Hi Jeremy,
Propulsion Marine has tested their external water cooling adapter and a 12V forced air fan and have documented a 30C reduction in motor temps under full load for a Motenergy ME0913. Data was collected using the manufacturer installed temp sensor buried in the windings.
Neither of these mods are overly difficult and don't require any modifications of the motor itself. There is some fabrication needed, programming of the controller, and of course wiring the fan and plumbing the cooler. To me, the results seem worth it for customers that need the extra power throughput. The price premium for the cooled drive system seems reasonable for someone like me that doesn't want to refine (rebuild) their modifications multiple times while performing their own R&D. Apparently, another part of the price difference between the 5.5kW and 7kW systems is a beefier gearbox to handle the increased power.
If I had a bigger boat, around 14,000lb displacement, I would probably go this route. Of course, I'm already a satisfied customer so I might be biased.
Fair winds,
Eric
Marina del Rey, CA
--- In electricboats@yahoogroups.com, "Jeremy" <jeremy_harris_uk@...> wrote:
>
> I'd say that cooling the motors is always a very good thing to do, if you can find an efficient way to do it. Because the motor winding resistance is strongly temperature dependent (it increases with increasing temperature) the cooler you can keep the windings the lower their resistance will be and hence the lower their resistive losses will be. A side effect is that because cooler windings have less loss they don't produce as much heat for a given torque, so keeping them cool even when you're not drawing a lot of torque from them is beneficial.
>
> Most motors don't easily lend themselves to water cooling, without some fairly difficult modifications, which is a shame, as we are almost always surrounded by water that is both cooler than the air around us and around 24 times better than it at getting rid of heat. If you can arrange direct water cooling of the motor windings, then there will be both a modest efficiency gain in normal use and a significant increase in the maximum continuous current that the motor will handle.
>
> Jeremy
>
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