Hemonster's ACIM conversion

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Post by Johny » Mon, 18 May 2009, 20:17

I just had a response about BMS changes.
See what you make of this reply from them.
"it can charge with 1C and discharge with 2C together, and also can charge with 5C and discharge with 10C in moment." worried me a bit.

----------------------------------------------------------
Image

1, This system has 10 battery packs, each pack has 38120- 40 cells, 20 in series, the nominal capacity is 20Ah, nominal voltage is 60V. The totally capacity is 20Ah,and 600V. The worhing voltage is between 500V—660V, the max charge voltage is 730V, it can charge with 1C and discharge with 2C together, and also can charge with 5C and discharge with 10C in moment.
2, each battery pack dimension is 150×158×500㎜。Weight is 15.5Kg。
3 . A single battery pack installed capacity module type balanced to ensure that its charge, discharge and still have a balanced role of state.
4 A single battery pack has the 27 holes outlet inside, as a communication sample, and if the temperature testing requirements, can provide jack.
5. The system has a control box. Each battery pack has sampling line and the control box to connect, control box to control every single battery and the battery packs of over-charge and over-discharge,over-current protection, short circuit protection, control box with 400A fuse and indicator light 10 shows that the equilibrium state of the battery pack any anomaly, the master cartons have 17 core socket as battery charge and discharge current and the overall battery voltage and all the work of the state of the main circuit of the communication module sample used;
6 6.Master box dimensions of 220 × 160 × 120 mm, weight about 6Kg, have four mounting holes.
PS:every 38120 cells we have 3V10Ah to calculate.

Edit: Added image
Last edited by Johny on Tue, 19 May 2009, 08:02, edited 1 time in total.

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Post by weber » Mon, 18 May 2009, 20:21

Hemonster wrote: Can your battery do that? ie. 1C continous charge rate?
No trouble. Particularly since charging is endothermic. But I don't know what it does to their life. 0.5C is recommended.
Sorry, let me clarify ... the high resistance is from batt +ve to chasis, and another one from -ve batt to chasis, each monitored separately. Insulation failure from mid pack to chasis will generate a warning because a conduction path will flow through the high resistance via the chasis to the mid pack.
I beg to differ, unless I am still not understanding what you propose. With two equal resistors from chassis to battery extremes, mid pack will be sitting at the same potential as the chassis therefore insulation failure from mid pack to chassis will not cause any additional current to flow anywhere, until someone connects themselves between chassis and some other part of the battery (and thereby becomes the second fault, with the first having gone undetected).
I have learnt from another forum that small leakage currents over long periods of time can corrode contacts as you are wearing the metal away. This is exemplified with the process of electrolysis, using a high voltage DC small current source, place the electrodes in a water solution with electrolyte mixture (baking soda say). Even with small currents you will see corrosion on the electrodes. A similar issue occurs with these high impedance resistance connections.
OK. But, as you say, that will be taken care of by pack-breakup contactors as pioneered by acmotor, which in his and my opinion are not optional.
The leakage detector doesn't detect short across the pack, only leakage from pack or traction circuit to chasis.
Agreed. Only I prefer to use the term "insulation failure" rather than "leakage" because an earth "leakage" circuit breaker (ELCB) only detects potentially lethal currents (and interrupts them quickly) while an insulation monitor must detect sub-lethal currents that it tries to create itself.
So if water bridged across mid pack to chasis, the leakage detector would sound.
A proper insulation monitor would, but not the simple one you describe above.

If you were to switch the resistors in alternately, and allow for some delay due to capacitance, then you could detect a fault from any part of the battery to chassis. But, as I think you mentioned, you must not detect false positives due to AC voltages between pack and chassis caused by perfectly normal, fully insulated, VFD operation. (e.g. the 3rd-harmonic common-mode "neutral wobble").
If it bridged across the internal batteries inthe pack without touching the chasis, then you either have to rely on your BMS for the warning, or fusing per pack. You could however encase the batteries in a metal box that is connected to chasis ground, and if water gets in, there is a good chance that it will short from battery terminal to its box, hence triggering the leakage detection.
Agreed.
Do you know pricing for these [Bender insulation monitors]?

No, sorry. Haven't got that far. These from Farnell may be an indication. $300 to $600. I haven't looked at the specs to see if they are suitable.
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Post by woody » Mon, 18 May 2009, 20:25

Johny wrote: I just had a response about BMS changes.
See what you make of this reply from them.
"it can charge with 1C and discharge with 2C together, and also can charge with 5C and discharge with 10C in moment." worried me a bit.
My Engrish<->English translation:

Discharge: 2C (40Amp) continuous, 10C (200Amp) peak
Charge: 1C (20Amp) continuous, 5C (100Amp) peak.
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Post by antiscab » Mon, 18 May 2009, 20:28

weber wrote:
I beg to differ, unless I am still not understanding what you propose. With two equal resistors from chassis to battery extremes, mid pack will be sitting at the same potential as the chassis therefore insulation failure from mid pack to chassis will not cause any additional current to flow anywhere, until someone connects themselves between chassis and some other part of the battery (and thereby becomes the second fault, with the first having gone undetected).


the twin connection point approach *requires* that the high resistance paths are *not* always present. its always one or the other, or neither.
if you have both continuously, you will get severe corrosion problems.
if you run both at the same time, both would detect the other, and give a false positive *all* the time.

Matt
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2007 vectrix - 156'000km
1998 prius - needs Batt
1999 Prius - needs batt
2000 prius - has 200 x headway 38120 cells

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Post by Johny » Mon, 18 May 2009, 20:33

Johny wrote: Dear Mr John,
20Ah60V battery with 40 cells of 38120 cell battery, so the max current is 300A and the continuance current is 200A.
Hmmm! I thought we were onto something here - now not so sure.

hemonster, your thread has become a battery, BMS stamping ground - sorry.
Do you want to split all these off now or just start a new thread about your vehicle later (or keep going)?

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Post by Hemonster » Mon, 18 May 2009, 20:39

weber wrote:
I beg to differ, unless I am still not understanding what you propose. With two equal resistors from chassis to battery extremes, mid pack will be sitting at the same potential as the chassis therefore insulation failure from mid pack to chassis will not cause any additional current to flow anywhere, until someone connects themselves between chassis and some other part of the battery (and thereby becomes the second fault, with the first having gone undetected).
Good point (I missed that), and as you mention the missing ingredient of course is to measure them asynchronously. This way the chasis isn't at mid-pack voltage when each are measured.

weber wrote:
OK. But, as you say, that will be taken care of by pack-breakup contactors as pioneered by acmotor, which in his and my opinion are not optional.
Agreed Image

weber wrote:
Agreed. Only I prefer to use the term "insulation failure" rather than "leakage" because an earth "leakage" circuit breaker (ELCB) only detects potentially lethal currents (and interrupts them quickly) while an insulation monitor must detect sub-lethal currents that it tries to create itself.
Subtle, but a good point ... still need to learn up the jargon proper. Image

weber wrote:
fully insulated, VFD operation. (e.g. the 3rd-harmonic common-mode "neutral wobble").
I'm not sure I know what that means, but sounds important enough to avoid. ie. perhaps only do detection when the car starts up (during precharging say) then remove, or resume detection 5 seconds from when the accelerator microswitch disengages.


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Post by Hemonster » Mon, 18 May 2009, 20:41

Johny wrote:
hemonster, your thread has become a battery, BMS stamping ground - sorry.
Do you want to split all these off now or just start a new thread about your vehicle later (or keep going)?


It's all good, keep it going Image

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Post by Hemonster » Mon, 18 May 2009, 21:01

antiscab wrote:
the twin connection point approach *requires* that the high resistance paths are *not* always present. its always one or the other, or neither.
if you have both continuously, you will get severe corrosion problems.
if you run both at the same time, both would detect the other, and give a false positive *all* the time.


Hi Matt, true indeed. I'll use a relay for each of the resistors to chasis and energise them separately using a micro.

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Post by weber » Mon, 18 May 2009, 21:04

There is some explanation of VF-drive neutral-wobble with graphs, by coulomb, here:
viewtopic.php?keywords=neutral%2Bwobble ... 8919#p8919
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Post by Johny » Mon, 18 May 2009, 23:14

Reassuring news. We still need to check the individual cell specs.

Hello John,
600V20Ah battery maximum continuous current (over 60 seconds) is 200A,

Michelle


    
    Hello Michelle
    I am concerned.
    In one of your first emails you stated:
     
    "20Ah60V battery with 40 cells of 38120 cell battery, so the max current is 300A and the continuance current is 200A."
     
    Then within the Word document your sent it stated:
    "it can charge with 1C and discharge with 2C together, and also can charge with 5C and discharge with 10C in moment."
    which seems to indicate 2C continuous dischange rate - 40 Amps."
     
    Can you tell me what the maximum continuous current (over 60 seconds) of these packs is please?
     
    Thank you
    John


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Post by Johny » Tue, 19 May 2009, 16:20

I hadn't much attention to this test before because I was never going to build my own pack from cylindrical cells but Ian Hooper (Zeva) has tested Headway cells with these results.
(Thanks Ian)

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Post by Johny » Tue, 19 May 2009, 18:03

I have added the sketched image from headway for the 600V system with control box to the post at the start of this page.

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Post by Hemonster » Sat, 23 May 2009, 01:17

Hi Johnny,

Thanks for the update. I've found a local guy in NZ who's selling his lightly used Headway cells, I'm getting 8 of them to test - so at least I know what I'll be getting. I will let you know when I get them.

I did write to Headway but found that they were quoting 700USD to ship 14x 48V 20AHr packs to NZ via air ... yikes!! But what got me was that it is 500USD to ship via sea! I was very surprised by this as greensaver quoted me 97USD for 360kgs (54x 12V 20AHr) of PbA batteries which have higher volumes as well. I questioned Victoria about this, but she went quiet all of a sudden. Could it be that Headway are charging more for freight to compensate for their cheaper cells? (hmmm ....)

Mind you I also questioned her about cell failure rates, and existing customer websites (so I could send a friendly email to them to ask them about reliability) and haven't heard on those fronts either. She assures me however these are a mature product and sell into many countries such as France, US, Canada and Oz, used in electric motorbikes.

Johnny, were you quoted pricing for shipping?








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Post by Johny » Sat, 23 May 2009, 01:33

No, I haven't had a shipping price as I assumed it would be reasonable - Hmmm.
----------------------------------
Here is another email I got when I asked about any price change for the 600V control box.
The 300V chargers puts a dent in the battery break-up system for safety.



Hello John,
About 10--60V20Ah to be 600V20Ah, the battrey cost is add cost to the 10 x 60V packs, but that battrey pack need two chargers in enough, each charger is 300V.

Michelle




    Hello Michelle.
    Thank you - I understand now.
    Will the system to make a 600V battery pack add cost to the 10 x 60V packs and chargers?
     
    Regards
    John

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Post by Nutz » Mon, 25 May 2009, 04:33

It's a shame you are on the wrong side of the ditch over there in N.Z.
All of a sudden I could have offered you a cheap Mitsubishi Nimbus (Chariot) with a blown transmission.
I'll Put a post in the classifieds section. Image

Edit. Unless anyone can offer a cheap 2nd hand set of parts for a conversion.
Last edited by Nutz on Sun, 24 May 2009, 18:36, edited 1 time in total.
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Post by Hemonster » Mon, 25 May 2009, 17:39

Oh that's a pity Nutz ... did you rev it too much Image   I'm leaning more towards a Galant now anyway as I'm inclined towards LiFePO4 just for a more elegant design despite the upfront cost. But haven't found a suitable car yet, so may yet flip and flop a few times in the decision making process until I get something Image

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Post by woody » Wed, 27 May 2009, 05:35

woody wrote:
Richo wrote: The EVPST cells are cylindrical cells spot welded together.
Where do you get this from? (All I have to go on is the pictures)
Image
The 7Ah above could be welded cells
Image
This one looks like TS-style with vent...


I asked EVPST:
michael.zzf wrote: Hi Woody,

Thank you very much for your inquiry for our LiFePo4 battery .
Yes .Our high rate cells (7,8,10 Ah) are Prismatic LiFePO4 cells as we as our 12Ah ,40Ah, 55Ah and 120Ah high capacity cells.
And we also have high capacity LiFePo4 polymer cells at 10,12,15,20Ah .For more details at www.evpst.com

To put them upright would be better than to lie them down when storage.

As for the cycle life of the cells, Guarantee is 1500cycles with DOD at 80%.
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Post by Hemonster » Tue, 02 Jun 2009, 02:38

Thought I would give an update:

I got my Headway sample cells from a guy locally who was selling them after he had done some experimentation. Here is what is looks like:
Image

I'm trying to get myself setup with aLabJack U3unit and I've setup the test station as shown below:
Image

It isn't quite complete yet and I have to add some relays in there and potentially some voltage monitoring safety circuits to protect the cell. Possibly with a FET that is PWMed to get the right current for both charge/discharge testing. I'd use the same FET perhaps to do a discharge test, and have relays (my NanFeng ones due to arrive sometime) select between charge/discharge paths. I intend to charge the battery with a higher voltage battery so I can get the amps (perhaps a car battery?).

I made my own shunt from a bit of joining metal strip - works out that tip to tip is almost exactly 15mohms which I calibrate using a 1A source. Basically this is done using a bench supply set to 1A, and the amps are checked with a Fluke - good thing is they both agree with each other Image. Then I take the voltage drop across the shunt terminals to work out its resistance - it's a large surface area so I'm hoping it is thermally stable across the current test range.

I'm testing the cell to 50A which is 5C and see how well it performs for AHrs and voltage dipping. This should give me an indication of internal resistance. I have some charts from Headway which I can compare these discharge ratings against.

For the moment I'm using a simple load made out of curtain wire, see below:
Image
This is immersed in water bath to ensure it doesn't just glow white hot (which is what happenned to the first one I used). Instead is makes a funny buzzing noise. With the battery mostly fully charged, this load draws about 30A and battery dips from 3.3 down to 3.0V - I didn't think this was too bad. The load can be changed by cutting down the curtain wire - it was really the only thing I had lying around that was handy - I'm sure there are other means to this end Image

These cells have M6 screw hole terminals on the ends, which make it nice and easy to attach ring terminals to.
Image


Apparently Headway was using a shipping forwarder who was charging heaps. When I suggested to them to use a different forwarder (same one as Greensaver) the shipping price dropped to USD95, from USD500 - more inline with the quote from GS. This makes a HUGE difference! Also the pricing quoted to me for the 48V 20AHr pack was with a 6A charger which is a bit much for my poor 2400W socket - to make it more universal I've asked instead for a 3A one (6-7 hour charger) which reduces the pack price (I think) by USD30, I'm getting confirmation of this.

edit: Oh yea, the bread board in my test setup is there for voltage divider resistors because the max voltage on the LabJack terminals it can measure is a piddly 2.5V Image This works in favour of the shunt however which is around 15.5mV at 1A, and about 700-800mV during 50A discharge. I'm also going to push that boundary to peak discharges of 100A and 150A (ie. 10C and 15C) which Headway have also provided me charts for. I'm hoping to also implement some thermistors to measure battery temperature, and maybe load temperature? (for fun)

edit: spelling.
Last edited by Hemonster on Mon, 01 Jun 2009, 16:44, edited 1 time in total.

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Post by Johny » Tue, 02 Jun 2009, 02:50

Fantastic work hemonster. I have high hopes for these cells and I'll be watching with interest.

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Post by Johny » Tue, 02 Jun 2009, 17:57

Hemonster wrote:... Also the pricing quoted to me for the 48V 20AHr pack was with a 6A charger which is a bit much for my poor 2400W socket - to make it more universal I've asked instead for a 3A one (6-7 hour charger) which reduces the pack price (I think) by USD30, I'm getting confirmation of this.
That makes the 48V packs less expensive (by about US$80 than the 60V packs.
60V was (600+44)x10 = 6440
48V now 530*12 = 6360
I was going for the 60V ones partly due to price and partly because it reduced to series resistance of break-up contactors (8 instead of 10, not counting the main contactor). A bit picky I know - probably not worth it.
Incidently I asked and got email response that the 60V pack dimensions are 150 x 158 x 500mm. Don't know which is height but I think it's the 150 - do you know? Oh, and the 60V packs have mysteriously disappeared from their web site - still on alibaba though.

Have you given any thought yet to the issue that their BMS(s) won't handle packs in series and have you asked about this? It may impact on the charger arrangement.


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Post by Hemonster » Wed, 03 Jun 2009, 03:03

Hey Johny,

Nice blog Image I'm considering starting mine too ... would make things much easier to read. Forum is nice too for good interaction.
Johny wrote:
That makes the 48V packs less expensive (by about US$80 than the 60V packs.
60V was (600+44)x10 = 6440
48V now 530*12 = 6360
I was quoted for the combined cost, I don't have a break down. I'm waiting back to hear from them what the deal is. Was the 44 you were quoted for the BMS or the charger?
Johny wrote:
I was going for the 60V ones partly due to price and partly because it reduced to series resistance of break-up contactors (8 instead of 10, not counting the main contactor). A bit picky I know - probably not worth it.

Incidently I asked and got email response that the 60V pack dimensions are 150 x 158 x 500mm. Don't know which is height but I think it's the 150 - do you know? Oh, and the 60V packs have mysteriously disappeared from their web site - still on alibaba though.
Alibaba lists the 48V pack as 293x110x160, I'm not sure which is the height - but I guess that depends on what the orientation is.
Johny wrote:
Have you given any thought yet to the issue that their BMS(s) won't handle packs in series and have you asked about this? It may impact on the charger arrangement.


I thought I would remove the FETs or short them out but have the gate signal come out via an opto for controller and charger control. The BMS can't break the 600V because it will break them under load.

Thinking out loud, I'm wondering if my relays can be configured to bypass the cell. Its a SPDT so that when the relay was off the terminals are connected through (bypassing the cell), but when turned on it breaks that connection and inserts the cell in series. I'll post a quick schematic soon.


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Post by Johny » Wed, 03 Jun 2009, 03:47

Thanks for the kind words about the blog. Hopefully it will start to get some "meat" in it soon rather than just being an "I've collected this" document.

I was concerned that modifying the BMSs would void whatever warranty we could hope to have on the packs. I have asked them about the 300V chargers (current - same concern as you about 240V, 10A outlet) they suggested, but the answer is not decipherable. I'll post when I know something for real.

The $44 was for chargers.

I tend to agree, other than warranty, about modding the BMSs. Short out the Drain/Source and use the gate drive to drive the LED side of an opto. Put all the opto outputs in series and use that to "trip' the VFD - 24 VDC input on VFD should be about right.
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Post by Hemonster » Wed, 03 Jun 2009, 14:02

Here is a quick schematic of the my proposed switch out topology:
Image

Some concerns I have ...
1. It needs to break-before-make contact, otherwise the battery will be shorted.

2. Not sure if it is safe to break under load, even though it should technically be momentary only before the load can resume. (I'm hoping <50ms). In that time I'm hoping the bus caps may handle sourcing the diffence in the short duration.

3. Have to ensure that the main contactors cut out the series string if too many of the cells start doing this, as the bus caps will dump energy into the remaining packs and probably setup a chain reaction for all the other BMSes to shut down as well (for over voltage). Also definitely ensure that the main contactors cut out before shorting the bus caps to GND!! This is probably where the idea dies a horrible death ... but I'm open to ideas.


Why do this?
... the idea is because it would enable each pack's BMS to safely? take itself out of the series string if it is under stress, but still enable the car to run. In this way you aren't dominated by the weakest cell. The problem then lies in ensuring there is enough monitoring to let the controller/driver know this event has occurred and not to stress the car as you are working with less voltage.

I appreciate your collective thoughts and ponderings Image

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Post by coulomb » Wed, 03 Jun 2009, 14:32

Hemonster wrote: 2. Not sure if it is safe to break under load, even though it should technically be momentary only before the load can resume. (I'm hoping <50ms). In that time I'm hoping the bus caps may handle sourcing the difference in the short duration.
I don't think you want to change this under load. If the current doesn't break, I don't think that the other contact will "take it over" without shorting the battery.
3. Have to ensure that the main contactors cut out the series string if too many of the cells start doing this, as the bus caps will dump energy into the remaining batts ...

Even with a step change from say 624 V to 576 V, there will be a rather large current dump into the pack from the capacitors. If the main contactor is on, this will happen regardless of whether it is switched under load or not. I suspect that this will shorten the life of the contactors, and possibly the caps as well.
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Post by Hemonster » Wed, 03 Jun 2009, 14:50

Thoughts are still brewing Image, thanks for the reply Coulomb.

It would probably have to be a bit more sophisticated and actually inform a sub controller to
- stop the VFD and allow the motor to freewheel,
- break the main contactors
- cut the 48V pack out
- wait for the precharge resistors to do their work (albeit in reverse),
- reenergise the main contactor

Yup, that should do it ... Image

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