Charging Speed at 10%?

[Expat Ever]

Today I inadvertently ran the main battery down lower than usual and just now plugged it into our MG wall charger when I got home. The charger reliably provides 7.2Kw when topping up in my usual range of 25 - 75%, but with the battery at 10% it was only working at 2watts. The charging port 0-25% light came on blue for a few minutes and then went out. The display on the MG wall unit behaved normally showing its cycle of nine green flashes.


The charging rate is second from the bottom (my power used so far this month)

The driver's display reported the charging door open and "High voltage battery shut down" with a red symbol at the top right and a yellow one in the bottom left. Other than that, electrics in the car interior appeared to work normally. Clearly, at 2watts it wasn't going to charge so I have connected the Granny Brick instead and that looks like it's working normally, drawing 9.5A at 229V from a domestic socket.



Anyone had issues with using the supplied wall box with an almost empty battery? (mine is a Thai 230V 7Kw ingle phase version: see the picture attached).View attachment 20304

 

[SimonS]

Leave it plugged in for an hour or two. As the charge level increases the rate will increase. Remember, the charger does not set the rate - the car does.

 

[mg4mc]

But that isn't charging is it? At 2 W you'd have to wait nearly 4 weeks to get a 1 kWh increase.

 

[siteguru]

I ran my SE SR (51kWh) down to 13% and started a charge this morning ... all is charging OK. (Same happened - i.e. all OK - when I'd gone down to 6% last winter).

Which version MG4 have you got? Is yours a 51kWh "Trophy" spec car?

 

[mg4mc]

Same here, I have home charged (7kW) from 7% without any issues.

 

[Jomarkh]

What rate does it charge at using the granny 2.2kW EVSE?

 

[Rolfe]

I have never heard of a battery charging slowly just because it was at a low state of charge. And 2 watts is ridiculous - even when it's just balancing at 100% mine takes 20 watts.

I can't speak to this directly because I don't have a wall box and both times I got home under 10% I took the car straight to the rapid charger to save time on the granny lead, but it sounds very abnormal. For what it's worth, on the 50 Kw rapid charger my car took off at about 48 Kw within less than a minute, even from 4%.

 

[fnegroni]

The user manual states that every 3 to 6 months you should do a slow charge from <10% to 100%. Whether by accident or not, it’s a good thing.

 

[Rolfe]

I don't remember reading that. That's the problem, there's so much to take in when you first get the car. I don't usually go that low and if I do I put it on the rapid charger to save time. I suppose I should make a point of doing it then. Although since that's going to take well over 24 hours on the granny charger I'll have to pick the right time.

I take it that recommendation applies to the LFP battery as well as the NMC?

 

[fnegroni]

I don't remember reading that. That's the problem, there's so much to take in when you first get the car. I don't usually go that low and if I do I put it on the rapid charger to save time. I suppose I should make a point of doing it then. Although since that's going to take well over 24 hours on the granny charger I'll have to pick the right time.

I take it that recommendation applies to the LFP battery as well as the NMC?

According to the manual maintenance of both batteries is identical.

There’s a difference between charging to >80% regularly and never doing it.
NMC batteries prefer it less often, but the circuitry that monitors state of charge and builds up a profile for the battery and balances it wants it at some point, possibly weekly if you use the car daily and recharge often.

 

[Rolfe]

The SR battery will balance every single time you take it to 100%. I've seen mine do it five evenings in a row. I think it's advantageous to do this often and there's no harm in taking it to 100% and leaving it there. MG doesn't give SR owners any facility to stop a charge at under 100% short of intervening manually to stop it. I always let mine go to 100% and balance whenever it's on an AC charger, and I don't cycle it up and down at lower states of charge unless I'm on a long journey hopping from one rapid charger to the next.

I wasn't aware of the recommendation to take it right down to 10% and then all the way to 100% on an AC charger though. It's something I'd need to plan, as usually, if I'm that low, I'd use a rapid charger to get up to maybe 75% before moving to the granny charger, just to save time.

 

[Expat Ever]

But that isn't charging is it? At 2 W you'd have to wait nearly 4 weeks to get a 1 kWh increase.

Exactly, the wall charger was going nowhere so I used the Granny Charger to take it up to about 20% and switched back to the wall charger that took it up to 87% at about 7kw before I stopped it.
I'll just keep an eye on it next time it comes home Low.

 

[philip456]

What rate does it charge at using the granny 2.2kW EVSE?

Approx. 2 kWh

Assuming it doesn’t blow a fuse in your house. It’s like two 1000 watt kettles going on non-stop.

 

[mg4mc]

Every kettle I have had has been 2-3 kW

 

[Tig170]

I ran my SE SR (51kWh) down to 13% and started a charge this morning ... all is charging OK. (Same happened - i.e. all OK - when I'd gone down to 6% last winter).

Which version MG4 have you got? Is yours a 51kWh "Trophy" spec car?

Same here, SR - We've just done nearly 1000+ miles in the last week on holiday, each day taking it down to well below 10% battery (as we've had the car 12 months, we know it well on the range left), so even took it down to 4 miles left. No issues, getting it back upto 100% battery for the next day (at an amazing rate of 39p / Hr - using an app called Vend Electric) - I must admit that using the car daily does keep everything working (i.e. 12 volt battery, although we have gone on holiday for 2 weeks at airport without issue), although just like our old Tiguan the A/C is now like a smelly dog - but do find a quick blast in either side of the MG4's bulkhead with Dettol All-in-One Disinfectant Spray does remove this.