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#### xrotaryguy

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Here are a couple of simple calculations that a person can use to estimate range.

range[km]=250 x capacity[kWh] / (mass[kg]^0.6)
-or-
range[miles]=250 x capacity[kWh] / (mass[lbs]^0.6)

Obviously these calculations do not take wind resistance, drive train efficiency, rolling resistance, etc, but comparing these results to results from sites like EvConvert.com may give a good idea of what range to expect from various EV configurations.

Here is another good site for graphs and formulas of this type.

#### xrotaryguy

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Thot = Tcold + (K x ((Rhot - Rcold) / Rcold))

where K = 256.4 for copper
Thot = hot temperature in deg.C
Tcold = cold temperature in deg.C
Rhot = resistance at hot temperature in ohms
Rcold = resistance at cold temperature in ohms

#### xrotaryguy

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Hp=(torque*RPM)/5252

#### KiwiEV

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For those looking to calculate the maximum electric motor RPM in each gear, I recommend clicking on this RPM Calculator
This is essential for those not wanting to over-spin your motors.
The 9 Inch "FB1-4001A" motor from Advanced DC has a maximum RPM of 5600 RPM and without a rev-counter or reliable speed/gear chart memorised, it'll happily overspin and you won't hear it or notice it until it goes pop. That terrifies me a little.

#### xrotaryguy

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Having a tachometer would be nice too. No sense in spending thousands of \$\$ on an EV conversion and not wiring up a tach.

#### KiwiEV

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I hear ya. The Tredia has a tachometer and I think I've figured out a way to make it work on a Curtis controller that doesn't support tachometers.
I've rewired the back of the dash and found that 1.5 volts displays just over 4000 RPM.

This means in theory by using a variable resistor (for tweaking) and a very small generator on the tail shaft of the motor, I can send small voltages through to the tachometer relative to the speed of the motor.
It's crude but it could work with tweaking.
It means I can avoid purchasing and installing an expensive optical sensor to measure the tailshaft RPM and feed it in pulses to the tachometer. That's the professional way apparently. I prefer my idea.
I wonder if it'll work?

Here's me experimenting the other night:

#### Mr. Sharkey

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Hmm, I think we have a lot to discuss concerning tachometers.

First of all, tachometers, as you are probably already aware, requre some kind of frequency-to-voltage conversion to work from a spinning shaft/ignition pulse train/etc.

Your experiment that 1.5 volts DC sends the tach meter movement to about mid scale is a good start, but simply connecting the meter movement to any source of signal derived from a rotational generator is not going to give you what you are after. Even if the match-up was corrected via a variable resistor, you would still be looking at a reading that was non-linear with the speed of the shaft.

A petrol engine tachometer takes a pulses train from the ignition system of the distributor and converts the frequency of the pulses (which is directly proportional to the engine speed) and converts it to a DC voltage/current to run the meter.

The optical sensor tachs do the same thing, except that the pulses are generated by an optical interrupter.

On some diesel engines, a sample of the three phase AC power from inside the alternator is supplied to the V/T converter .There are "black boxes" that can do the conversion and will program for rough calibration of a petrol tach from a variety of frequency generators. See this page for a \$60 converter that does this. The generation of the pulse train is up to you.

I can show you how to build a complete tachometer using junk box parts costing \$10. All you need to do is couple a disc, gear, or similar serrated interrupter to your motor shaft. A small AC generator of some sort would also work. It's possible that the circuit could be cobbled together to sense motor commutation spikes, but I've never fiddled with that.

#### xrotaryguy

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