# 144V or 288V



## Woodsmith (Jun 5, 2008)

From what I gather, higher voltages results in fewer losses and so greater efficiency.
High voltage equates to lower current and lower current produced less heating of cables, motor and other bits the current flows through.
The higher voltage also means less volt drop at the end of a long run of cable.
The lower current draw also means it is easier on the batteries and so you can use a bit more of the capacity and they should last longer.

All in all, you can use smaller cable, have less transmission losses, run a cooler motor, happer batteries and so on.
The difficulty comes in switching and controlling high DC voltages and protection from shock and big sparks.

If you go high voltage it may be worth having the pack with a number of removable links to split it up when working on it. Saves you having a live 288V at one place when making that last connection to the main contactor.


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## DavidDymaxion (Dec 1, 2008)

You can accelerate faster with a typical series conversion with 288 V. Suppose you have a Warp motor that you wanted to limit to 160 V. With voltage sag, 144 V, and back EMF you can't hold the motor at 160 V. With a 288 V pack, you can hold the motor at 160 V longer, and get better high rpm performance.

The other option is you can exploit 2 motors with 288 V, if you are going all out for acceleration (like John Wayland's White Zombie).


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## rillip3 (Jun 19, 2009)

If you don't have a 288v motor to pair it with, I don't see where this does you any good. You're hauling around a lot of batteries to not use half of your voltage. When your batteries are so drained that the voltage sag takes you to the motor's optimum range, you're probably destroying them.

If you have a 288v motor, I agree with all the points Woodsmith brings up. But if you're using a regual 120-144v DC motor, then you're hauling around a lot of batteries just to step-down the voltage most of the time.


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## TX_Dj (Jul 25, 2008)

rillip3 said:


> If you don't have a 288v motor to pair it with, I don't see where this does you any good. You're hauling around a lot of batteries to not use half of your voltage. When your batteries are so drained that the voltage sag takes you to the motor's optimum range, you're probably destroying them.


The motor will never see pack voltage unless you are racing, anyhow. You have to have a higher voltage if you want to overcome back emf and get more RPM out of the motor.

A motor that is rated for 120v can typically be spun at a higher voltage without adverse consequences.

Besides, there are motors out there rated for 280+V (WarP11 HV comes to mind) if you do intend to design a system which can run the motor at max voltage (most cannot).

The point of running a higher voltage at the pack has many facets. All those facets pretty much summarize into this statement: The higher your pack voltage, the less amps required from the pack for the motor to do the same work. The less amps required, the less Peukert comes into effect. The pack voltage will sag less, thus requiring less amps from the pack than a lower voltage. As the pack sags, the amp requirement increases to do the same work, thus the pack sags more, etc.

There is a breaking point on this, depending on what controller you use. Tesseract has pointed out before where this breaking point is on the Soliton1, and if I recall, it's near 280v. Anything over that and you start to encounter switching losses in the controller, which any loss is a bad thing.


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## DavidDymaxion (Dec 1, 2008)

I agree that it might be easier and a worthy trade-off to do 144 V instead of 288 V for the vast majority of driving. However, you do get some additional power benefit even at modest currents.

Don't forget the original post said 50 Ahr for 288 V, and 100 Ahr for 144 V, so the total battery pack weights are the same.

Let's take 24 Optimas with 3 milliOhms (0.0015 Ohm for buddy pairs) of internal resistance each, at a modest 500 Amps.

144 V pack: (12 V - 500 A * 0.0015 Ohm) * 12 = 135 V

288 V pack: (12 V - 500 A * 0.003 Ohm) * 24 = 252 V

Let's say your controller limits voltage to 144 V. Then for power you have:

144 V pack: 135 V * 500 A = 67.5 kW
288 V pack: 144 V * 500 A = 72 kW

So even at a modest 500 A, same weight in batteries, the 288 V pack delivers about 7% more power once far enough out of current limit.

If we do the same exercise with floodies with 10 milliOhms of resistance, at a mere 300 Amps you get 14% more power. At 500 Amps, it is 26% more power.

I'll agree that if you drive gently, you may never see the benefit of this additional power. It can certainly be an intelligent trade-off to go with 144 V for packaging, cost, or other reasons.


rillip3 said:


> If you don't have a 288v motor to pair it with, I don't see where this does you any good. You're hauling around a lot of batteries to not use half of your voltage. When your batteries are so drained that the voltage sag takes you to the motor's optimum range, you're probably destroying them.
> 
> If you have a 288v motor, I agree with all the points Woodsmith brings up. But if you're using a regual 120-144v DC motor, then you're hauling around a lot of batteries just to step-down the voltage most of the time.


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## Bottomfeeder (Jun 13, 2008)

What controllers are you guys talking about?

Most DC controllers I know about give the motor full voltage, but use pulse width modulation to limit the time the motor sees the voltage.

I've never heard of a controller that actually limits the output voltage.


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## paker (Jun 20, 2008)

Woodsmith said:


> From what I gather, higher voltages results in fewer losses and so greater efficiency.
> High voltage equates to lower current and lower current produced less heating of cables, motor and other bits the current flows through.
> The higher voltage also means less volt drop at the end of a long run of cable.
> The lower current draw also means it is easier on the batteries and so you can use a bit more of the capacity and they should last longer.
> ...


So I would do better with 79 Headway 3.65v, 10AH cells at 288 volts than with 43 Thundersky 3.4v, 60ah cells at 146v?


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## Woodsmith (Jun 5, 2008)

paker said:


> So I would do better with 79 Headway 3.65v, 10AH cells at 288 volts than with 43 Thundersky 3.4v, 60ah cells at 146v?


Don't know yet.
Just saying from what I gathered reading on here as a generalisation.

The general case I think is that higher voltages gives more efficiency through cooler running from lower current.


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## peggus (Feb 18, 2008)

Which is better depends entirely on what your goals are and what components you intend to use. It's a system design issue. You can't take one variable out of the system and ask if x is better than y without specifying the rest of the system and the performance/cost goals the system has to meet.
<rant off>

Higher voltage may give you lower current but also longer battery chain, more interconnects, more BMS modules, so did you gain anything in the end? Efficiency wise, probably not due to the higher interconnect resistance or higher weight of copper if you stick to the same gauge. Cost savings, definitely not. 

So that leaves a minor gain in output power as explained by mr dymaxion.



High end motor controllers like the Zilla and Soliton do limit the average voltage to the motor. The motor still sees the full pack voltage every switching cycle but the commutator (prone to arcing) sees something closer to the average due to the inductance of the field. I'm sure Tesseract has pretty graphs to post.....


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## peggus (Feb 18, 2008)

DavidDymaxion said:


> ....
> Let's take 24 Optimas with 3 milliOhms (0.0015 Ohm for buddy pairs) of internal resistance each, at a modest 500 Amps.
> 
> 144 V pack: (12 V - 500 A * 0.0015 Ohm) * 12 = 135 V
> ...


A controller outputting 144V * 500A would not be drawing 500A from the 288V pack so voltage drop would actually be about half of what you calculated.

But your point remains valid.


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## DavidDymaxion (Dec 1, 2008)

The Zilla and I believe EVnetics Soliton will limit voltage to the motor. Because of the inductance of the motor, and the capacitors in the controller, when the controller is PWMing the motor sees an average current and voltage with ripple on it.


Bottomfeeder said:


> What controllers are you guys talking about?
> 
> Most DC controllers I know about give the motor full voltage, but use pulse width modulation to limit the time the motor sees the voltage.
> 
> I've never heard of a controller that actually limits the output voltage.


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## DavidDymaxion (Dec 1, 2008)

That's true! That's a good point, that even though the 288 V has smaller batteries, it'll have lower current draw, too, so it can drive as far.


peggus said:


> A controller outputting 144V * 500A would not be drawing 500A from the 288V pack so voltage drop would actually be about half of what you calculated.
> 
> But your point remains valid.


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## major (Apr 4, 2008)

Some similar discussion on this thread. http://www.diyelectriccar.com/forums/showthread.php?t=48006


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