MetroMPG.com: Electric pusher trailer

[P-hack]

Originally Posted by razordave

Why does this thread keep dying?

Part of it may be that this isn't the hybrid section of the forum.

[Astro]

Originally Posted by P-hack

Well a conversion can cost a lot also, have you looked at how long your commute is and speeds, and figured out how much battery you would need? And how much motor/controller you need? It is tempting to rely on a generator but you have to have an EV to attach it too, and have determined the energy requirements before you can sort out how/if to augment the main pack.

The EV will be my daily commute vehicle and the battery pack will be sized to deal with that daily trip plus some local trips to the supermarket, etc.

Adding another say 50% to the battery pack size for just that one long trip each month would mean i would be carrying around that extra weight every day and not getting any benefit from it.
I could look at making the extra battery pack capacity removable but the size, weight and cost of that extra battery capacity would be quite high compared to a small generator.

I have to register and insure the EV but if the generator can increase my range enough to deal with my long trip then it saves me at least $757 dollars a year as i don't have to pay the registration and insurance on a second car (not to mention the maintenance) that would only be driven 12 times a year. Also the EV gets a $100 dollar discount on it's registration for being eco friendly.

Then if later on a charging station opens up near the mid point of my trip then the EV would be able to make the trip without assistance. And i would only be left with a useful generator rather than a surplus and costly second car.

The generator would only be an interim solution until the charging network improved and it would save me having an extra, seldom used ICE vehicle.

[Astro]

Originally Posted by redpoint5

...The first problem to tackle is having an over-ride mode that allows the car to charge and drive at the same time.

With the car being a conversion rather than a factory electric such a mod would be fairly straight forward. I imagine the lockout on driving whilst charging is to prevent somebody driving off when the charger is still plugged in.
Even if i can't charge whilst driving and have to plan on a one hour rest and recharge around the mid point of the trip that could be done.

Originally Posted by redpoint5

...I'd like to see batteries become more modular so that individual banks can be added/removed from a car, and added/removed to a motorcycle, lawn mower, leaf blower, chain saw, etc. The cost of ownership of all these items would be greatly reduced if the same power source could be utilized...

It is annoying to have each device have its own unique battery pack configuration.
If there was some standardisation then the number of battery packs i would need would be greatly reduced as i don't run every device simultaneously. Also when a device fails (as they tend to do) the battery pack could be salvaged and re-purposed to another device.
I have seen that a few of the power tool manufacturers have released power tool ranges that share the same battery. Still quite expensive. Also they seem to be compromising on capacity. Picking an average capacity that leaves the more power hungry power tools lacking performance. The more power hungry tools really need to have provision for two standard battery packs. Then the average sized battery pack would make sense.

[P-hack]

Originally Posted by Astro

Adding another say 50% to the battery pack size for just that one long trip each month would mean i would be carrying around that extra weight every day and not getting any benefit from it.

It really isn't unused, the less you cycle your pack the longer it lasts, the more capacity the less you cycle. Plus you have more power available if you want to have some "fun". You can upsize the motor and controller for better acceleration/top speed. It works for tesla.

How many miles are we talking about here, commute vs once/month?

[jray3]

I have both a generator trailer and a pusher trailer (based on an aircooled VW). The pusher is great for long highway trips, but on sub-100 mile journeys where it would only serve to prevent one fast-charge session in my i-MiEV, it is on balance, impractical. Driving the pusher is fun- it turns the MiEV into a vehicle with some serious passing power on the highway, having doubled the power available! I'm working on refinements, as binary control (WOT vs lugging a dead engine at speeds under 30 mph and when stopping/starting) is inefficient and yeilds a a blended city/hwy mpg of only 20.
My genset trailer charges the Karmann Eclectric at 4 kW, which only extends highway range by about 15 minutes/15 miles, but it does enable continuous recharging while crawling through traffic or stopped somewhere that has no EV charging options...

An automatic-transmission Metro drivetrain could make a very good EV pusher, but I built with what I know best and had on hand.

[Astro]

Originally Posted by P-hack

...How many miles are we talking about here, commute vs once/month?

Simple answer.
35.4 miles versus 54.7 miles.
So an increase in range of 54% is required.

More involved answer.
There are two different routes i can take in my commute.
Route 1 is a 57km (35.4 miles) round trip at 60mph.
Route 2 is a 42km (26 miles) round trip at an average speed of 30mph.
Route1 is via a freeway so almost the entire trip at freeway speeds with only 6 sets of traffic lights. However the wind resistance will be quite high and it has tolls so an extra $10 per day.
Route2 is a shorter distance and at lower speeds however it has 34 sets of traffic lights. So significantly less wind resistance but more stop and go. My drive system will have regen so i will win back a small amount of the stop go energy.

I gave the round trip figures for the commute as i have not secured any sort of charging at work so i have to do the round trip on a single charge. Whereas the once a month trip has charging available at the destination.

The once a month trip is 88km (54.7 miles) one way all at freeway speeds.

If i can secure charging at work then i will be using a 6kWh battery pack and no hope of doing the once a month long trip even with generator assistance. If i can't charge at work then it will be a 12kWh pack which makes the long trip feasible with generator assistance.

So my build is a 6kWh battery pack with provision to add another 6kWh.

It's never simple is it.

[P-hack]

You'd be better off with an econobox 5 speed and good technique. The plug in prius 4.4kwh battery is only good for 11 epa miles, and it is well engineered. I don't think your commute is a good fit for a budget "ev", and you will get crummy hybrid efficiency if you don't know exactly what you are doing.

[Astro]

Originally Posted by P-hack

You'd be better off with an econobox 5 speed and good technique. The plug in prius 4.4kwh battery is only good for 11 epa miles, and it is well engineered.

The Prius is nearly 400kg heavier than my vehicle.
I would also imagine a hybrid vehicle would have many compromises in it's design to allow for the dual power systems.

Originally Posted by P-hack

I don't think your commute is a good fit for a budget "ev", and you will get crummy hybrid efficiency if you don't know exactly what you are doing.

Even the most efficient gas guzzler still guzzles gas.
Electricity is cheaper and can be cleaner. Some of the electricity will come from my solar panels so cheaper still.
I am quite hopeful of my EV being able to cope with my daily commute.
Worst case scenario is it will require further expansion of the battery pack.
There are few problems in the world that can't be solved by throwing large sums of money at it.

[P-hack]

Ah, you have a build thread, and you live in OZ If I thought the EPA (or the DMV) wouldn't pown me, I would definately entertain a hitch mounted small diesel chained to a wheel on a swingarm (with raising/lowering perhaps). Just one speed to help at higher speeds.

edit, like this but with a small diesel:

[jray3]

General update- I took my longest trip yet with the pusher trailer this week. 353 miles total in the i-MiEV with a single quick charge and one L2 charge en route. Otherwise, it was all hillbilly-hybrid! There were two 145 mile highway legs and 63 in-town miles in-between, during which I was towing around the dormant pusher.

Pusher control is still binary- meaning it's either running at wide open throttle, or not... This is enough power from the salvaged 1600cc aircooled VW engine to average 65 mph on hilly interstate, using the electric drive to boost power up the hills, and scrubbing off speed with regen on the way down (though I also slowed to 60 mph uphill and sped to 70+ downhill). That is 'charge sustaining' mode, in which I maintained SOC within two bars over more than 100 miles.
In this charge sustaining mode, I once again hit 19.5 mpg. BUT, throwing in the around-town errands at my destination, the trip averaged 29 mpg overall. Not great, but about 7 mpg better than I could have expected with the family minivan. A whopping 3.88 gallons of fuel saved.

Economically, I would've been better off with a borrowed pass to the West Coast Electric Highway, as I refuse to pay Aerovironment's $7.50/session DCFC fee for non-subscribers, and it was logistically very helpful to not spend almost four extra hours waiting on charging sessions... The approximate $32.32 I spent on gas and $10.10 I spent on EVSE come out to 12 cents per mile, which is a lot more than MR BEAN's long term average of 2.4 cents, but equals the fuel-only cost in our minivan, and after all, I did save 3.88 gallons and about 73 lbs of CO2, given that I was recharging mainly on hydro and my home solar array. NOx and HCO, unburnt hydrocarbons, etc.. are another question.....

SO in summary, no better-than-OEM hybrid mpg numbers or great financial savings to report, but enough to continue refining the pusher, perhaps with a tune-up and throttle control.
:roll:

The maneuverability of an i towing a trailer is compromised ONLY by parking stalls, and that's not bad when the tongue length is tuned to allow a full 90 degree parking angle between car and trailer (especially for an i at charging stations). Otherwise it can still go anywhere.