PHEV conversion using CAN-View and BMS+

I'm starting my thread again in the proper category (I hope)
I'm slowly converting a 2008 Prius to PHEV using the CAN-View and BMS+ with two extra (total of three) Prius traction batteries. Both batteries came from low mileage 2008 Prius.

Charger is simple capacitive doubler which sags under load, i.e. when charging the batteries, to some V lower than 2x the mains peak of 170V. So open circuit is 340V but when I plug it in to one of the battery packs for testing, it just shows the voltage of that battery, but slowly rising. It's about $40 in parts including two caps, two diodes, and two resistors to bleed the caps down when you unplug it. Very simple. Also dangerous, since I'm not sure at what voltage it would stop charging. So several safeguards will be added such as temp, voltage, current (fuse).

Progress is slow, but charger prototype is built, tested to put out about 3.5 A at 220V. It gets a little warm but not bad. The Prius battery doesn't change temperature at all (that I can tell) when charging from 213V up to 230V then discharged back to 213V. I haven't pushed it much - I'm load testing it on an old 220V baseboard heater which draws by coincidence about 3.5A DC at 230V.

I'm wiring in EV mode button tonight (homemade) and will begin testing the car as a plugin with just one battery (stock) to make sure the BMS+ is working OK. WIll post pictures soon.

 

are you using the fet to pump high frequency pulses to drive a transformer (as opposed to mains frequency)? I'm curious how the FET can limit current. In simulation software, the cap doubler has low average current but some pretty nasty spikes. the battery seems to soak these up. i hope.

 

It's interesting - I found the same problem in simulation, needing high capacitance. Probably because you can't easily simulate a battery. But in the real world, I'm using two 60amp diodes and two 390uF caps in a typical doubler arrangement (which I think means the capacitance is additive to 780uF) and in this arrangement, the output "follows" the battery's voltage right up to 238V. All that ripple is just swallowed up and obviously even if average voltage is low, a lot of current is going to the battery. efficiency on this setup is about 70% as measure by kilowatt meter and amps measured going to battery. I don't have a scope but someone else with the same rig as mine had a scope put on during charging and said the spikes at least (if not the ripple), were gone during charging.

Using 390uF caps, I'm getting average current of 3.5 A, and that's measuring through my little $10 multimeter, which seems quite happy to be part of the current path. If you use 680uF caps instead of 390, current jumps up to more like 8 amps. Prius battery doesn't even get noticeably warm after 5 minutes of that.

It bugs me though that I can't get the simulation software to more closely follow the bench results. it's an awfully simple circuit, except of course the battery.

last thought - my understanding is that these batteries will go up in smoke at constant voltage charging, no? Above about 240V, you get a lot of heat generated even after charger is removed (from self discharge I assume) but even if you held at 238V, I think you can still in some sense be charging. In an idealized flat line DC current maybe not since in theory the voltages would "cancel out" but for safety I think it's better to just kill the charging current at some set point in time, plus temp cutout of course. I wanted to do voltage based kill switch but the voltage reads 242V then you turn off the charger and it sags down to 236V or something. Too imprecise. Might still do it as a safety device.

 

update on PHEV Prius

Update: Slow progress, I know, I know. I charged the OEM pack up to 238V with my prototype charger and did some test runs. Man, one pack even charged beyond what Toyota allows doesn't get you far. I drove about a half mile up a gentle hill and the voltage was 213V (after I stopped and let the car rest a minute). Drove home which was of course mostly downhill. Voltage back at home was 208V. 25 minutes on the charger put it back to 238V.

So, success! My harness is in place, wired for one extra pack at this point, will test two then add the third. Or maybe I'll just throw both in there. I'm using 6 AWG wire from Lowes. It's not very fine-stranded (not like OEM wires) but it's OK. I sort of half-crimped on the connectors, enough so that they wouldn't budge with a hard pull, then soldered them. I know it's not ideal but I don't have a heavy guage crimper and the environment is mostly isolated, minor vibrations, etc. so I'm not worried about metal fatigue around the solder/copper. Needless to say I will periodically inspect.

To connect the HV lines, I'm using 1/4" stainless steel nuts, bolts, washers, lockwashers and lead free solder on silver coated crimp-terminals. Not too worried about galvanic corrosion since the environment is dry and lead-free solder is close to 300 series stainless, silver, and copper in reactivity.

Power cord to my charger gets warm so I need to upgrade that - it was some salvaged power cord to a computer monitor I think, probably 18 or 20 ga wire and the charger according to kill-o-watt meter is pulling just about 1kW or 14A at 117V. This is more than I thought I would get based on other's similar charger, but he runs his through a cheap multimeter to monitor current, and I'm suspicious now that the multimeter in his setup is slowing things down. Either that or this charger is incredibly inefficient. I'm assuming 112V x 14A = 230V x X so X=7A but when I place my multimeter in line with the current flow it read 3.5A, about what the other guy got doing the same thing. I don't think 3.5A of current is being wasted as heat. The heat sinks on the diodes get warm and the caps get warm, but not 500W worth. I'm thinking more like 100-200W wasted heat. Will do more testing and post pictures soon.

Oh, final bits of data, difference in V between subpacks is very good after a couple charge/discharge cycle, less than .06V (high-low). Temp of battery on charge cycle from 208 to 238V raised battery from 75 to 85 degrees F in ambient temp of 68 degrees F. I checked ten minutes later for any temp. elevation but the temp had actually gone down.

The Prius does some very strange thing if the 12V gets low (like when you leave the traction pack disconnected by mistake - oops). First it warns you that your parking brake pawl is not engaged anymore and to use emergency brake. That was the first hint. Then CAN-View turned off. Finally light on dash get dim (duh). I charged back up the gel-cell for a few minutes because at that point i couldn't even get the car to start.

 

Wow, I needed to update this a long time ago. I want to post my progress properly but for the impatient, I'll summarize with good news. I have had no problems with my three total packs but I find myself constantly a little short on volts (you know what I mean) so I've added a fourth battery!!! Yeah! This one is from 2007 with 30K miles and I got for much less money. And after selling off some of the unneeded parts (like the battery ECU) the cost was brought down to under $200. Now I'm getting greedy and want to add more packs under front driver and passenger seat, but that will have to wait.

I built an upgraded charger which can switch between two "banks" of capacitors and is continuously cooled. Fast speed is 9A, and the slow speed is about 4 Amps, which is really slow on 4 packs, less than an Amp per pack. Only problem with fast speed is it pulls about 24Amps from 120V outlet. (Power factor of ~75%) That's fine for 30A dedicated breaker at home on a short run of 12 gauge wire to an unhappy GFCI then 25 feet of 12 gauge extension cord. It's not fine when plugging into a public charger, most of which are 20A. So I use the slow setting in town Even worse, power factor on 'slow' drops to 60%, so still close to 15A draw at 120V

At home I almost always use the fast setting, which uses a cluster of 4 440 microFarad caps. I decided just for the fun of it to use some 1 Oz copper PCB and etched two stripes off with FeCL (I used packing tape as a resist ) So much easier than using punchboard!!!! OMG, I can't believe how much easier, smaller and tidier this was.So here are some pictures, 1st is my splice into OEM traction battery. Note that what looks like a short between + and - is actually just a little spacer i taped in to keep them apart:

Next picture is my silly punchboard charger prototype. The nonsense on the left is just a 120V to usb adapter to power a little 5V fan I had lying around. It didn't do much in the way of cooling but I wasnted to be sure my components would survive a fan failure without cooking. They did! 105 deg C rating helps on the caps.

This next picture shows my priorities! It's a hack to replace my dome lights and map lights in the front with LEDs. Total cost, about $8. There not quite bright enough,but the auto dimming still works and they cast an eerie bluish glow at night. Fun stuff - 12V seems so comfortable after 238V!!!

Here's the backside
And here's the LED modules, they are 12V waterproof with built in current limiting resistor. They come in a string, as many as you order, and cost about $2 each. If you look closely, you can see the little plugs i added were salvaged out of the guts of some of the traction batteries, i think they energized the contactors, now they have the much easier duty of energizing LEDs.

If anyone's interested I can add more pics and info. I'll add pictures of my newer charger soon. Here's a teaser of my first PCB etching Capacitor board thingamawhatsit. If you look closely, you can see the lighter stripes through the PCB where the copper was removed, so it's just three stripes of copper, width based on an online calculator I found for 1 Oz copper, 10A current, 170V each lane.
Here's the full charger's guts spread out on our new rug (Fancy! From Target!! Made somewhere else besides China!!!) You can see the big DPDT switch that toggles between slow/fast charging and the new punchboard housing the the "slow" 390microF caps and the two diodes. I swapped in a different diode which takes a more conventional heatsink and mica spacer. Heatsinks were a $1 at Radio Shack, diodes are Vishay, rated at 30A continuous and were like $2 each or something. I like them better than the stud mount, even the stud diodes were rated for 60A. Without fan cooling, the smaller 30A ones don't even get that hot.

 

Charger explosion

My "new and improved" charger blew up! Actually the caps exploded - one of the diodes shorted, exposing the caps to full swings of the mains polarity. Since caps are polarized, they go "boom" when reversed (or when the polarity of the voltage reverses). Trunk was open so i just got a face full of cap steam.
Building yet another charger, this time doubling up the diodes, since at $1.75 each, there is no reason to skimp.
Total cost (blown caps, diode) = $12

In the mean time, I'm commuting 120 miles each day without a charger in hilly terrain and getting 48 mpg. I'm going to try the commute with fewer batteries, see what if anything happens.

Also my wife just leased a new 2010 Prius III with nav for $230 a month, no money down. Love the styling, handling but hate the low resolution nav screen. Wth Toyota? Looks like my 5 year old cheap cell phone screen. And I miss the integration of the Gen II controls - I tried using voice command to turn on AC in the new Prius and nothing happens. Ohhhh, Climate is now "normal" (translated 10 years out of date) control, looks like our 1998 Civic!

Overall I give it a B+ so far. Styling A+, navigation C-, especially for the price (although on a lease, and after all of the price-cutting by the dealer, i'm not really sure what we paid)

 

Re: Charger explosion

Yeah, that's the plan. Actually the capacitors are plenty beefy, but the diodes were for sure the weak link.

I had been pushing the limits of this capacitor type charger by adding more and more capacitors. It of course charges faster, but everything gets hot.

According to "kill-a-watt" meter, power factor is as follows:

390uF - 55% - 4A at 230V. So the poor extension cord gets ~15A (230/120V x 4A /.55pf )
880uF - 76% - 10A at 230V. So better pf but now 25A! Extension cord's getting warm! Circuit breaker trips so I put in a 30A breaker.

Then I added all the capacitors together. let's call it 1300uF.

1300uF about 14A at 230V. Extension cord is now HOT! Batteries charge FAST. Kill-o-zap caught on fire!!! (It still works but now has nice melted/scorched hole, which helps vent heat )
Power factor is 82% - probably the max, same pf as many wall warts)
1300uF - 82% - 14A at 225V. The 30A breaker blew when the batteries first starts charging - more current at the beginning ~210V at the battery. The mains sags to 110V at this rate and the cooling fans audibly slow down.

So that's why my charger finally went up in smoke - the diodes are only rated for 30A and they are actually two diodes on one chip, 15A each. Now they are matched on the die but probably not perfectly and I was pushing over 30A through them with big spikes as the caps charged each cycle.

New charger has similar diode but single, not dual (looks similar but only two pins instead of three on the chip) and I've doubled them up. So 60A theoretical, although diodes don't parallel perfectly but even if it's like an 80/20 split, that still keeps me under the limit.

I'll post some pictures once it's put together.

http://www.irf.com/product-info/datasheets/data/30eph03pbf.pdf
Datasheet - Datasheets, Search, Parameters

 

It totally depends on range and whether you can plug in at your destination. In theory, you get infinite mileage for up to 10 miles per charge (keeping under 34mph). If you do lots of little trips to the grocery store, movie store, etc, then no gas. But in the real world, you of course need to occasionally go over 33 mph. Or maybe you have to always go over 33 if you have a highway commute.

My wife used the car a few times on a twenty-five mile commute all freeway and she got about 75mpg instead of the usual 45 of a normal gen ii prius on the freeway. remember that at any speed, the bms+ tricks the ecu into thinking the battery if fully charged and so diverts power from the battery to supplement the ICE. It only contributes about 30% of the total power to the wheels, depending on speed.

Hope that helps answer the question.

 

Well, "jawshoeaw" is of course Joshua.

I forgot to mention that I am using 3 add on packs for a total of four.
Mr Big is right about retraining your driving style. I gave 75mpg as a number for someone (like my wife) who wants to get in the car, drive to work, and not "fuss with the car". Constant speed on the freeway - probably 60mph, let the Prius and BMS+ do their thing.

Here is a good example of driving style with Oregon gas which always has 10% ethanol, AFAIK. Tires at 38/36psi, 0W20 synthetic oil. No BMS+, no extra batteries, no charging the batteries, just stock Prius.

110 mile commute (temporary, thank goodness) when I am in a hurry, i.e. driving 65mph most of trip, I get 42mpg. With careful driving, I get 52mpg. That's with a little pulse and glide but mostly just being careful and driving slower. This trip involves lots of hills, a 1000ft elevation gain, lots of stopping and when I'm getting 42mpg, takes 65 minutes, and when I'm getting 52mpg, takes 85 minutes.

That's a half gallon of gas a day difference, and all I'm doing is driving slower and less aggressively. When driving on winding mountain roads for example, if you try to keep your average speed high, you have to brake harder entering the curves and then accelerate harder leaving the curves.

Anyway, now that Mr. Big has upped the ante to 5 batteries, I'm jealous! Maybe I will have to match. I'm excited about the battery monitors via can-view - I've been doing manual measurements every so often (which so far show well balanced packs).

 

You can charge the batteries with anything that outputs 240VDC and at least a couple amps. But....
You have to have a temperature cut-off, or two or three
You have to have a timer plus a second backup timer (and maybe a third, just in case )

The Zivan or other off-the-shelf charger may not always turn off.

An alternative would be to charge the batteries to some safer value like 234V to provide some margin of safety.

This is why I decided to build my own. The charger itself is super super easy to build - took me a few hours with near-zero knowledge of electronics. The hard part is all the safety stuff, which you need to add to a commercial charger anyway. But hey, we're all out here willing to help if you do decide to build a charger. It's time consuming but fun. The basic 4A charger cost me about $50 in parts including a timer.

 

I bought the parts from allied electronics and a few small things from radio shack. If you want a circuit diagram, I'll have to scribble something down - it's a very simple diagram which you can look up online - a capacitive doubler or just voltage doubler.

I've attached a crude drawing of what mine looked like with electrolytic capacitors (the cans) and chip-style diodes - the rectangles with two leads. The little squiggly lines are resistors which bleed down the capacitors once you shut the thing off. I used 56K 1W rated. Capacitors are 390uF 300V or 400V, 105 degree reated. Note that both capacitors and diodes have polarity - they only work in one direction and go poof in the wrong direction. Also note that the voltages involved are lethal - use appropriate precautions such as electrical gloves. There is no isolation with this circuit - no transformer to sit between you and mains.

Here's a few links:

Voltage Multipliers

Voltage multipliers : DIODES AND RECTIFIERS
Voltage multipliers