Hi Myles,
Thats interesting information. I've passed it on to Claude for his consideration.
I only just heard about the pre-charge resistor idea a couple of days ago when talking to my battery supplier. We were discussing a coil operated contactor which I'd ordered to enable better control of the main power supply. He pointed out that the transient high current that occurs when you apply power to the controller ca,n at worst, weld the contactor closed, thus preventing later switching off of that contactor, and otherwise just cause deterioration of the contacts. So I've ordered one of these resistors as well.
What I have in mind is a manual battery switch as the main isolator, and switching this on would apply power to the resistor. This might be turned on and off at the beginning and end of each days sailing. Then for each use of the motor, the contactor is switched on to have full power available. This contactor would also supply power to any ancilliary devices such as cooling fans and so on.
Cheers
Chris
On 24/12/2009, at 7:07 AM, Myles Twete wrote:
This sounds similar to what has happened with many brush motor controllers where the distance from the batteries to controller is long and the load high.
The controller is limited in space internally and so there's only so much bulk capacitance that can be placed at the power input to the controller.
While it is enough capacitance for many instances, the combination of long battery cable lengths, high loads cause either the output silicon devices to fail or the capacitors themselves due to overvoltage.
A straightforward solution is to add external bulk capacitance across the switched power cables near the motor/controller.
In doing so, both the PWM switching transient stresses on the controller as well as the stress induced by the sudden unloading of the long battery cable will be reduced.
It also sounds as if his main power switch is remote from the motors. If so, he should instead be driving a remote contactor/solenoid located near the motors to switch power On/Off.
Also, in doing that, he'll want to consider adding the very common precharge resistor across the main contactor to precharge the controller's capacitors and electronics- --bulk capacitors can get very stressed by sudden inrushes of current when turned on.
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