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Old 12-28-2011, 05:24 PM
Gary B Gary B is offline
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Default No load motor test 12 v

O.K. guys, i really did try to search for info on this. - No find.
I will soon be getting my first ever EV motor to use (and test first).
I'm very fearful of hooking this up directly to 12 v without a controller.
(And, i have no controller, yet.)
I would still like to see if it turns.-
Of course, i have to tie the motor down firmly to keep it from rolling down the hall.
Then, i'm thinking i could use standard automotive bulbs (or a headlight) to put in series with the motor to limit the current to the motor from the 12 v battery supply. - (?) -
These bulbs run off of 12 v anyway. - So, they should not blow out when they are effectively shorted to ground through the motor windings (series DC motor)(which has such a low low coil resistance). - The resistance of those bulbs (headlight for higher current ?) should limit the current going through the motor coils. This what i'm thinking, anyway.
It may be possible to get enough current going through the motor to make it turn to some degree and indication. - I would be happy if it would just turn a little bit.
I don't even know how many amps it takes to get one of these things to turn (with no load). - Otherwise, i would just put in a series resistor to limit the current to that value (assuming zero resistance for the motor coils). -
5 amps, 12 v, 2.4 ohms, 60 watt (100 watt) resistor, for example. -
None of these performance charts go down into that region of operation. -
Any ideas in relation to this initial testing? - (O.K. - I'm inexperienced) -

Thanks !
Gary B.
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Old 12-28-2011, 07:02 PM
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Default Re: No load motor test 12 v

Quote:
Originally Posted by Gary B View Post
O.K. guys, i really did try to search for info on this. - No find.
I will soon be getting my first ever EV motor to use (and test first).
I'm very fearful of hooking this up directly to 12 v without a controller.
(And, i have no controller, yet.)
I would still like to see if it turns.-
Of course, i have to tie the motor down firmly to keep it from rolling down the hall.
Then, i'm thinking i could use standard automotive bulbs (or a headlight) to put in series with the motor to limit the current to the motor from the 12 v battery supply. - (?) -
These bulbs run off of 12 v anyway. - So, they should not blow out when they are effectively shorted to ground through the motor windings (series DC motor)(which has such a low low coil resistance). - The resistance of those bulbs (headlight for higher current ?) should limit the current going through the motor coils. This what i'm thinking, anyway.
It may be possible to get enough current going through the motor to make it turn to some degree and indication. - I would be happy if it would just turn a little bit.
I don't even know how many amps it takes to get one of these things to turn (with no load). - Otherwise, i would just put in a series resistor to limit the current to that value (assuming zero resistance for the motor coils). -
5 amps, 12 v, 2.4 ohms, 60 watt (100 watt) resistor, for example. -
None of these performance charts go down into that region of operation. -
Any ideas in relation to this initial testing? - (O.K. - I'm inexperienced) -
Hi Gary,

A 12 volt battery should work just fine. You could use a 6 or 8 volt battery or 2 or 3 Lithium cells. If it is an 8 or 9" motor commonly used for EVs, it will likely draw 30 to 50A and maybe spin up to 2000 RPM, maybe 3000. Go ahead and try a resistor, but it should be less than 0.25Ω and capable of the current.

major
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Old 12-28-2011, 08:21 PM
Gary B Gary B is offline
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Default Re: No load motor test 12 v

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Originally Posted by major View Post
Hi Gary,

A 12 volt battery should work just fine. You could use a 6 or 8 volt battery or 2 or 3 Lithium cells. If it is an 8 or 9" motor commonly used for EVs, it will likely draw 30 to 50A and maybe spin up to 2000 RPM, maybe 3000. Go ahead and try a resistor, but it should be less than 0.25Ω and capable of the current.

major
O.K., Major. - Thank you for considering my question an honest one.
Iím trying to clarify (for myself) my understanding of what you have said and follow up on its implementation. If the motor (and resistor) draw (conservatively) 30 amps from a 12 v supply, then I should have a total effective impedance of about 0.4 ohms. - I believe that is correct. You suggest I should use a resistor of less than 0.25 ohms (letís say 0.20 ohms). - Then 30 amps of current through that resistor (0.2 ohms) should drop 6.0 volts. - That indicates, I believe, that the resistor should have a watt rating of at least 180 watts. - (Say 200 watts.) - So if I used 5 ea 1ohm resistors in parallel that would give me 0.2 ohms. And each resistor should be capable of running 40 watts. (Say 50 watts.) - This should do the job, shouldnít it? 5 ea 1 ohm 50 watt resistors. -

I will pursue the details of cost implementation later.

Thanks for your input. (Always welcomed and respected.)
Gary B
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Old 12-29-2011, 04:29 PM
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GizmoEV GizmoEV is offline
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Default Re: No load motor test 12 v

Gary,

If you are worried about start-up current then you could just use some longer small diameter wire than what you will use in the end. I've run a 6.7" motor with standard 12 gauge house hold wire. It does warm up a bit but not to the point of melting the insulation. You could double up on the wire if you want. Even if you had zero resistance between the 12V battery and the motor you would be fine. That is what Major was saying. Just that IF you decide to use a resistor it has to be able to handle the current.

Using a headlight in series might limit the current so much that the motor won't turn. The resistance is too high. A 65W bulb at 12V will only pass 5.4A of current.
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