[jddcircuit]

Originally Posted by green caveman

Jeff,

Are you using a voltage divider on each circuit to avoid the problem of high (120V+) common mode?



I've just sent you a PM offering an Android App-builder. It's beta and so I don't want to just publish the link, but if anyone else is interested, feel free to PM me. It should do more than you need, including "real-time", historical data and charting. You can use bars, meters, etc. etc.

The bluetooth app in the digital BMS thread represents a couple of hours work (the displays could be bars, instead of text boxes).

Let me know if I can help.

Not really using voltage dividers to handle voltage difference. The way I am handling the high common mode voltage of the stack is by using locally referenced analog to digital conversion by dedicated circuits and then pass the digital information between each circuit to the next. In this way each cell only sees its neighbor which is a much smaller voltage level shift between them to deal with.

I can then capture and decode the digital information at the end of the daisy chain bus. There are other circuits I have seen like ones that use a micro per cell and special purpose ICs that can handle 12 cells at a time and then use a daisy chain serial bus to propagate the digital information.

Thanks for the Android stuff. I will check it out. I am not an experienced programmer. I don't plan on using blue tooth. The Ardunio board that I have can act as a USB host so I will need to put my Android tablet in what is called accessory mode. I don't have the tablet yet and not real familiar with the programming so this is going to take me a little while.

Thanks
Jeff

[green caveman]

Jeff,

Originally Posted by jddcircuit

I can then capture and decode the digital information at the end of the daisy chain bus. There are other circuits I have seen like ones that use a micro per cell and special purpose ICs that can handle 12 cells at a time and then use a daisy chain serial bus to propagate the digital information.

That sounds to be a very slick design. Where do you feel you are on the hardware side? Ready to put out a board layout and a BOM? I'd be very happy to build it up, test it and build out the software.

I would really like to be able to balance the cells with a charger rather than by discharging. I think that it can be done using the Arduino outputs, two MOSFETs and a single cell charger. With two MOSFETs you can "switch" in any cell. With the Arduino, you can create a custom balancing strategy, whether that's a top balance, bottom balance or anywhere in between.

I suspect this may need to be completely separate because there's the possibility to put some amps.

Originally Posted by jddcircuit

Thanks for the Android stuff. I will check it out. I am not an experienced programmer. I don't plan on using blue tooth. The Ardunio board that I have can act as a USB host so I will need to put my Android tablet in what is called accessory mode. I don't have the tablet yet and not real familiar with the programming so this is going to take me a little while.

You can buy a $2 BlueTooth USB dongle (dealextreme) for the Arduino/USB host. This adds a couple of neat features. The tablet is now isolated. No matter how badly you mess up your Arduino, the tablet will survive.

You can also move the tablet to a mount on the dash and be able to carry it away from the vehicle without unplugging anything.

Downside is that you need a tablet with BlueTooth.

How interested are you in learning the programming and doing it all yourself? If you're willing to keep working on the hardware and let us help on this end with the software, we might get a better product faster.

From a feature perspective I think we have the same goals. I want year-over-year data and to be able to correlate it to any outside factors
anyone can think of a way to measure. I really want Aerodynamics - a way to get Cv and see if you can change it with simple aeromods. I also want realistic estimate of power vs hills - mainly because that's not really included at all in range estimates because no one really has any data.

Strain gauges would give you a measure of the weight of the car, but I'm not sure that you could find a stable enough spot or a spot that would give you good estimate regardless of the position of the load. I'm probably willing to try if I have some way to measure power.

Others have already pointed out that you can add OBDII, if you have a new enough car and a tablet with BlueTooth. The data manipulation capabilities are endless, once you can gather the data.

[jddcircuit]

Originally Posted by green caveman

Jeff,



That sounds to be a very slick design. Where do you feel you are on the hardware side? Ready to put out a board layout and a BOM? I'd be very happy to build it up, test it and build out the software.

My hardware is not ready for prime-time. However it is looking promising and unique to other solutions in a couple ways. I am not prepared to post the full schematic and layout yet. Possibly soon.

I am looking forward to doing the software but I will be reaching out for assistance when I hit a wall.

My cell monitoring method is only a piece of my project. It will be integrated with my own battery charger and motor controller that interfaces with a junkyard Prius inverter.

I have several balancing ideas. Plan A is to not have any on board but know when it is time to balance using the cell voltage monitoring.

With the voltage monitoring I should know which cells are at a higher state of charge than the rest because they reach the high voltage cutoff first each time during charging.

A simple circuit to remove a specified amount of amp hours from those high cells should be enough to improve the balance. I plan to use the same wiring harness that my monitoring circuit uses to tap the cells for this periodic balance.

Jeff

[green caveman]

Originally Posted by jddcircuit

My hardware is not ready for prime-time. However it is looking promising and unique to other solutions in a couple ways. I am not prepared to post the full schematic and layout yet. Possibly soon.

I am looking forward to doing the software but I will be reaching out for assistance when I hit a wall.

OK, let me know. I just wouldn't want a slick hardware design to be buried for months because you get lost in the Android world. I created the BlueTooth stack for Arduino (it's a port of BTStack), so let me know if you want to go that way - it may give me some incentive to work on an upgrade that I haven't, yet, made time for.

Android is actually a pretty easy platform to program.

As I say, I'd be happy to build up the circuit and test it so that you have at least one other installation before you send it out to the world. On the other hand, there may be better candidates watching this list since my expertise is definitely on the software side rather than hardware debugging.

Originally Posted by jddcircuit

My cell monitoring method is only a piece of my project. It will be integrated with my own battery charger and motor controller that interfaces with a junkyard Prius inverter.

Yep, a little local intelligence opens up a whole world of possibilities.

One of the problems with conversions is that they need TLC. For the most part, you couldn't give your grandmother your conversion and have her just drive it.

The system you're building brings us closer to a system that automates what can be automated and will provide a notification so that your grandmother can call and tell you what the system says needs attention.

Originally Posted by jddcircuit

I have several balancing ideas. Plan A is to not have any on board but know when it is time to balance using the cell voltage monitoring.

With the voltage monitoring I should know which cells are at a higher state of charge than the rest because they reach the high voltage cutoff first each time during charging.

Surely, and for the bottom balancers the same hardware applies, it's just a minor software change to balance before charging rather than after (if I understand bottom balancing correctly).

Originally Posted by jddcircuit

A simple circuit to remove a specified amount of amp hours from those high cells should be enough to improve the balance. I plan to use the same wiring harness that my monitoring circuit uses to tap the cells for this periodic balance.

I wonder about mixing "high" power, I suspect to balance you'd be looking at 10W+, in with the low power monitoring circuit.

I would expect to use, say 1A, fuses for the monitoring circuit - connected directly to the terminals or the straps of the cells. Inline glass fuses seem to be the lowest cost if you're not anticipating replacing them. I think that you can embed them in a battery lug in the style of the zeners in the Lee Hart Balancer.

My other problem with dissipative is that, well, it's dissipative. You go to the trouble of charging the cells and then start discharging them. I know it's infrequent and the charge loss is minimal, but it still bothers me.

[green caveman]

A little offtopic and a future development rather than an immediate idea. One other thing that you might consider as an Arduino substitute is the RaspberryPI with the GertBoard

There's an availability problem on these. The $35RPi is delayed (again) waiting compliance testing. I suspect the GertBoard won't become a reality until the RPi exists. I also haven't seen final specs on the GertBoard (Analog In?).

It's a much more powerful solutions and easier to program for a given value of "easy". (I think that simple programs on Arduino are easy but it doesn't scale well and complex programs are non-linearly more difficult - mainly a lack of threads).

[fb_bf]

Originally Posted by green caveman

From a feature perspective I think we have the same goals. I want year-over-year data and to be able to correlate it to any outside factors
anyone can think of a way to measure. I really want aerodynamics - a way to get Cv and see if you can change it with simple aeromods. I also want realistic estimate of power vs hills - mainly because that's not really included at all in range estimates because no one really has any data.

.

I'm not sure what your looking for, but it sounds a little like what I've tried. I used a GPS running watch to log how my car slows down after I push in the clutch. From this I calculate Cd and Rolling Resistance. I also developed a spreadsheet to calculate energy use for any route you can document with the GPS. The data is recorded once a second. Form my Cd estimates I can then calculate energy required to overcome drag. From the change in velocity, I can calculate energy to accelerate, and from the altitude change I can calculate energy gained or lost on hills. I've posted my spreadsheets for download on my site. They are crude in that they'll need to be modified for your own data, but I'd love to hear your opinions on the ideas. I also use my logging feature in my Soliton Jr. controller to measure energy use. This is good because all of your drive train losses are being measured as well. My latest measurement was to see what the luggage rack on my car was costing me. From the data It looks like it was around a 5% increase in drag force at 50 to 60 mph. I hope I'm not interrupting this thread. We can discuss this elsewhere if you’re interested.

[jddcircuit]

WithAndroid_1.jpg

I have made some progress on my development. I made a video.
http://www.youtube.com/watch?v=XpjJN...ature=youtu.be




I am getting about a .1% repeatability which is good but I want to improve the accuracy a little. Another engineer pointed me to a likely source of current leakage that may be creating an imbalance in my RC time constant. The circuit is designed to draw very low currents from the cells (20uA approx) which makes small leakage currents that much more significant.

Quick test will be to change from 1meg to 500k resistor for my charging time constant and see what happens. I also have a redesign on paper but I am shooting for good enough at the moment with this design.

The Android tablet I am using has version 4.0.3 operating system and cost me $107 including shipping (Novo 7 Paladin). I wanted this latest version of Android to hopefully take advantage of the Android Open Accessory Development (ADK) library for USB devices but I spent days without being able to get it to work as advertised.

I am currently using a work around for my USB protocol using the Android Debug Bridge (ADB). This USB method might have some hidden advantages. It should work with earlier Android versions and may give me the ability to shut down or reset my tablet if needed.

Thanks
Jeff

[green caveman]

Very cool! Are you planning to publish the circuit before or after the redesign? At the minute it appears from random hand-measurements that the odd pack in the little van is staying pretty well in balance, so I'm not quite as worried about individual cell measurement as I was.

The downside of ADB is that you have to enable "USB Debugging" under "Applications Setting-> Development" on the tablet - not a big deal for a project like this.

[jddcircuit]

Originally Posted by green caveman

Very cool! Are you planning to publish the circuit before or after the redesign? At the minute it appears from random hand-measurements that the odd pack in the little van is staying pretty well in balance, so I'm not quite as worried about individual cell measurement as I was.

The downside of ADB is that you have to enable "USB Debugging" under "Applications Setting-> Development" on the tablet - not a big deal for a project like this.

Thanks

I need to hold back a while before publishing the schematic of the monitoring circuit. There is quite a bit of testing to be done still. Even though it is not directly related to my work I went ahead and submitted the concept for an innovation award. I guess I need to wait until they decide whether to pursue a patent or not.

In the meantime I will post my progress with integrating it into my battery management system, data logging with Android GUI, and homemade battery charger and controller.

Jeff

[jddcircuit]

It has been a while but I am back to working out my battery pack monitoring and control strategy and I wanted to give an update.

Here is a picture of the setup so far.
BuildLogUpdate_1 (1024x765).jpg

The company I work for did end up pursuing patent on the concept but I am thinking publishing a schematic for DIYers might not be out of the question. I think I just have to wait until the patent application is made public information. This prototype circuit is not my preferred design but will work for now as I get the rest of the pieces in place.

You can see some inaccuracies for the cell voltages in the bar graph but I think this can be improved. The Y axis range in the display is 2.5V to 4.0V so you can get an idea of the voltage measurement variation. It is about +/- .1 volt at this time. I have some ideas on how to improve it to +/- .01 volts. My pack voltage sum is showing about a 2% inaccuracy at this time. Since the measurements seem very repeatable and stable for now I can handle the inaccuracies in software.

My main goal is to have an intelligent controller that can detect changes in the cell characteristics over time. In addition to detecting the high and low voltage extremes I want to be able to analyze the relative cell to cell to behavior under the same current draw.

I am getting a little better at my Android programming. This week I want to get some data logging working in preparation for running some charge and discharge cycles.

The precharge, main contactor, and battery charger control will get added into the system through the Arduino IO. This way my BMS software in the Android can activate and deactivate them based on the pack condition.

My strategy is to use the Android as the master controller for making decisions about the health of the batter pack and each cell at all times. The Arduino will be its slave and the interface to the outside world. The Arduino will default to safe state if USB communication to master is lost.