[PSUBS-MAILIST] Minn Kota 101 - thread spec

[Jon Wallace via Personal_Submersibles]

Cliff, if you cut the temp rise by two doesn't the volume displacement 
become 1.6 teaspoons?  Regardless, I accept the need for a reservoir but 
it would seem the vinyl tube design would meet that role in the case of 
small MK motors and can be achieved via extra length or diameter.  My 
memory of Alec's and Jim's configuration is that both have more than 3 
teaspoons worth of extra volume in their tubes and perhaps this is why 
they haven't seen issues during dives.

Jon


On 7/21/2014 9:47 PM, Cliff Redus via Personal_Submersibles wrote:
> Concur Jon that water will act as thermal sink and that the duty cycle 
> on the thrusters are not severe but I don't agree that the thermal 
> expansion in negligible. If you assume that the temperature change I 
> estimated was high by a factor of two, then you would still end up 
> with 3 teaspoons of oil that would be forced into the ambient tube.  
> Small but not negligible.  There will be a change in the internal 
> temperature of the motor from the off position to on and given the 
> amount of oil in the 101 body, there will be  oil that has to escape.
>
> Granted, the primary purpose of the compensation is to keep from 
> exposing the housing to a high differential pressure but thermal 
> expansion still has to be accounted for in sizing the ambient reservoir.
>
> These MK 101 are powerful at almost 1.8 HP at 47 amps when air filled 
>  but there has to be some degradation in power when filled with 
> oil due to the viscosity difference with air. At 75F, light oil is 
> over 1800 times as viscous as air. IS there enough power to push a 
> psub about, sure.   I am just trying to come up with what kind of HP 
> loss you get with oil compensation.
>
> Does anyone know what rpm these motors max out at in the water?
>
> Good point Vance on trying to make the armature as hydraulically 
> smooth as possible to maximize power when oil compensated.  I wonder 
> how hard this would be to do?
>
> Cliff
>
>
>

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