[PSUBS-MAILIST] Pre-Charge Resistor

[Stephen Fordyce via Personal_Submersibles]

Hi Alan,
Yes, basically resistance * capacitance == a time constant, which is a
common theme in analog electronics design (RC = tau).  So it's all nicely
linear, ie. to double the time you double the resistance.

By my reading of it, the resistor won't actually flatten your battery -
ie. when the capacitors are fully charged through the capacitor, there is
no driving voltage so no current will flow through the resistor, thus it
theoretically draws no power.  But the capacitors will have a leakage rate
that may draw a small current and as you pointed out, the LED on the
controller may draw some current through to power the circuitry and
indicator LED.

Probably best practice to isolate the batteries close to the source when
not using for a while - and so the problem would still stand!

Cheers,
Steve

On Sat, Apr 9, 2016 at 10:49 AM, Alan James via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

> Thanks Steve,
> I didn't know there was such a calculator.
> The resistor Kelly supplied was  1K, the link I posted was misleading.
> I would need to contact Kelly to find out about the capacitors in my
> controller.
> I have seen figures elsewhere of anywhere up to 4 seconds delay.
> The 1k resistor will run my test battery (48V 40ahr) down in about 800
> hrs. if I
> don't disconnect the battery or resistor; unless there is some
> electronics that I
> don't know about that monitors the state of charge of the capacitors &
> turns their
> power supply off & on.
> Cheers Alan
>
>
>
> ------------------------------
> *From:* Stephen Fordyce via Personal_Submersibles <
> personal_submersibles at psubs.org>
> *To:* Personal Submersibles General Discussion <
> personal_submersibles at psubs.org>
> *Sent:* Saturday, April 9, 2016 10:50 AM
> *Subject:* Re: [PSUBS-MAILIST] Pre-Charge Resistor
>
> Hi Alan,
> Just putting it out there, it could actually take a while to charge a
> large capacitor bank through a 10k resistor - not sure if you've checked
> this but there are calculators on the web for that.
> Cheers,
> Steve
> On 9 Apr 2016 8:28 am, "Alan James via Personal_Submersibles" <
> personal_submersibles at psubs.org> wrote:
>
> OK figured out what I am doing.
> For this experimental stage I will just have a circuit breaker on the
> battery + side of the main switch
> & pre-charge resistor. I will trip this breaker when finished to take
> current off the resistor.
> When operational on the sub I will have a relay to a solenoid switch.
> When the relay is turned on, the pre-charge resister will see current &
> charge the capacitors
> but there will be a timer circuit with a delay of 1 second before power
> goes to the solenoid switch.
> Cheers Alan
>
> ------------------------------
> *From:* Alan James via Personal_Submersibles <
> personal_submersibles at psubs.org>
> *To:* Personal Submersibles General Discussion <
> personal_submersibles at psubs.org>
> *Sent:* Saturday, April 9, 2016 4:26 AM
> *Subject:* [PSUBS-MAILIST] Pre-Charge Resistor
>
> Does anyone have any experience with pre-charge resistors.
> I am wiring up my Kelly controller & they provide a pre-charge resistor
> similar to this one.
>
> http://www.electricmotorsport.com/wirewound-pre-charge-resistor-5w-10k-ohms.html
> They are put across the terminals on a main power switch so that they
> charge up the banks
> of capacitors that motor controllers have. Without them there is a large
> inrush of current to
> the capacitors that can cause arcing to switches & damage to controller
> components.
> However if you wire it across the power switch there is always some
> current going to the
> controller. It probably only drives the ON LED on the motor controller,
> but I am not sure
> of this. I can have another switch or circuit breaker up stream of
> the main switch, but you
> would have to turn them on in the right sequence. I have heard of circuits
> that have delays,
> so that when the power switch is turned on, power runs through the
> pre-charge resistor first.
> Are there marine switches with built in pre- charge circuits?
> Regards Alan
>
>
>
>
>
>
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