Fisker Buzz Forums banner
1 - 8 of 8 Posts

·
Registered
Joined
·
829 Posts
Discussion Starter · #1 ·
The Plug In America EV Car group recently produced a video of info for EV drivers. One item briefly mentioned was a claim that Lithium batteries will last longer if you don't charge them to 100% all the time. Charging to 80-90% will make the batteries last longer than forcing every possible electron in. Also, they were saying that Level I is nicer to your batteries than Level II charging.

Do any of the experts here think that stopping my charger an 30-60 minutes at around 45 miles early is a worthwhile idea?
 

·
Premium Member
Joined
·
4,662 Posts
The Plug In America EV Car group recently produced a video of info for EV drivers. One item briefly mentioned was a claim that Lithium batteries will last longer if you don't charge them to 100% all the time. Charging to 80-90% will make the batteries last longer than forcing every possible electron in. Also, they were saying that Level I is nicer to your batteries than Level II charging.

Do any of the experts here think that stopping my charger an 30-60 minutes at around 45 miles early is a worthwhile idea?
Not an expert, but I have heard both of these recommendations before. I know that Tesla's default daily charge cycle on their batteries are only up to 80% and that you have to request a "deep charge" to 100% for longer trips.

The challenge with both of these recommendations is that the Karma has a fairly small HV battery, and a very anemic on-board charger, and you would significantly reduce your EV range and increase your charging time by following these recommendations. Of course, YMMV, and if 80% charge over 12+ hours works for your driving pattern, there is no harm in trying.
 

·
Liked, but not well liked
Joined
·
1,172 Posts
100% capacity of the A123 pack is not normally accessible. There is a ~3kWh reserve or 15% that is used as a buffer. Essentially you are charging to 85% (of total pack capacity) when you see the magic "50" miles on the display.

I would recommend against proactively stopping the charging of your vehicle because there is a battery balance circuit that is enabled once a full charge has been completed. If you do not allow the car to balance its pack you could see huge cell deviations and brick modules in your pack.
 

·
Registered
Joined
·
30 Posts
100% capacity of the A123 pack is not normally accessible. There is a ~3kWh reserve or 15% that is used as a buffer. Essentially you are charging to 85% (of total pack capacity) when you see the magic "50" miles on the display.

I would recommend against proactively stopping the charging of your vehicle because there is a battery balance circuit that is enabled once a full charge has been completed. If you do not allow the car to balance its pack you could see huge cell deviations and brick modules in your pack.
What is the final voltage of single cell for BMS in Fisker to command charger to stop charging? I'm asking because if somebody (like me) has weaker cells in the battery pack, then the only thing you can do for more balancing is to charge Fisker to 100% as often as possible (to slow down higher self-discharging effect of weaker cells). I hope Fisker stops charging at 3.6V per cell and lower, because the more LiFePO4 will get above 3.6V the worse for it's lifetime. If you say 15% and 3 kWh, that by my guess that would mean charging to 3.45V to 3.5V per cell. An this voltage level gives not much time for balancing, since balancing LiFePO4 is reasonable from 3.4V up. When I saw those tiny balancing resistors at Fisker BMS, my thinking is that Fisker is balancing roughly with maximum 50 to 100 mA. This is about o.k. for healthy 58 Ah battery cell, but definitely not for cell which already has higher self-discharging. Can you please tell me more about how charging process at Fisker looks like? I don't want to write nonsense, but since I have no access to any diagnostics which could tell me more, I have to guess from my general experience which I have with A123 pouch cells.
 

·
Liked, but not well liked
Joined
·
1,172 Posts
What is the final voltage of single cell for BMS in Fisker to command charger to stop charging? I'm asking because if somebody (like me) has weaker cells in the battery pack, then the only thing you can do for more balancing is to charge Fisker to 100% as often as possible (to slow down higher self-discharging effect of weaker cells). I hope Fisker stops charging at 3.6V per cell and lower, because the more LiFePO4 will get above 3.6V the worse for it's lifetime.
Nominal pack voltage, according to fisker specs, is 347v

So you have 7 cells in series for each module and 15 modules (each module is approximately 23-24v) so the nominal voltage is around 3.3v, I have seen packs as high as 360v (3.42v/cell)

The cell is never charged to 3.6v unless there is something very wrong.




If you say 15% and 3 kWh, that by my guess that would mean charging to 3.45V to 3.5V per cell. An this voltage level gives not much time for balancing, since balancing LiFePO4 is reasonable from 3.4V up. When I saw those tiny balancing resistors at Fisker BMS, my thinking is that Fisker is balancing roughly with maximum 50 to 100 mA. This is about o.k. for healthy 58 Ah battery cell, but definitely not for cell which already has higher self-discharging. Can you please tell me more about how charging process at Fisker looks like? I don't want to write nonsense, but since I have no access to any diagnostics which could tell me more, I have to guess from my general experience which I have with A123 pouch cells.
We do not have access to the A123 diagnostics, but this is what we have seen.

Fisker uses bleed resistors that can bring an out of balance cell into balance by approximately 100mv...Anything over 200mV- it is very unlikely the balance algorithm can bring back the cell/module. You could remove the pack and try balancing it externally- this sometimes works but can take a while. The bleed resistors will just be wasting a ton of energy and nothing will likely happen. If you have a weak module it is worth a shot to drop the pack and try to externally balance the pack (disclaimer this is only for someone who knows what you are doing you could cause some serious damage/fire if you don't know how to bottom balance or top balance cells and attempt to do so).

Once the Karma reaches "100%" SOC, the BMS then monitors cell deviation (through the voltage sensing leads) and then if there is significant deviation (if I recall over 20mv it will start the balancing program)

When Karma released the 530 software they removed this balancing algorithm and for several months, vehicles on 530 were not able to balance their packs.

We have a prototype TOM unit where we can balance the pack via the solar panel- if certain conditions are met. Seems to work well and a better use of the panel; in our opinion.
 

·
Registered
Joined
·
30 Posts
Nominal pack voltage, according to fisker specs, is 347v

So you have 7 cells in series for each module and 15 modules (each module is approximately 23-24v) so the nominal voltage is around 3.3v, I have seen packs as high as 360v (3.42v/cell)

The cell is never charged to 3.6v unless there is something very wrong.






We do not have access to the A123 diagnostics, but this is what we have seen.

Fisker uses bleed resistors that can bring an out of balance cell into balance by approximately 100mv...Anything over 200mV- it is very unlikely the balance algorithm can bring back the cell/module. You could remove the pack and try balancing it externally- this sometimes works but can take a while. The bleed resistors will just be wasting a ton of energy and nothing will likely happen. If you have a weak module it is worth a shot to drop the pack and try to externally balance the pack (disclaimer this is only for someone who knows what you are doing you could cause some serious damage/fire if you don't know how to bottom balance or top balance cells and attempt to do so).

Once the Karma reaches "100%" SOC, the BMS then monitors cell deviation (through the voltage sensing leads) and then if there is significant deviation (if I recall over 20mv it will start the balancing program)

When Karma released the 530 software they removed this balancing algorithm and for several months, vehicles on 530 were not able to balance their packs.

We have a prototype TOM unit where we can balance the pack via the solar panel- if certain conditions are met. Seems to work well and a better use of the panel; in our opinion.
Thank you very much for explanation. I'm happy to hear Fisker is charging cells to only 3.4xV. Sooner or later I will go for TOM for sure, but I must first make car working as it should before adding more options.
 
1 - 8 of 8 Posts
Top