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Old 09-13-2017, 12:25 PM   #1
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Solar Hybrid Electric Skoolie Adventure Begins!

Ok, not really. Not that kind of solar hybrid electric anyway, cool as that would be. But a bus electric system powered by solar, using batteries from a Nissan Leaf Electric, and recharged when needed from a Toyota Prius Hybrid.

We're just getting started on our Skoolie journey, and I thought it might be fun to start a thread so you can all see what happens when a EE who dabbles in electric cars, plugin hybrids, and home solar tries to design a Skoolie electric system (and conversion to put it in). Should be entertaining. At least to me. Some day when its all over ;)

If things go to plan (ha!) our family of five is going to take the plunge and start full timing next summer. Enough of the big city and the Phoenix summers already. Hopefully we'll be spending a lot of time out boondocking in places with trees and water, gradually rehydrating from our overlong stay in the desert. We're likely putting down a deposit on our bus this week, a 1997 Blue Bird All American RE 40' Activity bus with transit style windows, under bus storage, freshened Cummins 8.3 and an Allison MD3060.

To that end I'm hoping to design a pretty robust solar electric system to keep us functional out there. I designed and installed a 5.5kW system on our house, so I at least have some idea what I'm in for. My basic thought going forward is to try and model the design more on off grid homesteaders, whose systems are geared toward maximal efficiency, rather than traditional RVs which seem based more around convenience and presumed access to utilities.

I also have two assets to start with that I'm hoping will come in handy. One is a complete functional disassembled salvage Nissan Leaf. The other is a Toyota Prius that we will likely dolly behind the bus. At a minimum the Leaf will probably be donating its battery pack to the bus, about 15kWh of Lithium batteries weighting 400lbs and about the size of suitcase. High on my list of favorite stupid Prius tricks is the little know fact that you can tap into the High Voltage battery and draw up to about 5kW (maybe as high as 9) without any modifications, and the engine will kick on and off as needed to keep it's own battery in a safe operating range. That would at least give us a backup power source without having to worry about a generator. And when we do need to use it, it should be as efficient as the best diesel generators, with emissions approaching the best propane models.

So here's my basic plan, still lots to be fleshed out. It's pretty much all based around that big Leaf battery, most likely reconfigured to 48V. Primary charging is from solar, with options for charging from the Prius, shore power, or the bus alternator when driving. Having a way to charge the bus battery off the 48V also seems like a nice backup.



About the only piece of equipment I've looked into in detail is the Morningstar Tristar MPPT 600V charge controller which should work equally well for charging the 48V battery off the Solar or the Prius's 230VDC output. It could also handle a wind turbine should we decide to add one for overnight charging.

If I can figure out a way to keep the Leaf battery in it's original 360V configuration, there might be some other goodies I can use as well. The BMS and 3.6kW charger for sure, and possibly the electric AC compressor and coolant heater as well. But 360VDC compatible inverters seem to be a bit rare. I wonder how hard it would be to modify the 80kW drive inverter to put out 120/240V AC at 60Hz

I've also been working on a spreadsheet to start modeling our usage, to get a better sense of sizing for the inverter, solar and battery. Not much real data in there yet, but the solar output is scaled off our home system production, and the frame work is in place so we can model basic appliance usage and cycling loads like the fridge and AC once we have better consumption numbers.



Rob
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Old 09-13-2017, 12:45 PM   #2
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Post often with lots of pictures. I drive a Chevy Volt and have often wondered how I could incorporate a similar battery pack into my build.

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Old 09-13-2017, 01:09 PM   #3
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Sounds fun Rob, I'll be watching!
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Old 09-13-2017, 01:11 PM   #4
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If I can figure out a way to keep the Leaf battery in it's original 360V configuration, there might be some other goodies I can use as well. The BMS and 3.6kW charger for sure, and possibly the electric AC compressor and coolant heater as well. But 360VDC compatible inverters seem to be a bit rare. I wonder how hard it would be to modify the 80kW drive inverter to put out 120/240V AC at 60Hz
I don't know if you're going to find an inverter that natively accepts 360vdc. Maybe you could run the 360vdc down to 170vdc and feed it into the high side of an SMPS high frequency transformerless inverter?

Starting with high voltage dc means you're already part of the way there. Usually a major piece of an inverter is boosting the dc up from battery voltage levels of 12-48vdc.
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Old 09-13-2017, 01:37 PM   #5
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I don't know if you're going to find an inverter that natively accepts 360vdc. Maybe you could run the 360vdc down to 120vdc and feed it into an SMPS style high frequency transformerless inverter?

Starting with high voltage dc means you're already part of the way there. Usually a major piece of an inverter is boosting the dc up from battery voltage levels of 12-48vdc.
Agreed. It's really bugging me to have to go down to 48V. I'm going to keep digging, but ultimately there will have to be a tradeoff between time, cost, and efficiency. In the limit I know I could do this all full custom and do it the way it should be, but given the realities of life it would probably take me a couple years to complete ;)

Rob
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Old 09-13-2017, 01:57 PM   #6
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Quote:
Originally Posted by T-Bolt View Post
Post often with lots of pictures. I drive a Chevy Volt and have often wondered how I could incorporate a similar battery pack into my build.

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I was able to do 2 kinds of taps into my Volt when I had it, I first was ablew to gain 2000 watts continuous from the 12 volt system, and it worked well.. and did just as the OP described, the engine started pewriodically to keep the battery charged... and that worked well...

I then tapped the 360 Volt DC battery (carefully and what a TOTAL PITA!!!). and had a friend who worked for a compant that makes power conversion devices loan me a DC to AC inverter (10 kw).. and it worked.. EXCEPT that it caused the volt to throw codes related to the battery system .. for awhile the engine would start and stop as needed.. but at one point the engine shut down and marked itself as Unavailable and the car turned off so no more charging... without a full power-off reboot of the car..

now im sure there are more tactile ways to do this than just buying the connectors and making big old honkin Y-cables like we did from the main battery to the vehicle and to the external inverter.. it was purely experimental so not too much pre-thought went into it as making it permanent..

it was another one of those "I was bored lets do some crazy experiment moments"..

-Christopher
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Old 09-13-2017, 02:12 PM   #7
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Very cool, Christopher!

Same idea on the Prius, only difference is people have had more time to mess with them over the last 15 yrs. A lot was leveraged off the learnings of the early efforts to add plugin in packs in terms of understanding the limits of the hardware/software. The Prius has a 100A 12V dc:dc converter, so you can run up to 1.5kW or so off the 12V system. The high voltage system is monitoring current in and out various components and will throw an error and shut down when it senses too much unexplained draw. The limits are in the 20-30A range, so 5kW is pretty safe. The Enginer plugin packs exploited this method to feed charge into the system through a dc:dc converter keeping the current below the limit. Higher power/current plugin conversions had to add an additional custom CAN controller to keep the system happy by spoofing certain commands.

Here are some examples of past projects using the Prius for backup power for anyone that's interested.

http://priusgen.sandbox.org
http://www.priups.com
http://hiwaay.net/~bzwilson/prius/priups.html
http://www.converdant.biz/home



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Old 09-13-2017, 02:36 PM   #8
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this is some cool stuff using the Prius!.. and it looks like more refimninmg has been done so it works better.. the Prius has a similar system to the volt.. people claimed 1500 watts is all you could get from the DC-DC inverter.. however I pulled 2000 off mine and never burned it up.. I supposed some wattage couldve been coming from the battery however I never ended up wit ha dead 12 volt battery.. and it wasnt that big.. so i have to believe the inverter itself was pushing most of that power if not all of it.

but going from the 360 volt to 120 VAC seems like the best way to go.. eliminating the 12 volt middleman.

does the Prius engine run efficiently like you speak of when its cold too? the issue I found was the engine on the volt never warmed up.. I used the 12 volt inverter method out of necessity after an ice storm took my power.. i had a full tank of gas in the car.. those 2000 watts ran my modern gas furnace and refrigerator and some lights perfectly...

the OBD2 monitor showed my gas engine never got into its efficiency zone.. as it did a start-run-stop cycle.. and since the onboard generator is huge it didnt run very long when only pulling 2KW so it spent more time off than on.
-Christopher
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Old 09-13-2017, 03:08 PM   #9
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Agreed. It's really bugging me to have to go down to 48V.
Rob
You might be able to use a pre-built EGS002 pcb unit to start with. That little board integrates an EG8010 signal generator with an IR2110 mosfet driver. Various regulating and control bits for a sine wave inverter are already on the logic board. Some versions come with a display screen.

The IR2110 chips should be able to drive multiple mosfets per leg for increased capacity. Feed the whole thing with 170vdc and you'd just have to dial in capacitor and inductor values on your output filter to get nice clean 120vac.

On the other hand, you might be able to find an inverter with a blown input stage and salvage a pre-built high-side that way.

Though, as you point out, there does come a point when you just don't have time to re-invent any more wheels. It would be a great project, though.
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Old 09-13-2017, 04:33 PM   #10
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all good thoughts..
I am using nissan leaf and also chevy volt packs in both our electric solectria vehicles.

Talking about DC to ac converters. I am using apc surt8000 series . That is ac-dc -dc to AC UPS and can run full time of DC. The internal small battery bank is192 Volt positive and negative so total 384 volt. That is pretty close to chevy volt and leaf batteries alike. Best part .. they are very cheap used, come with all the software gadgets and pure sine wave.


On the leaf batteries we are using the original BMS system.
The volt's BMS is a little harder to crack.

later J
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