T-Pain Is On A Boat: Re: [Electric Boats] Charging batteries in series?

Thursday, February 12, 2015

Re: [Electric Boats] Charging batteries in series?

I second the industrial approach.

I work with industrial stuff like VFDs and servo motors.
Tuning them is not hard, once youve done one.

Basically, specify volatges and motor, if appropriate, then there are 3 or 4 parameters you set and thats it.
Usually PID (3 parameters) for motor tuning and load conditions.
Max amps, incoming hertz (many will take in either 50 or 60, 220 or 380 V).

The same applies to DC drives and all motor drives in general.
Theres 3-4 pots or electronic settings you need to do.
This will get you very close to the optimum settings.

As a boat does not do positioning, you wont need to hunt for the ideal, perfect settings anyway.

You can do it by feel, and it gets pretty good.
Efficiency does not change, afaik.

Vs tuning by software or a scope, you can get perfect settings.
These just mean a bit faster acceleration in industrial motors, say 0.15 seconds vs 0.16 seconds to max speed, and 5% less overshoot, and 20 ms faster settling.
As the difference is in ms, these are not probably going to matter in a boat setting.

Industrial gear is cheap, robust and meant to run 24x7 at 100% load.
My old, old Bridgeport industrial 3-phase motor was built around 1940.
Runs perfectly, still in original package, never been opened.
Likely has 20.000 hours of use on it, but could just as well be 50.000.

I run it off a Hitachi VFD from 12 Hz to 100 Hz.
At 12 Hz is runs at 25% (of 50 Hz) of base speed, near silent.
There is less cooling, so I dont run it hard or for long at these settings.
(I could overload the motor by upto 300% with the VFD I have, and dont want to or have a need to do so).

3-phase industrial motors, fullly enclosed, are practically maintenance free.
Change bearings (20$) every 20 years or 20.000 hours, whichever comes first.
If they feel fine, just go on until they dont.

As for electronics, under heavy use (upto 24x7) suitable servo drives tend to have a 1-2% per year mortality rate.
If they are light for the load, ie overheat, and used 24x7 at 100%, they tend to die at say 1/15 drives/3 months.
That means 15 drives x 24 x 90 days = every 32.000 use hours one drive dies.
Based on experiences on 500 machines x 3 drives each x 10 years => 150.000 years of use experience.

Essentially, properly sized industrial electronics are very reliable.
New models often have 10-20x moer problems, until component issues are sorted out.

On 12/02/2015 13:08, Jason Taylor jt.yahoo@jtaylor.ca [electricboats] wrote:

An 11kw system at 48v would mean 200A. Maybe consider increasing voltage, and since you're planning to run off a genset anyway, why not just go for a 3-phase industrial motor with a standard (marine/harsh industrial) AC genset and controller? Component count will be lower and probably be less expensive, and readily available. Still seek expert advice on installation since I'm by no standard certified.