Switching electric car charger on and off frequently

[nikki]

I have a Peugeot Ion (a badge engineered iMiev). I also have a 4KW solar array, grid linked.

In order to make sure I am using all the power I generate (rather than exporting it to the electricity company for free, effectively), I am installing an Immersun immersion heater controller. This senses when I am exporting power, and trickles the excess to my hot water immersion heater.

It has an option to switch on an external load (e.g. my car charger) when the export exceeds a certain amount. However, it will switch the charger off again every 30 minutes (so it can see if the export amount is still big enough), and switch it on again if there is still enough power.

Will this power cycling damage the charger, or, even worse, the car or battery?

 

[JoeS]

nikki, very good question.

First off, "trickling off excess power" tells me that the source current is variable, which a resistive heater element can easily work off.

Is your iOn using J1772? If it is, then the EVSE would need to tell the car how much current it can draw. If less than the minimum programmed, does it result in a voltage drop? Our i-MiEV charger can handle a wide input voltage range, but what happens when that minimum is reached? Does it turn off, the voltage rises, and does the system then go into oscillation?

Turning power electronics on and off often is never a good thing, which is why I cringe every time I unnecessarily activate the car just to open a window or take an instrument reading. But, I'm being told that I'm an old fuddy-duddy and that the electronics is "designed to take it" (problem is, the people telling me aren't exactly technically competent). Can't answer whether cycling every 30 minutes for days, weeks, or months on end would have a deleterious effect on the car's charging system.

The last one is that there would have to be some means of stopping the charging system once the car's battery is 'full'. Repeatedly trying to top up the battery is definitely bad.

More questions than answers, I'm afraid. Anyone else?

 

[nikki]

I was hoping to use the charger that came with the car, and just turn the mains power to the charger on and off.

The charger turns itself off when the car is charged. I guess I would have to go and unplug the charger, to avoid cycling the charger when charging has finished, otherwise it might keep topping it up when already full.

There is no question of reduced voltage or current - when dealing with non-resistive loads, the Immersun just works a relay, giving the charger full power.

 

[Phximiev]

Can the Immersion communicate with a storage battery or controller for a storage battery rather than a heater? The website doesn't address the notion. It seems that would be ideal. Store to the battery and take from the battery when needed and give/get the balance from the grid.

 

[Aerowhatt]

I have a Peugeot Ion (a badge engineered iMiev). I also have a 4KW solar array, grid linked.

In order to make sure I am using all the power I generate (rather than exporting it to the electricity company for free, effectively), I am installing an Immersun immersion heater controller. This senses when I am exporting power, and trickles the excess to my hot water immersion heater.

I run into this perspective a lot. Most of us with solar systems are net exporters of electricity during full sun hours. Many utilities don't pay you extra to produce power for them. Hence the idea that you are giving it away, if you let it go back to the grid. I'm not aware of anywhere that is not "net metered" though. If your meter runs backwards when you make more than you use then you are indeed getting paid retail rates for the power you are sending back out to the grid. If you step back and think about it. If you use every watt that you produce on site you effectively have stopped the meter from turning. So no use charges for that time period. If you instead allow the power to go back to the grid you run the meter backwards. Gaining "credit" towards more usage later (it has to run forwards again to get back to where it would have been, if it were stalled all day). In most every case it is a wash financially. That said, I'm a strong proponent of doing most of your elective power usage while your array is producing, but not for financial reasons.

As for stressing the charger etc. I would add a second preheater water tank before turning my charger on and off twice an hour! Electronics generally function best and longest in the middle of their "allowed" specifications. Just charge the car normally during the day and don't concern yourself with banking a few retail KWH for later use.

Aerowhatt

 

[PV1]

The biggest problem I'd have with cycling the system is wear on contactors and relays. Every cycle creates a bit of arcing and pits the contacts over time.

I believe the J1772 protocol allows for the pilot signal to vary current in realtime if you could get a setup where current is controlled vs. pulsing on/off.

I personally let my PV system do its thing while most loads in the house do whatever, and I charge the car at night using presumably excess power. kWh out during the day offset kWh in at night.

Do you have a 2-way electrical meter (net-meter)?

 

[nikki]

Unfortunately the electricity company has recently changed the meter - I used to have one of the really old mechanical meters that went backwards when I was exporting. Now I have one of the new digital ones that don't. (As I understand it, that is how it is supposed to be - you get much less for exported power than you pay for imported. The export rate is so low they don't bother to meter it, just assume a certain percentage of the generated power. Of course, I do get the "feed in tariff" for everything I generate, which is much higher than either.)

I reckon if I take no action, this meter change could increase my bill by up to 50%.

Hence installing the Immersun to use all the excess power.

On the car charging, I will admit defeat, and just try to put the car on charge manually when the forecast is good and the sun is out, and leave it on until it is charged.

However, I reckon I can still use the relay in the Immersun to power my existing electric drainage pump. It already has a float switch, so it must be happy with bring turned on and off a fair bit. And there is scope for delaying running it until there is spare power (provided I have an override option to make it run anyway when it rains all week - I live near the Welsh border, so this happens!)

Nikki

 

[Aerowhatt]

Now I have one of the new digital ones that don't. (As I understand it, that is how it is supposed to be - you get much less for exported power than you pay for imported. The export rate is so low they don't bother to meter it, just assume a certain percentage of the generated power. Of course, I do get the "feed in tariff" for everything I generate, which is much higher than either.)

I reckon if I take no action, this meter change could increase my bill by up to 50%.

Hence installing the Immersun to use all the excess power.
Nikki

Hmmmm . . . If your bill is going up from a meter change then one of two things are happening. You previously were perhaps getting credit at retail for what goes out to the grid and are also getting paid for everything that you generate as well through the feed in tariff. If this is the case you had the good fortune to be double dipping (for lack of a better term) for a period of time until the utility was able to get to changing your meter so that you don't benefit twice from the excess KW that you generate in full sun. If that's the case it's been a nice bonus, but wasn't a fair arrangement while it was in force.

To be definitive we would need more information like the various rates applied etc. These utility structures are convoluted and confusing (on purpose I think). Worse than income tax law often. It's important to have a full understanding of how one's work.

If it were me and I wasn't sure that I fully understood the rate structure and metering practices, I would wait a couple of months (before investing in new infrastructure) to see if there is anything worth mitigating.

Aerowhatt

 

[nikki]

I was having my cake and eating it before.

Now things are as they should be according to the rules.

I get about 48p/kwh for all I generate.

I also get just over 3p/kwh for the power I am deemed to have exported, based on half what I generated.

And I pay about 14p/kwh for what I import.

 

[Aerowhatt]

I get about 48p/kwh for all I generate.

I also get just over 3p/kwh for the power I am deemed to have exported, based on half what I generated.

And I pay about 14p/kwh for what I import.

I wouldn't change a thing If I were you. That is one sweet deal!!

Aerowhatt

 

[Lic]

I would worry about power cycling if it hapened once in 1-5 min, but I would not worry about it if it hapened once in 30min.

 

[JoeS]

I would worry about power cycling if it hapened once in 1-5 min, but I would not worry about it if it hapened once in 30min.

Every 30 minutes 24/7? :shock:

 

[Lic]

Why not? I don't see why it should be problem for charger. It starts slow so it will be less stress for electronics.