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[aprssig] Re: OT - DC Auto Charger with auto cutoff

Al Wolfe awolfe at Route24.net
Tue Jul 20 03:55:21 UTC 2004


Robert,
    I don't think there is any danger of you over-charging this auxilary
battery from the van's electrical system. The regular battery in the van and
the battery you plan to use are both nominal 12 volt lead acid batteries I
assume. With all the load you propose to run the aux battery will probably
never reach full charge anyhow. The length of wire running to the back will
probably limit the charging current to a safe level.
    I used to do something similar using a relay that hooked up the aux
battery to the main battery only when the engine was running. The coil of
the relay was energized from the "Ign" terminal on the ignition switch. Have
used that system in several vehicles with never a problem.
    You do need to consider some means to disconnect this auxilary battery
when the vehicle isn't running so you don't run down the main battery. You
also need some way to prevent the aux battery from trying to help start  the
car. This is not usually a good thing . A diode in the line to the aux
battery will prevent it but also adds a bit more voltage drop. That's why I
used a relay and number 4 wire.
    You could use two relays, one to supply power to the aux battery when
the ignition is on and one to interupt power to the first relay when power
was applied to the starter.

Good luck with your project
Al, K9SI

> Date: Mon, 19 Jul 2004 21:40:15 GMT
> From: "kd4ydc at juno.com" <kd4ydc at juno.com>
> Subject: [aprssig] OT - DC Auto Charger with auto cutoff
> To: aprssig at lists.tapr.org
> Message-ID: <20040719.144018.29248.410988 at webmail04.lax.untd.com>
> Content-Type: text/plain
>
>
> Because of a wreak in my van....I am forced into my yl's van while she
gets the new one (isn't that the way it always is ;-)
>
> The electrical system is her van is pretty bad, so putting more stress on
it with radios may put it over the edge.  I was thinking about putting a
battery (this battery looks sealed - Power Battery Company PRC-1265) in the
back and running everything off of it.  There is a accessory plug back there
that I was going to "charge" it off of.  Is there any device that could be
made that would automatically shut off when full charge is reached?  I hope
to run my laptop's inverter, dual band radio, 2mtr mobile (for APRS), tnc,
gps off of this battery (if that needs to be considered).
> Thanks and sorry for the OT,
> Robert






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