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Discussion Starter · #1 ·
I've had my A250e Premium Plus since June 2020 (ordered Jan 2020, just before Covid!). However, I had a ' 7.4 kw' charger installed by BP Chargemaster and although all the advertising 'blurb' said it would fully charge in under 2 hours, the minimum time I've ever been able to charge in is around 3 hrs 45 min from 0 miles. The charging rate on the Mercedes Me app says 3.5 KW/hr and the same on BP Chargemaster (I don't use it anymore because it only tells me how much electricity I'm using and my Smart meter already tells me that!). Initially I thought it was the Mercedes supplied cable, which was only rated at 20Amps and as my basic physics goes, Power = Current x Voltage, therefore 20amps x 240volts = 4.8kw so to charge the 15.6 kw battery would take around 3 and a quarter hours with the supplied cable at maximum input. I had numerous conversations with Mercedes and they 'denied everything'. I thought that it must be down to charging cable so I purchased a guaranteed 32Amp charging cable, (32amps x 240volts = 7.68kw) so everything should be fine and having a 7.4kw wall box MB say it "can be charged via this with alternating current (AC) within 1 h 45 min from 10-100 percent SoC (State of Charge)". So now it charges at 3.6kw/hr with a charge time of 3hr 45 min as before.
BP deny that the box fitted is a 3.6kw box and, as far as I'm aware, the spec of the A250e 'on board charger, was not changed.
Short of getting an electrician in to check the BP box, or finding someone locally who has a 7.4 kw box I can try out, does anyone have any other suggestions why I cant get the shorter charging time? Most of the time through 'lockdown/Covid' the charging time was not a concern, but now everything is fully 'opened up', I find I'm needing to charge more often and a 3-4 hr charging time is becoming a problem.
Thanks
 

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You just have to eliminate the possibility that it’s the car or cable.

So go to a 7.4kW box or Tesco to charge and see what power your are drawing, if it’s 7.4kW, then you know it’s the BP box at fault.

Have a look through the A250e section of this forum, plenty of complaints about the BP box.

Eg this poster found that the BP box had a software bug that only charged at a low rate when scheduled.

 

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Discussion Starter · #3 · (Edited)
You just have to eliminate the possibility that it’s the car or cable.

So go to a 7.4kW box or Tesco to charge and see what power your are drawing, if it’s 7.4kW, then you know it’s the BP box at fault.

Have a look through the A250e section of this forum, plenty of complaints about the BP box.

Eg this poster found that the BP box had a software bug that only charged at a low rate when scheduled.

Thanks veeeight.
I'm pretty sure its not the cable and I don't think it could be the car as all the specs say the on-board charger is 7kw. Somebody mentioned in another forum that all the initial UK A250e's (of which mine has to be one because of Covid) were supplied with 20A cables, but as I mentioned, I've bought a 32A cable and that still only gives me 3.6kw.
However, I have had another look at my incoming electricity supply and find I only have an 80A fuse and I'm told that that can give a problem if you have high wattage electric showers, we have 9kw with a 40A fuse, and induction hobs, although they are both on a separate circuit and the electric shower is probably only used around 10-15 times a year and never when I'm charging.
I've also read on another (different) forum that Chargemaster supply both 16A and 32A boxes that look exactly the same and that they sometimes put a switch in the outside junction box to change it from 32A to 16A if the fuse domestic supply fuse is 'too low' (60A). That will now be my next investigation, as it is an easy one. If they have, my next point of contact will be with Western Power as I am sure I contacted them before I had the charger installed about 'upgrading' the fuse and they came and said I didn't need to.
I will let you know how it goes.
 

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There are solutions for a limited incoming supply, although 80A shouldn’t be an issue.

There are products on the market that offer a halfway house solution (eg Garo Priority board/switch/relays) that will switch from one charger or shower, to another charger automatically so as not to overload the incomer, or a very modern Zappi 2 charger, that monitors via a CT the load and modulates the charge accodingly, and won't overload even if you have 2 electric showers and 2 EV chargers.
 
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