Is error 15 common?
With lithium, voltage drops off fast near the bottom. It’s easy to get stranded, as more voltage is required to start than to continue running.
Every thing is working fine, you stop for a bit, car is dead. -15 Fortunately for me, I’m using my “voltage spoof”. This allows me to switch to bypass mode, and get to a charger.
If this happens also with stock batteries, might be an easy fix to add a switch. It would be like having a reserve tank.
I’ve been using lithium batteries for many, many years. You should never allow the battery state to drop that low where the voltage drops off fast. You will shorten the life of your batteries. That is out-of-operating spec.
Lithium batteries have a very flat power curve in the operating range. This is one of lithium’s many advantages in that this provides a more consistent power throughout the charge cycle than flooded cells.
Imho, if you are hitting the fast voltage drop off point, you are trying to get more range than you should out of your battery pack. If you want more range I recommend adding more battery ah.
RWD
This may be a solution to a problem that doesn’t exist.
Anyone who encounters -15 low or -16 high voltage would like this.
Also if you want to prevent running too low. The very thing you say to avoid.
This will shut down early with ability to override and get home.
My 2008 and 2002 gems have a Built in low voltage protect. It works like this. Most all Controller will not allow the car to run when the voltage drops below 60 volts. (Code -15) my Lithium pack starts getting damage below 56 volts so because the car quits at 60 Volts you theoretically can’t damage the pack. It you left the lights on or something like that you could realistically drain the pack all the way down and damage the batteries. But anyone that’s taking the time and effort to install a P and pack I think is cognizant of that. Your shunt or stop would work good in addition for people that are too stupid or careless and could possibly find downnthe pack so low as to damage the pack.
A real solution to the problem would be a Dash display that shows realtime pack voltage so as to give you the info as far as pack voltage wether to continue on your journey or start looking for a charge.
My stock gem car state of charge gauge on the dash is very un reliable you can’t depend on it. Only for sure way to read pack voltage is plug in a cell gauge.
rwd,
I believe you are using lithium iron ? LiFePo4
chevy volt and Nissan leaf use advanced lithium manganese cells, very different .
minimum voltage is 2.5v per cell . typical install uses 20 cells . so what dave is talking about is minimum startup voltage 68v . that is 3.4v/cell .
gem controllers shut off @ 60v so even that is 3.0v /cell .
so in a gem application it would be hard to damage them by running them too low
The idea is to switch the voltage spoof out of circuit to get you home. Even with stock voltage, raising the limits a couple volts will allow this.
As stated by Mike previous:
The car will run down to 60v. However if you turn off key it will not restart below 68.3v.
This has stranded me more than once. Even though I had plenty juice to get home.
My concern, and the reason I commented, was over the comment that the “voltage drops off fast at the bottom”. Regardless of LiFePO4 or Lithium Manganese, it is very important to use them above the minimum operating voltage (which is 2.5v/cell on my batteries too). You are right in that, if they are balanced, lnwo is not actually seeing the fast drop off at the bottom and they should be fine (i.e., 3.0v/cell). Either lnwo is not seeing the true fast voltage drop off at the bottom if all cells are 3.0 volts, or they are out of balance and at least one cell is operating at a lower voltage.
I say this from personal experience. Friends “in the know” told me a BMS was a waste of money and so I built a pack for that car without a BMS. I ended up with a cell out of balance and I damaged that cell driving the car (i.e., I didn’t notice one cell was low until it was too late). I replaced that cell, added a BMS to monitor each cell and keep them balanced, and never had a battery issue with that car again.
If it was me, it would be worth it to check and verify all cells are balanced. Or, maybe I misunderstood what lnwo was observing and posted.
Just my 2 cents.
RWD
Oh, I check!
Every charge and in between. I have been building and testing high current shunt balancers.
Now that I’m getting the bugs out, my bms samples from China come in and put me out of business. 
See other thread.
the lithium manganese drop off pretty hard at 3.5v . I experience the same thing . dave runs a 24s monitor so he well know if he has a bad cell .
I on the other hand don’t run a monitor or a bms . the cells have all stayed within .01v on the high end every time they are checked . But I do think about it once in a while so I may consider one . just hate to fix something that’s not broken.
Glad to hear that. BTW, my BMS was designed, manufactured, and sold in Florida, ten years ago.
who makes it ?
CleanPowerAuto. Since then they’ve shifted their focus some and partnered with a battery manufacturer but, based on their web store, they still may sell parts for the DIY.
CleanPowerAuto LLC – Lithium Battery Management Systems
RWD