Lithium batteries make me happy

[Oonrahnjay]

    In the article, you wrote:  "... we actually had to disassemble five 100 amp hour 12-volt batteries of four cells each, which we then re-assembled (using a hydraulic press) into 4x 500 amp hour 3.2 volt batteries (with 5 cells each). We then bolted these batteries together in series to make a single 500 amp hour 12.8 volt block... weighing in at just 140 lbs."

    I immediately thought "why?".  I think I know the answer, but will you please discuss.  Weren't the batteries already 12V?  (Apologies if this is a stupid question from somebody who don't know nothin' about them electrictrons.)

[technomadia]

   In the article, you wrote:  "... we actually had to disassemble five 100 amp hour 12-volt batteries of four cells each, which we then re-assembled (using a hydraulic press) into 4x 500 amp hour 3.2 volt batteries (with 5 cells each). We then bolted these batteries together in series to make a single 500 amp hour 12.8 volt block... weighing in at just 140 lbs."

   I immediately thought "why?".  I think I know the answer, but will you please discuss.  Weren't the batteries already 12V?  (Apologies if this is a stupid question from somebody who don't know nothin' about them electrictrons.)

Yes, we could have put them in parallel, like you would other battery types and have it functionally work as a 500 aH bank.  

However, with LFP - the EMS (energy management system) is pretty critical to preventing under/over charging of the individual cells, which it needs to monitor each directly.  If we had just put them in parallel, then the EMS would not have been able to do its job - as it could not have hooked up to each pack.

So, instead we broke apart the 12v 100 aH packs, and created 4 3.2v 500 aH batteries hooked up in series - that could then be hooked into the EMS individually and monitored. This way we know when one cell is out of balance as well.

Hope that's at least clear as mud

- Cherie

[Oonrahnjay]

   In the article, you wrote:  "... we actually had to disassemble five 100 amp hour 12-volt batteries of four cells each, which we then re-assembled (using a hydraulic press) into 4x 500 amp hour 3.2 volt batteries (with 5 cells each). We then bolted these batteries together in series to make a single 500 amp hour 12.8 volt block... weighing in at just 140 lbs."

   I immediately thought "why?".  I think I know the answer, but will you please discuss.  Weren't the batteries already 12V?  (Apologies if this is a stupid question from somebody who don't know nothin' about them electrictrons.)

Yes, we could have put them in parallel, like you would other battery types and have it functionally work as a 500 aH bank.  

However, with LFP - the EMS (energy management system) is pretty critical to preventing under/over charging of the individual cells, which it needs to monitor each directly.  If we had just put them in parallel, then the EMS would not have been able to do its job - as it could not have hooked it up to each pack.

So, instead we broke apart the 12v 100 aH packs, and created 4 3.2v 500 aH batteries hooked up in series - that could then be hooked into the EMS individually and monitored. This way we know when one cell is out of balance as well.

Hope that's at least clear as mud

- Cherie

     OK, a total series voltage of 12.8V.  Sounds good to me.  (My meager electrical background gives me no clue why you couldn't monitor them as well in parallel but I'm sure that there must be a technical explanation.)  Keep us up to date on how they perform, please!

[technomadia]

(My meager electrical background gives me no clue why you couldn't monitor them as well in parallel but I'm sure that there must be a technical explanation.)  Keep us up to date on how they perform, please!

The EMS need to monitor each individual cell.  If we had wired the 100 aH batteries in parallel, the individual battery cells would not have been connected to each other - only the ends of each battery would be.

This past post we made after building the bank back in August has pictures of the before and after:
http://www.technomadia.com/2011/08/we-built-a-lithium-ion-battery-bank/

In the pic showing the pack mostly assembled towards the end of the post - the parts with the ribbon cable coming in/out of it is the EMS sensors being installed.  In this setup, each of the 5-piece, 3.2v 500 aH 'packs' is treated as a single cell that can be effectively monitored by the EMS. Thus creating a 4-cell system, and only needing 4 EMS sensors.

Keeping in mind, the source we went with are designed with electric vehicles in mind, where folks are typically just stringing packs together in series  (not parallel) to create higher voltage systems.  Which is why they come in 100 aH 12v packs to begin with.  And they end up hooking up a bunch of EMS sensors as they increase the voltage.

- Cherie

[Oonrahnjay]

   Thanks.  I noted in another thread that I was recently given a couple of practically new 8-D (flooded cell) takeouts that I can use for house batteries.  Maybe the Lith-Ion technology will have advanced by the time that I need new batteries.  I really like this technology - moving beyond the "50% drawdown" and "limited recharge cycle" limits of flooded (or AGM) batteries is a good thing.

[viento1]

I am in discussion with the Lithium distributor in Vancouver and this is the same problem we are dealing with now. My Magnum inverter/Charger has the capability to set the charge and discharge perimeters for the 24V bank. The potential problem is if a single cell in the bank goes into a severe under or over charge condition the Inverter would not pick it up until it is too late.

One of the solutions was to have a super hydrogen fancy pants relay that each EMS would report to. if there was an issue with any cell - the pack would disconnect. As mentioned, this technology is borrowed from EV vehicles.

I am about to drop 4k on replacing my Trojens and I am seriously considering the taking on the challenges that come with a Lithium pack that does not cost much more... well, unless I burn the bus to the ground.

[technomadia]

I am about to drop 4k on replacing my Trojens and I am seriously considering the taking on the challenges that come with a Lithium pack that does not cost much more... well, unless I burn the bus to the ground.

Nah.. not much risk of burning your bus to the ground from the LFP alone at these voltages, this isn't the same chemistry known for explosive results when overcharging.  The LiFePO4 is quite stable.

Biggest risk is killing the bank itself, as even one over or undercharge and kill them permanently.  Lead acid is more forgiving and slow to death from neglect.

If you take the leap.. welcome to the front range   We welcome another victim taking arrows in the chest with us. It's definitely not been a smooth implementation, and we're still working out issues and tweaking.  All fun tho for us tho

- Cherie

[viento1]

Are you using the factory ems? what inverter/charger are you using?