A friend of mine wants to run a 90V, 1.4A motor with a 12V, 4A car battery. I'm just wondering if anyone can tell me whether or not this is even possible? Thanks in advance for any response/suggestions.

 

Not with the given specifications.

 

Does anyone know of a simple way to power a mobile, 90V DC motor?

 

Your given specifications are a 90V, 1.4A motor.
Let's express that in Watts.
P=E*I, which means Power in Watts = Voltage x Current

So, for the motor you're talking about, you need 90v * 1.4A = 126 Watts.

You don't mention if this is with no load, or at stall - that's a mighty important piece of information that you omitted.

Anyway, let's assume for the moment that your motor draws 126 Watts when it's just running at no load.

You'll need a DC-DC converter capable of boosting your battery voltage up to the motor's voltage. Generally, DC-DC converters are between 75% and 99% efficient. Let's take the average, or 87% efficient.

So, you need 126W at 90 Volts, and an inverter that's 87% efficient. Let's say you're using a car battery (poor choice, but that's what you gave in your initial requirement statement.)

We're stuck with 12v.

Isource = 90 / (12 x 87%) * 1.4 Amperes
Isource = 90 / 10.44 * 1.4A
Isource = 8.62 * 1.4
Isource = 12.068 Amperes.

You will need a battery that can source over 12 Amperes, rather than one that can source only 4 Amperes - and that is if you can find a circuit that is at least 87% efficient.

 

Thanks for the response. I was confused. The battery he has does 12V, 400A. Also, I think the motor draws 1.4A at a stall.

So now the question is, would it be fairly easy to make a DC-DC boost circuit for this, or does anyone know where you can buy one for relatively cheap? Thanks again for the help.

 

I would buy a cheap [square wave output ], 12V DC to 120 VAC inverter rated at about 200W , half wave rectify, and minimal filtering, just enough to keep hum tolerable. V to low- use full wave bridge, still to low add more cap.

 

If you want to build something yourself, have a look at Ronald Dekker's "Flyback Converters for Dummies" page:
http://www.dos4ever.com/flyback/flyback.html

This is a really good resource for your type of project.