DIY Rex :)

[Surge]

This is what I plan to do when I get my i3 - any thoughts?

Honda EU2000i portable generator + non-Rex i3 = get you out of a jam if you run out of battery power

- 2000 watts will charge the i3 via 110V
- 4 hours run-time at full power draw
- should charge the i3 to 50% in 4 hours (on one tank of gas)

 

[mindmachine]

This is what I plan to do when I get my i3 - any thoughts?

Honda EU2000i portable generator + non-Rex i3 = get you out of a jam if you run out of battery power

- 2000 watts will charge the i3 via 110V
- 4 hours run-time at full power draw
- should charge the i3 to 50% in 4 hours (on one tank of gas)

I hate to burst your bubble, but it will take closer to 10 hours before any charging loss is even considered. 2000 watts is 2kw, the battery i3 traction battery is 18.8 kw, charging losses are around 10 to 15% so 18.8x 1.15 charging loss = 21.6 kwh now 21.6/2.0 kwh = 10.8 hrs. This number is actually high as the actual charger system will probably only average 1.8 kwh as the charging cycle current is high for only a part of the cycle and then tapers off toward the end, usually heavy for the first 2/3 and trickles down during the last 1/3 of the cycle, so 21.6 kwh/1.8 kwh= 12 hrs for a full charge. Plus you are limited to 1.8 kwh per hour anyway as the on board charger works in increments when it makes the handshake with the car, in increments of 1.8 kwh, 3.6 kwh, 7.2 kwh I believe. It might be 1.9 kwh, 3.8 kwh and 7.6 kwh. I am not 100% sure of this part as to which. If it is 1.9 kwh then the time would be 11.4 hrs.

So a 50% charge at best would be around 6 hours I would suspect, also I dont know about the BMW i3 , but my Prius plug in in owners manual says not to use a portable generator to charge the car. Not sure why but I would suspect the power is not as clean and steady as home house current.

 

[ultraturtle]

Also that generator is rated for 1.6 kW continuous (2 kW peak), so you would only get about 29% charge before running out of fuel in 4 hours. Also, you would have to sit there and wait for 4 hours.

Here's a bargain for you - for a little more than 3 times the price, BMW makes a water cooled gen-set that is roughly 15 times as powerful, takes up no room in the trunk, does not stink up the car with gasoline fumes, and best of all, is fully integrated with the electrical system, so you do not have to stop at all to charge.

Also, assuming (from CARB BEVx requirements) that 1.9 gallons of fuel gets the REx as much range as 18.8 kWh, the REx gen-set is about 74% more fuel efficient than this unit.

 

[TomMoloughney]

I have used portable generators to charge my electric BMW (ActiveE), but nothing this small and weak. I suspect the power may also not be "clean" enough and the portable EVSE may just go into protection and shut off.

Even if it does accept the charge, expect only a little over 1kW continuous draw so you are roughly looking at gaining about 5-6 miles of range per hour of charging. Take ultraturtle's advice if you really think you may need to do this often.

 

[ultraturtle]

I forgot about minimum power requirements, and I believe Mindmachine and Tom are correct. Assuming you are in the U.S., you would need a generator capable of at least 15 A (1.8kW) continuous and 20 A (2.4kW) peak. You are smart to choose an inverter based model, which would address any power quality concerns, but the next step up in Honda's inverter based gen-sets is the EU3000iS which retails for about $2,330. From there, the REx gen-set is only $1,520 more.

At 154 lbs fully fueled and 25.8" x 18.9" x 22.4", it would not only be a bear to lift into the car, but probably not fit in the hatch without at least one seatback folded flat.

 

[Surge]

Also that generator is rated for 1.6 kW continuous (2 kW peak), so you would only get about 29% charge before running out of fuel in 4 hours. Also, you would have to sit there and wait for 4 hours.

Here's a bargain for you - for a little more than 3 times the price, BMW makes a water cooled gen-set that is roughly 15 times as powerful, takes up no room in the trunk, does not stink up the car with gasoline fumes, and best of all, is fully integrated with the electrical system, so you do not have to stop at all to charge.

I would be happy with a 29% charge in 4 hours. This is only something I would take on a long distance drive, as an emergency if the planned recharge points are not working or full.

I personally don't believe in the Rex, as it defeats the purpose of the car. I don't want to lug around a 265 lb generator at all times.

Thanks for your answers! For $1000, it's great piece of mind to know that in 4 hours you can drive about 50 km.

 

[mindmachine]

Also that generator is rated for 1.6 kW continuous (2 kW peak), so you would only get about 29% charge before running out of fuel in 4 hours. Also, you would have to sit there and wait for 4 hours.

Here's a bargain for you - for a little more than 3 times the price, BMW makes a water cooled gen-set that is roughly 15 times as powerful, takes up no room in the trunk, does not stink up the car with gasoline fumes, and best of all, is fully integrated with the electrical system, so you do not have to stop at all to charge.

I would be happy with a 29% charge in 4 hours. This is only something I would take on a long distance drive, as an emergency if the planned recharge points are not working or full.

I personally don't believe in the Rex, as it defeats the purpose of the car. I don't want to lug around a 265 lb generator at all times.

Thanks for your answers! For $1000, it's great piece of mind to know that in 4 hours you can drive about 50 km.

I suggest before you plunk down $1000 for it you try it out if you could test one with the ESEV you intend to use with it to see if it will work at all. First of all your ESEV may not like the source and not charge, but show a fault. 2.) I am not going to do the math again but you are looking at 40 km(20 to 22 miles) at best in 4 hours. Good luck.

I personally don't know how you can suggest this is OK but you don't believe in the the Rex as it defeats the purpose of the car, if you truly believe this BS then forget the portable gen set and live up to your own aspirations about being a pure EV battery power only enthusiast!!!!! You can't have it both ways!!

 

[Surge]

I will try it just as soon as my i3 arrives.

The ability to charge should not be an issue. Honda generators have an inverter and very likely generate cleaner power than our household AC.

(On a side note, have you ever read up on how "dirty" household AC is? Not pretty, especially if you are running high end AV equipment. That's what a regenerator is for, but that's a topic of another forum.).

Oh and actually, it DOES seem like you can have it both ways

 

[mindmachine]

I will try it just as soon as my i3 arrives.

The ability to charge should not be an issue. Honda generators have an inverter and very likely generate cleaner power than our household AC.

(On a side note, have you ever read up on how "dirty" household AC is? Not pretty, especially if you are running high end AV equipment. That's what a regenerator is for, but that's a topic of another forum.).

Oh and actually, it DOES seem like you can have it both ways

You can fool yourself if you want but that's your choice! Your not fooling the rest of us, and generator power is not cleaner than American Electric Power, I have a 20 HP Honda Gen Set rated at 13,500 watts and a Trace Engineering 8000 watt continuous sine wave (not step wave/square wave) inverter in my home. I know a lot about clean power and what it means. Your little 2000 watt Honda is far from clean power! And if you really believe what you say about the purity of i3 BEV then forget about the Honda, go naked. Live up to what you believe in.

I ordered the Rex myself, and for me it makes way more sense then carrying around a smelly and polluting portable that will leak and smell up the car inside. Again if you are a purist go naked BEV. If you are honest it is more about the cost. Good luck.

 

[Surge]

Mindmachine, why so angry? Chill dude.

I do plan to go without the Rex.
Knowing I can use a small generator for long trips, in case of emergency makes perfect sense and will give piece of mind.

Most new generators, especially honda, produce clean power. So that's not a worry.

Smell - if you keep it in a box it won't smell. Maybe it will fit in the front trunk?

Obviously it wouldn't run often!

 

[mindmachine]

Mindmachine, why so angry? Chill dude.

I do plan to go without the Rex.
Knowing I can use a small generator for long trips, in case of emergency makes perfect sense and will give piece of mind.

Most new generators, especially honda, produce clean power. So that's not a worry.

Smell - if you keep it in a box it won't smell. Maybe it will fit in the front trunk?

Obviously it wouldn't run often!

Whatever pal. Good luck with your experiment.

PS: I am not angry I just don't like it when people aren't true to what they really believe in. "I personally don't believe in the Rex, as it defeats the purpose of the car" so does the Honda, in my book!

 

[kentheteaman]

Hello Surge,

I have had the Rex i3 for 7 weeks now.
Done about 5500km so far.

I must confess, having Rex is bliss, indeed. I hardly ever use it but when I need it, it is there. No range anxiety what so ever. I have used it couple of times when I had to drive bit longer than I had to. Such a peace of mind indeed

Few days ago I did a long trip of 650km. Filled up the tank 5 time in total. Spent 10mts for every fill up in the gas station. Thats it. Every fill gave me 80miles more. Now compare that with 4 hours of charging for 20miles in your Honda gen.

Buying Rex is money well spent and worth every penny.

DIY Rex is dodgy.
Just go for the real thing.

regards,
ken

 

[mindmachine]

Hello Surge,

I have had the Rex i3 for 7 weeks now.
Done about 5500km so far.

I must confess, having Rex is bliss, indeed. I hardly ever use it but when I need it, it is there. No range anxiety what so ever. I have used it couple of times when I had to drive bit longer than I had to. Such a peace of mind indeed

Few days ago I did a long trip of 650km. Filled up the tank 5 time in total. Spent 10mts for every fill up in the gas station. Thats it. Every fill gave me 80miles more. Now compare that with 4 hours of charging for 20miles in your Honda gen.

Buying Rex is money well spent and worth every penny.

DIY Rex is dodgy.
Just go for the real thing.

regards,
ken

Amen and hallelujah!!! Exactly... :mrgreen:

 

[Surge]

Thanks for your comments.

I completely agree that the Rex has real merit,
Just not for me.

I probably mislabeled this thread, rather than DIY Rex, it should have read something like "emergency generator alternative if you don't want/need the Rex"

I would never get the Rex, but that's just me, and I'm not putting it down at all.

Just had this idea for us non-Rex owners and thought I'd post. I will definitely post my experience with it when I get my car.

 

[ultraturtle]

Assuming you are in the U.S., you would need a generator capable of at least 15 A (1.8kW) continuous and 20 A (2.4kW) peak. You are smart to choose an inverter based model, which would address any power quality concerns...

I forgot about the 1.4 kW (12 amp) Level 1 standard, so there is an outside chance the EU2000i might work, but there are a few "ifs":

• - If the supplied BMW EVSE is a 12 amp (rather than 16 amp) unit. This is likely. BMW will not want to deal with complaints of blown circuit breakers as owners likely do not have many 20 amp circuits, and will likely ignore BMW instructions not to share other loads on the charging circuit.
  - If the gen-set can in fact sustain a continuous 1.4 kW load. It is only rated at 1.6, so we are talking about 87% capacity. I have this unit's bigger brother, the EU3000is, and have found it necessary to reduce the load to 85% of its rated continuous output, or it will overload and shut itself down every couple of minutes
  - If environmental conditions are ideal. Any atmospheric pressure or temperature deviation from ideal will lower the gen-set's maximum output.
  - If, in fact the power is electrically "clean" enough. Under high load, it needs to maintain stable voltage, frequency, and approximate sine wave output closely.

In my opinion, not likely, but possible.

Smell - if you keep it in a box it won't smell.

Keeping any gasoline supply contained inside a fully enclosed container is dangerous. It must be vented, or you face an explosion hazard as pressure and temperature change. Whenever the generator is aboard, you face a choice between dealing with constant gasoline fumes or having your car explode now and then.

Honda generators have an inverter and very likely generate cleaner power than our household AC.

Probably not. Grid power is pure sine wave. Any inverter can only approximate it, and an inexpensive one such as on the EU2000i is not likely to approximate it well.

Speaking of "clean", small gasoline generators are ridiculously polluting devices. I already mentioned that the REx gen-set is roughly 74% more efficient than this portable unit, meaning that it will generate approximately 74% more kWh per gallon of gas. What I did not mention is that the EU2000i spews over a hundred times the pollution per kWh as the REx gen-set. Here's the math:

• The 99cc gasoline engine output of the EU2000i generates 15.8 grams of Hydrocarbons plus Oxides of Nitrogen per kWh. (http://www.arb.ca.gov/msprog/offroad/cert/cert_results.php?order=0) This is only the input to the generator side of the gen-set, so after generator efficiency losses it actually emits more guck per kWh of electricity generation.
  
  We don't yet have numbers for the REx, but we do know that its sophisticated emissions control system allows it to meet CARB SULEV criteria (0.010 g/mi hydrocarbon plus 0.020 g/mi NOx = 0.030 g/mi total, see page 49 of http://www.arb.ca.gov/msprog/levprog/cleandoc/cleancomplete lev-ghg regs 4-13.pdf), so assuming (again from CARB specs) that it gets 4.0 miles per kWh (75mi/18.8kWh), its worst case emissions would be:
  
  4.0 mi/kWh x 0.030 g/mi = 0.120 g/kWh

15.8 divided by 0.120 is 132, so best case, the portable generator emits more than 132 times the harmful emissions per unit of power than the REx gen-set.

So many people talk about the "purity" of a BEV vs REx, that I sometimes forget that they place battery powered locomotion as having some inherent value in itself, and not as merely a helpful contributor to a greater good such as environmental responsibility. For me, and I suspect a great many others, the REx is far and away the more environmentally responsible choice. For those that will never have to exceed a 30 mile radius from their primary charging point, or are willing to go through the hassle of renting (expensively through BMW 360, or inexpensively through a local rental company) when they need to go farther, the BEV is a great pick. Anyone that needs to venture further, however, is now burdening the planet with not only the embodied energy and pollution of a second, fossil fuel powered vehicle, but the mile by mile pollution it generates. Consider a round trip to a destination 40 miles away. A REx owner would be able to make that trip 75 miles on electricity and only 5 miles on gas, whereas a BEV owner would need to take the gas burner and operate the entire 80 miles on gasoline - 16 times the gasoline usage of the REx.

In many ways, the REx is the "purer" EV. For a very reasonable price, no volume penalty, and about the weight of an adult passenger and his stuff, it is the smartest way I can think of to avoid having to own a second car.

I believe your portable generator solution to be a really bad idea for many reasons, but am curious to see how it turns out. Keep us posted!

 

[Surge]

Actually grid power is FAR from a pure sine wave.
Just Google "AC power regenerators for home audio" and you'll see that grid power coming into homes is terribly dirty.
I happen to have a device that measures THD of the incoming signal (a way to measure how non-smooth the sine wave is). Where the ideal is 0% THD (perfect sine wave), I average 3% in my home. And that's considered quite good. So grid power is not at all clean.


I think a backup solution for long trips is much better than carrying a 265 lb gen at all times (and losing the heat pump).
But that's largely because I never plan to exceed 100 km per day. I would never rely on the Honda generator. It would be strictly for emergencies on long trips.

Finally, it's designed to be portable and if you are worried about Honda's gas engines exploding... Well, don't be! Honda knows a thing or two about small gas engines.

Output- it's rated at 2kw max and 1.6kw continuous.

 

[Stevei3]

Hi guys,

I don't know if this thread is deviating too much from its starters intentions, but as we are talking about engines now, I can't resist to add my two cents: I have to agree with Ultraturtle about the relative eco un-friendliness of many small gas powered machinery. But the eco-balance is actualy far more askew, for an engine like i3's REx has full electronic fuel injection and a catalytic converter in compliance with (future) EURO-6. I have forgotten the real data, but I have a vague recollection that one hour of lawnmowing equals 5000 km (3000 mi) of driving in a normal car, polution wise. This number didn't take CO2 in account though, for CO2 is (essentialy) not poisonous. Please Google if interested in hard data. Or does someone here have more data about this @ hand ?

Regards, Steven

 

[mindmachine]

I know from your past responses you really don't want any advice, especially after reading your comments re: Ultraturtle's excellent write up; but, please pay attention to this one item as it is important. Most ESEV's at least Toyota does for their plug-in cars (i have a Prius plug-in) require a ground fault type circuit in order to maintain your warranty. It is also a necessity to have a proper ground or it is possible that the ESEV will show a fault and not allow the handshake with the car at all. The quote below was copied right out of the manual for the Honda you are intending to use. Also I am going to say again, manufacturers of EV's and PHEV's alike recommend against trying to recharge your car with a portable generator. I haven't read enough to claim that I know but I would not be surprised if there was an issue that developed due to the use of a portable gen set that they might even void your warranty.

"Honda portable generators have a system ground that connects the
generator frame components to the ground terminals in the AC output
receptacles. The system ground is not connected to the AC neutral
wire. If the generator is tested with a receptacle tester, it will not show
the same ground circuit condition as for a home receptacle."

Sorry if you thought I was angry, I am not, but I am a professional engineer retired with 36 years experience in equipment acquisition and installation in an energy related industry. I also spent time in our engineering research and development department. Your super idea of using the Honda just smells like trouble (to me) for you down the road, and I don't me the smell of gasoline for the gen set either. Again I wish you good luck, and let us know how it works out for you if you choose to take the risk because I know you are going to do it no matter what anyone tell you on this forum.

 

[Surge]

Yes, thanks for your comments. I am also a professional engineer. Definitely you must ensure the generator is properly grounded (and note that rules here may be different by country).

Re- pollution of the generator vs. the BMW Rex- you have to consider frequency of use. Again, the generator will be for emergencies - it may never get used. It certainly won't be frequent. If you have the Rex, you will need to run it at least once a month (?) to use the fuel and prevent it from going stale and damaging the engine. So you need to factor that in, if pollution is a concern.

Overall, I will use far less energy driving without a generator (Rex or Honda) 99% of the time, vs with a Rex all of the time.

Finally, as far as fumes - I'm not sure if any are exhausted from the Honda when not in use. Even so, it may fit in the front trunk of the i3, which is vented anyway.

I think it's clear that you should be able to do this. I will try it when I have my car.

Please try to be more open to new ideas - that is one of the benefits of a forum such as this.
We do not do anyone any good if we immediately jump on new ideas and try to crush them, because they are unconventional.

 

[Surge]

Consider a round trip to a destination 40 miles away. A REx owner would be able to make that trip 75 miles on electricity and only 5 miles on gas, whereas a BEV owner would need to take the gas burner and operate the entire 80 miles on gasoline - 16 times the gasoline usage of the REx.

ultraturtle, I do appreciate your comments. Let's make sure that is clear first!

Now, the comment I quoted above, I cannot see how this is a fair comparison of BEV vs REX. If I were to drive 80 miles, I would use the BEV but just be more economical in how I drive. Should not be a problem in ECO or ECO Pro, from what I'm reading.

Now if you look at a longer trip, sure the REX is incomparable to a gas burner, IF your long distance driving is sufficiently frequent.

You'd have to make those longer trips often enough to justify the daily weight, performance, and cost penalty of the REX vs the BEV + a gas car rental.