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Re: Range: 156Volts vs 312 volts
by Roger Stockton
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Zevutah wrote:
> David said
> "Maybe a better
> comparison might be 25 T-145s for a 150v pack to 22 T-1275s
> for a 264 volt pack (1800lbs vs 1804lbs)? "
>
> This is is a very interesting question and similar to one
> that I worked on recently. I found Uve's Battery page to be a
> great tool for looking at this question. The factory battery
> ratings are at the 20 hr rate and we need to discharge at a
> much faster ( 1/2 hr rate ) for an EV. Here are the numbers
> that I came up with using your 2 batteries listed above.
> See http://www.geocities.com/CapeCanaveral/lab/8679/battery.html
>
> T 145 6 volt battery 150 volt pack. qty 25 Peukert Exponent =
> 1.179 ( lower is better ) Amp Hr at 1/2 hr rate = 142 150
> volt * 142 amp hr = 21,300 watt hr 21,300 divide by 350 watt
> hr per mile = 60.8 mile range ( 100% DOD )
>
> T 1275 12 volt 264 volt pack. qty 22
> Peukert Exponent = 1.252
> Amp Hr at 1/2 hr rate = 74
> 264 volt * 74 amp hr = 19,536 watt hr
> 19,536 divide by 350 watt hr per mile = 55.8 mile range
One drawback of this sort of comparison is that it assumes a fixed 1/2hr discharge, which is really working floodies at a rate where AGMs would probably perform better.
The fixed discharge duration assumption also neglects that the battery power that represents will vary from pack to pack even though the vehicle will require the same power with any pack of the same weight.
If we compare instead at a fixed power level (after all, the vehicle will draw the same power going down the road with the same weight of either battery onboard):
T145: 181Ah @ 75A; 150V * 75A = 11.25kW
11.25kW / 264V = 42.6A
T1275+: 102Ah @ 42.6A
T145: 181Ah * 150V = 27.15kWh
T1275+: 102Ah * 264V = 26.9kWh
Basically, the numbers are close enough to be considered a wash given the uncertainty involved in these sorts of estimates; either pack would deliver about the same capacity at the same power level (about 15HP).
Obviously, as one compares at shorter and shorter discharge durations the scale tilts toward the battery with the lowest Peukert value.
> They are pretty close, but the 6 volt option looks like
> slightly better range. I talked to the Trojan customer
> service about this question also and they told me that the 6
> volt battery had more plates per cell and would thus handle a
> fast discharge rate better.
I think this means that if your application requires 75A discharges, the 6V battery is a better choice. However, in this case, for the same power the higher voltage string of 12V batteries is discharged at a lower rate and so they come out about the same.
> My guess is that the higher voltage pack would have better
> acceleration and top speed. The lower voltage pack would have
> better range. Maybe others with more experience could comment on that.
I would expect the range to be similar, provided the vehicle is driven similarly. I would expect the higher voltage pack to provide a wider powerband and this should translate into better acceleration.
I would, howerver, expect the 6VGCs to last better than the 12ers.
1800lb options that haven't been considered here are 27x T125 = 162V, or 29x T105 = 174V. The T105 option might be the cheapest simply because the T105 tends to be more favourably priced than its larger siblings. Not sure how many there are to a pallet, but taking a full pallet of any model should translate to a better price also.
26x T125 = 156V, which would max out a Z1K-LV and save a few bucks vs going to the -HV model for only a few volts more is worth considering.
Cheers,
Roger.
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> David said
> "Maybe a better
> comparison might be 25 T-145s for a 150v pack to 22 T-1275s
> for a 264 volt pack (1800lbs vs 1804lbs)? "
>
> This is is a very interesting question and similar to one
> that I worked on recently. I found Uve's Battery page to be a
> great tool for looking at this question. The factory battery
> ratings are at the 20 hr rate and we need to discharge at a
> much faster ( 1/2 hr rate ) for an EV. Here are the numbers
> that I came up with using your 2 batteries listed above.
> See http://www.geocities.com/CapeCanaveral/lab/8679/battery.html
>
> T 145 6 volt battery 150 volt pack. qty 25 Peukert Exponent =
> 1.179 ( lower is better ) Amp Hr at 1/2 hr rate = 142 150
> volt * 142 amp hr = 21,300 watt hr 21,300 divide by 350 watt
> hr per mile = 60.8 mile range ( 100% DOD )
>
> T 1275 12 volt 264 volt pack. qty 22
> Peukert Exponent = 1.252
> Amp Hr at 1/2 hr rate = 74
> 264 volt * 74 amp hr = 19,536 watt hr
> 19,536 divide by 350 watt hr per mile = 55.8 mile range
One drawback of this sort of comparison is that it assumes a fixed 1/2hr discharge, which is really working floodies at a rate where AGMs would probably perform better.
The fixed discharge duration assumption also neglects that the battery power that represents will vary from pack to pack even though the vehicle will require the same power with any pack of the same weight.
If we compare instead at a fixed power level (after all, the vehicle will draw the same power going down the road with the same weight of either battery onboard):
T145: 181Ah @ 75A; 150V * 75A = 11.25kW
11.25kW / 264V = 42.6A
T1275+: 102Ah @ 42.6A
T145: 181Ah * 150V = 27.15kWh
T1275+: 102Ah * 264V = 26.9kWh
Basically, the numbers are close enough to be considered a wash given the uncertainty involved in these sorts of estimates; either pack would deliver about the same capacity at the same power level (about 15HP).
Obviously, as one compares at shorter and shorter discharge durations the scale tilts toward the battery with the lowest Peukert value.
> They are pretty close, but the 6 volt option looks like
> slightly better range. I talked to the Trojan customer
> service about this question also and they told me that the 6
> volt battery had more plates per cell and would thus handle a
> fast discharge rate better.
I think this means that if your application requires 75A discharges, the 6V battery is a better choice. However, in this case, for the same power the higher voltage string of 12V batteries is discharged at a lower rate and so they come out about the same.
> My guess is that the higher voltage pack would have better
> acceleration and top speed. The lower voltage pack would have
> better range. Maybe others with more experience could comment on that.
I would expect the range to be similar, provided the vehicle is driven similarly. I would expect the higher voltage pack to provide a wider powerband and this should translate into better acceleration.
I would, howerver, expect the 6VGCs to last better than the 12ers.
1800lb options that haven't been considered here are 27x T125 = 162V, or 29x T105 = 174V. The T105 option might be the cheapest simply because the T105 tends to be more favourably priced than its larger siblings. Not sure how many there are to a pallet, but taking a full pallet of any model should translate to a better price also.
26x T125 = 156V, which would max out a Z1K-LV and save a few bucks vs going to the -HV model for only a few volts more is worth considering.
Cheers,
Roger.
_______________________________________________
For subscription options, see
http://lists.sjsu.edu/mailman/listinfo/ev
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