Stop battery discharge when charging EV overnight

[NDFox99]

Hello, we are new to this and the system only went live 2 days ago so we are still fine tuning it (and learning!). You can see the setup we have in the signature box below. The issue we are trying to work out is how to stop the EV overnight charge drawing from the house DC coupled battery (not AC coupled, as this should be straight forward I think).

On the first day we had enough sun to fill the batteries and then run house overnight which took the battery to 35%, so all good. Eddi was not fully installed.

Then yesterday we had enough sun to fill up the batteries, heat the hot water and a little bit spare and would have got us through the night be we needed to charge the EV. We set it to run 23:00 - 03:00 as we had the feeling it would take from the battery because the battery is DC into the inverter so the Myenergi Eco-system cannot see it. Sure enough this morning it had taken the battery to 16% (it is set to 20% min SoC so probably just overshot) and the data showed it had pulled this during the EV charge.

We do know you can set export margin (e.g.100W) on the invertor to stop this happening on DC coupled batteries but as far as I can tell that is only for day time solar charging to allow the solar to charge the car. We intend to use this occasionally but the system is not big enough so it really needs the overnight charge on cheap electricity. Is there an option on the inverter to limit the output during some set night time hours e.g. max 300W 00:00 - 06:00. This would run the house overnight but would only pull a little bit on the battery on the overnight charge and the majority would be the grid? Or some other option?

The inverter seems to have other CT inputs (apart from CT1 on the grid) so perhaps one around the EV charger output would let it know the charger was running and not to allow the battery to drain?

The other thing I was wondering is there appear to be ways to measure current on DC cables (I think), so if a device could be made up to do this and act as an AC CT perhaps that would open up some options?

I'm sure this has been asked before so apologies in advance!

[Ched]

I think there is a way to add a ct clamp to the Zappi so it knows when it's drawing through the inverter. i.e. the zappi ct would go round the mains cable that goes from the inverter to your consumer unit.

Hopefully there will be some with more knowledge to help properly as I don't have a zappi or an ev.

[NDFox99]

Hi Ched,
OK thanks for that but already added a CT around the output of the inverter during the installation and commissioning and it can be seen on the Myenergi app. But it is a combination of solar and battery so I have labelled it "Gen and Battery" or something like that. So the Zappi cannot tell if it is free solar energy or it is pulling on the house battery. The issue is the battery and panels are both DC coupled into the invertor so it just sees the resulting total output.

I've been reading around and thinking a bit more today. Something I'm going to try tonight is charge the car from 00:00 to 05:00 on cheap overnight, then in the inverter settings I have also set the house batteries to charge from the grid at exactly the same time. I think the batteries right now (about 10:00 at night) are around 60% (Fox App is not very quick to update battery status!). So one of 2 things might happen tonight, either the EV charger will pull from the house battery but the house battery will immediately replace it and therefore will remain at 60% SoC (or whatever it gets to at 00:00 tonight since it is running the house now) and be at 60% SoC at 05:00 in the morning (this will be ideal!), or the battery and EV charger will both run at max capability and the house battery will end up at 100% SoC at 05:00 (less ideal since we prefer to use the sun the next day to charge it.)

I'll report back on which option occurred!

On another note from reading / YouTube videos today it seems fairly straightforward to make / buy / adapt a DC current clamp and run it through an op amp circuit with a few other components to create the required signal to turn it into the equivalent of an AC CT clamp. The circuits have an offset adjustment to get the output to pass through zero, and a gain adjustment to create the correct calibration slope relating sense current to output voltage. If it really is that straightforward why has no-one made up these devices and sold them? It would surely open up the benefits associated with AC coupled batteries, namely the EV charger can be told whether to allow the house battery drain etc. plus the other advantage of the "Gen and battery" display on the Myenergi app would also now show what the battery was doing. I'm guessing there is a catch somewhere!

[calum]

Set a charge period on your Fox inverter that covers the period you're charging the EV. You can opt to charge the home battery or not during this time, it doesn't matter. It's the "force charge" option that you need.

[NDFox99]

Ok thank you Callum I will try that.

To report back on my investigation in my previous post I did try charging the home batteries at the same time as my car last night but all it did was charged them both, not topped up the battery to maintain the SoC. I woke up at 00:30 and we were pulling 12kW from the grid, 7 for the car and 5 for the home battery. So I switched off the forced charging on the inverter app and in the morning the car was charged but the house battery was flat.

So I think what you are suggesting is subtly different so I’ll try that instead. I can’t check now as the Fox server has been down since this morning!

[calum]

If you don't want to charge the battery beyond a certain SoC, you can set this in the inverter menu.

(You can set everything you can set on the website, on the front panel, it's just a bit more fiddly!)

[Ian345]

Not sure if this is relevant, or not - What we do when we are charging our EV overnight is to set the Battery 'minimum SoC' to a higher value (e.g. 30%). This means that we use half battery draw and half grid until the battery get down to 30%. We only have a 3.7 Inverter.

First thing in the morning, we then reset the Battery 'minimum SoC' to normal (10%) - That then gives us the now spare 20% battery to use in the morning, until our west facing Solar kicks in.

Not ideal, but is the best way we have found it to work, so far. We are on Octopus Flux - So have 3 hours of cheaper elec at night.

[calum]

If you are running something big like an EV charger during an offpeak electricity tariff window, you just need to set one of the battery charge windows to cover that time, and make sure that "Force Charge Enabled" is ticked. This will stop the battery discharging during that time, ensuring the power is taken from the grid.

If you want, you can also tick the "Grid Charge" option for that charge period, then you can charge the house battery and the car battery at the same time, if you wish.

If you want to "leave room" to capture solar gain during the day, you can set the Max SoC parameter (from the front panel of the inverter) to a desired value, the battery won't charge beyond this from the grid, but it will charge up beyond it if there is sufficient solar gain.

I just have a single charge period that also matches my Octopus Go Offpeak time, then I change the Max SoC to suit. If we're away I deactivate that charge period so the house runs effectively 'off grid'.

[NDFox99]

@Ian345, OK yes I can see how that would work and it is an option but I would have to wake up early and change the min SoC over!

@callum, OK it finally makes sense although I find the naming of that option a bit confusing! Not a big deal when setting the car to charge for the night to also slide that switch across in the app. Thinking it through it would mean the ~200W of background power required for the house overnight would now come from the grid but this should be cheap rate anyway, so yes it does make sense.
Car is full now as the sun over the weekend topped it up nicely, so we will try that option next time.

Thanks everyone for your help.

[dvdt]

Hello,
New here and I want to buy basically the same setup and I was looking around for this exact topic.
I want the inverter to support the house using the battery during the night even on cheap energy but I don't want to use it to charge the car in the days I put it in charge. I could just put the clamp on everything less the garage but i also have some about 15/20 W usage from the garage constant that I would like to cover.

Could I run a second clamp?

Any idea if I can run a automation to do this changes? I have homeassistant running and maybe I can interact with the inverter and when the status of the charger changes i kill the output from the battery.

Other option in if I can had something max max battery draw power during the a time period. I have around 150w to 200w usage during the night so if I could lock it to this values, If I tray to charge the car I will not empty the battery due to the low power allowance.

[calum]

How are you connecting to the inverter? If you're using the RS485 connection you can probably do something, have a look at these:

https://github.com/nathanmarlor/foxess_em
https://github.com/nathanmarlor/foxess_modbus

[LABBETTAL12QH]

Hello, I’m new to this as well (install was 2 weeks ago - 7kW system, 5kW hybrid inverter and 10kWh batteries). I am with EDF so get cheap electricity from 0030 to 0730 which is when I charge my EV (once or twice a week). All good with the system (apart from the lack of sun……) but my battery always runs out in the “cheap” period so at 0730, I am fully on the grid and the battery will charge if the sun comes out and there is excess juice.

How do I get my battery to be fully charged by 7:30am in the morning when the grid kicks in with a cost of 5 times my night rate?

My EV is controlled by my PodPoint app and when I plug it in, it will charge from 1am to 7am so I don’t want any conflict that that.

Any and all replies gratefully received.

Thanks, Chris.

[calum]

Set a charge period on the inverter (you can do this via the front panel controls, or via the app or the website) with a start and end period that matches when your off-peak time is. Then ensure that both the Force Charge and Charge from Grid options are ticked. This will mean your battery won't discharge during this time, and will be fully charged when you get to the end of that period.

As we get into the summer months you may wish to consider setting a Max SoC on the inverter to ensure you have some room to capture the increasingly early morning sunshine! Although this will depend on how much you get for power sent back to the grid...

[awignall1]

From looking at videos it looks like the battery settings interface has changed since this advice was given - with no documentation that I can find to explain what each thing does (when I hover over/click on the "?", either get get an empty box or a toast that pops up saying NOTICE and nothing else). Does anyone know the equivalent I would need to do with this:

Screenshot 2023-07-31 at 10.28.16.png (10.66 KiB) Viewed 10141 times

I'm on Octopus Go so will be charging car between 00:30 and 04:30 when it needs it, but for the summer it seems I'll be getting enough solar to last on batteries overnight, unless they're drained by the car.

Thanks in advance!

[calum]

https://www.foxesscommunity.com/viewtopic.php?t=337

Long story short, they've changed the interface but you can still stop the battery from discharging overnight while charging an EV

[awignall1]

Thanks!

[markcarline]

....
The inverter seems to have other CT inputs (apart from CT1 on the grid) so perhaps one around the EV charger output would let it know the charger was running and not to allow the battery to drain?
....

Sorry to reply to this old post but this line in your original post does make complete sense.

I wonder if this is a feature request that CT2 or even a 2nd/3rd Meter RS485 could be used to monitor a load which *should not* cause the inverter to generate power from the battery?

[Dave Foster]

....
The inverter seems to have other CT inputs (apart from CT1 on the grid) so perhaps one around the EV charger output would let it know the charger was running and not to allow the battery to drain?
....

Sorry to reply to this old post but this line in your original post does make complete sense.

I wonder if this is a feature request that CT2 or even a 2nd/3rd Meter RS485 could be used to monitor a load which *should not* cause the inverter to generate power from the battery?

No CT2 on the hybrid can only be used for monitoring external generation (other solar inverters), the best way to avoid the EV draining the battery is to fit the EV charger before the house load / inverter connection at a Henley block on the smart meters live tail. (Or set a charge period at the same time to stop the drain).