Sorry for stupid question - charging costs

[Zippee]

Hi all - We've just purchased a PHEV (Volvo XC90) with the 18kw battery.
Apologies if a daft question or one thats been answered a hundred times but how do I work out cost to charge at home?

We don't have a wall charger, mainly as it's a small battery, so will be using 3 pin overnight - just waiting on a smart meter install before changing to a reduced rate night tariff at 7p per KWH (currently 25p). Is it as simple as 18.8 * the unit rate?
How do we also find out time to fully charge from a normal connection?

[essayer]

Basically yes, although charging isn’t 100% efficient, so say 10% extra for losses.
The car might not fully drain the battery so you may not be starting from 0 each day.

[eldar]

Zippee said:

Hi all - We've just purchased a PHEV (Volvo XC90) with the 18kw battery.
Apologies if a daft question or one thats been answered a hundred times but how do I work out cost to charge at home?

We don't have a wall charger, mainly as it's a small battery, so will be using 3 pin overnight - just waiting on a smart meter install before changing to a reduced rate night tariff at 7p per KWH (currently 25p). Is it as simple as 18.8 * the unit rate?
How do we also find out time to fully charge from a normal connection?

Pretty much, yes. Fully charge around 3 hours, 20 to 90% less than 2 hours with a 32A wall charger, or 6 hours with the 13A granny cable. 7Kw vs 3Kw.

[Zippee]

Thank you both.
Not sure it's worth the expense of a wall charger 😀

[Zippee]

Thank you both.
Not sure it's worth the expense of a wall charger 😀

[Quattr04.]

Generally with a PHEV a granny charger is fine, it might take all night but you’ve only got a small battery to fill in that time compared to a larger battery in a EV

[ZesPak]

Zippee said:

Thank you both.
Not sure it's worth the expense of a wall charger ??

Well, I don't have exact numbers or tests of it, but there's a general consensus that higher charging rates = more efficiency.

Charging the car means it's "awake" and has some inherent use. Charging it 5x faster avoids that own drain and is generally more efficient.
The difference is so negligble that it might never justify the expense of a wall charger, but there are some definite pros:

1. Faster charging can be convenient: when you come home and need to go somewhere in the evening, you can add meaningful range in a couple of hours. I've had it when I woke up and thought: I forgot to plug in the car, but it takes 16kw at home which is about 80km/h for me.
2. I've used the charger for a friend who drove a long way for dinner. Means he didn't have to stop at a fast charger on the way home at night.
3. I've melt a wall socket that was a bit corroded. It might be able to handle 2000W+, but can it handle that for 10h continuously?
4. Timing for cheaper rates if it matters, more flexibility in that sense

I agree though, I know plenty of people that run an EV without a wall box, and so could I, but I'm glad I have one.

[PBCD]

Zippee said:

Not sure it's worth the expense of a wall charger ??

It probably depends how likely you feel that your next car will be a full EV?

[survivalist]

PBCD said:

Zippee said:

Not sure it's worth the expense of a wall charger ??

It probably depends how likely you feel that your next car will be a full EV?

And whether you plan on moving house before that happens. The chargers seem to be pretty expensive for what they are.

[gmaz]

I think the only reason to get a wall box is for convenience. With a tethered cable you just plug it straight into the car. With a 3-pin you have to get the cable out, unravel it and plug both ends in.

[blank]

How long is the cheap rate on your new tariff?

A 3 pin charge will (should!) be limited to 10A which is 2.3-2.4kW.

So 18kWh will take 7.5-8 hours which is longer than the cheap window on most tariffs.

[Zippee]

Thanks again, night rate is 7p per kwh between 12 & 6.
After 3 hours it's only up to 10% from zero, just found out the 3 pin charge keeps tripping the garage electrics as well. Might just bite the bullet and get a box installed - are there still grants available for these?

Edited by Zippee on Wednesday 7th May 20:48

[rfn]

Zippee said:

Thanks again, night rate is 7p per kwh between 12 & 6.
After 3 hours it's only up to 10% from zero, just found out the 3 pin charge keeps tripping the garage electrics as well. Might just bite the bullet and get a box installed - are there still grants available for these?

Does your granny charger have the ability to change the amps? Dropping it to 10A should reduce the likelihood of it tripping electrics.

[Rough101]

Zippee said:

are there still grants available for these?

Edited by Zippee on Wednesday 7th May 20:48

No, but you’ll be a long time recovering the £1000 in savings with a hybrid.

Try lowering the charge current.

[ZesPak]

rfn said:

Does your granny charger have the ability to change the amps? Dropping it to 10A should reduce the likelihood of it tripping electrics.

This. Also for heat, Joule's law (P=I²R) means that dropping a couple of amps makes all the difference in heat buildup in your electric wiring/plug.

Your charger will probably not allow it, but the Volvo should be able to do it in both the infotainment as the app.

[Zippee]

Thanks all, I'll take a look tomorrow

[Back2theFuji]

The Masterplug cables tend to get good reviews and are capped at 10amps. I've just bought one as they are £25 off today:

https://amzn.eu/d/gIZk01f

[RotorRambler]

Could almost make it in the cheap window, if the electrics are healthy, from 0-100%

• Charge speed at 10A / 230V = ~2.3 kW
• Usable battery size: ~14.8 kWh
• Charging time: 14.8 ÷ 2.3 = ~6.4 hours (realistically a bit less due to tapering and losses)

Even if it goes an hour over, is that worth £1k charger install?

Shifting other appliances into the cheap rate, where possible, will easily offset that.

The xc90 phev is max 3.6kwh even on an EV charger.
Which would get it inside the 6 hours on EV charger, but not that fast

Usable battery capacity: ~14.8 kWh
• Charging power: 3.6 kW
• Time = 14.8 ÷ 3.6 ≈ 4.1 hours
• Add ~10–15% for charging overhead and tapering → ~4.5–5 hours total

[lesR]

I might have missed it but the OP does not say the cars use, will it need charging every night?

With my PHEV, the supplied charging cable (3 pin Mercedes) only charges at 1.7 kW/h. The car is garaged so only one end of cable needs plugging into the car as the other is permanently in a switched socket, so no difference to a wall box. If you need to use car with low charge, no problem as you have an ICE to use. I've had no problems with just using a 3 pin plug

[Zippee]

Thanks again all, this is very much a learn from scratch time for me.
After some overnight thinking I reckon getting an uprated outside socket with a timer for cheap rate use would be better in order to take the increased load (garage has boiler and freezer so don't really want to risk those going off each time).
My wife has a 12 mile each way daily commute hence the phev spec.