Weber & Coulomb's LyteFyba BMS

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Weber & Coulomb's LyteFyba BMS

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The moment I spotted the battery in the thumbnail pic of the video. I thought to myself...he's not going to make a fuse out of that track is he Image

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Weber & Coulomb's LyteFyba BMS

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like i always say

" get a bigger hammer :-) "

well done
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Weber & Coulomb's LyteFyba BMS

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Coulomb and I recently had two days all-expenses-paid at Cabarita Beach. There was a catch. We had to work on installing and testing a Demand Charge Management system based on lithium-ion cells, protected by a LyteFyba BMS, at a location nearby. Wot fun.

Image

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Weber & Coulomb's LyteFyba BMS

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[Edit: You can skip to a new version of this low-cost RS232-to-CMU interface, that has the ability to use wired comms as well as fibre.]

When working with the Industrial Fibre Optic (IFO) used in the LyteFyba Battery Management System, we usually use a Novus USB i485 device with a custom fibre interface. We've published the design for this interface elsewhere. It allows for either Fibre Optic or electrical connections to the LyteFyba BMS. And it allows for sniffing and injecting signals into existing fibre comms paths.

But the Novus i485 device is somewhat expensive. We've had reason to knock up a simpler cheaper interface recently, and now we've had to make a second one. So we thought we'd publish the schematic and layout. This inexpensive interface doesn't have the ability to talk to the LyteFyba BMS electrically, so you need to add the optional IFO connectors at the start and end of the chain of CMUs (Cell Management Units). It's RS232 to optic fibre, so you'll probably need a USB to RS232 adapter, such as the Prolific model available from Jaycar.

Here is the schematic:

Image

It can be made up on a small piece of Veroboard with this layout:

Image

The female D9 connector (technically, a DE9 connector, but it's often misnamed as a DB9 connector) must have pins 1-5 under the board, since connections are required to pins 2-5 (pin 1 is unused, as are pins 6-9 in the second row of pins). The solder bucket type is best, since the Veroboard fits tightly between the two rows of pins. So the PCB should look similar to this, when the D9 connector is soldered, the holes drilled, and the appropriate tracks are cut:

Image

The tracks can be cut using about a 4 mm drill.

The final board, from above:

Image

The IFO connector pigtails have to be spread out a little to accommodate the 2.54 mm pitch of the Veroboard holes. This seems to be by far the best way to fit these connectors to Veroboard.

Note that I tried to use a film capacitor for C2, of value 0.27 uF, since I had a bag of these on hand. But I found that file transfer was not reliable; it really needs a 1 uF capacitor. These can be bought as tiny "sky caps" (monolithic, ofen blue in colour) with 5.08 mm (0.2") spacing, or you can solder an 0805 surface mount capacitor under the board, between the GND trace on pin 5 of the D9 connector, and the track next to it (away from the D9 connector) labelled -8V. I did that, and left the 0.27 uF capacitor in place.


[ Edit: blue caps -> sky caps (monolithic) ]
[ C1 and C2 were swapped in diagram; added needed cut tracks; added C1 and C2 alternate positions under the PCB; no need for 1 mm holes ]
[ Added IFO part numbers to schematic; redrew slightly for neatness ]
[ Added note re spreading IFO connector pigtails ]
[ Added links to Prolific USB to RS232 adapter, Novus interface post. ]
Last edited by weber on Mon, 26 Jun 2017, 11:22, edited 1 time in total.
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Weber & Coulomb's LyteFyba BMS

Post by weber »

Here's a slightly more compact version of Coulomb's simple RS232 to IFO interface design. This one omits C2, which has been proven unnecessary, and swaps the order of R1 and D2 on the schematic. It also allows the IFO mounting screw heads to contact tracks which are in use, but one of these is GND, and the other is DTR which we are using as a +9 V supply. If the two are accidentally shorted, only 30 mA flows.

Image

Edit: I note that the DE-9 female connector is of the solder-bucket type, not the PCB-pin type, because this provides mechanical support, as it lets the board wedge tightly between the two rows of pins.
Last edited by weber on Sat, 26 Mar 2016, 08:21, edited 1 time in total.
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Post by weber »

Darn. After posting the above, I realised it could be reduced a little more in size, but only by increasingly "cheating", by putting more parts on a diagonal.

Image
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Post by coulomb »

The other piece of hardware that is needed with these Celltop Management Units (CMUs) and Battery Management Units (BMUs) is a JTAG (Joint Test Action Group) programmer. This is needed for initial programming of the processors, and for debugging if needed.

We use an inexpensive TI Launchpad Development board, available from RS-Online, element14, Digi-Key, direct from TI, and others. It just needs a small cable (250 mm maximum) added to it, and the jumpers moved to one side of their headers as shown:

Image

The header is industry standard 2.54 mm spacing. The wires are soldered to pads 2, 3 and 4, counting from the end near the single-row header. These are GND, JD_RST and JC_TEST respectively. This will allow you to program both BMUs and CMUs.

The development software we use is called IAR Embedded Workbench. It's free to use for assembly language projects, and C projects up to 8 KiB. Download here (use the "Download a free trial" button, and select the Kickstart, size-limited evaluation license when prompted after installing.

[ Edit: had IAR size limits incorrect. ]
Last edited by coulomb on Mon, 27 Mar 2017, 14:30, edited 1 time in total.
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Weber & Coulomb's LyteFyba BMS

Post by weber »

We haven't posted about LyteFyba BMS development for quite some time. But that doesn't mean it hasn't been happening. In fact there have been two major innovations:
• wireless infrared comms (optional) between adjacent CMUs (Cell-top Management Units), and
• the elimination of 16 bypass resistors in favour of a single zero-cost "printed resistor" covering most of the underside of the CMU.

And I'm pleased to announce that after 8 years (including building an electric MX-5 and several solar Monoliths to test it on Image ), we've finally stopped fiddling with the design and have gone to production. Hoorah!

We've licensed production to Lithium Battery Systems here in Brisbane, and here's the first panel of 12, hot off the production line on Friday, tested over the weekend, and its CMUs are going into the first customer's system as we speak.

Image

Other recent innovations are:
• increased voltage measurement range to 4.35 V for use with Lithium chemistries other than LFP,
• a low-cost watch crystal for comms frequency precision,
• a yellow-green LED for receive comms, in addition to the existing blue for transmit, amber for bypass and red for cell stress (an LED in each corner),
• a 3-pin comms header so orientation doesn't matter when you plug them in, and ready-made leads are available in various lengths at ridiculously low cost from the radio-controlled hobby industry,
• a 4-pin expansion port that allows a tiny daughter board to be added to the first CMU for monitoring a current shunt, and to the last CMU for controlling two contactors,
• a break-out that allows them to be fitted to the cells that use M10 studs at 73 mm spacing, in addition to all the common M6 and M8 spacings,
• width reduced to 30.4 mm to allow them to be fitted to cells as narrow as the CALB 72 Ah cells in the blue aluminium cases, and Nissan Leaf cell modules.

The reduction in width has meant reducing the bypass current from 800 mA to 650 mA, but we've added holes that allow the fitting of a 5 watt resistor if more bypass current is required.
Last edited by weber on Mon, 08 May 2017, 14:02, edited 1 time in total.
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Weber & Coulomb's LyteFyba BMS

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We've added a new feature to our low-cost RS232-to-optic-fibre adapter -- the ability to use wired comms as well as fibre. This makes it useful in more situations, for changing CMU parameters, data-logging, and reflashing to update firmware.

This required the addition of an optocoupler, two 3-pin headers and a new layout on a slightly larger piece of veroboard. All the parts are readily available (e.g. from Jaycar), except for the optic fibre connectors which are only available from Digikey. It is intended for use with a USB-to-RS232 converter cable such as this one. https://www.jaycar.com.au/usb-to-db9m-r ... m/p/XC4834

Image

Here's the schematic.

Image

And here's the veroboard layout.

Image


The TX header could be moved further away from the blue fibre connector, by swapping rows with the wire link above it.

If you only need wired comms, you can omit the fibre connectors. You can also shorten the board from 13 to 9 spaces.

If you only need fibre comms, you can omit the optocoupler and the headers.

The track cuts and mounting holes:

Image

The wire links: These can be made from resistor and diode lead offcuts.

Image

The finished underside:

Image

[Edit: I realised that the TX header did not require a fourth pin and a jumper. So I edited all the images and the text accordingly.]
Last edited by weber on Tue, 27 Jun 2017, 05:31, edited 1 time in total.
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Re: Weber & Coulomb's LyteFyba BMS

Post by macks »

Very nice guys, how did you go the PCB material compressing and loosening connections? Not an issue?
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macks wrote: Tue, 28 Jan 2020, 06:32 Very nice guys, how did you go the PCB material compressing and loosening connections? Not an issue?
That's right. Not an issue. We're currently about half way through replacing all the cells in the MX-5 (but reusing the CMUs). The 218 cells have been bolted up for 7 years now, and travelled 23.5 Mm, and we have not had any loose connections. I think the main cause of loose connections in DIY EVs is not clamping the cells to prevent them moving relative to each other.

You may be thinking: Why did I only get 7 years out of the LFP cells? The cells are actually 10.5 years old, but spent the first 3.5 years of their life on the shelf. I didn't realise how long it would take to finish the conversion. And the higher temperatures in Brisbane. And the bursts at 200 amps (5C). :)
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Re: Weber & Coulomb's LyteFyba BMS

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weber wrote:We're currently about half way through replacing all the cells in the MX-5
Are they going to have a second life as house bank?

Regarding Brisbane weather and 5C discharge.
  • What's you thoughts on battery cooling?
  • Using LTO batteries?
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macks wrote: Tue, 28 Jan 2020, 12:26 Are they going to have a second life as house bank?
Yes.
Regarding Brisbane weather and 5C discharge.
   • What's you thoughts on battery cooling?
Great idea. One theory says you can double the calendar life of pretty much any battery chemistry by lowering the temperature 10 °C. It's usually just too hard to do in a conversion. But Franciso has a cool :sunglasses: design.

In Brisbane, and warmer climes, cycle life is pretty much irrelevant unless your EV is a taxi. Mexy (the MX-5) only did the equivalent of 180 full cycles in those 7 years. Calendar life is almost everything. And temperature is almost everything re calendar life.

However, staying away from high cell voltages can also have a significant effect. That's what I plan to pay some attention to in future. I may attempt to implement end of charge at 70% SoC for the new LFPs (i.e. stay on the middle voltage plateau, 3.29 V), with 100% SoC as an option if you know you will need it the next day, and when cell balancing is required.
    • Using LTO batteries?
Also a great idea, provided you can accept the lower range due to the lower energy density, and the price. But they seem to have been coming down in price lately. They have longevity and safety and they just laugh at 5C discharges.
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Re: Weber & Coulomb's LyteFyba BMS

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Weber said:
"The 218 cells have been bolted up for 7 years now, and travelled 23.5 Mm".

23.5 mega-miles isn't bad over 7 years. My H2 only traveled around 1.6*10^9 m before someone pranged it and I had to sell it. :)
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Re: Weber & Coulomb's LyteFyba BMS

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Your use of a low cost optical fibre is interesting. Adds about $30 to total cost? no problem with that. What is the main incentive to use this, the high volt isolation - then noise immunity?
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Re: Weber & Coulomb's LyteFyba BMS

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macks wrote: Wed, 29 Jan 2020, 08:51 Your use of a low cost optical fibre is interesting. Adds about $30 to total cost? no problem with that. What is the main incentive to use this, the high volt isolation - then noise immunity?
You got it. High voltage isolation and noise immunity. The additional cost depends on how many fibre hops you have between battery boxes, and to the master units, versus wired (but optoisolated) connections between adjacent cells. It's about $10 per fibre hop and about $2 per metre of fibre. The MX-5's battery is broken into 12 sections, so we end up with 16 hops for the BMS, and another 4 for the chargers. And maybe 40 m of fibre.
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Re: Weber & Coulomb's LyteFyba BMS

Post by weber »

LyteFyba can be modified to work with LTO cells without any artwork changes, only component and firmware changes. The 1N4004 reverse protection diode can be replaced with an ultra-low forward voltage Schottky (although this may only have 20 V to 60 V reverse withstand). The voltage regulator should be replaced with a wire link. The blue LED will need to be replaced with green, and the voltage sense resistors can be rescaled to maximise the resolution.

We already have an octagonal PCB layout for LyteFyba CMUs, that works with cylindrical cells down to 42 mm diameter (no matter whether they are square packed or hexagonal packed).

OctCMU.png
OctCMU.png (48.31 KiB) Viewed 1682 times
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Re: Weber & Coulomb's LyteFyba BMS

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Would these use optic fibre links or wire links? Would it require one board per cell group or a board per cell?
The reason I'm asking, I'd like to use LTO cylindrical cells in my VW Kombi conversion and liquid cool them by submerging them with one of the battery coolants coming on the market.

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T1 Terry wrote: Thu, 30 Jan 2020, 10:15 Would these use optic fibre links or wire links?
They can use either optic fibre or wire links.

They can also use line-of-sight free-space infrared comms (like a TV remote control, but deliberately reduced in power to work only over typical inter-cell distances). Since the fibre and IR require additional components that add to the cost, typically you'd use wired links inside a single battery enclosure (using readily-available short cables that plug onto the 3-pin headers on the CMUs) and you'd use fibre (or IR through a transparent window) to enter and exit the box.
Would it require one board per cell group or a board per cell?
It would only require one board per group of parallel cells.

The boards bolt to one end of one cell and a flying lead with a lug goes to the other end. The boards come in two isomers — one that bolts to a negative terminal and one that bolts to a positive terminal. This allows all the CMUs to be on one side of the battery box, so their LEDs can all be seen from one side, and so all their comms connections can be on one side.

The CMUs are raised above the high-current links or lugs by spacing them with copper washers. The bypass resistor consists of 1.3 metres of PCB track (mostly the zig-zagging blue in the image). 600 mA bypass current (with LFP).
The reason I'm asking, I'd like to use LTO cylindrical cells in my VW Kombi conversion and liquid cool them by submerging them with one of the battery coolants coming on the market.
Very interesting. I had to go search. I see they are fluorocarbons which are greenhouse gasses with long atmospheric lifetimes and very high global warming potential, e.g. GWP = 9000. I'd think very hard about whether you can't get away with using air as your coolant. Internal resistance of LTO is much lower than LFP and so self-heating is much less.

The board layout would need to be modified to work with the Yinlong LTOs. The above board was designed for LFP cells with M5 or M6 studs. I understand the Yinlong LTOs have M12 studs.
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Re: Weber & Coulomb's LyteFyba BMS

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"Very interesting. I had to go search. I see they are fluorocarbons which are greenhouse gasses with long atmospheric lifetimes and very high global warming potential, e.g. GWP = 9000. I'd think very hard about whether you can't get away with using air as your coolant. Internal resistance of LTO is much lower than LFP and so self-heating is much less."

I hadn't looked into what the chemical make up was of these new to the market "E" fluids were, I certainly didn't expect them to be high GWP products. I did find this on a very quick Google search http://www.inventecusa.com/assets/novec-7200.pdf and a scroll down shows the 7100 formula has a boiling point of 61*C and mentions heat transfer as one of the potential uses.
There is other sites with info about the 7000 formula http://www.me.umn.edu/courses/me4331/FI ... EC7000.pdf that has a boiling point of 34*C, zero ODP (ozone depleting potential), a GWP of 370 and an atmospheric life time of 4.9 yrs. The rest of the information went way over my head but no doubt I could find someone who could make sense of it if it had the potential to do what I want.
My thoughts were around using this 7000 formula and a vapour compression cooling cycle using the phase change to move the heat away from the cells and out into the atmosphere. I'm probably way off track here because I've missed something very important along the way, so please point it out , get my head out of the clouds and put me out of my misery :lol:

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Re: Weber & Coulomb's LyteFyba BMS

Post by francisco.shi »

The flurocarbon coolants are extremely expensive and have to be kept in an airtight loop. They absorb water which makes them conductive.
I was considering to use them for a cooling loop in a 3kv inverter. After funding out about the problems I decided that air cooling was good enough.
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Re: Weber & Coulomb's LyteFyba BMS

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francisco.shi wrote: Sun, 02 Feb 2020, 05:02 The flurocarbon coolants are extremely expensive and have to be kept in an airtight loop. They absorb water which makes them conductive.
I was considering to use them for a cooling loop in a 3kv inverter. After funding out about the problems I decided that air cooling was good enough.
Do you know if the 3M Novec products are hydroscopic? This one in particular https://multimedia.3m.com/mws/media/199 ... -fluid.pdf

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Re: Weber & Coulomb's LyteFyba BMS

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I do not know.
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