New Camper Arrival

[glenm64]

I barely classify as an amateur let alone an expert but from my understanding 12.6v is 100%, about 11.4v is 50% and about 9v is roughly 0% (can probably actually go a lower), as richee said you can discharge lithiums down to 0%/9v so when the OP has 200AH of lithium batteries it's roughly equivalent to 400AH of AGM batteries. These figures probably aren't perfect but would be close.

Lithium have an extra 40% discharge over lead acid.
Lifepo4 recommended 70% discharge.
eg 100ah lead acid have 50ah discharge, lifepo4 have 70ah discharge = 40% gain
Lifepo4 have a flatter voltage discharge curve than lead acid. Better to work on ah discharge rather than battery voltage.
If youve spent the money on lifepo4 then put a BMS on it and work on 70% discharge, ie 100ah lifepo4, 70ah discharge is flat.
Lithium cycle life vary on discharge rates. 80% is considered safe but lowers cycle life.
Around 3000 cycles at 80% and 5000 cycles at 70% discharge.

Cheers Glen

[Lobster]

Just reading this and thought I would add that I think this bit.

Would make this bit incorrect.

Would you prefer I  say 2 x lithium 100AH (amp hour) batteries? To be politically correct.

[Lobster]

I barely classify as an amateur let alone an expert but from my understanding 12.6v is 100%, about 11.4v is 50% and about 9v is roughly 0% (can probably actually go a lower), as richee said you can discharge lithiums down to 0%/9v so when the OP has 200AH of lithium batteries it's roughly equivalent to 400AH of AGM batteries. These figures probably aren't perfect but would be close.

That would be a correct assumption  and my understanding as well.

[glenm64]

http://www.evworks.com.au/page/technical-information/lifepo4-care-guide-looking-after-your-lithium-batt/
http://www.cobox-ebikes.com/296/basic-understanding-of-lipo-li-ion-and-lifepo4.html
https://www.ev-power.eu/BatteryPacks/


Cheers Glen

[tryagain]

Lithium have an extra 40% discharge over lead acid.
Lifepo4 recommended 70% discharge.
eg 100ah lead acid have 50ah discharge, lifepo4 have 70ah discharge = 40% gain
Lifepo4 have a flatter voltage discharge curve than lead acid. Better to work on ah discharge rather than battery voltage.
If youve spent the money on lifepo4 then put a BMS on it and work on 70% discharge, ie 100ah lifepo4, 70ah discharge is flat.
Lithium cycle life vary on discharge rates. 80% is considered safe but lowers cycle life.
Around 3000 cycles at 80% and 5000 cycles at 70% discharge.

Cheers Glen

I think part of the confusion around lithium batteries is the differing battery chemistry and the continual evolution of the technology. What I said was in relation to Li-ion which is different to the  LiFePo4 you have talked about but not sure what the OP has. A BMS would be the way to go for Lithium as you said and is what the OP is using from his comment but I think there wouldn't be too many campers that would get anywhere near to 3000 cycles in the expected life of the battery let alone the 5000 so I think 80% and even lower would be more than fine in this situation.

[glenm64]

I would assume they would be Lifepo4 batteries, Lithium ion arent stable and have been known to explode.(just ask Mr Samsung) Not recommended for caravan and camper installs.
Being over twice the price of AGMs you need to get 10 years+ out of Lifepo4s to justify the outlay.
The reason manufacturers recommend not to discharge below certain voltage is to avoid permanent cell damage.
Just going by what ive read and what suppliers recommend when setting up my system. The supplied low voltage cut out switch on my system is prest at 11.5v

Cheers Glen

[tryagain]

I would assume they would be Lifepo4 batteries, Lithium ion arent stable and have been known to explode.(just ask Mr Samsung) Not recommended for caravan and camper installs.
Being over twice the price of AGMs you need to get 10 years+ out of Lifepo4s to justify the outlay.
The reason manufacturers recommend not to discharge below certain voltage is to avoid permanent cell damage.
Just going by what ive read and what suppliers recommend when setting up my system. The supplied low voltage cut out switch on my system is prest at 11.5v

Cheers Glen

You are probably right about them being LiFePo4 but my guess is it's probably more about longevity than safety, the problem with the Samsung batteries is a manufacturing issue more than a chemistry issue. From my understanding most electric car's phones, laptops etc have Li-ion batteries and are safe.

3000 deep discharge cycles in a camper situation in my head looks like something like this, assuming say 20 weeks use per year 1 cycle per day is 140 cycles per year, that works out to over 20  years and that is assuming high use regular deep discharges which would never be the case. Discharging below certain amounts can damage/kill a battery but most of the time the discharge rates are set to ensure cycle amounts that would never happen in a camper.

As 12v LiFePO4 are 4s and 12v Li-ion is 3s, your 11.6 cut out is 2.9v per cell which is the equivalent to 8.7v in a 3s Li-ion set up.

sorry about the thread hijack OP, if it's bothering you maybe get one of the mod's to move the offending bit's to a new thread.

 

[glenm64]

Agree with apologies OP, not meant to get side tracked.
Check with your batteries manufacturer, and go by their recommendation.

Cheers Glen