DC/DC converter box for solar panel on EV?

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Peter C in Canberra
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DC/DC converter box for solar panel on EV?

Post by Peter C in Canberra »

Hi,
Feel free to join in some idle speculation if you feel like it...
Thanks........
I know it would probably be better value to put an extra few cells in the car and put an extra few PV panels on my roof since my roof stays in the sun whenever it is available.
Also, I understand that if I put a rigid panel on a roof rack I could lose as much in extra drag as I might gain from the panel.
I also realise that the amount of solar power I could get from the car roof with even the best PVs would not push it very far down the road.
Nonetheless, I do keep coming back to thinking about some solar trickle charging when my car is sitting in the carpark all day at work.
I have seen various flexible PV cells that might be attached to the bonnet and roof. I don't like the idea of putting the PVs in series up to battery voltage (144V nominal). That would put dangerous voltages within reach and be hard to make both safe and neat.
Instead I am thinking that I might have low voltage PVs paralleled. These might put out a variable voltage depending on the amount of light that would feed a DC/DC converter box that outputs a regulated 160V (say). That could trickle charge through my TBS gauge's shunt so the gauge would register the battery charging. I have the EV power BMS so I could arrange for its over-voltage sensing to cut off the solar charging if any cell were going too high.
So, does anyone know if one can buy a DC/DC converter device that can be used for this purpose? Alternatively, is there a design I could build somewhere?
Thanks,
Peter
Daihatsu charade conversion 2009-18, Mitsubishi iMiEV 2013-2019, Holden Volt 2018-2019, Hyundai Kona 2019-present on the ACT's 100% renewable electricity.

Tritium_James
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DC/DC converter box for solar panel on EV?

Post by Tritium_James »

You want more than a plain DC/DC, to get optimal power out of the cells you want the DC/DC to also be a Maximum Point Power Tracker (MPPT). This is where it makes sure that the current/voltage on its input is the maximum that the solar cells can put out for the light level/temperature/etc. Having a MPPT as opposed to a converter that just draws a constant current or similar can make a large difference (30%? depends on the exact situation) to the power produced by the cells.

Having said that, I'm not sure where to recommend getting one, but they are used by EVERY solarcar team, so something like what you want is probably available. Most solarcar teams are running high voltage gallium arrays though, so usually have a buck converter, not boost.

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Johny
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DC/DC converter box for solar panel on EV?

Post by Johny »

Hi Peter
Firstly I would think that there is a way to double insulate the wiring from the panels so it is safe to have them in series - by far the most efficient way to do this. The right size sleeving and silicon sealant???

If you want to do the parallel thing then a cheapy 12VDC to 110VAC inverter most likely will have a high voltage DC rail inside it.
The reason I think this is:
I bought a 12V to 220VAC, 150 Watt inverter for $20 on eBay that uses a PWM chip and 2 FETs to invert up to 300 odd volts DC (at 15kHz) then uses another PWM chip to drive 4 IGBTs (little baby ones) to produce the 220 VAC from that DC rail. (I pulled it apart to see how it worked.)

Tapping into the DC rail (I estimate would be 154 VDC) would be quite easy (IMO). I am sure there are a number of us that would be happy to help with the reverse engineering side of things if your want to investigate this low cost, high risk (of failure - from the point of view of wasting $20) path. Image

I'd still go the series route though...

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acmotor
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DC/DC converter box for solar panel on EV?

Post by acmotor »

How to tap into the DC rail and get 154V if the DC is most likely to be 230 x 1.4 = 322V ? You need the 110V version of the inverter ?
Nice idea though. Should be 90% efficient or so.
The other way is the battery breakup to 48V that I use. Easy to fit solar panels at safe voltages then.
Personally I park the vehicle in the shade though. Image
iMiEV MY12     110,230km in pure Electric and loving it !

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Johny
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DC/DC converter box for solar panel on EV?

Post by Johny »

acmotor wrote: How to tap into the DC rail and get 154V if the DC is most likely to be 230 x 1.4 = 322V ? You need the 110V version of the inverter ?
I wasn't clear enough.
Johny wrote:If you want to do the parallel thing then a cheapy 12VDC to 110VAC inverter most likely will have a high voltage DC rail inside it.
The reason I think this is:
I was basing using a 110 VAC version on my experience with the 220 VAC one.

Acmotor brings up another point though (don't think he meant to) that the gain in SOC from using PVs in the sun is offset from extra cell heat from parking in the sun degrading cell life. If you HAVE to park in the sun (as I do) then ignore this point.

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acmotor
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DC/DC converter box for solar panel on EV?

Post by acmotor »

Yeah sorry, your encryption was quite effective (probably I was still asleep). Why did I doubt you !!! Image

I'd need 300W of PV (at 48V) for the day to charge my pack after a 10km drive. It just doesn't make sense to buy that ( $2500 +) and cart it around and park in the sun and....and.... I settle for a 5W panel to trickle the 12V aux battery all the time.

Fit the solar panels on your house and grid connect them.... better use of the money IMHO.

A carport in the carpark with a solar panel roof would be a good idea for a public charging station. People would want an EV so they could park in the shade ! Image

I do understand the 'statement' that a PV makes on an EV. As I say I have a 5W panel. People think it powers the vehicle. I leave them to it.   Image
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Johny
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DC/DC converter box for solar panel on EV?

Post by Johny »

acmotor wrote:I do understand the 'statement' that a PV makes on an EV. As I say I have a 5W panel. People think it powers the vehicle. I leave them to it.   Image
Yes, I get that a lot when I am describing what I am doing "are you going to have solar cells?". I am planning a small panel powering a PC fan to keep the boot area (and cabin if enough power) ventilated during the day though. Panel(s) may be mounted on the rear parcel shelf - heat might be an issue though - still thinking. Image

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acmotor
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DC/DC converter box for solar panel on EV?

Post by acmotor »

Just like parking a genIII prius in the sun !! Image

Peter, PV's in parallel solves some of the 'reduction of whole system power when 1 cell is shaded' problem that PVs in series have.
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Simon
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DC/DC converter box for solar panel on EV?

Post by Simon »

Peter C in Canberra wrote:
I have seen various flexible PV cells that might be attached to the bonnet and roof.

I think the flexible panels are too expensive and large. (Over 3 times the surface area of a normal panel)

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