Range extender !

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PV1 said:
Does anyone know a good way to limit the secondary pack's input/output to 30 amps? I can't seem to find resistors or a PWM current limiter that can handle the voltage, or if they handle the voltage, they don't have the amperage.

A PFC30 from Manzanita Micro would do the dc-dc job quite well, but those retail at $2900
http://www.manzanitamicro.com/products?page=shop.product_details&flypage=flypage.tpl&product_id=110&category_id=14

If you do this- talk directly to Manzanita first. Some models don't run well in dc-dc mode, and others can be optimized for this from the factory.
 
Thanks. Email sent to Manzanita.

Depending on their response, I may make the pack into two cases (which I think I'll have to do anyway to be able to lift them), so that I can use just one pack if I only need a few extra miles, or both packs if I need to go farther.
 
Best of luck to you PV1 we'll all follow with great interest. For reference, here is the most ambitious similar project that I'm aware of. Built by Seattle EVA president Stephen Johnsen, it uses a tweaked PFC75 by Manzanita Micro to transfer up to 30 kW from a huge bank of 200 Ah Thunder-Sky cells built into a custom aluminum trailer. The trailer powered a factory S-10 EV pickup over 2500 miles from Seattle to Mexico and back in less than 7 days (with a few recharging stops, but the trailer capacity is 66 kWh, IIRC).

https://www.facebook.com/pages/The-Range-Trailer/257589060955815
 
Looking for additional dc-dc sources, I found this nice little FAQ that claims losses of up to 30% in the transfer.
http://www.pluginsupply.com/competitors/
And that's only one-way. Throw in charging losses and that's 50% of your electrons going to heat before they hit the motor.
I'll ask for data on losses from the Range Trailer.

The main risk I see from the alternative of a second voltage-matched battery pack would be fooling the battery capacity and recharging algorithms to the point that the car fails to properly maintain the original pack.

Injection into the main DC bus between battery and inverter while underway would seem to be okay, assuming that the current would be interpreted as reduced load (ie: driving downhill), but recharging the secondary battery using the original charger would be strictly verboten.

Again, I'm chasing the ICE pusher trailer option due to a lack of electronic hacker skills.
 
jray3, thank you for the links. Yes, using a dc-dc to go from 48v to the i-MiEV's 360v would be lossy, compared to simply paralleling the existing i-MiEV pack with another HV pack. I also recognize that when using a dc-dc the current supplied wouldn't be sufficient to drive on; however, for me that's ok, as I'm only considering stretching the i-MiEV's range and a steady trickle of current into the main pack might be all one needs… (I should do the math first to determine a realistic minimum current, as this concept may be hopeless from the get-go).

What PlugInSupply seems to be doing is simply paralleling the HV packs (via a contactor), but I don't see any discussion of how voltages are equalized prior to closing the contactor. I imagine any significant inequality would result in a HUGE current spike and a short-term high current as the packs equalize. Perhaps it works ok on the relatively puny Prius pack, but doing that between two significantly-stiff packs (such as the i-MiEV's and LiFePO4 Headways or Li(NMC) EnerDels) may prove problematic without any sort of series impedance or current-limiting device between them. PlugInSupply is acknowledging steady-state current flows of 100A-135A in normal driving. Also, since they say that the vehicle's regen can charge the auxiliary pack, that means they're not diode-isolating that add-on pack.

As jray3 pointed out, how does this configuration avoid confusing the vehicle's BMS? In thinking about it some more, perhaps the BMS doesn't care because the contactor is closed AFTER the vehicle is energized and the BMS simply thinks the car's regen is providing all this excess energy? As long as the auxiliary pack does not exceed 360v, then it's ok? If I recall, saia47 has been doing this already.

Might be worth revisiting this parallel-HV-pack concept. As I said before, I was planning on using my '48v' EnerDel Lithium (NMC) packs simply because I already have a bunch of them (and going to build more for my Sparrows). The safety issue of dealing with high voltage is recognized but is not much different than already protecting the connections and wiring of the high-current 48v packs. The back seat would need to be pulled out and the whole works bolted down for safety. Before doing anything huge, I'd be inclined to build up a small HV pack using around 100 Headways just to determine this concept's feasibility…

In any case, I envision a completely independent charging (and BMS) setup for the auxiliary pack which would have no connection with the i-MiEV's charger.

All it takes is time …
 
JoeS said:
I don't see any discussion of how voltages are equalized prior to closing the contactor. I imagine any significant inequality would result in a HUGE current spike and a short-term high current as the packs equalize. Perhaps it works ok on the relatively puny Prius pack, but doing that between two significantly-stiff packs (such as the i-MiEV's and LiFePO4 Headways or Li(NMC) EnerDels) may prove problematic without any sort of series impedance or current-limiting device between them.…

Back in the lead-acid era of EV drag racing, this was accepted practice. Racers would "dump charge" between runs by connecting an offboard battery of significantly higher voltage to the onboard pack, usually with a set of Anderson SB350 connectors. There was some spark and sizzle, but as long as you kept an eye on things (and a fireman's axe next to the cables stretched across asphalt) nothing would melt down.... I still use magnets strapped to the side of relays and contactors to 'bend the arc' and reduce pitting of contacts, plus diodes to suppress inductive kickback from the contactor coil.

As long as the packs were of similar nominal voltage, and given the fairly flat discharge curve of lithium, I'd expect the current flows to be within reason. Careful planning and a simple control logic for the contactors could even give an advantage to putting a few extra cells in the boost pack, such that say: 20% SOC on the boost pack equals 60% SOC on the main pack. Manual operation would be to start cruising on the highway and then switch in the boost pack, but switch it out during any long downhill regen runs. Automated control could simply be activated by the "Ready" signal and switch in the boost pack any time there's a forward delta V of say, 10V or greater. To reduce short cycling, add a time component saying that delta V must be greater than X volts for Y seconds before the boost pack gets switched in. Based on the boost pack and cable size, one could also set a maximum ON time.

Our pack and it's cabling is capable of 49 kW continuous. CHAdeMO sessions start off at 120 amps till 360V, or 43.2 kW. It would have to be quite a big boost pack and quite an impressive hill climb to transfer 120 amps for longer than the 15 minutes or so that a DCFC session can entail. And keep in mind that unlike CHAdeMO, this technique would mainly be providing power as it's used, which would expose the pack to only small net average currents, and not require cooling like during a DCFC session.
 
My plan was to use some sort of current limiter (may be Manzanita, I still need to call them) to just limit current transfer between the main pack and my custom pack built with 18650 cells in 12P88S arrangement (more or less 88 modules of 3.7 volts, 31.2 amps each in series) with what'll probably be an eLithion BMS with balancing. I'll have a contactor between the converter and the car wired to only come on when the main contactor is engaged (I understand the connection point is under the rear seat by the EV-ECU) and a toggle switch is turned on. That way, the aux. pack can't solely power the i-MiEV, but it can engage during driving and charging with an easy override to keep the aux. pack disconnected.

The limiter will only allow up to 30 amps of transfer between the pack (both ways so that the aux. pack can be quick charged) so to not exceed the cells' amperage specs. From what I remember reading, Siai47 did parallel two i-MiEV packs on one car by tapping the HV in the motor controller where it enters from the battery. SoC and current readings are taken from inside the pack, so the added capacity from a paralleled pack or generator would look like regen or lighter acceleration depending on the demand. Also, when regenerating, some current will go to the aux. pack, making it look like extra load on the system (ex. Heavy 12 volt load, heat, etc.). I don't recall if he charged both packs with the car plugged into J1772 or not, but I remember him saying that he "fast charges" the car with an off-board Manzanita charger with the car in READY.

I don't see how this would affect calculated battery capacity as the energy delivered to the battery is measured from within the pack, not by the output of the charger (though if the battery receives more than ~5 kW, the charger shuts down). Unless the car measures 12 volt loads (anybody in the CAN world come across a PID for this?), it wouldn't know the difference of drawing power from HV or from 12 volts through an inverter.
 
Siai47, have you tried J1772 charging or CHAdeMO quick charging, with a parallel pack hooked up? How does the car handle it?
 
Pusher trailer updates:
Through the wonders of the interwebs, a gent named Hugh who's in Utah contacted me who went ahead and built the pusher trailer that I've been slowly progressing on for so long, because he needed to move the RAV4 EV that he inherited from his dad in California! It worked so well that he's also taken it on very long trips to Victoria BC and to EVCON in Missouri!
Here's a few remarks from Jack Rickard and a photo.
https://www.youtube.com/watch?v=kHN5PhaUD7U#t=1665
As you'll see, it's the entire pan from a junked VW beetle, with a trailer hitch replacing the front axle beam assembly!
I had mulled over a version of this approach, but decided the tongue weight would be too much for a Karmann Ghia or i-MiEV. He simply locked the throttle wide open, and ran the coil energizing wire up to the tow vehicle, where he starts and stops the engine by inserting and removing a cigarette lighter plug! Hugh tows in neutral with the engine off around town, and then pulls over and shifts the pusher into gear before getting onto the highway.
He's added a couple of refinements since, but the bottom line is that this approach worked much better than he expected, and now I'm extra pumped on doing it too!
 
PV1 said:
:mrgreen:
https://www.dropbox.com/s/qkfcm8gl3d51761/20140927_154232.jpg?dl=0

To paraphrase Forrest Gump: "His dream had come true. PV1 was a Solar Roller."
;)

I'm betting that's not been pulled down the road and is just a pose with a bicycle trailer at some alt energy fair.
 
That's a cute trailer. I hope you don't get a stupid letter of the law ticket for towing your trailer in the wrong lane on the freeway.

I'm not sure why that law exists. Some big box trucks are longer than your setup and they can go in any lane.

If thin film high efficiency PV's were not too expensive and a simple way exited to connect directly to the main battery, that could be useful. I figured it could let me avoid one charge per week when I don't do a lot of miles.

A fully covered PV roof with 1 kWh per sunny day would allow around 20 PV powered miles per week.
 
That trailer is for my electric bicycle. I was loading it into the i-MiEV (fits perfectly) when the idea hit me to hitch it to the car for a gag. I didn't drive anywhere with it.

Either way, that trailer can barely charge the bike under its current setup, let alone provide anything useful to the i-MiEV. Small format NiMH batteries can't deliver the amps I need for a inverter -> charger setup, so I need to get a DC-DC converter for it. It's great for running a booth at events, though. Plenty of power for a tablet and public phone charging. Still trying to figure out version 2 to have more power, weigh less, and still fit in the i-MiEV.

jray3 said:
I'm betting that's not been pulled down the road and is just a pose with a bicycle trailer at some alt energy fair.
Bingo.
 
On my Christmas travels, I linked up with a gent who was inspired by my pusher trailer musings and simply got 'er done! He used the entire pan(chassis) of an old VW beetle, welded a ball coupler to the front frame head, and just tied the throttle wide open! He drove two hours from home to meet us and allow me to experience driving the pusher without any detours on our part! After a 122 mile drive, we discussed the details over a nice dinner.

Operation is as follows; drive around town towing the pusher off and in Neutral, and then pull over and shift into 4th at the top of an on-ramp, lug the engine up to speed and flip on the ignition. Then it roars to life and starts adding power. Since his EV weighs over 4000 lb and has cruise control, the pusher engine can push it's little heart out without regard for hills or the speed limit. The cruise control simply brings in more regen to scrub off speed, or adds electric power to help climb hills. His pusher engine is completely unenclosed and has dual unmuffled exhausts, yet the engine is very quiet way back there. I had to roll down the window to listen for pinging, etc. when deliberately stressing the engine (briefly). Pusher operation was smoother and simpler than I had dared to imagine, and when deliberately operating in charge-sustaining mode (stayed above 80% SOC), we got 22 mpg at 55 mph over 122 miles on a very hilly highway; exactly his long-term average. Not bad for a salvaged aircooled engine with noticeable blow-by pushing nearly 5000 lbs through the mountains.

The gent and his EV particulars are anonymized for now due to his concerns about OEM warranty coverage. He is racking up EV miles at an unnatural rate. ;-)

Added Technical tidbits follow.
-Since the engine's too quiet to reliably hear if it experiences trouble, and the cruise control seamlessly maintains speed if the engine lags, he's tied the oil pressure sender to a LOUD backup alarm. This means that if the engine stops running with the key on (such as if you turn the key on while stopped) the trailer starts screeching horribly. He added this feature after blowing up his first engine... :eek:
-Even with the full VW pan and frame head (but no axle beam) and forged steel Bulldog coupler welded in place, tongue weight was very manageable, I'd estimate a bit over 50 lb.
-Fuel tanks were just two 5 gal plastic cans with a modified cap passing through the fuel hose.
-As a safety, he added a magnetic reed switch that depowers the engine when brakes are applied. This created an unwanted side effect causes the engine to surge on and off in sync with the turn signals! You see, trailer wiring harnesses combine the brake and turn signal into a single filament, so the turn signals were cutting power to his ignition coil! A fix is in the works.

This generous gent also presented me with a wiring harness that would literally turn any engine (or entire towed car) into a pusher with just two quick wiring connections. It's a 12 Volt 'cigarette lighter' plug that uses the tow vehicle accessory outlet to power the pusher's ignition coil. Of course, that's not quite as safe as his brake-interlock design because the engine will push until someone manually pulls the plug, but it'll do for testing purposes.

Thusly inspired, I installed it on the olde JB Straubel pusher trailer last night, and intend to do a road test tonight. I found some faults in JB's old control wiring, so bypassed that mess and wired it direct. I also fabbed up a better gearshift lever than the old vice-grips, and cut away the questionable fuel hose and tank selector valve, re-installing a single marine gas tank on the only properly fabbed bracket.

Today I'm ordering the last part for my planned electric clutch actuator, which will enable the operator to declutch without stopping and walking back to the trailer. That'll be good for unplanned stops and seamless merging onto the highway.
 
Believe it or not, your friend has been talked about before on an internet video. His EV is mentioned in the Video. I can't remember the name of the website the video is on, but it's from some guys in Cape Girardeau, Missouri that run an aftermarket EV shop. Their EV Video news podcasts are quite lengthy, running as long as 4 hours.
 
Yup, the gent got nervous after that EVTV spot. I was gonna write an article for insideevs.com, but he'd rather wait out the warranty!
;-)
 
Took my first test drives today after making a few minor repairs and getting the engine running. I Haven't opened the fixed throttle position past 75-80% yet, but that's enough to cruise at 55-60 on the flats. Going uphill, the little engine at 75% needs some electric boost, and full regen on even steep highway downhills (by barely touching the brake pedal) pours amps into the pack and keeps speed in check. The engine is luxury quiet back there on the trailer, and the pushing action is very smooth, as is the pulling when the engine is lugged up to speed before enabling the ignition. The only time the trailer bucks and rattles is when pulling away from a stop in 4th gear with the ignition switched off. Surprisingly, the 'dead'engine being pulled in 4th is smooth all the way down to 8mph before it bucks. Tonight I added a clutch actuator, built from an electric seat adjustment motor with a lead screw. Haven't run the control wires yet, so road testing of that enhancement is next, plus I need to gas up! The first gallon didn't last long! :twisted:
 
jray3 said:
On my Christmas travels, I linked up with a gent who was inspired by my pusher trailer musings and simply got 'er done! He used the entire pan(chassis) of an old VW beetle, welded a ball coupler to the front frame head, and just tied the throttle wide open! He drove two hours from home to meet us and allow me to experience driving the pusher without any detours on our part! After a 122 mile drive, we discussed the details over a nice dinner.
I think this is it. I blacked out his vehicle to help him stay anonymous.

rkHPzNg.jpg

TT69D4t.jpg
 
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