# EV Series/Parallel shift Passing Gear



## Jimdear2 (Oct 12, 2008)

I've had this thought floating around in the back alleys of my mind for a while and I think now is the time to bring it out.

As I have been reading through the threads, I have never seen the voltage shift idea used in this way. Plus I hear infered in all of the threads somewhere, the need for a little extra once in a while.

So here goes:
Design the vehicle components with enough redundancy that you could use a "TURBO" mode (for the lack of better name) switch to reconfigure the battery pack to a higher voltage for a short burst of higher speed for those rare but important times when you need a few seconds of "kick ass"

For example:
Your EV design criteria gives you the need for a 72 volt system at 450 amps maximum And your vehicle size limits you to a traction pack to give you a range of 30 miles

If instead, you bought a motor and controller that could withstand 144 volts and 500 amps then configured your pack to do a series/parallel shift, e.g. normally running at 72 volts with the ability to shift to 144 when needed.

I realize there would have to be some fancy switching to protect voltage sensitive equipment and hitting TURBO would seriously effect range, plus their may be other things I'm not smart enough to recognize.

In all that I have read, ie always seems show that EVs with lead acid always have to comparamise between distance without real speed or a racer with no endurance.

This I would give those with smaller vehicles with limited battery room the chance to use the higher voltages and still keep the capacity at lower speeds (voltages) for range.

I don't think (gut feeling) that this kind of design would increase the cost of conversion by more than 5%.

Am I nuts, is this kind of thing possible? Has it been done? If you know of one could you post a link.

Jim


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## notnull (Jul 30, 2008)

Jim,

I thought about this approach when I was building my electric bicycle. Two 36V - 10 Ah packs, In parallel mode, I would have 36V - 20Ah and in series mode have 72V - 10Ah. Before I really got going on this idea I tried riding in both configurations and found the 72V configuration had much better performance, so I just left it that way. I did find out that I could be very gentle on the throttle with the 72V setup and the amount of power used was basically the same as the 36V configuration. The bottom line is the total amount of Watt-hours available in your pack and that is not going to change no matter how you configure it. I finally figured I might get slightly more range if I built a parallel / series configuration that I could switch on the fly but the gain in range would be so slight that it just wasn't worth the effort.

Think of it this way. If you took your 72V configuration with twice the amp hours and drove a five mile course and then recorded the amount of energy used and compared it with driving the exact same vehicle reconfigured for 144V and half the amp-hours over the same five mile course at the exact same speed and acceleration, the energy used should be very close to the same. So, why not just go higher voltage and use less current which keeps your heat losses down as well. If you need more range just be very easy with the right foot.

Steve


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## jtmarten (Nov 14, 2008)

Bradley did it in the early 80's. My GTE, when it had the original GE EV-1 controller, had a switch on the dash to toggle 48/96v mode. I never used the 48v mode, way too slow. They claimed a huge gain in range, but you could probably get the same gain by driving 35mph in 96v mode.
Jeff


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## Zemmo (Sep 13, 2007)

notnull said:


> Jim,
> 
> Think of it this way. If you took your 72V configuration with twice the amp hours and drove a five mile course and then recorded the amount of energy used and compared it with driving the exact same vehicle reconfigured for 144V and half the amp-hours over the same five mile course at the exact same speed and acceleration, the energy used should be very close to the same. So, why not just go higher voltage and use less current which keeps your heat losses down as well. If you need more range just be very easy with the right foot.
> 
> Steve


There is also the Peukert Effect on the batteries, the lower you can make your Amp draw the more Ah there will be in the batteries. It isn't a linear line. But the general example you have given is pretty good.


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## Jimdear2 (Oct 12, 2008)

I guess I'll just float this idea right back (Way Back) into back alleys of my mind.

The sick thing about this is, I read all of the things that should have given me this answer. I got to rearrange my thinking or learn how to divide the electric half of my brain from the ICE half.

Man that sounds weird.

Jim


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## O'Zeeke (Mar 9, 2008)

Jim, check out this video of White Zombie where they use your series/parallel idea

http://www.youtube.com/watch?v=-PRkpn2xmjc


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## samborambo (Aug 27, 2008)

For a given power required and the same cells, the configuration of the cell string has no effect on the discharge performance. That said, a low voltage, high current config will introduce more losses in cabling and the controller. Go with the highest voltage that you're comfortable in dealing with.

Some brushless DC motors can have their windings configured for series/parallel in theory although I've never seen such a system. This would have the benefit of more power in the bottom end with lower motor/controller current when configured in series. In parallel you'd get higher attainable top speed due to lower motor BEMF. You'd have to build a manual 6 pole "gear" selector switch.

That idea is worth exploring. 

Sam.


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## TX_Dj (Jul 25, 2008)

Zeke,

Zombie does a series-parallel shift at the motors. It shifts the motors from being wired in series to parallel, not the battery pack.

Like Sam pointed out, kW = kW. Whether you feed the controller 500 amps at 72v or 250 amps at 144v, it's still 36 kW.

The difference is you'll never go as fast on 72v as you can on 144v.

And basically what you're talking about is what the controller does anyhow... when the motor is turning so slow it can only take 12v, the controller tries to pour as many amps into the motor as your right foot is asking for to give you the torque you want.


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## samborambo (Aug 27, 2008)

Yup, the Zombie is such a system - using a pair of 8" series DC motors. I didn't check out the you tube link before I posted!

I haven't seen the Zombie's phase advance on the brushes before. Is this a common thing on series DC motors? My research has been solely in BLDC and induction.

Sam.


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## xtian999 (Apr 26, 2009)

That is how my 1974 Citicar works. First gear is parallel with a resistor coil to slow the motor, second is straight to the motor, third is all batteries in series. 48 volts is good for 40mph with a tailwind.


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