Battery problem advice

[Gwynfor Hughes]

This advice is way out of order. There is no requirement to use the so-called Granny Charger at all. It is however stated in the manual (the table is on page 157) that in "the event of the high voltage battery low warning" "Slow charging" EITHER on "Residential Electricity" ie a level 1 Granny Charger or "AC charging station" ie a level 2 public or home 7 kW AC charger such as your Rolec, to "Equalize" the High Voltage Battery. This is also called a "Balance charge".

The manual also states on page 292-293 in the Maintenance section paragraph 3, that it is "recommended" "where possible" to carry out a "9-hour slow charge every month to extend the service life of the high voltage battery". This is a maintenance Balance charge which allows the Battery Management System or BMS to balance the voltages across the cells in the pack (108 cells in the ZS). In reality this can take upwards of thirty minutes (30 minutes) after Fully Charge State of Charge (100% SOC) has been reached. [There is a maximum voltage difference that can be Balance in any on session and I believe the maximum time in one session the BMS will do the Balance charge is 6 hours but @MilesperkWh can correct me on that]. During this "Balance charging," the charge rate drops the charging rate from 7 kW to trickle of about 300 watts (as I have described in other threads) and this allows the cells with lower voltage to continue to be trickle charged to "Balance up" or "Equalise" cell voltages in the pack. There is also a degree of balancing when driving from 100% SOC down to about 97% SOC. Balancing when charging though Only happens on AC charging ie on your Type 2 Cable and NOT on CCS DC Rapid chargers. A "Granny Charger" is also an AC charger.

My practice is to use a timed 4-hour charge (5p Octopus Go) when needed and every 2 to 3 weeks have an extended 6 hour timed charge and my energy monitor shows that even with a 6-hour window the car has finished any balancing charge well within 5½ hours and draws no more current.

If you're yet to get 5p / kWh charging and to share £100 with me (50:50) go to: share.octopus.energy/zappy-guppy-175

That tends to coincide with the advice given by the mechanic.
I'm not technical at all and the intricacies of all this has been lost on me.

 

[Gwynfor Hughes]

This advice is misleading. No need to use granny charger balancing using a 7kw is fine. You also do not need to run the battery as low as possible as long as you have one segment below full battery you can balance.
You have been given bad advice my the mechanic.

Thank you.

 

[JodyS21]

Just an update.
I had my car back on 31st August after the battery had been balanced.
A very slow process.
I have been informed by the mechanic that a warning signal will now show on dashboard at some time in future instructing to slow charge.
When this happens it seems I should run the battery to as low as possible and then use the granny charger for maybe up to 15 hours.
I have been told that no further action is required.

Hmm, that's a bit misleading/incorrect what the trained MG technician told you......lol

A warning only appears on the dash telling you to do a slow charge, IF the battery becomes too far out of balance. It doesn't really mean to do a "slow charge", it means a balance needs to take place - which happens automatically on AC charging once the battery is full up.
You do not have to run the battery to as low as possible before doing the AC charge and balance. Once the battery is fully charged, the balance process will run for as long as is necessary but with a limit of balancing for 10 hours maximum.

If you are doing regular AC charging (granny charger or a 7kW charger supply) and letting it fully charge, then you'll already be letting it do some balancing so it's highly unlikely you'd ever see that warning message.

BTW, have you checked what your voltage shows now after you've done a full AC charge? Is it at 449/450V which means your battery is all fully sorted now?