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higher voltage vs. more amp hours

7357 Views 8 Replies 7 Participants Last post by  dougingraham
I have a Warp9, a Soliton Controller feeded by 47 CALB 130Ah cells.

First we had 36 cells, than 45, now 47.
But it seems that the more voltage doesn't mean that we consume significant less amperage.

So if I want to increase the range, would "more cells" and higher voltage or bigger cells with more Ah would be the right way?
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I have a Warp9, a Soliton Controller feeded by 47 CALB 130Ah cells.

First we had 36 cells, than 45, now 47.
But it seems that the more voltage doesn't mean that we consume significant less amperage.

So if I want to increase the range, would "more cells" and higher voltage or bigger cells with more Ah would be the right way?
You are still in the low voltage arena and will still consume a significant amount of amperage. More voltage will allow higher rpm and slightly less amperage for a given load. In order to gain more RANGE you need to back off that throttle and be sure you have good LRR tires and that your suspension is set right and that your brakes are not binding.

Mostly just back off the throttle. Coast as much as you can too. Yes, more cells will give you more range.

You went from a 14.9kWh pack to a 19.5kWh pack. Should give a decent range boost as long as you keep your foot off the throttle.

More Power = More Fun = Less Range.
 

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Up to its limit the Soliton is pretty flexible, so you can feed it as much voltage as it will allow and have it limit the voltage to the motor.

Another difficult part of changing voltage is the charger. Will your charger let you add more cells? If not it's probably better to add cells in parallel to get more AH.
 

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I have a Warp9, a Soliton Controller feeded by 47 CALB 130Ah cells.

First we had 36 cells, than 45, now 47.
But it seems that the more voltage doesn't mean that we consume significant less amperage....
Adding a few more cells (ie - more voltage) will only result in drawing less amperage IF you continue to accelerate at the same rate as before AND you drive at the same average speed. Usually, though, adding more cells allows you to draw a given amount of battery current up to a higher RPM which can result in your range staying the same or even dropping slightly.

As has already been mentioned, 36 cells (115V) is pretty low for a modern EV while 47 cells (150) is about on par with a mid-1990's DC system. You probably got more of a performance boost going from 36 -> 47 cells than a range boost, per se (though I'm sure your range went up a few km at least).
 

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I have a Warp9, a Soliton Controller feeded by 47 CALB 130Ah cells.

First we had 36 cells, than 45, now 47.
But it seems that the more voltage doesn't mean that we consume significant less amperage.

So if I want to increase the range, would "more cells" and higher voltage or bigger cells with more Ah would be the right way?
Your original 36 cell motor voltage would have been capped at about 97 volts (Nominal pack voltage of 115 - a 15 % sag.) If you set the Soliton to limit motor voltage to that I would expect you to see the range increase you were expecting. An increase of about 1.3 times. If you are not seeing this it is because you are experiencing the joy of the additional power the extra voltage makes available and thus wasting the extra 30% that was added. Motor efficiency curves can eat all that up pretty easily. Limiting the current to the WarP9 to 600 amps will most likely give you a range boost of maybe as much as 15% vs 1000 amps if you do lots of stop and go driving and have a lead foot. Increasing the voltage can make this waste worse to a point. The Soliton was most likely limiting you in some way you didn't notice with 36 cells and that limit moves up when you go to 47 cells.

Either approach yields a pack with more energy. My preference is to increase the voltage because it will tend to decrease battery current and thus reduce the sag which gives an overall increase in system efficiency. Increase the cell count up to 96 cells and then you pretty much have to go to larger cells or reconfigure your current pack to 48 cells in paralleled pairs and continue adding pairs in parallel. There are problems with increasing the size of the battery and it is mostly about the weight you are adding to the vehicle. It looks like the sweet spot with LiFePO4 cells is around a 20kwh battery. This will give a realistic drop dead range of 60-100 miles in a 2000 to 3000 lb vehicle. Adding more batteries will work up to about double this and then the physics starts to beat you up too badly. The doubling of the batteries does not result in a doubling of range. It might give you 1.5 times the range. If you double it again you get even less than this the next time. You can ask yourself how does Tesla get 250 miles range and the answer is they didn't try to convert an ICE, they started out from scratch and did pretty much everything correctly.
 

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<snip>
So if I want to increase the range, would "more cells" and higher voltage or bigger cells with more Ah would be the right way?
I think you are sort of stuck with adding voltage [which is probably best as others have noted] because adding Ahr would require ditching your present pack or paralleling a string or buddies equal in number to your present pack.
 

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In theory
, there is no difference if the whole system is designed for the voltage chosen.

But in practice, because the controller steps down the voltage for the motor, increasing the pack voltage gives you more freedom in motor selection and configuring the controller settings for the performance you want.

Low voltage:
+ Safer (if low enough)
- more copper needed in cables
- harder to find a motor that can supply enough power at high rpm at low voltage
+ fewer BMS cell modules/taps needed, if you use one.
+ fewer cell interconnections to make.
- All connections carry higher currents and connection resistance is more important.

High voltage:
+ Can supply more power at high rpm's to a larger range of motors
+ copper savings in cables
+ lower current requirement for connections
- Higher insulation requirements
- Higher safety requirements
- More cell interconnections to make
+ Every cell interconnection carries less current, so higher-resistance connections are averaged out a bit.

If driven the same way, there is very little difference in efficiency or range. If the motor is matched properly, there is no difference in performance either, but if the motor is fixed (as it usually is), increasing voltage will increase maximum performance. You don't need to use all that performance however.

So, a higher voltage systems give you more freedom in the motor selection. There are very few motors available that give good performance at <100V. You can't go too high if you mind the controller limit (and components between the battery and controller, such as fuses and contactors).

Local regulations may apply. Some use <100V systems for regulatory reasons.
 

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Discussion Starter · #8 ·
Thanks to all.

I should have been more precise.
I use a Soliton Junior, maximum battery current is set to 390 amps (3C).

The chargers (NG3) are now at there limits (165V), so I have to get some new, if I get more cells.

I'm not sure which value would be the best for "max battery voltage at full current" for 47 CALB (blue) cells ... I took 117,5V (2.5V*47).

To power consumption:
@ constant 85km/h (53mph), 1320kg (2910 lbs), the average drain is 0.93Ah/km (1.5Ah/mi)

The 36 cells I had another motor (D&D) and controller (Curtis 1231C), so this is perhaps not 1:1 comparable, but I had approximately the same consumption.

45, 46 and 47 cells I had the Soliton Jr.

So what do you think:
If i increase battery up to 60 (+13 cells, +27.66%, +134kg, +10% more weight), would the average usage decrease by about 20%?

Any data to your average usage with similar motor/battery/weight combinations?

Thanks, Michael
 

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I'm not sure which value would be the best for "max battery voltage at full current" for 47 CALB (blue) cells ... I took 117,5V (2.5V*47).

So what do you think:
If i increase battery up to 60 (+13 cells, +27.66%, +134kg, +10% more weight), would the average usage decrease by about 20%?
Max battery voltage at full current... Because I operated in the winter with unheated cells and I drove with battery temps as low as 15F I set my full current voltage to 1/2 nominal per cell. 1.6v * 47 = 75.2 volts. Honestly this is not a critical value because unless the pack is dead or it is terribly cold you will never get close. If you use the batteries when it is cold you will want to lower it a lot. For the no current setting I would use 2.9 or maybe 3 volts per cell.

If you limit the motor voltage with the Soliton and leave the motor current limit unchanged, yes your range will go up. For 47 cells you currently have set the motor voltage to 128 volts (3.2*47*0.85). If you don't limit the motor voltage then you are widening the torque band and you will drive the vehicle differently, perhaps to the detriment of range.

This won't be as much fun but if your goal is increasing range then this is what you would need to do to do an apple vs apple comparison.
 
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