DIY Electric Car Forums banner

New EV Charger Design - Modular

43548 Views 68 Replies 14 Participants Last post by  PStechPaul
After delving deeply into the EMW 12 kW DIY charger, I think it would be best to make a new design. My concept is to make modules, each of which can be used on 120 or 240 VAC single or three phase, or up to 300 VDC. The modules would be 1.2 kVA for 120 VAC, and 2.4 kVA for 240 VAC or 300 VDC. They will be capable of being connected in parallel to obtain higher power. I think these modules could be built for a parts cost of less than $150 each. ;)

The IGBT I show here is an ultra-fast 35A 600V device that is designed for switching applications up to 100 kHz, so I think the inductor and capacitor size and cost may be greatly reduced. And this part is only about $1.50. :)

Here is a "first shot" at this design. It has been done using Mentor Graphics PADS 2004 and most of the parts are fully characterized with part numbers and approximate cost, as well as PCB decals so that a board can be made directly from the schematic. A BOM in Excel format can also be produced easily with a VBA script.

Here is a PDF which is a little easier to read:

And the BOM (preliminary) showing total parts cost less than $150:

This version is not PFC and non-isolated. It also has only a single pushbutton for start/stop, does not have a BMS connection, and has no display. But it has a serial port which can be connected to a Bluetooth module for viewing and logging data, and for commands. I am using only a 14 pin PIC16F1825 but it will probably need a 28 pin processor to provide the additional I/O needed. I have an Arduino UNO and I will try to add the connections to match its pinouts. I might also see if I can adapt the EMW control board with its display and function keys.

I am putting together an order to Mouser for some of the parts I will need for this design, and I am also going to get an AVR Dragon which is a $53 emulator/debugger/programmer which is really the very minimum needed for development of any serious design with the Atmel series microcontrollers. I plan to use this for analyzing the EMW charger (when I get a complete unit or the boards and parts needed), and hopefully be able to provide recommended modifications to the hardware and firmware to improve the reliability and performance. I think it may require a complete new set of boards, but many of the expensive components may be able to be re-used.
See less See more
1 - 12 of 69 Posts
Hi Paul, thx for sharing, curious what the motivation is here though (good learning experience if nothing else). Couple thoughts (hope you don't mind):

The original $200 charger thread was also a buck converter. IIRC using a mig reactor at 10s of khz, doing 350v and 35A. It morphed into the multi thousand dollar EMW.

The onboard (inverter) charger thread could use a buck stage, relegating the motor coils/bus caps to 60hz pfc. I'm gonna be busy refining the series cap approach (and other sub-projects) for my own purposes. Getting a charger sorted was the missing piece.

You are going to be playing by yourself if it is all done in Mentor Graphics.

While 8 bit is probably sufficient, there are lots of offerings from atmel (and others) that could probably reduce the external parts count a bit. (differential adc, 20x gain, etc).

There should be some economies of scale, i.e. the "power" section is the only modular part.

Toroids are nice at higher freq. powdered iron will handle higher power levels better than ferrite.

The relay/cap thing is kinda perplexing.

Have you considered the pros and cons of buck-boost (i.e. CUK)? Buck or boost only are always of limited flexibility. A well considered cuk can have good power factor without huge storage caps and be adaptable to a fairly wide range of input/output voltages with one switching element (if I understand it, probably some gotchas I haven't considered yet). Some of the most efficient converters are CUK.
See less See more
I like the idea of a transformer design where the inductive components are used to transfer power rather than store it and retrieve it as is the case with single inductor buck/boost/flyback designs. Once the needed voltage is available, then a rather simple buck circuit can be used as a current source for charging.

The magnetics are the trickiest bit to me (various core materials, flux densities, curie temps, etc etc etc). If you wan't isolation and lots of power, that typically means large iron core 60hz transformer, not well suited for onboarding. Unless you chop the input into higher frequency of varying amplitude, which is where pfc starts. I don't know how big a deal isolation is in general though, plenty of chargers don't seem to care. As well it seems like the isolated section would need it's own gfci, not sure of the value of the whole proposition, seems a little arbitrary overengineering to my naive self. But I don't think any of my home appliances have isolation (except as legacy transformer wall-warts, and even the newer adapters are not all that isolated, I get plenty of tingles with my bare feet using usb adapters).

FYI the CUK is a two inductor setup. You might be interested.
  • Like
Reactions: 1
I took a peek, this doesn't match the schematic in the screenshot FYI. Also 340 is probably more accurate than 320 (2x170)
fyi, inspired by the original $200 charger, I grabbed a few of these

$5 is hard to beat (green transflexive, don't use blue, it sucks night and day)
it only has 2 pwm and 5 adc left after the lcd pins, but that might be enough for a lot of things. Has INT0/1 exposed too. And of course duo/uno clones are like $10.
I was playing with LT1249, then I remembered this thread.

I was thinking that instead of arbitrary 500watt, that since the most you can get out of a 120 wall socket is ~1.5kw, that would make a better target, but makes good PFC critical as well (and efficiency, so continuous mode is important there).

The LT1249 has some "magic" that sorts out the best switching pattern (I'm sure it can be done in software too) but it takes a few cycles to get everything in sync (more than 30ms), but it can provide terrific power factor with low THD. I attached the log output and a pic. I need to experiment with more practical inductor values.

start: 180ms=0.18
end: 280ms=0.28
p: AVG(-v(+,-)*i(v1))=1471.16 FROM 0.18 TO 0.28
vrms: RMS(v(+,-))=120.208 FROM 0.18 TO 0.28
irms: RMS(i(v1))=12.2759 FROM 0.18 TO 0.28
s: vrms*irms=1475.67
pf: p/s=0.996947
pout: AVG(v(out)*v(out)/110)=1428.388 FROM 0.18 TO 0.28
eff: pout/p=0.970928


See less See more
here it is with a much more obtainable 110uh inductor:
start: 180ms=0.18
end: 280ms=0.28
p: AVG(-v(+,-)*i(v1))=1467.76 FROM 0.18 TO 0.28
vrms: RMS(v(+,-))=120.208 FROM 0.18 TO 0.28
irms: RMS(i(v1))=12.4954 FROM 0.18 TO 0.28
s: vrms*irms=1502.05
pf: p/s=0.977173
pout: AVG(v(out)*v(out)/110)=1401.51 FROM 0.18 TO 0.28
eff: pout/p=0.954859


See less See more
one of the challenges is to have the right buck inductor(number of turns and gauge) for a given output voltage (something I dont see in the EMW) so that you can deliver the "advertised" 1.5-2kw for various battery voltages.

There may be some optimizations in boost inductor selection for a specific battery voltage too, but it isn't critical.
Problem is the buck inductor (and switch/diode) is what needs to be flexible. if you are thinking transformer for isolation, typically that is part of the pfc side (and introduces extra magnetic components and rectifiers/switches)

I assume you want smooth power to the battery, i.e. some sort of buck converter feeding a battery instead of just a resistor there, and want pfc so you can get the most out of a 20A breaker. There may be a way to switch the transformer for good pfc without an additional inductor, haven't worried about isolation too much so I haven't thought about it really.

So a multi-winding buck inductor is probably more appropriate than a transformer, unless you have a different pfc/regulation scheme in mind. But it is still an interesting idea, some jumpers for different output voltages.

(and the advantage here is that you can use a high frequency transformer for isolation, as opposed to a 50hz transformer on the input, if you want isolation, but still a buck stage is an appropriate addition for a battery charger)
See less See more
It's looking smooth zoomed out, I find that a battery with a low esr is a lot more challenging than a resistor though, minor voltage fluctuations result in large current swings in the load. Post the asc if you would please, I would like to experiment with it a bit.

edit, disregard, got the link :)

edit2, looking pretty smooth with a 312.58v battery @ .2 ohms, and ferrites are cheap and don't like dc offset anyway.. will have to chew on it a bit.
I would say that three phase is not really the target market for a 1.5-2kw charger. The common denomiator for @home charging has to live with 100 amp service @ 240v. The next thing to look at is all the j1772 evse's out there, where the common denomiator is 240v and 30 amp as far as I know.

So probably 240v/30A or 7.2kw or 4 x 1.8kw will get you %98 market coverage, with "emergency" 120v capability.

3 phase is nice to have, but a little elitist at this point in time.
Well here we normally use 3x 230VAC single phase L1,L2,L3 and are fused at 16A towards N.
That adds up to 11kw, you will have a hard time getting 10k out of that without pfc per phase. but 6x 1.8kw pfc chargers would be a good fit if they can play nicely together.
I intend for this to be a collaborative open source effort to develop a relatively simple, robust, reliable, and inexpensive product. :)
Check out kicad, open source schematic/pcb tool (good for collaborating), runs on linux (open source operating system) and windows/crapple. Makes baby food files directly (gerber).
1 - 12 of 69 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.