Lithium battery project.

[MoominPapa]

My winter project is to install a LiFePO4 domestic battery bank, and design and build the control system for same.

 

The architecture will be that all the charge sources (alternator, charger and solar) and all the loads are permanently connected to the engine start battery, which will remain as conventional lead-acid. The lithium bank will connected to this via a contactor controlled by the BMS, allowing charge and discharge termination and emergency disconnect if enough unbalance builds up to take a cell out of the safe voltage range.

 

I decided that I'd rather risk a flat start battery on lithium low-charge disconnect then have all the lights go out without warning. The BMS will sound an alarm when it disconnects the lithium bank. Having the start battery always in circuit means I don't have to worry about alternator load-dump.

 

The BMS will be Arduino based, with a dedicated TI analog front-end chip for reading the cell voltages and pack current from a shunt.

 

Today I completed the first module, see photo below. The black box is a Tycho 250A magnetic latched relay. It uses no power when in connected or disconnected state, there are two coils which are pulsed to open or close the contacts. The control board is 4000 series CMOS logic and draws about 50 micro-amps when idle. This is important, as it will be connected direct (fused) to the lithium bank at all times. The logic generates 15mS open and close pulses for the relay coils, switched by MOSFETs. There are two input signals from the computer.  One opens the relay, and is conventional. The other closes the relay and is fail safe. The pulse has to repeated every second or so, or the logic will time out and open the relay. That's so if the Arduino fails, or crashes, or isn't running a valid program, or is powered down, this module automatically ensures that the lithium bank is isolated.

 

Next stage is the Ardunio hardware, which consists of a 128Kbyte EEPROM for logging, the TI analog front end, and an interface to a small OLED display. Logs of all parameters at second resolution for several weeks will be stored and transferred to my laptop over USB for diagnostics.

 

I have some 3.3Ah Lithium cells on order for doing the development, they are cheap enough to be able to do damaging tests, and small enough to use a 21W brake-light bulb as a load-bank and bench PSU as a charge source.

 

Final bank will probably be eight 180AH CALB prismatic cells connected 2P-4S to give 360AH at 12V.

 

MP.

 

 

 

 

[Kendorr]

Have you watched Journey with Jono on youtube?

https://www.youtube.com/watch?v=JW-v8PNx2C4

You've obviously looked into it in a lot of detail, his video's may give you a bit more info.

[nicknorman]

Interesting that you have chosen a separate watchdog system rather than using the one in the microcontroller. I suppose it comes down to whether the additional CMOS circuitry is more or less reliable than the microcontroller. I think I might have chosen one 8 pin PIC to do same, rather than several socketed CMOS chips (socketed chips always having potential for corroded contacts) but obviously there are swings and roundabouts. Careful use of a slow clock, sleep mode and interrupts can result in extremely low power consumption.

 

Did you find any issues with transients from the relay coil upsetting the CMOS? I once built a circuit to operate central locking on my car (in the days before remote central locking) and had to add Tranzorbs to get it to work properly due to the switching transients from the relays.

[Phil Ambrose]

Pity JohnV has been banned because his boat is now equipped with lithium and he has been running them for a while now in his domestics, of course Peterboat has also been running with lithium for a while too.

Phil 

[MoominPapa]

1 hour ago, nicknorman said:

Interesting that you have chosen a separate watchdog system rather than using the one in the microcontroller. I suppose it comes down to whether the additional CMOS circuitry is more or less reliable than the microcontroller. I think I might have chosen one 8 pin PIC to do same, rather than several socketed CMOS chips (socketed chips always having potential for corroded contacts) but obviously there are swings and roundabouts. Careful use of a slow clock, sleep mode and interrupts can result in extremely low power consumption.

 

Did you find any issues with transients from the relay coil upsetting the CMOS? I once built a circuit to operate central locking on my car (in the days before remote central locking) and had to add Tranzorbs to get it to work properly due to the switching transients from the relays.

The main microcontroller in the Arduino is going to have quite a lot of "stuff" around it like displays and i2c bus drivers, so I couldn't be certain that I would get the power consumption down far enough to be safe when the lithium system is isolated for some time. For instance when the boat is unoccupied or over the winter, when the lithium pack will be discharged to the idea storage state of 30%-50% and then isolated, leaving the boat running off the engine start battery floated by the AC charger. Parasitic loads in that state when the pack is unmonitored could drop one or more cells below the lower voltage limit which would be a disaster.

 

A dedicated 8-pin PIC would be a good alternative. I went the way I did because I could be sure a priori of making a design that would work. I don't have much experience of very-low-power microcontroller use. I'm not engineering here: the prototype is also the product, so something that works as designed first time is good. I slightly regret using sockets, it would have been fine without, in retrospect. The rest of the electronics will not be socketed.

 

No problems with transients in testing.  The power consumption of everything other than the relay coils is so tiny that the rail can be decoupled with large-R large-C filter. There's a 0.1uF ceramic across the electrolytic too, to handle fast transients.

 

MP.

 

ETA. The 8-pin chip visible on the board is an optocoupler on the incoming control signals, to make absolutely certain that the power domains are isolated, and power can't leak from this circuit to the Arduino when the Arduino is off.

 

 

Edited October 15, 2018 by MoominPapa

[MoominPapa]

1 hour ago, Kendorr said:

Have you watched Journey with Jono on youtube?

https://www.youtube.com/watch?v=JW-v8PNx2C4

You've obviously looked into it in a lot of detail, his video's may give you a bit more info.

That's about the one source I've not looked at. I hate getting technical information from videos: a written document is much better. Best source I've found is this:

 

http://nordkyndesign.com/category/marine-engineering/electrical/lithium-battery-systems/

 

MP.

 

[Victor Vectis]

I think you need to consult Professor Bizzard!

 

?

[Bee]

Its no good consulting me - I still work in Whitworth.

[rusty69]

.....I thought they closed down a few years back.

 

Great Winter project MP.Good luck with it!

[MoominPapa]

4 hours ago, nicknorman said:

Interesting that you have chosen a separate watchdog system rather than using the one in the microcontroller. I suppose it comes down to whether the additional CMOS circuitry is more or less reliable than the microcontroller. I think I might have chosen one 8 pin PIC to do same, rather than several socketed CMOS chips (socketed chips always having potential for corroded contacts) but obviously there are swings and roundabouts. Careful use of a slow clock, sleep mode and interrupts can result in extremely low power consumption.

 

Did you find any issues with transients from the relay coil upsetting the CMOS? I once built a circuit to operate central locking on my car (in the days before remote central locking) and had to add Tranzorbs to get it to work properly due to the switching transients from the relays.

 

I forgot in my previous reply to add that 4000 series CMOS (at least the ones I'm using) are specced to power voltage from low all the way to 20v, so there's no need to have a voltage regulator for this part of the circuit, just an 18v zener to do last ditch spike chopping. The Arduino comes with a series regulator that always costs some juice. I'm replacing that with a  12v - 5v switching module, but it's still a parasitic load. The Atmel processors in the Arduino need 3.3 - 5v, I think. I guess smaller microconrollers will have a larger range.

 

MP.

 

[Richard T]

Moomin talk to Eric of NB Firecrest. It is an all electric boat with a generator and land line. He does a blog so google firecrest blog to find him

[MoominPapa]

17 minutes ago, Richard T said:

Moomin talk to Eric of NB Firecrest. It is an all electric boat with a generator and land line. He does a blog so google firecrest blog to find him

We're in touch. Firecrest will overwinter at Crick and we'll be at Dunchurch Pools, so I hope we'll be able to get together and compare notes.

 

MP.

 

[system 4-50]

Would a FRAM be better than the EEPROM? I'm very amateur wrt electronics so feel free to laugh if appropriate.

[nicknorman]

Just on the subject of power consumption, coincidentally I am researching for a new project using a PIC16F series microcontroller, fully loaded with endless peripherals and lots of on board memory. Power consumption at 5v, without invoking sleep or doze mode and with 32MHz clock speed, is 3.5mA. Incredible!

[MoominPapa]

9 minutes ago, system 4-50 said:

Would a FRAM be better than the EEPROM? I'm very amateur wrt electronics so feel free to laugh if appropriate.

This isn't a very demanding application, and EEPROM chips are available for a quid or so that interface easily to the microprocessor using the I2C bus, so that's what I went for.  (Actually, the processor on an Arduino has some EEPROM built in, but not enough for comprehensive logging.)

 

I don't know much about FRAM, but it looks like it might be a good competitor to flash storage.

 

MP.

 

[Old Son]

I wish I understood all this stuff!!

[doratheexplorer]

23 minutes ago, Old Son said:

I wish I understood all this stuff!!

Gosh me too!  It sounds facinating but I only understand about 1 in 3 words.

[mrsmelly]

27 minutes ago, Old Son said:

I wish I understood all this stuff!!

Well basicaly you can have a perfectly good electricity supply from 3/400 squids worth of tried and tested lead acid batteries Or you can be a guinea pig boat and spend 3 or 4k on Lithiums and hope all is ok ?

[rusty69]

18 minutes ago, doratheexplorer said:

Gosh me too!  It sounds facinating but I only understand about 1 in 3 words.

Me three. I got as far as "My".

14 minutes ago, mrsmelly said:

Well basicaly you can have a perfectly good electricity supply from 3/400 squids worth of tried and tested lead acid batteries Or you can be a guinea pig boat and spend 3 or 4k on Lithiums and hope all is ok ?

Its called experminentation,research and development smelly.

 

Clever people like MP spend weeks on end developing these systems, then share their findings with us idiots so we can e.g spend all day typing rubbish on an internet forum.

[mrsmelly]

35 minutes ago, rusty69 said:

Me three. I got as far as "My".

Its called experminentation,research and development smelly.

 

Clever people like MP spend weeks on end developing these systems, then share their findings with us idiots so we can e.g spend all day typing rubbish on an internet forum.

Ahh a bit like when the government told us all to buy diesel cars ( Ive always hated them ) then after a few years they realize they pollute more than cyanide gas and tell everybody not to buy em?  ?  I wonder when/if succesive governments will find out that producing Lion batteries is far from a very green thing to do?

[rusty69]

2 minutes ago, mrsmelly said:

I wonder when/if succesive governments will find out that producing Lion batteries is far from a very green thing to do?

Well,unless clever people like MP develop these things we will never know if they should have been developed or not

[doratheexplorer]

1 hour ago, mrsmelly said:

Well basicaly you can have a perfectly good electricity supply from 3/400 squids worth of tried and tested lead acid batteries Or you can be a guinea pig boat and spend 3 or 4k on Lithiums and hope all is ok ?

I WANT A GUINEA PIG BOAT!

[rusty69]

Just now, doratheexplorer said:

I WANT A GUINEA PIG BOAT!

Here ya go

[doratheexplorer]

Just now, rusty69 said:

Here ya go

[mrsmelly]

Just now, doratheexplorer said:

I WANT A GUINEA PIG BOAT!

I hope it all works out for the people who try it out. I remember moving onboard 29 years ago and being informed by a couple of boaters about how fantastic composting bogs were and how give it ten years and everybody would have them. At a similar time diesel stoves for cooking were going to banish gas instalations on boats etc etc etc.