# Planning my pack - can someone check my numbers?



## PThompson509 (Jul 9, 2009)

From a brief read, your numbers appear to be correct. 

You should check out the reliability of the batteries (I have no idea how good the Winston are), and check out the possibility of other batteries as well (e.g. CALB and Thundersky).

In any case, you've gotten the worst of the calculations out of the way. 

Next up will be figuring out where to stuff all of those batteries. Something you *could* do if you are having problems is to create two packs of 130Ah each.

Cheers!


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## vocalnick (Aug 5, 2013)

PThompson509 said:


> From a brief read, your numbers appear to be correct.


Nick breathes a sigh of relief, opens bottle of wine 



> You should check out the reliability of the batteries (I have no idea how good the Winston are), and check out the possibility of other batteries as well (e.g. CALB and Thundersky).


I'm a fair way off purchasing yet, but I'll definitely shop around. That was just a random pick off a supplier in my country to see if i was in the ballpark.



> In any case, you've gotten the worst of the calculations out of the way.


Yup - now I just need to find a lazy fifteen-grand 

EDIT: That said, based on our rooftop solar, my current driving habits, and the current price of petrol in Tasmania, that cost will amortise out in less than five years. Even faster if fuel prices rise (which I'm virtually certain they will)



> Next up will be figuring out where to stuff all of those batteries. Something you *could* do if you are having problems is to create two packs of 130Ah each.


To be honest, I'm thinking I'm just going to tear out the "+2" seats in the Probe, make it an honest-to-goodness coupe, and put them in the centre. I think there'd be plenty of room. I don't love the idea of batteries in the crumple-zone, and I'm also a fan of having a spare tyre. The car arrives at home on Saturday, so I can get stuck in with the tape measure and see where the space is. 

Thanks for the reply


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## Qer (May 7, 2008)

Don't get stuck on 144 Volt.

144 Volt is a rest from the Pb-era and it's also the Pb-batteries that caused controllers of that time to be made for 96, 120 or 144 Volt. It was convenient with these numbers when batteries for EVs came in 6, 8 or 12 Volt and it was very impractical to go higher than 144 Volt due to weight and volume. The fact that most (all?) controllers back then were analog it was easier to construct them tailored for a fixed voltage.

Modern controllers are micro controller based and tend to have a wider range of allowed voltages (rather than a hard coded multiple of 12) and even if you're quite right that 144 Volt is a decent voltage, I'd say that it's not optimal. For example, in your case you could flip the calculations around and instead decide for a certain Ah (for optimum price or choosing a size that's easy to pack in the car etc), like 200 Ah:

30 kWh / 200 Ah = 150 Volt

150 Volt * 1.25 = 187.5 Volt

187.5 / 3.2 = ~59 cells

This will also give you better top RPM (since top RPM is defined by pack voltage) and more margin for sag plus that it decreases pack current so thinner wiring could be sufficient.

However, with higher voltages the switching losses increases (Tesseract has written about this in the forum somewhere...) so going for highest possible voltage is kinda pointless. I'd say sweet spot is somewhere around 200 Volt since a good DC-motor can't go much higher than a bit above 150 Volt anyway.

That said, there's nothing wrong with 144 Volt. Just don't get stuck on it.


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## PThompson509 (Jul 9, 2009)

Oh - Tasmania! See if you can find the specs for a Blade EV - they had a very nice pack stuffed into a tiny 4 seater.


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## vocalnick (Aug 5, 2013)

Qer said:


> Don't get stuck on 144 Volt.
> 
> 144 Volt is a rest from the Pb-era and it's also the Pb-batteries that caused controllers of that time to be made for 96, 120 or 144 Volt. It was convenient with these numbers when batteries for EVs came in 6, 8 or 12 Volt and it was very impractical to go higher than 144 Volt due to weight and volume. The fact that most (all?) controllers back then were analog it was easier to construct them tailored for a fixed voltage.
> 
> ...


I picked 144 to base my initial calculations on because it seemed to be a reasonably common and not "too low" voltage, but I'm by no means married to the idea, and I definitely appreciate the notion of better top speeds (highways will be in play for this car!)

The only thing that concerns me is that higher voltage = more cells, right? And I'm already looking at 400kg of batteries if I use the ones I linked above - I'm not sure how far I can push that...

But I guess now I've ascertained that I'm not screwing up the maths, I can plug different voltages into that equation and fine tune my plans.

Thank you for the reply


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## vocalnick (Aug 5, 2013)

Actually I'm circling back to this now, because it kind of highlights a gap in my understanding.

So let's say I go for a higher voltage, but use cells with a lower Ah rating to make the pack. Instead of 45 of those 260Ah cells for a 144v pack, I use 60 200Ah cells for a 192v pack. I understand the higher voltage will allow higher speeds on the motoer, but how will it affect my range?


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## Qer (May 7, 2008)

vocalnick said:


> Actually I'm circling back to this now, because it kind of highlights a gap in my understanding.
> 
> So let's say I go for a higher voltage, but use cells with a lower Ah rating to make the pack. Instead of 45 of those 260Ah cells for a 144v pack, I use 60 200Ah cells for a 192v pack. I understand the higher voltage will allow higher speeds on the motoer, but how will it affect my range?


260Ah * 144V = 37.4kWh
200Ah * 192V = 38.4kWh

Not much I'd say.


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## vocalnick (Aug 5, 2013)

Qer said:


> 260Ah * 144V = 37.4kWh
> 200Ah * 192V = 38.4kWh
> 
> Not much I'd say.


Ahhhhhhh, Ok cool... I think my understanding is coalescing. Back to the books.

Thank you


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## Yabert (Feb 7, 2010)

And after all this learning (you are in the good way), I suggest you to think another time about insert a 38 Kwh (400Kg) battery pack in your car... especially if you don't need 100 miles of range regularly.
Maybe going with a smaller battery pack and invest in a powerfull charger to charge quickly could be a better idea..., but you are the only one who know what you want.


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## vocalnick (Aug 5, 2013)

Yabert said:


> And after all this learning (you are in the good way), I suggest you to think another time about insert a 38 Kwh (400Kg) battery pack in your car... especially if you don't need 100 miles of range regularly.
> Maybe going with a smaller battery pack and invest in a powerfull charger to charge quickly could be a better idea..., but you are the only one who know what you want.


What's your main concern - the weight?

I'm pondering maybe trimming back on the batteries and investing a bit more money into an AC motor/controller so I can get regenerative braking, but I'm unsure how much benefit that's going to give me, and whether it would be enough to compensate for the smaller pack.

Also, if I trim that down to a smaller pack, that means a lower voltage, which isn't necessarily desirable...


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## Yabert (Feb 7, 2010)

vocalnick said:


> Also, if I trim that down to a smaller pack, that means a lower voltage, which isn't necessarily desirable...


Nope!

192v x 200Ah = 38,4 Kwh and... 192v x 130Ah = 25 Kwh or 250v x 100Ah = 25 kwh or 417v x 60Ah = 25 Kwh...


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## vocalnick (Aug 5, 2013)

Yabert said:


> Nope!
> 
> 192v x 200Ah = 38,4 Kwh and... 192v x 130Ah = 25 Kwh or 250v x 100Ah = 25 kwh or 417v x 60Ah = 25 Kwh...


I understand that, but if I'm trying to reduce the size and weight of the pack (which is what I thought you were talking about) then that means fewer cells, which means fewer volts, doesn't it?

Or am I missing something?


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## Qer (May 7, 2008)

vocalnick said:


> I'm pondering maybe trimming back on the batteries and investing a bit more money into an AC motor/controller so I can get regenerative braking, but I'm unsure how much benefit that's going to give me, and whether it would be enough to compensate for the smaller pack.


Depending who you ask you will get the answer that it gives anything from virtually nothing to 25%, but most seem to claim around 10% *if* you have the right driving conditions!

If you drive where it's very hilly or you do a lot of stop and go and have to break a lot, AC might be worth considering. If you mainly drive highway or generally keep a constant pace without braking much it's just pointless.

Also check the weight of the AC versus DC system. If it weights about the same or less than the DC system it's a bonus of course, but if it weights more it kinda gets pointless if you're trying to save weight...



vocalnick said:


> Also, if I trim that down to a smaller pack, that means a lower voltage, which isn't necessarily desirable...


Nope. A 100Ah battery weights roughly half the weight of a 200Ah battery, so no matter if you cut voltage or Ah in half, weight will be halved too.


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## Duncan (Dec 8, 2008)

Hi Vocalnick

The main driver is the 100 miles range,
I looked at my driving patterns 
What I found was
Less than 30 Km - most of the time
150 Km - about 8 times a year
400 Km - about once a year

So I have a tiny pack in my EV - and use the other family car for longer runs


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## vocalnick (Aug 5, 2013)

Qer said:


> Nope. A 100Ah battery weights roughly half the weight of a 200Ah battery, so no matter if you cut voltage or Ah in half, weight will be halved too.


Yup, OK, that makes sense. So you could end up with a greater number of cells, but a smaller overall weight. Got it 



Duncan said:


> Hi Vocalnick
> 
> The main driver is the 100 miles range,


Yeah, I'm beginning to think it might be a bit optimistic. It was an aspirational goal, and I can certainly trim it down some.



> I looked at my driving patterns
> What I found was
> Less than 30 Km - most of the time
> 150 Km - about 8 times a year
> ...


Seems like a very sensible approach  We're semi-rural, so my regular drive is considerably longer than yours - about 35km each way, so 70km (around 44 miles) all told. I'd still like to build in some headroom for the odd detour and to allow for aging batteries over time, but that still leaves room to compromise a bit from my nominal 100 mile goal. 

I wonder if it's worth crunching some numbers based on... say... 70 miles range? That feels like it might be a bit less bleeding edge, and I can always upgrade the pack in a few years as the technology improves


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## vocalnick (Aug 5, 2013)

OK now I'm cooking with gas 

Using Qer's flipped version of the equation from page 1 (starting with Ah) I've run a few permutations. For 70 miles I can do 21Kw/h at 201volts using 63 130Ah CALB cells. And at 4.4kg each, that's down to less than 280 kilos. 

I think a spreadsheet is in order...


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## vocalnick (Aug 5, 2013)

Quick questions for anyone who hasn't gotten bored and run away yet...

Is there a rule of thumb as to how much buffer to build into the calculations for all the ancillary electrical stuff that'll hang off the DC-DC converter? The Probe is pretty power hungry - windows, seat, mirrors, steering, brakes, and I'll probably be looking to implement heating an A/C down the road, so I'd like to factor it into the pack.

I'm thinking I'll allow 10% buffer, but that's just off the top of me head. Are there any conventions here?


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## Qer (May 7, 2008)

Windows and brakes might be high current, but it will be very intermittent so no real problem. Head lights etc will probably just chew up a few hundred Watts (some people replace them with LEDs, but I think it's more "feel good" than actually meaningful).

Typically the motor will use up several kW so the only thing that can even come close to making a difference is heating and AC. That's where you should worry.

One way I'd consider to estimate the heating needs would be to put an electrical heater in the car when it's cold outside and measure the power consumed. Just remember that that's the power needed when the car is standing still, when you drive the numbers will go up due to wind cooling...

Oh, and the intermittent current peaks is why you need an auxiliary battery! There are sometimes discussions about replacing the 12 Volt battery with the DC/DC, but I'd definitely wouldn't recommend it. If the current peak surpasses max current from the DC/DC you will get a brown out (or a total black out depending on the circuit protection) and if the DC/DC breaks you'll lose all auxiliary power instantly.

You can choose a smaller 12 Volt battery since you don't have to crank a big engine, but you most definitely SHOULD have a 12 Volt battery! Also, if I'm not entirely confused there's a requirement that the car must be able to power the hazard lights for at least 24 hours if your car breaks down on public roads. But don't quote me on that.


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## vocalnick (Aug 5, 2013)

Qer said:


> One way I'd consider to estimate the heating needs would be to put an electrical heater in the car when it's cold outside and measure the power consumed. Just remember that that's the power needed when the car is standing still, when you drive the numbers will go up due to wind cooling...


We live in a fairly temperate climate so I shouldn't need anything too extreme. I think with your comments in mind though, I might set up some sort of low-power heating that I can leave running over night when I'm charging. At least then I only have to maintain the cabin temperature rather than heat it from cold.



> Oh, and the intermittent current peaks is why you need an auxiliary battery! There are sometimes discussions about replacing the 12 Volt battery with the DC/DC, but I'd definitely wouldn't recommend it. If the current peak surpasses max current from the DC/DC you will get a brown out (or a total black out depending on the circuit protection) and if the DC/DC breaks you'll lose all auxiliary power instantly.


For some reason I had just assumed that I would retain a 12 volt accessory battery, but that's without having given it much thought. Feeling much more informed about that plan now


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## ElectricNoob (Aug 20, 2014)

I'm planing on converting a car to electric too and my thought was that $15k is a little pricey for batteries.
Is their any way of getting 100 miles a charge at hwy speeds wile not getting a loan at the same time?
And it would be nice if you could match up a control and motor that is not to expensive that would work with the batteries.
Thanks


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## dougingraham (Jul 26, 2011)

ElectricNoob said:


> I'm planing on converting a car to electric too and my thought was that $15k is a little pricey for batteries.
> Is their any way of getting 100 miles a charge at hwy speeds wile not getting a loan at the same time?
> And it would be nice if you could match up a control and motor that is not to expensive that would work with the batteries.
> Thanks


At the moment the least expensive battery options are salvage Leaf or Volt packs. In a lightweight vehicle you would need at least two of these in order to get to 100 miles. There are also sales of the CALB SE series cells at a couple of places. I believe these are on sale to flush inventories as they appear to be discontinued.

You simply reorganize the packs to get the voltage and current capability that you need for the motor/controller you have selected. HPEVS AC-50 setup would be an affordable AC setup.


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