs (Apr 12, 2014)

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

@FunctionalArtist: 

I thought I saw the blue one. It was a pleasant suprise. Thanks for the confirmation.

But I really only need one. 

Reason: I have designed a circuit that captures (holds) a fault status when significant differences in certain static and dynamic values of sections of the battery pack occur.
It is fast acting and very simple: less than ten parts. 

And it can be reset by push button action unless the cause persists.

But that digital meter is definitely a lot more accurate than the meter in the dash of the ICE donor for my senior citizen EV project when measuring the total pack voltage.


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## PStechPaul (May 1, 2012)

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

You can get them for as little as $1.49 each for yellow or green, and $1.99 for blue or white:


https://www.banggood.com/0_28-Inch-...258.html?rmmds=search&ID=231&cur_warehouse=CN


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## Functional Artist (Aug 8, 2016)

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



Duncan said:


> 300ms - so 600ms to be sure both are on the same time - nothing like good enough - that would give lots of false alarms as I am changing throttle
> 
> As to what I do when I get an alarm - same as if I had an oil light flash - back off and investigate later
> 
> ...


 
Investigate later = connect a digital meter, Duh! 

Plonker "Really" ...Whatever!

If a plonker is someone who don't let folks bully them or "push them around"
...don't take any BS 
...& calls 'em like they see 'em

Yup, that's me 


IF THE STUPID THING WORKED OR YOU"ALL WOULD OF HELPED ME FIGURE IT OUT, WE WOULDN"'T BE HAVING THIS STUPID CONVERSATION
(Remember "why bother doing the math")


I don't care what you do in/with your "homemade jalopy"
...race it, putter around the country side, whatever
(I still admire your skills)

BUT, I DO know that 

If you don't use the "right" resistors, A Batt-Bridge will "not work-right"

If you don't use the "right" LED's, A Batt-Bridge will "not work-right" 

If the center tap on your Batt-Bridge (or any Batt-Bridge for that matter) looses connection, a Batt-Bridge WILL give a "FALSE POSITIVE" reading
…& the user will still think, everything's "A OK", yup the "green light is on" so I'm kool

* While testing, I drained (& KILLED) a 12V battery all of the way down to ~6V waiting for that STUPID Batt-Bridge to "light up"
...come to find out the center tap "came loose"

**I also very much admire Mr. Lee Hart & ALL he has done for the EV world
...so, I am DONE with this conversation

Do whatever you'all want

If you want to rely on "idiot" lights 
...be my guest


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## Duncan (Dec 8, 2008)

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

Yep you are definitely a plonker

Goodbye Mr PlonkerArtist


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## Functional Artist (Aug 8, 2016)

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



Duncan said:


> Yep you are definitely a plonker
> 
> Goodbye Mr PlonkerArtist


 
We had Chinese for dinner the other night 
...I got this & thought of you LOL

Weather you (ever) admit it (to us) or not
...digital meters are in your future


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