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An affordable way to fit Lithium Batteries?


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16 hours ago, stuart said:

I've not been on the forum for years, but noticed the article in Canal Boat magazine this month on Lithium battery systems and LifePO4.

 

If you are looking for a DIY BMS - I've built/designed one thats proving to be quite popular.

 

There is another forum where the discussion takes place.

 

https://community.openenergymonitor.org/t/diybms-v4/11292

 

 

Stuart, good to see you on here.

The current thread discussing LiFePO4s for canal boats is at

 

Most of us here are looking at building a BMS (either a battery monitoring system or a battery management system) from available modules on the internet rather than building them ourselves and are focussed on how to disconnect or back off our charging sources before we get to the 'knees' in the voltage curve. Most peeps have an LA in circuit which is their engine start battery so any disconnect circuit may have 200A+ going through it so high power capabilities are important. Nick is looking primarily at building a module to control and alternator but also doing the balancing. Most of us are only charging to 80% so balancing not so much an issue. I am just manually balancing every 3-4 months. MP is using an arduino system. We are all on 2nd hand EV batteries.

Not looked at your video yet. Will try and do that later today.

 

 

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Hi @Dr Bob my BMS was designed originally for people recycling laptop 18650 cells but it works okay with LiPo and LifePO4 cells as well - aka DIY Powerwalls.

 

The DIY BMS has a simple moduler design, temperature monitoring, along with generic relay outputs which are controlled by software defined rules.

 

So it would be quite trivial to have rules designed to switch relays off at certain voltage set points or raise alarms when cells are above/below set voltages or temperatures.

 

The cost is also low, each cell module is about £5 and the controller about the same.  The code may need a bit of tweaking for use on a boat, but nothing that can't be easily solved.

 

Let me know if you'd like to have a chat about it, or even a demo unit or two.  I'm in the Midlands.

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57 minutes ago, stuart said:

Hi @Dr Bob my BMS was designed originally for people recycling laptop 18650 cells but it works okay with LiPo and LifePO4 cells as well - aka DIY Powerwalls.

 

The DIY BMS has a simple moduler design, temperature monitoring, along with generic relay outputs which are controlled by software defined rules.

 

So it would be quite trivial to have rules designed to switch relays off at certain voltage set points or raise alarms when cells are above/below set voltages or temperatures.

 

The cost is also low, each cell module is about £5 and the controller about the same.  The code may need a bit of tweaking for use on a boat, but nothing that can't be easily solved.

 

Let me know if you'd like to have a chat about it, or even a demo unit or two.  I'm in the Midlands.

If not already possible, and option to drive bistable relays of the Tyco BDS-A type would be useful. These need two coil circuits, one to open the relay and one to close it, with 10-15 mS pulses.

 

MP.

 

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32 minutes ago, MoominPapa said:

If not already possible, and option to drive bistable relays of the Tyco BDS-A type would be useful. These need two coil circuits, one to open the relay and one to close it, with 10-15 mS pulses.

At present the BMS drives 4 seperate relays (it could go up to 8 ) and you can configure what each relay is for based on need.

I don't do anything clever with the timing at the moment, but thats easy enough to do with a microcontroller. 

Assume for these bistable relays, a "disconnect" rule would just connect the relevant driving relay for 15mS and then disconnect.

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9 minutes ago, stuart said:

At present the BMS drives 4 seperate relays and you can configure what each relay is for based on need.

I don't do anything clever with the timing at the moment, but thats easy enough to do with a microcontroller. 

Assume for these bistable relays, a "disconnect" rule would just connect the relevant driving relay for 15mS and then disconnect.

That's it. The only wrinkle is that the dissipation in the coils will melt them if the current gets left on, so it needs some thoughts about avoid that in the case of a program crash or similar. I guess the biggest risk is that outputs get configured in error for normal relays, difficult to see how to mitigate against that.

 

MP.

 

Stuart, does you BMS read pack current?

 

MP.

 

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Should be easy enough to change my relay code to provide a pulse relay output instead of latching.

 

At the moment I'm not reading current, but the system is designed to allow this - I was looking to use the ACS758 (hall current sensor - up to 200A).

 

Although I could also design a seperate module specifically for this purpose if needed.

 

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6 hours ago, MoominPapa said:

outputs get configured in error for normal relays

@MoominPapa just for information, I've implemented the DIYBMS v4 code tonight to provide a pulsed output on the relays should it be required.  The relay switches on for about 100ms - anything less and the relay can't switch fast enough so nothing happens.

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Also made me realise that with my setup, I’d need a way to control the Mastervolt Combi’s charging as well as the alternator. I’ll add a CANBUS interface to the design. And I’d forgotten to have a warning buzzer, so that’s now added too.

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