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#Post#: 5529--------------------------------------------------
Newbie questions - coils
By: maximoney1 Date: February 17, 2015, 6:01 am
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Made my first coil today and getting weird results....
Using wire rated at 54.84 ohms/km.
Coil constructed 4 in hand. Each strand was 7.0 metres long.
Expected resistance on each individual strand = 7.0/1000 x 54.84
ohms =0.3839 ohms
(Actual measured on meter = 0.7 ohms)
4 strands in parallel expected resistance
1/(1/0.3839+1/0.3839+1/0.38394+1/0.3839) = 0.096 ohms per coil.
Actual meter reading was 0.4 ohms
Any of the board guru's explain why i should be getting the
large discrepancies between calculated and real figures? ???
#Post#: 5530--------------------------------------------------
Re: Newbie questions - coils
By: lynx wind Date: February 17, 2015, 7:11 am
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It's your meter. They have a hard time being accurate down to
near zero Ohms. Your calculated is correct. If you put several
coils in series the cumulative Ohm reading would start to get
closer to measured.
#Post#: 5532--------------------------------------------------
Re: Newbie questions - coils
By: maximoney1 Date: February 17, 2015, 7:43 am
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Cheers Lynx,
Suppose you get what you pay for meter wise, and mine was an 'el
chepo' lol. ;D
#Post#: 5538--------------------------------------------------
Re: Newbie questions - coils
By: maximoney1 Date: February 17, 2015, 10:46 am
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Cheers CG.
I was going to 'wrap'the coil 'legs' in black electrical
insulating tape (it really holds the coils tight when it is
stretched) but is this a big 'no - no' due to the insulating
properties preventing better conduction of heat through the
resin(epoxy)?
#Post#: 5542--------------------------------------------------
Re: Newbie questions - coils
By: maximoney1 Date: February 17, 2015, 1:30 pm
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CG,
I had thought about that, but dismissed it just in case it
created a certain amount of drag??? Had also thought about
inserting small vertical strips between the magnets (about same
height as magnets) to effectively push air onto stator, but
again dismissed for same 'drag' reasons.
#Post#: 5545--------------------------------------------------
Re: Newbie questions - coils
By: lynx wind Date: February 17, 2015, 2:57 pm
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I had tested the heat issue some years ago by putting the alts
in a machine that would spin them up under heavy load. The heat
from the stator was negligible - 3 degree C rise at what would
be upper limits of power curve. I think the actual stator
surface area is quite large and dissipates the heat effectively
enough. This test was with fully encapsulated coils in resin.
It wont hurt anything to leave a hole in between each coil for
extra heat dissipation. That resin really doesn't add any
strength.
#Post#: 5546--------------------------------------------------
Re: Newbie questions - coils
By: maximoney1 Date: February 17, 2015, 3:06 pm
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Well, thats a revalation lynx,
At heavy load, thinking about the IsquaredR that needs to be
dissapated, i would have thought the stators would have got
pretty hot! Good to know that the area involved is a big enough
heat sink.
#Post#: 5666--------------------------------------------------
Re: Newbie questions - coils
By: maximoney1 Date: February 23, 2015, 2:13 pm
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CG re post 353 on the DIY 75 Discussion thread...
More for the DIY hobbyist rather than the consumate engineers
that frequent this forum ;)
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