DIY Electric Car Forums banner

1 - 9 of 9 Posts

·
Registered
Joined
·
66 Posts
Discussion Starter #1
Hello wise folk,



I am planning a conversion using 5 Tesla modules to give total of 114V.


What is the highest charging rate I could achieve, and which charger could deliver it?


I am in the UK and am looking for something better than 6.6KWh. 22KWh stations exist near me, but I don't know if it's possible for me to get to that rate with my low-ish voltage pack.


Any help gratefully received.
 

·
Registered
Joined
·
774 Posts
The faster your charge rate relative to Ah capacity (C-rate) the worse for pack longevity.

Find out the mfg spec'd C-rate, that maximum is a "do not exceed" but very stressful rate.

Whenever you can, charging at 0.3C or below is much healthier wrt lifetime cycling.

Of course making pit stops out on the highway when driving on a schedule, fast charging is required. Personally I would pad the schedule and time meals, cuppa breaks, so 1-1.5C would be fast enough.
 

·
Registered
Joined
·
66 Posts
Discussion Starter #3
The faster your charge rate relative to Ah capacity (C-rate) the worse for pack longevity.

Find out the mfg spec'd C-rate, that maximum is a "do not exceed" but very stressful rate.

Whenever you can, charging at 0.3C or below is much healthier wrt lifetime cycling.

Of course making pit stops out on the highway when driving on a schedule, fast charging is required. Personally I would pad the schedule and time meals, cuppa breaks, so 1-1.5C would be fast enough.

I'm going to go with an onboard 6.6kW charger, and learn to live with it!


Many thanks.
 

·
Registered
Joined
·
5,044 Posts
Aside from the details of charging station configurations and supply voltages (discussed in another thread), I'll note that Tesla supports up to 120 kW charging (at Superchargers) of their Model S and X vehicles. Assuming that is only acceptable for variants with 16 modules, that's about 330 amps or 7.5 kW per module. With the same modules (meaning the later and higher-capacity version), a 5-module pack could then be expected to accept about 38 kW without causing problems for the modules or cells... if you have a source of 330 amps at around 114 volts (and nearly that current up to the cut-off voltage, of presumably 125 volts or so).

If you could use a Supercharger (which you can't), and it were able to turn the voltage down to your level (which it presumably can't), the 120 kW version of a Supercharger could supply the required current and thus charge your 5-module battery at 38 kW.
 

·
Registered
Joined
·
5,044 Posts
Of course making pit stops out on the highway when driving on a schedule, fast charging is required. Personally I would pad the schedule and time meals, cuppa breaks, so 1-1.5C would be fast enough.
That's good for battery life, but I can't imagine planning a long trip in which I would spend almost half my time on the road stuck at charging stations, waiting for electrons to flow. That might be okay in some areas, where there is a lot to see and do and available appropriate chargers everywhere; that's not a reality for most areas, if anywhere.
 

·
Registered
Joined
·
774 Posts
Yes, obviously the trade-off between bank longevity and convenience is a personal call, even on a per-stop basis.

Just don't want people thinking going to the max spec'd C-rate doesn't have a cost, especially those looking for good value per year with expensive packs.
 

·
Registered
Joined
·
5,044 Posts
Yes, obviously the trade-off between bank longevity and convenience is a personal call, even on a per-stop basis.

Just don't want people thinking going to the max spec'd C-rate doesn't have a cost, especially those looking for good value per year with expensive packs.
Absolutely agree! :)

Even Tesla admits on their web site that using their own fast charging (at Superchargers) reduces battery life.
 

·
Registered
Joined
·
2,045 Posts
Hello wise folk,



I am planning a conversion using 5 Tesla modules to give total of 114V.


What is the highest charging rate I could achieve, and which charger could deliver it?


I am in the UK and am looking for something better than 6.6KWh. 22KWh stations exist near me, but I don't know if it's possible for me to get to that rate with my low-ish voltage pack.
Tesla Superchargers will currently do up to 150kw at some stations. Ive seen 129kw on my 2013 Model S 85. This only happens at low states of charge. For my car this is between 5% and 20% SOC. 129 kw at around 300 volts would be 430 amps. I believe there are 72 cells in parallel on the 85 kwh modules. The 100 kwh modules managed to squeeze a few more cells in. 430/72 = 5.97 amps. This is about a 2C rate.

My understanding is that many of the Chademo chargers will not go below 200 volts even though the Chademo spec says they are supposed to. With your 114 volt limit (5 modules * 6 in series * 4.2 volts per cell max charge = 126 volts). Your max possible charge rate would be at a low state of charge (90 volts) and 430 amps. This would be 38kw from your AC source. You could parallel several chargers assuming you have a large enough AC source and room to hold several chargers.
 
1 - 9 of 9 Posts
Top