Upgrade to Lithiums?

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Post by Paul9 » Wed, 25 Jul 2012, 20:19

Hi People,

I am currently running my Suzuki Swift as a 96volt system using the "Goombi" kit with 100ah SLA batteries. I am preparing for when the SLA's expire and wish, funds permitting, to upgrade the batteries to LiFePo4. At least at the moment the high Aust$ means the prices of LiFePo4 have come down to more affordable levels. What I am wondering is:

a) Should I get 30 x 3.2 volt lithiums or 8 x 12volt lithiums complete with BMS of course?

b) Do I really need to replace the charger and the controller and the DC-Dc converter? This will increase my replacement cost significantly!

Anything else I should be wary of?

Thanks in advance,
Regards
Paul


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Post by Johny » Wed, 25 Jul 2012, 20:48

Hi Paul
I'm probably not the most informed to answer this but in the spirit of the forums I'll add to the opinion pool.

a) Get 3.2 V Lithiums. 12V will just be a set of 4 with unknown BMS or none. It MAY be cheaper and WILL be more controllable on your part to have a BMS that knows which cell is which.

b) CONTROLLER - The controller will be fine so long as you stay with the nominal 96V system. You could probably go to 32 cells for a nominal of 102 VDC without causing trauma to the controller - especially if you don't take the cells too high when charging (see following).
   CHARGER - Probably have to change it. It depends on whether it has a magic switch Lead Acid/LiFePO4. I would think not but check. It also could be that the careful selection of cell count could make the charger usable. For instance, if the charger had a maximum output of 14.5 V per lead acid battery, that would be 116 VDC. With 32 cells of LiFePO4 it would be 3.625 V per cell. It would have to be controlled by the BMS to shut it off or some such though.
   DC-DC - Should be fine.

Hope this helps

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Post by zeva » Wed, 25 Jul 2012, 23:53

Hi Paul,

Pretty much reiterating/expanding on what Johny said.. Internally the "12V lithiums" are actually just four LiFePO4s in series - and they cost the same as four individual cells of the same capacity. So in general you're better off going for individual cells, allowing better flexibility in packaging and per-cell BMS. You'll probably want to run 32 cells for a closer match to the original 96V (which would have been 8x 12V PbA I assume, and likely sits around 102V nominal really since 12V batteries are usually closer to 13V.. which matches four LiFePO4s very closely.)

If you match pack voltages, your existing charger, controller and DC/DC converter should work just fine with the lithiums instead of lead acids. Generally lead acid charge curves do work with lithiums, so long as no individual cells go above about 4V at any time, it doesn't matter a great deal to the cells how the energy gets pushed in. (But do make sure your BMS can shut off the charger if any cell does go out of range.)
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Post by Paul9 » Sat, 28 Jul 2012, 01:28

Thanks greatly Johny and Ian,

As a result of both your comments regarding charging, I monitored the battery voltage during charging over the last two days. Yesterday's peak battery voltage during charging was 124.4 volts and today's peak was 124.3 volts. If my current charger can get SLA's to 124.4 that would equal 32 lithiums getting to 3.8875volts? (124.4 / 32= 3.8875)??

Would getting 34 lithiums be better and give me a 109 volt nominal system and decrease the individual cell voltage to a lower 3.6588 volts (124.4 peak v / 34 cells)rather than the above 3.8875?

Too high do you reckon?
Thanks again,
Paul
Last edited by Paul9 on Fri, 27 Jul 2012, 15:31, edited 1 time in total.

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Post by Johny » Sat, 28 Jul 2012, 02:39

Yes 34 would be a good number of cells. You already know that the controller can cope with this.voltage too!
You will need to find a way for the BMS to shut off the charger. A resistor carefully chosen will allow you to do a manual cell balance every now and then if no auto system can be devised easily.

Sorry for typos - sent from phone.
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Post by antiscab » Tue, 31 Jul 2012, 16:09

most lead acid chargers do a float charge as the last stage

this isn't recommended for lithium's, but a timer to disconnect the charger after a couple of hours gets around this

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Post by Paul9 » Thu, 28 Nov 2013, 20:08

Hi people,

I am bringing this thread to light again because I am now up to the stage of fitting the CALB 100ah Lithiums. As per advice I received in this thread, I purchased 32 lithiums giving me a nominal voltage of 102.4 volts rather than the 96 volts I had with the SLA's.

We got the SLA's out of the "bays" without too much trouble. The configuration of the bays is that we had one bay under the rear boot which held 4 SLA's and two separate bays under the hood which held 2 SLA's each, thus giving us a total of four in the front and four at the back. The bays themselves are made of 25mm angle iron.

Fortunately the lithiums can be installed in the existing bays with only a 2 or 3mm gap between the battery packs and the walls of the bays. In fact I can fit 22 of the lithiums in the back bay (with a 2mm gap between the entire pack and the edge of the bay) and 10 lithiums in one of the front bays (with a 2mm gap between the entire pack and the edge of the bay) and leave the other bay under the hood completely free.

The minor(?) problem we have been grappling with is the "requirement" to pack the lithiums batteries tightly. Trying to pack them with that blue banding "tape" manually does not seem to give us a very tight fit. I could buy the machine which, I assume, tightens the batteries very tightly, but the $250 - $300 for a machine I will never use again is an expense I would prefer to avoid. Still, if there is no alternative I will spend the money.

I have already had some 2mm aluminium checker plate cut to size to act as a base in each bay as the bays are open and the lithiums simply fell through the bottom of each bay.

I suppose the questions I have are:

a) How necessary is it for the lithiums to be packed tightly? Would manually tightened be sufficient or would we need the machine?

b) Could I get some more aluminium 2mm checker plate and use it as walls in the battery bays which would then prevent the batteries from "swelling"? Our reservation about this idea is that the batteries would have very little air flow around them and thus could get warmer/hotter than if we kept the battery bays wall-less? I assume the batteries heat up if heavily discharged?

c) Any other ideas we may not have thought of?

Thanks in advance,
Regards
Paul

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Post by antiscab » Thu, 28 Nov 2013, 20:17

I don't bother compressing the cells - I haven't found any measurable advantage

swelling batteries basically means they have been damaged

heat isn't an issue (just stay below 60 deg C - the battery starts to fail at 65 deg C)

heat rise is lower as the batteries heat up as internal resistance starts to fall.
optimum temperature is 55 Deg C for fastest discharge rate (not that will be needed for your application)

given your battery size, in winter insulation will help, especially if you need to travel at 100kmh for any length of time

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Post by Johny » Thu, 28 Nov 2013, 21:04

I'd add aluminium packing pieces at the sides. Heat shouldn't be an issue considering the centre cells are packed against the others anyway.
There are too many folk packing those types of cells to ignore it.

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Post by Paul9 » Sat, 29 Mar 2014, 01:30

Hi people,

We are just about finished our upgrade! I have a TBS Pro Monitor and I need to set figures for:
a) Peukurt Constant. I used 1.25 when I had the SLA batteries but I think(?) the appropriate figure for Lithiums is 1.05??
b) For a 96 volt system I need a Low Voltage Warning figure. I used to use 70volts for the SLAs but I assume about 100 volts for lithiums or is this too high(?)
c) The 100AH CALB batteries I have installed do not, according to their voltage curve graphs, drop down to 3.2v per cell (at 1C rate) until they have used almost exactly 100AH. Any guesses as to how many AH I may get out of these new batteries in real life?
Thanks for all previous replies
Paul

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Post by 4Springs » Sat, 29 Mar 2014, 17:12

Paul9 wrote:c) The 100AH CALB batteries I have installed do not, according to their voltage curve graphs, drop down to 3.2v per cell (at 1C rate) until they have used almost exactly 100AH. Any guesses as to how many AH I may get out of these new batteries in real life?

My experience:
I had 12 x 12V AGM lead-acid batteries nominally 140AH (20C). This gave me about 13kWh of useable power. (i.e. I used 13kWh to charge the pack after completely flattening it)
I used this data to decide that I wanted about 1.5 times the power in my new lithium pack. I calculated this out and purchased 48 x 130AH cells.
Now the cells are in the car I have performed a range test. Charging up after the test used about 24kWh of power - quite a bit more than I had calculated.
If all of the complicated factors apply the same in your case, then use a voltage of 3.8V per cell to calculate your maximum pack capacity. You have 32 cells @ 100AH. So 32 x 3.8 x 100 = 12kWh. Do you know how much power your vehicle consumed previously?

Very happy with my upgrade - higher voltage means a bit more speed, and lower weight means a lot more go!

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Post by evric » Sat, 29 Mar 2014, 17:21

From my experience...For your calculations it would be better to use 3.25V per cell. This is a more typical voltage under general load conditions.
Just for interest my Thunderskys don't ever get to an average of 3.8V. The charger turns off at 3.69V average.

For my Xpert Pro I set my Peukurt figure to about 1.05.
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Post by 4Springs » Sat, 29 Mar 2014, 17:23

Paul9 wrote:b) For a 96 volt system I need a Low Voltage Warning figure. I used to use 70volts for the SLAs but I assume about 100 volts for lithiums or is this too high(?)

For mine I don't have a low pack voltage warning, I use a low cell voltage warning. This is because it is very important that no cell ever goes below about 2V - death may ensue! Do you have a BMS to monitor individual cell voltages?

Ignoring that point and attempting to answer your actual question:
In my range test my pack (48 cells) sat at about 152V for a long, long time. This is a bit strange after being used to the sag in a lead-acid pack! But once it started to move lower than that value I didn't have a lot of range left to go.
152V / 48 cells = 3.167 V per cell.
100V / 32 cells = 3.125 V per cell.
So 100V sounds about right.

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Post by 4Springs » Sat, 29 Mar 2014, 17:30

evric wrote: From my experience...For your calculations it would be better to use 3.25V per cell. This is a more typical voltage under general load conditions.
Just for interest my Thunderskys don't ever get to an average of 3.8V. The charger turns off at 3.69V average.

No, that 3.8 is just a shortcut way to get a kWh figure for estimating battery capacity. Doesn't mean that the cells actually get that high.
My capacity figures are not "real" either. The 24kWh in my calculations is not what the battery gives me, it is what I use to charge the battery. It includes all inefficiencies of charger etc., and so will be always be higher than the battery capacity. It may not be the same for anyone else anywhere!

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Post by acmotor » Sat, 29 Mar 2014, 18:16

4Springs,   Have I missed something ? are you doing any per cell under and over voltage monitoring ?
The Lithiums have no protection from one cell going overvoltage unlike Lead acid that just gasses when charged in a string. This is a very sharp transition and one cell can take off when others are still at 3.2V or less.
By counting Ah in and out and going around with a multimeter after manually balancing the cells you can 'get away' without more monitoring until the cells start to age and capacities vary.
   
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Post by Paul9 » Sat, 29 Mar 2014, 18:20

Thanks very much people,

4Springs - Yes I do have a BMS controlling individual cells. I note you also said that when your batteries get to 152V they stay at that level for a while and when they start to drop you have very little range left. Two questions:
a) How many kms range do you get on your batteries and
b) When your voltage drops below 152V do you have a couple of kms of range left or a couple of hundred metres?

Thanks again,
Paul

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Post by 4Springs » Sat, 29 Mar 2014, 20:04

acmotor wrote: 4Springs,   Have I missed something ? are you doing any per cell under and over voltage monitoring ?

Yes, I monitor each cell. I don't have any alarms on pack voltage, and was just musing.

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Post by 4Springs » Sat, 29 Mar 2014, 20:37

Paul9 wrote:4Springs - Yes I do have a BMS controlling individual cells. I note you also said that when your batteries get to 152V they stay at that level for a while and when they start to drop you have very little range left. Two questions:
a) How many kms range do you get on your batteries and
b) When your voltage drops below 152V do you have a couple of kms of range left or a couple of hundred metres?

a) 108 km for my range test.
b) Hang on, did I say 152? I meant 156! And come to think of it, that was from a voltmeter which I could only read when I stopped the car (so it didn't take voltage drop due to acceleration into consideration). I do have information on the voltage during driving though, so I've attached graphs below of what my BMS reported over a fairly long trip. This trip was probably about 70km.
ImageImage
First graph is individual voltage of all 48 cells over the 1st 40 minutes of the trip. Note how the cells quickly get back to 3.2V every time I stop using power.
Second graph is the total voltage over the entire trip (with a while sitting in a carpark in the middle).
You can see that it goes below 145V with hard acceleration, even with a fresh pack. This is 3V/cell, or 96V for your pack. Your controller/motor may or may not have the same effect, it would draw less current, but your cells have less capacity.

I think that total pack voltage is a poor way to monitor your capacity, but if I had to then I'd probably set my alarm to 140V based on the graphs above. What I actually do is have an alarm when any single cell gets down to about 2.6V. I then have a couple of km to go before damage occurs.

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Post by Paul9 » Sun, 30 Mar 2014, 03:38

Thanks very much 4Springs and others!

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Post by Paul9 » Fri, 27 Jun 2014, 20:00

Hi people,

We have finished the upgrade and I have been driving the vehicle for about a month. Very pleased with the upgrade. Both the 160kgs weight saving and increasing the voltage to 102v from 96v have made a noticeable improvement in performance. I have found lithiums to be less forgiving than my old SLAs but "4Springs" on this forum has been a massive help with advice. Those lithiums take getting used to!

A) I kept getting a BATTERY FAULT message when the pack voltage got down to 92volts. I re-read the manual and noticed that the manual said the cell interconnectors should go below the cell modules. It also said however that when cables are attached to the cell, the cable lugs should be placed above the cell modules. This seems odd to me but I am definitely no expert?

Realising we had placed the cable lugs under the cell modules I reset the cable lugs above the cell modules as per the manual. I hoped this would fix the BATTERY FAULT.

With my usual ability to stuff things up coming to the fore, I managed to screw in one of the bolts on an angle. I took the car for a drive and after a km or two the BATTERY FAULT came on immediately I touched the accelerator. I nursed the car home and smelled a faint wiff of burning. The thread in the cell has been stripped.

"4Springs" suggested getting an 8mm tap and retapping the hole but suggested I check with the rest of the forum as to whether this is a good idea or have I simply "cooked" a cell and need to replace it?

I have no problem taking my medicine and buying a new cell!

B) If I am to buy a new cell/battery, I am wondering whether to buy three new cells as I have room in my rear battery bay for two extra batteries. This would bring the pack voltage to a nominal 108.8 volts. I am wondering if this might be too high a voltage to put into the 96 volt motor?

Any ideas about A and B above?
Thanks in advance
Regards
Paul

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Post by Johny » Fri, 27 Jun 2014, 20:50

Paul9 wrote: Hi people,
"4Springs" suggested getting an 8mm tap and retapping the hole but suggested I check with the rest of the forum as to whether this is a good idea or have I simply "cooked" a cell and need to replace it?
Anything is a good idea that works. I'd try it - nothing tried nothing gained.
....This would bring the pack voltage to a nominal 108.8 volts. I am wondering if this might be too high a voltage to put into the 96 volt motor?.
It's NOT the motor - it'll be fine. It's the controller. The controller will be using MOSFETs that are available in 100V, 150V, 200V etc. It will totally depend on how "close to the wind" they are with respect to internal DC Link voltage spikes.

Have you got any info. on the controller as to "absolute maximum" battery voltage?

The other factor is that extra voltage will get you extra power at higher RPMs. It will also give a proportionally higher range. Two extra cells probably isn't worth the risk re: controller.

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Post by Paul9 » Sun, 29 Jun 2014, 03:56

Thanks Johny,

I checked with the distributor, SuziAuto on this forum, and he advised that he had previously asked this question of the manufacturer and they advised the absolute maximum voltage of a 96v contoller is 120v. The factory also added of course that at that voltage, if something goes wrong, I am not covered.

I can't see 34cells puting 120volts through the controller??

Thanks
Paul

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Post by coulomb » Mon, 30 Jun 2014, 03:22

Paul9 wrote: I can't see 34cells puting 120volts through the controller??

120 / 34 = 3.53 VPC. If you never charge beyond 3.5 VPC, then no problem. but if you charge higher, you need to be a little patient and careful just after a charge.

I don't know why they say to put the lugs on top. Maybe it's a way of preventing one BMU from seeing the whole pack voltage, but if everything is wired sensibly, that should never happen. With the lugs on top, traction current goes through the bolt and PCB, which is a terrible idea. Straps under is good. Sorry to say, but you may have to undo the change that cross threaded the cell. The threads are in soft aluminium or copper, so extra caution is advised.

Of course, you would have been more impressed with this advice if it was before the thread stripping...
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Post by Paul9 » Tue, 01 Jul 2014, 15:20

Thanks Coulomb,

I tapped the hole and followed up with a short drive and I think the battery is OK. I am going to give it a longer drive today to make sure the cell is OK. I have changed the lugs back to below the cell module.

The charger I am using used to get the old SLA pack of 96v nominal up to 124 volts max. I am unsure what the new BMS will allow the charger to charge up to. At present the BMS stops the charger at about 113v but that is, I think, because four cells commence shunting when they reach 3.65vpc and quickly get to 4.0vpc whereupon the BMS shuts the charging process off.

AT present I am not sure if the BMS shuts down the charger above or below 120v?

I assume your comment "you need to be a little patient and careful just after a charge." means that if the charger charges to above 120v pack voltage then I would have to go easy on the accelerator when driving straight after a charge?

Thanks again,
Regards
Paul

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Post by coulomb » Tue, 01 Jul 2014, 20:23

Paul9 wrote: I assume your comment "you need to be a little patient and careful just after a charge." means that if the charger charges to above 120v pack voltage then I would have to go easy on the accelerator when driving straight after a charge?

Unfortunately, I don't think that would be enough. I think you'd have to watch the voltmeter and not turn on till it dipped below 120 V. That sort of patience.



However, I suspect it may take as little as ten seconds for the pack voltage to dip below 120 V after a charge that brings it above 120 V. If not, using a load like your heater will accelerate the dip in voltage. So in practice, I don't think it will be a problem, but it might be best to set up your charge so that it never goes over 120 V immediately before you might need the vehicle.
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