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Re: [PSUBS-MAILIST] trolling motors?
Ken,
On MK and MG the controllers are certainly
Pulse Width Modulators for speed control, but I am not sure of their efficiency
for current surge protection, your controller seems to be the one and I d
be glad to look at your design if you fax it to me to include it in my subs,
since only the current limit interests me.
As of controller, I switch 36 V and 24 V
on the motors leads through high rating switches
and relays for speed control. Relays are activated by a temporary trigger
switch on a hand grip that must be pressed to keep running. I agree with you ,
you are never full power all the time but by bursts of thrust, so why bother
with a permanent switch that will require time to turn off in case of
trouble.
A battery computer indicates current flow. Main
reason for a current surge that could damage the magnet is a locked
prop. The comp is not a current limit I concur but a efficient current
monitoring. Normal max current rate for a MG107
is 36 Amps. I use a $50 relay, 40 amps 100 VDC rating with heat sink. Expensive
but much better than the one provided by MK or MG in their top
housing.
In my case any peak of current is detected and
displayed by the battery computer soon enough to release the trigger before
troubles.
It s been 2 years that I use motors with no factory
controller without any problems. and never had a locked or tangled
prop.
When I used MK, they had the factory controller,
failure came from a poor contact between the coil loops and the contacts (those
where the brushes touch) it took me a while to find out. Poor contact due to
moisture.
I had to slighty hammered the copper contact of
each contact that embraces the coil loops to re-establish the
contact.
If 1 or 2 contacts are poor the motor runs slower
with vibration which is interprated by MK tech by a bent shaft.
No demagnetized stator (that would require at least
60 amps), this unfortunate experience and a more complicated disassembling
process made me switch to MG along other details.
I am in Puerto Rico, I am about to move to FL which
is a more apropriate place for a mini submarine business.
Herve Jaubert
fax: 787 278 1505
----- Original Message -----
Sent: Sunday, November 26, 2000 4:17
PM
Subject: Re: [PSUBS-MAILIST] trolling
motors?
Herve,
Most of the permanent magnet motors
require a controller (current limit) to
prevent peak armature currents
from demagnetizing the stator magnets. I can
expand on this if you like
but if you take a look in the PSUBS archives
there's more information
there. If they don't answer your questions, I can
elaborate. Once you
design and build a current limit, it's easy to make it a
speed control. I
wonder, if you are not using any controller on the MK motor
you said
failed, perhaps the stator was demagnetized? I think you stated a
speed
control was not really needed on these subs and I agree, but for this
type
of motor you do need a current limit.
From what you have stated on
your previous messages and messages from others,
apparently the MG has
some of the electronics in the motor housing. Perhaps
the Dura amp modules
contain the power switches which require heat sinking. I
believe that's
why 5 wires are required, maybe. The four wires used in the MK
are simply
the two armature leads. Two red leads are used for the positive
lead and
two black for the negative armature leads. A review of your last
message
seems to imply you don't use any kind of current limit or speed
control.
Do you just switch 24 or 36 volts to the motor?
In any case, I'm not
too familiar with the Motor Guide motors in that much
detail. I just don't
like putting any electronics in the motor housing and
that's just a
personal preference.
I wish MK made a three blade prop, but I have not
been able to identify one.
From your address it looks like you operate
subs in the Caribbean. Can you
elaborate on that? I do a lot of diving in
that area.
Have fun,
Ken Martindale
In a message dated
11/26/00 2:58:50 PM Eastern Standard Time,
caribsub@coqui.net writes:
Ken,
I am not quite sure to understand what you mean by
"controller", because
there is not much electronic inside the lower unit
of a MG. please
elaborate.
MK lower unit has only red and black wires going
into the lower unit, an
electronic board is in the top housing for speed
controls
MG lower unit has 5 leads going inside, there is an
electronic module for
speed control in the top housing, like in MK, and
a brush card inside the
lower unit on which are connected the wires and
a Dura amp module.