EV MPPT for E-Golf 2020

[CoachX]

Hey guys,

I am new to the forum, I hope this topic has not yet been covered. So I have an E-Golf 2020 and I now designed a 50V to 400V 200W MPPT power electronic that I want to integrate into the car and charge the car from flex solar panels on the roof. I am a of course a little scared to destroy things and in particular the battery, would anyone be in position to answer some of my open questions:

A) Where in the engine room is the best place to tap directly into the 325V battery terminals?
B) Would the car electronic control system throw an error if I just charge the battery directly from my MPPT, so basically bypassing all usual ways of charging the car like from the CCS or 7kW AC charger?
C) Would the car allow me to even start it while its being charged when it detects a positive current into the battery that come from "nowhere"
D) Would the car BMS correctly manage the SOC if charging it directly from the terminals?

Thanks in advance !

[tmotion]

That sound pretty cool! A mppt that can directly feed the HVDC battery. Could you share some more details? There have been several topics on this forum on adding solar panels to a build. In the end most people connected it to 12v.

[celeron55]

In order to be able to feed power into the battery, the contactors internal to the battery case need to be closed, or you have to tap to the inside of the battery which is quite a lot of work. In order to close the contactors you need to make the BMS think the car is either driving or charging. You probably need to set up a CAN bridge for this, to cheat the BMS. You need to make sure as much of the vehicle as possible is actually shut down, othewise you'll easily be consuming more power than you produce.

You need to set up a system to stop charging if the BMS reports any cell is full. If you charge until the BMS opens the contactors, you probably get an error code and a check EV warning light. Or if it doesn't open contactors, you get a battery fire.

You also need to co-operate with the BMS when it does its precharge sequence.

Not a particularly easy project, but could be doable with enough CAN reverse engineering.

[CoachX]

Yes, sure let share some more details.

So here is a picture of the MPPT Electronic I designed since I didnt find a suitable Electronic on the market:

Charging the 12V battery is certainly way simpler but also not really effective since it gets full relatively quickly from 200W PV mounted onto the roof.

So my plan was to simply tap into the main battery terminals directly next to the car's ESC.

I am planning to tap into the terminals here:

failry effortless with what's called a "isolation piercing connector" like that one:

piercingconnector.PNG (125.12 KiB) Viewed 20328 times

The connector is basically eating carefully through the isolation and is desigend for high voltage, high power outdoor applications. Those connectors are typically designed to tap 230V AC transmission lines from the main line (copper or Aluminium). They can be connected "under power".
From the piercing connector I will use a 1.5mm2 Orange cable (to indicate high voltage) to the MPPT with a ca. 60cm long cable. I aim to put a differential fuse into the line so that it detects fault currents for extra safety. There is also a melting ATO fuse on the PCB just in case.

The PV cable will come down on the driver side, entering under the hood through one of the gaps. I want to use 2x 100W monocrystalline flex panels in series that can be bought for ca. 90€/pc on ebay. That would give ca. 36V MPPT voltage and 45V OC and hence a duty cycle of 10% on the MPPT to generate voltage in the range of 300-400V DC on the output. Since there is no galvanic separation between the main battery GND and the PV GND the isolation must be done with greatest care. I realized the car body is not connected to main battery GND but only to the low voltage battery GND. There will also be a melting fuse on the PV input side of the MPPT.

So my hope was that I dont need CAN bus because the BMS is integrated into the main battery. It will do balancing on its own and I dont aim to set the MPPT to top charge voltage but stop significanlty lower somewhere in the "idle voltage range", maybe around 335V or so.

Then I realized behind the 12V battery there is a way to enter the driver cabin through cable trees already entering the car. So I added an SPI bus connector to the PCB so that a small LCD display can be connected showing the current MPPT Power, current and voltage rating. This SPI is galvanically seperated from all data, VCC and GND lines just in case. It's too risky to bring any potential high voltage cable into the drivers cabin otherwise. Atlernatively one could also use an ESP with Bluetooth to display the data on an android phone but since the MPPT is only powered when the sun is up and in any case is working very intermittendly I decided to use just that display.

The MPPT will power cycle using an analogue hysteresis, e.g. swtiching the MPPT operation if voltage on the low side is greater 28V and goes off if lower than 20V. This way it doesn't go crazy in environments of rapidly changing irradince, e.g. when driving under trees or entering a tunnel

[CoachX]

In order to be able to feed power into the battery, the contactors internal to the battery case need to be closed, or you have to tap to the inside of the battery which is quite a lot of work. In order to close the contactors you need to make the BMS think the car is either driving or charging. You probably need to set up a CAN bridge for this, to cheat the BMS. You need to make sure as much of the vehicle as possible is actually shut down, othewise you'll easily be consuming more power than you produce.

You need to set up a system to stop charging if the BMS reports any cell is full. If you charge until the BMS opens the contactors, you probably get an error code and a check EV warning light. Or if it doesn't open contactors, you get a battery fire.

You also need to co-operate with the BMS when it does its precharge sequence.

Not a particularly easy project, but could be doable with enough CAN reverse engineering.

woud you know for fact that the battery behaves like as you describe? E.g. does the BMS really reuqired a CAN communication for persmission to charge? And what about that precharge sequence, is that documented? Because imagine, when recupating while driving the battery inrush current is significant, it is easily > C1 and changed seamlessly from charge to discharge when accelerating or respectively breaking.

[johu]

failry effortless with what's called a "isolation piercing connector" like that one:

You might need to think this over. HV cables in OEM vehicles are usually screened, so coaxial cables. You would pierce through screen and conductor, likely shorting them out on DC+ and DC- and thus shorting DC+ to DC- and to chassis.

[Age]

I thought about the same thing a few years ago with my old Clio electric. I found this company.

I wanted to use something like the ambiCONVERT DC-DC but in 2019 they only had prototypes.

Maybe this will help someone in this matter!?

[CoachX]

You might need to think this over. HV cables in OEM vehicles are usually screened, so coaxial cables. You would pierce through screen and conductor, likely shorting them out on DC+ and DC- and thus shorting DC+ to DC- and to chassis.

OK, you are right. They really seem to be shielded. Any idea where to reach the battery instead?

[celeron55]

You will need to mess with the cables somewhat, probably cutting them in half and adding an enclosure in between. But what you can do is pick which cable to cut.

I would go for the PTC heater or A/C compressor cable. It's relatively thin and easy to work with, and nevertheless 200W is almost nothing to it. Usually there are no extra switches to control that cable so it will be always energized with the rest of the HV system. But check first that this is the case.

By precharge I mean the thing the BMS does when it wants to close the main contactor. It could be that 200W will mess with that, altough if you add a start up delay of some seconds to your controller, it probably will be fine.

If your MPPT board works well, I might be interested in one. I have a 260W panel (30V? 35V? not sure) on my Previa conversion but it currently only charges the 12V system as I couldn't find any MPPT controllers suitable for this. The Previa has a 72S battery so it's 200-300V.

[CoachX]

Sounds good, would you have a picture of where to access those cables on the PTC or Compressor? You drive an EGolf?

So far I have ordered only two prototypes of this MPPT, it's still in the making but I could potentially spare one yes if you want to help a little on the RnD I wrote some basic MPPT PO algorithm in C with an STM32G07. I hope getting away with a 60kHz switching frequency, will use relatively large inductors since this CPU has not HTIM.

[golfdubcrazy]

Nice project,

I have to agree with johu. do not pierce the insolation as the battery module measures the insolation resistance every 60 sec and if out of spec shuts down the battery.

if you connect between the battery and inverter or to PTC / AC pump. the battery wont charge unless the ign is on. unless your planning on sending can bus message to wake up and close the contactors to wake up the system.

Hope that helps

[tom91]

I am fully against this project in its current state. You are planning on using PV panels and equipment that will be referenced to the HV negative battery on the OUTSIDE of the vehicle. This is defeating all the safety goals of the HV system design.

Please think very carefully about what you are trying to achieve and how to do this in a safe manner. Also keep in mind the kinds of risks you will be exposing yourself to and others with these sorts of modifications.

[mjc506]

Scary...

As above, you have a few issues.

First, safety - You do not want anything accessible from the outside of the vehicle that has any connection to HV (positive or negative). As designed, ALL EVs have their High Voltage bus (batteries, inverter, charger etc etc) completely isolated from the Low Voltage (12V) systems and chassis. A properly designed EV will shut down if it detects any connection between either battery terminal and chassis ground. If you want to do this safely, you will need to design (or use) an isolated DC-DC converter with sufficient HV clearances. At least you only have a few hundred Watts to worry about!

Do not try piercing HV cable insulation. At best, bridging the shielding with HV+ or HV- will cause the vehicle to shut down. Or if the BMS doesn't catch it quickly enough, a battery fire. Even if you avoid those scenarios, you've connected your chassis to one side of the battery, leaving it in a very dangerous state. I'm ignoring longer term issues like moisture ingress on the assumption that the car will catch fire long before that becomes an issue. To connect into the HV bus, either cut the cables properly, crimp new connectors, and fit within a suitably IP rated and mechanically robust enclosure. Note that the new connectors will be carrying significant current, and poor crimps will result in malfunctions at best, more likely fire.

Inside the battery pack on all OEM EVs are at least two contactors. These isolate the battery completely (both + and -) from the HV bus when the vehicle is shut down. Feeding voltage to the inverter with these contactors off will, at best, achieve nothing. (And the car may notice voltage on the bus when there should be none and trigger a fault). You will need some way of getting the BMS to close those contactors (including the full precharge sequence). You could decide that you only want to charge with the ignition on (will the power you get from the solar panels exceed any increased losses from increased air resistance?) or perhaps only when parked (this may solve a few problems - generate 50/60Hz 'mains' voltage AC and a CP PWM signal and just plug into the charge port - the charger will handle isolation, waking up the BMS etc etc. But you will get extra losses from converting to AC and back). Hoping to charge at all times will require significant reverse-engineering of the vehicle systems in order to be able to get the contactors closed without upsetting the car.

I applaud your engineering spirit, but there is a lot to learn before working with high voltage DC systems, especially in an automotive environment. There are significant hazards to yourself, property and the general public. You will need, at the very least, a good understanding of how your particular vehicle works (in detail), HV DC isolation and related hazards (DC is much more difficult to handle than AC), and a good understanding (and some practice!) at making connections for HV DC. (Solar connections are similar, being DC, but the voltages and currents you are dealing with here are massive in comparison. Do not solder connections, crimp only, but making good crimp connections is a skill in itself, and requires the right equipment).

Finally, is this all worth it? You're expecting approx. 200W peak from your panels, right? You'll lose a few percent through your MPPT, so perhaps 190W left. Assuming you find a way to safely connect to the HV bus and don't use an onboard charger (no losses from DC-AC and AC-DC etc) you've still got to hold a couple of contactors closed (roughly 10W each?), keep the BMS awake (5W? 10W? Maybe more). You may need to power a coolant circulation pump (15W for a good one at low speed). I suspect you'll need to wake other systems in the car, plus power your own module. Start up power draws will be much higher. That leaves less than 150W going in to the battery even in full sun, not accounting for losses within the cells while charging... How much will all the materials cost you? How much is your time worth? How much electricity (range) would that money buy you if you leave the car as-is?

[CoachX]

Scary indeed, therefore the question how to do it safe. Getting an estimated 2500km free charge per year on an EGolf is quite a nice feature, not so much for the monetary saving but more for the convenience of not having to charge much during the summer months as a city driver without access to ones own power wall.

Anyhow, is there actually some solid documentation on the HV part? Being able to charge the vehicle while parking is vital here. I would doubt the HV is depowered while "ignition" is switched off.

Connecting the MPPT without galvanic seperation is the biggest risk here, making the HV GND line more or less exposed if someone cuts it on the outside body of the car which is indeed not cool. So to make it really safe, using a transformer separating the high and low side from each other seems to be the best way forward and then using a shielded HV cable diversion if someting like that that exists

[mjc506]

HV will be isolated with ignition off. The car may periodically turn it on to power the DC-DC to keep the 12V battery charged, and it will be enabled with ignition on and while plugged in. That's it.

If you just want to charge while parked, use your panels to power a small inverter, add an arduino (or a PWM generator) to generate a CP signal with the right 'current available' signal to match the panel output, and plug it in to the charge port. The onboard charger will then handle isolation, waking the right systems to get the BMS to close the contactors... etc etc. You could even wire into the rear of the charge port (still need to be careful with some wiring having sheilding) if you want 'neater', but will have to handle plug detection (and not enabling the inverter if a 'real' wall charger or granny lead is plugged in - AC phase from your inverter and from the mains is unlikely to be synchronised (this is a solvable problem, but would take some effort) You will lose a fair amount of power from your panels in various inefficiencies, but you probably won't improve much on this with custom power electronics (at best, you lose the DC-AC and AC-DC losses, but an isolated DC-DC converter does pretty much the same thing, albeit with more flexibility on the AC frequencies)

[Dilbert]

I would definitely look to go in via the main ac charge port, not modify the car at all. You could get an off grid inverter as has been suggested above and provide an AC signal to the car. I wonder how many single phase ev chargers would mind if they got a dc supply. A quick look at the power electronics of the charger should reveal any issues.

Damian has had good results with e-golf chargers. If I was going to attempt this (which I am considering) I would get a spare charger and run it on the bench with dc. If you were really clever the control pilot signal could be modified in real time , so the charger provides the mppt function, so no major power electronics required.

I got the gen 2 Prius boost converter working as an mppt using an arduino. I must hack a granny cable at some point and run a signal gen into the control pilot to see how quickly/accurately the charger tracks the control pilot.

It would also be interesting to know the minimum ac voltage that a granny cable and charger will operate from, I could try this with a variac, I assume about 150V to allow for US operation.

[Dilbert]

I have about 1.8kw of panels which would be ideal for charging the car in summer, if it would accept the dc into the on board charger.

If anyone feels brave, variac -> rectifier -> caps -> socket -> granny cable -> charger , would prove the ac charger can take dc. But I would first check out the power stage on the charger.

[CoachX]

I believe it will be difficult to match the Charger input power with the MPPT but I agree most likely connecting DC to the charge port could work in many cases.
But going back to the idea of using an inverter, the 12V battery would function as a buffer so it wouldn't matter if a few extra Watt are drawn from the 12 battery as compensation until the MPP is met, it would make control fairly simple.

[CoachX]

another note on this one... The issue with using the AC port is that the current must be at least 6A @230V as per the PWM protocol used with SAE J1772 plugs so that makes using a small scale inverter like 250W Victron Phoenix impossible and in any case would required not a standard lead acid 12V car battery as buffer but rather a Lithium battery or supercap that could temporarily handle the high discharge current, maybe in a pulsed way while slowly being recharged by the PV.

[Clanarn]

Or.... only charge the 12v battery with solar and call that a day?=)
= DCDC will not work as hard when driving = range.
Maybe find a way to turn off(properly controll) the dcdc above a certain voltage of the 12v battery making sure it only used when needed.

[arber333]

OK, you are right. They really seem to be shielded. Any idea where to reach the battery instead?

You could make an interface using the same socket with the exact same connector on the other side of your splice which would allow you to put your device in line with DC link cables. However you need to think this through since most of the OEMs use some kind of interlock on connectors which will disable the car if tampered with.
I would advise you to splice your device into DC link on the underside where that orange cable is connected to the battery box. You can provide new enclosure with socket side to which OEM cable will lock to and buy a spare EGolf charge cable so you can directly connect to the battery
There is just one problem... OEM EVs usually disconnect main contactors while car is not in use.
You would need to keep the car in charge mode which would open the charge contactor so you can connect behind it...
If you do this correctly not only can you bypass contactors you can also keep the car incapacitated while your device is in use. That would get a long way towards improving safety.

I would think 200W panel is not enough to merit direct connection the way you are intending. But 800W system would be way better.

[arber333]

another note on this one... The issue with using the AC port is that the current must be at least 6A @230V as per the PWM protocol used with SAE J1772 plugs so that makes using a small scale inverter like 250W Victron Phoenix impossible and in any case would required not a standard lead acid 12V car battery as buffer but rather a Lithium battery or supercap that could temporarily handle the high discharge current, maybe in a pulsed way while slowly being recharged by the PV.

Hm... what about small 24V or 48V battery and 1500W AC inverter with EU plug? You could set the PP resistor inside the plug to limit current represented and simulate Cp PWM signal to 6A.
You would need to setup a lower battery limit to stop charging and upper limit to start Cp protocol and charge.
Also consider charging only to 3.9V per cell equivalent so you wouldnt necessarily need connection to BMS... in most cases

I dont think certification specifications would allow for charging without protocol. Might void your warranty or even TUV!

[bigmotherwhale]

If i were you i would go down the CCS route for interfacing the solar array, You can tap into the CCS before the charge port but you will need some kind of relay so that the CCS port wont be live when you are charging from solar.
As i understand it CCS charge current is determined at the charger so it should just be a case of giving the right voltage and the right CAN commands into the car to close the charge contactors, this is not going to be super easy but it is do able.
What Arber said seems also to be a good idea, although the car may have some kind of range calculator based on a current sensor that might get upset if you were to charge direct to the battery.

[whereswally606]

What you have is similar to James at realsolar cars. His system is 300w (limited i think by the transformers he could source, though i might have that wrong)
Anyway i believe his system only works whilst the car is running for safety reasons.

I have been musing this too for my env200 when camping. I think the route i may go is to carry an ecoflow river or delta. Solar charge that (or extend it via the solar port using more batteries) and periodically plug an evse on 6/8amps to top up the van and drain out the powerbank. Bluetti ac200 have good solar mppt 150v max input for this kind of thing too.
Also the ecoflows now have 800w house gridtie via an addon so having dual use could be beneficial.

[EV_Builder]

Using charger logic is what i would do then the car regulates and enables by default every function you need for external addition of energy.
most important one cooling (if needed) and shutdown when done charging?

Tapping into CCS2 wires with relais making choices (real CCS2 or solar) etc. is then possible.
If you ask me you need the CCS2 wall socket side portable into your MMPT architecture.

maybe these guys: http://senkumachinery.com/wallbox-dc-ch ... ation.html

can sell or point you into what you need. you want basically the communication part of them.