[ausev] need advice on power management doo-hickey

[Brian Lasseter]

On Jan 22, 2008 10:24 AM, Sarah & Erik <electricbasset at gmail.com> wrote:
> You can also just switch the DC-DC on only when the vehicle is on,
> just connect an additional relay to the keyswitch. You should be able
> to switch the input or output of the DCDC, unless the DCDC has a high
> idle load in which case you'll want to switch the input.

I have my DC-DC driven from a contactor that is controlled when the
key switch is set to "run".   Therefore when the key switch is
"off"... then the DC-DC is off, so I have very little phantom loading.

Don Carlson ( 800-951-8774 from
http://www.globalepower.com/DCContactors.htm ) would be happy to sell
you some small amperage high voltage contactors for your usage.  An
SW60B is rated for 80A continuous, which is overkill for a DC-DC
converter, but would work.  I'm not immediately sure of the price of
the SW60B's, but the SW80B's are $50, so the SW60B's should be less
than $50.  I am not sure if there are any other high voltage,
continuous duty contactors or relays that I would trust.   (I
personally have my DC-DC connected to one of the two SW200B contactors
that I use to connect the motor controller to the battery pack.  So by
turning on one of the two SW200B's, I can connect the DC-DC to the
pack voltage, while still having my motor controller unconnected.)

Creating a device to detect small current flows would likely use more
current than your detector is trying to prevent.  A timer, as Erik
suggested, would be a better option.  Have the timer just leave the
DC-DC connected to the pack for an hour or so after the car turns off.

A KD258 off delay timer would work swimmingly for this purpose.  It
operates at 12VDC, can have a 1 to 60 minute "off" delay, is plastic
wrapped for durability, and can drive 500ma of current... which is
exactly what the continuous duty SW60B contactor will require.
http://www.ics-timers.com/kdtimers1.html
http://www.ics-timers.com/pdfile/KD-Timer.pdf

This would work too...
http://www.airotronics.com/site/product-trueoff_TGMT.php

Or you could build your own...
http://www.doctronics.co.uk/pdf_files/555an.pdf
http://people.consolidated.net/fsmyth/pages/555apps.html
http://www.elecfree.com/electronic/relay-timer-switch-by-ic-555-and-741/


> The only worry is if you have a small DCDC charging a small accessory
> battery, the battery may never get fully charged especially if you
> drive a lot at night. It would be a medium sized electronics tinkering
> project to create a timer that started after you shut the car off that
> would leave the DCDC on for an extra hour or so.

Interesting... I had not thought of this case, but if I were doing a
lot of night driving, or running the car stereo loudly, then I suppose
that the 12V accessory battery may never get fully charged.  If I left
the car in "run" without ever turning the key switch to "start", then
the DC-DC would be on, and it would charge the battery.  Since the car
would require the key in the ignition to do that, I hope I would not
forget about it.  I will think about finding a way to leave my DC-DC
connected to a timer.


-- 
TTFN,
Brian "Lasso" Lasseter

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