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Old 18th March 2008, 12:48 PM   #1
Dan2 is offline Dan2  South Africa
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Default power consumption of "off" head unit.

does anyone know how much current is drawn from a head unit when it is off?? (just to keep the memory)

i want to run my head unit off a computer power supply, but i need to make a plan with (probably) batteries to hold the memory of the frontloader. it is going to be portable so it won't be plugged in all the time.
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Old 18th March 2008, 01:17 PM   #2
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They may vary between models so why not just measure yours? Should take all of 30 seconds with a multimeter.
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Old 18th March 2008, 04:11 PM   #3
MartyM is offline MartyM  United States
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Yes, you should probably see somewhere between 25-50mA (.025-.050 A) on average. Just my experience with it.

That's one of the useful bits of information to have when troubleshooting a vehicle in which the battery keeps getting drained. Some customers would never believe it wasn't the head unit draining it until I proved it (and had a number to start with for the typical current draw).

Note: I do mean truly off, when ONLY the BATT wire has voltage applied, not the ACC wire too.
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Old 20th March 2008, 06:48 AM   #4
Dan2 is offline Dan2  South Africa
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ok thanks guys.

as i said i want to have a battery hooked up to keep the memory - i once did an experiment with a capacitor (my old car had a bad battery so the HU's memory would get lost sometimes when starting) connected to the batt wire. the cap dropped down to about 1V (in my test) and then i turned the radio on and the memory was still there.

So i want to parallel some rechargeable batteries (which will be charged when the radio is plugged in) and connect them to the radio. do you think it would work??
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Old 20th March 2008, 07:20 AM   #5
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Put a diode in series with the line to the radio/nicd's so that when you start the car,they don't drain-back into the starter motor,etc..
A big cap should work in place of the nicds.
Some kind of big Schottky diode,or fast-recovery type would be best (lower forward-voltage drop)
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Old 21st March 2008, 11:45 AM   #6
Dan2 is offline Dan2  South Africa
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well i had a different solution - i got another car!!! Actually the reason i sold my old Corolla was 'cos someone gave me a really good offer for it.

i still want to know what the lowest voltage is i can use for the batteries.
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Old 23rd March 2008, 08:38 AM   #7
Dan2 is offline Dan2  South Africa
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how would i build the battery charger?? cos i know you get nicd chargers, NiMh chargers etc. whats the difference and what goes into a charger??
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