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Discussion Starter · #1 · (Edited)
Finished Soldering 6 Power Controller boards last night. :)

In my Solectria E10, I am planning on having 4 parallel groups of 20 Leaf modules in series (150V @ 65Ah per group), and thus I need a way to pre-charge, connect, and disconnect them to/from the main vehicle power bus.

That is the main function of my Power Controller board:
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The main problem with paralleling large battery packs together, is when one cell fails shorted. You now have lots of available power from the other good packs, attempting to charge the (now lower voltage) pack with the short in it.

This can cause thermal runaway (fire). :eek:


So the power controller monitors the stack and pack voltage (individual cell voltages, via the BMS), and current into and out of the pack.

If it detects an anomaly* it will disconnect that pack from the main bus.

*anomalies:
Pack over/under volt
Pack over/under temperature
Pack over/under charge (Amp Hours)
Cell over/under volt
Current over/imbalance (compared to other power controllers)
etc...

It can also send a CAN message and/or +12V signal to force a controller into limp home mode, and/or stop a battery charger.


Features:
Designed to bolt directly* on to the Nissan Leaf Contactor.
Standalone, or CAN controlled mode.
Solid state pre-charger.
Pre-charge resistor temperature sensor.
Two contactor drivers, with economizers.
Limp home / end charge signal.
Isolated voltage sense of the A and B side.
External current sensor.
Low power sleep mode.
4-bit unit ID (for CAN address / Standalone mode).
5V I2C with interrupt line for future expansion. ;)

*directly:
Power cables are bolted and torqued to the contactor first, then the power controller board is bolted on top.

Next, I need to build up the Current Sensor boards, and write some firmware, and test.

Then they go in the truck. :D

Here is a video:
 

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Discussion Starter · #5 ·
Yeah, it is mostly done...

Just need to write the CAN boot loader (for firmware updates), and port the config system over.

I moved over to getting the Pack Sniffer 2 done, since it is the gateway that will be used to program and setup the Power Controller.

New firmware / configuration changes are placed on the microSD card in the Pack Sniffer 2 and it will take care of programming the Power Controllers' firmware update / changes over CAN.

The same system will be used to program and setup the Modified Leaf BMS...
 

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Discussion Starter · #7 ·
I am re-using the Nissan Leaf BMS, it already has all the circuitry to monitor all the cells.

But even if I did build my own BMS from scratch, I would want to monitor each cell...

In your 2S, 5S, 6S, 10S example:
That section is reading a lower voltage under acceleration.
Which is the bad cell? ;)
 

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Discussion Starter · #9 ·
If the info is available, then it can always be boiled down to a single light...

I just would rather have an oil pressure guage rather than the oil light. ;)
 

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Discussion Starter · #11 ·
I have 4 parallel stacks, if one has an issue, it will be disconnected from the main system bus and the remaining 3 will still get you home. (I also have dual redundant motors, controllers, DC-DC, and chargers.)

The system is being designed for my truck, if others are interested, I am willing to sell them the parts...

If it is not a good fit for your design, that is ok, you don't have to use my design, it is just documented on here in the event that someone can use it, and / or take inspiration from it.

But what if the packs sit for a while and level out to different voltages?
I don't think this will happen, unless one pack has a REALLY bad self discharge... And then I would be using the BMS to find which is the bad cell. ;)

But, lets suppose, that your driving around, and a loose bus bar / bad cell causes that pack to get disconnected from the main system bus.

And you drive home, so now the packs connected to the main system bus are at a lower voltage.

You then fix the issue with the bad battery stack.


If the pre-charger can't get the battery voltages between packs synced, then that pack will not be connected to the main system bus, this prevents huge charge/discharge currents from flowing between parallel stacks.

So you will either have to charge / discharge the battery pack to get it closer to the main system bus voltage.


In this case I would plug in the truck, and let the "good" packs fully charge.
Once charged, I would then press the smart switches* for those packs, to disconnect them from the main system bus.

Then press the smart switch* for the newly repaired battery pack to pre-charge and connect it to the main system bus.

Then let the battery charger charge that remaining pack.

When it is charged, then with the press of the smart switches* the other packs can be pre-charged and connected back to the main system bus.

*smart switches:
I am using NKK smart switches, they have an LCD and Red/Green backlight.
One for each parallel stack, each will display voltage and current from that respective pack. Green if connected to the main system bus, Red if disconnected, and yellow if pre-charging. Flashing red if disconnected due to an over/under voltage/current/temp, etc... with the reason shown on the display.

Note: I work in the aviation industry (flight simulation), this is how aircraft handle redundant/multiple power systems. If it works for them, it will work for my truck. ;)
 

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Discussion Starter · #13 ·
I have those Fiat 500e samsung/Bosch modules that are blocked together in 5S modules. I have three strings of 6 modules (ends up being 30S3P) at 64Ah per cell. As I just introduced my second pack I've been wondering what best path to take to help isolate them. But also, since these are blocked together from the manufacturer, each module should have identical cells so why not just watch the 5S module. The end result would be the same, the system automatically shuts it down or turns on a light and I have to figure out what is going on.
I am not familiar with the Fiat modules...
But with the Nissan Leaf Modules, they are 2p2s.

So Nissan has determined that if a single cell shorts out, it will be able to thermally dissipate the energy of itself and of the cell connected in parallel with it...

I have seen where people connect several Nissan Leaf modules in parallel, then connect those in series to build a high capacity lower voltage battery pack.

This is dangerous!!!

If a single cell shorts out, it now has to thermally dissipate all the energy of the several other cells that are now connected in parallel with it.

This is the catch fire and explode outcome I am trying to avoid. ;)


So when you charge, does the contactor closes if the battery voltages are the same or within allowables?
Yeah, in auto mode, the power controller take care of everything for you.

Manual mode is for if you want to override or specifically want to do something with a particular pack.

When you turn the keyswitch off, all the packs are disconnected from the main power bus.

When you plug in the charger, the power controllers pre-charge and connect all the packs back to the main system bus, happens in under a second.

The power controller will then command 40A from the NLG5 chargers (20A each).

Then when any cell in a pack reaches its voltage cut off, the power controller will command 0A, and then disconnect that pack from the main system bus.

Then it will resume at 30A, until the next cell in a pack reaches its voltage cut off, then it gets dropped as well.

Then it will resume at 20A, until the next cell in a pack reaches its voltage cut off, then it gets dropped as well.

Then it will resume at 10A, until the next cell in a pack reaches its voltage cut off, then it gets dropped as well.

I expect the above to happen all within a few minutes of each other.

Then the packs sit disconnected and balance down the high cells.


The next day... ;)

When you turn the key switch, the power controllers pre-charge and connect all the packs back to the main system bus, happens in under a second.

Then, drive to work. ;P


Note: I also work aviation electrical but from modification standpoint. The aircraft systems are designed to automatically load shed in the case that a generator is lost or overloaded. But this system is backwards from how we do it in a car since your system shuts the battery down instead of the load (although you did say this could talk to the controller).
This is more of a Ground Power, Auxiliary Power Unit, Left Engine, Right Engine, etc... power selection. ;)

But yeah, I can reduce power to/from the motor controller, and/or battery charger.
 

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Discussion Starter · #17 ·
I am running 6 Volt Modules in Parallel (each module being 24S, or 4kWh), directly connected.

And it's a very basic, direct system - a 700 amp logisystem controller and not much else. Nothing fancy, my only readouts are pack voltage (analog) and pack amps.

Your controller would be a nice safety device.
It is still a work on progress...

In the meantime get 6 TPL-BH fuses (170VDC 200A).
Connect one to each of your positive battery terminals.
Then connect the other side of the fuses together, this will be your main power distribution bus.

Connect power distribution bus to your charger, motor controller, DC-DC converter, etc...


If any one pack shorts, the others will discharge into it and pop the fuse connected to the shorted pack.



I am also without any BMS.... I would need 6x 24s BMS to monitor/protect the whole pack. Wouldn't it be nice if your safety device was also a 24s BMS!!! I'd be saving for 6 of them...
I believe that the stock Volt BMS will work for your system, since it monitors each block individually.
 

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Discussion Starter · #21 ·
Have you reverse engineered the leaf BMS such that you can tap in to the cell monitoring and balancing, or is your microcontroller going to handle all those functions?
Yeah, that is this thread:
http://www.diyelectriccar.com/forum...nginnering-nissan-leaf-bms-serial-169225.html

Everything is still a work in progress...

Since I can't really test the system as a whole until it is all done.

Then I would really like to put some miles on it before I feel comfortable selling it to others. (make sure all the bugs are worked out).
 

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Discussion Starter · #23 ·
So that thing is actually a BMS? I have quite a few of those! You think I can just "plug one in" to the top of one of my modules and it balance the cells?
I am not sure, I only have really played with the Nissan Leaf BMS...
There are probably other threads on here that cover the Volt BMS.
 
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