Dream GreenSaver Charger - The GreenBMS

sparc5's picture

I'm moving this from a post to a blog to keep people up to date with my progress.

For those who haven't been following the threads I've posted to here are the problems I'm trying to solve:

1) Battery charging- Make sure our batteries live long and prosper.
2) Equalizing- Make sure they discharge at an equal rate so you're range isn't limited by your weakest battery.
3) Cost- Keep the price lower than the alternatives.
4) Patents- Must do this all without violating patents.

After three weeks of heavy brainstorming here's the leading plan for what I call the GreenBMS:

More than anything, we need a good temperature compensated bank charger. So I'm building a percision, programable, multichemistry, bank charger that uses PWM to provide desulfication and active monitoring of each battery's voltage. Woah, try saying that with one breath (adjusts glasses). This is the heart of the GreenBMS. By using a chip that came to the market only a month ago, you can provide your own DC power source to the charger it can accept anything from 3-75 volts DC. (Anything above 14V means higher efficiency). It is small enough to fit inside the scooter. You can save money by using the charger that came with the bike to power it or buy something beefier. You can even connect it directly to solar panels if you wish.

Extra add-on 1 (An auxiliary battery):

The other benefit to having a power converter that takes such a large range of voltages is you can charge the batteries as you drive, like an alternator does, but it will get it's current from an auxiliary battery instead of a car's engine. You can run the 12V electronics off it and get rid of the inefficient DC-DC converter. The charger will switch to a mode that charges the weakest battery and brings it up to the average state of charge of all the batteries. If the batteries are evenly matched, the auxiliary battery will never discharge much. If all the batteries are very low, or if told to do so, it switches to an extend range mode, where the auxiliary battery charges all the batteries at a rate in which it will be depleted at the same all the other batteries are. When you plug it in, the auxiliary battery gets bank charged with all the other batteries. You can make the auxiliary battery any capacity and chemistry you want. A small cordless power tool battery might be all you need, I need to do testing once I build the prototype. The only cost of this add-on is the price of the battery and the wires to connect it.

Extra add-on 2 (a display, and user interface):

Since the microcontroller (uC) is already monitoring battery voltages, amps, and temperature, it's very simple to display this on an LCD. It will have a graphical user interface and some buttons to let you interact with the BMS' parameters.

Extra add-on 3 (wireless communications):

Everyone can change their programs if they wish to. I know everyone here loves to tinker and share their improvements. I'll offer a long range wireless (102.15.4) data communications add-on so you can program the charger, install updates, monitor the charging, and download data from your rides, from anywhere in your house. It's cheaper than bluetooth, and easier to interface.

This is all going to be opensource to keep costs for everyone to a minimum. I'm doing this project for myself, and making the knowledge on how to do it free for everyone. Early adopters of electric scooters have a soft place in my heart. I'll have extra circuit boards made up, buy enough parts to construct a dozen kits, and sell them in kit form or assembled for a bit extra.

This week I'll be drafting schematics and ordering components.

This project is much more complicated then initially planed. My fears are the cost of the parts, and the complexity of making them all work in harmony. In the past I've programed uC's. I went through a clock making phase. One clock flickered 8 leds fast when you attach it to the ceiling fan it displays the time. I've made a SMPS to power a nixie clock. It turned out well. This time I'll be programming a uC with the most sophisticated program ever. The SMPS this time is powerful enough if I put a wire in the wrong place it could start a fire. If you guys don't hear from me in a while, you can assume I forgot to ground something. :P

As a request: Everyone please take out your multimeters and tell me the resistance of your batteries and voltages before charging and after. Include the temperature as well. Thanks in advance.

-=Jeff=-

Comments

sparc5's picture

What a novel idea. Embrace the noise, don't fight it! Would be fun to experiment while running the motor, but wouldn't be useful calculating time until charged. I was up until 4:30am making last minute design decisions. Too tired to post right now.

My EE friend last night introduced me to Mapnik open source map rendering. It has OSM imported TIGERS data, so that means there's map info for most of the US. It would look great on the 240*400 color oLED.

XM-3000...
-DC-DC converter replaced with a Dell D220P-01 power supply.
-72V mod
-Expensive bank charger until I come up with something better... Still trying.
-

jdh2550_1's picture

XM-3500Li charger takes about 30 seconds to ramp up to 9.6 amps at 64.3 volts, then it levels off there.

John H. Founder of Current Motor Company - opinions on this site belong to me; not to my employer
Remember: " 'lectric for local. diesel for distance" - JTH, Amp Bros || "No Gas.

jdh2550_1's picture

My EE friend last night introduced me to Mapnik open source map rendering. It has OSM imported TIGERS data, so that means there's map info for most of the US. It would look great on the 240*400 color oLED.

Two words for you.

Feature.

Creep.

;-)

But, it sounds great. Small GPS sensors with serial ouput of standard NMEA data are cheap - so are you going to add GPS to the list? Or am I?

BTW, now might be a good time to consider how to separate the BMS smarts from the UI. i.e. having a separate head unit. Now that you're considering higher level functional uses of that display (a good idea) you open up the whole "carputer" concept. I've long wanted to develop such a small compact device. My blue sky idea would be a Linux based hand held computer (like the www.dashdaq.com in form factor but not function). This would act as the head unit, data logger, user interface bit. Things like GPS and BMS and an audio system (amplifier and speakers - head unit wouldhave an MP3 player) would be systems built into the bike. The head unit would be easily removable to carry with you. I've had a couple of aborted attempts to start building a linux "PDA" around the gumstix (I have two gumstix boards in my basement).

See, I can feature creep with the best of them!

John H. Founder of Current Motor Company - opinions on this site belong to me; not to my employer
Remember: " 'lectric for local. diesel for distance" - JTH, Amp Bros || "No Gas.

sparc5's picture

I'm ahead of ya boss. The BMS slaves are programed what to do by the BMS master. This allows for a fault detection, redundancy, and scalability. The display has its own MCU, it was necessary for fast graphics. It is only an optional purchase, the BMS comes pre-programed, and you can edit the settings on the master's SD card.

I'm not adding the GPS feature to this list, but will include a spare RS-232 on the display unit (the master is out of I/O pins). Maybe next summer, or whenever the GreenBMS falls into a fellow tinkerer's hands.

XM-3000...
-DC-DC converter replaced with a Dell D220P-01 power supply.
-72V mod
-Expensive bank charger until I come up with something better... Still trying.
-

rossasaurus's picture

Hey Sparkie, I'm in for one....whatever it ends up being.
Hilarious watching the discussion and mission creep.
Can it clip my ceegar too?

Ross

As long as we are adding feature creep, how about putting in a charge timer? Let me plug the system into my scooter when I get home from work at 6pm, but the charger won't start charging until 2am, with the goal of reaching a full charge by 7am?

I'd suggest two simple modes: 1) fast recharge now! 2) take your time, I need it charged by o'clock.

My electric vehicle: CuMoCo C130 scooter.

sparc5's picture

Hi MikeB,

The charge rate IS adjustable and the optional display will tell you how long at present rate until the battery is full. I like your idea of giving it an end point and it will calculate the charging rate. Currently the only similar feature I have is the "Time until charged at present rate" and "Time until self discharged."

I uncertain what the point is in delaying the start of charging. The charge acceptance is directly related to the standing time of the battery before charging. The shorter the better to prevent the growth of lead sulfate crystals. My charger can fight them, but it's a slow process.

I'm really glad to see interest in this project. So far everything is going on schedule. Last night I had talks with a 3rd party who showed an interest in helping develop the GreenBMS. If anything comes from it the time to market should be dramatically reduced.

Phase 1 (the BMS part) is still on schedule to be ready for production in three weeks. One week prior to production I'll begin taking pre-orders to help pay for manufacturing of the circuit boards and gauge demand. The display and charger modules can be added to the system once they're tested and ready, they aren't required for the BMS to function.

Keep the suggestions coming people! I'm still in the brainstorming mode regarding user interface. Touchscreen is out. Everything else is is in. The iPod is my inspiration for uncluttered, easy to use, quick access interface. At this stage I'm very uncommitted to any one idea. Rotary knob that can be pushed or pulled similar to a car stereo? Four directional buttons and a center button? Soft buttons on the side of the display like an ATM machine? Keep in mind it must be waterproof. :)

XM-3000...
-DC-DC converter replaced with a Dell D220P-01 power supply.
-72V mod
-Expensive bank charger until I come up with something better... Still trying.
-

The big reason to delay the start of charging is because electricity demand is lower late at night, and rates are often cheaper. This doesn't apply to everybody, but it'd be a nice feature for those who can get off-peak rates.

Also, using off-peak power reduces the demand for peak power, and may slow the need to build new coal-fed power plants.

As for controls, you might look at how Garmin designed their Zumo GPS for motorcycles. Four rubber-coated buttons on the left side of the unit, and a touch screen. The buttons are easy to operate even when wearing standard motorcycle gloves. I think a star-pattern of buttons works well (4 directional plus one center).

My electric vehicle: CuMoCo C130 scooter.

I was just working on the software for the GreenBMS speedometer. I can have it show the usual boring MPH, KPH, RPMs, but just for fun I think I'll do meters/sec, and football fields per hour. Am I being too silly?

Furlongs per fortnight was a popular set of units for me and my friends back in High School, as well as Megaparsecs per microsecond. But if you want to get really silly, you need to add something like multiples of the speed of a Charging Rhinoceros (CR), for those rare occasions when you need to know if you speed is greater or less than 1.0 CRs.

My electric vehicle: CuMoCo C130 scooter.

sparc5's picture

Ah ok, makes sense. I'll include it in the list of features, it will be a very easy feature to add.

As for the touch screen, it would have to be resistive because a gloved finger might not activate a capacitive touch? If it was resistive, it would have to be exposed to the elements, and I don't have a solution for that yet. I've never worked with touch screens. It is easy for me to use bourn encoders and/or normal buttons.

XM-3000...
-DC-DC converter replaced with a Dell D220P-01 power supply.
-72V mod
-Expensive bank charger until I come up with something better... Still trying.
-

Mik's picture

Ah ok, makes sense. I'll include it in the list of features, it will be a very easy feature to add.

Could you get it to auto-calibrate the "CR" speed upwards if it encounters acceleration of more than, say, 5g?

That might save your African customers lots of time.

Mr. Mik

This information may be used entirely at your own risk.

There is always a way if there is no other way!

Jeff,

Great project! I've been looking at electric scooters the last few months and I'm impressed at how much DIY stuff is going on. I'm a chip designer developing digitally controlled DC-DC buck converters. Perhaps I can be of some help to you.
Not sure if you've settled on the uC you want to use but perhaps one of the PIC PWM controllers could help integrate both the UI stuff (buttons/LCD control) as well as the regulation/charger. Just a thought.

If you want to go touchscreen, I have personally developed some software for a WinCE based GPS navigator. I found that if the GUI controls are made large enough, the touchscreen can still work while wearing bike gloves.

Kevin

:jawdrop: I uncertain what the point is in delaying the start of charging. The charge acceptance is directly related to the standing time of the battery before charging. The shorter the better to prevent the growth of lead sulfate crystals. My charger can fight them, but it's a slow process.

WHo waite a miniute I thought you were building a BMS for 20-24 Cells of LiFePo4 cause ,there is no Lead in them ??? Lead Sulfate only happens in Lead & H2SO4 batterys !! LaTeR

thank GOD I wake up above ground !!!!

sparc5's picture

Hi Guys,

I'm back. The parts from Mouser came, the inductors are a bit small and the Pic32 hasn't arrived yet (for the master BMS). So far I've tested out the temp and current sensor. The next couple nights I'll test out the equalizing circuits, and post the results.

Hey Strawwihistle, the BMS is for lithium and lead acid, and eventually NiMH. I've decided to build universal hardware vs a chemistry specific one. It was a hard choice to make because I had to weigh running the slave PICs off each cell's lithium power vs supplying a single 3.5V buck converter from the 12V lead acid batteries and attaching power wires to each BMS. There is also the option of connecting to 12V worth of lithium batteries, but that is more complicated to hook up. I'm trying to keep the wire nest to a minimum. The other design issue is the current sensor runs off 15V ideally, but is acceptable at 12V.

So it looks like there will be from slave to slave:
Two 3.5VDC power wires (trying to figure out how to make it optional for lithium)
Three serial wires
One big current bypass wire.

Due to time constraints I am not going to build the auxiliary battery equalizing method. Instead it will use microprocessor controlled current shunts to keep the batteries equalized during charging and discharging. I'm concerned very much about patent infringement. I'm not using the switched capacitor design like the competition, but who knows what patents are out there? My simple four component design could have a patent on it, and that's the end of the project. It is irritating, imagine if McDonnalds could sue if people used "I'm lovin' it" in their books and magazines. If there were millions of four or five word combination patented no one could write anything commercially. I'll have to hire a patent lawyer for a consultation.

My OLED factory is taking their sweet time producing the displays, so for this first version, I'll have a RS-232 port you can connect an inexpensive PDA to if you want to monitor your cells and/or maybe a serial based transflective LED backlit display (to avoid the special requirements of a traditional LCD backlight). I'm optimizing the design so all the adventurous souls who bought the XM-3500 won't develop bad cells and then wait ages for X-Treme to ship new ones. I've also enlisted help with certain areas of development to get these units out all the more quickly.

To Kevin, I'm looking for one that has a wide voltage acceptance, 32-80V, but that's probably unrealistic, 60-80V is the second best. Dual outputs would be great too 15V and a 3.5V @ ~1A max, any ideas on which I could use? Tell me more about the touch screen, was it capacitive touch? Any idea how to waterproof it?

Pics and initial data coming this week.

XM-3000...
-DC-DC converter replaced with a Dell D220P-01 power supply.
-72V mod
-Expensive bank charger until I come up with something better... Still trying.
-

For that input voltage range you probably will want to "roll your own" and look for a suitable controller and FETs. I will try to do some research and see what I can find. Any other requirements other than the input/output voltage and current? How quiet does the output voltage need to be? Is there issues with big current loads on the 12V at power up that might cause inrush problems? Is the input voltage going to be pretty stable/quiet? I've never done any scope measurements on an EV stacked battery so I don't know how it behaves.

My intent on the GPS project was to seal the screen to the inside of the enclosure (gasket or silicone). I didn't do any testing in the rain but I did use the unit with racing gloves. Making the GUI controls large enough for gloves does limit the usable display area however so perhaps having waterproof buttons/switches might be the way to go. I can try to contact the factory in China to see how much the displays by themselves cost if it's of interest to you.

Since it sounds like you may have some time constraints, perhaps it might be easier to forgo all these "fancy" extras (like touchscreen, GUI, etc) and just concentrate on the main functionality you're looking for first. Once you get the basics ironed out you can look at adding all the other goodies. Just a suggestion.

In regards to the patent concerns is there an existing design that's already public domain (ie. schematics or design details in a released paper on the internet)?

Kevin

sparc5's picture

No other requirements. Doesn't need to be very quiet because I have decoupling capacitors. No soft start up necessary either. Input voltage will decrease as batteries drain, there is noise on the battery, I don't know how to quantify it.

What happened with your GPS project? Maybe for the sake of time we can integrate it? I'm with you on leaving off the bells and whistles. First goal is to protect the batteries. Everything else can be added later, I'm making provisions for it. Thanks for your offer to get in touch with the Chinese display manufacturer. I think for now I'll buy something in the US, or just leave an RS-232 port for people to buy a $10 Palm III to interface with it.

AFAIK the only public domain balancing scheme is the resistive current shunt. The drawbacks are wasted energy, heat, and nothing to fix uneven discharge. My first idea was to use what amounts to a battery charger for each cell that can run off an auxiliary battery while driving. This has a lot of drawbacks too, lots of wires, harder to scale, cost. So finally I went with a current bypass method. Similar to patent 5,479,083. Too similar perhaps. It's funny because it actually looks nearly identical to what the BattEQ does, who's operation is covered by a different patent. Pain in the ass.

XM-3000...
-DC-DC converter replaced with a Dell D220P-01 power supply.
-72V mod
-Expensive bank charger until I come up with something better... Still trying.
-

jdh2550_1's picture

I was just working on the software for the GreenBMS speedometer. I can have it show the usual boring MPH, KPH, RPMs, but just for fun I think I'll do meters/sec, and football fields per hour. Am I being too silly?

How about the official measurement of all EV scooter pioneers are already very familiar with - I'm talking of that little known unit the "XM". It's a bit like the KM only more x-treme dude (it should have flames associated with it!). It's actual real world rate should be user modifiable so that it can show without a doubt that the XM scooter is the fastest damn scooter on the planet. So there!!!

John H. Founder of Current Motor Company - opinions on this site belong to me; not to my employer
Remember: " 'lectric for local. diesel for distance" - JTH, Amp Bros || "No Gas.

I did some quick searching and found a similar National part LM5116 as the one you listed earlier. It seems pretty good if you're concerned about part count as it's highly integrated. There are other high voltage controllers but they only seem to handle up to around 70V input. You could design your own regulator from scratch using a conventional dual output controller and using an LDO to drop the input voltage for it's supply but then this leads to more components than perhaps you want.
For a quick and dirty design you might go with something like the LM5116 as a first stage from 80V -> 15V and then do a higher efficiency switcher from 15V to 3.5V.

You've got me interested at looking at that patent. I'll take a look at it tomorrow. I've done current balancing for power supplies but never for the discharging batteries. It sounds like an interesting problem.

I'm still hopeful the GPS project will work out but I've had some problems with the overseas suppliers recently. You might be able to use a system like that for your display unit. Even in small volumes, you can get them at a really good price.

Kevin

sparc5's picture

Good call Kevin. It was my #1 choice too. If you look up near the start of the thread, I was talking about it's cousin the boost/buck neighbor. They even have a nifty spreadsheet where you can plug in your desired parameters and it calculates the external component values.

Did you look at that patent? It's simplistic beauty.

I hear ya regarding overseas suppliers. The OLEDs I bought will officially not be manufactured until end of Sep. I asked for a refund, don't expect to get my wire transfer charge refunded though. :(

I'd be very interested in using your GPS platform as a display option if it's affordable. The two might compliment each other well. Can we use a serial interface with it? Can the software be updated? Any chance you'd want to make it open source? :D I posted a link for public domain maps a couple posts ago, maybe it can help you.

I'm going to be doing more working and less posting in the coming days to make my deadline of a working prototype on Monday.

XM-3000...
-DC-DC converter replaced with a Dell D220P-01 power supply.
-72V mod
-Expensive bank charger until I come up with something better... Still trying.
-

I didn't have time to look at the patent although I'm predicting today will be another uninspiring day at work so I'll have plenty of time :)

Ouch! Wire transfer hey. Is that the only method of payment they would accept? I've been doing all my payments through Paypal.

You should be able to hook up to the board's serial port. Yes, the software can be updated via USB. It also has an SD slot. The application I was targeting was more in line with auto racing so I developed custom software to do specific mapping for race tracks.

Heya sparc5, any updates for us? I might have a 21-cell EVD sometime in the next couple of weeks, sure would like a BMS for it...

My electric vehicle: CuMoCo C130 scooter.

sparc5's picture

In McCain voice: Hello friends!

I'm taking a breath from all the design work I've been doing. When the project got started I fell into that EV trap of spending more time writing everyone then actually designing.

So here's what I've been up to:

Created proof of concept inductive battery balancer. Using an inductor as in U.S. Patent no. 5,479,083, Dec. 26,1995. It took a lot of trial and error before I found a suitable inductor. When I did find one, it was prohibitively expensive for use on a 19-21 battery li-ion scooters.

Picture 13

I had other concerns as well. The master slave system I envisioned needs a lot of wires to be daisy chained from slave to slave. Each one being a weak point in the design, unless more expensive connectors are used. I also could include some redundancy in the firmware, that would shut off the charger if the master or slave detected a fault, but it just adds to the total complexity of the design.

Here are some behind the scenes pics:

Picture 14

Picture 12

Picture 9

Picture 6

Picture 5

Picture 4

Picture 15

The third fault with the GreenBMS, is that it is still covered by US patent law. I spoke to the inventor, he didn't know who owns the patent now, its probably been forgotten about, but none the less, I'd be taking a risk by using it.

Meanwhile in some Texas Instruments laboratory, engineers have been busy building their own solution. The BQ77PL900 came onto the market just weeks ago. It has all the cell protection features built in. It can run as a stand alone (see inexpensive for you) or can be interfaced with by an embedded controller. It's exactly what we're looking for and more. The only downside is it doesn't balance the batteries as they are being discharged. TI is working on another chip for that due out in a month or so (maybe next scooter season we'll have it). Now I wont have to worry about patent laws, or expensive inductors and transistors. The other downside is it doesn't help the people with Lead Acid or NiMH packs. Instead of master and lots of slaves. It will be slaves (5-10 batteries to a salve) and an optional master. This will lower costs, and increase reliability.
I'm going to order this BQ77PL900. Everyone anxious to get some protection NOW they can get the BQ77PL900 evaluation kit from TI's website.

In the meantime I'm working on storing data on an SD card (Fat32 connected via SPI port) and rigged my MacBook external monitor port so that it can send and recieve I2C signals (what the BQ77PL900 uses to communicate).

Expect another update in a week on my progress.

XM-3000...
-DC-DC converter replaced with a Dell D220P-01 power supply.
-72V mod
-Expensive bank charger until I come up with something better... Still trying.
-

Mik's picture

Nice toys!

How come the NiMH chemistry gets left out all the time?

Why is it that the BQ77PL900 cannot be used for Lead-acid or NiMH?

Thanks for your efforts, hope you succeed in the end!

This information may be used entirely at your own risk.

There is always a way if there is no other way!

sparc5's picture

Hi Mr. Mik,

The Lead-Acid can't be used because the voltages are too high. One could hypothesize they could be used with the proper voltage dividing resistors. I'll find out soon. NiMH might be able to work without any additional hardware.

The NiMH batteries are the most unfamiliar for me. I don't have any large NiMH batteries to test with. (I'll have 10Ah LiFePO4 batteries days after Halloween) I'm not familiar with the best charging method. My superficial glance at the literature says NiMH gives false dV peaks, making it harder to determine when exactly to stop charging, there is a method of using cell heat to gauge it better. Maybe someone else can look at this chip and tell me if it can be modified for use on NiMH or PbH.

After the BMS is built, hopefully all the programmers on V will come together to write the state of charge software.

XM-3000...
-DC-DC converter replaced with a Dell D220P-01 power supply.
-72V mod
-Expensive bank charger until I come up with something better... Still trying.
-

reikiman's picture

After the BMS is built, hopefully all the programmers on V will come together to write the state of charge software.

(Looks around) Who you talkin' to? :)

- David Herron, The Long Tail Pipe, davidherron.com, 7gen.com, What is Reiki
- Electrified Electra To

sparc5's picture

Hi Kevin,

Any news on your project? I still am looking for a good LCD with built in controller to use (to avoid pricey external controller). Check your private messages.

-=Jeff=-

XM-3000...
-DC-DC converter replaced with a Dell D220P-01 power supply.
-72V mod
-Expensive bank charger until I come up with something better... Still trying.
-

Hi Jeff,

Sorry for the dead silence. As far as my project goes, I've been trying to engage with a US GPS manufacturer since the one in Taiwan is ignoring me. I may just open source the project just to see it gets to completion.

What are your LCD requirements? Do you need touchscreen? What size? You can always find samples for prototyping at places like spark fun. Not the cheapest place but it might be what you need to get going.

Kevin

sparc5's picture

Hi Kevin. I'm looking for something sunlight readable, backlight and < $36 USD. Touch screen is optional. 2.5" diagonal min, LCD Controller (to avoid expensive external controller). Serial, SPI, i2c any of those would be an ideal interface.

XM-3000...
-DC-DC converter replaced with a Dell D220P-01 power supply.
-72V mod
-Expensive bank charger until I come up with something better... Still trying.
-

I found this on Digikey: http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=635-1000-ND
It's twice the cost you were looking for but it's has a serial I/F. I haven't looked overseas yet.

sparc5's picture

Hi Kev,

What about the LCD you were going to use on your GPS? That LCD is great, I love the i2c interface, but price is extreme.

I am going to try to use this:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=300263320239&ssPageName=ADME:X:RTQ:US:1123

The interfacing it seems straight forward, but the physical connector for it is an unsolved problem at the moment.

XM-3000...
-DC-DC converter replaced with a Dell D220P-01 power supply.
-72V mod
-Expensive bank charger until I come up with something better... Still trying.
-

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