Re: [MV] Run 12 volt radio on 24 v. system

jonathon (jemery@execpc.com)
Fri, 18 Dec 1998 23:04:32 -0600 (CST)

>You want to run a 12 v. CB on your 24 v. system. Was told could do this,
>and want to hear from you EE types (of all kinds) what you think: was
>told to use the "lower" battery. This is the one whose negative is
>attached to the
>body frame. run wires to CB from each side of this "lower" battery to CB
>plus and minus. It is ok to attach CB to body of jeep because it is
>grounded to this battery, but not the other one. Anyone tried it? Now
>if you hook a boat anchor 12volt military radio (if there is one, that
>draws megaamps)maybe not work. What say?

Well I is an EE, at least that's what the piece of paper says. Using
'lower' battery is just fine but be aware that you are unbalancing the
charging system and the 'top' battery will get more charge than the lower.
A standard 'legal' CB shouldn't be much of a problem. Maybe just swap
batteries every few months or keep an eye on the acid level of the 'top'
battery.

As to a 24V to 12V converter, first of all we really need to concider that
it's actually 28V and 14V (respectively) with the engine running. Two
simple methods.

1) 20 ea silcon diodes of sufficient (and then some) rating to handle
current of device connected in series (forward biased) between 24V terminal
(plus of top battery) and the 12V lead of the radio.

2) 1ea 14V Zener diode (or suitable number of suitable voltage diodes to
make 14V) of proper current rating connected same as diode string in #1 above.

That is all.

je

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