Battery pack voltage advice for EV datsun 1200

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Battery pack voltage advice for EV datsun 1200

Post by Brett_celicacoupe » Fri, 02 Dec 2011, 16:57

Hi all,

I am halfway through converting my datsun 1200 ute to electric powered.

so far I have a soliton jr controller, kostov 9" 144v motor and a 144v-12v dc converter.

I am looking at purchasing some D31T 75ah 12v yellowtop optimas.

the motor and DC-DC converter is rated for 144v nominal but would i see any substantial issues if i slipped 1 extra battery in the pack for addtional range? I would then have a nom 156v pack. the controller will be ok with this voltage but i am unsure of the extent of the impact on the motor and DC-DC converter?

obviously this limits the availability of chargers however i think the benefits would be worth it.

advice very welcome.

regards,
brett

here is a pic so far...
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Last edited by Brett_celicacoupe on Fri, 02 Dec 2011, 05:59, edited 1 time in total.

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Battery pack voltage advice for EV datsun 1200

Post by Tritium_James » Fri, 02 Dec 2011, 17:02

You've got a nice motor and controller, why limit yourself with relatively horrible batteries? Especially with the price of Optimas, I'd seriously consider a lithium pack, which will end up costing about the same amount, and last considerably longer.

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Battery pack voltage advice for EV datsun 1200

Post by evric » Fri, 02 Dec 2011, 17:22

I agree with James. Save up for Lithium cells. If you waste your money on Lead Acid now, in 18months you will then have to decide to buy more or then go to Lithium... wasting money.
With the Nominal voltage ratings - stick to them, they allow for a maximum rating of about 20% above the Nominal rating. If you go to 156V Nominal then you will probably be exceeding the maximum rating for each item. This would be asking for trouble.
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Battery pack voltage advice for EV datsun 1200

Post by Johny » Fri, 02 Dec 2011, 17:29

I third it. You will (IMO) be dissapointed with the weight and capacity of the Lead. Even if you go for a lower initial voltage (to save cost) with Lithium it will most likely out-perform the optimas.

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Battery pack voltage advice for EV datsun 1200

Post by Brett_celicacoupe » Fri, 02 Dec 2011, 18:36

Thanks for the quick replies.

i have done a decent spreadsheet to make a decision & give some valuble figures.

here are some of the key outcomes of my evaluation;

For ~5k budget

Lead acid (optima YT)
-75Ah
-12.2kwh capacity
-$384/kwh
-37.2 wh/kg (327kg total eight)
-should last 2-3 years (i work at a mine & am only home 11 days per month)
-no complicated BMS
-batteries capable of sustained high current draw
-12 components (less components = improved reliability)
-will be able to utlisise emerging technology should it arise
-can take more abuse
-reasonable reputation

lithium (Ts)(would have to spend extra $1k to get 90ah cells)
-90ah, 12.96kwh capacity
-$406/kwh
-87wh/kg (150kg pack)
-**could** last up to 10 years... but i highly doubt people will still want to continue to run these batteries if a better variant comes out before then?? I also think its a little risky to use the life as major argument for the purchase
-BMS system required
-there are conflicting reports on the effects of current draw higher than the C rating. i highly doubt i could pull 600A from these..?
-at least 96 components in the system - this has inherant reduced reliability and increased maintenance.
-these batteries seem more sensitive to abuse.
-repution is ok with a few ordinary reports about them
- i expect these batteries to have a high depreciation.


but back to the topic - can anyone answer the original question of 144v vs 156v or should i post in a different section or even forum?

Cheers,
Brett
Last edited by Brett_celicacoupe on Fri, 02 Dec 2011, 07:38, edited 1 time in total.

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Battery pack voltage advice for EV datsun 1200

Post by Johny » Fri, 02 Dec 2011, 18:50

All good points but the major disadvantage of the optimas is that you are not going to see anywhere near that 12.2kwh.
At EV current draw it will be more like 6 or 7kwh.
Provided that is enough for your needs (range) then it's a reasonable choice.
I would expect around 35-40km range.



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Battery pack voltage advice for EV datsun 1200

Post by Brett_celicacoupe » Fri, 02 Dec 2011, 19:08

yep i am aware on that drawback.

i still think the lithium is a pretty big investment and carries reasonable risk...

any comments on the voltage query?

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Battery pack voltage advice for EV datsun 1200

Post by Tritium_James » Fri, 02 Dec 2011, 19:13

I'd be sticking with the 144V. This is 'rated', the same way the optimas are '12V'. They go higher when charging, and the '144V' rating usually allows for this.

If you want 3 years out of a set of Optimas (which can't be balanced with a gassing charge, since they're AGM) then you also need a BMS. The complexity with either system is pretty much the same.

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Post by Johny » Fri, 02 Dec 2011, 19:35

Tritium_James wrote:If you want 3 years out of a set of Optimas (which can't be balanced with a gassing charge, since they're AGM) then you also need a BMS. The complexity with either system is pretty much the same.
If you are prepared to monitor (manually if you have no other choice) the batteries and top-up-charge with a 12V charger when necessary I guess you could run without BMS with the optimas. It would be best to have some low-voltage alarm so you knew if you had overtaxed one of them though - preferably all 12 batteries monitored. Will no-one else be driving it while you are away?

I do understand that LiFePO4 would be a lot more effort and for 11 days home out of the month I guess that it's a good argument for simpler/cheaper.

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Battery pack voltage advice for EV datsun 1200

Post by woody » Fri, 02 Dec 2011, 19:48

I fourth it on the lithiums :-)

But:
Soliton Jr does 8-340 Volts

So you could have 340/15 =~ 22-23 Optimas. You could limit the "output" voltage with the Solition to 144V if you like. 144V is the nominal, many go over.

The DC-DC may be a different animal - which DC-DC have you got?
Brett_celicacoupe wrote: -there are conflicting reports on the effects of current draw higher than the C rating. i highly doubt i could pull 600A from these..?
Possibly you have a misunderstanding here - the controller is a power converter - it takes power input from the batteries at a fairly fixed voltage (e.g. ~144V) at variable current, and outputs at enough voltage to produce the current desired by the throttle input.

e.g. the controller could be outputting 600A at 50V (30kW), but drawing 250 amps at 135V (32kW) from the batteries.

So the battery current limit is more of a power limit than a current (~ torque) limit.

cheers,
Woody

Edit: attributed quote
Last edited by woody on Fri, 02 Dec 2011, 08:50, edited 1 time in total.
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Battery pack voltage advice for EV datsun 1200

Post by Brett_celicacoupe » Sat, 03 Dec 2011, 01:15

Tritium_James wrote: I'd be sticking with the 144V. This is 'rated', the same way the optimas are '12V'. They go higher when charging, and the '144V' rating usually allows for this.

If you want 3 years out of a set of Optimas (which can't be balanced with a gassing charge, since they're AGM) then you also need a BMS. The complexity with either system is pretty much the same.


if i was to go with 156v system i would be using a charger to suit (not 144v). i know the controller is happy to take voltages up to 340v. i am not sure what the effects will be on the motor? this was one of the things i was hoping to get specific advice on.

i think it would be suitable to just run a multi over the 12/13 batteries each month or so to confirm voltages. it seems like they are less fiddly than the lithiums.

woody wrote: I fourth it on the lithiums :-)

But:
Soliton Jr does 8-340 Volts

So you could have 340/15 =~ 22-23 Optimas. You could limit the "output" voltage with the Solition to 144V if you like. 144V is the nominal, many go over.

The DC-DC may be a different animal - which DC-DC have you got?
Brett_celicacoupe wrote: -there are conflicting reports on the effects of current draw higher than the C rating. i highly doubt i could pull 600A from these..?
Possibly you have a misunderstanding here - the controller is a power converter - it takes power input from the batteries at a fairly fixed voltage (e.g. ~144V) at variable current, and outputs at enough voltage to produce the current desired by the throttle input.

e.g. the controller could be outputting 600A at 50V (30kW), but drawing 250 amps at 135V (32kW) from the batteries.

So the battery current limit is more of a power limit than a current (~ torque) limit.

cheers,
Woody

Edit: attributed quote


perhaps i am a little mistaken on its workings....

my understanding was that the input voltage = a square wave with the same voltage. the pedal input then varied the duty cycle of the square wave... 2 frequencies are selectable in the software.

Yes you are right about there being a power limit from your battery pack. i did actually come to this conclusion myself however no-one has defined any relationship between the kWh of your pack and the limit of 'power pull capacity'. i would be happy if someone could comment on this. my conclusions is that lithium is more sensitive to this. ie i would be more comfortable pulling 90kw from the optimas than the thunderskies.

just for the record, i am a mechanical engineer so not a complete noobie
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Battery pack voltage advice for EV datsun 1200

Post by coulomb » Sat, 03 Dec 2011, 15:43

Brett_celicacoupe wrote: if i was to go with 156v system i would be using a charger to suit (not 144v). i know the controller is happy to take voltages up to 340v. i am not sure what the effects will be on the motor? this was one of the things i was hoping to get specific advice on.
You can limit the motor voltage to 144 V and have a 156 V (or higher) pack. But a Kostov has interpoles, so I think it would be fine to go to 156 V. It will only see an average of over 144 V when the back EMF is almost that high, which will only be at high motor speeds.

However, the peaks of the square wave to the motor will always be pack voltage, less a volt or three. So the insulation of the motor needs to be able to handle the pack voltage. So I would not be putting a 300 V pack onto a motor that is rated for 144 V nominal. But 156 V should be OK (but that's just my guess).
i think it would be suitable to just run a multi over the 12/13 batteries each month or so to confirm voltages. it seems like they are less fiddly than the lithiums.
Once lithiums are set up and you have a balancing BMS for them, they are no fiddling at all. If you decide you want to not have balancing BMS, and do bottom balancing on your own, then they are a lot of fiddling. Lead acids could be a lot of fiddling.

woody wrote: So you could have 340/15 =~ 22-23 Optimas. You could limit the "output" voltage with the Solition to 144V if you like.
As noted above, I worry about the 340 V square waves, even at low average voltage, that the motor would be subjected to all the time that it is getting any power, even at low speeds and hence low average voltage.
Brett_celicacoupe wrote: -there are conflicting reports on the effects of current draw higher than the C rating. i highly doubt i could pull 600A from these..?
You can pull 600 A from a lithium pack, but it should preferably be a 200 Ah pack, so that the peak draw is 3C. But then of course at 144 V you have a 29 kWh pack, which is quite large. You could go to lower capacity cells, say 130 Ah, but then 600 A peaks is 4.6 C, and we don't really know the effect of 4.6 C peaks. I suspect it won't limit life too much, but that's just a guess, till we see some examples from real life.

[ Edit: so if you want a smaller pack but still lithium, an alternative to Thundersky / Winston / Sinopoly or Sky Energy / CALB would be headways or similar. These have higher current density, so you can pull 8C or more without harming them, so you can make a smaller lithium pack that way. But you need more cells, and there is a lot of interconnection to deal with. ]
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Post by antiscab » Sat, 03 Dec 2011, 22:18

The motor won't care about the higher voltage,
when switching the field winding takes most of the voltage anyway (less back emf), and the insulation on those are pretty good (same as the insulation on the 300V motors)

New optimas are nothing like as good as in previous years:
when Johnsons bought the optima line, they fired everyone who knew anything about the battery as a cost saving measure.

At some point something has gone wrong with the production line, and now we're seeing bad cells appearing in batteries.

That said, there are alternative high power AGM's

Re output power:
Optimas won't actually give you 600A once you are past 20-30Ah discharged (temperature dependant).

TS/CALB cells will only give you that kinda power when they are fairly warm (25 deg C or so).

600A @ 110-120V is ~66kw from the battery peak (much the same for either the optima AGMs, or 100Ah large format Lithium)

When the temperature heads down to around 5 deg C, it will be more like:
300A @ 110V (33kw) for the Lithium.
or
600A @ 90V (54kw)for the AGM's

The controller will allow you to apply the full 600A to the motor no matter what, but the max voltage it can apply that at will depend upon how many kw the battery can put out.

Chargers:
TC Charger make a 1500W charger in any voltage you like between 12V and 417V, and cost only ~$500

DC-DC's are cheaper for higher voltage conversions (above 288V there are more choices)

If you aren't planning on doing many km with this conversion, the AGM's will probably be an ok choice

7kwh of usable capacity with AGMs (75Ah @ 20hr @ 144v) won't give particularly good service life (~10'000km).
It depends upon whether power is more important than range or service life

I think there may be second hand optimas floating around in Perth from a couple of conversions that moved on to big Lithium packs (the triton had 40 of them, and the niki had 8)

that would probably swing things in favour of using the optima AGMs

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Post by Simon » Sat, 03 Dec 2011, 22:38

antiscab wrote: 7kwh of usable capacity with AGMs (75Ah @ 20hr @ 144v) won't give particularly good service life (~10'000km).
It depends upon whether power is more important than range or service life

I think there may be second hand optimas floating around in Perth from a couple of conversions that moved on to big Lithium packs (the triton had 40 of them, and the niki had 8)

that would probably swing things in favour of using the optima AGMs

Matt


My 55Ah Optimas from the Niki did 9000kms before I retired them. Been storing them for an electric boat conversion.
Plus the secondhand optimas will not be any good for brett as he is in Qld...
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Post by antiscab » Sat, 03 Dec 2011, 22:39

Brett_celicacoupe wrote:
my understanding was that the input voltage = a square wave with the same voltage. the pedal input then varied the duty cycle of the square wave... 2 frequencies are selectable in the software.


The Controller takes the battery voltage, and switches it across the motor, on and off.

In the case of the Soliton, you can select the switching frequency, lets call it 10kHz

That means every 0.00001 seconds, the switch turns on

Your throttle limits both current and voltage
So if your throttle is at 50%, it means 300A and 72V limit (actually 50% duty cycle limit)for a 144V pack)

so, for each of the 10'000 times the switch turns on, when the current goes past 300A, the controller turns the switch off.
At low speed, that can be as low as 1% duty cycle.

If your motor is spinning fairly quickly, and has substantial back emf, the 50% duty cycle limit (voltage limit) may be reached first, in which case it turns off before the current reaches the 300A limit.

It is setup this way to allow a relatively smooth transition between torque control and speed control.
Much more apparent when driving a conversion that has retained the gearbox.

With a direct drive conversion, the throttle mapping is usually reset so that the current limit curve is steeper. In the case of the Zilla, it means that at 50% throttle, current limit is 100%, duty cycle limit is 50%.
but at 25% throttle, current limit is 50%, and duty cycle limit is 25%.

The old way of doing it where the throttle only limits duty cycle (so 10% throttle = 600A or 10% voltage Max) has been done away with long ago.
Unless you use a curtis....

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Post by woody » Tue, 06 Dec 2011, 19:36

Brett_celicacoupe wrote:
my understanding was that the input voltage = a square wave with the same voltage. the pedal input then varied the duty cycle of the square wave... 2 frequencies are selectable in the software.


There is also a "free wheeling" diode which lets current circulate through the motor several times.

My understanding is that it's a Buck Converter circuit - the motor is the load.
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Post by Brett_celicacoupe » Thu, 15 Dec 2011, 02:50

Hi all,

Thanks for the help and explanations so far.

I ended up buying 13 x 75ah optimas.

Will perform a load test soon to make sure there are no duds!

regards,
Brett

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Post by Brett_celicacoupe » Thu, 15 Dec 2011, 12:51

antiscab wrote:
Chargers:
TC Charger make a 1500W charger in any voltage you like between 12V and 417V, and cost only ~$500


Thanks for the lead.

Has anyone got any leads on these chargers as i have tried contacting the supplier directly to buy but i havent got any response.

The charger is the last main component to purchase!

cheers,
Brett

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Post by coulomb » Thu, 15 Dec 2011, 14:37

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Post by antiscab » Fri, 16 Dec 2011, 13:01

Here's the sales contact:
nancylooloo@yahoo.cn
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Post by Brett_celicacoupe » Sun, 18 Dec 2011, 19:17

thanks for that, i have made contact with him.

I decided to load test the batteries to make sure there were no huge discrepancies in performance.

I basically shorted each battery across a piece of aluminum welding filler wire in a bucket of water for 5 mins and took voltage and current readings at various intervals. note that the ammeter i was using didnt have good resolution so current readings would be accurate to about +-10A.

for the sake of someones possible future interest, here are the plots.

Image

Image
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Post by Richo » Tue, 20 Dec 2011, 20:34

So 8.6mR per cell.
At 500A would be ~56V drop on your pack voltage giving ~56kW.
600A->~61kW
So the short answer is NO but the long answer is YES.
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Post by Brett_celicacoupe » Tue, 20 Dec 2011, 20:39

awesome.

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Post by Brett_celicacoupe » Mon, 17 Sep 2012, 04:59

I got my machine registered the other day.

performance is solid and range is around 30km (6.7kwh to charge, ~4.9c/km)

i have been trying to find SOC tables for the optimas but not much success other than an older website. any feedback here?

I would like to confirm 100% and 0% battery voltages.

here are a couple more pics

Image

Image

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Battery pack voltage advice for EV datsun 1200

Post by Jeff Owen » Mon, 17 Sep 2012, 14:44

Brett_celicacoupe wrote: I got my machine registered the other day.


Brett
Will you be bringing your car to the Brisbane branch meeting this Wednesday?

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