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[EVDL] adding range to existing pack

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From: Michael Mohlere
> If I wanted to add some range to my EV... what is the
> best/easiest/cheapest way to do same?

Best, easiest, and cheapest are probably three different solutions. Pick one! :)

Before looking at the battery pack itself, I'd start by finding out if there are any simple little things that are limiting your range. Things like soft or high rolling resistance tires, dragging brakes, bad wheel alignment, hot connections or wiring, etc. Fixing these could easily add 10-20% to your range.

Next, consider your driving style. Do you accelerate quickly and drive fast (drag race to the next stop light)? Are you shifting to run the motor at too low an RPM, so the motor and controller are getting hot? Do you drive until you are almost up to a stop sign, and then brake heavily? These are all bad for range. Changing your driving habits can easily add another 10-20% to your range.

Is your present battery pack in good shape? Are they well balanced (all at about the same voltage after a long drive)? Are there any weak ones that are limiting your range? If a battery is weak enough, removing it from the string will actually *increase* your range.

Are the batteries cold? Sometimes, all it takes to increase range is to add a heater to keep them around 80 deg.F.

Once you've gotten through all these "cheap / easy" improvements, then it's time to consider more expensive and elaborate ways to increase range.

> I have read a lot about "buddy pairs", but I was thinking more
> on the lines of creating another 120 volt pack with some smaller
> batteries...

The best solution is probably to have a single pack that meets your range and performance needs. Buddy packs and twin strings are "work-around" measures to avoid special case problems, such as the batteries you need weren't available or affordable, or didn't fit.

If you want to try a hybrid battery pack with two different strings of batteries, I think in general you should include some kind of charge controller to control/limit how much current comes from each pack. This charge controller will also need to manage charging, so each pack is charged correctly.

Just like motor controllers, this charge controller could be as simple as a set of contactors, or as complex as a full-blown motor controller. Luckily, it doesn't have to handle nearly as much power as the motor controller, and so can be smaller. It is only being asked to move power across a fairly small and limited voltage range, and can be sized for the average power rather than the peak power.

As a simple example, suppose your present system has ten 12v batteries; a 120v pack, controller, and motor. You could add an 11th 12v battery, 12v-to-120vac inverter, and simple battery charger. Let's say this new 12v battery is rated at 30 amphours at the 1-hour rate. Then you need a 360 watt inverter. Setup your charger to draw 12v at 30a, to produce 120v at about 2.5a (due to inverter and efficiency). You've added not quite 11/10 = 10% to your range.

The principle can be expanded to larger 2nd packs.

"Excellence does not require perfection." -- Henry James
Lee A. Hart, 814 8th Ave N, Sartell MN 56377,

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