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dc electromagnet question?

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vick

Jan 1, 1970
0
I have constructed a DC electromagnet for a special use at my shop. Being a
electrical contractor I thought this would be simple. (NOT) Made the
electromagnet, connected it to a 12vdc power supply at 5 amps and it works
great with one problem, it starts to heat up quickly. My desired results
was for it to run on a 80% duty cycle. Will resistors keep this heating
problem from happening? DC voltage is not something I have dealt with
indepth. Can anyone help me with this problem?
[email protected]
Vick
 
P

Palindrome

Jan 1, 1970
0
vick said:
I have constructed a DC electromagnet for a special use at my shop. Being a
electrical contractor I thought this would be simple. (NOT) Made the
electromagnet, connected it to a 12vdc power supply at 5 amps and it works
great with one problem, it starts to heat up quickly. My desired results
was for it to run on a 80% duty cycle. Will resistors keep this heating
problem from happening? DC voltage is not something I have dealt with
indepth. Can anyone help me with this problem?

A resistor in series will decrease the current, decrease the dissipation
in the coil and decrease the strength of the electromagnet. If that is
ok, then fine, stick a resistor in series or lower the voltage.

Otherwise, you need a way of getting rid of the 60W that you are dumping
into the coil - or redesign the electromagnet. A fan or two (or four)
might be an idea.

Another idea, that might be appropriate, is a resistor that can be
switched out. So, the full strength of the electromagnet will be
available when needed, but some form of automatic or manual switch
reduces the current when the full strength isn't.
 
V

vick

Jan 1, 1970
0
Is there a way to reduce the wattage from the power supply or should I just
get another power supply with less wattage? Thanks for your
help!!!!!!!!!!!!!!!!!
Vick
 
P

Palindrome

Jan 1, 1970
0
vick said:
Is there a way to reduce the wattage from the power supply or should I just
get another power supply with less wattage? Thanks for your
help!!!!!!!!!!!!!!!!!

You can get a power supply with less *voltage*. That will reduce the
current and hence the power dissipated - and the strength of the
electromagnet.
 
V

vick

Jan 1, 1970
0
Thanks for your help! It will be a do able solution hopefully.
Being a electrical contractor I (believe it or not) specialize in
design/build unique commerical electrical applications. I have dealt with
dc only with systems that have already been design for special equipment.
But, for me, this just did not compute in my brain compared to ac for what
ever reasons. But thats again for your help. Its people like you helping
people like me that make the world a better place.
Vick
 
V

vick

Jan 1, 1970
0
Thanks again for your help. I will be applying your suggestions. You help
me go back to school and you are a great teacher. Thanks again for you
willingness to share your knowledge.
Vick
 
D

Don Kelly

Jan 1, 1970
0
----------------------------
vick said:
I have constructed a DC electromagnet for a special use at my shop. Being
a electrical contractor I thought this would be simple. (NOT) Made the
electromagnet, connected it to a 12vdc power supply at 5 amps and it works
great with one problem, it starts to heat up quickly. My desired results
was for it to run on a 80% duty cycle. Will resistors keep this heating
problem from happening? DC voltage is not something I have dealt with
indepth. Can anyone help me with this problem?
[email protected]
Vick
-----
If you use resistors, you will reduce the heating-but you will also reduce
the force produced by the magnet in proportion. Using a lower voltage
source will also do the same.-
In that case increase the number of turns of wire to compensate -this will
also add some resistance.

For example, twice the number of turns (same wire) doubles the resistance
and halves the current resulting in half the heating for the same
force(proportional to ampere-turns)- but a bigger magnet. Life consists of
tradeoffs.
 
D

Don Kelly

Jan 1, 1970
0
----------------------------
Stuart said:
Being "positive" this time.

Rewind your coil with a finer gauge of wire but use more turns.

The higher resistance will reduce the current and hence the heating but as
magnetic flux is the product of the number of turns and the current you
can maintain the required strength of field/

For example, if you reduce the wire size from 1mm square to 0.5mm square
and double the number of turns. The current, and hence the power
dissipation, will be halved but you magnetic flux will remain virtually
the same.
-----
You indicate a doubling of the wire length and half the
cross-section--resulting in 4 times the resistance. From this the current
and losses will be 1/4 the original value but the force will also be
approximately 1/4 (proportional to {NI}^2). (unless the original setup was
driving the iron into saturation ).
 
V

vick

Jan 1, 1970
0
Sent email: Most associates where I am from will not share info, because of
there fear of lose of having a edge I guess. Thank you again.
 
P

Palindrome

Jan 1, 1970
0
Stuart said:
Hmm! I must remember not to post at 20 mins past midnight, when I'm
already half asleep, in future :)

Your other post is of course the correct answer.
That was why, at a slightly earlier time, I settled for writing, "Or
redesign the electromagnet" - without explaining how. :)

I thought, if he really wants to know, he can ask and I can answer -
when the old brain cell isn't still swimming in cherry brandy..
 
D

Don Kelly

Jan 1, 1970
0
Stuart said:
Hmm! I must remember not to post at 20 mins past midnight, when I'm
already half asleep, in future :)

Your other post is of course the correct answer.

--
Stuart Winsor

From is valid but subject to change without notice if it gets spammed.

For Barn dances and folk evenings in the Coventry and Warwickshire area
See: http://www.barndance.org.uk
 
D

Don Kelly

Jan 1, 1970
0
BFoelsch said:
Sorry about that.

A "senior moment," I guess.

Thanks again.

No problem- join the crowd and be glad that they are not Roy or chairman
moments.
 
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