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Discussion Starter · #1 ·
Hi, I am in the early stages of planning a conversion. I have a 1971 Super Beetle to use, and am based in the UK.


My question is around chargers and BMS systems.


My plan is to use 5 Tesla modules in series to get me to 114V.


I would like to be able to charge the car as fast as possible, and as I understand it, one can have on-board AC chargers at various power ratings for 'fast' charging (3.7KWh up to 22KWh), and potentially one could use the 'rapid' charging offered by Chademo (50KWh).


Firstly, can anyone recommend a charger that would work up to the 22KWh limit? Is it correct that I can use any charge rate lower than my charger is rated at?



Secondly, I understand that the Orion BMS2 can work with on-board AC chargers but also with the Chademo protocol, so is it feasible to use this BMS with Tesla modules and an up-to-22KWh onboard charger, and be able to use 50KWh rapid DC charging instead where available?


(I expect that cooling/temp management of the batteries would be needed, but I don't want to overload the questions in this post).


Many thanks, and apologies if this is answered elsewhere but I couldn't find it.
 

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About fast charge, you need to understand that 50 KW of charging power generally mean 400v x 125A. At 114V x 125A you will obtain 14 KW.
To add, probably than all fastcharge station can not handle such a low voltage (114V).
 

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Discussion Starter · #3 ·
Yabert - thanks.


I thought 50KW DC charging was referred to as 'rapid'? I didn't know it was current-limited in such a way.



Is the on-board AC 'fast charging' limited similarly by current?
 

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Onboard chargers are limited by the AC voltage supplied to them, the AC current allowed by the supply circuit, the limits of the charger hardware (voltage, current, and power), the battery voltage, and the current which the battery will safely accept.

As with the fast DC chargers, it would make sense to assume that every step of the charging system will be limited to the same current as it would be with the battery voltage for which it is designed; that would cut the charging power by the same ratio as the battery voltage has been cut. In addition, there's no reason to expect that an onboard charger would work at all with any battery voltage range other than that for which it was designed.
 

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Discussion Starter · #5 ·
Thanks for the info.


Please forgive my ignorance.


I note that charging cables are often rated at 32A, and I note that "Fast chargers, all of which are AC, are typically rated at either 7 kW or 22 kW (single- or three-phase 32A)".


To deliver 22kW at 32A, the voltage supplied to the on-board charger would have to be 688V - which seems very high when I thought UK 3-phase was 400V.



My battery pack would be at 114V, so does the car's charger take a higher input voltage from the external source, and step that down to charge my battery pack at a higher current (> 32A), in order to get to the 22kWH rate?
 

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I note that charging cables are often rated at 32A, and I note that "Fast chargers, all of which are AC, are typically rated at either 7 kW or 22 kW (single- or three-phase 32A)".


To deliver 22kW at 32A, the voltage supplied to the on-board charger would have to be 688V - which seems very high when I thought UK 3-phase was 400V.
I don't know where that quote is from; "fast charging" isn't a specific technical term but usually refers to DC charging. There was a proposed standard for fast AC charging (that is, higher power than Level 2), but as far as I know it was never implemented. Of course the power to the charger is normally AC in types of charging station; "DC" charging just means that the voltage conversion, rectification, and control is done by equipment in the charging station (so only DC at battery voltage is provided to the EV), in contrast to AC charging, in which all that equipment is onboard.

High-power DC charging equipment - at least in North America - is presumably all supplied with 3-phase power, not single-phase.

32 amps at 230 volts (single phase) would correspond to 7.4 kW, a common size of onboard charger and rate of Level 2 AC charging. 32 amps at 230 volts 3-phase would be 22 kW (that's 32 amps in each of three phase conductors) if that 230 V is the voltage seen by each charger section. My guess is that 230 V is being assumed in Europe (although that's out of date); it's 240 V here in North America (and 3-phase power is not available in residential locations). The standardized Euro 3-phase power is nominally 400 V (and actually higher in the UK and lower in most other locations), but if a three-phase supply is 400 V from line-to-line it is 230 V from each line to neutral, so three chargers running in parallel could each run a 230 V single-phase from a 400 V 3-phase supply.

My battery pack would be at 114V, so does the car's charger take a higher input voltage from the external source, and step that down to charge my battery pack at a higher current (> 32A), in order to get to the 22kWH rate?
Yes, the charger (onboard for AC or in the charging station for DC) needs to do any required voltage conversion, and current changes proportionally. For modern road-going production EVs that means raising voltage in the case of AC chargers, since the run on 120 V or 240 V power and EVs all use well over 300 V now. For golf carts and other low-speed vehicles lower battery voltages are still common, so the charger is converting that down. This is a challenge when wanting to charge a battery of a voltage commonly used only in DIY conversions with charging equipment intended for much higher-voltage production EVs.
 

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With a DIY setup tapping into public charge stations, I would aim for being fully self-sufficient.

In other words, rectifying and converting the DC onboard. Accept all the AC input possibilities from standard EVSEs, and maybe standard household 15A 120Vac through 30A & 50A 240Vac in a pinch if doing long trips out into the countryside

That's Stage 1.

Compatibility with (bypass your onboard rectifier/converters) DCFC and Chademo as rolled out in the US can be Stage 2, and you may find that not necessary or at least only worth the trouble later on.
 

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Discussion Starter · #8 ·
I don't know where that quote is from; "fast charging" isn't a specific technical term but usually refers to DC charging.

Hi Brian, the quote's from a UK site that provides maps of charging points, the article is here: https://www.zap-map.com/charge-points/connectors-speeds/


I guess some of the terminology is different between the UK and North America.



I note your explanation of the three phase, three charger route to 22KW. It is beyond my current ability, so I am going to go with a 6.6kW onboard charger, and see how I get on with it for the time being.



I am thinking I may use an Orion BMS2, which can handle the CHAdeMO protocol and as somone helpfully pointed out, it would get me 114V * 125A = 14kW charging -which is not the full 50kW but is better than 6.6kW. I don't intend to implement that on day one though.


So thanks to everyone for replying, it's very helpful.
 

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With a DIY setup tapping into public charge stations, I would aim for being fully self-sufficient.

In other words, rectifying and converting the DC onboard. Accept all the AC input possibilities from standard EVSEs, and maybe standard household 15A 120Vac through 30A & 50A 240Vac in a pinch if doing long trips out into the countryside

That's Stage 1.

Compatibility with (bypass your onboard rectifier/converters) DCFC and Chademo as rolled out in the US can be Stage 2, and you may find that not necessary or at least only worth the trouble later on.
This looks like a good plan to me. Avoiding DC charging means avoiding the likely compatibility problems caused by an unusually low pack voltage, since only the onboard equipment needs to be concerned with pack voltage.

From the cheapest to highest-performance production EVs, they all include a suitable cord to connect the onboard charger to common (non-EVSE) AC outlets (120 V single-phase and 240 V split-phase in North America, "230 V" single-phase and "400 V" three-phase in Europe), and I would definitely want that. Even if just visiting friends and family, this allows destination charging that would not be possible with dependence on EV-specific infrastructure, and of course it allows anyone with an outlet (on a building or a portable generator) to rescue a stranded EV.
 
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