Hello, name is Dave. Need help building a system to supplement the charge on a Tesla

Ampster

Renewable Energy Hobbyist
thought 11kw was practical max for most usa wall charging.
I have heard of some J1772 Chargers that go as high at 70 Amps (16.8kW) but they are rare. Most EVs do not have onboard chargers larger that 30 or 40 Amps. My Model 3 standard range Tesla has a 32 Amp charger and the long range version has a 48 Amp onboard charger. The Tesla HPWC can go as high as 80 Amps (64 Amps continious) but most Teslas do not have an onboard charger that big. I am not sure what the practical AC max is other than the above limits. DC charging is at typically 400 volts so more kW rates are possible. The practical limit there is how well the battery in the car can dissipate the heat generated from charging at 3 or 4 C rates
 

Ampster

Renewable Energy Hobbyist
240V * 48A -> 11,520W
Yeah he is talking about a 2018 Model S. That is the same as my 2016 Model X. That was and still may be the standard for those two models which don't have as efficient drive trains as the Model 3 and Model Y. The Long range versions of the Model 3 and Y have the 48 Amp charger but my Standard Range Model 3 is 32 Amps. Before Tesla went to the 48 Amp onboard chargers there was a smaller one but an option for two. I can't keep track of all the iterations. It looks like they have now settled at 32 and 48 Amps. I have a deposit on a Cybertruck and as my mid 2022 estimated delivery date approaches i will have to pay close attention.

I am still waiting for @Dave162 to tell us what he means by "supplement" the charge on his Tesla. He did stimulate two pages of conversation, It will be interesting to find out how much of that is relevant.
;)
 
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DisabledVet

Solar Enthusiast
I have a similar question so maybe y'all can help - because from what I have read here, it sounds like it should work. I bought Will's book, have watched his videos, and read multiple posts here so I think I have it figured out.

I have a 2018 Tesla Model 3 Mid-range (210 miles range with 50 kW battery) RWD. In other words, I got the cheapest Tesla they offered at the time. I charge it today in the garage using the standard 120V outlet at 12amps. Yes, this means it takes overnight to recharge from 20% to 80% ... and I am just fine with that.

We were considering putting 8 SanTan Solar T Series 250W solar panels (~$500) on the roof of the barn, hooking them into a PIP LV2424 MSD 24V 2.4kW, 120V Output, 2kW Solar Input 80A Mppt (~$700), and hooking it into a DIY 24V battery I would build (~$900 and 3 month wait for cells + ~$150 BMS). This would give us ~3,584 Wh battery at 24V to use to charge the Tesla using the 120V outlet. Total cost should be ~$2,500.

This would all be in the barn - nowhere near the house and not hooked up to the grid. Shouldn't need any permits.

If power goes out, we could partially charge the car or run an extension cord to the kitchen and have power in one room.

Any reason this wouldn't work? If so, if we got 4-5 hours of sun a day, how much could I charge the Tesla each day?

Thanks!
 

DerpsyDoodler

Photon Sorcerer
2kw (solar) * 5 hours = 10kwh (assuming peak efficiency), so 10kwh is what you have to use however you choose (charging a tesla battery or charging an intermediary battery. Also consider you lose power when charging a primary battery, and more loss when charging the secondary battery from the primary.
 

Ampster

Renewable Energy Hobbyist
Any reason this wouldn't work?
It will work but I can not tell you if it would be economical. Tell us more about your rates? I have been charging two EVs in California for eight years and it was worth the extra expense of getting a building permit because the Net Metering policy. That policy made it possible to store energy on the grid and get credit at $0.30 to $0.50 per kWh. I can use that power during off peak times to charge my EVs at $0.18 per kWh.
@DerpsyDoodler explained the inefficiencies of charging two batteries and I can tell you that charging at 120 volts adds to the inefficiencies because of the electrical overhead.
 
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Dave162

New Member
I have a similar question so maybe y'all can help - because from what I have read here, it sounds like it should work. I bought Will's book, have watched his videos, and read multiple posts here so I think I have it figured out.

I have a 2018 Tesla Model 3 Mid-range (210 miles range with 50 kW battery) RWD. In other words, I got the cheapest Tesla they offered at the time. I charge it today in the garage using the standard 120V outlet at 12amps. Yes, this means it takes overnight to recharge from 20% to 80% ... and I am just fine with that.

We were considering putting 8 SanTan Solar T Series 250W solar panels (~$500) on the roof of the barn, hooking them into a PIP LV2424 MSD 24V 2.4kW, 120V Output, 2kW Solar Input 80A Mppt (~$700), and hooking it into a DIY 24V battery I would build (~$900 and 3 month wait for cells + ~$150 BMS). This would give us ~3,584 Wh battery at 24V to use to charge the Tesla using the 120V outlet. Total cost should be ~$2,500.

This would all be in the barn - nowhere near the house and not hooked up to the grid. Shouldn't need any permits.

If power goes out, we could partially charge the car or run an extension cord to the kitchen and have power in one room.

Any reason this wouldn't work? If so, if we got 4-5 hours of sun a day, how much could I charge the Tesla each day?

Thanks!
 

Dave162

New Member
Hi Dave, name here is Dave too. I have a Model S on order, to arrive in 2022 so I am interested in how you make out. Keep me in the loop. Another guy that has a you tube channel is David Poz. He does a lot with batteries and in general building solar systems, with or without solar panels.
 

curiouscarbon

Science Penguin
I will be implementing a 120V charging backup system with Multiplus 24/3000 to provide grid transfer and Bluesolar MPPT for PV input. 8x302Ah CATL LFP cells with JBD 100A 24V 8S BMS. Maybe gigavac contactor.

BTW, I don’t care about economics in this case, I care about autonomy and uptime. Please factor that into context. Thanks.

Primary goal: enable EV charging during blackout to travel at least 10 miles in an emergency.

Secondary goal: enable supplemental PV input

8cellx302Ahx3.2V -> 7730Wh nameplate capacity
6700 Wh after 1.15 division.
5800 Wh after another 1.15 divison.

only charging at 1500W or less. outlet is 120V 20A branch.

due to lack of programmatic configuration of charge rate i will simply limit battery source charging to be the same rate as grid source charging to prevent excessive cycling.

happy to hear comments. again don’t care about eating conversion losses and don’t care about grid rates. it’s about autonomy not price. autonomy is priceless.
 

curiouscarbon

Science Penguin
for discharge, it’s about 250Wh to 500Wh per mile depending on the weather. 250Wh/mi for mild weather and efficient driving. 500Wh/mi for very cold or very hot weather and or inefficient driving. these are my rules of thumb, accurate or not.

as for input efficiency, i am expecting to eat the conversion and just be happy that i’m not making up excuses for an oil addiction :p

even with “only” 5000Wh deliverable, that’s 10 miles of adverse weather driving and 20 miles of “everyday” driving.

based on my understanding, the above hardware should be capable of delivering my requirement of ten miles in an emergency.

the CATL batteries should be at around 0.25-0.33C discharge which seems to be safe albeit with some self heating that i’ll blow off with a temperature triggered dc blower

edit:typo fix
 
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