Designing new RLEC boards, any interest?

[Zuikkis]

Hi,

I'm running a company Z-Power in Finland. I specialize in all kind of car electronics and chip tuning, but I also have 30 years of experience in all kinds of electronics design.

I have two broken Think Citys with Enerdel battery. Both batteries are broken but it seems I am able to combine them into one working, but I will be using all of my RLEC boards.

RLEC boards seem to be very badly designed because they break almost instantly if there is any leakage between channels (water damage).. Then they start draining the battery cells and eventually destroy the cell. Even if you can find new RLEC boards it's very likely to break again.

I know how the CAN messaging works between MLEC and RLECs. It would be reasonably easy to redesign the RLEC with modern technology, which is much simpler (=cheaper) and more reliable.

I was thinking of L9963E chip from ST:
https://www.digikey.co.uk/en/products/detail/stmicroelectronics/L9963E-TR/13986399

It's interesting because it has practically everything RLEC need in a single chip, and several L9963E's can be daisy chained with isolated SPI bus. So only single CAN->SPI bridge processor is needed to communicate between MLEC and the "master" RLEC. This also cuts down costs as the isolated CANbus drivers in original RLECs are expensive.

These new RLECs would be reasonably priced, perhaps about 30-50€ piece depending on quantity. So you need 16 of them and then the CAN converter box (which probably would be integrated to one RLEC).

However, this will take some design effort and I'm pondering if it's worth it. Do you think there is still enough of these cars?

[worry]

Hi,
I don't understand anything about such electronics, but.. Yes, I would say this is very interesting.

Since a couple of years or so a new source of original RLECs showed up, so we could save some batteries. I don't know how many he has left. The cost was around 100 euros each.

My experience is that; if you keep the battery dry, they last. But also the MLEC have been a problem, and they are even harder to find.

Couple questions:
Why do you need a CAN converter box?

The balancing current is quite low with the original RLECs. Sort of sufficient for a battery with cells of equal capacity. But if they differ because of age, or you need to change cells, it's often not enough. I have one Think which needs 10 hours or more balancing after a few driving cycles. Could your RLEC's have higher balancing current?

[Zuikkis]

Yes I have seen old RLECs for sale at about 80-100€, but in my opinion that is too high because it would cost just 1600€ for entire set.. These cars are not really worth that investment anymore. I bought my latest Think at 1100€..

MLEC and the RLECs use internal CAN bus for messaging. This protocol is thoroughly explained in this document:
https://www.metricmind.com/audi/images/_0387_programmers_guide.pdf

If I change the RLECs but keep original MLEC, I need a "CAN receiver" that can interpret balancing commands send by MLEC and command this new RLECs. This is not very complex hardware, just needs some software. You could also add things like Bluetooth so you could easily monitor the battery state with a phone app.

If MLEC was replaced too, then the battery internal CAN could be removed completely. But MLEC is much more complex, both hardware and software side of it..

About balancing, original RLECs have about 100mA balance current which I think is actually quite big? The chip I linked in first post supports 200mA, or even higher if using separate power mosfets. But to keep it simple I would like to avoid using external components.

Original Think probably balances only when charging? This could be changed, so out-of-balance pack could continue balancing even when charge cable is removed, and car is driven.. Then the 10 hours would not be that much of issue.

[worry]

The real value of the Think, is when using it. Economically it's hard to beat when used for daily commute. And it's cool. :-)

So, what you say, is that you can't talk to the RLECs directly, from the battery network? You need to talk via the MLEC?

I'm into deep water here, but do you know all the tasks done by the MLEC? Ie reporting SOC, control of charge, control regenerate. I guess the conversation between car and battery is programmed in the PCU, and adapted to the MLEC?

It would be cool to have a modern BMS and cells with higher capacity. I tried to calculate cells from Tesla into the original box, and found more than 40 kWh doable.

I have never found information about when balancing happens. Maybe just in the final part of charge? Since balancing is draining the battery, maybe it's just stupid to balance to often -or fast? 

[Zuikkis]

MLEC has two CAN buses, one connects to the car (PCU) and other connects to the 16 RLEC cards. That RLEC bus is not accessible from car side.

So if I replace RLECs with my own, they must understand the commands send by MLEC.

[worry]

Ok, thanks.
Good luck, if you do this. 

[Warlock]

 

I would probably buy a board or two, at least...

Are you considering open-source what you do? It would be preferalble to know how to repair even this solution after a decade or two

[Zuikkis]

Are you considering open-source what you do? It would be preferalble to know how to repair even this solution after a decade or two

Oh. This is possible, yes.

Also, I already have made a board for a bit different purpose, here's a picture:



If using Think batteries for other purposes, you can let one RLEC handle two batteries. Batteries must be connected in parallel! So it won't work inside a car where batteries are in series.

But I have a home energy storage built from Think modules. I'm using RLECs to control it, but since many were broken I designed this card so I only need half amount.

[Warlock]

Fascinating, and very cool! 

[pexic]

Hi
my advice : keep it simple , replace Mlec and all Rlec modules with
1- stand alone BMS (ballance current >1A)
This allow almost any type of BMS+cells to be used.
2- one new "Mlec" module who will communicate with PCU and and also measure : current ? module (12s) voltage / module temp. (you can divide by 12 and send "semi-fake" cell voltage to PCU since the BMS will owrk to keep all cells at the same level.)
This is a little harder but is doable, not so much communication are between Mlec and PCU.

good luck!

[Zuikkis]

Thanks for your input! I have already thought about some of these issues.

You are right that I should replace both MLEC and all RLECs. Get rid of that stupid internal isolated ribbon cable canbus, that's way too much complicated and expensive. The L9963E chip linked in first post uses simple isolated two wire SPI, and is powered directly from the lithium cells so they don't need external 12V supply like current RLECs.

I think 1) is not so easy. Standalone BMS would be very difficult for a 400V battery, as there are 96 cells. Actually Think battery has two chains in parallel, so 192 cells. BMS would need a separate wire coming from each of the cells, which would be a huge mess. And 400V BMS is not very cheap either.

"RLEC" approach is much cleaner. 16 pieces of 12cell BMS in every module, with only simple data wiring in between.

If I make MLEC software open source, it would be still quite easy to adapt it to different cell counts and completely different kind of BMS. But if working with the original Think modules, 16*RLEC is the way to go. Or perhaps 8 "double RLECs" that take care of two modules each, similar to my combiner board in above message.

100mA balancing current must be enough. There is an issue in Think's balancing logic. RLEC boards only get 12V power when car is either charging, or driving. This makes sense as they are powered from the tiny 12V battery which already looses charge too quickly. But this also means that balancing does not happen when car is idle. When car reaches 100% and charger turns off, RLECs stop balancing. This could be changed; the new RLEC could and should be powered from the lithium module it is monitoring, then it can continue balancing when car is sleeping.

Note that most chinese "1A active balancers" aren't necessarily any faster than 100mA passive balancing. Active balancers draw power from highest voltage cell, then push that into the lowest voltage cell. But only one cell at a time! Passive balancing can happen for any number of cells. Half of the cells in Think's 192 cell pack could be balancing at the same time, with 100mA each.

[pexic]

" But this also means that balancing does not happen when car is idle"  yes, it does. (top)ballancing works without 12v power on RLEC modules.

100mA is enough for enerdel cells but how long we will find these cells on the "market" ?
I think a more versatile approach is the way to go, especially for bussines.
good luck.

[Myles Twete]

In case anyone needs Enerdel THINK RLEC modules, send a PM to me (matwete at comcast dot net).  I still have many modules that were removed from new THINK Enerdel battery packs several years ago.  I test them before sending them to customers.  Let me know which CAN ID# you need.

[worry]

Thank you Myles!
It's good to know that you still have some. Your store have been a lifesaver for us.

Ønsker deg en fin sommer. Hilsen Espen   

[babjerke]

Hi

What is the current status of the new design for RLEC modules? I am interested to replace old cards both for Think use and standalone solar batteries use. I can also help with HW/SW development.

I also need a new TIM module...

/Bård