Tesla battery hacker ”wk057″ har skrivit ett intressant inlägg om räckviddsberäkningen och batteriets balansering. Om varför det kan visas för låg räckvidd. Han är även intervjuad här

Hans inlägg var så som följer nedan:

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Basically there are a couple of things at work causing the low range display on some cars.

1) Energy usage calibration.

This is probably the biggest offender. The car will keep track of energy usage and cell voltage, along with estimating losses due to internal resistance, wiring, etc. Eventually this will get thrown off if you never/rarely allow the pack to charge in the constant-voltage (100%) charge area and/or you never/rarely drain the pack close to 0%. So the solution is to give the algorithm new data by charging to 100% and draining as low as comfortable, but somewhere near 10% or lower is best. It won’t hurt anything as long as you charge immediately.

2) Cell balancing

There are 96 cell groups in the Model S 85/90 kWh packs, and 84 in the 60/70 packs. Eventually due to slight variations these cell groups will end up at slightly different voltages. However, the Model S uses the highest voltage out of all 96 to determine when to cut the charge. So, even if 95 of the cell groups are at say, 97% if one of them is at 100% it can’t safely charge anymore.

So the BMS system has balancing bleeder circuits. Once the BMS is aware of which cell groups are higher than the rest it activates a low power load specific to that cell group to drain the excess capacity they have and bring them back in line with the other cells. However, the BMS does not appear to activate any balancers until it gets a voltage reading during the constant-voltage phase of a charge, which is > ~93% SoC. So, charging to 100% also has the benefit of getting the BMS to activate the balancing circuits. These will stay active for hours/days/weeks until they bleed off sufficient power from the affected cell groups, and will happen continuously in the background even after driving and all and even if the pack is not at 100% since it knows how long it will need to bleed for based on the voltage difference during the 100% charge.

While the cells balance, as you charge over the coming days the cells will be able to charge more fully.

So essentially you want to get the car as much data about the pack as possible. This way it has more information to go by and thus have a more optimistic range prediction.

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Nu är ju hög och väldigt låg SOC dåligt för batteriet är ju bäst att tillägga. Så man ska inte hålla på att ladda 0-100% en massa gånger och låta den stå på 100% länge för att balansera . Men någon gång ibland kanske inte skadar.