Help required with variable input charging from solar array

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fluffflinger

New member
Joined
Jun 12, 2022
Messages
3
Hi

Just about to take delivery of 2018 i3 REX, very excited!!!

I have a solar array at home and the ability to divert excess production to charge my car. Not, at this point going to install a fast charger as we are probably moving in a few months and I am disabled and don't do a lot of miles anyway, so granny charger is fine!

Obviously the available wattage will vary dependent on time of day, other loads on the system etc.

eg 1st thing in the morning as sun rises the solar will slowly ramp up to, in summer, over 4kw. Way over the 2.4kw that the granny charger needs (10amps at 240v = 2.4kw). I'm in the UK so 240v is what we have.

I cant find anywhere what is the minimum current current required to charge the vehicle? Will it charge at say 250watts? And neither can a BMW Dealer or the i3 specialists from which I am buying!!! I really don't care how slow it maybe but am worried that it does require a certain amperage to initiate the charging. Which in the winter months might prove problematic!

Hope somebody can reply with an answer. Already found a couple of really useful things on the forum and I only joined to ask this question!

Best

Richard & Gill
 
There are some stock BMW OUCs (Delphi EVSEs) that are 8 amp units. That would equate to 960 watts as a reference minimum charge the i3 could accept. The J1772 standard probably defines an even lower limit, but I don't know one way or the other whether the i3 would accept it. Sounds like an interesting project! I've heard of devices like what you're describing to limit the EVSE to track what the panels are producing, so am curious how this works out fair you
 
Well I don't know that much about electrikery or EV's but I thought that when they get close to fully charged the wattage drops off but to what level I don't know?

What I need is an i3 owner close to me to test. It's not a deal breaker but I would be unhappy if it didn't work.

Thanks

Richard

You wouldn't have thought I was the only idiot in the world but I might be???
 
I'm presuming there's a difference between "advertised" vs. internal.

So, in other words, the J1772 standard likely has a minimum amperage the EVSE can communicate to the car. When I say "minimum" what I mean is the EVSE's job is to advertise a max amperage available from the circuit, and this Max might have some threshold that is the lowest Max it can offer. Maybe it's 8A, maybe it's lower, For instance I wouldn't be surprised if the protocol has no provision to advertise as low as 1A, but maybe it can.

Internally, the car's BMS sees the EVSE's Max amperage constraint, sees the voltage coming in, works underneath that amperage "hard cap," performs the calculations, performs the AC to DC conversion, and draws only the wattage the battery needs... very possibly below 100 watts (or below 1A – voltage dependent of course.

Thing is, at L1 rates I normally charge at 16A / 1920 watts, I'd be hard pressed to show you the draw tapering off towards the end of the charge. If it does, it's not noticable by timing it. I'd have to clamp up my RMS to know that for sure. When I connect, 16 amps is what my RMS meter shows. The tapering off of power that most owners reference is when topping off the battery during higher power DC fast charging.
 
I'm the kind of person to whom seeing is believing.

Any i3 owners in the East Midlands that want to come and test my system???

Best

Richard
 
The charging standard requires a minimum of 1.3kW. I have owned 2 by i3s and now an iX3.

Beware: in situations where the excess solar fluctuates around the 1.3kW level there will be frequent starts/stops. It is possible to deplete the 12VDC battery to a state where the computer sheds what aviators call ‘non essential DC electrics’. This includes the ability for the car to initiate a charge. This situation will persist until the plug is removed and re-inserted. BMW wants to ensure that there is sufficient DC power available to start the car. The same thing happens on the iX3.

I have a Zappi 2 EVSE: there are ways to play around with the settings to reduce the frequency of start/stops.

To put the problem into some context, my iX3 goes into charge delayed mode after 9 quick cycles.

Have a look at Page 12: (ECo++)

https://myenergi.com/wp-content/uploads/2022/06/zappi-v2.1-Full-Manual-V2_1_3-H-ENGLISH-1.pdf
 
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