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Posted: Fri, 14 Nov 2008, 17:49
Regarding SLA batteries.
BTW, I just checked red suzi logged data and the SLA batteries (20Ah) pack droops 72V at 60A (72/576) = 12.5% (34.56kW being supplied)
Note this droop INCLUDES all wiring, contactors and fuses so the lead acid batteries are performing better than than many LiFePo4 in ESR (but then we knew that already). ~15mOhm per battery effective for the pack of 48. This equates to less than 4mohm per cell if they were LiFePo4 in 20Ah ! however TS 40Ah are 4mOhm per cell so would be around 8mOhm in 20Ah size. Interesting.
Data logging is only a recent addition, so no early data available.
I go with the keeping cells / batteries happy idea.
I have never overcharged or over discharged these 20Ah SLAs.
Deepest discharge around 70%. (never tried to find the wall)
They are discharged at an absolute max of 3C (60A) and recharged at max 0.1C (2A). Edit... regen average .3C (low duty cycle) with peaks to 1C.
Simple zener (2x6.8V and 5ohm res.) battery eq.s are fitted.
They are always on float charge at 13.8V with one of the 12 chargers after full charge.
Posted: Sat, 15 Nov 2008, 01:01
Thanks for this informative thread, in terms of the "Charging connection box" do I read you correctly that the achieved benefits/goals are?
- cleaner wirelogy
- another layer of safety added via that interlocks to battery breakup contactor system link
- non permanent on-board charger (perhaps NCOP14?), apart from Danfoss, and easily upgradedable for the future
- 48V @ PV direct charging option
- (more) all of the above
In another thread you have mentioned that if time allows you might post wiring schematics of RedSuzi that would be another great contribution..
Did you consider running some cooling contraption for the battery boxes (air/water)? As you probably know keeping the avg. lifetime temp of batteries in certain (sub 25-40° Celsius) range is very desirable for the cyclelife. As we once discussed it will certainly cost you some overall EV efficiency (more energy) but that's a tradeoff between early replacement pack, I think some basic cooling/heat protection at least for charging phase could be done on energy sound budget. Your battery boxes look like as one giant heatsink so perhaps adding few blowers or water circuit on the sides can do it easily.
Basically all NiCd, NiMH, Li-ion batt. pack equiped production EVs have it as standard at least for the charging phase. Also, nightly charging with the usual temp drop is at least the minimum, temp corrected chargers with lower charging voltage is another layer. Just an idea would it be possible to incorporate rudimentary temp correction in SMPS family of chargers via adding picaxe board or similar?
Posted: Sat, 15 Nov 2008, 02:53
acmotor wrote:Integrating the speed column wrt time to give distance shows 4.8km so this looks correct. Integrating battery kVA (kW) shows about 0.97kWh nett. Looks about right, given this was very stop/start and playing around.
Distance traveled: 4.8km | Battery (netto/battery to wheel): 0.97kWh | => economy: ~202,1 Wh/km
Tesla Roadster in the latest hw&sw revision (8/2008) has gov. certified economy in EPA combined cycle (probably a bit higher avg. speeds than yours) in plug-to-wheel efficiency 174 Wh/km (28kWh/100mi).
So, for the RedSuzi, vehicle platform and AC Danfoss drive combo, if you similarly add the efficiency losses upstream/brutto (charging, bms etc.) for the fair comparison the result should be still very favorable to you, estimated guess <250Wh/km..
Now, recalculated for CO2 emissions, 50% mixed coal grid (650gCO2/kWh)turns out better than stock ICE car, 100% coal grid on par or slightly better in whole cycle, and solar charging = single digit % emissions.
One can only dream about the availability of more aerodynamic, low roll resistance platforms, ~70km range (netto) from the same lead pack of yours therefore possible..
Diagnostic software: most of the Danfoss VFDs (and other brands) can communicate over ModBus/ProfiBus/CanBus. This usually also needs commercial software but demos or first opensource alternatives exist. Moreover, the advantage over stock Danfoss sw/utilities is that with -bus communication you can integrate every possible components into one data/control stream (vfd, bms, charger, aux. units like heating etc.) with the option of remote control/safety while charging etc. I'm currently playing with my baby Danfoss FC302/3kW and these -bus connections/human user interfaces.
Posted: Sat, 15 Nov 2008, 04:57
Red Suzi's 202Wh/km vs Tesla's 174Wh/km is not really comparable.
Posted: Sat, 15 Nov 2008, 05:12
Mesuge wrote: Tesla Roadster in the latest hw&sw revision (8/2008) has gov. certified economy in EPA combined cycle
(probably a bit higher avg. speeds than yours) in plug-to-wheel efficiency 174 Wh/km (28kWh/100mi).
Well, it's not 1:1 that's what I mentioned there, anyway Tuarn can adopt ~EPA combined cycle kind of test procedures, and present a nice face off. The difference shouldn't be that big..
Here they cover the 2008 updated methodology:
http://cars.about.com/od/fueleconomyinf ... esting.htm
If not applicable for RedSuzi because of the 2008 mandated higher highway speeds for the test, we can focus only on the city cycle part and compare on that front.
Posted: Sat, 15 Nov 2008, 05:26
Funny it seems a lot of work so they can slap a sticker on a car to help people decide which car to buy.
Posted: Sat, 15 Nov 2008, 07:17
I'm glad you like the charging box. I find it very safe and flexible in charging options. Particulary in there only being 48V(nominal) at the time of charging.
Re battery temperatures....
I am in fact living in the best city in the world.
One of its advantages is an average temperature of 23 deg C. Never below zero and apart from a few hot hours on a few hot days above 40 deg C with low humidity, it is ideal EV country.
A garaged vehicle's batteries see 15 to 30 deg C during (slow 8hr)charging with almost no temp rise with the slow charge. Noted that many high charge rate systems in EVs will cause temperature rise - because the rate is too high and causes charging losses.
Discharge rate in red suzi is quite low at average of <1C with short peaks to 3C.
Mesuge, your point taken re temperatures. I shall log some as well so we can consider it.
Re efficiencies. It should be called "recharging energy source to km" not plug to wheel
These first logging runs were with minimal regen (10-20% torque) that is less than equivalent ICE engine braking. I will wind it up a bit more as I am still using mechanical brakes to stop.
I will tidy up the wiring diagram soon and post it up.
I am doing a crash course on bosch CAN bus at present, as the silicon labs micro that I work with in C has a hardware CAN bus system built in.
You are right about the control and logging potential of this.
No shortage of things to do !!
Posted: Mon, 17 Nov 2008, 01:09
Another comment on the batteries and temperatures...
Float voltage is specified as 13.5 to 13.8V at 20deg C with slope of -20mV per deg C
This means that for the 15-30deg C typical range I expect, that the float voltage range will be ...
(13.5 - .2 V) = 13.3V to (13.8 - .2) = 13.6V at 30 deg C
and (13.5 + .1) =13.6 to (13.8 +.1) =13.9V at 15 deg C
i.e. around 13.6 V covers most temperatures.
Measured float voltage with zener shunt is 13.60 13.70V at 20 deg C and 40mA float current so I think I can get away without any further temperture correction.
With predicted global warming of 5 deg C, I may have to adjust this slightly !
The batteries are only charged at up to 2A, so charge time is up to 8h depending on DOD. It takes 12 hours to drop the current to less than 100mA.
This is different to the (pushy) fast charge option for SLAs.
Note. Regen takes batteries up to 15V for short bursts when pack is full/near full.
Posted: Mon, 17 Nov 2008, 02:23
Yes slow charging is the rule of the day at the moment, and one of biggest "PR" problems with EVs, people are not used to alter their lavish (fossil energy abundance induced) lifestyles over appliances such as an automobile.
The cyclelife of most of the available batt. chemistry is quite temp picky (the numbers manufs. feed us is certified in narrow/lab controlled environment). Take sealed lead acids, avg. lifetime temps over 30C will kill the theoretically possible cycles quite rapidly.
PC UPS failures anybody? Even the expensive ones with temp adjusted charging kill batteries prematurely largely because of the heat/ventilation issue.
What I meant to say, and what is perhaps not applicable for your RedSuzi application as you described the location are for instance the following conditions:
Battery pack: located bellow the car's floor (former gas tank/exhaust tunnel), that's not very much vented area, just few centimeters above the pavement
Summer: during errands parking on the streets (receiving heat from all directions), driving through thick stop & go traffic for dozens of minutes, the car gets very hot, even after taking an hour rest at the final destination before charging, enforcing cool down of batt. pack might be desirable.
Winter: -15 to 1C temp (Central Europe), the pack should be a bit preheated before charging, at least to 15-20C etc. Yes, due to global warming sub zero temp days are slowly diminishing, especially in the populated areas which radiate their own extra heat.
Good intro into these batt./temp issues:
Posted: Mon, 29 Dec 2008, 21:33
Another graph of logged data...
A 3.1km run stop start in short hilly backstreets.
Battery data shows 189Wh/km
This run was with 100% regen selected (range 0 to 440%)
(full regen is too much, locks up rear wheels)
The calculated regen is the sum of Wh returned (at least offered) to battery pack. Almost no mechanical brake was used in this run despite the low speeds, hills and stop signs.
Vehicle was driven hard as the speed changes show.
Clearly regen is significant in city driving.
Posted: Tue, 30 Dec 2008, 04:27
Danfoss controller parameters for VLT5042 are numbered in groups 0,1,3,4,5,6,7 with numbers 001 to 711 (not all numbers are used)
Here are the changes I make from the default settings...
(they won't mean much to someone without a VLT)
These are the setting I use for speed open loop control.
008 .63 for kmph in red suzi
009 power kW
010 DC link V
012 output energy
107 do an AMA, this gives for my motor..
108 0.3579 ohm (resistance)
109 32.19 ohm (reactance)
128 ETR warning 1
129 yes (external fan)
200 0-132Hz both directions
300 no op. these I/O depend on your connections
301 stop inv. "
302 latched start "
306 no op. "
307 no op. "
309 0.2V accelerator min scaling
314 no op.
400 overvoltage control (no regen) (or resistor control when battery full for regen)
405 auto x 2 (restarts)
409 61 (trip delay torque)
410 35 (trip delay inverter)
411 14kHz (switching frequency)
422 7.9V (U0 voltage)
445 enable (flying start)
446 60deg AVM (switching pattern for high freq)
447 0% (torque compensation)
450 342V (low volts AC, ~ 470DC)
506 digital input
P.S. you can return the VLT to factory defaults by turning power off, holding down DISPLAY/STATUS + MENU + OK and turn power back on.
Display will show 'manual initialise'
Posted: Tue, 30 Dec 2008, 05:05
Hi Tuarn, thanks for the update, impressive regen for diy project. I'm wondering does this sw setup relate to that "hybrid charge mode" of yours as well, i.e. charging by VLT using brake resistor as overvoltage protection etc? It seems to me though this particular setup is just "driving mode only" right? So have you by now abandoned that previous VLT assisted charging method completely with the new wiring and individual SMPS charger links (12x)?
Posted: Tue, 30 Dec 2008, 06:23
The 'VLT charging' was simple but perhaps too simple.
I only use the 48V module charging method now. I should update evalbum on this point. (edit : done)
Shunt regulation with resistor worked but was wastefull of power.
Running the Danfoss all the time during charge was wastefull.
These power wastes show up on the 'plug to road km' efficiency.
Battery eq. in the string was a bit average. 2A of eq. would be required.
I consider that having to have the battery pack all connected up to 600V for charging was not a good safety principle. 48V modules is a lot smarter. EV converters should be mindful of this, even at 144V.
I must try 'tow charging' and log some data as well.
Posted: Tue, 30 Dec 2008, 18:25
Regarding regen and batteries. How do you think the battery life (your AGMs) will be effected with the high charge current that you briefly get during heavy regen braking?
Posted: Tue, 30 Dec 2008, 20:08
Simple answer - I dream of ultra caps !
The recharge current is something I have pondered on.
The Henda batteries are rated at .3C ideal constant rate charge.
These are 20Ah batteries so 6A charge. This equals 3.6kW of regen in this case with 600V pack. Quite a significant amount when driving, particulary since it still occurs at only a few kmph.
On the earlier graph, regen would only average this 6A amount with one pulse to over 1C (20A), so it is probably quite OK and should not be detrimental to battery life. After all, the average DOD is being reduced and lead acid likes that.
If more regen were used (and there is plenty more, 4x) then charge rate may be of more concern with these batteries.
The capacitor bank in the Danfoss goes a little way to smoothing the recharge ripple. I have also retained the 'DC chokes' internal to the Danfoss as they make the internal capacitors handle the ripple and not pass it on to the batteries.
Now I don't pretend that the SLAs are ideal for this regen exercise,
The recharge cycle efficiency may be only around 80%.
lithium or NiMH would be better (if no ultracap in use !).
The Rodeo with TS will be a better arrangement.
Your thoughts ?
Posted: Tue, 30 Dec 2008, 20:33
Thoughts. From the AGMs on my list I have pretty much decided on 6 to 7 Amps being the most reasonable current limit. I REALLY want to give the batteries the best chance at long life that I can.
Why I bring this up is the issue of whether or not to include a breaking resistor from the outset. I have been messing around with a system to limit battery regen to 7 Amps while maintaining full regen into a brake resistor but I think this one will have to wait until I see what my real-world driving looks like.
I don't really want to PWM control current into the batteries as this would be counter to what I have read that lead acids "like" (don't like ripple, low or high frequency). So I had pondered a 3 tiered system just using power resistors that generally held the regen current into batteries at less than 7 amps just by having preset current steps.
In your experience, do you regard around 4kW regen as more or less than regular ICE braking?
Posted: Wed, 31 Dec 2008, 07:09
The 3.6kW approx that I am using at present means that I don't use the mechanical brakes in normal driving unless it is downhill or pulling up for a dark amber light. It is a bit like an ICE in second gear with lots of engine braking. Regen could be more though. But perhaps not on RWD.
I am not using the brake resistor at present so I need to be careful about the braking in the first few km after a recharge otherwise it takes the batteries up to ~15V each and the Danfoss lets go. Not a big issue itself but the eq. is not certain to keep up.
I did consider connecting the battery pack to the Danfoss via a power diode (100A , not much PIV needed) shunted by a power resistor to carry the regen. I guess you don't need a diagram there.
Use a braking resistor as normal for the controller to dump into and the shunt resistor would be R=V/I say 100/7 = 14 ohm 200W (assuming small duty cycle).
This has the advantage of using the Danfoss capacitor bank to store some of the regen energy and take some (tiny) load off battery pack.
A PWM system instead of the resistor would be more efficient but if you are going to throw the excess power away anyway..
Do you follow my thinking ???
Posted: Thu, 01 Jan 2009, 01:25
I really like this conversion its so clean and almost factory like.
It would be nice if the chinese and Indians catch on to this vehicle
as it could be a great vehicle for those and other countries.
Im just wondering how much further it would go with high silicon road
tires of say 165, rwd only mode and lowered substantially to increase aero?
Posted: Thu, 01 Jan 2009, 02:10
Zook (Suzuki Sierra) fans would crucify it.
I guess neither of these are what you were thinking ?
Posted: Thu, 01 Jan 2009, 02:45
Regen at 7 Amps sounds perfect for me then. I have been donated 4 of 200W 100 Ohm resistors so they will be perfect in series parallel for about 7 Amps at 700 V so I'll go ahead with that based on your info. They should cope for short periods and they are aluminium cased so dead easy to mount. Thanks heaps that's all I needed.
Posted: Fri, 23 Jan 2009, 20:23
acmotor wrote:The 'VLT charging' was simple but perhaps too simple.
I only use the 48V module charging method now.
Can you explain how the VLT charging worked, please? I'm curious.
Posted: Sat, 24 Jan 2009, 04:29
the charging on the vlt was just the rectified 600vdc off the 3-phase mains input if im not mistaken.
Posted: Sat, 24 Jan 2009, 07:49
The mains input side of the VLT is simply a 3 phase bridge rectifier with some RFI filtering and inrush protection / soft start to charge capacitor bank.
The batteries are connected straight after the 3 phase bridge (not ideal, should be after the DC choke for a correct charger)
The AC voltage in x 1.4 gives DC bus voltage.
I used a 240V to 500V transformer ~ 1kVA with variable tappings to select a suitable voltage to feed the Danfoss input to charge the battery pack.
As I have noted, I don't use this any more, prefering to use the 48V charge mode.
I did use the brake resistor to limit charge voltage on the Gemini (385V system).
There is potential to use this charging method or an addition / modification of same.
Posted: Sun, 25 Jan 2009, 18:39
Ah, OK, thanks acmotor.
So it's basically a "not-so-badboy": isolated (assuming it's not an auto transformer), inrush protected, EMI filtering, etc. But it uses only a handful of components at the input end of the controller.
I had visions of you using the motor as a single phase to three phase converter, and using regen from the controller to efficiently charge the battery. In fact, on a conversion with a clutch, it may make a bit of sense. Disconnect the motor mechanically from the wheels and electrically from the controller. Connect the (isolated!) mains to one winding; start the motor with a capacitor. When up to speed, disconnect the the capacitor and reconnect the motor to the output of the inverter. (This is a scary part, for sure; you'd have to somehow prepare the inverter for full voltage on the output). Then tell the controller to regen at the desired charge current, possibly limiting the power to what you can draw from the presently used outlet. The motor then acts as a single phase to three-phase converter, and the controller efficiently converts the three phase energy to DC for the battery. You can use the controller's parameters to set the desired voltage and current limits.
Is this practical? Probably not. But it's an intriguing idea.
It uses a lot of contactors, and requires an isolation transformer (except for very, very bad boys with very well isolated non leaky packs), but re-uses the controller electronics for the charger. With mains chargers being fairly cheap these days, if you have the contactors to isolate all your 48-volt groups, that would probably be a lot safer and sensible.
I mainly mention it here because I thought that that (or a variation of it) was what you meant by VLT charging.
So acmotor, what's your charging plan for the Rodeo? Charge in 70v groups?
Posted: Sun, 25 Jan 2009, 23:38
Last question first... Yes, Rodeo will be the same idea of contactor isolated modules (around 22 x TS 3.2V nominal, maybe less like red suzi).
The advantage of 'module' charging is the intrinsic safety of lower voltage and the ability to efficiently charge parallel modules from low volatge solar etc.
No badboy ! I use isolated transformer. This also has the added impedance to provide current limiting when batteries start from low SOC.
Interesting you mention creating 3 phase using a motor (and cap). This is, as you know, a common technique and commercial units are available although it is rather historical (and low eff.) given modern inverter / VFD technology.
The first VFD I used was an old SCR model, you know with the commutating system to make the SCRs let go. It would not run from DC alone and required all 3 phases of AC on its input to fire up. I used a small 3PIM and run cap and a 50Hz inverter to provide a small abount of 3 phase to its input and then connected the DC from batt. to the internal bus.
It worked but was an old 'dumb' controller. I moved on to the Danfoss.
You are right about using the motor side of VFD as input. In theory this would work however without access to the VFD firmware I would not go that direction. Too much smoke would be likely to escape and a wrong adjustment might shut down the street !