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PHEV Charging Strategies

  • 02-06-2023 12:31pm
    Registered Users Posts: 82 ✭✭


    There are many information in the internet around this, but still not clear enough for me, and not really clarifying some doubts I have. Some information also contradict each other, so I decided to create a topic and ask people here.

    A few months ago I bought a PHEV car and installed home charger. My car has a range of 58 km with full battery and when it is at 80%, range is 45 km. Both figures assume that range is 0 km when battery charge drops to 17-20 %. My normal daily usage pattern and needs rarely exceed 45 km: I'm working from home 3 out of 5 days a week, office is 4.5 km from my home anyway, kid's school and local supermarkets are all within 2km; recreation spots are max 8.5 km and the most distant shopping center in the nearby city is 17 km. So, it can happen that I can go on a single charge for more than a day.

    Battery charges from those 15-20% to full in about 2h30' +/- 15 minutes.

    On the other hand, my electricity contract is about to expire in a month (I'm on a 24h rate currently), smart meter has been installed recently, so with these charging times I find rates designed for EV owners with 2 or 3 hours at night very attractive for me. With 24h rate, I don't care about the time when I charge. Therefore I can plug it when my range is 0km i.e. my battery hit 20% charge. If I move to one of these 'smart' plans, I will have to use that 2 hour window in the night. Clearly, with that I will not wait for the battery to drop down to 20% and this will cause more charging cycles.

    The other thing that I'm not really clear is about 20-80% rule for batteries. In order to maintain good health of the battery and to keep its capacity for many years it is recommended to keep its charge between 20-80%. Charging above 80% regularly will decrease battery life. That's clear. However, for batteries in PHEVs, I found one opinion that it is OK to charge it to 100%, because it will quickly drop below 80% which means that battery will not remain in state of high charge for long and therefore it won't be as damaging. I couldn't find information to confirm this. My question here is: is high charge destructive or is it destructive only if the battery stays charged above 80% for longer time ? And if so, how long ? I'm asking this because, as you can see from my distances above, I may have a fully charged battery and keep it above 80% for a whole day or maybe more.

    If it is really like that, then should I actually aim to have my car charged to only 80% if I know I won't make more than 13km journeys in next 24 hours ?

    If I go with charging to 80%, than on the other hand, I will have more charging cycles, which has negative effect on a battery. Now the question is, what has more negative effect ? High charge or higher number of charging cycles ?

    It is important for me to maintain health of the battery as I don't plan to change car in next 3 or 5 years. I really want to have it for as long as possible. That is why I'm trying to figure out the best charging strategy given circumstances (typical distances traveled and smart meter rates).

    Thanks for any advice and information


  • Registered Users Posts: 18,984 ✭✭✭✭Del2005

    Unless they have new plans the Smart rates are more expensive for most people. Just stick with your current 24 plan unless the Smart plans suit you, don't change just because you have a smart meter.

  • Registered Users Posts: 11,336 ✭✭✭✭the_amazing_raisin

    Best strategy with a PHEV is ABC, Always Be Charging. Grab electricity whenever you can get it for free or very cheaply to maximise your electric range 😁

    So for charging at home, you'll want to balance any EV charging rates against other consumers in the house. Those EV rates typically give 3-4 hours of cheap electricity, but the other rates are higher outside this time. You can shift some consumption to night rates to offset this, but you'll need to do the math to figure out whether it's worthwhile

    For the 80-20% rule, it's slightly overstated how important this is. You can charge above 80% as needed, and with a PHEV you'll want to do this a lot. The idea is to try and not leave the car sitting for a long time (several days) at 100% as that isn't good for the battery long term

    So if the car isn't needed one day then it probably makes sense to not charge it to full

    Don't fret if you do end up leaving it above 80% for a day or so, it isn't going to immediately destroy your battery and will likely have no significant effect on the lifetime

    Similarly for the 20% lower bracket, your car should have protection features to stop the battery being damaged by discharging it.

    It's likely the reason the car switches to petrol at 20% is because of the driving mode. The total power of the car is probably based on both engines, so it leaves some battery available for the electric motor to accelerate the car

    There's might be an Eco mode which will drain the battery lower to keep the car in EV mode for as long as possible

    "The internet never fails to misremember" - Sebastian Ruiz, aka Frost

  • Registered Users Posts: 1,914 ✭✭✭kanuseeme

    There is probably a 3 kWh buffer, split between full and empty. So you are never at 0 or 100%.

    My own 330e is 6 years old 70000km battery appears to be 100%, my last car was 8years and 150 000km that one seemed to be around 75%. But it had a tiny 4 kWh battery, it got cycled a lot.

    I would not worry too much about it, come 5 years it might be @ 90 %, it only means 52km instead of 58km.

    Electricity is expensive ATM. Might be prudent to check in a few months and pay 50 euro cancellation to get a better rate.

  • Registered Users Posts: 2,268 ✭✭✭Miscreant

    I had a PHEV for 2 years and always charged it to 100% regardless of what I was going to be doing. The car had 130k Kms on it when I moved it on at 4.5 years old, the battery SOH was 97% with 85k Kms travelled on pure electric (the remainder on petrol). I never noticed any loss in pure EV distance in the time I owned it, except for the winter time of course. By your 17% battery at 0kms quote, I am assuming you have either a Kia or a Hyundai PHEV as mine was. Get yourself an OBDII dongle and download the PHEV Watchdog app as this is what I used to keep an eye on battery health and fuel consumption over time. My driving patterns are very similar to yours and I never once had consideration for the battery in that time as I knew the car would not be sitting at 100% SOC for long. Leaving it for a day or two at that SOC is not going to kill the battery, just don't give it a full charge before heading on a 2 week holiday to the US or anything and it will be fine.

    As for the day/night rate thing: As Del2005 says, the smart rates are more expensive for most people. You may be able to find a standard Day/Night rate however and I have heard of people doing this despite the fact they have a smart meter. There is a thread on the forum somewhere for the best plans for EV owners so it may be worth your while having a look at that.

  • Registered Users Posts: 82 ✭✭Selenophile

    Thanks everyone for all the useful answers. I really appreciate it.

    I am aware how expensive are these smart plans and how much difference those standing charges make between plans and companies. I've been collecting my own electricity usage data for last two months as well as statistics around my car consumption. Now with all the data I want to do some serious math to evaluate electricity plans. I also use gas for heating, so there are different possible combinations that need evaluation. Possibility of getting simple day/night tariff with smart meter is a good news, as these usually have lower day prices IIRC.

    My car is indeed Kia :) It is Niro K4 (2023) PHEV. I'm driving it in ECO mode always and I'm absolutely maximizing pure EV drive. With all the answers WRT battery health maintenance I understand I don't have to be rigid about charging and can adopt some more convenient strategy. These are really encouraging.

    I didn't know about OBDII dongle and app ! That's another useful tip. I'll get it as soon as possible. I collected a good amount of data regarding pure electric drive, but I would like to see some more detailed data around total consumption which includes hybrid drive etc.

    A lot of analyzing and planning in front of me, but that's something I really enjoy doing.

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  • Registered Users Posts: 6,711 ✭✭✭zg3409

    Most PHEV protect their battery so there is a reserve at the bottom and top so no need to worry about "100%".

    Beware smart plans and 24 hour plans. Typically if you go to a smart plan you are never allowed to change back to 24 hour plans. Look at your annual consumption on a bill and try to figure out the best rates. It's hard to do without historical "smart" time based usage but you can estimate how much you use st peak times if you have electric hob etc.

  • Registered Users Posts: 82 ✭✭Selenophile

    Thanks !

    I have two months of data on my smart meter showing consumption across all three bands. Previous years statistics on 24 rate show small differences between winter and summer time and are fairly consistent in last 4 years (I've been tracking these values as I always try and shop around in time to switch providers). Now I just need to subtract times when I used charger to get a proper distribution of "home only" consumption across day/night/peak times. For all these calculations I have about a month now and maybe I won't immediately subscribe to any plan, in case there will be signs electricity prices will go down soon.