How should I design this EV battery system?

Batteries, Chargers, and Battery Management Systems.
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bigchief   100 mW

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How should I design this EV battery system?

Post by bigchief » Feb 06 2017 6:00pm

I currently have 14 Tesla 24v battery modules (75kwh total) and I'm going to wire them in series for 312v nominal for an EV.

There's two ways I want to charge the battery pack:

1) From any standard J1772 public charge station (PlugShare, etc.) at a minimum of 6.6kw charge rate

2) This is a box-van type vehicle (like u-haul truck) with a flat roof with room for ~1800w of solar panels, so I want to rig those up and charge the battery with a Solar MPPT charge controller. They max out around 48 vdc output, so I have to find an efficient way to step that up to ~350vdc for the battery pack.

What I'm trying to figure out is:

- Choice of onboard J1772 charger (I'm considering the eMotorWerks SmartCharge-12000)

- Choice of BMS (I'm considering the Orion BMS)

- What is the most efficient way to convert 48vdc output from the Solar MPPT up to the ~350vdc that the battery pack should be charging at? Anything off-the-shelf for that purpose?

- I would prefer if the solar panels could be "always charging" regardless of whether or not the J1772 plug is charging the car as well, but I assume there is no battery charger that can manage an incoming AC feed and DC feed at the same time, and that using two chargers in parallel would affect their ability to read the pack voltage correctly. Should I just use relays/contactors to switch off the solar panels when plugged in to a public charger?

Thanks for the help, I'm trying to plan out the most simple way to approach this.

Punx0r   100 GW

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Re: How should I design this EV battery system?

Post by Punx0r » Feb 13 2017 5:42am

Your project is a bit out of scope for most people on this forum - you might find more information on the diyelectriccar forum.

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wesnewell   100 GW

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Re: How should I design this EV battery system?

Post by wesnewell » Feb 13 2017 11:46am

Not into solar, but why not just hook the panels up in series to get the desired voltage of ~350VDC, then hook them direct through power diodes to the battery pack.
Need Advice? https://endless-sphere.com/forums/viewt ... =3&t=66302
Mongoose 26" Ledge 2.1 mtb bike $99, yescomusa.com 48V 1000W rear hub kit $200, Hua Tong 72V 40A controller $35, 10ah 24s lipo $217=~43mph, range=45 miles @ 20mph. 25K miles and still going strong.
Huffy Fortress 3.0 with MXUS 3000 4T motor, 24s lipo, 96V 60A controller. Total cost with extras <$700. Top speed ~50mph
My videos https://www.youtube.com/channel/UC0KW4U ... _G2wQhptMg

bigchief   100 mW

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Re: How should I design this EV battery system?

Post by bigchief » Feb 13 2017 5:19pm

wesnewell wrote:Not into solar, but why not just hook the panels up in series to get the desired voltage of ~350VDC, then hook them direct through power diodes to the battery pack.
Well, charging needs to be more controlled and tapered when charging lithium ion.
Punx0r wrote:Your project is a bit out of scope for most people on this forum - you might find more information on the diyelectriccar forum.
OK, I'll ask around there, thank you.

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amberwolf   100 GW

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Re: How should I design this EV battery system?

Post by amberwolf » Feb 13 2017 6:28pm

You can also check Kiwi Ev's threads here on ES. He uses solar for charging his homebuilt EVs.

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wesnewell   100 GW

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Re: How should I design this EV battery system?

Post by wesnewell » Feb 14 2017 1:51am

bigchief wrote:
wesnewell wrote:Not into solar, but why not just hook the panels up in series to get the desired voltage of ~350VDC, then hook them direct through power diodes to the battery pack.
Well, charging needs to be more controlled and tapered when charging lithium ion.
As long as you never exceed max no load voltage, there won't be a problem. Think about putting the panels in series and what the actual charge rate would be. Probably no more than 0.5C from 1800W of panels in series. Do the math, keep it simple.
Need Advice? https://endless-sphere.com/forums/viewt ... =3&t=66302
Mongoose 26" Ledge 2.1 mtb bike $99, yescomusa.com 48V 1000W rear hub kit $200, Hua Tong 72V 40A controller $35, 10ah 24s lipo $217=~43mph, range=45 miles @ 20mph. 25K miles and still going strong.
Huffy Fortress 3.0 with MXUS 3000 4T motor, 24s lipo, 96V 60A controller. Total cost with extras <$700. Top speed ~50mph
My videos https://www.youtube.com/channel/UC0KW4U ... _G2wQhptMg

bigchief   100 mW

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Re: How should I design this EV battery system?

Post by bigchief » Feb 16 2017 5:39pm

wesnewell wrote:
bigchief wrote:
wesnewell wrote:Not into solar, but why not just hook the panels up in series to get the desired voltage of ~350VDC, then hook them direct through power diodes to the battery pack.
Well, charging needs to be more controlled and tapered when charging lithium ion.
As long as you never exceed max no load voltage, there won't be a problem. Think about putting the panels in series and what the actual charge rate would be. Probably no more than 0.5C from 1800W of panels in series. Do the math, keep it simple.
Simple, yes, but it seems there would be two problems:

1) If all the solar panels were in series, a single shaded, faulty or dirty panel would kill the output of the whole array, I believe. Putting them mostly in parallel would give it some resilience?

2) If I wired them all in series, wouldn't that mean that I've have a live 350v line exposed on the roof at the solar panel junction? That seems very dangerous compared to running a 48v line to an MPPT near the battery, where it can then step it up to the pack's 350v in a place that isn't as exposed.

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wesnewell   100 GW

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Re: How should I design this EV battery system?

Post by wesnewell » Feb 17 2017 10:28am

1 Don't have any dirty, shaded, or faulty panels. With higher voltage you can use smaller wire. as the max amperage will be many times less, allowing for better transmission of power. Even in parallel, you'll lose the power of the bad panel.

2 Don't have any exposed connections.

Like I said, I' far form a solar system expert, but basic dc electricity is pretty simple, and simple is usually better.
Need Advice? https://endless-sphere.com/forums/viewt ... =3&t=66302
Mongoose 26" Ledge 2.1 mtb bike $99, yescomusa.com 48V 1000W rear hub kit $200, Hua Tong 72V 40A controller $35, 10ah 24s lipo $217=~43mph, range=45 miles @ 20mph. 25K miles and still going strong.
Huffy Fortress 3.0 with MXUS 3000 4T motor, 24s lipo, 96V 60A controller. Total cost with extras <$700. Top speed ~50mph
My videos https://www.youtube.com/channel/UC0KW4U ... _G2wQhptMg

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