Re: How do fewer volts / more amps effect brushes / heat?

I think the best way to look at it is "How many watts can my motor safely handle/produce?"

So, if your motor is rated for V Volts at I Amps, V x I= Watts.

So, if you lower the voltage, you need to find out how many amps the motor will see from the controller and determine if the new V x I = the same amount of watts as your previous configuration. If it does, then you're golden.

Now, let's say it turns out that you'll be exposing the motor to more power than it's rated for. Lee (I think) explained to me, that motor ratings are just points on a temperature graph. So if your motor is rated for 5 minutes at (I) Kw, 25 minutes at (Z) kw, and continuous duty at (B) Kw, then you just have to ensure that you don't exceed the duty cycle (running time) at your power level so that you don't melt down your motor.

For example, my motor L91-4003 is rated for 120 volts, 12 kw continuous, 46.5 kw peak or, 130 amps continuous, 150 amps for 30 minutes, or 500 amps peak. Well I'm running over 128 volts. I need to make sure that my duty cycle is SHORTER than the spec sheet provided.

Either that, or I have to run less than 130 amps at 128 volts in order to meet the "continuous" temperature point, less than 150 @ 128 volts for the 30 minute point, and I must peak at less than 500 amps at 128 volts or I could damage something.

If I'm wrong, hopefully someone will speak up and correct me.
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Message: 9
Date: Thu, 03 Jul 2008 11:15:04 -0700
From: Bob Tregilus
Subject: [EVDL] How do fewer volts / more amps effect brushes / heat?
To: ev@...
Message-ID:
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

Hi -

I've got a 48vdc motorcycle that's running a PM motor. I'm
changing it from a 48vdc to a 36vdc system. (Because I'm
switching battery chemistries.)

Given that as the voltage goes down amperage goes up, how
will that potentially effect:

1. Brush wear?

2. Operating temperature of controller and motor?

Thanks!

Bob


________________________________

Rich A.
Maryland
http://www.austinev.org/evalbum/371.html
http://patriotfuel.blogspot.com/




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