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Registered Member #49
Joined: Thu Feb 09 2006, 04:05AM
Location: Bigass Pile of Penguins
Posts: 362
One of my trucks has a 24V system (came from Japan) but naturally I run a number of 12V accessories; I have a "12V" DC-DC converter to power them. The DC-DC converter outputs a regulated 13.8V.
I had the converter set up to stay powered even when the truck was off so that my radio presets won't be lost... but the converter has a cooling fan and other "features" that slowly drain my batteries even without any load on the 12V side.
I'd like to move the converter to a switched voltage source to stop this, but then I'll need a small 12V battery on the radio to keep the presets. If I connect a small SLA battery in parallel with the radio and DC DC converter will 13.8V keep it charged indefinitely? I understand this is the proper voltage for a trickle charge, but will a trickle charge maintain the battery for years while it supplies the minuscule current needed to keep the radio memory?
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Yes, very likely. The small cheap SLA batteries are designed for just this application, backup power in burglar alarms. I'd add some sort of resistor/Schottky diode arrangement to limit charging current and stop the battery from draining back into the main system, though.
Every car radio I ever played with that had memory, also had a separate wire for the backup supply, that went straight to the battery. Maybe you could just connect that to the 24V battery through a 12V Zener.
Registered Member #902
Joined: Sun Jul 15 2007, 08:17PM
Location: North Texas
Posts: 1040
I'd also put a fuse with the backup battery, just in case as if something shorts. SLAs can put out a lot of current compared to a DC-DC converter. And the resistor/diode Steve mentioned wouldn't be a bad idea either. Most radios do have a backup battery built in for presets, but I guess sometimes things just don't for one reason or another (then again I should ask how old the truck is first before saying that).
Registered Member #49
Joined: Thu Feb 09 2006, 04:05AM
Location: Bigass Pile of Penguins
Posts: 362
Steve McConner wrote ...
Every car radio I ever played with that had memory, also had a separate wire for the backup supply, that went straight to the battery. Maybe you could just connect that to the 24V battery through a 12V Zener.
You sir are wise. I have a mental block about Zeners, I always forget they exist.
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13.8V continuous to a SLA battery
