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#### J_D

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Hi, I'm a complete newb on here, and I'm planning a future Mazda RX8 DC conversion using used parts and new lead batteries.

Could you advise me what voltage forklift motor I would require please?

I want something to match 200hp, the RX8 weights 1400kg and need to reach 70mph.

Jon

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#### J_D

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Hi Could somebody help me please?

Could someone tell me what voltage DC motor I would need to propel a 1400kg car to 70mph and the explanation behind it please too.

Thanks

Jon

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#### J_D

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Wow, you must be a professor or something , thanks so much for your post, it does actually make alot of sense in the way you've written it.

I'd like to propel the car to 60 in 6 seconds, with a top speed of 70mph.

I will have to get back to you about the batteries as I'll be using lead acid batteries as these are being provided free to me, until I can afford lithium.

I will provide the exact battery details and weights as soon as I am at work, hopefully you'll be able to tell me roughly If they need to be connected in parallel or series.

Thanks so much for your help I really appreciate it

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#### J_D

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#### J_D

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Re: fissiks

How quickly do you need to accelerate up to the 70 mph, e.g. 0 to 70 in xx seconds? For a rough estimate this determines the power rating of your motor.

So first i'm gonna convert some units; 1400 kg is about 3100 lbs, divide this Weight by gravity, g, to get mass, m; and 70 mph is a velocity, v, of about 103 ft/sec.

Now the kinetic energy of motion at 70 mph is (.5mv^2) = 510682 lb-ft

For a first order power estimate take the kinetic energy divided by your acceleration time, let's assume 0 to 70 in 13 seconds.

This gives a power of 39283 lb-ft/sec, a horse can pull 550 pounds over a distance of one foot in one second, so divide by 550 to get about 72 horsepower required for acceleration.

Your specific question of motor DC voltage can not be answered without additional information, such as the size of your battery energy storage system available to supply power for your vehicle. The voltage and current rating of your battery pack is the deciding and/or limiting factor for the motor selection. But we can take a look at some variables involved.

72 hp multiplied by 746 gives you power in Watts, about 54000 W.

Now this power can be supplied as Volts times Amps = 54000.

If you have 1000 Amps available, then you only need 54 Volts, or
if you have 500 Amps available, then you only need 108 Volts, or
if you have 400 Amps available, then you only need 135 Volts, or ....etc.

See how this is going? there is no unique voltage solution until you select the limits for your acceleration time and your battery pack current. Then you can determine how many cells you need to make the voltage necessary, and then you can specify the motor winding voltage rating for the peak power that you need.
Hi Kenny

Right, I have 4x 12v 50ah battery's and 2x 12v 26ah battery's , would this suffice?

I may be able to get hold of some more, and what motor voltage would you recommend?

Thanks again

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#### J_D

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Re: fissiks

That's only going to get you 72 volts, and you are limited to the capacity of the 26ah batteries. Charging would be really awkward, too. You will need to match the capacity of your batteries. Those batteries would store about 3kwh, and you can only use a fraction of that as they are lead acid batteries.

You may want to reconsider your battery choice. 72v could potentially be the bare minimum, but most systems run at least twice that. It will not get you to your performance goal, especially when you factor in the weight of the batteries.

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So how about if I could double the amount of batteries I had, would that work? (ps could potentially not use the smaller 26ah batteries and upgrade to the 50ah instead)

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#### J_D

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So If I have 8x 12v 50ah , what would that give me?

Also What motor would be best suited to the battery capacity I have?

And would it help me achieve my 1400kg car goal of 70mph?

With a range of 30miles?

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#### J_D

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Brilliant, thank you for your workings out, so in theory I would need more like 12x 50ah battery's to be safe.

Also in your opinion what, voltage DC motor would you choose? To try and get me to 60mph

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#### J_D

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Re: An Intuitive Approach to Fissiks and Mechanics

This conversation is probably better had elsewhere, as it's not very strongly related to finding a good motor.

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Apologies, I was trying to work out my battery capacity to choose the correct voltage DC motor for my requirements. I hope this is Ok

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