Eric
the lack of data is critical
A few changes to gear ratios and voltages can make the system very good given the compromises made
Using under rated components, more power packs and guestimates is fine when following a successful reapplication but taking apunt on electric combos is the best way to ensure one lets out the smoke.
The smoke must remain in the inside.
On 2/28/2012 8:26 AM, Eric wrote:
Hi Andrew,
I agree with your assessment on runninig the 36V controller on 48V, that's a generally bad idea.
As far as the motor, you and I have no specifics, but if the motor has a continuous rating of 11hp (8.25kW) then it should be fine in a 30' 10,500 lb sailboat. If his drive is put together well and is properly matched in gearing and prop, he should easily hit 6kts (90%+ of hull speed). If the motor is not 11hp (which he has stated multiple times) then all bets are off, however the math should work all the way down to 7hp continuous rating.
I seriously doubt that Robert will be trying to power his Coronado 30 at 20kts. He says that he's purchased some used lithium batteries, I my experience with electric boats and cars, Lithium batteries don't experience much voltage sag at discharge rates of less than 1C. My batteries drop from 53V at rest to 48.7V at 106A load (6kts in a boat very similar to Robert's). So running at full throttle for an hour shouldn't be an issue, it just comes down to how fast one want's to use up one's batteries.
It's all about matching all of the components to the boat and it's usage. All of my components are properly sized and running at full throttle, my controller stays cool, the ME0913 motor temp stabilizes at less than 90C (max rating is 150C) without extra cooling, the wiring stays cool, the batteries deliver most of their rated capacity, even with Peukert's effect, and the boat hits 92% of hull speed, 1/2 knot faster than max speed with the diesel engine that I took out. Balance the system and the whole thing will run with few problems and great reliability. Cobble together random parts and the boat will still go, but performance nd reliability may not be as good. This is why I continue to recommend the complete drive solutions available from vendors here on this list. Their experience keeps one from having to "re-invent the wheel". Working with James at Propulsion Marine, we nailed my boat's configuration from the batteries all the way through the gearing and! prop on the first try. I consider it money well spent.
Fair winds,
Eric
Marina del Rey, CA
--- In electricboats@yahoogroups.com, Andrew Gilchrist <andrew@...> wrote:
>
> I'll be matter of fact here - it sound dangerous to me
>
> the proposition your float is essentially a motor used to push 1500 lbs
> with short term usage, spikes dropping down rapidly to a very low
> average amperage and lots of cooling time, will now propel 7 times the
> mass at 50% more voltage than previously, through a underrated old tech
> speed control, through liquid.
>
> the load could be 10.5 times that of the buggy; and its long term 100%
> duty cycle instead of the short time light load of the buggy
>
> Establish the amp draw of the controller - but things don't look great
> a 36v controller being run at 48v and probably a much higher load than
> the cart could create if it is a resistive coil set up ditch it its
> dangerous and wasteful
>
> and a 10hp motor - is that max power or continuous power
>
> whats the kv - the the torque per amp and the efficiency levels
>
> * first make sure your charger is correct type for that battery type
> and you have a battery management system on it.
> * Make sure everything is well insulated
> * establish the motor kv, peak rpm, 92% of peak rpm and amp draw at max
> efficiency
> * get your prop pitch and use it to establish how fast the prop will try
> to push the boat at 92% of peak rpm; if its 20 knots you are barking up
> the wrong tree all round - if its 2-3 knots that may be survivable
> * ditch the electro mechanical controller and well overrated PWM type
>
> if you persist with the current setup try running it at the dock and so
> you can observe the controller directly - if it is electromechanical it
> will probably glow red hot - unworkable - have fire suppression ready
>
> At the very least you need an overrated PWM controller
>
> Andrew
-- AJ Gilchrist Fastelectrics 0419 429 201
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