veimi
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Location: Toronto Canada

The Necessity For Grounding An External Gasoline Generator Used For Emergency Charging?

Sun Oct 01, 2017 3:50 am

Some time ago when considering an electric car, I was curious about the cost of using an emergency backup gasoline generator to charge the car.

Taking into account the efficiencies, my calculation resulted in an equivalent mileage of about 25 miles per Imperial gallon, not much different than a typical internal combustion car if it became necessary to use the gasoline generator in case of a power outage.

When I posted this on the smartcar forum, it was brought to my attention that this wouldn't work unless the gasoline generator was physically grounded with a grounding rod connected to its chassis and actually driven into the ground. Although I understand the safety reasoning for doing this, I found it difficult to understand how the electronics could sense that the charger (in this case the gas generator) had been physically grounded.

My question is this. Would not the same result have been achieved by connecting the neutral output of the generator to the chassis (ground lead) of the generator?

Also, why is the possibility of using an inexpensive gasoline generator not mentioned more often as a viable alternative to counter potential range issues when taking longer trips.

I was hoping that anyone with more experience in this matter could comment.

JoeS
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Re: The Necessity For Grounding An External Gasoline Generator Used For Emergency Charging?

Sun Oct 01, 2017 5:36 am

veimi, we have quite a few threads on this topic - here's a discussion/solution for 120vac:

http://myimiev.com/forum/viewtopic.php?f=24&t=358#p1446

I'd be interested in seeing your efficiency calculation when using, for example, a Honda EU2000i generator to charge the i-MiEV batteries.

While a small genset will work in an emergency, think how long the darn thing would have to run to result in any meaningful range in the i-MiEV. Yes, a 240vac genset would be better, but need to find one that puts out 3.5kW and is still portable...

Besides, carrying gasoline inside an electric car... :o :twisted:
EVs: 2 Wht/Blu SE Prem., '13 Tesla MS85, 3 156v CorbinSparrows (2 Li-ion), 24v EcoScoot(LiFePO4)
EV Conv: 156v '86 Ram PU, 144v '65 Saab 96
Hybrids: 48v1kW bike
ICE: '88 Isuzu Trooper. Mothballed: '67 Saab (orig.owner), '76 MBZ L206D RHD RV

Don
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Re: The Necessity For Grounding An External Gasoline Generator Used For Emergency Charging?

Sun Oct 01, 2017 8:11 am

veimi wrote:When I posted this on the smartcar forum, it was brought to my attention that this wouldn't work unless the gasoline generator was physically grounded with a grounding rod connected to its chassis and actually driven into the ground. Although I understand the safety reasoning for doing this, I found it difficult to understand how the electronics could sense that the charger (in this case the gas generator) had been physically grounded.
You're right - It couldn't

I've read some pretty ridiculous, off the wall statements in my time - This one really takes the cake! . . . . and you found it on a 'Smartcar' website?? :lol:

Don
2012 iMiEV SE Premium, White
2012 iMiEV SE, White
2014 Ford Transit Connect XLT SWB wagon, 14,000 miles
1994 Miata 60K miles - Soon to be sold
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kiev
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Re: The Necessity For Grounding An External Gasoline Generator Used For Emergency Charging?

Sun Oct 01, 2017 9:49 am

i don't know how driving a metal rod into the earth could possibly make a portable generator "safe" since current must return to its source and the alternator current in a genset is floating with respect to the earth--no current would ever flow to the earth.

The reason a grounded rod into the earth provides a Safety Ground path for your house with respect to the Mains is because the center tap of the 460-to-120 transformer on the pole near your house has been driven into the earth, and this is also the Neutral line in your Mains service. Connecting Neutral and Ground in your panel box and then running this to a metal rod pushed into the earth provides a circuit path (if needed in the event of a shorting incident) thru the earth back to this center tap. In the event that you can't afford a path back to the tap, as they say in Miranda, one will be provided for you--current will arc and burn thru whatever necessary to make a path to get back to its source.

For the USA, i do know that the Mitsubishi and Panasonic EVSE units perform a two-part "ground check" during the boot sequence. It checks that a valid Ground path that carries and returns Line current exists, and that the ground-fault detection circuit works, before closing the relays to send 120 VAC to the SAE J1772 plug.

Ingineer's 100k Ohm Honda generator plug provides a current path thru the Ground wire back to the genset "Neutral". This tricks the EVSE control system into thinking a valid Ground path exists, so it passes the "ground check" and turns on the juice...
kiev = kenny's innovative electric vehicle

veimi
Posts: 62
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Location: Toronto Canada

Re: The Necessity For Grounding An External Gasoline Generator Used For Emergency Charging?

Sun Oct 01, 2017 10:20 am

JoeS wrote:I'd be interested in seeing your efficiency calculation when using, for example, a Honda EU2000i generator to charge the i-MiEV batteries.


Thank you for the link.

I found my original smartcar posting:
"A 1 KW generator would be sufficient and equivalent to the L1 charger on low charge rate.
Figures that I saw for a Honda 3300W generator running at half load which is roughly equivalent to the L1 charger at its 12 A rate, indicated that it used 0.46 U.S, gallons per hour.
A fully discharged 18 kWH smart battery would take 11 hours to charge, using 5 gallons.
Assuming a 160 km or 100 mile range, that equals 20 miles per U.S gallon or 25 miles per imperial gallon or 12 litres/100km."

and recently had some other thoughts assuming my i-miev gets 6 km (3.6 miles) per kWH input.

A Honda EU2000I with a 0.95 gallon tank runs 3.58 hours on a gallon of gas at rated 1600W load. That is 5.72 kWH per gallon or 34.4 km per gallon or 20.6 mpg.


The same Honda EU2000I runs 8.53 hours on a gallon of gas at 1/4 rated or 400W load. That is 3.41 kWH per gallon or 20.5 km per gallon or 12.3 mpg.

Don wrote:You're right - It couldn't

I've read some pretty ridiculous, off the wall statements in my time - This one really takes the cake! . . . . and you found it on a 'Smartcar' website?? :lol:

Don

The quote below is the original response that I received on the electric smartcar forum from my suggestion to use a gasoline generator.

"You would need to carry a large mallet and a copper grounding rod as well. You cannot charge any EV with a normal generator, unless you properly ground it. I tried it, just to be sure.
The car checks the ground, by intentionally leaking current to ground, and making sure that the ground voltage doesn't change. A little generator wont (and can't) pass this test. So, you'll plug it in, and the car will refuse to charge unless you pound a grounding rod into the ground, and wire it up correctly to your generator."

and a more recent response:

https://youtu.be/Nf6WgQfL7DY

jray3
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Re: The Necessity For Grounding An External Gasoline Generator Used For Emergency Charging?

Mon Oct 02, 2017 9:36 am

I love it that the leading advanced-technology consumer generator set (Honda EUxxxxi series) yields the same 20 mpg that my ancient pusher trailer] delivered.
http://insideevs.com/explained-mitsubishi-miev-range-extender-story/

Though it can't be carried in the cargo hold, a pusher trailer delivers that 20 mpg while also making forward progress at 60-70 mph, and can perform a DCFC via regen while moving at up to about 45 mph!

I'd love to build a pusher out of a modern engine tuned for efficiency, but other projects take priority. Here's my current "mobile charging" project, a tiny house-style car hauler that'll have 2.2.kW of solar on the roof and a 3 kW inverter with battery backup.
http://karmanneclectric.blogspot.com/search?q=tiny
2012 i-SE "MR BEAN" 76,000 miles
i-ES traded at 21,648 miles
2000 Honda Odyssey
1987 F250 Diesel
1983 Grumman Kurbwatt,170 kW, 32 kWh
1983 Mazda RX-7 EV 43 kW 10 kWh
1971 "Karmann Eclectric" EV 240 kW 19 kWh
1965 Karmann Ghia Cabriolet

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