Sent from my iPhone
Hi Chris,
Nope, I don't have details concerning the "tied to the dock" stress test since this situation can't happen while underway. I was just curious about max winding temps at loads higher than my boat will generate at full throttle.
Details about my conversion have been posted dozens of times, certainly a few times since yuor first post from January 2012. Here's one from March 2013
http://groups.yahoo.com/group/electricboats/message/23272
and another direct response to a similar question from you in Feb 2012
http://groups.yahoo.com/group/electricboats/message/20984
But it mught help if you can tell us more about your current performance. Your Morgan 41 should be around 13 tons, if so, I personally believe that an ME0913 is undersized for your boat. Your motor speed at 48V nominal should be around 1900 rpm, though the Sevcon Gen4 can artificially push the RPM higher through dynamic field-weakening (?), but I think that your efficiency drops if using that feature. I do not think that the Sevcon Millipak can do the same thing.
Motenergy rates the ME0913 at 125A continuous AC (180A DC into their controller) but my observation has been that the Sevcon Gen4 puts out about 100-110A AC while onsuming 106A DC (according to the Sevcon Clearview display), so the Sevcon Gen4 appears to be considerably more efficient than the Motenergy controller that was used to develop the motor's ratings. I think that the Motenergy controller is similar to the Millipak, which we all know needed heat sinks to operate near full rating. My Gen4 is mounted flat against a bulkhead and has never had a heat issue. My point is that while the Sevcon Gen4 48V size 4 (the common one supplied with marine drive kits) is rated for 180A continuous, I believe that it's potential output is way beyond the ME0913's actual continuous rating, especially when used in the bilge of a boat.
So if you are using a Gen4 and a ME0193 in a 48V nominal system, I suggest that you target for 1900 RPM and a max battery draw of 125A at full throttle in open water. So now you need to figure out your prop and gearing to put you near those specs. I'm sure that you rememebr fromyour earlier inquiries on this particular topic, all the calculations that you can do on paper are based on so many assumptions, that they will produce a rough estimate at best. If the paper guesstimate does not deliver to your performance targets, then you'll have to tweek the configuration and I think that is where you are today.
What is your current gearing? What is your current draw (watts or amps-volts) at full throttle while underway? Do you have any metrics on motor or controller temps besides "too hot". This might help us make some suggestions to reduce the number of trials and errors. But if you don't have empirical data or are not willing to share, then there is a simple evaulation process.
Since your boat is operational, the process is to run your boat at full throttle, let your boat speed stabilize and check your RPM and current. If the drive exceeds your target current without hitting your target RPM, then your boat is over-propped ar the gear ratio is too low. You would need to reduce your prop or increase your gear ratio. If you hit max RPM target without reaching your max current target, then you are under-propped or over-geared. You wouldd need to increase your prop or reduce your gear ratio. If you hit your target RPM at your target current, you're already there. This is a good as your drive can perform. Now if possible, check your motor temperature, if the motor is running cool (well under spec), you might be able to set a higher current target and run the process again, increasing the prop or decreasing the gear ratio. However, running closer to max temp is obviously harder on the equipment and accelerates the eventual end of life for the components. Please note that I did not include boat speed in your targets. Your speed will be whatever your speed will be when the drive is dialed in. If you boat motors at 4kts, 5kts, or 6kts at full throttle and you want more, you'll need to go to a more powerfull motor to get more speed.
So in my boat, I have already hit my performance targets (rpm, current, temp, boat speed) (beginner's luck?) and don't mind that everything runs below 100C. I ithink that this is much better in the long run.
Let me know if you need more info.
Eric
--- In electricboats@yahoogroups.com, Chris Hudson <clh5_98@...> wrote:
>
> Thanks Eric,
> So that would make your battery current at around 125 amps (I'm assuming your system is 48 VDC)? Do you recall your motor current, volts and RPM at that time? Also what is your reduction ratio? Reason is I'm planning a ratio change on my system as my motors get too hot at the speed I'd like to cruise at. RPM are low and motor current too high.
>
> Chris
>
> Sent from my iPhone
>
> On Jun 26, 2013, at 16:40, "Eric" <ewdysar@...> wrote:
>
> > Hi Chris,
> >
> > Just the internal fan on the ME0913. After 45 minutes at around 6000W of current (a load that is only available while tied to the dock), the temp appears to have stabilized right around 100C (it stopped climbing around 30 minutes). I don't know about longer than that, by then my battery bank was down to less than 20% remaining of my usable capacity and I was ready to recharge. I think that ambient air temp was around 75-80 deg F. although I did not make a note of it at the time.
> >
> > Eric
> >
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