iainventor
Posts: 6
Joined: Tue Jun 12, 2018 9:03 pm

Homemade EV HVDC Battery Charger

Tue Jun 12, 2018 9:33 pm

hi there

I am experimenting with building my own EV charger and range extender. I am hoping someone on here can help me. I am thinking of using a few 5kw hr refurbished Tesla battery packs = 90 x 4.1 volts charged lithium ion in series something like 369 volts full pack.

And what is the nominal voltage of the i3 60 AH battery. what constant charging voltage does it take to recharge the battery ?

And then creating my own battery charger for the 5kw hour brick , maybe to match the BMW i3 pack will need to take a few 4.1v lithium cells out and then though what voltage is the nominal and charge voltage that I would need for my homemade charger to match the onboard EV pack?

thanks Im probably leaving out something want to build my homemade range extender to tie into BMW i3 HV DC power cables and flip a switch while driving to charge and drive with my added lithium ion packs.

thanks in advance

iainventor
Posts: 6
Joined: Tue Jun 12, 2018 9:03 pm

Re: Homemade EV HVDC Battery Charger

Tue Jun 12, 2018 11:44 pm

i just found tech manual said nominal voltage 360 VDC can be as low as 290 VDC and as high as 396 VDC. Said 98 batteries X 3.75 VDC nominal in series = 360 VDC

So then the 369 VDC of the refurbished Tesla Pack should at least charge to the output voltage of 360 VDC when put in parallel then going to splice the V+ and V- at power line from battery to EME and put blocking diode and NO contractors as well between my extra pack and EV battery to turn on only after EV startup then turn on the contractors to my pack and feed high voltage dc into the path of battery and EME.

And I think just like on a Leaf I seen the guy had to turn off the power of his pack before the EV was shut down.

might work will know in about a week or so.

has anyone on this site ever done this before? If so, any luck or what issues came up?

jadnashuanh
Posts: 3881
Joined: Thu May 22, 2014 2:07 pm
Location: Nashua, NH USA

Re: Homemade EV HVDC Battery Charger

Wed Jun 13, 2018 6:45 pm

THere is a communications protocol that must be negotiated for a CCS charge to properly occur. The two line voltage pins, when trying to do a CCS charge get serial data superimposed over it that communicate between it and the car. This tells the CCS unit what voltage the car wants at the moment so that the charging rate is not going to damage things.

I'm not sure the car will actually charge itself without that communication and interlock functionality. It could be a very expensive experiment if you get it wrong. The actual specifications document, I'm sure, can be purchased, but you might have trouble finding it on-line for free.
Jim DeBruycker
2011 535i x-drive GT, 2014 i3 BEV

iainventor
Posts: 6
Joined: Tue Jun 12, 2018 9:03 pm

Re: Homemade EV HVDC Battery Charger

Sat Jun 16, 2018 12:01 pm

thanks, for your input. the 2014 model I have doesn't have a ccs just level 2. I was just going to splice the hv dc battery cable between battery and inverter power.

jadnashuanh
Posts: 3881
Joined: Thu May 22, 2014 2:07 pm
Location: Nashua, NH USA

Re: Homemade EV HVDC Battery Charger

Sat Jun 16, 2018 4:43 pm

iainventor wrote:thanks, for your input. the 2014 model I have doesn't have a ccs just level 2. I was just going to splice the hv dc battery cable between battery and inverter power.

IMHO, seems like a good way to fry your i3...dealing with high voltage, high current requires some very good understanding of the system. While the standards for hooking up a CCS certified device to a vehicle with the proper hardware is available, figuring out what the actual car's hardware is is proprietary verses being an open standard for the CCS unit itself and it's interaction with the vehicle attached. There are both safety interlocks and serial datalinks between a CCS unit and the vehicle. Then, you'd also have to activate the cooling circuits and charging logic that monitors charging to prevent overcharging or overheating, or risk damaging the cells themselves, and any other devices that may be connected to the HV.
Jim DeBruycker
2011 535i x-drive GT, 2014 i3 BEV

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