0% SOC

[ruples]

Testing a battery for a solar powered electric boat project. Wondering if anyone knows how to stop charging when it reaches 0% state of charge. Battery model: Mastervolt MLi Ultra 12/2500

Thanks in advance!

[smac999]

do you have a solar controller?... or panels direct to battery?

[StuM]

When it reaches 0% SOC, you need to start charging, not stop charging.

And you should have started charging long before it got that low.

[noelex 77]

Welcome to the forum Ruples.

Lithium batteries are great, but perhaps even more than lead acid batteries they can be severely damaged by overcharging or very low SOC.

There are others with far more practical knowledge of this type of battery, but aiming to keep the SOC in the range 20-85% is sensible for the best life.

Your battery has some sophisticated electronics installed, but really needs to be connected to a Masterbus system to work well. A minimium system would be a Mastershunt and Masterview. The charge sources such as battery charger and solar regulator should also ideally be connected to the Masterbus system.

You can wire up Litium batteries to charge and discharge safely using more generic components than the Masterbus system, but if planning to go down this route Mastervolt litium batteries are not the ideal choice. These batteries are really designed to work as part of an integrated system. The batteries are expensive partially because they are not just batteries but have electronics installed to facilitate this integration.

[ruples]

Hi guys.

Yes, I do have a charge controller. Sorry, I should've been more specific; stop charging my devices i.e. phones, laptops, lights, etc. I understand it is not ideal to have SOC to reach so low, but again, this is for battery testing purposes.

Thanks!

[ruples]

Originally Posted by smac999

do you have a solar controller?... or panels direct to battery?

I do have a charge controller

[ruples]

Originally Posted by StuM

When it reaches 0% SOC, you need to start charging, not stop charging.

And you should have started charging long before it got that low.

Sorry, I should've been more specific; I would like to stop charging my devices. I would like to redirect all power coming in to go straight to battery

[noelex 77]

Originally Posted by ruples

Hi guys.

Yes, I do have a charge controller. Sorry, I should've been more specific; stop charging my devices i.e. phones, laptops, lights, etc. I understand it is not ideal to have SOC to reach so low, but again, this is for battery testing purposes.

Thanks!

The Masterbus system can do all of this by opening a relay when the SOC reaches a predetermined level. I am afraid I not familiar enough with the system to advise you what is the simplest and cheapest way of achieving this, but Mastervolt documentation is quite good so you should be able to devise something that works quite easily.

[ruples]

Originally Posted by noelex 77

The Masterbus system can do all of this by opening a relay when the SOC reaches a predetermined level. I am afraid I not familiar enough with the system to advise you what is the simplest and cheapest way of achieving this, but Mastervolt documentation is quite good so you should be able to devise something that works quite easily.

Thanks noelex 77. A flaw in the design is that the relay can only be operated by computer. It is lodged internally within the battery and is out of reach. I would also like to have it automatically stop charging devices without someone constantly monitoring the SOC. I will continue looking. Thanks for all your help. It is greatly appreciated.

[smac999]

Stop using the word charging when you mean draining....

If you don't want your devices to draw power from the battery then unplug them...

If makes no difference when and where the solar goes. At the end of the day you'll consumed a certain amount and made a certain amount. When each happens is ilrelivent.

Having the solar all go to the battery then charging your devices later vs having them charge during solar charging is the same daily net ah loss / gain on the battery.

If you are worried about draining the batery too low there are voltage cutoff devices. But these are 't going. To work very well on a li batt because the voltage doesn't drop.

[noelex 77]

Originally Posted by ruples

Thanks noelex 77. A flaw in the design is that the relay can only be operated by computer. It is lodged internally within the battery and is out of reach. I would also like to have it automatically stop charging devices without someone constantly monitoring the SOC. I will continue looking. Thanks for all your help. It is greatly appreciated.

I think you can simply fit a smart external relay. This can be controlled by the Masterview device. Put all the systems you want to disconnect on a circuit with the smart relay and instruct the Masterview to open this relay at the desired SOC.

Please note I only have a very rudementary understanding of the capabilities and limitations of the Masterbus system. So please confirm the above. Hopefully someone with better knowledge will chime in shortly and tell you exactly how it should be done.

[Dockhead]

Originally Posted by noelex 77

I think you can simply fit a smart external relay. This can be controlled by the Masterview device. Put all the systems you want to disconnect on a circuit with the smart relay and instruct the Masterview to open this relay at the desired SOC.

Please note I only have a very rudementary understanding of the capabilities and limitations of the Masterbus system. So please confirm the above. Hopefully someone with better knowledge will chime in shortly and tell you exactly how it should be done.

His terminology is extremely confusing -- I guess he means "shut off CONSUMERS", and if that's right, he's looking for a battery protection circuit.

I have no doubt that the MasterVolt system has this function -- I believe all lithium BMS systems do this.

Apparently it should not be done, with lithium, in the classical way using low voltage as the trigger. See here: Li-Ion BMS - White Paper - Low voltage cut-off: a false sense of security

It's because the voltage of the whole bank may not tell you if one cell is down to the critical level. The bank should be cut off when even one cell is down.

As others have said, this should not be 0%, as lithium batteries are destroyed by overdischarging even once, unlike lead-acid, which are degraded but not immediately destroyed. There should be a decent margin of error.

[noelex 77]

I THINK this connected to a standard relay should work:

http://www.mastervolt.com.au/product...ct-output/pdf/

You will also need a Masterview and Mastershunt. The above should disconnect any individual loads you wish at any specified SOC.

[john61ct]

Victron makes its "Battery Protect" LVD units.

Basically designed to isolate the "non-essential loads", usually to ensure enough juice for cranking, safety/navigation etc.

But you can choose from a variety of voltage level setpoint combinations, from about 10 up to 12 on the disconnect side, to suit your purpose.

Bay-marine sells them on eBay. ​http://www.ebay.com/itm/Victron-Ener...-/172245073143

I'd be surprised MasterVolt doesn't offer similar?

[noelex 77]

Originally Posted by john61ct

Victron makes its "Battery Protect" LVD units.

Thanks for the link.

This system is based on voltage rather than SOC. It might do what the OP wants, but a system based on SOC is going to be more accurate.

I suspect the Mastervolt system could be set to disconnect on both SOC and voltage if desired.

The Mastervolt system is very sophisticated and yet quite simple with a plug and play capability. The components are expensive, but considering the capabilities not outrageously so with the exception of the batteries.

I think a hybrid lithium system using the Masterbus system with generic lithium batteries could work well, but it needs some more investigation.