Honda EU7000iS is a great generator but bulky and heavy which is probably a reason why it was left running in the shed. Switching to multiple EV's over the last few years I have seen many advantages over ICEV but after seeing some outages made me realize the downside of EV's during outages. I have since tested several generators for charging EV's during outages and Tesla is definitely more picky than others. In general, governor controlled engine generators do not work well consistently with Tesla as it's very sensitive to voltage level and frequency variations. Inverter generators generally work well for charging Tesla provided there is neutral-ground bond as others have pointed out. However, one challenge is that practical portable (i.e. carry in Tesla) inverter generators (e.g. Honda EU2000iS) only provide 120V output which does seem as efficient as 240V output for charging EV's in general. So, borrowing from solar/PV community, I tested autotransformer to get 240V split phase power from 120V inverter generators and it has worked well. Now I have a compact and portable EV charging backup power solution that includes a dual fuel 2200W inverter generator (<50lb), an autotransformer (<15lb) and mobile 240V EVSE (<5lb) that can be easily moved and setup anywhere. I chose dual fuel inverter generator because propane is cleaner which helps me feel less guilty about using and provides significantly longer run time. Also, if more power is desired then additional inverter generators can be added in parallel.
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Charging from a generator, 2 red blinks
- Thread starter timk225
- Start date
Yeah, if there's a efficiency difference from 120V to 240V, its likely less than 1%. The issue is on 120V at 12A, the charge rate is really low, and the car has moderate fixed overhead whenever its 'awake' like while its charging. So charging at 120V12A is wasteful mainly since it takes so long and the car has to be awake the whole time, consuming a fair bit of the charge power. You can get European model EU2000iS's that put out 240V, but that won't really help. What you really need is more charge power, and that's currently not really practical in a small and light package. Ideally you'd want at least 6kW for any reasonable emergency charge rate, and to get that you'd probably need a 10kw+ generator or a very good 6kw+ one. That's going to be big and heavy.
One side note, efficacy != efficiency.
One side note, efficacy != efficiency.
Increasing voltage is not about increasing generator power but rather increase the efficiency of the EV charger in converting the generator power into actual stored battery energy.
I see a much bigger difference than 1% between 120V and 240V charging. There are various Tesla forum power postings describing up to 30% efficiency difference. Given the relatively low power capacity of portable inverter generators I want to get the EV charger to convert as much of the power into actual battery energy as possible. Also, another limitation of charging at 120V is that the EVSE only allows up to 12A current. At 240V, EVSE allow for much higher current capacity (e.g. 32A) which is necessary if higher power generators are used. I agree it would be ideal to have higher power generators which is one reason I mentioned additional inverter generators could be added in parallel. I am hoping to test 4Kw parallel inverter generators soon.
Based on the Tesla charging tests I have done at 240V, I see ~0.9Kwh batter charge per pound of propane or about 18Kwh per 20lb propane tank. This is consistent with 90% Tesla charger efficiency that others have reported in forums.
No way. I've seen the charts showing a lot of different variations of voltage and current and all of the efficiencies of each. And if you are talking about the same power level, there is a little bit of efficiency gain from starting at a higher voltage. It's just a little higher than 1%, but certainly not double digits percent. Nothing near 30%.
The assumption about EV charger overhead being static is problematic. EV chargers are basically AC to DC converter power supplies at its core that their efficiency are definitely lower at lower AC voltage levels. You can check the specs for power supplies that can accept 120V and 240V and even the high end ones used for servers typically have 10% lower efficiency at 120V compared to 240V.
I tried 120V charging and observed lower efficiency than I had expected and that's the main reason I went to 240V. From my experience, I see 10%+ lower efficiency for 120V but others have reported even bigger efficiency difference at 120V. Here is one example:
120v vs 240v charging | Tesla
With a 5-20 plug on the mobile connector, an EU2200 is already beyond it’s rated power. If you wanted to run a pair of them, then yes, the car won’t charge beyond the ~1900W or so at 120V. This has absolutely nothing to do with efficiency though. Charging at 120V and 16A is going to result in near enough identical power into the car as 240V at 8A. And for portable use, the size and weight of the generator is more often the driving factor behind charge rates. Carrying around two suitcase generators in the off chance you’d drive somewhere that far out of civilization sounds like a bit of an edge case. And I’m not convinced it’s terribly practical. You’d expect around 20MPG charging off an EU2200 at full load. The range extension isn’t so great considering the size, weight, cost, and concern associated with the setup. I suppose there’s a use case, but it sounds like a gasoline car would be a better choice.
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It depends on the charger topology, but assuming they’re using an llc resonant, 1% or less is a good assumption. At least at that power level.
eprosenx
Active Member
Also, stepping up the voltage from 120v to 240v is going to have some loss that is likely greater than the lower efficiency of lower voltage charging?
I find it extremely hard to believe that it is worth it to buy an autotransformer to bring up the voltage when charging from a generator. The cost/weight/energy losses/hassle seems like it would not be worth it.
I find it extremely hard to believe that it is worth it to buy an autotransformer to bring up the voltage when charging from a generator. The cost/weight/energy losses/hassle seems like it would not be worth it.
davewill
Active Member
Yeah, but those discussions usually revolve around 120v 12a vs 240v at the same (or often much higher) amperage. This brings the whole overhead issue into play and accounts for the lion's share of the efficiency gain. At the same power level (wattage), like would be the case with using a transformer or the same wattage generator, but with 240v instead of 120v, the difference will be pretty small...and the transformer losses would probably swamp the charging efficiency gain.
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People are being blatantly careless with their terminology and specifications of what they are comparing. They are incorrectly just using the oversimplification of referring to "120V" or "240V", which implies it being the only variable, but almost always what they are actually looking at is a large power difference of 1.44kW versus something like 6kW.
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